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

Area of Science:

• Optics and Photonics
• Optical Filter Design
• Spectroscopy

Background:

• Traditional optical filters often struggle to achieve sharp spectral cutoffs.
• Achieving specific spectral shapes like quasi-rectangular profiles is challenging.
• Conical incidence offers unique possibilities for manipulating light-matter interactions.

Purpose of the Study:

• To design and characterize an optical filter with a quasi-rectangular spectrum.
• To investigate the effect of incident angle on spectral features under conical incidence.
• To demonstrate a method for achieving stable quasi-rectangular spectral filtering.

Main Methods:

• Design and simulation of an optical filter structure.
• Analysis of spectral response under varying incident angles (fully conical incidence).
• Experimental characterization of the filter's spectral properties, including bandwidth and rejection ratio.

Main Results:

• A quasi-rectangular spectrum was achieved at a central wavelength of 475 nm with a 75° incident angle.
• The filter demonstrated a bandwidth of 7.3 nm (reflectance R>90%) and a relative bandwidth (Δλ/λ) of approximately 1.5%.
• The quasi-rectangular spectral feature remained stable for incident angles between 75° and 85°, with a rejection ratio >10 dB.

Conclusions:

• The study successfully demonstrates a method to obtain quasi-rectangular spectral filtering using conical incidence.
• The merger of double resonance peaks under conical incidence is identified as the mechanism for the quasi-rectangular spectrum.
• The proposed approach provides a viable route for developing novel optical filter devices with tailored spectral characteristics.