Slope-Assisted Brillouin Optical Wavemeter

We introduce a slope-assisted Brillouin optical wavemeter. Existing Brillouin-based spectrum analyzers measure the Brillouin gain as the frequency of a pump laser is swept across the frequency band of interest. However, this process is slow since only one spectral channel is measured at a time and the spectral resolution is typically limited to the Brillouin gain linewidth. In this work, we introduce a technique that uses both the Brillouin gain and phase to construct a single-shot wavemeter with frequency resolution orders of magnitude below the Brillouin linewidth. We also show that combining information from the Stokes and anti-Stokes interactions allows us to reduce the sensitivity to environmental fluctuations such as temperature, enabling a robust system with frequency noise of 20 Hz/ $\surd $ Hz. This noise level enables a measurement of a 200 Hz frequency shift with a 10 ms measurement.