Tunable multichannel isolation filter using a fiber-to-LiNbO 3 coupler with intermediate coupling layer

Abstract

ABSTRACT We report the periodic filtering properties of a side-polished single-mode fiber-to-MMOW coupler using a polished LiNbO 3 overlay waveguide. The tuning beh aviors by thermo-optic effect of an IMCL with a photopolymer have been demonstrated. A possibility to be used for multi-channel isolation filter of WDM and multi-channel light source is investigated. The coupling phenomenon with an IMCL and without an IMCL is simulated and compared to the experimental results. The output spectra of this filter show a free spectral range with 4nm when the X-cut LiNbO 3 with 200 thickness are used to an MMOW. This filter was applied to a fiber ring laser and tunable dual-wavelength operations have been demonstrated. Keywords: Multi-channel filters, Wavelength tunable filters, Side-polished fiber couplers, Evanescent field coupling, EDF ring lasers 1. INSTRUCTION Wavelength-division multiplexing (WDM) to send many independent channels on a single-mode fiber has been introduced to meet the growing data traffic. In a WDM-based system, a large number of channels, accurate center wavelengths, deep isolation depth between adjacent channels, and low and uniform insertion loss are required. For such system applications, various technologies have been reported to isolate these channels over a broad bandwidth and generate the multiple lasing wavelengths. Dual-pass Mach zehnder fiber interferometers [1], all fiber Sagnac interferometers [2-3], cascaded long period fiber gratings [4], and wide-band Fabry-Perot filters using two chirped bragg gratings [5] are included. These components achieved in in-line optical fiber have the advantages that all channels are boosted simultaneously in a pure optical mode by an EDFA and low interconnection losses are promised. But the fabrication system to form the fiber grating and careful and complex technique to control the system are required. Furthermore, if they demand the two identical fiber gratings, precise control techni ques are n eeded. In this work, we have used the side-polished fiber-to-thick multi-mode overlay waveguide (MMOW) coupler [6-8] based on the evanescent field coupling between two waveguides for obtaining the periodic filtering properties [9]. The proposed structure is simulated by the 2-D beam propagation methods (BPM). And the thermally tuning