Ultra-fast full-field optical characterization of CW lasers based on optical frequency comb, wavelength-to-time mapping and phase-diversity.

Optical frequency comb (OFC), a periodic optical pulse train in time domain, has been widely employed to measure optical frequency due to its equidistant modes in the frequency domain. Here, we propose and demonstrate a novel optical spectrum analyzer for CW lasers based on stretching the OFC in a dispersive element and mapping the frequency comb into the time domain. The optical spectrum analyzer also provides instantaneous full-field (wavelength, amplitude and phase) optical characterization capability by combining with optical phase-diversity technology. Experimental results show that we successfully trace the evolution of modulated lasers with a measurement speed of ∼51 MHz (related to the pulse repetition of the OFC) and a high spectral resolution of ∼21 pm. Thanks to the use of wavelength-to-time mapping and OFC, the single channel measurement range of the proposed system can reach ∼10 nm, which breaks the restriction of the bandwidth of photodetector.