Edge couplers are widely utilized in photonic integrated circuits and are vital for ensuring efficient chip-to-fiber coupling. In this paper, we present a high-efficiency and compact polarization-insensitive multi-segment linear silicon nitride edge coupler for coupling to high numerical aperture fibers. By optimizing the thickness of the up cladding and introducing air slots in the transverse direction, we have further modified the limiting effect of the mode field. This innovative edge coupler scheme boasts a compact structure and is compatible with existing mature standard processes, with a total length of only 38 μm. We numerically demonstrate that the proposed edge coupler exhibits a low coupling loss of 0.22 dB/0.31 dB for TE/TM modes at λ = 1550 nm. Furthermore, the proposed coupler displays high wavelength insensitivity within the range of 1400–1850 nm and maintains a coupling loss of less than 0.2 dB with a manufacturing deviation of ±20 nm.

We report a novel photonic approach for generating FSK microwave signal based on an optoelectronic oscillator (OEO) loop and a polarization modulator (PolM). A polarization-division multiplexing Mach-Zehnder modulator (PDM-MZM) is used in the OEO loop to obtain two microwave signals with two frequencies at two orthogonal polarization states. The optical signals modulated by two generated microwave signals of OEO are injected into a PolM with a proper adjustment of input polarization states. Applying a binary coding signal in the PolM, a FSK microwave signal can be successfully realized after photodetection. This proposed scheme is theoretically analyzed and experimentally proved. Experimental results demonstrate the generation of a 2Gb/s FSK microwave signal at 10/16 GHz. This work with no need of external microwave sources and low phase noise is pretty promising in integrated microwave systems for wireless communication and radar system.