Polarization-independent photonic Bragg grating filter with cladding asymmetry

Integrated polarization-free Bragg filters with subwavelength gratings for photonic sensing

We present polarization-free Bragg filters having subwavelength gratings (SWGs) in the lateral cladding region. This Bragg design expands modal fields toward upper cladding, resulting in enhanced light interaction with sensing analytes. Two device configurations are proposed and examined, one with index-matched coupling between transverse electric (TE) and transverse magnetic (TM) modes and the other one with hybrid-mode (HM) coupling. Both configurations introduce a strong coupling between two orthogonal modes (either TE-TM or HM1-HM2) and rotate the polarization of the input wave through Bragg reflection. The arrangements of SWGs help to achieve two configurations with different orthogonal modes, while expanding modal profiles toward the upper cladding region. Our proposed SWG-assisted Bragg gratings with polarization independency eliminate the need for a polarization controller and effectively tailor the modal properties, enhancing the potential of integrated photonic sensing applications.

Ultracompact parabolic sidewall-profiled hybrid plasmonic waveguide Bragg grating with optimized spectral properties of long-wavelength passband

An ultracompact hybrid plasmonic waveguide Bragg grating (HPWBG) with improved spectral properties of long-wavelength passband is proposed. A hollow HPW is introduced to suppress the entire loss, and a parabolic profiled sidewall is designed to optimize the spectral properties for specific wave bands. The transfer matrix method and finite element method are combined to ensure the efficiency of numerical research. The results show that the parabolic profile effectively reduces the reflection and strengthens the resonance of the mode in the long-wavelength passband, suppressing the oscillations and realizing significant smoothness and improvement in transmission. The optimized transmittance is greater than 99%, and insertion loss is as low as 0.017 dB. A wide bandgap of 103 nm is also attained. The structure also has a compactness with a length of 3.4 µm and exhibits good tolerance. This work provides a scheme for designing and optimizing wavelength selecting devices and has potential application value in integrated photonic devices.