In recent years, silicon nitride has drawn attention for the realisation of integrated photonic devices due to its fabrication flexibility and advantageous intrinsic properties that can be tailored to fulfill the requirements of different linear and non-linear photonic applications. This paper focuses on our progress in the demonstration of enhanced functionalities in the near infrared wavelength regime with our low temperature (<350 • C) SiN platform. It discusses (de)multiplexing devices, nonlinear all optical conversion, photonic crystal structures, the integration with novel phase change materials, and introduces applications in the 2 µm wavelength range.

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.

The integration of fast and power efficient electro-absorption modulators on silicon is of utmost importance for a wide range of applications. To date, Franz-Keldysh modulators formed of bulk Ge or GeSi have been widely adopted due to the simplicity of integration required by the modulation scheme. Nevertheless, to obtain operation for a wider range of wavelengths (O to C band) a thick stack of Ge/GeSi layers forming quantum wells is required, leading to a dramatic increase in the complexity linked to sub-micron waveguide coupling. In this work, we present a proof-of-concept integration between micro-metric waveguides, through the butt-coupling of a $${1.25}\,{\upmu \hbox {m}}$$ 1.25 μ m thick N-rich silicon nitride (SiN) waveguide with a $${1.25}\,{\upmu \hbox {m}}$$ 1.25 μ m thick silicon waveguide for O-band operation. A numerical analysis is conducted for the design of the waveguide-to-waveguide interface, with the aim to minimize the power coupling loss and back-reflection levels. The theoretical results are compared to the measured data, demonstrating a coupling loss level of $${0.5}\,\hbox {dB}$$ 0.5 dB for TE and TM polarisation. Based on the SiN-SOI interconnection simulation strategy, the simulation results of a quantum-confined Stark effect (QCSE) stack waveguide coupled to a SiN waveguide are then presented.

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.