Design of a micro-ring resonator electro-optical modulator embedded in a reverse biased PN junction

Transcription

1 Eindovn, T Ntrlands, Jun 11-13, 2008 TD4 Dsign of a micro-ring rsonator lctro-optical modulator mbddd in a rvrs biasd PN junction A. Brimont 1 F.Y. Gards 2, P. Sancis 1, D. Marris-Morini 3, P. Dumon 4, J.M. Fdli 5, L. O'Faolain 6, W. Bogart 4, L. Vivin 3, J. Martí 1, G.T. Rd 2, T.F. Krauss 6 1 Nanopotonics Tcnology Cntr - Univrsidad Politécnica d Valncia (Spain) abrimont@ntc.upv.s 2 Advancd Tcnology Institut, Univrsity of Surry (UK) F.Gards@surry.ac.uk 3 Institut d Elctroniqu Fondamntal, CNRS, Univrsité Paris Sud (Franc) 4 Gnt Univrsity IMEC (Blgium) 5 CEA-Lti (Franc) 6 Scool of Pysics & Astronomy, Univrsity of St Andrws (UK) Abstract. In tis papr, t dsign of a micro-ring rsonator lctro-optical modulator using a PN junction mbddd in a rib wavguid is rportd. A rvrs bias of 10V is applid to t junction and sows t possibility to aciv a ig modulation dpt. T figur of mrit of tis compact dpltion modulator is stimatd to b Lp.Vp=3.46 V.cm for a loss varying from about 5 db/cm to 8.6 db/cm dpnding on t voltag applid. 1. Introduction Silicon potonics aims at scaling down dramatically t dimnsions of optical componnts so lctronic and optical functionalitis could b intgratd monolitically into an all-silicon cip at vry low cost. Most of rsarc activitis in t fild of silicon av bn so far focusd on passiv structurs, ligt mitting dvics, dtctors and modulators. Significant progrss as bn mad, pusing pysical limits of silicon byond initial xpctations. In t fild of ligt modulation in Silicon, t callnging aspct is to altr t rfractiv indx as silicon dos not xibit any linar lctro-optic (Pockls) ffct, usually usd in III-V smiconductors. Altrnativ ways to altr t rfractiv indx in all-silicon structurs av bn proposd. So far, t last xprimntal vidncs sown tat t only viabl mcanism to aciv multi-gz modulation in all-silicon dvics is provn to b t plasma disprsion ffct. Tis pysical ffct is basically basd on fr carrir concntration variation in a smiconductor, wic altrs bot t ral and imaginary part of t rfractiv indx, rspctivly known as lctrorfraction and lctroabsorbtion. Ts paramtrs wr drivd xprimntally by R.A.Sorf [1] from t Drud-Lornz quations at t spcific tlcommunication wavlngts (1.3 m and 1.55 m). His conclusions ld to t following mpirical quations: At = 1.55 m: = + = [ α = α + α = ( ) 0. 8 ] 321

2 TD4 ECIO 08 Eindovn Wr n is t cang in rfractiv indx rsulting from cang in fr lctron concntration; n is t cang in rfractiv indx rsulting from cang in fr ol concntration; is t cang in absorption rsulting from cang in fr lctron concntration; is t cang in absorption rsulting from cang in fr ol concntration Combining ts quations wit a mod solvr it bcoms possibl to work out t ffctiv indx cang of a mod and trfor t rsulting pas sift for a givn voltag. Exprimntal dmonstrations of ig spd modulation in fr carrirs dpltd silicon-basd structurs was dmonstratd tortically by [2,3] and xprimntally by [4-7] to work in t multi-ghz rgim. Howvr, t nd for compactnss, t ky for VLSI intgration motivatd rsarcrs to mov toward rsonating structurs among otr altrnativs. T us of a ring rsonator to modulat an optical signal was alrady sown by [8] to rac bit rats as ig as 12.5 Gbit/s undr a pr-mpasizd voltag driving scm. In tis papr, w propos also t us of a ring rsonator modulator, in wic modulation is acivd sifting t rsonanc paks by mans of carrir dpltion witin a PN junction. 2. Dvic dscription T proposd ring rsonator modulator (Fig. 1) is basd on a 300nm wid, 150nm tc dpt and 200 nm ig rib wavguid, wic nabls to aciv singl mod transmission. P-typ 300nm 75nm/225nm P-typ N-typ 150nm 50nm P-typ Box Fig1. Scmatic of t proposd ring rsonator modulator sowing t positioning of t junction insid t ring modulator Fig2 : Elctrical structur of t modulator As sown on Fig.2, t PN junction is asymmtrical in siz and in doping concntration in ordr to maximiz t ols dpltion ara ovrlappd by t optical mod. T n- typ rgion is 75 nm wid and t p typ 225 nm wid, t nt doping concntration of tis particular junction is varying btwn 6E17/cm3 and 2E17/cm3, for n and p typ rspctivly. T rsistiv contacts ar formd by igly dopd rgions (1E20/cm3) in ordr to form a good rsistiv contact and ar placd 1µm away from t junction to minimis intraction wit t optical mod and tus absorption losss. T position of t contacting lctrods is a ky aspct in t cas of a rvrs biasd PN basdmodulator bcaus t RC constant cut off frquncy, wic rsults from capacitiv ffcts witin t junction, limits t modulation spd. T modulator prformanc was simulatd using Atna for t procss dvlopmnt and ion implantations and Atlas for DC and transint analysis, bot part of t 322

3 Eindovn, T Ntrlands, Jun 11-13, 2008 TD4 smiconductor CAD softwar Silvaco. Optical Caractristics for t optical loss, fficincy and transint analysis wr calculatd using an in ous mod solvr. Fig. 3 rprsnts t variation of t ffctiv indx for diffrnt rvrs voltags; t loss of t activ ara is also displayd, and varis from 8.6dB/cm wn no bias is applid, to about 5 db/cm wit a rvrs bias of 10 volts. T fficincy of tis spcific modulator is Lp.Vp=3.46 V.cm. maning tat a lngt of 3.46 mm would b ncssary to obtain a -pas sift wit a 10 volt rvrs bias in a Mac Zndr intrfromtr. Fig3. Simulatd ffctiv indx cang and loss of du to t carrir for diffrnt rvrs voltag bias As t activ part of t modulator is insrtd in t ring rsonator, t rspons of t ring modulator is calculatd by combining t rsults in figur 3 in t quation blow ([9], [10]) 2 2 2π K + t 2K t cos NL 2 λ b = π 1+ K t 2K t cos NL λ Wr N is t total ffctiv indx including disprsion or group indx, K is loss factor of t ring (K=1 is losslss), L is total pysical lngt of t ring (nm), t is transfr or coupling cofficint of t couplr, is t wavlngt. Fig4. Simulatd ring rspons for diffrnt radius 10, 30 and 50 µm and rvrs bias voltag varying btwn 0 and 10 volts. T rsults ar displayd in Fig4 for tr diffrnt ring radii. Tos rsults ar drivd from an idal coupling factor matcd to t loss factor of t ring in ordr to obtain t bst rspons, also only t loss inducd by t fr carrirs insid t wavguid is takn into account. T intrsting rsult r is to sow tat for a similar PN junction 323

4 TD4 ECIO 08 Eindovn dsign, a similar xtinction ratio can b acivd rgardlss of t ring siz. Tis is du to t fact tat as t ring dcrass in siz, t fr spctral rang (FSR) incrass nc a small cang in rfractiv indx insid t wavguid will induc a biggr sift in wavlngt compard to largr rings wr t FSR is smallr. Nvrtlss, it is important to not tat dcrasing t bnd radius incrass t intrinsic losss insid t ring du to t wavguid wall rougnss, nc incrasing t loss factor and t xtinction ratio of t ring. Conclusion Tis papr sown t tortical possibilitis of modulating fficintly an optical signal propagating troug a ring rsonator and using a PN junction mbddd in rib wavguid. Du to t intrinsic possibilitis offrd by a PN junction, ig spd modulation can tn b acivd by sifting t ring rsonanc pak undr a rvrs biasd voltag, cancling t nd of using complicatd pr-mpasizd voltag driving scms. Furtrmor suc a dvic would b bnficial and a major improvmnt in trms of powr rquirmnts as wll as ral stat of t dvic compard to dpltion modulators insrtd in MZI. Acknowldgmnts Autors acknowldg financial support by EC undr NoE PIXnt. Rfrncs [1] R A. Sorf, B.R. Bntt, Elctrooptical ffcts in Silicon IEEE J. Quantum Elctron. QE-23, pp , [2] F. Y. Gards, G. T. Rd, N. G. Emrson, and C. E. Png, "A sub-micron dpltion-typ potonic modulator in silicon on insulator," Optics Exprss, vol. 13, pp , [3] D. Marris, E. Cassan, L.Vivin, Rspons tim analysis of SiG/Si modulation-dopd multiplquantum-wll structurs for optical modulation, Journal of applid pysics, Vol 96, nº11, pp , [4] A. Lupu, D. Marris, D. Pascal, J-L. Crcus, A. Cordat, V. L Tan, S. Laval, Exprimntal vidnc for indx modulation by carrir dpltion in SiG/si multipl quantum wll structurs, Applid pysics lttrs, Vol 85, nº 6, pp , 2004 [5] D. Marris-Morini, X. L Roux, L. Vivin, E. Cassan, D. Pascal, M. Halbwax, S. Main, S. Laval, J. M Fdli, and J. F. Damlncourt, "Optical modulation by carrir dpltion in a silicon PIN diod," Optics Exprss, vol. 14, pp , [6] L. Ansng, L. Ling, D. Rubin, N. Hay, B. Ciftcioglu, Y. Ctrit, N. Izaky, and M. Paniccia, "Higspd optical modulation basd on carrir dpltion in a silicon wavguid," Optics Exprss, vol.15, pp , [7] D. Marris-Morini, L.Vivin, J.M. Fédéli, E. Cassan, P. Lyan, S. Laval, Low loss and ig spd silicon optical modulator basd on a latral carrir dpltion structur, Optics xprss, vol.16, pp , [8] Q. Xu, S.Manipatruni, J. Sakya, M. Lipson, 12,5 Gbit/s carrir-injction-basd silicon micro ring ring silicon modulators, Optics xprss, vol. 15, pp , [9] J. M. Coi, R. K. L, and A. Yariv, "Control of critical coupling in a ring rsonator-fibr application to wavlngt-slctiv switcing, modulation, amplification, and oscillation," Optics Lttrs, vol. 26, pp , [10] A. Yariv, "Critical coupling and its control in optical wavguid-ring rsonator systms," IEEE Potonics Tcnology Lttrs, vol. 14, pp ,

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