Photonic crystal add–drop filter: a review on principles and applications

Add–drop filter (ADF) is a key component in optical integrated circuits that can be used in all-optical communication networks and wavelength division multiplexing (WDM) systems. The quality factor, coupling efficiency, transmission efficiency and coupling length are important parameters in add–drop filters. Photonic crystal (PC) optical devices have become popular among researchers because their structure is suitable to embed into optical circuits. This paper covers a comprehensive review of the principle structure of ADF, coupled mode theory (CMT), types and recent applications in WDMs, accelerometer and bio/chemical sensors. Although there are some different categories of photonic crystal ring resonator-based ADF in general, all of them can be divided into photonic to two class of non-circular and circular. This article is reported a comprehensive study about ADF and improvement of these ADF.