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VISIBLE LIGHT DATA COMMUNICATIONS Electronics and Electrical Engineering www.glasgow.ac.uk/engineering Name of Student: Mario Gancedo Sanz Matric Number: 1103773 Academic Year: 2011-2012 Title of Project: Visible Light Data Communications First Supervisor: Dr. Anthony Kelly Second Supervisor: Dr. Scott Roy ____________________________________________________________________________ Mario Gancedo Sanz VISIBLE LIGHT DATA COMMUNICATIONS ABSTRACT In the first part of this paper, a general overview of Visible Light Communications (VLC) is described. After an introduction which covers a short historical overview, the main characteristics of this technology including applications and comparisons with other wireless technologies (radiofrequency and infrared communication) are presented. Next, the basic configuration of a VLC system will be covered, including the VLC transmitter, the VLC channel, the VLC receiver and the main modulation techniques used. This part concludes with some challenges being worked, standardization efforts and general conclusions. In the second part, the practical work of the project is presented. We focused on the electrical and optical characteristics of the VLC transmitter: Light Emitting Diodes (LEDs). Experiments carried out in different commercial LEDs such as I-V characteristics, spectra measurements, Light Power vs. Current characteristics, pulse response and frequency response are described and discussed. ____________________________________________________________________________ Mario Gancedo Sanz VISIBLE LIGHT DATA COMMUNICATIONS CONTENTS PART I. VISIBLE LIGHT DATA COMMUNICATIONS. ...................................................................... 1 1. Introduction............................................................................................................................... 1 1.1 Brief history of Visible Light Communication. ..................................................................... 1 2. VLC Characteristics. ................................................................................................................... 3 2.1 VLC versus Radio Waves. ..................................................................................................... 4 2.2 VLC versus Infrared Communications. ................................................................................ 5 2.3 VLC Disadvantages. ............................................................................................................. 5 2.4 VLC Potential Applications. ................................................................................................. 5 3. VLC System Architecture. .......................................................................................................... 8 3.1 VLC Transmitter. .................................................................................................................. 8 3.1.1 White light LEDs. .......................................................................................................... 8 3.1.1.1 White light sources based on LEDs......................................................................... 8 3.1.1.2 White light sources based on wavelength converters. .......................................... 9 3.1.1.3 RGB LEDs vs. Phosphor-based LEDs. ...................................................................... 9 3.2 VLC Channel ....................................................................................................................... 10 3.2.1 Interferences with other light sources. ...................................................................... 10 3.3 VLC receiver. ...................................................................................................................... 11 3.4 Modulation for VLC. .......................................................................................................... 12 3.4.1 Modulation schemes. ................................................................................................. 12 3.4.2 The physical layers. .................................................................................................... 14 4. Challenges. .............................................................................................................................. 14 4.1 Equalisation. ...................................................................................................................... 15 4.2 Parallel data communication. ........................................................................................... 15 4.3 Providing an uplink. ........................................................................................................... 15 5. Standarisation activities. ......................................................................................................... 16 6. Conclusions.............................................................................................................................. 16 PART II. EXPERIMENTAL WORK. ................................................................................................. 17 1. I-V Characteristics. ................................................................................................................... 17 1.1 Introduction. ..................................................................................................................... 17 1.2 Motivation. ........................................................................................................................ 20 1.3 Equipment Required. ........................................................................................................ 20 1.4 Setup. ................................................................................................................................ 21 1.5 Results. .............................................................................................................................. 22 1.5.1 Blue LED 3 mm. .......................................................................................................... 22 ____________________________________________________________________________ Mario Gancedo Sanz VISIBLE LIGHT DATA COMMUNICATIONS 1.5.2 Blue LED 5 mm. .......................................................................................................... 23 1.5.3 Green LED 3 mm. ........................................................................................................ 24 1.5.4 Green LED 5 mm. ........................................................................................................ 25 1.5.5 Red LED 3 mm. ........................................................................................................... 26 1.5.6 Red LED 5 mm. ........................................................................................................... 27 1.5.7 White LED 3 mm. ........................................................................................................ 28 1.5.8 White LED 5 mm. ........................................................................................................ 29 1.6 Conclusions. ...................................................................................................................... 30 2. Spectra Measurements. .......................................................................................................... 31 2.1 Introduction. ..................................................................................................................... 31 2.2 Motivation. ........................................................................................................................ 32 2.3 Equipment needed. ........................................................................................................... 33 2.4 Setup. ................................................................................................................................ 33 2.5 Results. .............................................................................................................................. 35 2.5.1 Blue LED 3 mm. .......................................................................................................... 35 2.5.2 Blue LED 5 mm. .......................................................................................................... 36 2.5.3 Green LED 3 mm. ........................................................................................................ 37 2.5.4 Green LED 5mm.......................................................................................................... 38 2.5.5 Red LED 3 mm ............................................................................................................ 39 2.5.6 Red LED 5 mm. ........................................................................................................... 40 2.5.7 White LED 3 mm. ........................................................................................................ 41 2.5.8 White LED 5 mm. ........................................................................................................ 42 2.6 Conclusions. ...................................................................................................................... 43 3. Light Power vs. Current Characteristics. ................................................................................. 45 3.1 Introduction. ..................................................................................................................... 45 3.2 Motivation. ........................................................................................................................ 45 3.3 Equipment required. ......................................................................................................... 45 3.4 Setup. ................................................................................................................................ 45 3.5 Results. .............................................................................................................................. 47 3.5.1 Blue LED 3 mm. .......................................................................................................... 47 3.5.2 Blue LED 5 mm. .......................................................................................................... 47 3.5.3 Green LED 3 mm. ........................................................................................................ 48 3.5.4 Green LED 5 mm. ........................................................................................................ 49 3.5.5 Red LED 3 mm. ........................................................................................................... 49 3.5.6 Red LED 5 mm. ........................................................................................................... 50 3.5.7 White LED 3 mm. ........................................................................................................ 50 3.5.8 White LED 5 mm. ........................................................................................................ 51 3.6 Conclusions. ...................................................................................................................... 52 ____________________________________________________________________________ Mario Gancedo Sanz VISIBLE LIGHT DATA COMMUNICATIONS 4. Pulse Response. ....................................................................................................................... 53 4.1 Introduction....................................................................................................................... 53 4.2 Motivation. ........................................................................................................................ 54 4.3 Equipment needed. ........................................................................................................... 54 4.4 Setup. ................................................................................................................................ 54 4.5 Results. .............................................................................................................................. 57 4.5.1 Blue LED 3 mm. .......................................................................................................... 57 4.5.2 Blue LED 5 mm. .......................................................................................................... 57 4.5.3 Green LED 3 mm. ........................................................................................................ 58 4.5.4 Green LED 3 mm. ........................................................................................................ 58 4.5.5 Red LED 3 mm. ........................................................................................................... 59 4.5.6 Red LED 5 mm. ........................................................................................................... 59 4.5.7 White LED 3 mm. ........................................................................................................ 60 4.5.8 White LED 5 mm. ........................................................................................................ 60 4.6 Conclusions. ...................................................................................................................... 61 5. Frequency response. ............................................................................................................... 62 5.1 Introduction. ..................................................................................................................... 62 5.2 Motivation. ........................................................................................................................ 62 5.3 Equipment needed. ........................................................................................................... 62 5.3 Setup. ................................................................................................................................ 63 5.4 Results. .............................................................................................................................. 64 5.4 Conclusions. ...................................................................................................................... 65 6. LEDs Efficiency. ........................................................................................................................ 66 6.1 Introduction. ..................................................................................................................... 66 6.2 Results. .............................................................................................................................. 66 6.2.1 Blue LED 3 mm. .......................................................................................................... 66 6.2.2 Blue LED 5 mm. .......................................................................................................... 66 6.2.3 Green LED 3 mm ......................................................................................................... 66 6.2.4 Green LED 5 mm. ........................................................................................................ 66 6.2.5 Red LED 3 mm. ........................................................................................................... 67 6.2.6 Red LED 5 mm. ........................................................................................................... 67 6.2.7 White LED 3 mm. ........................................................................................................ 67 6.2.8 White LED 5 mm. ........................................................................................................ 67 6.3 Conclusions. ...................................................................................................................... 67 ACKNOWLEDGMENTS ................................................................................................................. 68 REFERENCES ................................................................................................................................ 69 ____________________________________________________________________________ Mario Gancedo Sanz VISIBLE LIGHT DATA COMMUNICATIONS APPENDIX A. LEDs DATASHEETS .................................................................................................. 71 APPENDIX B. TECHNICAL SPECIFICATION DOCUMENT......................................................... 110 _____________________________________________________________________________ Mario Gancedo Sanz 1 VISIBLE LIGHT DATA COMMUNICATIONS PART I. VISIBLE LIGHT DATA COMMUNICATIONS. 1. Introduction. Nowadays, wireless communications has become fundamental to our lives and we transmit a lot of data every day. The main way we transmit wireless data is by using electromagnetic waves, in particular radio waves. However, radio waves can support only limited bandwidth because of restricted spectrum availability and interference. Furthermore, radio spectrum is full to bursting and it is difficult to find radio capacity to support media applications. There is an emerging wireless communication with a promising future and which can be a complement of radio waves: Visible Light Communication (VLC). VLC is a data communication technology that uses a visible light source as a signal transmitter, the air as a transmission medium or channel and a signal receiving device. Generally, the transmitters are Light Emitting Diodes (LEDs) while the principal device of the receiver is a photodetector, usually a photodiode. By using VLC in short distance applications, we can supplement radio waves achieving high data rates and a larger bandwidth. Light is part of the electromagnetic spectrum, specifically the visible light spectrum, which covers wavelengths between 380-780nm. We have already a lot of LED-based lights installed in the world and we can use them for communications. A LED is a semiconductor device that has the advantages of fast switching, power efficiency and emits visible light that is safe for the human because it is not harmful to vision. Therefore, we can both illuminate and transmit data everywhere. 1.1 Brief history of Visible Light Communication. Human being has used a visible light source as a form of data transmission since ancient times. Light sources used and their respective main systems of communication invented by human are listed below [1,2]: Fig. 1: Historical perspective of Visible Light Communications. _____________________________________________________________________________ Mario Gancedo Sanz 2 VISIBLE LIGHT DATA COMMUNICATIONS  Sunlight . -The heliograph was used to send information over large distances by using reflecting mirrors. -In 1880, Alexander Graham Bell invented the “Photophone”, which allowed transmitting sounds over long distances on a beam of light. It is considered as the first sophisticated wireless communications device. (a) (b) Fig. 2: (a) Photophone transmitter. (b) Photophone receiver and handset.  Fire . -Beacons were fires lit located on hills or high places, used either as lighthouses for navigation at sea, or for signaling over land that enemy troops were approaching, in order to alert defenses. -Lighthouses in ancient times were used to help ships navigate by fires built on hilltops. -Burning kites were used in the battlefield for communication.  Lamps . -In ship to ship communication lamps were used for communication (using Morse code). -Traffic lights are used to control the flow of vehicles or pedestrian crosses using three colors (red, amber and green) to communicate three different messages.  LEDs . More recently, since 2003, there have been various researches in VLC for data transmission using LEDs. The most important were made by the Nakagawa Laboratory, Smart Lighting Engineering Centre, Omega Project, D-Light Project, UC-Light Centre and work at Oxford University. These days, many lighting devices can incorporate a VLC system - we will go into detail later explaining some VLC applications. _____________________________________________________________________________ Mario Gancedo Sanz 3 VISIBLE LIGHT DATA COMMUNICATIONS 2. VLC Characteristics. As mentioned above, visible light communication is a data communication technology that uses visible light between 380 nm and 780 nm. These wavelengths correspond to a frequency range of approximately 384 THz to 789 THz. In Fig.3, we can see a diagram of the visible light spectrum [3]. Fig.3: The visible spectrum. The main characteristics of this technology [4, 5] are summarized below:  Bandwidth : The bandwidth is virtually not limited; it offers a frequency band of approximately 400THz.  Efficiency : We can both transmit data and illuminate so it is a high efficiency technology.  Data rates : VLC can achieve high data rates (hundreds of Mb/s) and it can therefore be used for high speed wireless communications.  Cost : As VLC uses the visible light spectrum it is free of cost. Furthermore, transmitters and receivers are cheap.  Human safety : VLC is harmless to human health and it is not injurious to the human eye.  Omnipresent nature . We have the infrastructure because there are already a lot of LED-based lights installed in the world which are potential VLC transmitters and therefore we can use them for communications.  Security : As light waves do not penetrate opaque objects they can not be intercepted, so it offers a very secure communication. It is very difficult for an intruder to make use of your signal. _____________________________________________________________________________ Mario Gancedo Sanz 10 VISIBLE LIGHT DATA COMMUNICATIONS (a) (b) Fig. 10: (a) Phosphor-based LED. (b) RGB LED 3.2 VLC Channel The VLC optical channel consist of a line of sight (LOS) or a number of LOS components that correspond to the paths from lighting sources to the receiver and a diffuse component created by reflections of walls or objects in the room. The LOS component is modeled in [10] and the approaches described in [11-13] can be used for the diffuse component. (a) (b) Fig. 11: (a) Diffuse channels. (b) Line of sight channel. 3.2.1 Interferences with other light sources. Ambient light interference affects the VLC channel. Ambient light noise can be caused by other light sources such as incandescent lights, fluorescent lamps or the sunlight. Incandescent lights emit high levels of infrared radiation, fluorescent lamps emit higher levels in the visible spectrum range and the sunlight emit both high levels of ultraviolet radiation and a considerable amount of infrared radiation. Sunlight causes extra photocurrent which depends on the wavelength detected and on the environment. This photocurrent can be blocked by an AC coupling of the receiver. However, the white noise of the shot noise that this light contributes is not blocked and at high light levels the photodetector can lead to saturation. One possible solution to avoid this noise source would be the use of an optical interference filter. This filter (placed on the photodiode) would allow the receiver to detect signals of a certain wavelength. On the other hand, the use of such a filter would reduce the strength of the detected signal making the device less sensitive and therefore more susceptible to receiving errors. [1, 14-15] _____________________________________________________________________________ Mario Gancedo Sanz 11 VISIBLE LIGHT DATA COMMUNICATIONS Incandescent lights and fluorescent lamps create electrical interference photocurrent harmonics. This problem could be reduced with electrical filtering. [1, 15] There have been few published researches about the effects of other light sources interferences on the VLC channel and more investigation is required on this area. 3.3 VLC receiver. The VLC receiver is composed of an optical concentrator, optical filter, photodetector and amplification circuit. Fig.12 shows a schematic diagram of a typical receiver. [15, 16] Fig. 12: Block diagram of the optical receiver. The main element is the photodiode that is a type of photodetector able to convert light into a photocurrent. For VLC, Silicon Photodiodes are used; they operate in a wavelength range of 190-1100 nm, so they show a good responsivity at the visible light wavelength region (380- 780 nm). Both PIN photodiodes and avalanche photodiodes (APD) can be used, but for usual applications PIN photodiodes are sufficient. The PIN photodiode has not a high gain like the APD, but it is cheaper, presents a larger active area and it is more convenient in high noise scenarios.(Further information about photodetectors, see [17]). To detect the maximum signal (power) a big active area is required, but increasing the area of the detector often decreases the bandwidth. When the VLC bandwidth requirements are relatively low a large detector area can be utilized. The optical concentrator is used to compensate for high spatial attenuation due to the beam divergence from the LEDs to illuminate large area. The VLC system is vulnerable to the _____________________________________________________________________________ Mario Gancedo Sanz 12 VISIBLE LIGHT DATA COMMUNICATIONS sunlight and other illuminations, so it is important to implement a suitable optical filter to receive signals of a certain wavelength band and reject unwanted noise components. Regarding to the amplifier, there are several types of amplification circuits that we will not go into detail. 3.4 Modulation for VLC. In order to send out data via LEDs it is necessary to modulate the information into a carrier signal. The IEE 802.15.7 standard [18] for VLC covers both the physical layer (PHY) and the medium access control (MAC), but we will focus on the physical layer. The physical layer is divided into three types (PHY I. PHY II and PHY III) and each PHY contains different modulation schemes. In this chapter, a brief description of the data modulation schemes and the physical layer will be presented. 3.4.1 Modulation schemes. The main modulation methods for VLC are introduced in the following. Note that for all the modulation schemes listed below there are many variants that we will not go into detail.  On-Off Keying (OOK) . OOK modulation is the simplest modulation scheme for VLC, as the LEDs are turned on or off depending if the data bits are “1” or “0”. In the easiest form, a digital 1 represents the light ON state and a digital 0 represents the light OFF state. The 802.15.7 standard uses Manchester encoding which embeds the clock into the data by representing a logic zero as an OOK symbol “01” and a logic one as an OOK symbol “10”. In this manner, the period of the positive pulses is the same as the negative ones but also doubles the bandwidth required for OOK transmission. For higher data rates run length limited (RLL) coding is used because is more efficient. Fig. 13: Manchester coding for OOK.  Variable Pulse Position Modulation (VPPM) . VPPM changes the duty cycle of each optical symbol which is distinguished from others by the pulse position to encode bits. The variable term in VPPM represents the change of the pulse width (duty cycle) in response to the requested dimming level. The logic 0 and logic 1 are symbols are pulse width modulated depending on the dimming duty cycle requirement. _____________________________________________________________________________ Mario Gancedo Sanz 13 VISIBLE LIGHT DATA COMMUNICATIONS Fig.14: Variable Pulse Position Modulation.  Colour Shift Keying (CSK) . This system can only be used if the light source of the VLC system uses RGB LEDs and the bit patterns are encoded to colours. CSK has the following advantages: -The final output colour, e.g white, is guaranteed by the colour coordinates. -The output data can be carried by the colour itself so the total output power is near constant. -It provides higher data rates at a lower clock frequency. The x-y chromaticity diagram in Fig. 15 shows the colour space and the associated wavelengths in the outer curve (in nm). Mixing of the red, green & blue primary sources produces the different colours which are coded as information bits. Fig.15: Chromacity diagram for CSK. _____________________________________________________________________________ Mario Gancedo Sanz 14 VISIBLE LIGHT DATA COMMUNICATIONS 3.4.2 The physical layers.  PHY I . It is defined for a single light source in outdoors low data rate applications. It operates from 11.67 to 266 Kb/s and supports OOK and VPPM.  PHY II . It is defined for a single light source and it is designed for indoor applications with data rates between 1.25 and 96 Mb/s. It supports both OOK and VPPM.  PHY III 4. Challenges. . It uses multiple optical sources with different frequencies (colours) and operates from 12 to 96 Mb/s. The modulation method is CSK. The major challenge for VLC is to increase the modulation bandwidth of the LED, including RGB and phosphor-based LEDs. When using a phosphor-based LED, the most common method is to use an optical filter to detect only the blue component at the receiver and block the slow time constant of the phosphor. Although this increases the bandwidth, the channel bandwidth is still low. In [19], the effect of the slow phosphor is demonstrated. The modulation bandwidth of a Luxeon Star device is measured and results show a bandwidth of about 3 MHz for the white emission and 12 MHz for the blue emission (see Fig.16 below). Fig.16: Measured bandwidths in [19] of Luxeon Star device, showing white and blue responses. _____________________________________________________________________________ Mario Gancedo Sanz 15 VISIBLE LIGHT DATA COMMUNICATIONS 4.1 Equalisation. The channel response can be equalised at the transmitter (pre-equalisation), at the receiver (post-equalisation) or a combination of both. At the moment it is not known which technique will provide highest data rates. Many investigations have been carried out in this area: a) Pre-equalisation. Equalisation at the transmitter has been investigated and this can increase the data rate and the bandwidth; this technique allow to compensate the quickly fall-off in response of white LEDs at high frequencies. Most LED lighting applications consist of an array of LEDs, and it is possible to equalise each device separately so the overall response of the array provides higher bandwidth than individual devices. A prototype has been built using this technique [20]. Results show that using an array of 16 LEDs, each with a bandwidth of 3 MHz, the overall response of the system was 25 MHz and a data rate of 40 Mb/s using Non-Return to Zero (NRZ) On-Off Keying (OOK). Equalisation of a single chip combined with blue filtering has also been undertaken in [21], where a data rate of 80 Mb/s was achieved using NRZ-OOK. b) Post equalisation Equalisation at the receiver has been tested in [22] and this can improve data rates using a simple first order equaliser to compensate the narrow bandwidth of the phosphor-based LED. 4.2 Parallel data communication. In lighting applications many LEDs are used to provide the required illumination. Sending different data from each LED to a receiver array with each photodetector illuminated by one device (different information from each stream) is a good option to increase the overall data rate of the system. This technique is called Optical Multi-Input Multi-Output (MIMO). 4.3 Providing an uplink. Although VLC in a natural broadcast medium, sometimes it is required to send information back to the transmitter and providing an uplink is challenging. Several approaches have been considered: 1) A retroreflector can be used to return incident light back to the source. The light is modulated upon reflection with the data that is to be sent back to the transmitter. In [23] low data rates were achieved and this technique requires further studies. 2) The use of RF [24] has also been considered. The VLC downlink can be combined with a RF uplink. Although relative high data rates can be achieved there is no VLC used for the uplink which could be undesirable in sensitive scenarios. _____________________________________________________________________________ Mario Gancedo Sanz 16 VISIBLE LIGHT DATA COMMUNICATIONS 3) Also, the VLC light source can be co-located with a VLC receiver, but this will increase the price of the system, it is less energy efficient and it might look unsightly to some smart applications. 5. Standarisation activities. In Japan, the Visible Light Communication Consortium (VLCC) [4] have published two JEITA (Japan Electronics and Information Technology Industries Association) standards, JEITA CP-1221[25] and JEITA CP-1222[26]. In the Institute of Electrical and Electronics Engineers (IEEE), The IEEE 802.15.7 [18] Visible Light Communication Task Group has completed a PHY and MAC standard for Visible Light Communications (VLC). In the Wireless World Research Forum (WWRF), the working group 5 has published a white paper on VLC. 6. Conclusions. In this part, the main ideas on Visible Light Communications (VLC) have been presented. Although most existing efforts are still in development, VLC is a wireless technology with a promising future and with a wide prospective of applications where other wireless technologies (i.e. Radiofrequency) cannot be implemented, like underwater communications, aircrafts, hospitals, etc. Also, it can be considered as a good to complement to them; the radio spectrum is full to bursting and it is difficult to find capacity for media applications, so the capacity can be loaded off to the visible spectrum. As LEDs are considered the next generation of lighting devices, VLC using LEDs both for illumination and communications can be a viable option in outdoor and indoor environments. By using VLC we can achieve high data rates in short distances and a secure communication as data is sent where the light is and light waves are difficult to intercept. Probably, the main limitations of a VLC system are the modulation bandwidth of the LEDs and that it presents interferences with other light sources, so further work need to be carried out in these areas. Other challenges for VLC are increasing the transmission rate improving both the LED and receiver bandwidth through equalisation, the provision of an uplink and improving the standardization in order to commercialize VLC systems in a near future. _____________________________________________________________________________ Mario Gancedo Sanz 17 VISIBLE LIGHT DATA COMMUNICATIONS PART II. EXPERIMENTAL WORK. In this section, experiments carried out that are very useful to investigate both the electrical characteristics and the optical properties of LEDs are described: I-V Characteristics, Spectra Measurements, Light Power versus Current Characteristics, Pulse Response, Frequency Response and calculations of the LEDs efficiency. We tested 8 different commercial LEDs of different colours and diameters: Red, Green, Blue and White of 3 mm and 5 mm each. Datasheets of the LEDs can be found in the Appendix A section. 1. I-V Characteristics. 1.1 Introduction. [9, 17, 27] The operation of an LED is commonly described by a special graph called I-V characteristic curve. This curve shows the relationship between the voltage applied from anode to cathode and the resulting current that flows through the device. Fig.1: Ideal I-V characteristic of a diode. The ideal I-V characteristic of a p-n junction is given by the Shockley equation: I = Is �eqV KBT−1� Where “IS” is called the saturation current, which depends on the size of the device, material, doping, temperature and other parameters of the material. “q” is the elementary charge. “KB“is Boltzmann constant. “T” is the temperature, in Kelvin. In forward bias conditions, when the diode voltage is larger than the thermal voltage V>>𝐾𝐵 𝑇 𝑞, the “-1” can be dropped and we can rewrite the Shockley equation as I≅Is �eqV KBT� _____________________________________________________________________________ Mario Gancedo Sanz 18 VISIBLE LIGHT DATA COMMUNICATIONS The Shockley equation gives the expected theoretical I-V characteristic of a p-n junction, but to describe experimentally measured characteristics the following formula is used: I≅Is �eqV nKBT� Where “n” is the ideality factor of the diode that measures how close the diode is to this equation. Thus, an ideal diode has n=1, and the closer the ideality factor is to 1 the closer the diode is to the ideal case. For real diodes values higher than n=2 have been found. The most important parameter in the I-V curve of a LED is the turn on voltage or threshold voltage. The threshold voltage for a LED is the point from which the current increases sharply with the voltage. The turn on voltages are slightly different for each LED colour, but usually of order 1 to 4 Volts. Normally, red LEDs have the lowest turn on voltages and as the color moves up in the colour spectrum toward blue, the turn on voltage increases. A typical I-V curve for an LED is shown below: Fig.2: Typical I-V characteristic of an LED. In the curve above, notice that the LED draws no current under 1.5 volts and therefore the LED is off. Above 1.5 volts the LED draws almost no current with the voltage until at 2 V the current starts increasing steeply and the LED is fully on: the threshold voltage for this LED is 2 Volts. Moreover, the turn-on voltage for a light emitting device is approximately the bandgap energy divided by the fundamental charge: V = Eg q Forward Voltage (V) Forward Current (mA) _____________________________________________________________________________ Mario Gancedo Sanz 19 VISIBLE LIGHT DATA COMMUNICATIONS Normally a diode has parasitic resistances and a detailed inspection of the diode I-V characteristic as well as logarithmic scale allows for the diagnostic of potential problems such as series resistances, shunts, premature turn on and parasitic diodes. Some deviations from the I-V characteristic are listed below:  Diode with series resistance : A series resistance can be caused by excessive contact resistance. A diode with a series resistance shows a deviation at high currents. Fig.3: Diode with series resistance I-V characteristic.  Diode with shunt (parallel resistance): A parallel resistance can be originated by a damaged region of the p-n junction or surface defects. The characteristic by which a shunt can be recognized is shown above. In the logarithmic plot we can appreciate that there is “hump” at forward bias about the same level the reverse saturation current. Fig.4: Diode with a parallel resistance I-V characteristic.  Photocurrent: When carrying out practical measurements with transparent diodes in lighted spaces a photocurrent could be generated. That is why measurements should be done in the dark to reduce the photocurrent. Fig.5: Diode with a photocurrent I-V characteristic. _____________________________________________________________________________ Mario Gancedo Sanz 26 VISIBLE LIGHT DATA COMMUNICATIONS 1.5.5 Red LED 3 mm. Fig.18: Red LED 3 mm - I-V Characteristic. For the red LED 3 mm, there is almost no current for voltages below 1.5 V and the threshold voltage is about 1.8 V. Fig.19: Red LED 3 mm - Log I vs. Voltage. In this case, the Log I vs. Voltage graph shows that the deviation from the ideal I-V characteristic of the red LED 3mm can be caused by a series resistance. 0 20 40 60 80 100 120 140 160 180 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Current (mA) Voltage (V) -4 -3 -2 -1 0 1 2 3 4 5 6 0 1 2 3 4 5 Log I (mA) Voltage (V) _____________________________________________________________________________ Mario Gancedo Sanz 27 VISIBLE LIGHT DATA COMMUNICATIONS 1.5.6 Red LED 5 mm. Fig.20: Red LED 5 mm - I-V Characteristic. For the red LED 5 mm, voltages under 1.5 V draw no current and the turn on voltage is reached at about 1.9 V. Fig.21: Red LED 5 mm - Log I vs. Voltage. The I-V curve in a logarithmic scale shows that this device presents a parasitic series resistance. 0 20 40 60 80 100 120 140 160 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Current (mA) Voltage (V) -4 -3 -2 -1 0 1 2 3 4 5 6 0 1 2 3 4 5 6 Log I (mA) Voltage (V) _____________________________________________________________________________ Mario Gancedo Sanz 28 VISIBLE LIGHT DATA COMMUNICATIONS 1.5.7 White LED 3 mm. Fig.22: White LED 3 mm - I-V Characteristic. For the white LED 3mm, we can see in the I-V characteristic that the threshold voltage corresponds to about 3.2 V. Fig.23: White LED 3 mm - Log I vs. Voltage. For the white LED 3mm, the deviation observed from the ideal I-V characteristic is caused by a series parasitic resistance. 0 20 40 60 80 100 120 140 160 180 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 Current (mA) Voltage (V) -4 -3 -2 -1 0 1 2 3 4 5 6 0 1 2 3 4 5 6 Log I (mA) Voltage (V) _____________________________________________________________________________ Mario Gancedo Sanz 29 VISIBLE LIGHT DATA COMMUNICATIONS 1.5.8 White LED 5 mm. Fig.24: White LED 5 mm - I-V Characteristic. In this case, we can notice from the graph that the threshold voltage for the white LED 3 mm is 3.4 V. Fig.25: White LED 5 mm - Log I vs. Voltage. The non-ideal characteristic of the white LED 5 mm is produced by a parasitic series resistance. 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 Current (mA) Voltage (V) -5 -4 -3 -2 -1 0 1 2 3 4 5 0 1 2 3 4 5 6 Log I (mA) Voltage (V) _____________________________________________________________________________ Mario Gancedo Sanz 30 VISIBLE LIGHT DATA COMMUNICATIONS 1.6 Conclusions. The following table contains a summary of the results obtained from the I-V characteristics of the LEDs: LED Colour Diameter Measured threshold voltage Deviation observed Red 3 mm 1.8 V Series resistance Red 5 mm 1.9 V Series resistance Green 3 mm 2.1 V Series resistance Green 5 mm 2.1 V Series resistance Blue 3 mm 3.2 V Series resistance Blue 5 mm 4.1 V Series resistance White 3 mm 3.2 V Series resistance White 5 mm 3.4 V Series resistance 1) As expected, the turn on voltages of the measured LEDs are slightly different for each colour. The device which has a higher turn on voltage is the blue LED 5 mm (4.1 V) while the red LED 3 mm has the lower turn on voltage (1.8 V). 2) The turn on voltage increases as we move from red toward blue in the visible light spectrum. 3) The logarithmic plots of the I-V characteristics for all the devices show that all the LEDs seem to have a parasitic series resistance. A suggestion for further work about this could be to make an evaluation of the parasitic LED resistance. _____________________________________________________________________________ Mario Gancedo Sanz 31 VISIBLE LIGHT DATA COMMUNICATIONS 2. Spectra Measurements. 2.1 Introduction. [9, 17, 27] In the output spectrum of an LED, the most important parameter is the peak wavelength, which determines the colour of the LED. Also, one can measure the linewidth (∆λ) of the output spectrum, which is defined as the width between the half intensity points. Sometimes it is also referred as Full Width at Half Maximum (FWHM). The linewidth of an LED emitting in the visible range is relatively narrower than the range of the entire visible spectrum. The LED emission is even narrower than the spectral width of a single colour as perceived by the human eye. For example, red colours range in wavelength are between 610 nm-760 nm, which is much wider than the typical emission of an LED, so the human eye perceive the LED emission as monochromatic. A typical output spectrum (relative intensity vs. wavelength) from a LED is shown below: Fig.26:Typical output spectrum of an LED. The wavelength of the light emitted and therefore the colour of the LED depends on the bandgap energy of the semiconductors of which LEDs are made, so the desired emission wavelength can be achieved by choosing a semiconductor material with an adequate bandgap energy. The wavelength of the light emitted by the LED is inversely proportional to the bandgap energy; the bigger the wavelength the smaller the energy. We can determine the forbidden energy gap of an emitted photon from an LED with the following relation: Eg= hν=hc λ Where: Relative Intensity Wavelenght Eg + KBT = (hc)/ λ 1 ∆λ ∆λ = (2.5-3)KBT Eg = (hc)/ λ 0 1 2 _____________________________________________________________________________ Mario Gancedo Sanz 32 VISIBLE LIGHT DATA COMMUNICATIONS “h” is Planck’s constant h = 6.62 ×10−34J∙s “c” the speed of light is vacuum c = 3 × 108 m s “λ” is the wavelength, usually in nm. The photon energy for the peak emission is Eg+ KBT and the linewidth is typically between 2.5KBT to 3KBT. (KB is Boltzmann constant, which value is 1.38 ×10−23 J K), although these values can vary depending on the LED structure. We can therefore calculate the theoretical linewidth in the output spectrum of a LED as follows: λ=c ν=h∙c Ephoton If we differentiate λ respect to the photon energy Ephoton we get dλ dEphoton =−h∙c Ephoton 2 We can represent small intervals by differentials, ∆λ/∆Ephoton ≅ |dλ/dEphoton| Then ∆λ ≅ℎ∙𝑐 𝐸𝑝ℎ𝑜𝑡𝑜𝑛 2∆𝐸𝑝ℎ𝑜𝑡𝑜𝑛 Considering that the energy width of the output spectrum of a LED is about 3KBT. ∆Ephoton= ∆hν ≅ 3KBT Thus, substituting we get that: ∆λ=λ23 KBT h∙c The semiconductors used for the fabrication of visible LEDs must have at least a bandgap of 1.6 eV (spectral range of visible light is from about 380-780 nm i.e from about 3.2 eV to 1.6 eV). 2.2 Motivation. -To investigate the spectral emission properties of several LEDs. -To determine the peak wavelength, the linewidth and estimate the bandgap energy for the semiconductor materials of the different LEDs. Compare the measured results with the theoretical values. _____________________________________________________________________________ Mario Gancedo Sanz 33 VISIBLE LIGHT DATA COMMUNICATIONS 2.3 Equipment needed. -DC power supply. -LEDs. -Spectrometer. -Computer (SpectraSuite software). 2.4 Setup. The main item of equipment for this experiment is a spectrometer interfaced to a PC, which displays the intensity of light as a function of wavelength in the screen. The program that displays the output spectrum is called SpectraSuite. The sensitivity can be changed by adjusting the integration time. The LED is turned on with a forward bias current of IF=20 mA provided by a DC power supply and the output light is detected by the spectrometer. Fig. Shows a schematic diagram of the setup for the experiment and in Fig. we can see some photos taken during the experiment. Fig.27: Block diagram for the LEDs spectra measurements. Spectrometer SpectraSuite DC POWER SUPPLY LED High-speed wire _____________________________________________________________________________ Mario Gancedo Sanz 34 VISIBLE LIGHT DATA COMMUNICATIONS (a) (b) (c) Fig.28: (a) DC power supply, LED and spectrometer interfaced to a PC. (b) DC Power supply, LED and spectrometer. (c) The output light of the LED is detected by the spectrometer. _____________________________________________________________________________ Mario Gancedo Sanz 35 VISIBLE LIGHT DATA COMMUNICATIONS 2.5 Results. Note that all LEDs were switched on with the same forward current of IF=20 mA. 2.5.1 Blue LED 3 mm. Fig.29: Blue LED 3 mm Spectrum. The peak wavelength is about 465 nm and the FWHM or linewidth equals to 30 nm. Looking at the datasheet we can see that this blue LED is made with Indium Gallium Nitride (InGaN). The wavelength at which the LED starts to transmit optical energy is about 430 nm. Thus, we can calculate the bandgap energy of the semiconductor using the formula stated above: Eg= hυ=h∙c λ=6.62 ×10−34J∙s ∙3 × 108ms ⁄ 430 nm = 4.618 ×10−19J = 2.886 eV The theoretical linewidth for this LED can also be calculated from the equation above (considering that the room temperature is T=300 K): ∆λ=λ23 KBT h c = (465nm)23∙1.38 ×10−23J/K ∙300 K 6.64 ×10−34 J∙s ∙3 × 108 m/s =13.48 nm The theoretical linewidth is much narrower than the measured result. The experimentally determined linewidth corresponds to 6.67 KBT. 0 10000 20000 30000 40000 50000 60000 70000 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Intensity (number of counts) Wavelenght (nm) Peak wavelenght = 465 nm ∆λ = 30 nm _____________________________________________________________________________ Mario Gancedo Sanz 42 VISIBLE LIGHT DATA COMMUNICATIONS 2.5.8 White LED 5 mm. Fig.36: White LED 5 mm Spectrum. The emission spectrum of the phosphor-based white LED 5 mm spectrum consists of a blue luminescence (peak at about 470 nm) and longer wavelength phosphorescence (from about 500 nm to 700 nm and peak at 560 nm). We can therefore calculate the wavelength conversion efficiency as the previous spectrum: 𝜂𝜆−𝑐𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 =𝜆1 𝜆2×100 =470 𝑛𝑚 560 𝑛𝑚×100 =83.9% 0 10000 20000 30000 40000 50000 60000 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Intensity (number of counts) Wavelenght (nm) Phosphorescence Blue luminescence _____________________________________________________________________________ Mario Gancedo Sanz 43 VISIBLE LIGHT DATA COMMUNICATIONS 2.6 Conclusions. The following table contains a summary of the results obtained: 1) The peak wavelengths of the LEDs are as expected and thus the results obtained did not have discrepancies with theory. The table below shows the colours of the LEDs with typical wavelength ranges: Colour λ (nm) Blue 440<λ<500 Green 500<λ<570 Red 610<λ<760 White Broad spectrum As we can notice, the measured wavelengths are inside the range of the typical wavelength values, and for the white LEDs the broad spectrum formed was shown. 2) The blue LED 5 mm linewidht is particularly broad (70 nm). The devices with the narrower FWHM are the green LEDs both of 3 mm and 5 mm. 3) The experimentally determined linewidths differ from the theoretical values (see the table below). LED Colour Diameter ∆λ (measured) ∆λ (theoretical) Blue 3 mm 30 nm 13.48 nm Blue 5 mm 70 nm 12.07 nm Green 3 mm 25 nm 19.69 nm Green 5 mm 25 nm 19.69 nm Red 3 mm 40 nm 24.51 nm Red 5 mm 40 nm 24.43 nm White 3 mm - - White 5 mm - - LED Colour Diameter λ peak Eg semiconductor ∆λ Blue 3 mm 465 nm 2.886 eV 30 nm Blue 5 mm 440 nm 3.266 eV 70 nm Green 3 mm 562 nm 2.341 eV 25 nm Green 5 mm 562 nm 2.341 eV 25 nm Red 3 mm 627 nm 2.121 eV 40 nm Red 5 mm 626 nm 2.121 eV 40 nm White 3 mm Broad spectrum - - White 5 mm Broad spectrum - - _____________________________________________________________________________ Mario Gancedo Sanz 44 VISIBLE LIGHT DATA COMMUNICATIONS 4) By way of illustration, the bandgap energy of the semiconductor material GaP at room temperature is 2.26 eV, and for GaN is 3.425 eV. This shows that our estimation of the bandgap energy of the LEDs semiconductor materials is similar to the theoretical values. 5) Regarding to the white LEDs, the wavelength conversion efficiency is relatively high. _____________________________________________________________________________ Mario Gancedo Sanz 45 VISIBLE LIGHT DATA COMMUNICATIONS 3. Light Power vs. Current Characteristics. 3.1 Introduction. [9, 17, 47] The Output Light Power vs. Current characteristic is a very important characteristic of an LED. The increase in the output light power is not linear with the LED current; surface-emitting LEDs with a small light-emitting diameter tend to have sublinear L-I characteristics. At high current levels, strong injection of carriers leads to saturation. A typical output light power vs. forward current of an LED is shown below. Fig.37: Typical Output Light Power vs. Current Characteristic of an LED. 3.2 Motivation. The aim of this experiment is to measure the Light Power vs. Current (L-I) characteristic of different LEDs. 3.3 Equipment required. -LEDs. -DC power supply. -Digital multimeter. -Optical Power Meter. 3.4 Setup. The LED is switched on through a high-speed cable with a bias current provided by a DC power supply. The output power of the LED is detected by an optical power meter and we take pair of readings of Output Power-Current to plot the results later. I (mA) Relative Light Intensity _____________________________________________________________________________ Mario Gancedo Sanz 46 VISIBLE LIGHT DATA COMMUNICATIONS High-speed wire Fig.38: Block diagram of the setup for the L-I Characteristics experiment. Fig.39: Pictures taken during the experiment. We can see how the LED is switched on with a DC power supply and the output light of the LED is detected by the optical power meter. OPTICAL POWER METER DC POWER SUPPLY LED _____________________________________________________________________________ Mario Gancedo Sanz 47 VISIBLE LIGHT DATA COMMUNICATIONS 3.5 Results. 3.5.1 Blue LED 3 mm. Fig.40: Blue LED 3 mm - Output Power vs. Current. Above 65 mA, the light intensity seems to have reached a maximum level. Increasing the current over this saturation point has no effect on the light intensity. The maximum output optical power for this LED is 5.4 mW. 3.5.2 Blue LED 5 mm. Fig.41: Blue LED 5 mm - Output Power vs. Current. 0 1 2 3 4 5 6 0 10 20 30 40 50 60 70 80 Output Power (mW) Current (mA) 0 100 200 300 400 500 600 0 5 10 15 20 25 30 35 output Power (µW) Current (mA) _____________________________________________________________________________ Mario Gancedo Sanz 48 VISIBLE LIGHT DATA COMMUNICATIONS For the blue LED 5 mm, for larger currents than 30 mA the light intensity remains constant. The maximum output power is 500 𝜇W. 3.5.3 Green LED 3 mm. Fig.42: Green LED 5 mm - Output Power vs. Current. The Light vs. Current characteristic of the green device of 3 mm is shown above. The current through the green LED and the output power seem to be directly proportional for small currents. For larger currents the curve bends over until the saturation point is reached at 70 mA. The maximum output power for the green LED 3 mm is 262 µW. 0 50 100 150 200 250 300 0 10 20 30 40 50 60 70 80 Output Power (µW) Current (mA) _____________________________________________________________________________ Mario Gancedo Sanz 49 VISIBLE LIGHT DATA COMMUNICATIONS 3.5.4 Green LED 5 mm. Fig.43: Green LED 5 mm - Output Power vs. Current. For the green LED 5 mm, the Light-Current characteristic is almost linear for low currents and above 120 mA the saturation point is reached. The maximum output power is 182 µW. 3.5.5 Red LED 3 mm. Fig.44: Red LED 3 mm - Output Power vs. Current. For the red LED 3 mm Output Power-Current characteristic, the saturation point corresponds to 40 mA and the maximum output power is 530 µW. 0 20 40 60 80 100 120 140 160 180 200 0 20 40 60 80 100 120 140 Output Power (µW) Current (mA) 0 100 200 300 400 500 600 0 5 10 15 20 25 30 35 40 45 Output Power (µW) Current (mA) _____________________________________________________________________________ Mario Gancedo Sanz 50 VISIBLE LIGHT DATA COMMUNICATIONS 3.5.6 Red LED 5 mm. Fig.45: Red LED 5 mm - Output Power vs. Current. For the red LED 5 mm, at 40 mA the saturation point is reached and the output power at this point is 325 µW. 3.5.7 White LED 3 mm. Fig.46: White LED 3 mm - Output Power vs. Current. 0 50 100 150 200 250 300 350 0 5 10 15 20 25 30 35 40 45 Output Power (µW) Current (mA) 0 0.5 1 1.5 2 2.5 0 10 20 30 40 50 60 70 80 Output Power (mW) Current (mA) _____________________________________________________________________________ Mario Gancedo Sanz 51 VISIBLE LIGHT DATA COMMUNICATIONS For the white LED 3 mm, above 65 mA the light intensity remains constant (saturation point). The maximum output optical power is 2.25 mW. 3.5.8 White LED 5 mm. Fig.47: White LED 5 mm - Output Power vs. Current. In the Output Power vs. Current characteristic of the white LED 5 mm, we can see that the saturation point is reached at 30 mA and the maximum output power is 226 µW. 0 50 100 150 200 250 0 5 10 15 20 25 30 35 40 Output Power (µW) Current (mA) _____________________________________________________________________________ Mario Gancedo Sanz 58 VISIBLE LIGHT DATA COMMUNICATIONS 4.5.3 Green LED 3 mm. (a) (b) Fig.54: (a) Green LED 3 mm rise time. (b) Green LED 3 mm fall time. τrise = 740 ns τfall =900 ns ∆f =≅1.2 (τrise+τfall)=1.2 740 ns +900 ns =731.7 KHz 4.5.4 Green LED 3 mm. (a) (b) Fig.55: (a) Green LED 5 mm rise time. (b) Green LED 5 mm fall time. τrise = 980 ns τfall =840 ns ∆f =≅1.2 (τrise+τfall)=1.2 980 ns +840 ns =659.34 KHz _____________________________________________________________________________ Mario Gancedo Sanz 59 VISIBLE LIGHT DATA COMMUNICATIONS 4.5.5 Red LED 3 mm. (a) (b) Fig.56: (a) Red LED 3 mm rise time. (b) Red LED 3 mm fall time. τrise = 700 ns τfall =680 ns ∆f =≅1.2 (τrise+τfall)=1.2 700 ns +680 ns =869.56 KHz 4.5.6 Red LED 5 mm. (a) (b) Fig.57: (a) Red LED 5 mm rise time. (b) Red LED 5 mm fall time. τrise = 840 ns τfall =780 ns ∆f =≅1.2 (τrise+τfall)=1.2 840 ns +780 ns =740.74 KHz _____________________________________________________________________________ Mario Gancedo Sanz 60 VISIBLE LIGHT DATA COMMUNICATIONS 4.5.7 White LED 3 mm. (a) (b) Fig.58: (a) White LED 3 mm rise time. (b) White LED 3 mm fall time. τrise = 2.4 µs τfall = 2.4 µs ∆f =≅1.2 (τrise+τfall)=1.2 2.4 µs + 2.4 µs=250 KHz 4.5.8 White LED 5 mm. (a) (b) Fig.59: (a) White LED 5 mm rise time. (b) White LED 3 mm fall time. τrise = 3 µs τfall = 3 µs ∆f =≅1.2 (τrise+τfall)=1.2 3 µs + 3 µs=200 KHz _____________________________________________________________________________ Mario Gancedo Sanz 61 VISIBLE LIGHT DATA COMMUNICATIONS 4.6 Conclusions. The table below shows the results obtained to make a comparison between them: Colour Diameter Rise Time Fall Time Bandwidth Blue 3 mm 1 µ s 1.14 µ s 560.75 KHz Blue 5 mm - - - Green 3 mm 740 ns 900 ns 731.7 KHz Green 5 mm 980 ns 840 ns 659.34 KHz Red 3 mm 700 ns 680 ns 869.56 KHz Red 5 mm 840 ns 780 ns 740.74 KHz White 3 mm 2.4 µ s 2.4 µ s 250 KHz White 5 mm 3 µ s 3 µ s 200 z 1) The fastest devices listed in descending order are: Red, Green, Blue and White. We can notice that the slowest device is the white LED; this is due to the fact that the phosphor limits the speed of the overall response. It could be interesting to filter the slow phosphor response to achieve a higher bandwidth. 2) The measured bandwidth of these commercial LEDs are of hundreds KHz of order. 3) In general the LEDs do not have the same rise and fall times and they are slightly different, except for the white device that are exactly the same. 4) By analyzing the results, we can appreciate that the smaller the diameter of the LED, the bigger the bandwidth. _____________________________________________________________________________ Mario Gancedo Sanz 62 VISIBLE LIGHT DATA COMMUNICATIONS 5. Frequency response. 5.1 Introduction. The frequency response is one of the most important parameters to be considered in LEDs for optical communication systems. The graph below shows a typical frequency response of an LED: Fig.60: Frequency response curve of an LED. From the graph, we can calculate the 3 dB frequency or bandwidth at the point that the response is reduced by 3 dB compared with the low frequency value. In the example above, the bandwidth of the LED is about 1 MHz. 5.2 Motivation. The purpose of this experiment is to determine the bandwidth of different commercial LEDs. 5.3 Equipment needed. -LEDs. -Photodetector. -Bias Tee. -DC power supply. -S-parameter analyzer. -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 0 2 4 6 8 10 Response (dB) Frequency (MHz) 3dB frequency _____________________________________________________________________________ Mario Gancedo Sanz 63 VISIBLE LIGHT DATA COMMUNICATIONS 5.3 Setup. The emitted light of the LED is modulated and driven by a radiofrequency signal and a direct current via a bias tee. At the photodetector, the light is received and converted into a electrical signal and in the S-parameter analyzer we can see the frequency response of the LED for different applied currents. Bias TEE Photodetector S-parameter analyzer Fig.61: Block diagram of the setup for the frequency response of LEDs. Fig.62: Photography of a part of the setup for the frequency response experiment. RF RF & DC DC LED DC POWER SUPPLY _____________________________________________________________________________ Mario Gancedo Sanz 64 VISIBLE LIGHT DATA COMMUNICATIONS Fig.63: S-parameter analyzer used during the experiment. 5.4 Results. Unfortunately, the results we obtained were not as expected. The frequency response of the LEDs should increase with the applied current (i.e the bandwidth for a bias current of 20 mA should be bigger than for a bias current of 30 mA) but this did not happened. Also, the measured bandwidths were too low, only a few KHz. The experiment was repeated several times because there could be any error in the setup, but the results achieved were similar. In Fig.64 we can see an example of the measured frequency response of the red LED 5 mm: Fig.64: Measured frequency response of the red LED 5 mm. We can notice that the bandwidth either increases or decreases as we increase the current, which does not make sense. All the devices presented the same problem. Probably, a reason for the unexpected measurements could be the heating of the devices. -12 -10 -8 -6 -4 -2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Response (dB) Frequency (MHz) 12 mA 14 mA 16 mA 18 mA 20 mA 25 mA 30 mA _____________________________________________________________________________ Mario Gancedo Sanz 65 VISIBLE LIGHT DATA COMMUNICATIONS 5.4 Conclusions. Although the results were not as expected, I still understood the purpose of the experiment and the subject matter. I investigated in depth possible problems and solutions but I did not achieve the desired results. Sometimes you learn more from errors than for getting the right results!. _____________________________________________________________________________ Mario Gancedo Sanz 66 VISIBLE LIGHT DATA COMMUNICATIONS 6. LEDs Efficiency. 6.1 Introduction. In this section, the LEDs power efficiencies are calculated. With the measured I-V and Light Power-Current characteristics, we can determine the power efficiency of the LEDs using the formula: npower =P I∙V×100 6.2 Results. In order to get a better comparison of the results obtained, we need to consider the same operation conditions for all the devices. For instance, we can calculate the power efficiency when all devices are operated at 20 mA. 6.2.1 Blue LED 3 mm. For IF=20 mA→ V=3.1 V, P=2.718 mW npower =P I∙V×100 =2.718 mW 20 mA ∙3.1 V ×100 = 4.38% 6.2.2 Blue LED 5 mm. For IF=20 mA→ V=4.1 V, P=476.6 µW npower =P I∙V×100 =476.6 µW 20 mA ∙4,1 V ×100 = 0.58% 6.2.3 Green LED 3 mm For IF=20 mA→ V=2.1 V, P=86.78 µW npower =P I∙V×100 =86.78 µW 20 mA ∙2.1 V ×100 = 0.20% 6.2.4 Green LED 5 mm. For IF=20 mA→ V=1.95 V, P=44.79 µW npower =P I∙V×100 =44.79 µW 20 mA ∙1.95 V ×100 = 0.11% _____________________________________________________________________________ Mario Gancedo Sanz 67 VISIBLE LIGHT DATA COMMUNICATIONS 6.2.5 Red LED 3 mm. For IF=20 mA→ V=1.75 V, P=305.6 µW npower =P I∙V×100 =305.6 µW 20 mA ∙1.75 V ×100 = 0.87% 6.2.6 Red LED 5 mm. For IF=20 mA→ V=1.85 V, P=183.6 µW npower =P I∙V×100 =183.6 µW 20 mA ∙1.85 V ×100 = 0.49% 6.2.7 White LED 3 mm. For IF=20 mA→ V=2.9 V, P=1.163 mW npower =P I∙V×100 =1.163 mW 20 mA ∙2.9 V ×100 = 2% 6.2.8 White LED 5 mm. For IF=20 mA→ V=3.4 V, P=202.7 µW npower =P I∙V×100 =202.7 µW 20 mA ∙3,4 V ×100 = 0.29% 6.3 Conclusions. The obtained results are shown in the table below: LED COLOUR DIAMETER 𝐧𝐩𝐨𝐰𝐞𝐫 Blue 3 mm 4.38 % Blue 5 mm 0.58 % Green 3 mm 0.20 % Green 5 mm 0.11 % Red 3 mm 0.87 % Red 5 mm 0.49% White 3 mm 2 % White 5 mm 0.29% 1) All these commercial LEDs have low power efficiencies. 2) The highest power efficient device is the blue LED 3 mm (4.38%) whereas the lowest power efficient device is the green LED 5 mm (0.11%). SPEC NO: DSAE4833 REV NO: V.7 DATE: JUL/06/2007 PAGE: 2 OF 5 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: Y.H.CHEN ERP: 1101013158 Selection Guide Notes: 1. θ1/2 is the angle from optical centerline where the luminous intensity is 1/2 the optical centerline value. 2. Luminous intensity/ luminous Flux: +/-15%. Absolute Maximum Ratings at TA=25°C Electrical / Optical Characteristics at TA=25°C Notes: 1.Wavelength: +/-1nm. 2. Forward Voltage: +/-0.1V. Notes: 1. 1/10 Duty Cycle, 0.1ms Pulse Width. 2. 2mm below package base. 3. 5mm below package base. Part No. Dice Lens Type V iewing Angle [1] Min. Typ. 2θ1/2 L-7104PBD-A Blue (InGaN) BLUE DIFFUSED 180 700 30° Iv (mcd) [2] @ 20mA Symbol Parameter Device Typ. Max. Units Test Conditions λpeak Peak Wavelength Blue 468 nm IF=20mA λD [1] Dominant Wavelength Blue 470 nm IF=20mA Δλ1/2 Spectral Line Half-width Blue 21 nm IF=20mA C Capacitance Blue 100 pF VF=0V;f=1MHz VF [2] Forward Voltage Blue 3.2 4 V IF=20mA IR Reverse Current Blue 10 uA VR = 5V Parameter Blue Units Power dissipation 120 mW DC Forward Current 30 mA Peak Forward Current [1] 100 mA Reverse Voltage 5 V Operating/Storage Temperature -40°C To +85°C Lead Solder Temperature [2] 260°C For 3 Seconds Lead Solder Temperature [3] 260°C For 5 Seconds SPEC NO: DSAE4833 REV NO: V.7 DATE: JUL/06/2007 PAGE: 3 OF 5 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: Y.H.CHEN ERP: 1101013158 Blue L-7104PBD-A SPEC NO: DSAE4833 REV NO: V.7 DATE: JUL/06/2007 PAGE: 4 OF 5 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: Y.H.CHEN ERP: 1101013158 SPEC NO: DSAE4833 REV NO: V.7 DATE: JUL/06/2007 PAGE: 5 OF 5 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: Y.H.CHEN ERP: 1101013158 DATA SHEET Page 1 of The enclosed information is believed to be correct, Information may change ‘without notice’ due to product improvement. Users should ensure that the product is suitable for their use. E. & O. E. Revision A 12/12/2006 Sales: 01206 751166 Technical: 01206 835555 Fax: 01206 751188 [email protected].uk [email protected] www.rapidelectronics.co.uk 5mm LEDs 5mm LEDs5mm LEDs5mm LEDs5mm LEDs Order codeOrder codeOrder codeOrder code Manufacturer codeManufacturer codeManufacturer codeManufacturer code DescriptionDescriptionDescriptionDescription 55-1480 L-7113MBD 5MM HI.INTENSITY DIFF.BLUE LED (RC) 4 SPEC NO: DSAC2320 REV NO: V.4 DATE:DEC/12/2006 PAGE: 1 OF3 APPROVED: J. Lu CHECKED: Allen Liu DRAWN: F.ZHANG Package Dimensions T-1 3/4 (5mm) SOLID STATE LAMP Description The Blue source color devices are made with GaN on SiC Light Emitting Diode. Static electricity and surge damage the LEDS. It is recommended to use a wrist band or anti-electrostatic glove when handling the LEDs. All devices, equipment and machinery must be electrically grounded. Part Number: L-7113MBD BLUE ATTENTION OBSERVE PRECAUTIONS FOR HANDLING ELECTROSTATIC DISCHARGE SENSITIVE DEVICES Notes: 1. All dimensions are in millimeters (inches). 2. Tolerance is ±0.25(0.01") unless otherwise noted. 3. Lead spacing is measured where the leads emerge from the package. 4. Specifications are subject to change without notice. Features LOW POWER CONSUMPTION. POPULAR T-1 3/4 DIAMETER PACKAGE. GENERAL PURPOSE LEADS. RELIABLE AND RUGGED. LONG LIFE - SOLID STATE RELIABILITY. AVAILABLE ON TAPE AND REEL. RoHS COMPLIANT. SPEC NO: DSAC2320 REV NO: V.4 DATE:DEC/12/2006 PAGE: 2 OF3 APPROVED: J. Lu CHECKED: Allen Liu DRAWN: F.ZHANG Selection Guide Part No. Dice Lens Type Iv (mcd) [2] @ 20 mA V iewing Angle [1] Min. Typ. 2θ1/2 L-7113MBD BLUE (GaN) BLUE DIFFUSED 36 60 20° Electrical / Optical Characteristics at TA=25°C Absolute Maximum Ratings at TA=25°C Symbol Parameter Device Typ. Max. Test Conditions Units λpeak Peak Wavelength Blue 430 nm IF=20mA λD [1] Dominant Wavelength Blue 466 nm IF=20mA Δλ1/2 Spectral Line Half-width Blue 60 nm IF=20mA C Capacitance Blue 100 pF VF=0V;f=1MHz VF [2] Forward Voltage Blue 3.8 4.5 V IF=20mA IR Reverse Current Blue 10 uA VR = 5V Parameter Blue Units Power dissipation 105 mW DC Forward Current 30 mA Peak Forward Current [1] 150 mA Reverse Voltage 5 V Operating / Storage Temperature -40°C To +85°C Lead Solder Temperature [2] 260°C For 3 Seconds Lead Solder Temperature [3] 260°C For 5 Seconds Notes: 1. 1/10 Duty Cycle, 0.1ms Pulse Width. 2. 2mm below package base. 3. 5mm below package base. Notes: 1. θ1/2 is the angle from optical centerline where the luminous intensity is 1/2 the optical centerline value. 2. Luminous intensity/ luminous Flux: +/-15%. Notes: 1.Wavelength: +/-1nm. 2. Forward Voltage: +/-0.1V. SPEC NO: DSAC2320 REV NO: V.4 DATE:DEC/12/2006 PAGE: 3 OF3 APPROVED: J. Lu CHECKED: Allen Liu DRAWN: F.ZHANG Blue L-7113MBD SPEC NO: DSAB2674 REV NO: V.14 DATE: SEP/30/2010 PAGE: 1 OF 6 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: J.Yu ERP: 1101025084 T-1 (3mm) SOLID STATE LAMP Part Number: L-7104GT Green Features zLow power consumption. zPopular T-1 diameter package. zGeneral purpose leads. zReliable and rugged. zLong life - solid state reliability. zAvailable on tape and reel. zRoHS compliant. Description The Green source color devices are made with Gallium Phosphide Green Light Emitting Diode. Package Dimensions Notes: 1. All dimensions are in millimeters (inches). 2. Tolerance is ±0.25(0.01") unless otherwise noted. 3. Lead spacing is measured where the leads emerge from the package. 4. The specifications, characteristics and technical data described in the datasheet are subject to change without prior notice. SPEC NO: DSAB2674 REV NO: V.14 DATE: SEP/30/2010 PAGE: 2 OF 6 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: J.Yu ERP: 1101025084 Selection Guide Notes: 1. θ1/2 is the angle from optical centerline where the luminous intensity is 1/2 of the optical peak value. 2. Luminous intensity/ luminous Flux: +/-15%. Absolute Maximum Ratings at TA=25°C Electrical / Optical Characteristics at TA=25°C Notes: 1.Wavelength: +/-1nm. 2. Forward Voltage: +/-0.1V. Notes: 1. 1/10 Duty Cycle, 0.1ms Pulse Width. 2. 2mm below package base. 3. 5mm below package base. Part No. Dice Lens Type V iewing Angle [1] Min. Typ. 2θ1/2 L-7104GT Green (GaP) Green Transparent 20 60 34° Iv (mcd) [2] @ 10mA Symbol Parameter Device Typ. Max. Units Test Conditions λpeak Peak Wavelength Green 565 nm IF=20mA λD [1] Dominant Wavelength Green 568 nm IF=20mA Δλ1/2 Spectral Line Half-width Green 30 nm IF=20mA C Capacitance Green 15 pF VF=0V;f=1MHz VF [2] Forward Voltage Green 2.2 2.5 V IF=20mA IR Reverse Current Green 10 uA VR = 5V Parameter Green Units Power dissipation 62.5 mW DC Forward Current 25 mA Peak Forward Current [1] 140 mA Reverse Voltage 5 V Operating/Storage Temperature -40°C To +85°C Lead Solder Temperature [2] 260°C For 3 Seconds Lead Solder Temperature [3] 260°C For 5 Seconds SPEC NO: DSAB7799 REV NO: V.7 DATE: NOV/15/2005 PAGE: 3 OF 3 APPROVED: J. Lu CHECKED: Allen Liu DRAWN: Z.K.ZHANG Green L-7113GT Remarks: If special sorting is required (e.g. binning based on forward voltage, Luminous intensity/ luminous flux, or wavelength), the typical accuracy of the sorting process is as follows: 1. Wavelength: +/-1nm 2. Luminous intensity/ luminous flux: +/-15% 3. Forward Voltage: +/-0.1V Note: Accuracy may depend on the sorting parameters. SPEC NO: DSAA5802 REV NO: V.13 DATE: SEP/30/2010 PAGE: 1 OF 6 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: J.Yu ERP: 1101029117 T-1 (3mm) SOLID STATE LAMP Part Number: L-7104IT High Efficiency Red Features zLow power consumption. zPopular T-1 diameter package. zGeneral purpose leads. zReliable and rugged. zLong life - solid state reliability. zAvailable on tape and reel. zRoHS compliant. Description The High Efficiency Red source color devices are made with Gallium Arsenide Phosphide on Gallium Phosphide Orange Light Emitting Diode. Package Dimensions Notes: 1. All dimensions are in millimeters (inches). 2. Tolerance is ±0.25(0.01") unless otherwise noted. 3. Lead spacing is measured where the leads emerge from the package. 4. The specifications, characteristics and technical data described in the datasheet are subject to change without prior notice. SPEC NO: DSAA5802 REV NO: V.13 DATE: SEP/30/2010 PAGE: 2 OF 6 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: J.Yu ERP: 1101029117 Selection Guide Notes: 1. θ1/2 is the angle from optical centerline where the luminous intensity is 1/2 of the optical peak value. 2. Luminous intensity/ luminous Flux: +/-15%. Absolute Maximum Ratings at TA=25°C Electrical / Optical Characteristics at TA=25°C Notes: 1.Wavelength: +/-1nm. 2. Forward Voltage: +/-0.1V. Notes: 1. 1/10 Duty Cycle, 0.1ms Pulse Width. 2. 2mm below package base. 3. 5mm below package base. Part No. Dice Lens Type V iewing Angle [1] Min. Typ. 2θ1/2 L-7104IT High Efficiency Red (GaAsP/GaP) Red Transparent 20 60 34° Iv (mcd) [2] @ 10mA Symbol Parameter Device Typ. Max. Units Test Conditions λpeak Peak Wavelength High Efficiency Red 627 nm IF=20mA λD [1] Dominant Wavelength High Efficiency Red 625 nm IF=20mA Δλ1/2 Spectral Line Half-width High Efficiency Red 45 nm IF=20mA C Capacitance High Efficiency Red 15 pF VF=0V;f=1MHz VF [2] Forward Voltage High Efficiency Red 2 2.5 V IF=20mA IR Reverse Current High Efficiency Red 10 uA VR = 5V Parameter High Efficiency Red Units Power dissipation 75 mW DC Forward Current 30 mA Peak Forward Current [1] 160 mA Reverse Voltage 5 V Operating/Storage Temperature -40°C To +85°C Lead Solder Temperature [2] 260°C For 3 Seconds Lead Solder Temperature [3] 260°C For 5 Seconds SPEC NO: DSAA5802 REV NO: V.13 DATE: SEP/30/2010 PAGE: 3 OF 6 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: J.Yu ERP: 1101029117 High Efficiency Red L-7104IT SPEC NO: DSAA5802 REV NO: V.13 DATE: SEP/30/2010 PAGE: 4 OF 6 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: J.Yu ERP: 1101029117 PACKING & LABEL SPECIFICATIONS L-7104IT SPEC NO: DSAA5802 REV NO: V.13 DATE: SEP/30/2010 PAGE: 5 OF 6 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: J.Yu ERP: 1101029117 SPEC NO: DSAA5802 REV NO: V.13 DATE: SEP/30/2010 PAGE: 6 OF 6 APPROVED: WYNEC CHECKED: Allen Liu DRAWN: J.Yu ERP: 1101029117 SPEC NO: DSAB9098 REV NO: V.4 DATE: MAR/17/2005 PAGE: 1 OF 3 APPROVED: J. Lu CHECKED: Allen Liu DRAWN: B.H.LI T-1 3/4 (5mm) SOLID STATE LAMP Features LOW POWER CONSUMPTION. POPULAR T-1 3/4 DIAMETER PACKAGE. GENERAL PURPOSE LEADS. RELIABLE AND RUGGED. LONG LIFE - SOLID STATE RELIABILITY. AVAILABLE ON TAPE AND REEL. RoHS COMPLIANT. Package Dimensions Description The High Efficiency Red source color devices are made with Gallium Arsenide Phosphide on Gallium Phosphide Orange Light Emitting Diode. L-7113IT HIGH EFFICIENCY RED Notes: 1. All dimensions are in millimeters (inches). 2. Tolerance is ±0.25(0.01") unless otherwise noted. 3. Lead spacing is measured where the leads emerge from the package. 4. Specifications are subject to change without notice. SPEC NO: DSAB9098 REV NO: V.4 DATE: MAR/17/2005 PAGE: 2 OF 3 APPROVED: J. Lu CHECKED: Allen Liu DRAWN: B.H.LI Selection Guide Note: 1. θ1/2 is the angle from optical centerline where the luminous intensity is 1/2 the optical centerline value. Electrical / Optical Characteristics at TA=25°C Absolute Maximum Ratings at TA=25°C Notes: 1. 1/10 Duty Cycle, 0.1ms Pulse Width. 2. 2mm below package base. 3. 5mm below package base. Part No. Dice Lens Type Iv (mcd) @ 10mA Viewing Angle Min. Typ. 2 θ θ θ θ 1/2 L-7113IT HIGH EFFICIENCY RED (GaAsP/GaP) RED TRANSPARENT 28 80 20° Symbol Parameter Device Typ. Max. Test ConditionsUnits λpeak Peak Wavelength High Efficiency Red 627 nm IF=20mA λDDominant Wavelength High Efficiency Red 625 nm IF=20mA ∆λ1/2 Spectral Line Half-width High Efficiency Red 45 nm IF=20mA C Capacitance High Efficiency Red 15 pF VF=0V;f=1MHz VFForward Voltage High Efficiency Red 2.0 2.5 V IF=20mA IRReverse Current High Efficiency Red 10 uA VR = 5V Parameter High Efficiency Red Units Power dissipation 105 mW DC Forward Current 30 mA Peak Forward Current [1] 160 mA Reverse Voltage 5 V Operating/Storage Temperature -40°C To +85°C Lead Solder Temperature [2] 260°C For 3 Seconds Lead Solder Temperature [3] 260°C For 5 Seconds SPEC NO: DSAB9098 REV NO: V.4 DATE: MAR/17/2005 PAGE: 3 OF 3 APPROVED: J. Lu CHECKED: Allen Liu DRAWN: B.H.LI High Efficiency Red L-7113IT Remarks: If special sorting is required (e.g. binning based on forward voltage, luminous intensity, or wavelength), the typical accuracy of the sorting process is as follows: 1. Wavelength: +/-1nm 2. Luminous Intensity: +/-15% 3. Forward Voltage: +/-0.1V Note: Accuracy may depend on the sorting parameters. DATA SHEET Page 1 of The enclosed information is believed to be correct, Information may change ‘without notice’ due to product improvement. Users should ensure that the product is suitable for their use. E. & O. E. Revision A 12/12/2006 Sales: 01206 751166 Technical: 01206 835555 Fax: 01206 751188 [email protected].uk [email protected] www.rapidelectronics.co.uk 5mm LEDs 5mm LEDs5mm LEDs5mm LEDs5mm LEDs Order codeOrder codeOrder codeOrder code Manufacturer codeManufacturer codeManufacturer codeManufacturer code DescriptionDescriptionDescriptionDescription 55-1602 L-7113MWC L-7113MWC 5MM WATER CLEAR_WHITE LED (RC) 4 SPEC NO:CDA0565 REV NO: V.1 DATE:NOV/01/2001 PAGE: 1 OF 3 APPROVED : J. Lu CHECKED : DRAWN:X.Q.ZHENG T-1 3/4 (5mm) SOLID STATE LAMP Notes: 1. All dimensions are in millimeters (inches). 2. Tolerance is ±0.25(0.01") unless otherwise noted. 3. Lead spacing is measured where the lead emerge package. 4. Specifications are subject to change without notice. Description The source color devices are made with GaN on SiC Light Emitting Diode. Static electricity and surge damage the LEDS. It is recommended to use a wrist band or anti-electrostatic glove when handling the LEDs. All devices, equipment and machinery must be electrically grounded. L-7113MWC WHITE Features !HIGH EFFICIENCY. !WHITE EMISSION,HIGH LUMINOUS INTENSITY. Package Dimensions SPEC NO:CDA0565 REV NO: V.1 DATE:NOV/01/2001 PAGE: 2 OF 3 APPROVED : J. Lu CHECKED : DRAWN:X.Q.ZHENG Optical Characteristics Note: 1. θ1/2 is the angle from optical centerline where the luminous intensity is 1/2 the optical centerline value. Absolute Maximum Ratings at T)=25°° °° °C Electrical / Optical Characteristics at T)=25°° °° °C Notes: 1. 1/10 Duty Cycle, 0.1ms Pulse Width. 2. 4mm below package base. lobmySlobmyS lobmyS lobmySlobmySretemaraPretemaraP retemaraP retemaraPretemaraPeciveDeciveD eciveD eciveDeciveD.pyT.pyT .pyT .pyT.pyT.xaM.xaM .xaM .xaM.xaMstinUstinU stinU stinUstinUsnoitidnoCtseTsnoitidnoCtseT snoitidnoCtseT snoitidnoCtseTsnoitidnoCtseT V F egatloVdrawroFetihW8.35.4V Am02=FI I R tnerruCesreveRetihW01AuV5=RV X setanidrooCyticitamorhCetihW 04.0 Y34.0 CecnaticapaCetihW56FpzHM1=f,V0=FV retemaraPretemaraP retemaraP retemaraPretemaraP etihWetihW etihW etihWetihWstinUstinU stinU stinUstinU noitapissidrewoP 501Wm tnerruCdrawroFCD 03Am ]1[tnerruCdrawroFkaeP 051Am egatloVesreveR 5V erutarepmeTgnitarepO 04- °58+oTC °C erutarepmeTegarotS 04- °58+oTC °C ]2[erutarepmeTredloSdaeL 062 °sdnoceS5roFC .oNtraP.oNtraP .oNtraP .oNtraP.oNtraPeciDeciD eciD eciDeciDepyTsneLepyTsneL epyTsneL epyTsneLepyTsneL )dcm(vI)dcm(vI )dcm(vI )dcm(vI)dcm(vI Am02@ gniweiVgniweiV gniweiV gniweiVgniweiV elgnA .niM.niM .niM .niM.niM.pyT.pyT .pyT .pyT.pyT 2/1θ22/1θ2 2/1θ2 2/1θ22/1θ2 CWM3117-L)NaG(ETIHWRAELCRETAW08002°02 SPEC NO:CDA0565 REV NO: V.1 DATE:NOV/01/2001 PAGE: 3 OF 3 APPROVED : J. Lu CHECKED : DRAWN:X.Q.ZHENG White L-7113MWC ____________________________________________________________________________ Mario Gancedo Sanz 110 VISIBLE LIGHT DATA COMMUNICATIONS APPENDIX B. TECHNICAL SPECIFICATION DOCUMENT ____________________________________________________________________________ Mario Gancedo Sanz 111 VISIBLE LIGHT DATA COMMUNICATIONS ELECTRONICS & ELECTRICAL ENGINEERING UNIVERSITY OF GLASGOW INDIVIDUAL PROJECT 2011-2012 1. Project Planning Document Name of Student: Mario Gancedo Sanz Matric Number: 1103773 1 st Supervisor: Dr. T. Kelly Supervisor initials (plan approved): AEK 2 nd Supervisor: Dr. S. Roy Project Number: 48 Title of Project: Visible Light Data Communications Aims of project: To investigate, in collaboration with Thales Optronics, the use of commercial components in producing a Visible Light Communication (VLC) prototype system as well as its operation. Workplan and Milestones: Description of task Oct/Nov 25 30 December 1 16 January 9 31 February 1 28 March 1 16 Find information and background reading to understand how Visible Light Communication works. Milestone: Background reading completed. System definition: search suitable devices for the main components of the VLC transmitter (LEDs) and the VLC receiver (Photodiode). System testing. Write up the final report. Oct/Nov 25 30 December 1 16 January 9 31 February 1 28 March 1 16 Milestones (completion of a significant task) are indicated by ____________________________________________________________________________ Mario Gancedo Sanz 112 VISIBLE LIGHT DATA COMMUNICATIONS ELECTRONICS & ELECTRICAL ENGINEERING UNIVERSITY OF GLASGOW INDIVIDUAL PROJECT 2011-2012 2. Project Specification Name of Student: Mario Gancedo Sanz Matric Number: 1103773 1 st Supervisor: Dr. T. Kelly Supervisor initials (plan approved): AEK 2 nd Supervisor: Dr. S. Roy Project Number: 48 Title of Project: Visible Light Data Communications Topics Outcome/Specification Background reading: VLC transmitter (Phosphor-based LEDs): VLC receiver (Photodiode): VLC prototype: Writing: - Familiarise with VLC technology, know how it works and its applications. - Look at the main features of LEDs for optical communication: frequency response and power efficiency. - Phosphor bandwidth filtering. - Analyze critical performance parameters of a photodiode: responsivity, dark current and noise-equivalent power. - Test the system and estimate the data rate transfer, bit error rate, maximum transmitter-receiver distance for data transmission... - Write up the final VLC thesis report.