Tunable ultra-high-resolution spectral analysis using a frequency-shifted loop

Ultra-high-resolution spectral analysis supports advanced fiber-optic sensing. Limited resolution hinders the study of fine spectral details. We propose a swept frequency pulsed light source based on the positive and negative frequency shifting loop. A tunable modulator achieves frequency steps on the kHz scale. By cascading frequency shifting loops, the bandwidth of 36.15 GHz with the pulsed frequency shifted step of 500 kHz is experimentally verified. Coupled to a Mach-Zehnder interferometer, the source resolves spectra with 5 kHz resolution. In addition, based on the time-domain scanning characteristics, the light source has a multi-channel spectra analysis capability to interrogate serial sensors.