An optical filter of adjustable finesse using an amplified fiber ring resonator

Abstract

We consider an optical filter constructed from a simple ring resonator with two electro-optical directional couplers and a fiber amplifier in the ring. By adjusting the coupling coefficient of the electro-optical directional couplers, the finesse of this optical filter can be controlled over a specified range. The variation in the insertion loss of the optical filter can be overcome by adjusting the gain of the fiber amplifier simultaneously. This paper analyzes theoretically the performance of the optical filter, as a function of the coupling coefficient of the electro-optical directional coupler and the gain of the fiber amplifier. We also show that it is possible to design an optical filter of wide adjustable finesse by changing only the coupling coefficient of the electro-optical directional couplers, leaving the gain of the fiber amplifier unchanged. This simpler method results only in a slight change in the insertion loss if an appropriate condition is chosen. The filter will be useful in coherent optical systems, where the bandwidth of the optical filter needs to be appropriately adjusted under varying biasing and signaling conditions, or as an optical discriminator with an adjustable Q-factor.

Design and tolerance analysis of a router with an amplified resonator and Bragg gratings

“…This property has been used in designing a RR with tuning finesse and constant loss. 3 In summary, it has been shown that device performance depends on the value of ͉H͉.…”

“…Several applications of RR's, including routers in self-routing frequency-division multiple-access networks, 1 as filters in optical frequency-division multiplexing transmission systems, [2][3][4] and as converters from frequency-shift to amplitude-shift keying modulation, 5 have been reported. RR's have also been used with Bragg gratings 2,6 as tuning filters.…”

Tunability of optical filter based on fibre-optic ring resonator using polarisation and birefringence effects in the resonator loop

“…Tunability of these filters is an essential element of their work, which is to be carried out, at least, in modern wavelength division multiplexing (WDM) systems with the carrier spacing of less than 50 GHz [8]. Optical filters based on the FORR may be tuned using various methods such as changing of a coupler ratio [9], a Sagnac phase-shift [1], a finesse of a resonator [10], and phase matching conditions of a loop resonator [11]. In a recent work [12], a highbirefringence (HBF) fibre ring resonator with an inline reflector has been proposed where a piece of single-mode fibre is replaced with a piece of HBF in order to obtain a narrowband filters based on Vernier effect for the use in single-frequency fibre lasers.…”