Photonic integrated circuits currently use platform intrinsic thermo-optic and electrooptic effects to implement dynamic functions such as switching, modulation and other processing. Currently, there is a drive to implement field programmable photonic circuits, a need which is only magnified by new neuromorphic and quantum computing applications. The most promising non-volatile photonic components employ phase change materials such as GST and GSST, which had their origin in electronic memory. However, in the optical domain, these compounds introduce significant losses potentially preventing a large number of applications. Here, we evaluate the use of two newly introduced low loss phase change materials, Sb 2 S 3 and Sb 2 Se 3 , on a silicon nitride photonic platform. We focus the study on Mach-Zehnder interferometers that operate at the O and C bands to demonstrate the performance of the system. Our measurements show an insertion loss below 0.04 dB/µm for Sb 2 S 3 and lower than 0.09 dB/µm for Sb 2 Se 3 cladded devices for both amorphous and crystalline phases. The effective refractive index contrast for Sb 2 S 3 on SiNx was measured to be 0.05 at 1310 nm and 0.02 at 1550 nm, whereas for Sb 2 Se 3 , it was 0.03 at 1310 nm and 0.05 at 1550 nm highlighting the performance of the integrated device.

In this review we present some of the recent advances in the field of silicon nitride photonic integrated circuits. The review focuses on the material deposition techniques currently available, illustrating the capabilities of each technique. The review then expands on the functionalisation of the platform to achieve nonlinear processing, optical modulation, nonvolatile optical memories and integration with III-V materials to obtain lasing or gain capabilities.

A new family of phase change material based on antimony has recently been explored for applications in near-IR tunable photonics due to its wide bandgap, manifested as broadband transparency from visible to NIR wavelengths. Here, we characterize $$\hbox {Sb}_{2} \hbox {S}_{3}$$ Sb 2 S 3 optically and demonstrate the integration of this phase change material in a silicon nitride platform using a microring resonator that can be thermally tuned using the amorphous and crystalline states of the phase change material, achieving extinction ratios of up to 18 dB in the C-band. We extract the thermo-optic coefficient of the amorphous and crystalline states of the $$\hbox {Sb}_{2}\hbox {S}_{3}$$ Sb 2 S 3 to be 3.4 x $$10^{-4}\hbox {K}^{-1}$$ 10 - 4 K - 1 and 0.1 x 10$$^{-4}\hbox {K}^{-1}$$ - 4 K - 1 , respectively. Additionally, we detail the first observation of bi-directional shifting for permanent trimming of a non-volatile switch using continuous wave (CW) laser exposure ($$-5.9$$ - 5.9 to 5.1 dBm) with a modulation in effective refractive index ranging from +5.23 x $$10^{-5}$$ 10 - 5 to $$-1.20$$ - 1.20 x 10$$^{-4}$$ - 4 . This work experimentally verifies optical phase modifications and permanent trimming of $$\hbox {Sb}_{2}\hbox {S}_{3}$$ Sb 2 S 3 , enabling potential applications such as optically controlled memories and weights for neuromorphic architecture and high density switch matrix using a multi-layer PECVD based photonic integrated circuit.

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