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Segmenting a silicon modulator can substantially increase its electro-optic bandwidth without sacrificing modulation efficiency. We demonstrate a segmented silicon IQ modulator and experimentally explore both modulator design and operating point to optimize systems trade-offs in coherent detection. An electro–optic bandwidth of greater than 40 GHz is measured for a 4-mm-long segment, and greater than 60 GHz for a 2-mmlong segment. We evaluate optical transmission experimentally at 120 Gbaud for 16-ary quadrature amplitude modulation (QAM) and 32QAM. The segments are operated in tandem with identical data at each segment. We present an experimental method to align data timing between the segments. Through the optimization of segment biasing and linear compensation, we have achieved a bit error rate (BER) of 16QAM well below the 20% forward error correction (FEC) threshold (2 × 10−2 ). Adding nonlinear pre-compensation allows for 32QAM with a BER below the 24% FEC threshold (4.5 × 10−2 ), enabling a net rate of 483 Gbs per polarization. The modulator can also be operated as an optical digital analogy converter for complex optical signal generation, for which 100 Gbs is achieved for a proof of concept.

We propose a novel design of a silicon photonic modulator that has a high modulation efficiency and that is tolerant to temperature variations. A series of phase-shifted Bragg gratings are placed in each arm of a Mach-Zehnder interferometer in order to provide enhanced phase modulation. The slow light effect in these ultra-compact coupled resonators improves phase modulation efficiency compared to conventional silicon phase shifters. These Bragg grating cavities are designed such that the optical bandwidth is increased compared to other coupled resonators such as micro-rings. This improved bandwidth reduces the temperature sensitivity of the devices. We present in detail how to optimize these modulators considering properties such as modulation efficiency (Vπ×L), optical modulation amplitude (OMA), and optical bandwidth (λBW); the latter property determining the operating temperature range (T). As examples, we present two designs that meet different target specifications for short-reach or long-haul applications. We further provide a model, based on coupled mode theory, to investigate the dynamic response of the proposed modulators. A large signal analysis is performed using finite difference time domain (FDTD) in order to simulate on/off keying (OOK) modulation and eye diagrams up to 110 Gb/s.

Silicon photonics has enormous potential for ultrahigh-capacity coherent optical transceivers. We demonstrate an IQ modulator using silicon photonic traveling-wave modulators optimized for higher-order quadrature amplitude modulation (QAM). Its optical and RF characteristics are studied thoroughly in simulation and experiment. We propose a system-orientated approach to optimization of the silicon photonic IQ modulator, which minimizes modulator-induced power penalty in a QAM transmission link. We examine the trade-off between modulation efficiency and bandwidth for the optimal combination of modulator length and bias voltage to maximize the clear distance between adjacent constellation points. This optimum depends on baud rate and modulation format, as well as achievable driving voltage swing. Measured results confirm our prediction using the proposed methodology. Without pre-compensating bandwidth limitation of the modulator, net data rates up to 232 Gb/s (70 Gbaud 16-QAM) on single polarization are captured, indicating great potential for 400+ Gb/s dual-polarization transmission.

We establish experimentally the suitability of an all-silicon optical modulator to support future ultra-high-capacity coherent optical transmission links beyond 400 Gb/s. We present single-carrier data transmission from 400 Gb/s to 600 Gb/s using an all-silicon IQ modulator produced with a generic foundry process. The operating point of the silicon photonic transmitter is carefully optimized to find the best efficiency bandwidth trade-off. We present a methodology to split pre-compensation between digital and optical stages. For the 400 Gb/s transmission, we achieved 60 Gbaud dual-polarization (DP)-16QAM, reaching a distance of 1,520 km. Transmission of 500 Gb/s was further tested using 75 Gbaud 16QAM and 60 Gbaud 32QAM, reaching 1,120 km and 480 km, respectively. We finally demonstrated 72 Gbaud DP-32QAM (720 Gb/s) transmitted over 160 km and 84 Gbaud DP-16QAM (672 Gb/s) transmitted over 720 km, meeting the threshold for 20% forward error correction overhead and achieving net rates of 600 Gb/s and 576 Gb/s, respectively. To the best of our knowledge, these are the highest baud-rate coherent transmission results achieved using an all-silicon IQ modulator. We have demonstrated that we can reap the myriad advantages of SiP integration for transmission at extreme bit rates.

Silicon photonics has enormous potential for ultrahigh-capacity coherent optical transceivers. We demonstrate an in-phase and quadrature (IQ) modulator using silicon photonic traveling-wave modulators optimized for higher order quadrature amplitude modulation (QAM). Its optical and RF characteristics are studied thoroughly in simulation and experiment. We propose a system-orientated approach to optimization of the silicon photonic IQ modulator, which minimizes modulator-induced power penalty in a QAM transmission link. We examine the tradeoff between modulation efficiency and bandwidth for the optimal combination of modulator length and bias voltage to maximize the clear distance between adjacent constellation points. This optimum depends on baud rate and modulation format, as well as achievable driving voltage swing. Measured results confirm our prediction using the proposed methodology. Without precompensating bandwidth limitation of the modulator, net data rates up to 232 Gb/s (70 Gbaud 16-QAM) on single polarization are captured, indicating great potential for 400+ Gb/s dual-polarization transmission.

Bragg gratings with phase-shifts are inserted in a Mach-Zehnder modulator to enhance phase modulation, reduce device length and improve efficiency (Vπ×L=0.28 Vcm). Simulations show 3 nm optical bandwidth corresponding to 50 K operating temperature range.

Silicon photonic (SiP) electro-optic modulators are a key component in cost-efficient and integrated optical transmitters. Modulator design traditionally uses figure of merits (FOMs) that characterize modulation efficiency and propagation loss of light, which underestimate the modulator-induced power penalty due to intersymbol interference, as they do not consider the electro-optic bandwidth limitation. We show that in the presence of limited electro-optic bandwidth of the SiP modulator, the conventional FOMs, such as VπL and V παL, are unable to predict the minimum transmitter power penalty (TPP). Normalized optical modulation amplitude (OMAN) is proved through simulation to be a reliable tool to predict the minimal TPP point. Then, we introduce a new FOM that includes not only the efficiency of the modulator, but also the bandwidth limitation from the SiP electro-optic modulator. The new FOM that is derived from OMAN translates the system-level requirements of a PAM-M optical link to the device-level design parameters. This FOM can be hired to optimize driving voltage swing, bias voltage, and phase-shifter length or to simply choose a SiP modulator with minimal imposed TPP.

High-speed optical interconnects are crucial for both data centers and high performance computing systems. High power consumption and limited device bandwidth have hindered the move to higher optical transmission speeds. Integrated optical transceivers in silicon photonics (SiP) using pulse-amplitude modulation (PAM) are a promising solution to increase data rates. In this paper, we review recent progress in SiP for PAM transmissions. We focus on materials and technologies available CMOS-compatible photonics processes. Performance metrics of SiP modulators and crucial considerations for high-speed PAM transmissions are discussed. Various driving strategies to achieve optical PAM signals are presented. Some of the state-of-the-art SiP PAM modulators and integrated transmitters are reviewed.

On-chip frequency comb generation is a promising solution for seeding a chip-scale optical transmitter for both Nyquist wavelength-division multiplexing (WDM) and orthogonal frequency-division multiplexing. We demonstrate flexible frequency comb generation using a silicon photonic dual-drive Mach-Zehnder modulator fabricated on a CMOS-compatible process. Our on-chip comb has five lines spaced at 20 GHz with a high tone-to-noise ratio of about 40 dB after one stage optical amplification. Our back-to-back transmission achieves bit error rates (BERs) well below 2e-2, the threshold for 20% overhead forward error correction (FEC), for 800 Gb/s using 16-GBd 32QAM on five WDM channels. We also test a seamless 800-Gb/s super-channel using 5×20 GBd 16QAM, with BER below the 7% overhead FEC threshold of 3.8e-3. To the best of our knowledge, this is the first demonstration of high-spectral-efficiency data carried by an all-silicon optical frequency comb. This establishes that a silicon optical frequency comb has sufficient optical signal-to-noise ratio for high-order QAM, as well as excellent stability for super-channels without guard bands, paving the way to an integrated high-spectral-efficiency multi-carrier optical transmitter.

Silicon based Mach Zehnder modulators, unlike lithium niobate, suffer from nonlinear pattern-dependent behavior beyond simple intersymbol interference. We experimentally demonstrate a novel predistortion method based on the iterative learning control (ILC) technique to address this issue using quasi-real-time adaptation with hardware-in-the-loop. We compare bit error rate performance to that of linear solutions at several M-QAM modulation levels and baud rates. We demonstrate 256QAM at 20 Gbaud which linear compensation alone cannot achieve. For 40 Gbaud 128QAM, we improve power sensitivity by 4.4 dB. We combine optical compensation with ILC to improve power sensitivity by ∼ 5 dB for 60 Gbaud 32QAM.

High-speed optical interconnects are crucial for both data centers and high performance computing systems. High power consumption and limited device bandwidth have hindered the move to higher optical transmission speeds. Integrated optical transceivers in silicon photonics (SiP) using pulse-amplitude modulation (PAM) are a promising solution to increase data rates. In this paper, we review recent progress in SiP for PAM transmissions. We focus on materials and technologies available CMOS-compatible photonics processes. Performance metrics of SiP modulators and crucial considerations for high-speed PAM transmissions are discussed. Various driving strategies to achieve optical PAM signals are presented. Some of the state-of-the-art SiP PAM modulators and integrated transmitters are reviewed.

Codesign and integration of optical modulators and CMOS drivers is crucial for high-speed silicon photonic (SiP) transmitters to reach their full potential for low-cost, low-power electronic-photonic integrated systems. We present a CMOS-driven SiP multi-level optical transmitter implemented using a commercially available lateral p-n junction process. It uses a Mach-Zehnder modulator (MZM) segmented to increase speed and to lower the required power on a per segment basis to a level achievable with CMOS. A multi-channel driver is designed and implemented in 130 nm RF CMOS, providing a swing of 4 V in a push-pull configuration at 20 Gbaud. Binary data at the CMOS input is manipulated via digital logic to produce the proper per-segment drive signals to generate a four-level pulse-amplitude modulation optical signal. Multi-level modulation is achieved using only binary signals as input (DAC-less). Cosimulation of the optical and electrical circuits shows good agreement with experiment. Reliable transmission is achieved without post-compensation at 28 Gb/s, and at 38 Gb/s when using post-compensation.

Silicon based Mach Zehnder modulators, unlike lithium niobate, suffer from nonlinear pattern-dependent behavior beyond simple intersymbol interference. We experimentally demonstrate a novel predistortion method based on the iterative learning control (ILC) technique to address this issue using quasi-real-time adaptation with hardware-in-the-loop. We compare bit error rate performance to that of linear solutions at several M-QAM modulation levels and baud rates. We demonstrate 256QAM at 20 Gbaud which linear compensation alone cannot achieve. For 40 Gbaud 128QAM, we improve power sensitivity by 4.4 dB. We combine optical compensation with ILC to improve power sensitivity by ∼ 5 dB for 60 Gbaud 32QAM.

Codesign and integration of optical modulators and CMOS drivers is crucial for high-speed silicon photonic (SiP) transmitters to reach their full potential for low-cost, low-power electronic-photonic integrated systems. We present a CMOS-driven SiP multi-level optical transmitter implemented using a commercially available lateral p-n junction process. It uses a Mach-Zehnder modulator (MZM) segmented to increase speed and to lower the required power on a per segment basis to a level achievable with CMOS. A multi-channel driver is designed and implemented in 130 nm RF CMOS, providing a swing of 4 V in a push-pull configuration at 20 Gbaud. Binary data at the CMOS input is manipulated via digital logic to produce the proper per-segment drive signals to generate a four-level pulse-amplitude modulation optical signal. Multi-level modulation is achieved using only binary signals as input (DAC-less). Cosimulation of the optical and electrical circuits shows good agreement with experiment. Reliable transmission is achieved without post-compensation at 28 Gb/s, and at 38 Gb/s when using post-compensation.

Silicon photonic modulators have strong nonlinear behavior in phase modulation and frequency response, which needs to be carefully addressed when they are used in highcapacity transmission systems. We demonstrate a comprehensive model for depletion-mode Mach–Zehnder modulators (MZMs) on silicon-on-insulator, which provides a bridge between device design and system performance optimization. Our methodology involves physical models of p–n–junction phase-shifters and traveling-wave electrodes, as well as circuit models for the dynamic microwave-light interactions and time-domain analysis. Critical aspects in the transmission line design for high-frequency operation are numerically studied for a case of p–n–junction loaded coplanar-strip electrode. The dynamic interaction between light and microwave is simulated using a distributed circuit model solved by the finite-difference time-domain method, allowing for accurate prediction of both small-signal and large-signal responses. The validity of the model is confirmed by the comparison with experimental results for a series push–pull MZM with a 6 mm phase shifter. The simulation shows excellent agreement with experiment for high-speed operation up to 46 Gb/s. We show that this time-domain model can well predict the impact of the nonlinear behavior on the large-signal response, in contrast to the poor prediction from linear models in the frequency domain.

Silicon photonic modulators have strong nonlinear behavior in phase modulation and frequency response, which needs to be carefully addressed when they are used in high-capacity transmission systems. We demonstrate a comprehensive model for depletion-mode Mach-Zehnder modulators (MZMs) on silicon-on-insulator, which provides a bridge between device design and system performance optimization. Our methodology involves physical models of p-n-junction phase-shifters and traveling-wave electrodes, as well as circuit models for the dynamic microwave-light interactions and time-domain analysis. Critical aspects in the transmission line design for high-frequency operation are numerically studied for a case of p-n-junction loaded coplanar-strip electrode. The dynamic interaction between light and microwave is simulated using a distributed circuit model solved by the finite-difference time-domain method, allowing for accurate prediction of both small-signal and large-signal responses. The validity of the model is confirmed by the comparison with experimental results for a series push-pull MZM with a 6 mm phase shifter. The simulation shows excellent agreement with experiment for high-speed operation up to 46 Gb/s. We show that this time-domain model can well predict the impact of the nonlinear behavior on the large-signal response, in contrast to the poor prediction from linear models in the frequency domain.