Multimode optical fiber based spectrometers

TL;DR

This paper demonstrates that standard multimode optical fibers can be used as high-resolution, low-cost spectrometers by calibrating speckle patterns, enabling measurements from laser lines to broadband spectra with enhanced techniques.

Contribution

It introduces a calibration and reconstruction method for multimode fiber spectrometers, improving spectral resolution and bandwidth, and discusses effects of fiber geometry and polarization imaging.

Findings

A 20m fiber resolves 8 pm laser line separation.

A 2cm fiber measures broadband supercontinuum spectra.

Polarization imaging enhances bandwidth and reduces reconstruction error.

Abstract

A standard multimode optical fiber can be used as a general purpose spectrometer after calibrating the wavelength dependent speckle patterns produced by interference between the guided modes of the fiber. A transmission matrix was used to store the calibration data and a robust algorithm was developed to reconstruct an arbitrary input spectrum in the presence of experimental noise. We demonstrate that a 20 meter long fiber can resolve two laser lines separated by only 8 pm. At the other extreme, we show that a 2 centimeter long fiber can measure a broadband continuous spectrum generated from a supercontinuum source. We investigate the effect of the fiber geometry on the spectral resolution and bandwidth, and also discuss the additional limitation on the bandwidth imposed by speckle contrast reduction when measuring dense spectra. Finally, we demonstrate a method to reduce the spectrum reconstruction error and increase the bandwidth by separately imaging the speckle patterns of orthogonal polarizations. The multimode fiber spectrometer is compact, lightweight, low cost, and provides high resolution with low loss.