In eg a ion o ib a ion sensing in ime ans e in as uc u e
Jose Voj echa, Tomas No aka,d, Elisabe h And ian sa azoa,c, Vladimi Smo lachaa,, Ja omi Simaa,
Ond ej Ha lisa, Michal Spaceka,c, Ma in Slapaka, Tomas Ho a ha, Rudol Vohnou a, Lada
Al manno aa, Radek Velca, Pe Pospisila, Jan Kund a a, Ma in Cizekb, Jan H abinab, Ond ej Cipb,
Ja osla Roz ocilc
aCESNET z.s.p.o., P ague, Czechia; bIns i u e o Scien i ic Ins umen s o he Czech Academy o
Sciences, B no, Czechia; cFacul y o Elec ical Enginee ing, Czech Technical Uni e si y, P ague
Czechia; dFacul y o Nuclea Science and Physical Enginee ing, Czech Technical Uni e si y, P ague
Czechia
ABSTRACT
The dissemina ion o p ecise ime and cohe en op ical equency o e dedica ed ibe s o „da k“ channels wi hin Dense
Wa eleng h Di ision Mul iplexing (DWDM) ne wo ks is c ucial o ad anced scien i ic esea ch, geophysical moni o ing,
and eme ging indus ial applica ions. By le e aging ac i ely s abilized phase-cohe en op ical equency ans e
echnique, we main ain ul a-low iming ji e and equency s abili y o e long-haul ibe links wi hou dis up ing o da a
channels. This con ibu ion explo es u iliza ion o a sha ed da k spec um wi hin exis ing DWDM in as uc u e o enable
high-p ecision ime ans e and s able op ical equency dissemina ion while simul aneously acili a ing dis ibu ed
ib a ion sensing. Fu he mo e, he in eg a ion o dis ibu ed ibe sensing wi hin he same spec al alloca ion enables eal-
ime de ec ion o en i onmen al dis u bances such as seismic e en s and s uc u al ib a ions. Expe imen al esul s
demons a e he easibili y o his dual-pu pose app oach, showcasing i s po en ial o enhancing geophysical moni o ing,
sma in as uc u e, and nex -gene a ion me ology applica ions while op imizing he use o exis ing elecom ne wo ks.
Keywo ds: p ecise ime; cohe en op ical equency; sha ed ibe in as uc u e; Raman sca e ing; ib a ional sensing;
quan um-sa e communica ion
1. INTRODUCTION
P ecise ime and cohe en equency ans e o e op ical ibe s has become a ma u e echnology o applica ions equi ing
ul a-high synch oniza ion accu acy. By u ilizing ad anced modula ion schemes, phase-s abilized links, and ul as able
op ical ca ie s, his me hod enables he dis ibu ion o iming and equency e e ences wi h sub-nanosecond ime
de ia ion and ac ional equency ins abili ies below 10⁻¹⁸ o e hund eds o housands o kilome e s. Such pe o mance
has been demons a ed in nume ous s udies, including he wo k by P edehl e al. [1], who achie ed a equency ans e
o e a 920 km s abilized ibe link wi h an ins abili y o 10⁻¹⁸, and Lopez e al. [2], who demons a ed a 540 km ime and
equency dissemina ion ne wo k in F ance wi h compa able p ecision. These capabili ies a e c ucial o scien i ic and
indus ial applica ions, including op ical clock compa isons [3], e y long baseline in e e ome y (VLBI) [4],
synch oniza ion o la ge-scale esea ch in as uc u es such as pa icle accele a o s, and ime-c i ical se ices in
elecommunica ions and inance. Fibe -based ime and equency ans e sys ems hus p o ide a supe io al e na i e o
sa elli e-based me hods such as GNSS, ensu ing obus , aceable, and in e e ence- esilien synch oniza ion e en in
complex en i onmen s. Sha ing exis ing elecom ibe in as uc u e o he ans e o ul as able ime and equency
signals o e s signi ican economic ad an ages by a oiding he high capi al and ope a ional cos s o deploying dedica ed
links. This app oach le e ages al eady-ins alled op ical ne wo ks, enabling p ecise synch oniza ion se ices o esea ch,
inance, ene gy, and elecommunica ions sec o s wi hou majo addi ional in es men . Mul iple wo ks indica e ha
coexis ing da a and me ology signals o e he same ibe s can be achie ed wi h negligible deg ada ion o pe o mance,
making i a cos -e icien and scalable solu ion o na ional and in e na ional ime– equency dissemina ion ne wo ks [5].
2. COHERENT REFERENCE TRANSFERS AND FIBER SENSING
Techniques such as phase-sensi i e op ical ime-domain e lec ome y (φ-OTDR) ha e been success ully used o de ec
seismic e en s, moni o s uc u al heal h, and localize acous ic pe u ba ions wi h high spa ial and empo al esolu ion
[6,7]. Howe e , p esence o high-powe pulses in o he ibe may be limi ing o o he s mean o anspo [11]. On o he
hand op ical ibe s deployed wi h cohe en e e ence ans e echniques p o ide no only ul a-s able op ical equency
dissemina ion, bu ha e also eme ged as powe ul ools o sensing o ib a ions and acous ic phenomena. Recen
ad ancemen s show ha cohe en equency ans e schemes used in me ology ne wo ks can be epu posed o combined
wi h sensing modali ies o pe o m simul aneous ansmission o equency e e ences and de ec ion o mechanical
dis u bances along he same ibe [8,9]. This dual-use capabili y is especially a ac i e o applica ions in c i ical
in as uc u e moni o ing, geophysical esea ch, and sma ci ies, whe e le e aging exis ing elecom ibe ne wo ks o
bo h p ecision iming and dis ibu ed sensing educes deploymen cos s while enhancing unc ionali y [10].
3. POLARIZATION CHANGES MONITORING
Changes in he s a e o pola iza ion (SOP) in op ical ibe s caused by ex e nal pe u ba ions—such as ib a ions, acous ic
wa es, o mechanical s ain—can be exploi ed o sensing. When an ex e nal o ce induces mic o-bending o s ess, he
bi e ingence in he ibe changes locally, esul ing in measu able a ia ions in he SOP o backsca e ed o ansmi ed
ligh [12,13]. Unlike phase-sensi i e sys ems, pola iza ion-based sensing does no equi e in e e ome ic s abili y and can
ope a e e ec i ely wi h simple se ups, making i a ac i e o applica ions such as pe ime e in usion de ec ion,
in as uc u e moni o ing, and seismic sensing [14]. SOP changes in backsca e ed signal can be used o pola iza ion
op ical ime domain e lec ome y (P-OTDR), de ec ing en i onmen al dis u bances by moni o ing SOP luc ua ions along
he ibe link. Howe e , each o P-OTDR is qui e limi ed and high/powe pulses launched in o he ibe a e necessa y
[12]. On o he hand SOP moni o ing can be implemen ed as non-in usi e me hod allows i o be deployed alongside
con en ional op ical communica ion sys ems wi hou dis up ing da a ansmission, hus po en ially enabling dual-use
capabili ies in exis ing elecom in as uc u es [15].
Figu e 1. Fou ou pu signal alues om Pola ibox de ice eco ded du ing se ice wo ks in inline hu
CESNET wi h pa ne s de elops ime and equency in as uc u e CITAF. I also deploys Whi e Rabbi (WR) echnology,
an ad anced p o ocol ha synch onizes clocks wi h sub-nanosecond p ecision o e E he ne . WR employs Synch onous
E he ne (SyncE) and IEEE 1588 P ecision Time P o ocol (PTP), u ilizing wo-way message exchanges o ensu e p ecise
clock phase and o se synch oniza ion [16]. Con a y o [15] we decided no o use dedica ed signal o SOP sensing, bu
o lis en ( ia op ical couple ) on WR ans e . On 322km ield deployed line we deployed WR ans e using comme cial
Small Fo m Pluggable (SFP) anscei e s, channels 8 and 9 o Dense Wa eleng h Di ision Mul iplex (DWDM)
(wa eleng hs 1571.24 and 1570.42 nm) ea u ing ex ended inpu sensi i i y o -32 dBm and +1 dBm o highe ou pu
powe . Loss o he line has been compensa ed by i e bidi ec ional EDFAs CzechLigh SDN bidi. In on o hei ecei e s
we placed 50/50 couple s and ins all SOP moni o ing de ices desc ibed in [15]. In Figu e 1. a e clea ly illus a ed eco ded
SOP changes du ing se ice wo ks, ack doo open/close, ansmission sys em doo s open/close, and also ibe ouching
by se ice s a . Ins alla ion o moni o ing couple s caused dec ease o ecei ed powe bu in luence on ime ans e
s abili y eaching TDEV o 8.10-12s o 103s a e aging has no been obse ed.
4. PROSPECTIVE APPLICATION OF VIBRATIONAL SENSING
This in as uc u e also includes a ib a ional sensing op ion, which allows moni o ing o en i onmen al changes in eal-
ime. This capabili y enables de ec ion o physical dis u bances o s uc u al changes along he ibe ou e, enhancing he
sys em's u ili y o applica ions beyond me ology. The e a e mul iple possibili ies, he mos a o dable ones a e
ep esen ed by u ilizing Dopple noise canceling p ocesses on lines wi h cohe en equency ans e s [10] o pola ime y
[11]. Such a capabili y would be aluable o applica ions like de ec ing seismic ac i i ies, and ensu ing secu i y by
iden i ying physical dis u bances o po en ial b eaches along he ibe ou e. This addi ion would u he enhance he
CITAF in as uc u e’s e sa ili y, o e ing an ex a laye o u ili y o scien i ic, secu i y, and en i onmen al moni o ing
pu poses.
5. CONCLUSIONS AND FUTURE PROSPECTS
We showed ha p ecise ime ans e using Whi e Rabbi echnology can also be u ilized o non-in usi e
ampe ing/ ib a ion sensing e en o e y long (300+ km) lines wi h bidi ec ional ans e . The e is massi e po en ial o
be la gely deployed in elecom like in as uc u es, e.g. he Czech Republic’s na ionwide, sha ed ibe in as uc u e o
p ecise ime and cohe en op ical equency dissemina ion. Ob iously, he e a e mul iple challenges, as au oma ic e en
de ec ion and classi ica ion and also localiza ion.
ACKNOWLEDGEMENTS
◦This wo ks was suppo ed by Minis y o educa ion, You h and Spo o he Czech Republic as a pa o he QUEENTEC
p ojec , eg. n . CZ.02.01.01/00/22 008/0004649 Quan um Enginee ing and Nano echnology.
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