VLC transmitter with plastic optical fibers for indoor free space optic networks

OPTICS AND OPTOELECTRONICS VOLUME: 12 |NUMBER: 6 |2014 |SPECIAL ISSUE VLC T ansmi e wi h Plas ic Op ical Fibe s o Indoo F ee Space Op ic Ne wo ks Jan VITASEK, Pe SISKA, S anisla KEPAK, Jakub CUBIK, Radek POBORIL and Jan LATAL Depa men o Telecommunica ions, Facul y o Elec ical Enginee ing and Compu e Science, VSB–Technical Uni e si y o Os a a, 17. lis opadu 15, 708 33 Os a a, Czech Republic. [email p o ec ed], pe .sisk[email p o ec ed], s anisla .k[email p o ec ed], [email p o ec ed], adek.pob[email p o ec ed], [email p o ec ed] Abs ac . This a icle deals wi h he cons uc ion de- sign o op ical ansmi e o indoo F ee Space Op ic (FSO) ne wo ks. This op ical ansmi e will be able o p o ide he ligh ing and communica ion a he same ime. Thanks o special solu ion in spec al cha ac e is- ic o ansmi ed ligh i is necessa y o use wo LEDs adia ion sou ces. The ligh beams o hese LEDs ha e o be spa ially o e lapped in c issc oss di ec ion and hen he ansmi e can ealize bo h unc ions. The e is desc ibed a cons uc ion o op ical ansmi e wi h plas ic op ical ibe s which me ges wo LED beams o- ge he and p o ide ligh ing and communica ion a he same ime. Keywo ds Illumina ion, indoo FSO, LED, plas ic op i- cal ibe , ansmi e , Visible Ligh Communi- ca ion VLC. 1. In oduc ion The mos impo an pa ame e s o communica ion o no mal use a e high da a a e and mobili y. Radio wi eless ne wo ks could ealize hese wo pa ame e s, he e o e hey became so success ul. Howe e , use de- mands on da a a e con inuously inc ease; he e o e i is necessa y o ind o he solu ions and imp o e- men s. In his ield op ical links begin g adually mo e and mo e es ablish, because hey a e able o p o ide high da a a e and mobili y is also possible. Visible Ligh Communica ion (VLC) is a p omising example o op ical echnology, which could be used in indoo spaces. VLC holds a en ion in academia and indus y hanks o la ge p og ess in de elopmen o LEDs. Cu - en LED ea u es a e a he le el, which enables hem g adually eplace classical illumina ion sou ces (incan- descen ligh bulbs and luo escen lamps). Mo eo e , LEDs could be modula ed a high bi a es in compa - ison o classical illumina ion sou ces. The e o e LED ea u es di ec ly challenge using hem o illumina ion and communica ion a he same ime. The ad an age o op ical communica ion is high da a a e, no legisla i e es ic ion, no in e e ences wi h a- dio links, small size, low powe consump ion and da a sa e y. On he o he side, i is necessa y o keep limi s o op ical powe o human eyes and o squa e up wi h op ical noise. 2. Cu en Indoo F ee Space Op ic Ne wo ks Indoo FSO ne wo ks could be di ided acco ding o he line o sigh be ween ansmi e and ecei e and ac- co ding o di ec i i y o anscei e s [1]. The o he classi ica ion is acco ding o used op ical spec um, which is mo e impo an and mo e in e es ing o his a icle. P esen ly, he in a ed (IR) ligh o isible ligh a e used o communica ion indoo [2]. IR ansmis- sion is de ined by se e al s anda ds wi h di e en bi a es. The highes bi a e acco ding o I DA asso- cia ion is 16 Mb·s−1[1]. Using isible ligh o com- munica ion has se e al ad an ages, which ha e been men ioned abo e. Mo eo e , VLC also p o ides illu- mina ion. Se e al expe imen s ha e been done, when he bi a e g ea ly exceeds 100 Mb·s−1[2]. This is sub- s an ially mo e han IR can p o ide. This is also he eason, why using o whi e ligh o illumina ion and IR o communica ion is no ad an ageous. In addi ion, s ic e op ical powe limi s hold o IR. As expec ed, VLC also has a disad an age. This disad an age is whi e ligh emi ing LED. c 2014 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 617 OPTICS AND OPTOELECTRONICS VOLUME: 12 |NUMBER: 6 |2014 |SPECIAL ISSUE 3. Cu en Visible Ligh Communica ion VLC Whi e LEDs a e key elemen s o Visible Ligh Com- munica ion VLC. Whi e ligh c ea ion is no simple issue, which e lec s in VLC ea u es. P esen ly, VLC uses he whole emi ed spec um o whi e LED o da a ansmission. The e exis wo main me hods, how o c ea e a whi e ligh using LEDs. The i s me hod uses mo e colo ligh sou ces; he o he me hod uses a blue ligh sou ce and a sui able wa eleng h con e e , e.g. yellow phos- pho [3] [4]. The i s ype o whi e LED consis s o h ee ligh sou ces (blue, g een, ed) which a e sup- plied in co ec p opo ion. This me hod is mo e com- plex and mo e expensi e [2], bu enables o c ea e any o he colo . VLC needs powe LEDs o a su icien co e age o equi ed space by ligh . The o wa d cu - en o powe LED is up o 700 mA [5]. I powe LED should p o ide illumina ion and communica ion a he same ime, i has o be modula ed as enough. Bu qui e high o wa d cu en can limi he modula ion a e hanks o swi ching on and o [6]. The o he ype o whi e LED consis s o a blue ligh emi ing chip. A po ion o blue ligh exci es a yel- low phospho (Y ium Aluminium Ga ne Y3Al5O12), which c ea es yellow ligh . Mixing o blue and yellow ligh s c ea es a whi e ligh . The modula ion a e is limi ed by slow esponse o phospho . This me hod is simple and cheape . Thanks hese limi a ions we p oposed a new ype o ansmi e o indoo FSO ne wo ks which uses only a pa o isible spec um o da a ansmission. The pa o o iginal spec um emi ed by whi e LED is pu posely supp essed by op ical no ch il e . The supp essed pa is hen eplaced by ligh om ano he LED which will be modula ed. Bo h hese LEDs c ea e oge he o iginal whi e ligh . The ad an age is, ha whi e powe LED emi s con inuously, he e o e he dis- ad an ages o high cu en swi ching o phospho delay do no appea . The use ul da a will be ansmi ed by a na ow spec al LED, which eplaces he supp essed pa . I will be supplied by lowe o wa d cu en and he e o e i can be modula ed as e . The p oblem is how o me ge wo op ical beams om he powe LEDs spa ially oge he . The aim o his a icle is no a de- sc ip ion o new VLC me hod, i has been desc ibed in [7] and [8]. The aim is a solu ion o p oblem how o spa ially me ge wo op ical beams oge he in o one beam. Nowadays, VLC is e y in e es ing a ea o esea ch, many calls and p ojec a e aimed a imp o ing and sea ching new possibili ies o VLC. 4. Spa ial Me ging o Beams om LEDs The one solu ion o his p oblem has been ound and p esen ed in [9]. We ha e hough ou , se and mea- su ed s ill ano he solu ion. The basis o beams me g- ing a e again pa abolic e lec o s [10], which we e se o he powe LEDs and beamspli e 50T/50R. The beamspli e 50T/50R me ges wo op ical beams in powe and spa ial p ope ies co ec ly and i c ea es o iginal whi e ligh . The disad an age o beamspli e 50T/50R is a de lec ion o a hal o op ical powe . In [9], a mi o was used o pa allel di ec ion o beam. The basis o his ype o op ical ansmi e is wo plas ic op ical ibe s [11]. The plas ic op ical ibe s we e chosen hanks o hei la ge diame e . The di- ame e o cladding is 10 mm; he diame e o co e is 8.6 mm. O he op ical p ope ies a e summa ized in Tab. 1. The ligh which passed h ough beamspli e would be e y di icul o couple in classical op ical ibe and he loss o op ical powe would be g ea . Tab. 1: Op ical p ope ies o plas ic op ical ibe . Ti le Symbol Value Co e Diame e d18.6 mm Ou e Diame e d210 mm Re ac i e Index: n11.492 Co e Re ac i e Index: n21.343 Cladding Nume ical Ape u e NA 0.65 Spec al T ans. Range ∆λ380–750 nm The i s beam om beamspli e ’s ou pu is coupled in o he i s plas ic ibe ; he o he beam om o he beamspli e ou pu is coupled in o he o he plas ic ibe . Fo coupling beams in o plas ic ibe s wo ach o- ma ic lenses AC254-030-A-ML [12] we e used. The lens is ach oma ic double s o isible pa o spec um. The diame e o lens is 25.4 mm; ocal leng h is 30 mm. All impo an pa ame e s o ach oma ic lens a e w i - en in Tab. 2. Tab. 2: Impo an pa ame e s o ach oma ic lens. Ti le Symbol Value Lens Diame e D25.4 mm Focal Lengh 30.0 mm Back Focal Lengh b22.9 mm Radius o Cu a u e R120.9 mm Radius o Cu a u e R2-16.7 mm Radius o Cu a u e R3-79.8 mm Cen e Thickness c112.0 mm Cen e Thickness c22.0 mm Edge Thickness e8.8 mm When he ligh is coupled in o plas ic op ical ibe s, he ends o plas ic ibe s could be sui able loca ed on he ceiling o oom and pe o m he bes ligh co e- age o oom. Fo sui able co e age wo ibe s will c 2014 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 618 OPTICS AND OPTOELECTRONICS VOLUME: 12 |NUMBER: 6 |2014 |SPECIAL ISSUE no be su icien , he e o e ano he ligh di iding in o mo e ibe s is supposed, which ensu es equi ed co e- age. The ends o ibe s will be specially modi ied o e ec i e oom co e age. In his a icle he coupling om beamspli e in o plas ic op ical ibe s is sol ed. The scheme o op ical ansmi e is in Fig. 1. whi e LED communica ion LED beam spli e op ical il e plas ic op ical ibe plas ic op ical ibe ach oma ic lens ach oma ic lens Fig. 1: Scheme o op ical ansmi e . The cons uc ion o his ansmi e depends on he co ec placing o plas ic ibe s inpu s o he u mos ligh coupling. Fo his pu pose a simula ion in so - wa e Ligh Tools was done and i s esul s we e e i ied in labo a o y on ansmi e p o o ype which was se om op ical componen s on op ical able. 5. Simula ions in Ligh Tools So wa e Ligh Tools enables modelling o a ious op i- cal sys ems. I s unique design and analyzing ea u es combined wi h i s simple way o ope a ion, i s suppo o a quick design and op imiza ion make ob aining o esul s acco ding o he p ede ined condi ions possible. This so wa e includes a la ge componen lib a y. I is possible o change many pa ame e s. The esul s a e e y p ecise [13]. In so wa e Ligh Tools he op ical ansmi e wi h plas ic op ical ibe s was c ea ed, as shown in Fig. 2. The a ge o simula ion was o ind ou whe he i is possible o couple he beams om beamspli e in o plas ic ibe s. The impo an elemen is ach oma ic lens which collima es he beam in i s ocus. Thanks o he so wa e Ligh Tools i was possible o simula e how small beam spo he ach oma ic lens c ea es and in wha dis ance om he end o lens i is. In his place, he inpu s o plas ic ibe s we e placed o he bes ligh coupling. Fig. 2: Simula ion in Ligh Tools. In so wa e Ligh Tools a measu ing plain was c e- a ed. This measu ing plain was placed in dis ance 18 mm om he end o ach oma ic lens and he sim- ula ion was un. The e alua i e c i e ion was a Full Wid h a Hal Maximum (FWHM). A a ge was o ind such dis ance in which a beam spo is he na ow- es . The esul s calcula ed by simula ion a e summa- ized in Tab. 3. F om his able i is ob iously ha he na owes beam spo is in dis ance 24 mm om he end o ach oma ic lens. Tab. 3: Simula ion o he na owes beam spo . Dis ance FWHMxFWHMy [mm] [mm] [mm] 18 8.59 8.59 19 8.54 8.54 20 8.47 8.48 21 8.41 8.41 22 8.40 8.41 23 8.39 8.39 24 8.37 8.38 25 8.41 8.41 26 8.44 8.43 27 8.49 8.48 28 8.53 8.54 29 8.59 8.59 30 8.66 8.65 Fu he i was simula ed in Ligh Tools how much o op ical powe eaches he co e o plas ic op ical ibe and how much eaches he cladding. The so wa e cal- cula ed ha 96.6 % o op ical powe , which passed h ough he lens, eaches he co e in he i s one way, in he o he one way i was 96.4 % o op ical powe . c 2014 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 619 OPTICS AND OPTOELECTRONICS VOLUME: 12 |NUMBER: 6 |2014 |SPECIAL ISSUE 6. Measu emen in Labo a o y The simula ion in so wa e Ligh Tools showed ha i is possible o se an op ical ansmi e wi h plas ic op ical ibe s. In labo a o y on op ical able, he op- ical ansmi e was cons uc ed. The scheme is in Fig. 2. The cons uc ed ansmi e is consonan wi h ansmi e which was c ea ed in so wa e Ligh Tools. I was measu ed in which dis ance om he end o ach oma ic lens he spo o me ged beam is he na - owes . Fo his pu pose a measu emen was done, i s aim was o measu e he beam spo in se e al dis ances om he end o ach oma ic lens and o ind in such way he dis ance in which he beam spo is he na owes . Two mo o ized linea ansla ion s ages and powe me- e wi h pho ode ec o we e used o measu emen . Beam p o iles we e measu ed in se e al dis ances om he end o ach oma ic lens. The powe me e was placed in dis ance 18 mm om he end o ach oma ic lens. Powe me e mo ed in ans e se di ec ion wi h s ep 1 mm. In his he beam p o iles we e measu ed in he ange om −15 mm o 15 mm. Then he pow- e me e was mo ed in dis ance 19 mm om he end o ach oma ic lens and he beam p o ile was measu ed again. In his way he beam p o iles we e measu ed up o dis ance 30 mm om he end o ach oma ic lens. Fo each dis ance a g aph o ela i e op ical powe was se o measu e FWHM. The measu ed esul s a e summa- ized in Tab. 4. I is ob iously om his able ha he na owes beam spo was in dis ance 24 mm om he end o ach oma ic lens. This esul is consonan wi h he simula ion in Ligh Tools which is summa ized in Tab. 3. The p o ile o beam spo in y-axis di ec ion was also measu ed in dis ance 24 mm. FHWMywas 8.99 mm in his dis ance. Tab. 4: Measu emen o he na owes beam spo . Dis ance FWHMx [mm] [mm] 18 9.42 19 9.35 20 9.25 21 9.18 22 9.13 23 9.11 24 9.04 25 9.13 26 9.18 27 9.25 28 9.35 29 9.54 30 9.73 7. Conclusion The simula ion and he eal measu emen o op i- cal ansmi e wi h plas ic op ical ibe s in es iga ed abo e all he coupling o ligh beams in o plas ic ibe s by ach oma ic lenses. The simula ion showed ha he beam could be ocused o couple in o plas ic op- ical ibe , because he beam spo is enough na ow. The Ligh Tools calcula ed how much pe cen o op i- cal powe couples in o op ical ibe . The measu emen ound he posi ion in which he op ical powe is he g ea es . A e ha he measu emen o beam p o iles behind he ach oma ic lens was done. The simula ion measu ed na owe FWHM han he measu emen . I is gi en by highe p ecision o simu- la ion in compa ison o measu emen . The impo an is ha he na owes beam spo is in dis ance 24 mm om he end o ach oma ic lens. Simula ion and mea- su emen ag eed well. The simula ion and he measu emen showed ha i is possible o se an op ical ansmi e wi h plas- ic op ical ibe s. This ansmi e is no inished ye , u he i is necessa y o deal wi h dis ibu ion o ligh coupled in o plas ic op ical ibe s. O he nex s ep is a cons uc ion o modula o wi h sui able modula ion and line code o bi a e es ing. I seems ha OOK wi h Manches e coding should be in e es ing o his VLC ansmi e . Acknowledgmen This a icle was c ea ed wi h he ac i e suppo by he Minis y o Educa ion o he Czech Republic wi hin he p ojec s no. SP2014/77, SP2014/147 and SP2015/182 o he VSB–Technical Uni e si y o Os- a a. This a icle was also suppo ed by p ojec s VG20102015053, TA03020439 and TA04021263. The esea ch has been pa ially suppo ed by he p ojec No. CZ.1.07/2.3.00/20.0217 "The De elopmen o Excellence o he Telecommunica ion Resea ch Team in Rela ion o In e na ional Coope a ion" wi hin he ame o he ope a ion p og amme "Educa ion o com- pe i i eness" inanced by he S uc u al Funds and om he s a e budge o he Czech Republic. Re e ences [1] RAMIREZ-INIGUEZ, R., S. M. IDRUS and Z. SUN. Op ical wi eless communica ions: IR o wi eless connec i i y. Boca Ra on: CRC P ess, 2007. ISBN 978-0-8493-7209-4. c 2014 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 620 OPTICS AND OPTOELECTRONICS VOLUME: 12 |NUMBER: 6 |2014 |SPECIAL ISSUE [2] GHASSEMLOOY, Z., W. POPOOLA and S. RA- JBHANDARI. Op ical Wi eless Communica ions: Sys em and Channel Modelling wi h MATLAB R . Boca Ra on: CRC P ess, 2013. ISBN 978- 1439851883. [3] SCHUBERT, E. F. Ligh -Emi ing Diodes. Cam- b idge: Camb idge Uni e si y P ess, 2006. ISBN 978-0521865388. [4] HELD, G. In oduc ion o Ligh Emmi ing Diode Technology and Applica ions. Boca Ra on: CRC P ess, 2009. ISBN 978-1420076622. [5] LXHL-LW6C Luxeon 5W S a : Tech- nical Da a DS30. 2012. A ailable a : h p://www. oi hne -lase .com/da ashee s/ led_single/hexagonal/lxhl_5w.pd . [6] AGALLIU, R., M. LUCKI. Bene i s and Limi s o Modula ion Fo ma s o Op ical Communica ions. Ad ances in Elec ical and Elec onic Enginee ing. 2014, ol. 12, iss. 2, pp. 160–167. ISSN 1804-3119. [7] VITASEK, J., J. LATAL, P. SISKA, P. KOUDELKA and V. VASINEK. Res o a ion o Op ical Spec um. Ad ances in Elec ical and Elec onic Enginee ing. 2013, ol. 11, iss. 3, pp. 227–234. ISSN 1804-3119. [8] VITASEK, J., J. LATAL, P. SISKA, J. SKAPA, M. PAPES and V. VASINEK. Reco e y o LED diode op ical spec um. In: P oceedings o SPIE: Lase Communica ion and P opaga ion h ough he A mosphe e and Oceans II, ol. 8874. Belling- ham: SPIE, 2013, pp. 1–7. ISBN 978-0-8194-9724- 6. DOI: 10.1117/12.2023862. [9] VITASEK, J., P. SISKA, J. LATAL, S. HEJ- DUK, A. LINER a V. VASINEK. The T ans- mi e o Indoo F ee Space Op ic Ne wo ks. In: 36 h In e na ional Con e ence on Telecommunica- ions and Signal P ocessing (TSP). Rome: IEEE, 2013, pp. 290–293. ISBN 978-1-4799-0403-7. DOI: 10.1109/TSP.2013.6613938. [10] CLP se ies REFLECTORS o Lambe ian. Roi h- ne Lase Technik [online]. 2011. A ailable a : h p://www. oi hne -lase .com/da ashee s/ led_op ics/clp17c _clp20c .pd . [11] BOHAC, L. The Soli on T ansmissions in Op i- cal Fibe s. Ad ances in Elec ical and Elec onic Enginee ing. 2009, ol. 8, iss. 5, pp. 107–110. ISSN 1804-3119. [12] AC254-030-A-ML. Tho labs [online]. 2013. A ailable a : h p://www. ho labs. de/ ho P oduc .c m?pa Numbe = AC254-030-A-ML. [13] Ligh Tools Illumina ion Design So wa e. Op i- cal Resea ch Associa es [online]. 2011. Synopsys. A ailable a : h p://www.op ical es.com/l / LIGHT_TOOLS.pd . Abou Au ho s Jan VITASEK was bo n in Opa a. In 2009 he ini- shed M.Sc. s udy a B no Uni e si y o Technology, Facul y o Elec ical Enginee ing and Communica ion. In 2014 he inished Ph.D. s udy a Depa men o Telecommunica ions, VSB–Technical Uni e si y o Os a a. His in e es s a e F ee Space Op ics, indoo F ee Space Op ics ne wo ks and isible ligh commu- nica ion. He is a membe o SPIE. He is engaged in p ojec dealing wi h VLC. Pe SISKA was bo n in 1979 in K ome iz. In 2005 he comple ed his M.Sc. s udies a VSB– Technical Uni e si y o Os a a. Th ee yea s la e he comple ed his Ph.D. s udies. He is cu en ly employed a he Depa men o Telecommunica ions. He is in e es ed in op ical communica ions, ibe op ic senso s and Dis ibu ed Tempe a u e Sensing sys ems. S anisla KEPAK was bo n in 1987 in Os- a a. In 2009 he ecei ed Mas e ’s deg ee in he ield o Telecommunica ions. He is cu en ly Ph.D. s uden , and he wo ks in he ield o op ical communica ions and ibe op ic senso sys ems. Jakub CUBIK was bo n in 1986 in Olomouc. In 2011 he ecei ed Mas e ’s deg ee in he ield o Telecommunica ions. He is cu en ly Ph.D. s uden , and he wo ks in he ield o op ical communica ions and ibe op ic senso sys ems. Radek POBORIL was bo n in Valasske Mezi ici. He ecei ed his M.Sc. deg ee om he VSB–Technical Uni e si y o Os a a, Facul y o Elec ical Enginee - ing and Compu e Science in 2013. Cu en ly in a Ph.D. s uden , he ocuses on op ical echnologies and especially on WDM/TDM PON. Jan LATAL was bo n in P os ejo . In 2008 he was awa ded his M.Sc. deg ee a VSB–Technical Uni- e si y o Os a a, Facul y o Elec ical Enginee ing and Compu e Science, Depa men o Elec onics and Telecommunica ions. He is cu en ly Ph.D. s uden , and he wo ks in he ield o Wi eless Op ical Commu- nica ions, Op ical Communica ions and Dis ibu ed Tempe a u e Sensing Sys ems. c 2014 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 621