High-resolution and broadband all-fiber spectrometers

Abstract

The development of optical fibers has revolutionized telecommunications by enabling longdistance broad-band transmission with minimal loss. In turn, the ubiquity of high-quality lowcost fibers enabled a number of additional applications, including fiber sensors, fiber lasers, and imaging fiber bundles. Recently, we showed that a multimode optical fiber can also function as a spectrometer by measuring the wavelength-dependent speckle pattern formed by interference between the guided modes. Here, we reach a record resolution of 1 pm at wavelength 1500 nm using a 100 meter long multimode fiber, outperforming the state-of-the-art grating spectrometers. We also achieved broad-band operation with a 4 cm long fiber, covering 400 nm -750 nm with 1 nm resolution. The fiber spectrometer, consisting of the fiber which can be coiled to a small volume and a monochrome camera that records the speckle pattern, is compact, lightweight, and low cost while providing ultrahigh resolution, broad bandwidth and low loss.

High-resolution optical spectroscopy using multimode interference in a compact tapered fibre

“…Matrix left-inversion gives a least-square solution s ¼ L À 1 W, which applies in situations even when W = 2 spanfu i g i where u i are the calibrated frequencies, that is, the spectral reconstruction works even for a continuous input spectrum. In addition, this solution can be treated as an initial solution s 0 to the more general minimization problem kLs À Wk 2 where || Á || 2 denotes the 2-norm [19][20][21][22][23]29 . By eliminating the non-physical negative solutions and then solving this minimization problem using a nonlinear optimization algorithm, we can reconstruct the spectra of a measured signal more accurately (see Supplementary Methods for further discussion).…”

“…We can estimate the spectral resolution of the device from a correlation function [20][21][22][23] Fig. 4b.…”

“…Recent research 21 on the transverse speckle patterns in multimode fibres additionally indicates that the B15-cm-long fibre used in our experiment would remain correlated up to DTB10°C. A shift of Do may be applied 22 to correct the calibration for temperature variations 4DT, and active thermal stabilization could also be implemented in applications where high spectral accuracy is needed in the presence of large ambient temperature changes.…”

“…In recent years, there has been a strong effort to develop novel spectrometers that are compact and have high resolving powers and operational bandwidths 5,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] . In addition to miniature grating spectrometers 12 , resonant structures such as nanocavities [13][14][15][16][17][18] have also been employed to separate spectral components into unique detectors.…”

“…Another class of compact spectrometers relies on imaging the speckle patterns of a photonic bandgap fibre bundle 19 or a multimode optical fibre [20][21][22] . However, these spectrometers are centimetres to metres long, which can result in the instability of the interference pattern due to environmental fluctuations, hence limiting their long-term operation.…”