Enhancing sensitivity of trace copper detection based on coupled optoelectronic oscillator

We propose to employ coupled optoelectronic oscillator (COEO) for trace copper detection to achieve an enhanced sensitivity and stability. By replacing the optical source of the traditional OEO with an optical feedback loop, the oscillation frequency is determined by the cavity loop length in conjunction with the laser output wavelength. The sensing head, which is fabricated by inserting a fusion spliced fiber with large lateral offset fusion splicing in a Sagnac loop, act as a wavelength selection component in the laser loop. Hence, the oscillation frequency changes with the varying solution concentration. Benefitting from the matching of the laser loop and the OEO loop, the final oscillation mode is more stable. By comparing the performance of the COEO-based, single-loop and dual-loop OEO-based sensors, the highest sensitivity of 41.1 Hz/(uMol/L) is obtained by the COEO-based sensor. Since the positive feedback of two loops, the single mode oscillation can be implemented without additional devices.