Femtometer-resolved simultaneous measurement of multiple laser wavelengths in a speckle wavemeter

TL;DR

This paper introduces a speckle-based method capable of simultaneously measuring multiple laser wavelengths with femtometer resolution, significantly advancing optical spectrum measurement precision and enabling applications in quantum tech and telecommunications.

Contribution

The authors develop a novel technique that enhances resolution and allows for concurrent measurement of multiple wavelengths using a simple multimode fiber and PCA analysis.

Findings

Independent wavelengths separated by 1 fm are retrieved with 0.2 fm precision.

The method can measure sparse spectra with multiple lines.

It demonstrates femtometer-level resolution in multi-wavelength measurements.

Abstract

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 is likely to find application in the tracking of multiple lasers in fields such as portable quantum technologies and optical telecommunications.