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€ICs fiber based optical star riel for automotive applications K. i3aiicrIc, S . lJoferl, S. Sciffei-i, 1:. Zeeb DaimlcrChryslcr Research Center C h i ,

89013 Ultn, Germany

Sincc 1998 first optical data buses, based on a riiig topology inid polyructl~yltnetacrylat (PMMA) fibers with I min core tliatrictcr a i d red emitting LEDs wcrc iiitroduccd in cars to interconnect infonnatioii and ciitcriainnierit curtiporients [ I ] . 'l'hcsc systeirls corrently arc limited to thc passengcr couipartnicnt, hccause PMMA tibcrs do iiot tolerate ciivironrnerital temperatures above 85 "C, the data rate oi'llicsti syslctris is lirriited to well bclow 100 MBit/s and the ring to[JOlogy docs iiot allow the iritercoiiiicctioli of- safety critical control tinits. Optical daixoiil buscs based 011 staiitktrd iritiltiinodc lilrci's are not useable iri cars bectrusc of the scvcre cnvironuiicntal conditioiis and because of the cxtrciiicly low-cost demands for in- car data transmission systems. Here we propose and dcrlionstfiitc a star conpled t ld t i bus system tiascd on 200 ~ I I I corc diameter hard clad silica (HCS) fibers for I6 tcrrnitials cvitli a data latc ofup to 200 MBit/s.

17igtii'c I stwws ii schematic of the 16 gatc rcilcctive star coupler togcthcr with measmcd irlseriion losses ofthc dcvicc. As a inixirig rod ii I100 pni cure diainctcr IfCS fiber. is used. Ai otic cncl facc of the rniximg rod sixteen %001%30 pi11 1LCIS tibcrs tii'c fixed. The other end facc wrisists of a ictlcctoi,. l l i e divisioti of ihc i i q i ~ t light io 16 output iihcrs litnii {.tit:

thcorcticxil itiscitioii loss to 12 dU. llccausc o f the so fiir not upiitrikzcd iriixiiig rod gcoinetry in n ~ r armrigc!ncrit fhc insci-tiori loss is ihcorcticdly litnitcd lo 14..8 dtJ ciuc io the ratio lletwecti the fihcr and thc mixing rod cntl t i icc iirciis. Mtiasurecl iiiseriioii losses of- the star couplcrs show values bchvccu 17. I cil3 ancl 1X.53 dH indicutiiig i h a i boih ihc hornogcncity i ~ s

well a s the cxccss losscs iiic already quitc good bui still have a polcutid to bl: optirrii-rcd in thc iiiturc.

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Fig.1: Schematic ofa 16 gatc rcflcctive star coupler (a) and incasurcd inscition losscs (b).

0~7803-5947-W00/$10.00@2000 IEEE 496

As transceiver modules prcviousl y reported 121 compact vcitical-cavity surface-cinitting laser (VCSEL) transceiver modules with irrtegratcd couplcrs wcrc optimized for the use with 200/230 piu diarneter HCS fibcrs. A schematic of the module is shown in Pig. 2a. Using commercially available VCSEI, dies [3J and it simple driving circuit with a bias-l' and without tcinperatiirc control we achieved fiber coupled powers of 0 dBtn to -2.5 dBin at a bias currcnt of9.5 inA over the tcmpcraturc range o f 4 0 "C to + 85 "C and wide open optical eye-diagrams up to data rates of 200 MBitis (see Pig. 2(b)), liniitcd by the electrical driving circuit. The rcccivcr circuit is build with a lerised photodiode followcd by a transimpcdance and a limiting amplifier. The scnsitivity of thc rcccivcr circuit is about - 20 dBm up to clata ratcs of 500 MBit/s.

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6) (b) Fig.2: Schematic oftlic transceiver modulc (a), tcmpcrature dependant fiber coupled powcr and eyc diagram oi-thc output signal at 200 MBit/s (b).

ritnents with the star bus architecture using the described reflectivc star and ow that bit crror rates of 10.' are acliievablc with a power margin of about 1

dB. Due to the low fiber attciiuation, espwially compared to PMMA fibers link lengths between transceivers and star couplers are not limited by power coiisiclcrations but by thc bandwidth len@h producl of the HCS tibcrs. For a data rate of 500 MBit/s link length therefor is limited to about 40 In, allowing such fiber nctworks to bc uscd not only in ~iasseiiger cars but also it i large trucks, buses or cvcn airplanes.

In conclusion we have deinonstrattcd a potentially low cost rcflcctivc star based data net for automotive application using 200 p n corc cliainctcr HCS fibers as waveguides and 850 inn ernittirig VCSBLs as transmitters. A UER of 10 -'' is achieved at a data rate of 200 MBit/s with a system margin of about 1 dB. Improvements of thc insertion loss of ihc star couplcr and of the scnsitivity of the rcccivcr will allow in thc future much higher system margin or star bus architectures with terminal number well above 32.

Rekrences : I D. Scidl et al., in Proc. POI: 98, pp. 205 - 21 1, Berlin, Germany 199X.

J. Heinrich ct al., in Proc. LEOS L997, pp. 58 - 59 San Francisco, LISA, 1997. Cotntnercial VCSEI, 1SD-RA12 from TrucLight Coopcration.

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