Resonant waveguide grating reflection filter with a quasi-rectangular spectrum under fully conical incidence.

We present the design, analysis, and characterization of a filter with a quasi-rectangular spectrum. The spectral features of the filter are achieved by adjusting the incident angle under fully conical incidence. When the incident angle is 75°, the filter with a quasi-rectangular spectrum is presented at the central wavelength of 475 nm. The proposed filter has a bandwidth of 7.3 nm (>90), its corresponding / is approximately 1.5%, and the estimated rejection ratio is larger than 10 dB. Furthermore, the quasi-rectangular filtering feature is stable in the incident angle range of 75° to 85°. Our approach reveals the quasi-rectangular spectrum attributes of double resonance peaks merger under fully conical incidence and thus can be used to exploit filter devices.