High speed modulation of hybrid silicon evanescent lasers

Transcription

1 High speed modulation of hybrid silicon evanescent lasers Daoxin Dai, AW Fang and John E Bowers University of California anta Barbara, ECE Department, anta Barbara, CA 936, UA dxdai@ece.ucsb.edu This research was supported by DARPA MTO (Jag hah)

2 Outline Background & motivation ilicon light emission ilicon modulators τ p modulation Two structures for τ p modulation Loss modulation Mach-Zehnder coupled ring cavity ummary & conclusion. 2

3 Background & motivation 3

4 Higher Capacity Required 4

5 Long-distance DWDM system 5 Add Drop Interleaver EDFA DEMUX witch MUX Dispersion compersator MUX DEMUX High peed Optical Transmitter

6 Long-haul Optical communications Last mile hort-distance Fiber to the home Optical interconnect Ultra-short distance overcoming communications bottlenecks. 6

7 Optical interconnect ilicon photonics has many advantages for chip-to-chip and intra-chip communication The advantages: Large transparent window (.~4µm) Low loss (~.db/cm) Process compatibility with CMO Integrate photonics and electronics on the same chip Minimized footprint due to the ultrahigh index contrast of OI nanowires (R~2µm): very attractive for ultrasmall passive components, (AWG, microring ) 7

8 How to make a laser on silicon? Nanocrystals (Pavesi L, Nature. 48, 44, 2) i/io 2 superlattices (Lockwood D, PRL. 76, 539, 996) Erbium-doped silicon-rich oxides (Kik PG, APL. 76, 2325, 2) i/ige quantum cascade structures (Dehlinger G, cience. 29, 2277, 2) Optically pumped Raman lasers (Rong H, Nature , 25) Hybrid III-V silicon laser UCB (H. Park, et al. Opt. Expr. 3, 946, 25 ) Intel (M. N. ysak, et al. Opt. Expr. 6: 2478, 28) Ghent Univ (G. Roelkens, et al. Opt. Expr. 4: , 26 ) Tokyo Univ (Hiroshi Wada, et al. IEEE JTQE. 3: 937, 997). 8

9 Hybrid III-V silicon laser III-V/i photonics by die-to-wafer bonding (Roel Baets, Ghent Univ) 9

10 Hybrid III-V silicon laser structure UCB and Intel io 2 insulator i ubstrate elf-alignment.

11 The L-I-V characteristics of DFB-EL

12 Hybrid III-V silicon laser structure DBR laser. AW Fang, et al. JTQE, 5(3): 535, 29. Ring laser. AW Fang, et al. Opt. Expr. 5(5): 235, 27. 2

13 Modulation in optical transmitters Two ways: Direct-Modulation External-Modulation 3

14 Direct-Modulation modulated by changing the pump current directly I-modulation Laser cavity 7 fdb (GHz) ε= ε= 23 ε= (I I th ) /2 4

15 Direct-modulation of the DFBhybrid silicon laser (b) 2.5 Gb/s (c) 4. Gb/s (a) AW Fang, et al. JTQE, 5(3): 535, 29. 5

16 External-Modulation modulated by an external modulator Constant I- current ignal Laser cavity Modulator e.g., using directional Couplers, MZI, EAM, etc Low chirp, high speed. 6

17 ilicon optical modulators () MZ silicon modulator Intel. A. Liu. 4Gbps (L>mm) IBM. W. Green. Gbps (L>um) (2) Microring/disk modulator HKUT. A. Poon..5 Gb/s Cornel Univ. M. Lipson. 2.5Gpbs 7

18 External modulator MZM: utilizes carrier depletion within AlGaInAs quantum wells Cross section EAM MZM Gb/s NRZ H. Chen, Y. Kuo, J. E. Bowers. Opt. Expr. 6: 257, 28. PTL. 2: 92, 28. 8

19 Drawbacks of Direct modulation: Large frequency chirp mall modulation bandwidth Drawbacks of external modulation: Large size Difficult integration with laser 9

20 Increasing the modulation speed of hybrid silicon lasers 2

21 2 τ p -modulated laser τ p modulation Laser cavity Constant I Γ Γ = = n p t n t N N N g t N qv I N N g t N τ β τ ε τ ε ) ( d d, ) ( d d ) ln ( R l v g p = α τ Distribution loss reflectivity

22 22 mall-signal modeling t j p p p e ω τ τ τ ~ = t j t j se ne N N ω ω = =, s g j N N g n n t τ ε ω ε ) ( 2 = ( ) CD AB B A j B j s p = ) ( ~ 2 ω ω τ ω Γ Γ = = = Γ = n t n t p g D N N g C g B N N g A τ β ε ε τ ε ε τ 2 2, ) ( ) ( ), ) ( (,, ~ s N n p p << << << τ τ

23 Comparison I-modulation τ p -modulation s = 2 ω i D qv jω( A B) AB CD s = 2 ω ( jω B) ~ τ jω( A B) AB CD p log[s(ω)/s()](db) - τ p -modulation I-modulation I=5I th f GHz) 23

24 3dB bandwidth I-modulation τ p -modulation f3db(ghz) f3db(ghz) (I I th ) / (I I th ) /2 24

25 Time-domain response Output power (mw) τ p -mod: 5Gbps τ p_on =.73ps, τ p_off =.788ps, I =.5A I-mod: 5Gbps I on =.5A, I off =.5A, τ p =.788ps t (ns) (b) 2.5 Gb/s (c) 4. Gb/s 25

26 How to realize τ p -modulation? 26

27 Two ways for τ p -modulated laser τ p = ( α v g ln l ) R Two ways of modulating the photon lifetime τ p : () change the distribution loss α; (2) change the feedback coefficient R. io 2 insulator i ubstrate 27

28 Free carrier dispersion plasma effect in i Metal contact (a) (b) Normalized Modulator Output (db) ~3 GHz roll-off (c) Phase shifter waveguide -8 EM picture of p-n phase shifter Frequency (GHz) Intel A. Liu. High speed modulation in ilicon by depleting the carriers. 28

29 change the distribution loss α () F-P cavity laser τ p v g = ( α ln l ) R III-V Region n-contact p-contact H H p-ingaas p-inp Cladding p-algainas CH AlGaInAs MQWs OI Region N P N P P io 2 insulator i ubstrate p-contact n-inp n-inp/ingaasp L 29

30 Chirp due to the modulation section n = N e 8.5 ( N h α = 8.5 N e N h ).8 λ = nγ n i l L mod cav λ A solution to minimize the chirp: Modulate the carrier concentrations in the III-V region and the i region simultaneously. When depleting the carriers from the i waveguide, increase the inject current to the III-V gain section in the same time. p-contact III-V Region n-contact H H OI Region N P N P P io 2 insulator i ubstrate 3

31 (2) Mach Zehnder coupled Ring laser τ p = ( α v g ln l ) R The coupling coefficient k 4 Modulation section 4 4 The configuration: MZI-coupled MRR laser 4 3

32 The ring laser modulator Modulation section feed-back line N-contactor P-contactor Gain section n-contact p-contact OI Region N P N P P io 2 insulator i ubstrate io 2 insulator i ubstrate 32

33 Ring structures io 2 insulator i ubstrate maller ring III-V i io 2 AW Fang, et al. Opt. Expr. 5: 235, 27. Di Liang, et al. GFP conference,

34 Chirp due to the modulation section ( k 2 ) /2 # ( k 2 ) /2 n = N e 8.5 ( N h ).8 k #2 k α = Ne 6. N h 2 Modulation section: l mod (a) δφ MZI φ = tan = φ 2 2() nefflmod 2 κ γ sin( φ2) 2 2 ( κ ) κ γ cos( φ 2π λ 2π δφmzi( λ ) neff Lcav = m2π m λ m 2 ) λ (nm) τp (ps).3 (b) The carrier density (/cm 3 ) x 6 L mod =4 µm 34

35 ummary & Conclusion Many recent advances in hybrid laser and modulator technology High speed direct modulation possible using τ p modulation τ p modulation possible with loss modulation or Mach Zehnder couple rings Zero chirp possible with dual drive III-V Region OI Region n-contact N P N P P Modulation section feed-back line p-contact H H io 2 insulator i ubstrate p-ingaas p-inp Cladding p-algainas CH AlGaInAs MQWs N-contactor P-contactor Gain section p-contact n-inp n-inp/ingaasp L 35

36 Thanks. 36