Time-Stretch Spectroscopy Based on Laser Cavity Tuning With a Dual-Function Delay Line

Time-stretch spectroscopy has established as a viable technique with high resolution and single-shot capability. However, it generally requires ultra-wideband photodetectors and electronics, and its performance is often restricted by a fundamental tradeoff between spectral resolution and signal-to-noise ratio. Here, we report a time-stretch spectrometer based on the concept of optical sampling by laser cavity tuning. A kilometer-scale dual-function fiber-optic link serves as both a pulse stretcher and a long delay line in an imbalanced Mach-Zehnder interferometer. Measurement results based on several device and atomic samples are presented. Theoretical forms of the total spectral range and spectral resolution are derived and compared with experimental data. A spectral resolution as small as 8 GHz has been achieved. Resolution-limiting factors are discussed and possible solutions are presented.