420 Gbit/s optical signal reception enabled by an inductive gain peaking Ge-Si photodetector with 80†GHz bandwidth.

Based on the commercial silicon photonics (SiPh) process platform, a flat 3 dB bandwidth of 80 GHz germanium-silicon (Ge-Si) photodetector (PD) is experimentally demonstrated at a photocurrent of 0.8 mA. This outstanding bandwidth performance is achieved by using the gain peaking technique. It permits an 95% improvement in bandwidth without sacrificing responsivity and undesired effects. The peaked Ge-Si PD shows the external responsivity of 0.5 A/W and internal responsivity of 1.0 A/W at a wavelength of 1550 nm under -4 V bias voltage. The high-speed large signal reception capability of the peaked PD is comprehensively explored. Under the same transmitter state, the transmitter dispersion eye closure quaternary (TDECQ) penalties of the 60 and 90 Gbaud four-level pulse amplitude modulation (PAM-4) eye diagrams are about 2.33 and 2.76 dB, 1.68 and 2.45 dB for the un-peaked and peaked Ge-Si PD, respectively. When the reception speed increase to 100 and 120 Gbaud PAM-4, the TDECQ penalties are approximatively 2.53 and 3.99 dB. However, for the un-peaked PD, its TDECQ penalties cannot be calculated by oscilloscope. We also measure the bit error rate (BER) performances of the un-peaked and peaked Ge-Si PDs under different speed and optical power. For the peaked PD, the eye diagrams quality of 156 Gbit/s nonreturn-to-zero (NRZ), 145 Gbaud PAM-4, and 140 Gbaud eight-level pulse amplitude modulation (PAM-8) are as good as the 70 GHz Finisar PD. To the best of our knowledge, we report for the first-time a peaked Ge-Si PD operating at 420 Gbit/s per lane in an intensity modulation direct-detection (IM/DD) system. It might be also a potential solution to support the 800 G coherent optical receivers.

Experimental demonstration of a 160 Gbit/s 3D-integrated silicon photonics receiver with 1.2-pJ/bit power consumption.

By using the flip-chip bonding technology, a high performances 3D-integrated silicon photonics receiver is demonstrated. The receiver consists of a high-speed germanium-silicon (Ge-Si) photodetector (PD) and a commercial linear transimpedance amplifiers (TIA). The overall 3 dB bandwidth of the receiver is around 38 GHz with appropriate gain. Based on this 3D-integrated receiver, the 56, 64, 90, 100 Gbit/s non-return-to-zero (NRZ) and 112, 128 Gbit/s four-level pulse amplitude (PAM-4) modulation clear openings of eye diagrams are experimentally obtained. The sensitivities of -10, -5.2 dBm and -6.6, -2.7 dBm were obtained for 112 Gbit/s NRZ and 160 Gbit/s PAM-4 at hard-decision forward err correction (HD-FEC,3.8 × 10-3) and KP4 forward err correction (KP4-FEC,2 × 10-4) threshold, respectively. Additionally, the lowest power consumption of this receiver is about 1.2 pJ/bit, which implies its huge potential for short-reach data center applications.

214.7 Tbit/s S, C, and L-band transmission over 50†km SSMF based on silicon photonic integrated transceivers.

We experimentally demonstrate a 214.7 Tbit/s generalized mutual information (GMI) estimated throughput by ultra-wideband wavelength division multiplexing (WDM) transmission in standard single-mode fiber (SSMF). With 50-GHz grid, 396 transmission channels are used to deliver 49 GBaud probabilistically constellation-shaped (PCS) 256 quadrature amplitude modulation (QAM) and PCS-64QAM signals. Silicon photonic integrated transceiver is employed to complete electro-optic and optic-electro conversion of the modulated signals. S, C, and L-band rare-earth-doped amplifiers enable the 19.8 THz bandwidth WDM transmission without the assistance of distributed Raman amplification. The measured data rate shows great potential for Silicon photonic devices deployed in ultra-wideband WDM transmission.

400Gb/s real-time coherent PON based on a silicon photonic integrated transceiver.

We experimentally demonstrate the real-time 100/200/400 Gb/s/λ coherent passive optical networks (PONs) based on silicon photonic integrated transceiver. We investigate different configuration schemes of coherent PONs including: (1) using a Erbium doped optical fiber amplifier (EDFA) as a booster at the transmitter side; (2) using a semiconductor optical amplifier (SOA) as a booster at the transmitter side; (3) using EDFA at the transmitter side and a pre-amplified SOA at receiver side; (4) using an SOA at the transmitter side and an SOA at the receiver side. The performance of these schemes for different data rates of downstream transmission is evaluated, and the appropriate choices under different circumstances are analyzed. The real-time experimental results indicate that the EDFA can be replaced by SOA as a booster at the transmitter side in 100/200 Gb/s/λ coherent PON based on the dual-polarization QPSK (DP-QPSK) scheme with a small performance penalty. In dual-polarization a 16 quadrature amplitude modulation (DP-16QAM) 400 G/s/λ PON system, EDFA booster is preferred because an SOA introduces more nonlinearity for the 16QAM scheme. The power budget of 32.5 dB is achieved for 400 Gb/s/λ coherent PON after the 20 km standard single mode fiber (SSMF) transmission under the soft-decision feedforward error correction (SD-FEC) threshold.

C + L band polarization rotator-splitter based on a compact S-bend waveguide mode demultiplexer.

A novel high-fabrication-tolerance mode demultiplexer (MD) based on an S-bend waveguide is designed, which is used to split TE1 mode and TE0 mode, and convert the TE1 mode to TE0 mode. Based on the MD, a polarization-rotator-splitter (PRS) is demonstrated. The transmission losses of the fabricated PRS are lower than 0.5 dB and 0.6 dB for TE0 mode and TM0 mode, respectively, in the wavelength span of 1520-1630 nm. And the corresponding polarization extinction ratios are larger than 19.5 dB and 17.6 dB, respectively. This MD has the most compact size comparing with other experimentally demonstrated MDs used in PRS.

100 Gbit/s co-designed optical receiver with hybrid integration.

We demonstrate a co-designed optical receiver, which is hybrid-integrated with a silicon-photonic photodetector (PD) and silicon-germanium (SiGe) trans-impedance amplifier (TIA). Accurate equivalent circuit models of PD and electrical parasitic of chip-on-board (COB) assembly are built for co-simulation with TIA. Inductive peaking and equalizer (EQ) techniques are proposed in the design of TIA to extend the bandwidth of the optical receiver. The measured electrical 3-dB bandwidth of TIA and optical-to-electrical (O-E) 3-dB bandwidth of optical receiver are above 36.8 GHz and 36 GHz, respectively. For the optical receiver, clear eye diagrams up to a data rate of 80 Gbit/s are realized. The bit-error ratios (BER) for the NRZ signal with a different bit rate and received optical power are experimentally measured, and 100 Gbit/s NRZ operation is successfully achieved with a soft-decision forward error correction (SD-FEC) threshold.

180 Gbit/s Si3N4-waveguide coupled germanium photodetector with improved quantum efficiency.

A high quantum efficiency (QE) and high-speed silicon nitride (Si3N4) waveguide coupled germanium-on-silicon photodetector (Ge-on-Si PD) is presented. The proposed device is fabricated in a commercial 90 nm silicon photonics process platform. By decreasing the spacing between the tapered Si3N4 waveguide and the bottom Si to 200 nm and the Si3N4 thickness to 300 nm, the QE is significantly improved. Although the theoretical responsivity can reach up to 0.92 A/W at 1550 nm, the measured value is calculated to be approximately 0.61 A/W. The maximum experimental responsivity is about 0.9 A/W at 1485 nm. The 3 dB optoelectrical bandwidth of up to 54 GHz is demonstrated at a -3.3V bias. Additionally, the 80, 90, 100, and 105 Gbit/s non-return-to-zero on-off-keying and the 150, 160, 170, and 180 Gbit/s four-level pulse amplitude modulation clear openings of the electrical eye diagrams are attained. Overall, the Si3N4-waveguide coupled Ge-on-Si PD in this work possesses higher QE and operates at the highest data rates reported so far.

High-performance germanium avalanche photodetector for 100 Gbit/s photonics receivers.

A high-bit rate and low-bias voltage waveguide-integrated vertical germanium avalanche photodetector is reported with doping optimization. This scheme alleviates the necessity of complex epitaxial single-crystal silicon layer and multiple ion implantation schemes. The optical absorption and carrier avalanche multiplication gain occur in the same germanium layer. The maximum gain is estimated to be 112.4 at an input power of -30.2dBm. With the input optical power of -16.1dBm, the gain-bandwidth product of nearly 141 GHz is obtained at 7.8 V bias. Meanwhile, a 4.6 dB sensitivity improvement for 60 Gbit/s signal reception is demonstrated with an avalanche gain of 5.1 at a soft-decision forward-error correction threshold (SD-FEC), i.e., bit-error-rate of 2×10-2. The absolute sensitivities of photonics receivers are -21, -18.6, -15.9, and -11.5dBm for 40, 60, 80, and 100 Gbit/s non-return-to-zero signals at the SD-FEC threshold. These demonstrated characteristics enable the reliable and robust on-chip photodetection for energy efficienct silicon photonic interconnects in the future.

High-speed lateral PIN germanium photodetector with 4-directional light input.

We experimentally demonstrate a high-speed lateral PIN junction configuration germanium photodetector (Ge-PD) with 4-directional light input. The typical internal responsivity is about 1.23 A/W at 1550 nm with 98% quantum efficiency and dark current 4 nA at 1V reverse-bias voltage. The equivalent circuit model and theoretical 3-dB opto-electrical (OE) bandwidth of Ge-PD are extracted and calculated, respectively. Compared to the conventional lateral PIN Ge-PD with 1-directional light input, our proposed device features uniform optical field distribution in the absorption region, which will be benefit to realize high-power and high-speed operation. In particular, in the condition of 0.8 mA photocurrent, the measured 3-dB OE bandwidth is about 17 GHz at bias voltage of -8 V which is well matched to the theoretical estimated bandwidth. With additional digital pre-compensations provided by the Keysight arbitrary waveform generator (AWG), the root raised cosine (RRC) filter and roll-off factor of 0.65 are employed at transmitter (TX) side without utilizing any offline digital signal processing (DSP) at receiver (RX) side. The 50 Gbit/s, 60 Gbit/s, 70 Gbit/s, and 80 Gbit/s non-return-to-zero (NRZ), and 60 Gbit/s, 70 Gbit/s, 80 Gbit/s, and 90 Gbit/s four-level pulse amplitude modulation (PAM-4) clear opening of eye diagrams are realized. In order to verify the high-power handling performance in high-speed data transmission, we also investigate the 20 Gbit/s NRZ eye diagram variations with the increasing of photocurrent.

Design and demonstration of ultra-high-Q silicon microring resonator based on a multi-mode ridge waveguide.

We present the design and experimental demonstration of the ultra-high-Q-factor silicon microring resonator based on a multi-mode ridge waveguide. The multi-mode ridge waveguide is designed to decrease the propagation loss and to improve the Q factor. The ultra-high Q factor of 1.1×106 is experimentally demonstrated, with the free spectrum range of 0.208 nm. The single-mode ridge waveguide is used in the coupling region to reduce the dimension of the microring resonator, and the bend radius is only 20 µm. To precisely control the resonance wavelength, a small heater is implemented on the silicon microring resonator with the tuning efficiency of 7.1 pm/mW. The degenerate four-wave mixing of the silicon microring resonator is investigated, and the conversion efficiency is measured to be -15.5 dB without optimizing the dispersion of the microring resonator and carriers extraction.

Silicon nitride O-band (de)multiplexers with low thermal sensitivity.

In this paper, four-channel cascaded Mach-Zehnder interferometer-based wavelength (de)multiplexers in the O-band are demonstrated experimentally by utilizing silicon nitride (SiN) optical waveguides. By reference to the commonly used 100 Gigabit Ethernet standards, two types of (de)multiplexer devices with different channel spacings are designed and fabricated. Both the devices exhibit low insertion loss and flat passbands. The lower thermo-optical coefficient provided by SiN brings benefits of reduction in thermal sensitivity. The fabricated (de)multiplexers show a temperature-dependent wavelength shift of about 18.5 pm/°C, which is reduced by 75% compared to the standard silicon-based devices.

Mode-selective wavelength conversion of OFDM-QPSK signals in a multimode silicon waveguide.

We experimentally demonstrate on-chip mode-selective wavelength conversions based on the degenerate four-wave mixing (FWM) nonlinear effect in a few-mode silicon waveguide. A multimode waveguide with tapered directional coupler based mode (de)multiplexers is designed and fabricated. Using signals with advanced modulation formats all-optical wavelength conversions of 102.6-Gb/s OFDM-QPSK signals are verified. Experimental results show that only small optical signal-to-noise ratio (OSNR) penalties are observed after wavelength conversion of both modes, which are less than 2 dB for OFDM-QPSK at 7% forward error correction (FEC) threshold.

Highly efficient silicon optical polarization rotators based on mode order conversions.

We design and demonstrate the novel silicon optical polarization rotators (PRs) based on the TM(0)-TE(n)-TE(0) mode conversions inside the waveguide. The TM(0)-TE(n) mode converters are realized by the mode hybridization of the tapered rib waveguides. The TE(n)-TE(0) mode converters based on the beam shaping method are followed to complete the PRs function. By using the TE(1), TE(2), and TE(3) mode as the transitional mode, the fabricated PRs show the insert losses of less than 0.4, 0.5, and 1 dB, respectively. The corresponding polarization extinction ratios of larger than 21, 18, and 23 dB, over a wavelength range of 100 nm.

Low-loss and fabrication tolerant silicon mode-order converters based on novel compact tapers.

We propose large bandwidth and high fabrication-tolerance mode-order converters on the silicon-on-insulator platform based on novel compact tapers structures. Each of the converters is in a single waveguide. Designs of different symmetries with and without breaking the parities between odd and even modes are illustrated. The fabrication tolerances of the devices are also investigated. The simulation results show that high conversion efficiencies can be readily achieved over a wavelength range from 1520 nm to 1580 nm for all of the proposed devices. The average conversion efficiencies of TE1-to-TE0, TE2-to-TE0, TE3-to-TE0, TE2-to-TE1, TE3-to-TE1, and TE3-to-TE2 converters are -0.061 dB, -0.052 dB, -0.11 dB, -0.119 dB, -0.168 dB, and -0.154 dB, respectively. The conversion efficiencies have negligible degradations under normal width and thickness deviations.