Characteristics of tuneable optical filters using optical ring resonator with PCF resonance loop

¹ Physics Group, Islamic Azad University, Tehran Shomal Branch, Tehran, Islamic Republic of Iran
² Optical Communication Group, Iran Telecom Research Center, Tehran, Islamic Republic of Iran

^a e-mail: feseraji@itrc.ac.ir

Received: 14 September 2011
Revised: 15 February 2012
Accepted: 26 March 2012
Published online: 9 May 2012

Abstract

A theoretical analysis of a tuneable optical filter is presented by proposing an optical ring resonator (ORR) using photonic crystal fiber (PCF) as the resonance loop. The influences of the characteristic parameters of the PCF on the filter response have been analyzed under steady-state condition of the ORR. It is shown that the tuneability of the filter is mainly achieved by changing the modulation frequency of the light signal applied to the resonator. The analyses have shown that the sharpness and the depth of the filter response are controlled by parameters such as amplitude modulation index of applied field, the coupling coefficient of the ORR, and hole-spacing and air-filling ratio of the PCF, respectively. When transmission coefficient of the loop approaches the coupling coefficient, the filter response enhances sharply with PCF parameters. The depth and the full-width at half-maximum (FWHM) of the response strongly depend on the number of field circulations in the resonator loop. With the proposed tuneability scheme for optical filter, we achieved an FWHM of ~1.55 nm. The obtained results may be utilized in designing optical add/drop filters used in WDM communication systems.