Sai T. Chu

SURFACE-ROUGHNESS-INDUCED CONTRADIRECTIONAL COUPLING IN RING AND DISK RESONATORS

Reflections that are due to random surface roughness in periodic structures such as dielectric rings and disks inherently phase match forward- and backward-propagating modes. Small reflections are thus considerably enhanced and may impair the performance of traveling-wave resonators. In addition, such contradirectional coupling leads to a splitting of the resonant peak. These effects are studied analytically.

High index contrast photonics platform

A new low-loss high-index-contrast photonics platform has been developed for integrated optics and microwave photonics. The platform consists of a material system that has an index contrast that is adjustable from 0 to 25% and which is processed using conventional CMOS tools. The platform allows one to four orders of magnitude reduction in the size of optical components compared with conventional planar technologies. As an example, meter long path lengths occupy coils that are millimeters in diameter. Microwave photonic building blocks that are enabled include large bit count programmable delay lines for beam steering and shaping that fit in less than a square centimeter and which have delays controllable from 5 fsec to 10 nsec. Also enabled are arrays of high order tunable filters, a hundred micrometers in size, having linewidths ranging from tens of MHz to tens of GHz. These filters can be tuned over several hundred GHz, and when placed in Vernier architectures can be tuned across the C band (5 THz). An optical chip typically consists of dozens of optical elements. Each element is placed in its own micro-control loop that consists of a thin film heater for thermo-optic control and a thermistor for electronic feedback. The micro-control loops impart intelligence to the optical chip.

A Radio Frequency Channelizer based on Cascaded Integrated Micro-ring Resonator Optical Comb Sources and Filters

We report a broadband RF channelizer based on an integrated optical frequency Kerr micro-comb source, with an RF channelizing bandwidth of 90 GHz, a high RF spectral slice resolution of 1.04 GHz, and experimentally verify the RF performance up to 19 GHz. This approach to realizing RF channelizers offers reduced complexity, size, and potential cost for a wide range of applications to microwave signal detection.

High-order Radio Frequency Differentiation via Photonic Signal Processing with an Integrated Micro-resonator Kerr Optical Frequency Comb Source

We demonstrate the use of integrated micro-resonator based optical frequency comb sources as the basis for transversal filtering functions for microwave and radio frequency photonic filtering and advanced functions. Keywords—frequency comb, microwave, micro-resonator

Integrated Kerr comb-based reconfigurable transversal differentiator for microwave photonic signal processing

An arbitrary-order intensity differentiator for high-order microwave signal differentiation is proposed and experimentally demonstrated on a versatile transversal microwave photonic signal processing platform based on integrated Kerr combs. With a CMOS-compatible nonlinear micro-ring resonator, high quality Kerr combs with broad bandwidth and large frequency spacings are generated, enabling a larger number of taps and an increased Nyquist zone. By programming and shaping individual comb lines’ power, calculated tap weights are realized, thus achieving a versatile microwave photonic signal processing platform. Arbitrary-order intensity differentiation is demonstrated on the platform. The RF responses are experimentally characterized, and systems demonstrations for Gaussian input signals are also performed.

Four-Photon Entanglement Generation with Integrated Optical Frequency Combs

We demonstrate the generation of four-photon entangled quantum states with integrated optical frequency comb sources. We measure four-photon quantum interference with a visibility above 89%, and perform quantum state tomography revealing a fidelity above 64%.

Dual mode mode-locked laser based on an integrated nonlinear microring resonator

A potential solution for the demand for highly stable pulsed lasers at hundreds of GHz repetition rates is represented by passively mode locked fiber lasers. These lasers are composed of a band-limited amplifier, a dispersive element and a nonlinear element. When a high finesse resonant filter is added intracavity, they emit pulses with a repetition rate equal to the filter free spectral range (FSR) - a configuration known as dissipative four wave mixing (DFWM) [1,2]. The main cavity (MC) modes selected by the filter exchange energy by four wave mixing (FWM) and lock their mutual phase as a traveling pulse emerges. However, this approach leads to several unsolved instability problems [3], and so it has basically no impact in practical applications. By moving the nonlinear element inside the filter [4], we demonstrated stable pulsed emission at 200 GHz of repetition rate using a novel design we term Filter-Driven Four Wave Mixing (FD-FWM), that takes advantage of the high nonlinearity of an integrated micro-ring resonator [4] in a doped silica platform [5]. The stability arises as only one main cavity mode oscillates in each nonlinear resonator resonance. Here we present the first example of a stable operating regime for the FD-FWM scheme where two MC modes per resonator linewidth are allowed to oscillate [6]. This novel stable operating regime leads to the formation of two spectral 200GHz-comb replicas separated by the FSR of the external main cavity (FSRC = 65MHz). The beating of the two combs generates a sinusoidal modulation of the 200GHz output pulse train at the radio-frequency (Fig 1a) of the main cavity FSR, a quantity that is readily detectable with photodiodes.

Self-locked OPO in CMOS-compatible microring resonators

We report a novel geometry for OPOs in a CMOS-compatible microring resonator. It exploits non-critical lasing of the pump inherently positioned within the resonances of the microcavity, thus counteracting the effect of thermal fluctuations.

Efficient Wavelength Conversion and Net Parametric Gain via Fwm in a High Index Doped Silica Waveguide

We demonstrate C-band subpicosecond wavelength conversion over > 100nm, exploiting four wave mixing in a high index doped silica waveguide spiral of 45cm, showing a +16.5dB net gain for a 40W peak pump power.

Temperature Insensitive Glass Microring Resonator Add/Drop Filters by Means of a Polymer Overlay

Compact and highly wavelength selective microring resonator add/drop filters [1-4] are attractive building blocks for dense integration of WDM components.