Silicon Photonic Devices for Advanced Modulation Formats

Transkript

1 Silicon Photonic Devices for Advanced Modulation Formats M. Berroth, W. Vogel, W. Sfar Zaoui, T. Föhn, S. Klinger IX. ITG Workshop FG Photonische Komponenten und Mikrosysteme

2 Content Motivation Silicon Waveguiding Structure Fiber Coupling Polarization Splitting Devices Multimode Interference Coupler Germanium on Silicon Photodiodes Summary 2

3 INT Research Vision Electronics Discrete Circuits Resistors, Capacitors, Inductors, Transistors, Integrated Circuits Resistors, Capacitors, Inductors, Transistors, Optics Classic Optics Prisms, Lenses,... Integrated Optics Waveguides, Splitters, Optical Switches,... Optoelectronic Integrated Circuit (OEIC) Integrated Photodetector Integrated Amplifier + Signal Conversion and Processing 3

4 Optical Communication: 100 Gbit/s Link Example E/O-IQ-Modulator O/E-IQ-Demodulator 4

5 Silicon Waveguides Why Silicon? - Si is transparent at telecom wavelengths - high refractive index (n Si 3.5) - Si waveguide thin Si film required Silicon on Insulator (SOI) - SOI wafer commercially available - Standard process with nm structure size - VLSI Electronics - Intensity modulators do work (Intel) SiO 2 - no (good) Si light sources Si 220 nm - no (pure) Si detectors SiO 2 5

6 SOI Waveguides 500 nm Typical structure Air or SiO2 Luft / SiO 2 Si 220 nm SiO 2 Attenuation about 2 db/cm 6

7 Core of a single mode fiber Grating Coupler Motivation Si-waveguide ~ 0.5 μm mode mismatch between small rectangular waveguide and large circular core high losses ~ 10 μm solutions: Taper Prism Grating 7

8 Core of a single mode fiber Grating Coupler Motivation Si-waveguide ~ 0.5 μm mode mismatch between small rectangular waveguide and large circular core high losses ~ 10 μm solutions: Taper Prism Grating 8

9 Core of a single mode fiber Grating Coupler Motivation Si-waveguide ~ 0.5 μm mode mismatch between small rectangular waveguide and large circular core high losses ~ 10 μm solutions: Taper Prism Grating 9

10 Grating Coupler Definitions TM β -1 β 1 TE θ m = -1 m = 1 θ TM TE k in Λ objective: efficient coupling from fiber to waveguide and vice versa utilize polarization dependency (polarization beam splitter) k in β sinθ 2π λ 0 n 2π m Λ eff β 10

11 Grating Coupler in epixfab (imec04) Technology [nm] air SiO2 Si SiO2 Si tunable laser (1550nm)/ DBR laser (1310 nm) OPT IN OPT OUT polarization control RF IN SMF fiber holder SMF optical power meter DUT xyz-manipulator with piezo actuator Hosni 11

12 Grating Coupler in epixfab (imec04) Technology Taper Grating coupler Device under test Single mode waveguide w = 500 nm w = 10 μm 12

13 TE polarization: Coupling Efficiency / Measurement Results 1300 nm grating coupler Efficiency dependence on input angle 13

14 Transmission [db] Transmission [db] Improved Coupling Efficiency Standard design Improved design (additional technological steps required) BW 1dB = 49 nm -10 BW 1dB = 38 nm Measurement Wavelength [m] Bandwidth: BW 1dB = 38 nm BW 3dB = 65 nm Transmission max = db -15 Simulation Wavelength [m] Bandwidth: BW 1dB = 49 nm BW 3dB = 81 nm Transmission max = db 14

15 Transmission Grating Coupler as Polarization Beam Splitter SiO 2 Si SiO 2 TM Λ θ TE Si-thickness = 250 nm SiO 2 -thickness = 1 μm Depth = 70 nm Λ, θ TM: m = -1 Filling factor= 0.5 TE: m = 1 Λ = 630 nm Λ = 630 nm 640 nm 650 nm 660 nm 670 nm 640 nm 650 nm 660 nm 670 nm TE TM θ [deg] θ [deg] 15

16 Grating Coupler as Polarization Beam Splitter TE input TM input Λ = 640 nm θ = 17 λ = 1550 nm max - max T = db t SiO2 = 1 μm T = db t SiO2 = 3 μm T = db T = db Efficiency depends on thickness of buried SiO 2 layer 16

17 Transmission 2D-Grating Coupler Simulation θ TM x y Λ, R, θ TE SiO 2 Si SiO 2 2R Λ TM: x-direction TE: y-direction Si-thickness = 250 nm SiO 2 -thickness = 1 μm Depth = 70 nm Circular holes R = 175 nm R = 215 nm Grating period [μm] 17

18 2D-Grating Coupler Simulation Λ = 580 nm R = 200 nm θ = 10 TE TM T = db t SiO2 = 1 μm T = db T = db t SiO2 = 3 μm T = db T = db t SiO2 = 3 μm + improved design T = -2.1 db 18

19 Normalized transmission at output 1 [db] Normalized transmission at output 2 [db] Photonic Crystal Polarisation Splitter 1 TM 2 1 TE 2 a = 660 nm R = 200 nm Width of waveguide = 400 nm 10.6 μm min max 8.7 μm TM db TE db TE TM Simulation Measurement Simulation Measurement Wavelength [nm] Wavelength [nm] 19

20 Multimode Interference Coupler (MMI) Wide waveguide: several guided modes 2D-model: Even modes: even number of nodes Odd modes: odd number of nodes y y sin 1 WMMI 20

21 Multimode Interference Coupler (MMI) Field of one single mode: yexp jt z L n f W MMI L Input field: y, 0 c y Field at z = L: y, L c exp 2 j 3L L 21

22 Multimode Interference Coupler (MMI) L p3l, p 0,2,4,... All modes in phase L p3l, p 1,3,5,... Even modes in phase Odd modes in opposition 0 3 L π 6.0 L π z y, L c exp ν ν(ν+2) j 3L L 22

23 Multimode Interference Coupler (MMI) L p 2 3L - Even modes in phase p 1,3,5,... - Odd modes in quadrature, y, L c exp 0.5*ν(ν+2) mod ν ν(ν+2) , , ,5 2 j 3L L z L π 3 L π 4.5 L π 6.0 L π 3dB coupler 23

24 Multimode Interference Coupler (MMI) Application as 2 x Hybrid E 1 y,0 E 2 y,0 Δx 1 Δx 2 L MMI W MMI y,0expj E y,0exp 1 E1 1 2 j E E 1 E y,0exp j E y,0exp j 0. 5 z 1 2 y,0exp j E y,0exp j 0 1 y,0exp j E y,0exp j

25 Multimode Interference Coupler (MMI) 2 x Hybrid Dimensions: about 10 µm x 200 µm (picture is not to scale!) Further applications: 1 x N splitter / combiner 25

26 Ge on Si Photodetectors for Oblique Light Incidence R TT R 2 R DS L S C TT R 1 AC C D R D C P R P transit time VCVS inner diode contact structure 26

27 Measurement Results: PDs, Frequency Domain Improvements: 39 GHz Reduced series resistance R S More accurate setup (LCA = Light Component Analyser) 49 GHz Photodiode with r = 5 μm λ 0 = 1550 nm 27

28 voltage SiGe Bipolar Limiting Amplifier 50 Gbit/s 580 µm V CC I Bias V EE V CC V CC dummy metal structures V CC 100 µm in p in n out n out p 580 µm up to 12.5 Gbit/s V CC V CC dummy metal structures V EE V EE V CC V CC 300 mv SiGe Bipolar Process Infineon (B7HF200) 10 ps f T = 200 GHz time 28

29 Slave Master clk-distribution Architecture of 25 GS/s 6 bit INT-ADC V out1 <1:6> Logic Switch MUX & OD 12 Logic Switch Thermometer- Thermometer- to-binary- to-binary- Converter Converter Reference- Ladder + Calibration Flash-ADC Flash-ADC Calibrated Buffers+ 2 nd T&H Reference- Ladder + Calibration V in T&H V clk 360 Bit Control- Register Calibrated Buffers+2 nd T&H Flash-ADC Flash-ADC Reference- Ladder + Calibration Thermometer- to-binary- Converter Logic Switch 12 MUX & OD Thermometer- to-binary- Converter Logic Switch Reference- Ladder + Calibration V out2 <1:6> 29

30 Layout + Chip of 25 GS/s 6 bit INT-ADC 30

31 Performance of 25 GS/s 6 bit INT-ADC ADC V1 V2 Number of cores 2 4 Die-Size 2116x1916 um x1916 um 2 Core-Size 600x500 um 2 750x1000 um 2 Power supplies VDD ovdr =+0.5 V VDD =0 V VSS =-1.25 V VDD ovdr =+0.5 V VDD =0 V VSS =-1.25 V P loss 2.3 W W 2.1 W W f S ~25 GS/s >25 GS/s f 3dB of the S&H <14 GHz 14 GHz Nominal resolution n 6 Bit 6 Bit Effective resolution GS/s GS/s 5.2 <

32 VLSI-Viterbi-Equalizer for 43 Gbit/s Architecture: Sliding-Window 32-fold parallel Input data: 3 bit (4 x Gb/s) Branch metric: 6 bit Trace metric: 8 bit Power consumption: 2.6 W Power supply: 1 V Technology: CMOS 90 nm Area: 5.7 mm² (ca Transistors) Components: 256 Add-Compare-Select-Units (8 bit RCA f. Addition u. Compare) bit Memory for branch metric 32 trace back memories Internal clock: 1.34 GHz (CMOS) External clock: 5.35 GHz (half rate CML) Layout Chip photo 32

33 Summary Integration of complex optical receiver is feasible! - grating couplers with low loss and arbitrary location on chip surface - act as polarization splitter simultaneously - photonic crystal polarization splitters are even smaller - MMI as small area hybrids - Germanium photodetectors -Postprocessing with fast CMOS 3-D-Integration in the future? 33