Spectrometers are widely used tools in chemical and biological sensing,
material analysis and light source characterization. Traditional spectrometers
use a grating/prism to disperse light. The
spectral resolution scales with the optical
path length from the grating to the detectors, imposing a trade-off between device
size and resolution. The recent development of miniature spectrometers has
enabled a host of new applications, owing
to their reduced cost and portability.
However, these implementations are still
based on grating dispersion, and therefore
the spectral resolution is lower than large
bench top spectrometers. As a potential
solution to this problem, we proposed and
demonstrated that a single multimode
fiber can function as a high-resolution,
low-loss spectrometer. 1
Our fiber spectrometer is compact,
lightweight and low-cost. It also provides resolution that is competitive
with the top commercially available
grating-based spectrometers. It utilizes
the speckle pattern from a multimode
fiber for spectral reconstruction. The
speckle pattern, generated by interference among the guided modes, is unique
for each wavelength and can be used
as a fingerprint to identify the spectral
content of input light. We used a camera
to record the speckle patterns at individual wavelengths and stored them in
a transmission matrix. After calibration,
we retrieved an arbitrary probe spectrum
from the speckle pattern by matrix inversion and non-linear optimization. 1–5
The spectral resolution of the multi-
mode fiber spectrometer scales with the
fiber length. A standard 1-meter-long
multimode fiber (105 μm core diameter,
NA = 0.22) provides 100 nm band-
width with 0.15 nm resolution at
about 1,500 nm wavelength. Using a
20-meter-long fiber, we could resolve
two lines separated by 8 pm. The
fiber spectrometer can also recover
broadband spectra. 2
In addition to providing fine spectral resolution and broad operation
bandwidth, our fiber spectrometer has
low insertion loss. The signal-to-noise
ratio can exceed 1,000. Furthermore,
the fiber can be coiled to provide a
compact, lightweight and low-cost
spectrometer that will enable a host of
new spectroscopic applications.
(a) Speckle patterns at the end of a 1-meter-long multimode fiber for three
input wavelengths. Small changes in the input wavelength produce uncorrelated
speckle patterns, enabling high resolution. (b) Spectra reconstructed using a
1-meter-long fiber. The probe for each is a narrow laser line. (c) A 20-meter-long
fiber is used to reconstruct a spectra consisting of two narrow lines (red) separated by only 8 pm.
Brandon Redding (brandon.
email@example.com), Sebas-tien Popoff and Hui Cao
Yale University, New Haven,
1. B. Redding et al. Op. Lett.
37, 3384 (2012).
2. B. Redding et al. Opt.
Express 21, 6584 (2013).
3. Z. Xu et al. Opt. Express 11,
4. T. W. Kohlgraf-Owens et al.
Opt. Lett. 35, 2236 (2010).
5. Q. Hang et al. Appl. Opt. 49,
Multimode Fiber as a High-Resolution,
1,450 1,475 1,500 1,525 1,550
0 1,500.46 1,500.48 1,500.5 1,500.52
l = 1,500 nm
l = 1,501 nm
Dl = 8 pm
L = 20 m
L = 1 m
l = 1,502 nm