Passive Beam Combining for the Development of High Power SOA-Based Tunable Fiber Compound-Ring Lasers Using Low Power Optical Components

Abstract

A simple, stable, compact, and cost-effective dual-output port widely tunable SOA-based fiber compound-ring laser structure is demonstrated. Such a unique nested ring cavity enables the splitting of optical power into various branches where amplification and wavelength selection for each branch are achieved utilizing low-power SOAs and a tunable filter, respectively. Furthermore, splicing Sagnac Loop Mirrors at each end of the bidirectional fiber compound-ring cavity not only allows them to serve as variable reflectors but also enables them to channel the optical energy back to the same port thus omitting the need for high optical power combiners. Further discussed is how the said bidirectional fiber compound-ring laser structure can be extended to achieve a high-power fiber laser source by exclusively using low power optical components such as N × N couplers and (N > 1) number of SOAs. More than 98% coherent beam combining efficiency of two parallel nested fiber ring resonators is achieved over the C-band tuning range of 30 nm. Optical signal-to-noise ratio (OSNR) of +45 dB, and optical power fluctuation of less than ±0.02 dB are measured over 3 h at room temperature.