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All-optical wavelength converters and frequency synthesizers represent essential components for the development of advanced and reconfigurable optical communications systems. In this respect, the exploitation of intermodal nonlinear processes in integrated multimode waveguides has received significant attention in recent years for all-optical processing applications. Here, we discuss our recent results on the realization of fully-integrated and broadband wavelength converters utilizing the Bragg scattering intermodal four-wave mixing nonlinear process in a silicon-rich silicon nitride platform.

We present designs and experiments of single-etched amorphous silicon (α-Si) surface grating couplers on a silicon nitride (SiN) waveguide, operating at the telecom (C-band) and datacom (O-band) wavebands. SiN-only grating couplers demonstrate experimental coupling loss of -3.9 dB at 1.55 μm wavelength with a 1-dB bandwidth of 37 nm. Utilizing the hybrid α-Si/SiN platform with subwavelength grating structure, we obtain improved coupling performances, with the optimized fiber-chip coupling loss of -2.0 dB and a 1-dB spectral bandwidth of 42 nm centered at 1.31 μm.

Optical phased arrays (OPAs) are now at the forefront of photonic research as a key beam steering technology for myriad of photonic applications, including in light detection and ranging (LIDAR), communications, and metrology, among others. Integrated OPAs with narrow beam widths and wide-angle steering are in critical need, especially for LIDARs in autonomous vehicle, drone and airplane navigation, or satellites. In this work, we numerically study the performances of OPAs having a circular layout arrangement. Compared to recently available solutions with 1D linear or 2D rectangular arrays, the proposed circular OPAs are poised to deliver effective suppression of the grating sidelobes, while improving beam steering range and obtaining narrower beamwidths. We demonstrate 110-element circular arrays with sidelobe suppression better than 10 dB and an angular beamwidth of 0.5°. Under a monochromatic operation at a 1550 nm wavelength, such array provides a solid angle steering range of 0.21π-sr, with a perspective for performance improvement by using large number of OPA elements and operating under broader spectral range.

The silicon-on-insulator (SOI) platform enables high integration density in photonic integrated circuits while maintaining compatibility with CMOS fabrication processes. Nevertheless, its inherently high modal birefringence hinders the development of polarization-insensitive devices. The dispersion and anisotropy engineering leveraging subwavelength grating (SWG) metamaterials makes possible the development of polarization agnostic waveguide components. In this work we build upon the bricked SWG metamaterial nanostructures to design a polarization independent 2×2 multimode interference (MMI) coupler for the 220 nm SOI platform, operating in the telecom O-band. The designed device exhibits a 160 nm bandwidth with excess loss, polarization dependent loss and imbalance below 1 dB and phase error lower than 5°.

The use of subwavelength grating structures in silicon waveguides have fuelled the development of integrated optical components with superior performance. By a judicious lithographic patterning of the grating, the optical properties of the synthesized metamaterial can be accurately tailored. In this work, we review our latest advances in subwavelength-grating-engineered silicon and germanium planar devices.

Existing OPAs are typically based on 2D rectangular arrays or 1D linear arrays. Both approaches present a limited field-of-view (FOV) due to the presence of the grating lobes when the element spacing is larger than λ/2. To address the need for an increased steering range, we propose a new design strategy of an OPA system utilizing a 2D circular phased array, with a substantially increased FOV. We present a circular OPA using a demonstrated antenna element design, with an 820-element array. A steering range ΩSR calculated as a solid angle of 0.51π sr, and an angular beamwidth of 0.22°, was achieved. The array exhibits a sidelobe suppression larger than 10 dB, and a FOV of 2π sr. Although the performance is limited by the far field pattern of the individual antenna we chose, our circular OPA achieved, to the best of our knowledge, the largest steering range reported to date compared to the state-of-the-art integrated optical phased arrays reported in literature.