40-Gb/s Optical Buffer Design and Simulation

Transcription

1 40-Gb/s Optical Buffer Design and Simulation Hyundai Park, Emily F. Burmeister, Staffan Björlin, and John E. Bowers Electrical and Computer Engineering Department University of California at Santa Barbara This work supported by DARPA through the LASOR program 1

2 Outline Introduction - Motivation and Device Structure Simulation Model and Method - Flow Chart - Model Description Results: Performance Dependence on - - Waveguide - Bandpass Filter - Optical Input Power Conclusions

3 Motivation Goal: To investigate 100 Tbit/s transparent optical packet switched networks Problem: Provide a means to store optical packets to reduce contention and packet loss Input Buffering ing& ing Output 3

4 Motivation Goal: To investigate 100 Tbit/s transparent optical packet switched networks Problem: Provide a means to store optical packets to reduce contention and packet loss. Solution: OPTICAL BUFFER should be realized with.. -Low signal degradation during storage -Fast switching time Requirements: -Buffering time increment; 10 ns corresponding to 40 bytes with guard signals (40 Gb/s) -Hold a packet up to 100 ns 4 -ing time less than 1ns

5 Proposed Device Silica Waveguide IN OUT InP Si Recirculating loop with spiral silica waveguide Length of 10 cm with 0.05 db/cm propagation loss InP and MZI based optical switch Provide gain and fast switching time 5 1 cm with 5 db/cm propagation loss

6 Flowchart Signal Input Initial Loss Silica Waveguide BER estimation 40 Gb/s, RZ Gaussian Pulse shape TE Polarization Input Field S in (t) 6

7 Flowchart Signal Input SiO Waveguide Initial Loss Silica Waveguide IN OUT BER estimation Initial Loss at the Input S sw (t) = S in (t) L 0 (L 0 = L C +L INP ) 7

8 Flowchart Signal Input SiO Waveguide Initial Loss Silica Waveguide IN OUT BER estimation Noise Filtering in Band Pass Filter S (t) = IFT(S sw (f) T (f)) 8

9 Model - & x InP MZI based Optical - Propagation Loss: 5 db per roundtrip - Assumptions: No crosstalk Ideal switching characteristics (Step function response) Band Pass Filter - Super Gaussian Shape Transfer Function T (ω) = exp f f f 0 m 9

10 Flowchart Signal Input SiO Waveguide Initial Loss Silica Waveguide IN OUT BER estimation Propagation in Waveguide S W (t) = IFT(S (f) D(f)) N(t) 10

11 Model - Silica Waveguide - Signal propagation Standard Fourier Domain Split-Step (FDSS) Method 1, - Assumption: Polarization is maintained in the waveguide. A( z + z, t) = IFT( A( z, ω)exp( Dˆ ( ω) z)) exp( Nˆ ( t) z) ˆ i D( ω) = α SiO + βω + Nˆ ( t) = iγ A( z, t) i 6 3 β ω 3 3 λ λ β = D β 3 = ( D + λs) πc (πc) γ = n ω 0 ca eff 1 R. H. Hardin and F. D. Tappert, SIAM Rev. Chronicle 15, 43 (1973) R. A. Fisher and W. K. Bischel, Appl. Phys. Lett. 3, 661 (1973); J. Appl. Phys. 46, 491 (1975) 11

12 Flowchart Signal Input SiO Waveguide Initial Loss Silica Waveguide IN OUT BER estimation Amplification in S (t)= IFT(FT(S W (t) G(t)) T G (f))+s ASE (t) 1

13 Gain Characteristics Model MQW - Rate Equation in Multiple Quantum Well s - Confinement factor (Γ): Length from 500 μm to mm τd τn τe dn dt dn dt B W dp dz I N B N Γ B qn 0 w = + evsch τ n τ d τ e N B Nw N w N = vga ln Γqτ d τ n τ e N w tr N N w vg hνv p = Γa ln P N, P = N P tr L P 13

14 Noise - Assumption: white Gaussian noise σ = f ) f N ASE N ASE ( 0 0 ) = ( G 1) nsphf0 ( G 1) Model MQW ( f NF hf Gain Ripple due to Reflection between facets 0 R) T G = iωnl / c 1 (1 G R e G 14

15 Flowchart Coupling Loss, Propagation loss Signal Input SiO Waveguide Initial Loss Silica Waveguide IN OUT BER estimation Optical S out (t)=s (t) L SW (L SW = L C + L INP ) 15

16 Gain Regulation G 0 G Final Roundtrip Loss P 1st P nd P 3rd P 4th P 5th P in - Amplifier gain is saturated to roundtrip loss typically within10 circulations. - Gain saturation occurs due to gain regulation behavior. 16

17 17 Maximum Delay (µs) Dependence on Dispersion 10 9 L round = 1.5 db 8 Delay per roundtrip = 10ns 7 D=5 ps/km-nm P in =13 dbm D=15 ps/km-nm P in =7 dbm Gain (db) - Without gain dynamics of the, the performance is limited by ASE noise accumulation at low gain Dispersion at high gain - Dispersion of 5 ps/km-nm is expected in the silica waveguide. 5 μsec delay with moderate input power and gain Maximum Number of Roundtrips

18 Dependence on Gain Dynamics Maximum Delay (ns) P in = 7 dbm Delay per roundtrip = 10 ns P 3dB = 0dBm P 3dB = 17dBm P 3dB = 14dBm Roundtrip Loss = 1.5 db Maximum Number of Roundtrips Gain (db) - Typical carrier life time in the ; ~50ps ns maximum delay with P sat = 17 dbm - Pattern effect dominates the overall performance. 18

19 Dependence on Facet Reflectivity Maximum Delay (ns) R= Gain (db) W avelength (nm) P in = 10 dbm Roundtrip Loss = 1.5dB Delay per roundtrip = 10 ns Gain (db) db Gain G 0 =db and R= db accumulated distortion at 10 circulations R=0 - Reflectivity should be kept less than 10-5 to achieve large delay Maximum Number of Roundtrips 19

20 Dependence on Bandwidth Maximum Delay (ns) m = 3 10 m = m = Filter Bandwidth (nm) Maximum Number of Roundtrips - Filter Bandwidth < nm; limited by passband flatness - Filter Bandwidth > nm; limited by ASE noise accumulation 0 - Optimum bandwidth is a compromise between distortion and noise.

21 Dependence on Input power Maximum Delay (ns) P 3dB = 0dBm Delay per roundtrip = 10 ns L C = 1dB G 0 = 18dB L C = 3dB L C = 5dB G 0 = db G 0 = 6dB Average Input Power (dbm) Maximum Number of Roundtrips Maximum Pin = 10 dbm 160 L round = 17.5 db 110 L round = 1.5 db 60 L round = 5.5 db -Maximum delay tends to be saturated at high input power. -It can be attributed to fast gain saturation. 1

22 Overall Device Performance P db = 13dBm 17dBm Carrier Life Time = ps

23 Conclusions Performance of optical buffer was predicted using FDSS and a rate equation model. The maximum delay is limited to 100 ns in 40Gb/s system by the pattern effect due to gain dynamics. Nonzero reflectivity of the and non-ideal transfer function of the can degrade the performance due to accumulated distortion. 3