Many areas of optical science require an accurate measurement of optical spectra. Devices based on laser speckle promise compact wavelength measurement, with attometer-level sensitivity demonstrated for single wavelength laser fields. The measurement of multimode spectra using this approach would be attractive, yet this is currently limited to picometer resolution. Here, we present a method to improve the resolution and precision of speckle-based multi-wavelength measurements. We measure multiple wavelengths simultaneously, in a device comprising a single 1-m-long step-index multimode fiber and a fast camera. Independent wavelengths separated by as little as 1 fm are retrieved with 0.2 fm precision using principal component analysis. The method offers a viable way to measure sparse spectra containing multiple individual lines and may find application in the tracking of multiple lasers in fields such as quantum technologies and optical telecommunications.
Bibliographical noteFunding Information:
Leverhulme Trust (RPG-2017-197); Engineering and Physical Sciences Research Council (EP/R004854/1, EP/P030017/1).
© 2020 Optical Society of America
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics