Abstract:

When measuring length, we learn in school that a vernier scale that uses two rulers, slightly offset, can reduce human estimation error and improve the resolution of a measurement. Yang et al. apply the same vernier principle with optical combs to develop a spectrometer that can determine the wavelength of light with high accuracy and precision. Two phase-locked counterpropagating optical microcombs generated in a miniature microresonator provided the rulers. Matching up of the “teeth” of the combs was then used to measure the wavelength of the optical light sources. Science, this issue p. 965 Counterpropagating optical microcombs can be used as a vernier spectrometer to determine the wavelength of light. Determination of laser frequency with high resolution under continuous and abrupt tuning conditions is important for sensing, spectroscopy, and communications. We show that a single microresonator provides rapid and broadband measurement of optical frequencies with a relative frequency precision comparable to that of conventional dual-frequency comb systems. Dual-locked counterpropagating solitons having slightly different repetition rates were used to implement a vernier spectrometer, which enabled characterization of laser tuning rates as high as 10 terahertz per second, broadly step-tuned lasers, multiline laser spectra, and molecular absorption lines. Besides providing a considerable technical simplification through the dual-locked solitons and enhanced capability for measurement of arbitrarily tuned sources, our results reveal possibilities for chip-scale spectrometers that exceed the performance of tabletop grating and interferometer-based devices.