Enhanced Ultrawideband Wavelength-Swept Laser Covering a 440-nm Bandwidth for Fiber-Optic Sensors

This study details the implementation of an ultra-wideband wavelength-swept laser (WSL) employing a polygonal scanning mirror-based wavelength tunable filter (PSM-TF) and four semiconductor optical amplifiers (SOAs). The system incorporates two independent gain media with center wavelengths of 1250 nm and 1450 nm, each configured in a Mach-Zehnder interferometer, with the PSM-TF shared between the two SOAs. Precise angular alignment between the optical axes of the two wavelength bands incident on the PSM-TF is critical for achieving ultra-wideband WSL. The theoretically calculated angle was 33.725°, whereas the experimentally measured angle was 33.788°, yielding a relative error of approximately 0.19%, a value considered negligible in relation to the full-scanning wavelength range. The WSL achieved a 10 dB bandwidth of 442.8 nm in the spectral domain (1130.8 to 1573.6 nm) and a temporal output duration of 329.4 μs at a scanning frequency of 2.338 kHz. The conversion ratio between the spectral and temporal domains across the scanning range was determined to be 1.344 nm/μs, closely aligning with the ratios observed in the two resonators. The duty cycle in the temporal domain was 77.0%, and a free spectral range in the spectral domain was 575.0 nm. In addition, the ultra-wideband WSL demonstrated excellent wavelength repeatability and stability in both short-term and long-term measurements. This system exhibits significant potential for real-time multipoint dynamic fiber-optic sensing applications and offers promising enhancements for image resolution in biophotonics.