Transmission comb of a distributed Bragg reflector induced by two surface dielectric gratings

TL;DR

This study uses transfer matrix theory to analyze how dielectric gratings on a distributed Bragg reflector create a stable, comb-like transmission spectrum suitable for multichannel filtering and polarization applications.

Contribution

It demonstrates the formation of a robust, narrow-band transmission comb induced by surface gratings on a DBR, with detailed analysis of spectral properties and effects of structural randomness.

Findings

Transmission spectrum forms a comb-like pattern with red shift as grating period increases.

Number of peaks increases with the number of DBR cells, maintaining a consistent FWHM to free spectral range ratio.

Transmission peaks are stable against 15 extpercent{} randomness in layer heights.

Abstract

With transfer matrix theory, we study the transmission of a distributed Bragg reflector (DBR) with two dielectric gratings on top and on the bottom. Owing to the diffraction of the two gratings, the transmission shows a comb-like spectrum which red shifts with increasing the grating period during the forbidden band of the DBR. The number density of the comb peaks increases with increasing the number of the DBR cells, while the ratio of the average full width at half maximum (FWHM) of the transmission peaks in the transmission comb to the corresponding average free spectral range, being about 0.04 and 0.02 for the TE and TM incident waves, is almost invariant. The average FWHM of the TM waves is about half of the TE waves, and both they could be narrower than 0.1 nm. In addition, the transmission comb peaks of the TE and TM waves can be fully separated during certain waveband. We further prove that the transmission comb is robust against the randomness of the heights of the DBR layers, even when a 15\% randomness is added to their heights. Therefore, the proposed structure is a candidate for a multichannel narrow-band filter or a multichannel polarizer.