We propose and demonstrate mode coupling as a viable dispersion compensation technique for phase-matched resonant four-wave mixing (FWM). We demonstrate a dual-cavity resonant structure that employs coupling-induced frequency splitting at one of three resonances to compensate for cavity dispersion, enabling phase matching. Coupling strength is controlled by thermal tuning of one cavity enabling active tuning of the resonant frequency matching. In a fabricated silicon microresonator, we show an 8 dB enhancement of seeded FWM efficiency over the noncompensated state. The measured FWM has a peak wavelength conversion efficiency of $-37.9\mathrm{dB}$ across a free spectral range (FSR) of 3.334 THz ($\sim 27\mathrm{nm}$), which is, to the best of our knowledge, the largest in a silicon microresonator to demonstrate FWM to date. This form of dispersion compensation can be beneficial for many devices, including wavelength converters, parametric amplifiers, and widely detuned photon-pair sources. Apart from compensating dispersion, the proposed mechanism can alternatively be utilized in an otherwise dispersionless resonator to counteract the detuning effect of self- and cross-phase modulation on the pump resonance during FWM, thereby addressing a fundamental issue in the performance of light sources such as broadband optical frequency combs.

Heterogeneous III-V-on-silicon photonic integration has proved to be an attractive and volume manufacturable solution that marries the merits of III-V compounds and silicon technology for various photonic integrated circuit (PIC) applications. The current main-stream Ethernet trends for larger bandwidth are pushing higher modulation baudrate or employing advanced modulation format for datacom applications. However, neither solution is likely able to significantly drive overall solution cost and energy efficiency to the best sweet spot, nor to unfold the full potential of heterogeneous integration. Here we review our innovations on a special heterogeneous III-V-on-silicon platform, and the development of a dense wavelength division multiplexed (DWDM) transceiver. A 40-channel DWDM architecture and platform fabrication are discussed first, followed by experimental demonstration of each high-quality building block. InAs/GaAs quantum dot material is the choice for building robust multi-wavelength lasers, amplifiers, and high-speed avalanche photodetectors (APDs) which complements the more mature SiGe APDs. A metal-oxide-semiconductor capacitor phase shifter is a mission critical structure to provide athermal and efficient tuning for deinterleavers and microring resonators, and high-speed modulation. A successful 8 × 25 Gb/s link demonstration paves the way for the world's first fully-integrated DWDM PIC on Si with Terabit/s aggregated bandwidth and energy efficiency likely to ∼100 fJ/bit.

Correlated photon pairs are a fundamental building block of quantum photonic systems. While pair sources have previously been integrated on silicon chips built using customized photonics manufacturing processes, these often take advantage of only a small fraction of the established techniques for microelectronics fabrication and have yet to be integrated in a process that also supports electronics. Here we report the first demonstration of quantum-correlated photon pair generation in a device fabricated in an unmodified advanced (sub-100-nm) complementary metal-oxide semiconductor (CMOS) process, alongside millions of working transistors. The microring resonator photon pair source is formed in the transistor layer structure, with the resonator core formed by the silicon layer typically used for the transistor body. With ultralow CW on-chip pump powers ranging from 4.8 to 400 μW, we demonstrate pair generation rates between 165 Hz and 332 kHz using $>80\%$ efficient WSi superconducting nanowire single-photon detectors. Coincidences-to-accidentals ratios consistently exceeding 40 were measured, with a maximum of 55. In the process of characterizing this source, we also accurately predict pair generation rates from the results of classical stimulated four-wave mixing measurements. This proof-of-principle device demonstrates the potential of commercial CMOS microelectronics as an advanced quantum photonics platform with the capability of large volumes and pristine process control, where state-of-the-art high-speed digital circuits could interact with quantum photonic circuits.

A CMOS-compatible avalanche photodiode (APD) with high speed and high sensitivity is a critical component of a low-cost, high-data-rate, and energy-efficient optical communication link. A novel waveguide-coupled silicon–germanium APD detector with three electric terminals was demonstrated with breakdown voltage of $-6\mathrm{V}$, bandwidth of 18.9 GHz, DC photocurrent gain of 15, open-eye diagram at a data rate of 35 Gb/s, and sensitivity of $-11.4\mathrm{dBm}$ at a data rate of 25 Gb/s. This three-terminal APD allows high-yield fabrication in the standard CMOS process and provides robust high-sensitivity operation under small voltage supply.

Silicon-germanium (Si-Ge) avalanche photodiodes (APDs) have large gain bandwidth product (GBP) and low excess noise due to the low impact ionization coefficient ratio of silicon. Optical receivers using APDs are able to achieve high-speed and energy efficient optical transceiver systems. We demonstrate a waveguide Si-Ge APD with low breakdown voltage of -10 V, achieving 60 Gb/s PAM4 successfully. A compact APD circuit model was constructed to allow photonic devices and transceiver circuitry co-design. The APD receiver has achieved -16 dBm sensitivity at 50 Gb/s PAM4 with a bit error rate (BER) of ${2.4\times 10^{-4}}$ . The sensitivity of APD receivers changes with the multiplication gain. In our analysis, compared to a PIN PD receiver the APD receiver operating at optimum gain can obtain ∼8 dB more sensitivity for NRZ signaling at <50 Gb/s and 3-4 dB more sensitivity for PAM4 signaling at 50-100 Gb/s. Also, the APD receiver operating at optimum gain can reduce power consumption by ∼10% at PAM4 data rates of 50 Gb/s and ∼15% at 100 Gb/s in a silicon carrier-depletion microring modulator based WDM photonic link.

We experimentally demonstrate broadband waveguide crossing arrays showing ultralow loss of $0.04\mathrm{dB}/\text{crossing}$ (0.9%) on average and converging to $0.033\mathrm{dB}/\mathrm{crossing}$ (0.075%) matching theory and cross-talk suppression over 35 dB in a CMOS-compatible geometry. The principle of operation is the tailored excitation of a low-loss spatial Bloch wave formed by matching the periodicity of the crossing array to the difference in propagation constants of the first- and third-order TE-like modes of a multimode silicon waveguide. Radiative scattering at the crossing points acts like a periodic imaginary-permittivity perturbation that couples two supermodes, which results in imaginary (radiative) propagation-constant splitting and gives rise to a low-loss, unidirectional breathing Bloch wave. This type of crossing array provides a robust implementation of a key component enabling dense photonic integration.