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 (FSRs) 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 where 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 ultra-widely 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" that is established by radiative interference coupling and bears a direct analogy to parity-time (PT) symmetric Hamiltonians in optical systems. Variants of this concept should be extendable to parametric-gain based oscillators, enabling use of ultrabroadband parametric gain for 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 localized mode coupling as a viable dispersion engineering 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 control of the resonant frequency-matching. In a fabricated silicon microresonator, we show an 8 dB enhancement of seeded FWM efficiency over the non-compensated state. The measured four-wave mixing has a peak wavelength conversion efficiency of -37.9 dB across a free spectral range (FSR) of 3.334 THz ($\sim$27 nm). Enabled by strong counteraction of dispersion, this FSR is, to our knowledge, the largest in silicon to demonstrate FWM to date. This form of mode-coupling-based, active dispersion compensation can be beneficial for many FWM-based devices including wavelength converters, parametric amplifiers, and widely detuned correlated photon-pair sources. Apart from compensating intrinsic 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

Wide-band On-chip Four-Wave Mixing via Coupled Cavity Dispersion Compensation

Abstract: We demonstrate a dual-cavity resonant structure that employs frequency splitting at one of three resonances to structurally compensate dispersion. We show seeded four-wave mixing across the largest free spectral range to our knowledge of 26nm. On-chip four-wave mixing (FWM) has received much attention recently for applications from wavelength conversion [1] to quantum photonic circuits In this paper, we propose and demonstrate FWM in a dispersion compensating device consisting of two coupled resonators referred to as the 'primary' and 'auxiliary' cavities with different FSRs as illustrated i

Large, Wafer-Thin Optical Apertures Leveraging Photonic Integrated Circuits to Replace Telescopes for Communications

To aid in driving down the size, weight, and power (SWaP) of space-based optical communications terminals, we present a large-aperture telescope-replacement technology that reshapes a beam from a single-mode fiber to ~5 cm and larger apertures on a silicon wafer by using photonic integrated circuit (PIC) components. We achieve multi-centimeter apertures by sacrificing wide-angle steering in favor of good beam quality and manageable controls. Light from a single-mode fiber is coupled to a silicon chip consisting of low-loss silicon nitride waveguides for signal distribution to large phase-controlled emitters. Our demonstrations of beam phasing across a 1.8-cm-diameter, 16-emitter phased array show excellent agreement with simulations. We have designed and simulated a 4.7 cm, 64-emitter array and have begun fabrication as of 2023. This architecture removes the need for beam expansion optics, free-space propagation for beam expansion, and the support structure and housing used in traditional telescope assemblies. Its low size and weight make it compatible with current and future beam steering mechanisms, and its reduced loading provides added potential for size and weight reductions in those subsystems. We believe the architecture can eventually be expanded to larger apertures of 10 cm or more without significantly increasing thickness

Tunable source of quantum-correlated photons with integrated pump rejection in a silicon CMOS platform

A wavelength-tunable, silicon photon-pair source based on spontaneous four-wave mixing, integrated with a pump rejection filter in a single, flip-chip packaged CMOS chip, is demonstrated with a coincidence-to-accidentals ratio of 9.1 with no off-chip pump filtering.Accepted manuscrip

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 &deg;C as well as below 1 K. The process is well suited for augmentation of existing foundry capabilities or as a stand-alone process.</p

A discrete resonance, all-order dispersion engineering method for microcavity design for four wave mixing

Abstract: We propose a rigorous method for tailoring the dispersion of azimuthallysymmetric microresonators for four-wave mixing applications and show example designs. The method implicitly includes momentum conservation and directly reveals phase mismatch via resonance detuning, avoiding Taylor expansions. Four-wave mixing (FWM) in microresonators is the subject of current research efforts with applications including wavelength conversion [1], correlated photon-pair sources In this paper, we propose and demonstrate direct computation of the energy matching between resonances of a microresonator. Since waveguides inherently support a continuum of wavelengths, it is natural to assume energy matching (2ω p = ω i + ω s ) and to simulate the effect of material and modal dispersion on momentum matching. The phase mismatch between wavelengths is often found through Taylor expansion about the pump frequency to be ∆β = 2β p − β s − β i = ∑ n=2,4,6... (2/n!)β n (ω s − ω p ) n where β n is the n th derivative of the propagation constant β with respect to angular frequency ω at the pump. It is readily apparent that reducing β 2 to zero only approximate

Monolithic source of entangled photons with integrated pump rejection

We demonstrate a photon pair source with pump rejection filter on a single CMOS chip. Cascaded microring-based filters exhibit \u3e 95 dB pump extinction, providing a raw visibility in time-energy entanglement of 81.4% ± 2.3%