Room-temperature-deposited dielectrics and superconductors for integrated photonics.

We present an approach to fabrication and packaging of integrated photonic devices that utilizes waveguide and detector layers deposited at near-ambient temperature. All lithography is performed with a 365 nm i-line stepper, facilitating low cost and high scalability. We have shown low-loss SiN waveguides, high-Q ring resonators, critically coupled ring resonators, 50/50 beam splitters, Mach-Zehnder interferometers (MZIs) and a process-agnostic fiber packaging scheme. We have further explored the utility of this process for applications in nonlinear optics and quantum photonics. We demonstrate spectral tailoring and octave-spanning supercontinuum generation as well as the integration of superconducting nanowire single photon detectors with MZIs and channel-dropping filters. The packaging approach is suitable for operation up to 160 °C as well as below 1 K. The process is well suited for augmentation of existing foundry capabilities or as a stand-alone process.

Four-wave mixing in silicon coupled-cavity resonators with port-selective, orthogonal supermode excitation.

We propose coupled-cavity triply-resonant systems for degenerate-pump four-wave mixing (FWM) applications that support strong nonlinear interaction between distributed pump, signal and idler modes, and allow independent coupling of the pump mode and signal/idler modes to separate ports based on nonuniform supermode profile. We demonstrate seeded FWM with wavelength conversion efficiency of -54 dB at input pump power of 3.5 dBm, and discuss applications of such orthogonal supermode coupling.

Dark state lasers.

We propose a new type of laser resonator based on imaginary energy-level splitting (imaginary coupling or quality factor Q-splitting) in a pair of coupled microcavities. A particularly advantageous arrangement involves two microring cavities with different free-spectral ranges in a configuration wherein they are coupled by far-field interference in a shared radiation channel. A novel Vernier-like effect for laser resonators is designed in which only one longitudinal resonant mode has a lower loss than the small-signal gain and can achieve lasing while all other modes are suppressed. This configuration enables ultrawidely tunable single-frequency lasers based on either homogeneously or inhomogeneously broadened gain media. The concept is an alternative to the common external cavity configurations for achieving tunable single-mode operation in a laser. The proposed laser concept builds on a high-Q "dark state," which is established by radiative interference coupling and bears a direct analogy to parity-time symmetric Hamiltonians in optical systems. Variants of this concept should be extendable to parametric-gain-based oscillators, enabling widely tunable single-frequency light sources.

Tunable coupled-mode dispersion compensation and its application to on-chip resonant four-wave mixing.

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 dB across a free spectral range (FSR) of 3.334 THz (∼27 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.