Wavemeter capable of simultaneously achieving ultra-high resolution and broad bandwidth by using Rayleigh speckle from single mode fiber

Rayleigh speckle with random jagged pattern resulting from the interference of Rayleigh backscattering lightwave in a single-mode fiber contains the wavelength information of the incident lightwave. We propose an all-fiber wavemeter based on the relation between Rayleigh speckle and wavelength. The system does not suffer from the resolution-bandwidth trade-off relation and simultaneously achieves an ultra-high resolution of 40 attometers and a broad bandwidth of 80 nm covering 1520 to 1600 nm. The wavemeter could enable precise measurement of continuous-wave optical waveforms at time resolution of 100  $\mu$ s. Combined with a dynamic laser, the system can be regarded as a high-resolution spectroscopy for absorption spectrum analysis. To demonstrate the broad applicability of the techinique, we use a laser step-scanned over 80 nm to measure the spectral response of hydrogen cyanide absorption line, and use a continuous-wave laser to measure its nonlinear wavelength scan over 1 nm. The proposed all-fiber wavemeter provides great prospects for ultra-precise spectrum analysis with ultra-broad bandwidth and ultra-high resolution.