Phase change materials present a unique type of materials that drastically change their electrical and optical properties on the introduction of an external electrical or optical stimulus. Although these materials have been around for some decades, they have only recently been implemented for on-chip photonic applications. Since their reinvigoration a few years ago, on-chip devices based on phase change materials have been making a lot of progress, impacting many diverse applications at a very fast pace. At present, they are found in many interesting applications including switches and modulation; however, phase change materials are deemed most essential for next-generation low-power memory devices and neuromorphic computational platforms. This review seeks to highlight the progress thus far made in on-chip devices derived from phase change materials including memory devices, neuromorphic computing, switches, and modulators.

We report simulation and fabrication of a grating coupler for coupling of light between an on-chip lithium niobate ridge waveguide and an optical fiber. A grating coupler with an insertion loss of less than 10 dB for C-band frequencies (1530-1565 nm) was achieved.

We present a hybrid dual-gain integrated external cavity laser with full C-band wavelength tunability. Two parallel reflective semiconductor optical amplifier gain channels are combined by a Y-branch in the Si₃N₄ photonic circuit to increase the optical gain. A Vernier ring filter is integrated in the Si₃N₄ photonic circuit to select a single longitudinal mode and meanwhile reduce the laser linewidth. The side-mode suppression ratio is ∼67 dB with a pump current of 75 mA. The linewidth of the unpackaged laser is 6.6 kHz under on-chip output power of 23.5 mW. The dual-gain operation of the laser gives higher output power and narrower linewidth compared to the single gain operation. It is promising for applications in optical communications and light detection and ranging systems.

A ridge slot waveguide on 220 nm silicon-on-insulator platform is proposed and theoretically investigated. The confinement factor of the ridge slot waveguide is much higher than the fully etched slot waveguide in the case of air-cladding. The sensitivity of sensors based on ridge slot waveguides is higher than that of the fully etched slot waveguides when the cladding refractive index is in the range of 1.0-1.18.