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.

We demonstrate the possibility of post-fabrication trimming of the response of nitrogen-rich silicon nitride racetrack resonators by using an ultraviolet laser. The results revealed the possibility to efficiently tune the operating wavelength of fabricated racetrack resonators to any point within the full free spectral range. This process is much faster than similar, previously presented methods (in the order of seconds, compared to hours). This technique can also be applied to accurately trim the optical performance of any other silicon photonic device based on nitrogen-rich silicon nitride.

Silicon nitride (SiNx), has been widely regarded as a CMOS photonics enabling material, facilitating the development of low-cost CMOS compatible waveguides and related photonic components. We have previously developed an NH3-free SiN PECVD platform in which its optical properties can be tailored. Here, we report on a new type of surface-emitting nitrogen-rich silicon nitride waveguide with antenna lengths of L > 5 mm. This is achieved by using a technique called small spot direct ultraviolet writing, capable of creating periodic refractive index changes ranging from -0.01 to -0.04. With this arrangement, a weak antenna radiation strength can be achieved, resulting in far-field beam widths < 0.015 0 , while maintaining a minimum feature size equal to 300 nm, which is compatible with DUV scanner lithography.

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