Integrated High Rejection Ratio Pump Filter Using a Simple Waveguide Bragg Grating

On-chip optical filters with ultra-high rejection are essential for quantum photonics, nonlinear optics, and communication systems, where strong pump fields must be suppressed to isolate weak signals. Bragg gratings are attractive for these applications due to their compactness, large free spectral range, and CMOS compatibility, but their rejection levels have often been limited by various leakage noises. Here we present a z-shaped Bragg grating filter that achieves an extinction ratio of 83 dB. The design mitigates unwanted modes and scattering while maintaining a simple and compact geometry. Experimental results confirm stable high-rejection performance, making this filter a strong candidate for integration into quantum photonic circuits and other advanced photonic platforms.