![Optoelectronic Systems Integration in Silicon
DC-86GHz, low power TIA, in 130nm BiCMOS
64 Ran Ding, et al., Power-efficient low-noise 86 GHz broadband amplifier in 130-nm SiGe BiCMOS, under review at Electronics Letters
0 200 400 600 800 1000
0
0.2
0.4
0.6
0.8
1
[1][2]
[3]
[4]
[5]
[6][7]
This work
Power (mW)
Gain*bandwidth(THz)
• 86 GHz bandwidth, 20 dB gain transimpedance amplifier
(TIA), consuming only 89 mW DC power
– Best power efficiency compared to the state-of-the art
Q1
Q2
Q3
Q4
Q5
IN
OUT
Rfb
R1
R2
R3
R4
R6
R5L2
L3
L4
L1
L5
Vcc
Vcc
Vcas
Comparison to other SiGe broadband amplifiers](https://image.slidesharecdn.com/rdthesisdefense2014slidesharereduced-170622134302/85/High-Speed-Optical-Modulators-and-Data-Communication-Systems-in-Silicon-Photonics-64-320.jpg)
High-Speed Optical Modulators and Data Communication Systems in Silicon Photonics
- 1. Optoelectronic Systems Integration in Silicon Grating Coupler Germanium Photodetector Si Modulator or Rib Waveguide Si substrate Si BOX SiO2 AI Ge Channel Waveguide 750 nm 220 nm 500 nm 600 nm 750 nm 600 nm 60 nm 130 nm 1.5 µm 2 µm The Building Blocks of Silicon Photonics Systems Focuses and organization of this work 1 Modulator device innovations (Ch. 2 &3) Platform development and system design (Ch. 4) Interfacing electronics (analog front-end) and E-P co-design (Ch. 5) Vtb Vcas Vcas Vcas Vcas Vtb_main Vcas Vcas In+ In- To next In+ To next In- Out+ Out- Vtb_relay Vtb_relayVtb Vtb Vtb Vtb Vtb Vtb_main To relay stage To relay stage Vcas Vcas G S G G S G Vcc Vcc Diff. RF in Optical waveguide Silicon pn junction traveling-wave optical phase- shifter In+ In- Flip-chip bump bonding interface Delay/relay stage Main driver amplifier stage (a) (b) (c) 13 ps (d) DC bias Input Out1+ Out1- Out2+ Out2- Out3+ Out3- Out4+ Out4- 1mm 2.9mm IN OUT Vcas G G G G G GG Vcc Vcc2 L1 L2 L3 L5 L4 L6 L7 Cpd 0.9 mm 0.6 mm Vtb Vcas Vcas Vcas Vcas Vtb_main Vcas Vcas In+ In- To next In+ To next In- Out+ Out- Vtb_relay Vtb_relayVtb Vtb Vtb Vtb Vtb Vtb_main To relay stage To relay stage Vcas Vcas G S G G S G Vcc Vcc Diff. RF in Optical waveguide Silicon pn junction traveling-wave optical phase- shifter In+ In- Flip-chip bump bonding interface Delay/relay stage Main driver amplifier stage (a) (b) (c) 13 ps (d) DC bias Input Out1+ Out1- Out2+ Out2- Out3+ Out3- Out4+ Out4- 1mm 2.9mm Image credit: OPN (a) (b) 1mm
- 3. Optoelectronic Systems Integration in Silicon The need for (silicon) optical interconnects 3 • Optical interconnect is a promising and necessary approach to meet the ever-increasing demand in data communication capacity, – Clouding computing, mega data centers – Metro-area link, long-haul telecom – Inter-rack, inter-chip interconnects • Need a cost-effective, versatile, scalable optical interconnect technology
- 4. Optoelectronic Systems Integration in Silicon What makes silicon photonics attractive? 4 • Silicon is not an intrinsically good material for optics – It fails to provide material properties for almost any active optical components one would need (more details later) • Being able to scale is the key reason – Referring to the success of microelectronics in silicon – Silicon photonics can (potentially) achieve complex functionality and high performance on-chip, with low cost Baehr-Jones, Tom, Thierry Pinguet, Patrick Lo Guo-Qiang, Steven Danziger, Dennis Prather, and Michael Hochberg. "Myths and rumors of silicon photonics." Nature Photonics 6, no. 4 (2012): 206-208. Image credit: Intel
- 5. Optoelectronic Systems Integration in Silicon An example optical link 5 • Key components – CW Laser: the signal carrier – Modulator: data encoder form electrical to optical domain – Waveguide/Fiber: optical path from point A to point B – Detector: convert signal from optical to back electrical Figure from: Long Chen, et al., “Integrated GHz silicon photonic interconnect with micrometer- scale modulators and detectors”, Optics Express (17) 17, 2009
- 6. Optoelectronic Systems Integration in Silicon Progress and challenges in silicon photonics 6 • Basic passive components are available in silicon – Low loss waveguides, grating-couplers, couplers – Advanced components under active research: polarization diversity components for example • Lasers – Difficult to make silicon lase, due to indirect bandgap – III/V hybrid integration (e.g. Intel/UCSB, IMEC/LETI) used in Intel’s recent demo • Photo-detection – Working wavelength is chosen in the silicon transparent window, narrower bandgap material is needed for detection – Ge on Si waveguide detectors with BW of 120GHz (Vivien et al. 2012) • Modulation – Silicon lattice is symmetric, no electro-optic (Pockel) coefficient – Efficient modulators are critical components, yet remain to be a key challenge – But • New material (such as polymers) can be incorporated • Plasma dispersion effect can be exploited • Co-design with electronics can potentially enhance modulator and overall performance • Significant barrier to system level design – Lack established / stable fabrication processes – Lack process design kits (PDK) or EDA based design flow • SPICE – empirical extracted models; Design Rule Checking (DRC); Layout versus Schematic (LVS); Parasitic extractions, corner models and more…
- 7. Optoelectronic Systems Integration in Silicon Grating Coupler Germanium Photodetector Si Modulator or Rib Waveguide Si substrate Si BOX SiO2 AI Ge Channel Waveguide 750 nm 220 nm 500 nm 600 nm 750 nm 600 nm 60 nm 130 nm 1.5 µm 2 µm The Building Blocks of Silicon Photonics Systems Focuses and organization of this work 7 Modulator device innovations (Ch. 2 &3) Platform development and system design (Ch. 4) Interfacing electronics (analog front-end) and E-P co-design (Ch. 5) Vtb Vcas Vcas Vcas Vcas Vtb_main Vcas Vcas In+ In- To next In+ To next In- Out+ Out- Vtb_relay Vtb_relayVtb Vtb Vtb Vtb Vtb Vtb_main To relay stage To relay stage Vcas Vcas G S G G S G Vcc Vcc Diff. RF in Optical waveguide Silicon pn junction traveling-wave optical phase- shifter In+ In- Flip-chip bump bonding interface Delay/relay stage Main driver amplifier stage (a) (b) (c) 13 ps (d) DC bias Input Out1+ Out1- Out2+ Out2- Out3+ Out3- Out4+ Out4- 1mm 2.9mm IN OUT Vcas G G G G G GG Vcc Vcc2 L1 L2 L3 L5 L4 L6 L7 Cpd 0.9 mm 0.6 mm Vtb Vcas Vcas Vcas Vcas Vtb_main Vcas Vcas In+ In- To next In+ To next In- Out+ Out- Vtb_relay Vtb_relayVtb Vtb Vtb Vtb Vtb Vtb_main To relay stage To relay stage Vcas Vcas G S G G S G Vcc Vcc Diff. RF in Optical waveguide Silicon pn junction traveling-wave optical phase- shifter In+ In- Flip-chip bump bonding interface Delay/relay stage Main driver amplifier stage (a) (b) (c) 13 ps (d) DC bias Input Out1+ Out1- Out2+ Out2- Out3+ Out3- Out4+ Out4- 1mm 2.9mm Image credit: OPN (a) (b) 1mm
- 8. Optoelectronic Systems Integration in Silicon Outline 8 • Introduction - summary – Need for more data transmission capacity – Silicon photonics as a promising technology – Challenges remain, especially in modulators and systems – Organization of this work • Modulator device innovations • Platform development and system designs • Electronics and E-P co-design
- 9. Optoelectronic Systems Integration in Silicon Outline 9 • Introduction • Modulator device innovations – Silicon slot + EO polymer • First demonstration of silicon-organic modulator with GHz bandwidth • First RF device with < 1V Vπ – Silicon PN junction + traveling-wave design • Traveling-wave design study and device results • Slow-wave electrode traveling-wave Mach-Zehnder (TWMZ) • Platform development and system designs • Electronics and E-P co-design
- 10. Optoelectronic Systems Integration in Silicon Electro-optical Modulators 10 Principle of operation, Mach-Zehnder • Combining two voltage-controlled phase shifters, you can build an amplitude modulator with a Mach-Zehnder geometry Input Optical Radiation Δφ = 2π λ neff λ( )L Δφ = 2π λ neff λ( )+ ∂neff λ( ) ∂V ⎛ ⎝ ⎜ ⎞ ⎠ ⎟L I0 I1 1 2 1+ cos 2π λ L ∂neff λ( ) ∂V V ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ ⎛ ⎝ ⎜⎜ ⎞ ⎠ ⎟⎟ 10*log10 I1 I0 ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ Note I0, I1 indicate the modulator Insertion loss:
- 11. Optoelectronic Systems Integration in Silicon Vπ and VπL 11 • Vπ – voltage required to create pi phase difference between two arms – i.e. output changes from max transmission to min transmission – Commercial 40Gb/s Lithium Niobate modulator nowadays has ~6V Vπ • Phase shifter accumulate phase by – Efficient phase shifter means higher – Longer phase shifter has lower Vπ, so a length- independent parameter Vπ*L is often used to compare efficiency of the modulator arm design, the lower the better Δφ = 2π λ ∂neff λ( ) ∂V ⎛ ⎝⎜ ⎞ ⎠⎟ L ∂neff ∂V Vπ L = π 2k0 ∂neff /∂V( )
- 12. Optoelectronic Systems Integration in Silicon EO polymer as voltage-controlled phase shifter 12 • Using second order nonlinear polymer as voltage controlled phase shifter material to achieve Dx = ε0 εEx + χ2 Ex 2 ( ) Fundamental equation Dx = ε0 ε EOx + ERFx( )+ χ2 EOx + ERFx( )2 ( ) In the presence of an RF field Dx = ε0 ε + 2χ2 ERFx( )EOx( ) The result: an effective change in dielectric constant due to the RF field Here, terms that do not guide in waveguide are neglected (in other situations they would lead to frequency doubling, optical rectification, etc) Dx = ε0 ε ERFx( )EOx( ) ∂neff ∂V
- 13. Optoelectronic Systems Integration in Silicon More on why use polymers 13 • Performance: – Nonlinear activity > 10x Lithium Niobate. (and material is commercially available) – Continued advances in activity and theoretical understanding (active research here at UW Chemistry and Material Science) • CMOS compatibility – Spin coating on chip – Very low temperature cure (~100 oC) • Low optical index (1.4~1.8) – Can easily work with existing silicon structures without disturbing the optical mode
- 15. Optoelectronic Systems Integration in Silicon Leveraging field enhancement, twice 15 • Optically, index change needs to overlap well with optical mode to affect nneff • Electrically, applied voltage should induce Erf efficiently – although polymer based phase shifter is a voltage controlled device, what really matters is Erf as it shows up in – How to make the two silicon arm as RF electrodes? dneff dnmaterial = 2nmaterial dneff dεmaterial = 2nmaterial E 2 dS R1∫ µ0 ε0 ExHy * − Hx * Ey + Ex * Hy − Ey * Hx( )dS R2∫ = 2nmaterial Z0 E 2 dS R1∫ 2 Re Ex * Hy − Ey * Hx ⎡⎣ ⎤⎦dS R2∫
- 16. Optoelectronic Systems Integration in Silicon Modification on slot waveguides 16 Striploading • 0.8 dB/coupler • 2 dB/cm R. Ding, et al., Opt. Express 18, 25061-25067 (2010).
- 17. Optoelectronic Systems Integration in Silicon Asymmetric strip-loaded slots 17 Design consideration • Asymmetric configuration is for – fabrication robustness – easier coupling – better tradeoff between silicon conductivity and optical loss (due to shorter e-folding distance) R. Ding, et al., Applied Physics Letters, 98, 233303 (2011).
- 18. Optoelectronic Systems Integration in Silicon Slot waveguide silicon-polymer modulator 18 3 GHz device • Device layout R. Ding, et al., Opt. Express 18, 15618-15623 (2010). • 200 nm slots • 1 mm length • 80um length difference in two arms • Boron 1018 cm3 blanket, 1020 cm3 contact doping • 10um metal-waveguide clearance
- 19. Optoelectronic Systems Integration in Silicon Slot waveguide silicon-polymer modulator 19 Polymer poling • AJSP100 series EO polymer, spin coat • Poling field 100V/um to orient polymer molecule • Push-pull configuration • Poling temperature 110C
- 20. Optoelectronic Systems Integration in Silicon Slot waveguide silicon-polymer modulator 20 • DC Vπ = 8V, i.e. VπL = 0.8V-cm • Corresponding to r33 = ~40pm / V – Polymer fully poled in bulk has r33 65pm / V – 80% poling efficiency
- 21. Optoelectronic Systems Integration in Silicon Slot waveguide silicon-polymer modulator 21 • Bandwidth measurement (EO S21) Laser (+ possibly EDFA) Modulator (DUT) VNA Port 1 Photo- detector Port 2 - Bandwidth 3GHz, measurement from 200Hz to 3GHz - S21 absolute value is matched with DC Vπ, broadband operation was indeed due to polymer index change S21 = 20log10 RPl 1 2 π Vπ ⎛ ⎝⎜ ⎞ ⎠⎟
- 22. Optoelectronic Systems Integration in Silicon Sub-Volt silicon-polymer modulator 22 • 0.68 Vπ, ~0.8 Vπ-cm – It can be estimated that only 0.23V is required to generate an 5dB extinction ratio eye-diagram – Severe BW limitation due to low-res substrate R. Ding, et al., Journal of Lightwave Technology, 29 (8), 1112-1117 (2011).
- 23. Optoelectronic Systems Integration in Silicon Limitations of polymer-based devices 23 • Several reliability-related characteristics remain to be improved significantly to be practically useful – Material thermal stability – Light sensitivity – Repeatability – Power handling • Expensive ($$$$/gram) • Each device require individual poling and will depole other devices – Practical schemes of poling multiple devices simultaneously need to be devised before large-scale integration • Nonetheless, linear phase shifter, highly efficient, attractive for low density analog applications
- 24. Optoelectronic Systems Integration in Silicon Plasma dispersion effect in silicon 24 • Soref’s pioneer work on the effect of free carrier density changing the refractive index – Some dynamic loss, usually tolerable Soref, Richard A., and Brian R. Bennett. "Electrooptical effects in silicon." Quantum Electronics, IEEE Journal of 23, no. 1 (1987): 123-129.
- 25. Optoelectronic Systems Integration in Silicon Silicon PN junction modulators 25 • PN junction integrated in waveguide • Depletion region largely overlap with optical mode • Voltage controlled depletion region (carrier density change) generating optical index change Reed, Graham T., G. Mashanovich, F. Y. Gardes, and D. J. Thomson. "Silicon optical modulators." Nature photonics 4, no. 8 (2010): 518-526.
- 27. Optoelectronic Systems Integration in Silicon Comparison between slot-polymer and PN junction modulators, key differences 27 • Modulation efficiency is lower in PN junction -> larger device footprint, more challenging RF design – i.e. VπL in plasma dispersion device is inferior (larger) compared to slot modulators due to lack of the highly active polymer material • Capacitance per device length is much higher in PN junction devices -> more difficult to drive at high speed – Slot width ~200nm, εpolymer ~4 – PN junction depletion width 50~100nm, εsilicon ~12 • PN junction devices are less “analog-friendly” – Depletion width / carrier density has square root dependence on voltage in stead of linear – Dynamic loss • More CMOS compatibility and scalability by moving to all-silicon devices
- 28. Optoelectronic Systems Integration in Silicon Drive PN junction with transmission lines 28 Why using transmission line electrode? - Large total Cpn hard to drive at high speed - Large device size can’t function as a lumped device at high speed Treat device as a modified transmission line Zdev = L C = Ltl Ctl + Cpn Approximately: vp = 1 Ltl Ctl + Cpn( )
- 29. Optoelectronic Systems Integration in Silicon Δφ f( ) = Δβfulle−αx/2 dx = 0 Lrf ∫ Δφ 0( ) Lrf e−αx/2 dx = 0 Lrf ∫ Δφ 0( ) Lrf 1− e −α f( )Lrf /2 α f( )/ 2 1 Lrf 1− e −α f6 dB( )Lrf /2 α f6dB( )/ 2 = 1 2 ⇒ α f3dB( )Lrf ≈ 0.74neper ≡ 6.4dB Traveling-wave modulator, ideal in brief 29 • Absorb PN junction capacitance into a transmission line • Modulation voltage signal travel at the same speed as optical wave – At the moment, let’s assume it can be achieved by design • RF loss would determine the 3dB bandwidth – 3dB bandwidth is the frequencywhen the accumulated modulation strength falls to 1/sqrt(2) V(z) = V0 exp α f( )z( ) End-of-line loss Frequency dependent RF loss
- 30. Optoelectronic Systems Integration in Silicon RF loss mechanisms 30 • Two mechanisms for RF loss: metal skin resistance (Rtl) and silicon resistance (Rpn) α = αmetal +αsilicon ≈ 1 2 Rtl f( ) Zdev + 2π 2 RpnCpn 2 Zdev f 2
- 31. Optoelectronic Systems Integration in Silicon Rpn loss, likely the dominate source of RF loss at high frequencies 31 α = αmetal +αsilicon ≈ 1 2 Rtl f( ) Zdev + 2π 2 RpnCpn 2 Zdev f 2 (1) In principle, sqrt(f) dependence, scales slow with frequency, is more significant at low frequencies (2) Scales fast with frequency, dominant source of RF loss, limiting bandwidth Rtl and Rpn loss for an actual TWMZ
- 32. Optoelectronic Systems Integration in Silicon Device performance scaling 32 • A few observations regarding achievable device length (and Vπ): – 1. Building long device (low Vπ) is increasing difficult at high frequency – 2. Junction metric: • Highly efficient junction (low VπL) need to come with a decent RpnCpn^2 to maintain a low Rpn loss at high frequencies – 3. Designing at low impedance seems advantageous Ldev = 0.74 2π 2 fEO,3dB 2 Zdev 1 RpnCpn 2 or 0.74 π fEO,3dB 2 Zdev frc Cpn Vπ ≈ Vπ Lπ( )/ Ldev ∝ fEO,3dB 2 Ldev ∝ 1 Zdev ,Vπ ∝ Zdev Ldev ∝ 1 RpnCpn 2 ,Vπ ∝ Vπ Lπ( )RpnCpn 2 1 2 ⇒ α fEO,3dB( )Ldev ≈ 0.74Neper = 6.4dB 1 2 Rtl f( ) Zdev + 2π 2 RpnCpn 2 Zdev f 2
- 33. Optoelectronic Systems Integration in Silicon Device implementations using our findings 33 • A 30 GHz Traveling-wave Mach-Zehnder modulator – Target for 40 Gb/s applications – Lower impedance for overall improved performance – 6-layer implants to optimized Rpn – Relatively low implantation in junction to achieve a good tradeoff in R. Ding, et al., Optics Communications 321 (2014): 124-133. Ldev ∝ 1 RpnCpn 2 ,Vπ ∝ Vπ Lπ( )RpnCpn 2
- 34. Optoelectronic Systems Integration in Silicon 10 20 30 40 50 −15 −10 −5 0 5 EO S21 Frequency (GHz) EOResponse(dB) 0V bias −1V bias −3dB marker 30GHz Traveling-wave Mach-Zehnder modulators 34 • 3mm long, 7.8V small signal Vπ, 2.6 Vπ-cm • 30 GHz bandwidth • 3.2 dB low loss on phase shifter • State-of-the-art combined performance metrics
- 35. Optoelectronic Systems Integration in Silicon 0 10 20 30 40 50 −40 −30 −20 −10 0 Frequency (GHz) RFS21andS11(dB) 0 10 20 30 40 50 −15 −10 −5 0 5 Frequency (GHz) NormalizedEOS21(dB) Analytical modelling of EO response at different termination impedance S21, Zterm =50 S11, Zterm =50 S21, Zterm =33 S11, Z term =33 S21, Z term =25 S11, Z term =25 EO S21, Zterm =50 EO S21, Zterm =33 S21, Zterm =25 −3dB marker13GHz 29GHz 23GHz 30GHz Traveling-wave Mach-Zehnder modulators 35 • Effects of mismatched termination – A tradeoff between extended bandwidth and reduced DC response
- 37. Optoelectronic Systems Integration in Silicon 40 Gb/s slow-wave electrode TWMZ 37 • Silicon pn junction traveling-wave modulator is challenging to design at high impedance (50Ω) – Highly capacitive junction – Need to maintain velocity matching to optical wave • A new type of RF design in Si TWMZ – Slow-wave electrode instead of GS coplanar strip GS coplanar strip Slow-wave Tline
- 38. Optoelectronic Systems Integration in Silicon 40 Gb/s slow-wave electrode TWMZ 38 • Slow-wave tline provides more inductance with little capacitance overhead, effectively raising impedance – (b) (c) (d) • However, two problems to be solved – it slows down the wave velocity considerably (e) • Optical group index: ~4 • RF index: ~7 – RF loss due to metal (Rtl) also increases (a) 5 10 15 20 0 5 10 Frequency (GHz) Rtl(Ohm/mm) 5 10 15 20 0 0.5 1 1.5 Frequency (GHz) Ltl(nH/mm) 5 10 15 20 100 200 300 Frequency (GHz) Ctl(fF/mm) 5 10 15 20 20 40 60 80 Frequency (GHz) real(Z)(Ohm) 5 10 15 20 2 4 6 8 Frequency (GHz) n eff coplanar GS strip TLine pn junction loaded coplanar GS strip TLine slow−wave TLine pn junction loaded slow−wave TLine pn junction capacitance 5 10 15 20 0 5 10 Frequency (GHz) Rtl(Ohm/mm) 5 10 15 20 0 0.5 1 1.5 Frequency (GHz) Ltl(nH/mm) 5 10 15 20 100 200 300 Frequency (GHz) Ctl(fF/mm) 5 10 15 20 20 40 60 80 Frequency (GHz) real(Z)(Ohm) 5 10 15 20 2 4 6 8 Frequency (GHz) neff coplanar GS strip TLine pn junction loaded coplanar GS strip TLin slow−wave TLine pn junction loaded slow−wave TLine pn junction capacitance (a) (c) (e) (b) (d)
- 40. Optoelectronic Systems Integration in Silicon 40 Gb/s slow-wave electrode TWMZ 40 • Key considerations: – RF loss – RF multi-mode – Velocity matching • Periodical phase-matching 0 10 20 30 0 5 10 15 20 25 30 Frequency (GHz) RFlossduetoRtl andRpn (dB/cm) R tl loss Rpn loss Total loss 0 2 4 6 8 10 10 15 20 25 Number of optical delay loops EOBandwidth(GHz) periodical phase matched contiuously velocity matched (a) (b) (a) (b) 1mm
- 41. Optoelectronic Systems Integration in Silicon 40 Gb/s slow-wave electrode TWMZ 41 • 3mm long active length, 3.5mm overall length • ~8V small-signal Vπ similar as before • S-parameter measurements, 27 GHz bandwidth • S11 below -18 dB, good matching to 50Ω • Smooth curve; differential mode measurement overlaps with single-ended measurements – G-tie is effective in suppressing RF multi-mode (a) (b)
- 42. Optoelectronic Systems Integration in Silicon 40 Gb/s slow-wave electrode TWMZ 42 • Eye diagrams and BER vs OSNR measurements – Optical signal to noise ratio (OSNR) describes channel “quality”, thus put device in fair comparison – Bit-error-rate test using a reference receiver gives a quantitative measurement of data transmission (231-1) 90% 10% EDFA (Eye diagrams) (Bit-error-rate) (OSNR and spectrum) 50% 50% Electrical connections Optical connections (a)
- 44. Optoelectronic Systems Integration in Silicon 40 Gb/s slow-wave electrode TWMZ 44 • At 4.8 Vpp diff drive, Si TWMZ showed comparable performance relative to a commercial Lithium Niobate modulator in BER-OSNR • At 1.6Vpp, Si TWMZ showed 2dB OSNR penalty EDFA Electrical connections Optical connections (b)
- 45. Optoelectronic Systems Integration in Silicon 40 Gb/s slow-wave electrode TWMZ 45 • Corresponding eye diagrams at error-free (BER <1e-12) • Si-TWMZ Full-drive extinction ratio R. Ding, et al,“High-speed silicon modulator with slow-wave transmission line electrodes,” under review at JLT 10% EDFA (Eye diagrams) (Bit-error-rate) (OSNR and spectrum) 50% 50% (c) Lithium Niobate, 5.4Vpp drive (d) Si TWMZ, 4.8Vpp dual drive (e) Si TWMZ, 1.6Vpp dual drive (a) 12.4dB ER at 28Gb/s (b) 10.4dB ER at 40Gb/s
- 46. Optoelectronic Systems Integration in Silicon Outline 46 • Introduction • Modulator device innovations • Platform development and system designs – OpSIS-IME platform development: • 25 Gb/s to 50 Gb/s, 1550 nm and 1310 nm – System designs and implementations: • 320 Gb/s WDM transmitter • Highlights of other systems • Electronics and E-P co-design
- 47. Optoelectronic Systems Integration in Silicon Latest OpSIS-IME process, device examples 47 1549.4 1549.5 1549.6 1549.7 1549.8 −40 −35 −30 −25 −20 Wavelength/nm power/dBm −0.5V 0V 0.5V 1V 1.5V 2V 3V 0 10 20 30 40 50 60 70 −75 −72 −69 −66 −63 −60 −57 Frequency (GHz) EOS21Mag(dB) 0 10 20 30 40 50 60 70 −20 0 20 40 60 80 100 EOS21Phase(Deg) 60 GHz detectors Packaging Grating couplers 45 GHz Ring Modulators EC2-Optimized passives Sub-1V modulators: 40 Gbit modulators
- 48. Optoelectronic Systems Integration in Silicon Publications on OpSIS-IME Si Photonics platform 48 • R. Ding, T. Baehr-Jones, T. Pinguet, J. Li, N. C. Harris, M. Streshinsky, L. He, A. Novack, A. E-J. Lim, T- Y. Liow, S. H-G. Teo, G-Q. Lo and M. Hochberg, "A Silicon Platform for High-Speed Photonics Systems", (upgraded as invited paper at OFC/NFOEC 2012). • Y. Liu, R. Ding, M. Gould, T. Baehr-Jones, Y. Yang, Y. Ma, Y. Zhang, A. E.-J. Lim, T.-Y. Liow, S. H.-G. Teo, G.-Q. Lo, M. Hochberg, “30 GHz Silicon Platform for Photonics System”, (invited), Optical Interconnects 2013 • M. Streshinsky, R. Ding, Y. Liu, A. Novack, C. Galland, A. E-J. Lim, P. G.-Q. Lo, T. Baehr-Jones, and M. Hochberg, “The Road to Affordable, Large-Scale Silicon Photonics”, Optics and Photonics News, OSA, Sept. 2013 (Cover and featured article) • M. Hochberg, N. C Harris, R. Ding, Y. Zhang, A. Novack, Z. Xuan, T. Baehr-Jones, “Silicon Photonics: The Next Fabless Semiconductor Industry”, IEEE Solid-State Circuits Magazine, 5 (1), 48-58, 2013
- 49. Optoelectronic Systems Integration in Silicon A very brief overview of ring modulators 49 1553.8 1553.9 1554 1554.1 1554.2 1554.3 1554.4 1554.5 1554.6 1554.7 −20 −15 −10 −5 0 Wavelength (nm) Transmission(dB) 0.2 V −0.4 V −1V −2V −3V −4V −5V 0 1 2 3 4 5 −20 0 20 40 60 80 100 Voltage (V) Peakwavelengthshift(pm) ~25pm/V ER 7.5um radius Q=5,000
- 50. Optoelectronic Systems Integration in Silicon 320 Gb/s, 8-ch WDM Ring Tx 50 • 8ch WDM transmitter based on thermally tuned PN junction ring modulators • Ring mod offers compact footprint and low power consumption • Largest aggregated data rate in silicon Tx Ran Ding*, Yang Liu*, (*equal contribution) and et al., manuscript under preparation, preliminary results to be presented at OFC 2014
- 51. Optoelectronic Systems Integration in Silicon Spectra and eye-diagrams 51 • Thermal tuning to equal channel spacing – Ring sizes are slightly different to have a roughly equal spacing – Thermal fine tuning on to 200 GHz grid: 17 mW overall • Eye diagrams of each channel – Ring capacitance ~25fF – Energy per bit with 4.8 Vpp drive (2.6V bias, ~5dB ER, 5dB bias loss): 144 fJ/bit – Energy per bit with 2.4 Vpp drive (1.1V bias, ~3dB ER, 7dB bias loss): 36 fJ/bit 1540 1545 1550 1555 1560 −20 −15 −10 −5 0 Wavelength (nm) Normalizedopticalspectrum(dB) Before tuning After tuning Ch1 Ch2 Ch3 Ch4 Ch5 Ch6 Ch7 Ch8
- 53. Optoelectronic Systems Integration in Silicon Bit-error-rate tests 53 • 8 channels showed relatively uniform performance (OSNR penalty variation <2dB) • At 4.8 Vpp drive, exhibit 3.5 dB OSNR penalty compared to commercial Lithium Niobate modulator • Additional 2.7 dB penalty when at low drive (2.4 Vpp)
- 54. Optoelectronic Systems Integration in Silicon Other systems at a glance 54 • 160 Gb/s Mod-MUX transmitter, a new topology – Zero cross-talk – Easy to integrated with single-wavelength lasers – Convenient to interface with control circuitry 2.4Vpp drive, BER ~1e-12Yang Liu*, Ran DIng*, (*equal contribution) and et al., manuscript under preparation, preliminary results to be presented at OFC 2014
- 57. Optoelectronic Systems Integration in Silicon Other systems at a glance – tunable 4:1 MUX/deMUX 57 • Mach-Zehnder interleaver (MZI) provides an ideal solution for wavelength MUX – a key component in WDM, we demonstrate – The first silicon MZI MUX at 1310 – Also, the first tunable MUX with fully integrated monitor photodetector, thermal tuner, and loss tuner for precise tuning and fully configuration feedback loop – For a 1-to-4 MUX, 14 tuning and monitoring knobs are provided, while desired operation can be achieved with a minimum of 3 control knobs 1-to-4 MUX/deMUX device cell Spectra, after tuning - 18 mW tuning power - 200 GHz channel spacing - < 1dB variation - < 1.5 dB insertion loss IBM, 2013 Intel, 2008 Luxtera, 2007 Our work # of channels, and spacing 8-ch, 200 GHz 8-ch, 200 GHz 4-ch, 200 GHz 4-ch (16-ch design to be tested), 200 GHz Center λ 1550 1550 1550 1310 & 1550 Tuning elements Not tunable Thermal tuner Thermal tuner Thermal tuner, loss tuner and monitor PD Insertion Loss 0.4 ~ 1.6 dB 2.6 dB Not reported 1.5 dB Worst-case Xtalk -18 dB -13 dB -20 dB -17dB Comparison to other MZI MUX in silicon
- 58. Optoelectronic Systems Integration in Silicon Other systems at a glance - – tunable 16:1 MUX/deMUX 58 • We also implemented the largest tunable MZI MUX in silicon: 16- channel MUX/deMUX – Thermal tuner, loss tuners and 14 bi-directional monitor photodetector are integrated – Minimum number of tuning knob needed is 15 • Chip is to be packaged before testing. Electrical layout by Yunchu Li 2.7 mm 5 mm
- 59. Optoelectronic Systems Integration in Silicon Other systems at a glance – 4x40G WDM Tx and Rx 59 On-chip PBSR is designed by Hang Guan & Yang Liu TWMZs Laser input fiber couplers 4:1 MUX Output fiber coupler 5 mm 5 mm λ1 λ1 PBSR PD array , with dual input for TE and TM branches VOA$ VOA$ PR$ PBS$ TE TM TE λ2 λ1 λ3 λ4 λ2 λ1 λ3 λ4 EC$ 1:4 deMUX 2.5 mm 2.5 mm
- 60. Optoelectronic Systems Integration in Silicon Outline 60 • Introduction • Modulator device innovations • Platform development and system designs • High speed electronics and E-P co-design – Co-designed driver • showing the possibility of 100 Gb/s NRZ in today’s silicon- base technologies – Receiver circuitries: • 86 GHz TIA, broadband & high efficiency in GBW/power • 40 GHz pTIA, tunable gain peaking 20 to 32 dB • 50 Gb/s parasitic-insensitive full receiver
- 61. Optoelectronic Systems Integration in Silicon Typical optical transceivers, analog front-end 61 Modulator driver CW laser Modulator Photodetector Transimpedance amplifier deMUX ... MUX ... Fiber channel (pre-amp) (VGA / LA) 2.5 3 3.5 onTWMZ ventional m) 5 6 7 uirement V/3)(V) (a) • Modulator driver – Generating sufficient voltage swing to create optical modulation – State-of-the-art in Si/SiGe: 3Vpp on each output at 40Gb/s • Transimpedance amplifier (TIA) – Low-noise is key to better sensitivity (usually reported in average optical power) – State-of-the-art with non-avalanche PD: -15 dBm at 25 Gb/s, -10 dBm at 40 Gb/s
- 62. Optoelectronic Systems Integration in Silicon Modulator scaling to higher channel data rate 62 • Adopting higher channel data rates – greatly reduce the complexity in optics communication systems – further improve interconnect capacity and density • Follow the analysis in TWMZ designs we project the scaling of Si TWMZ towards higher data rates – Voltage required is substantially higher than the state-of-the-art today Modulator driver CW laser Modulator Photodetector Transimpedance amplifier deMUX ... MUX ... Fiber channel (pre-amp) (VGA / LA) 40 50 60 70 80 90 100 0 0.5 1 1.5 2 2.5 3 3.5 Data rate (Gb/s) MaxlenghtofsiliconTWMZ modulatorinconventional driverscheme(mm) 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 Drivervoltagerequirement (differential−driveV/3)(V) (a) (b) Ldev = 0.74 2π 2 fEO,3dB 2 Zdev 1 RpnCpn 2 or 0.74 π fEO,3dB 2 Zdev frc Cpn
- 63. Optoelectronic Systems Integration in Silicon Multi-section TWMZ driver, in 130nm BiCMOS 63 • Distributed traveling-wave modulator driver – Significantly reduce driver voltage requirement – 100Gb/s NRZ made possible for the first time with today’s silicon modulator performance Ran Ding, et al. 100-Gb/s NRZ Optical Transceiver Analog Front-End in 130-nm SiGe BiCMOS, submitted to Optical Interconnect Conference 2014 DC bias Input Out1+ Out1- Out2+ Out2- Out3+ Out3- Out4+ Out4- 1mm 2.9mm Diff. RF in Optical waveguide Silicon pn junction traveling-wave optical phase- shifter In+ In- Flip-chip bump bonding interface 40 50 60 70 80 90 100 0 0.5 1 1.5 2 2.5 3 3.5 Data rate (Gb/s) MaxlenghtofsiliconTWMZ modulatorinconventional driverscheme(mm) 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 Drivervoltagerequirement (differential−driveVπ/3)(V) 10 ps 2Vpp Post-layout simulation: 100G eye-diagrams Driveroutput Modulator response Chip is to be packaged with photonics chip before testing
- 64. Optoelectronic Systems Integration in Silicon DC-86GHz, low power TIA, in 130nm BiCMOS 64 Ran Ding, et al., Power-efficient low-noise 86 GHz broadband amplifier in 130-nm SiGe BiCMOS, under review at Electronics Letters 0 200 400 600 800 1000 0 0.2 0.4 0.6 0.8 1 [1][2] [3] [4] [5] [6][7] This work Power (mW) Gain*bandwidth(THz) • 86 GHz bandwidth, 20 dB gain transimpedance amplifier (TIA), consuming only 89 mW DC power – Best power efficiency compared to the state-of-the art Q1 Q2 Q3 Q4 Q5 IN OUT Rfb R1 R2 R3 R4 R6 R5L2 L3 L4 L1 L5 Vcc Vcc Vcas Comparison to other SiGe broadband amplifiers
- 65. Optoelectronic Systems Integration in Silicon DC-86GHz, low power TIA, in 130nm BiCMOS 65 • State-of-the-art low-noise performance: 20.4 pA/sqrt(Hz) input referred noise current density • Projected average optical power sensitivity: -14.6 dBm at 100 Gb/s NRZ – Assuming 1A/W photodetector and 60 GHz electrical filter bandwidth Measured 50G Extracted 100G performance from measured S-parameters 0 20 40 60 80 100 20 30 40 50 60 Transimpedance(dB) Frequency (GHz) 0 20 40 60 80 100 10 20 30 40 50 Inputreferrednoise(pA/Hz) 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 ba
- 66. Optoelectronic Systems Integration in Silicon 40 GHz BW tunable gain-peaking TIA (pTIA) 66 – TIA designed with simple tuning knob to tune the peaking profile for compensation of slow elements in a optical receiver IN OUT Vcc Vcc Vcc2 Vcas M1 M2 M3 M4 L1 L3 L2 L4 L7 L6 L5 R1 R2 R3 R4 Cpd ron 1/gm i i IN OUT Vcas G G G G G GG Vcc Vcc2 L1 L2 L3 L5 L4 L6 L7 Cpd 0.9 mm 0.6 mm 5 10 15 20 25 30 35 40 45 50 −60 −40 −20 0 20 40 Frequency (GHz) S−parameters(dB) S21, 12 dB peaking S11, 12 dB peaking S22, 12 dB peaking S12, 12 dB peaking S21, flat response S11, flat response S22, flat response S12 , flat response
- 67. Optoelectronic Systems Integration in Silicon 40 GHz BW tunable gain-peaking TIA (pTIA) 67 • Measurements and characterization in an optical test bed Ran Ding, et al., 40-GHz bandwidth transimpedance amplifier with adjustable gain-peaking in 65-nm CMOS, manuscript under prep (a) (d) (f) (e) (c) (b) CW#Laser# 12.5G#PPG# 1:4#spli4er#and#delay# 4:1#MUX,#50Gb/s#output#(231-1 PRBS) Tektronics#DSA# PhotoI detector# (Eye diagrams) Reference# Clock# Electrical connections Optical connections pTIA Lithium Niobate modulator Modulator driver 10 20 30 40 50 0 10 20 30 40 50 60 Transimpedance(dB) Frequency (GHz) 10 20 30 40 50 0 5 10 15 20 25 30 Inputreferrednoise(pA/Hz) 50 Gb/s eye diagrams
- 68. Optoelectronic Systems Integration in Silicon 50Gb/s input-parasitics-insensitive receiver 68 • One significant challenge for electronics-photonics integration is the RF parasitics at the interface. • Typical packaging parasitics – Bump bonding: ~40 fF – Wire-bonding: 300~500 pH • Typical device capacitance – Photodetector: 15 fF – Ring modulator: 25 fF • A receiver that is tolerant to packaging parasitics is highly desirable
- 69. Optoelectronic Systems Integration in Silicon 50Gb/s input-parasitics-insensitive receiver 69 • While maintaining state-of-the-art performance: – 60 mW DC power consumption, ~10 mW due to biasing – 50 uApp sensitivity for BER = 1e-12, this is equivalent to -13dBm optical modulation amplitude sensitivity with 0.5A/W detector, this is comparable to the best in literature at 25 Gb/s – Receiver enters limiting mode above 40 uApp, overload level ~800 uApp – Output swing 300mVpp , can directly interface with BERT • Rx designed to be very tolerant to parasitics at input node Output eye-diagrams at 50Gb/s - red: PD only - Blue: 800pH additional inductance Output eye-diagrams at 50Gb/s - red: PD only - Blue: 100fF additional capacitance
- 71. Optoelectronic Systems Integration in Silicon Closing remarks, future work 71 • Silicon-polymer modulators – Substantial device performance improvement possible with polymer innovation and novel optics designs – Larger scale, more complexity – New applications Korn, Dietmar, Robert Palmer, Hui Yu, Philipp C. Schindler, Luca Alloatti, Moritz Baier, René Schmogrow et al. "Silicon-organic hybrid (SOH) IQ modulator using the linear electro-optic effect for transmitting 16QAM at 112 Gbit/s." Optics express 21, no. 11 (2013): 13219-13227. Weimann, C., P. C. Schindler, R. Palmer, S. Wolf, D. Bekele, D. Korn, J. Pfeifle et al. "Silicon-organic hybrid (SOH) frequency comb sources for terabit/s data transmission." Optics Express 22, no. 3 (2014): 3629-3637.
- 72. Optoelectronic Systems Integration in Silicon Closing remarks, future work 72 • Silicon PN junction modulators – Novel PN junction design – Large scale integrations – Advanced applications Liu, Yang, Scott Dunham, Tom Baehr-Jones, Andy Eu-Jin Lim, Guo-Qiang Lo, and Michael Hochberg. "Ultra-responsive Phase Shifters for depletion mode silicon modulators." Journal of Lightwave Technology 31, no. 23 (2013): 3787-3793. Conventional junction geometry New PN junction geometry Credit: Matt Streshinsky, Ari Novack
- 73. Optoelectronic Systems Integration in Silicon Closing remarks, future work 73 • System designs and electronics – More complete EDA tools enabling PCell, LVS, parasitic extraction – Yield and corner simulation in early design phase – Closer integration and co-design with electronics for improved overall performance