Monolithically integrated 112 Gbps PAM4 optical transmitter and receiver in a 45†nm CMOS-silicon photonics process.

We demonstrate a transmitter and receiver in a silicon photonics platform for O-band optical communication that monolithically incorporates a modulator driver, traveling-wave Mach-Zehnder modulator, control circuitry, photodetector, and transimpedance amplifier (TIA) in the GlobalFoundries Fotonix (45SPCLO) platform. The transmitter and receiver show an open 112 Gbps PAM4 eye at a 4.3 pJ/bit energy efficiency, not including the laser. Extensive use of gain-peaking enables our modulator driver and TIA to achieve the high bandwidths needed in the 45 nm CMOS-silicon photonics process. Our results suggest an alternative to the frequent approach of bump-bonding BiCMOS drivers and TIAs to silicon photonics.

Silicon microring modulator for 40 Gb/s NRZ-OOK metro networks in O-band.

A microring-based silicon modulator operating at 40 Gb/s near 1310 nm is demonstrated for the first time to our knowledge. NRZ-OOK signals at 40 Gb/s with 6.2 dB extinction ratio are observed by applying a 4.8 Vpp driving voltage and biasing the modulator at 7 dB insertion loss point. The energy efficiency is 115 fJ/bit. The transmission performance of 40 Gb/s NRZ-OOK through 40 km of standard single mode fiber without dispersion compensation is also investigated. We show that the link suffers negligible dispersion penalty. This makes the modulator a potential candidate for metro network applications.

A high-responsivity photodetector absent metal-germanium direct contact.

We report a Ge-on-Si photodetector without doped Ge or Ge-metal contacts. Despite the simplified fabrication process, the device shows a responsivity of 1.14 A/W at -4 V reverse bias and 1.44 A/W at -12V, at 1550 nm wavelength. Dark current is less than 1µA under both bias conditions. We also demonstrate open eye diagrams at 40Gb/s.

WDM-compatible mode-division multiplexing on a silicon chip.

Significant effort in optical-fibre research has been put in recent years into realizing mode-division multiplexing (MDM) in conjunction with wavelength-division multiplexing (WDM) to enable further scaling of the communication bandwidth per fibre. In contrast, almost all integrated photonics operate exclusively in the single-mode regime. MDM is rarely considered for integrated photonics because of the difficulty in coupling selectively to high-order modes, which usually results in high inter-modal crosstalk. Here we show the first microring-based demonstration of on-chip WDM-compatible mode-division multiplexing with low modal crosstalk and loss. Our approach can potentially increase the aggregate data rate by many times for on-chip ultrahigh bandwidth communications.

Error-free transmission of microring-modulated BPSK.

We demonstrate the generation of error-free binary-phase-shift-keyed (BPSK) data at 5 Gb/s using a silicon microring modulator. The microring-modulated BPSK signal is propagated at fiber lengths up to 80 km, maintaining error-free performance, while demonstrating resilience to chromatic dispersion. Bit-error-rate measurements and eye diagrams show near equivalent performance of a microring-based BPSK modulator as compared to commercial LiNbO3 phase modulators.

Width-modulation of Si photonic wires for quasi-phase-matching of four-wave-mixing: experimental and theoretical demonstration.

We experimentally demonstrate quasi-phase-matched (QPM) four-wave-mixing (FWM) in silicon (Si) nanowire waveguides with sinusoidally modulated width. We perform discrete wavelength conversion over 250 nm, and observe 12 dB conversion efficiency (CE) enhancement for targeted wavelengths more than 100 nm away from the edge of the 3-dB conversion bandwidth. The QPM process in Si nanowires is rigorously modeled, with results explaining experimental observations. The model is further used to investigate the dependence of the CE on key device parameters, and to introduce devices that facilitate wavelength conversion between the C-band and mid-IR. Devices based on a superposition of sinusoidal gratings are investigated theoretically, and are shown to provide CE enhancement over the entire C-band. Width-modulation is further shown to be compatible with zero-dispersion-wavelength pumping for broadband wavelength conversion. The results indicate that QPM via width-modulation is an effective technique for extending the spectral domain of efficient FWM in Si waveguides.

Wavelength conversion and unicast of 10-Gb/s data spanning up to 700 nm using a silicon nanowaveguide.

We report extremely large probe-idler separation wavelength conversion (545 nm) and unicast (700 nm) of 10-Gb/s data signals using a dispersion-engineered silicon nanowaveguide. Dispersion-engineered phase matching in the device provides a continuous four-wave-mixing efficiency 3-dB bandwidth exceeding 800 nm. We report the first data validation of wavelength conversion (data modulated probe) and unicast (data modulated pump) of 10-Gb/s data with probe-idler separations spanning 60 nm up to 700 nm accompanied with sensitivity gain in a single device. These demonstrations further validate the silicon platform as a highly broadband flexible platform for nonlinear all-optical data manipulation.

Simultaneous wavelength conversion of ASK and DPSK signals based on four-wave-mixing in dispersion engineered silicon waveguides.

We experimentally demonstrate four-wave-mixing (FWM)-based continuous wavelength conversion of optical differential-phase-shift-keyed (DPSK) signals with large wavelength conversion ranges as well as simultaneous wavelength conversion of dual-wavelength channels with mixed modulation formats in 1.1-cm-long dispersion-engineered silicon waveguides. We first validate up to 100-nm wavelength conversion range for 10-Gb/s DPSK signals, showcasing the capability to perform phase-preserving operations at high bit rates in chip-scale devices over wide conversion ranges. We further validate the wavelength conversion of dual-wavelength channels modulated with 10-Gb/s packetized phase-shift-keyed (PSK) and amplitude-shift-keyed (ASK) signals; demonstrate simultaneous operation on multiple channels with mixed formats in chip-scale devices. For both configurations, we measure the spectral and temporal responses and evaluate the performances using bit-error-rate (BER) measurements.

First demonstration of long-haul transmission using silicon microring modulators.

We report error-free long-haul transmission of optical data modulated using a silicon microring resonator electro-optic modulator with modulation rates up to 12.5 Gb/s. Using bit-error-rate and power penalty characterizations, we evaluate the performance of this device with varying modulation rates, and perform a comparative analysis using a commercial electro-optic modulator. We then experimentally measure the signal integrity degradation of the high-speed optical data with increasing propagation distances, induced chromatic dispersions, and bandwidth-distance products, showing error-free transmission for propagation distances up to 80 km. These results confirm the functional ubiquity of this silicon modulator, establishing the potential role of silicon photonic interconnects for chip-scale high-performance computing systems and memory access networks, optically-interconnected data centers, as well as high-performance telecommunication networks spanning large distances.