Detecting optical frequency in weak signal light using injection-induced frequency modulation

In fiber-optic sensing, long-distance transmission and demodulation of weak signal light (SL) are critical. This study improves the system by relocating an external cavity tunable laser (ECTL) to the transmission end. Directly injecting the SL into the ECTL modulates the output light and uses the high-power ECTL light for transmission, reducing loss. At the demodulation end, an orthogonal Mach-Zehnder interferometer (MZI) and an H 13 C 14 N gas absorption cell (GAC) extract SL wavelength information. Results demonstrate effective modulation with SL intensity as low as 1 nW and a demodulation resolution of up to 10 MHz, offering significant improvements in long-distance fiber-optic sensing. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement