Single-Pixel Multimode Fiber Spectrometer via Wavefront Shaping S ahin K urekci1 2 S. S uleyman Kahraman1 3 and Emre Y uce1 2

2025-05-03 0 0 1022.9KB 9 页 10玖币

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Single-Pixel Multimode Fiber Spectrometer

via Wavefront Shaping

S¸ahin K¨urekci ∗1, 2, S. S¨uleyman Kahraman1, 3, and Emre Y¨uce1, 2

1Programmable Photonics Group, Department of Physics, Middle East Technical University,

Ankara, Turkey

2The Center for Solar Energy Research and Applications (ODT ¨

U-G ¨

UNAM), Middle East

Technical University, Ankara, Turkey

3Caltech Optical Imaging Laboratory, Andrew and Peggy Cherng Department of Medical

Engineering, Department of Electrical Engineering, California Institute of Technology, Pasadena,

CA, USA

Abstract

When light passes through a multimode ﬁber, two-dimensional random intensity

patterns are formed due to the complex interference within the ﬁber. The extreme sen-

sitivity of speckle patterns to the frequency of light paved the way for high-resolution

multimode ﬁber spectrometers. However, this approach requires expensive IR cameras

and impedes the integration of spectrometers on-chip. In this study, we propose a

single-pixel multimode ﬁber spectrometer by exploiting wavefront shaping. The input

light is structured with the help of a spatial light modulator, and optimal phase masks,

focusing light at the distal end of the ﬁber, are stored for each wavelength. Variation of

the intensity in the focused region is recorded by scanning all wavelengths under ﬁxed

optimal masks. Based on the intensity measurements, we show that an arbitrary input

spectrum having two wavelengths 20 pm apart from each other can be reconstructed

successfully (with a reconstruction error of ∼3%) in the near-infrared regime, corre-

sponding to a resolving power of R≈105. We also demonstrate the reconstruction

of broadband continuous spectra for various bandwidths. With the installation of a

single-pixel detector, our method provides low-budget and compact detection at an

increased single-to-noise ratio.

∗Corresponding author: kurekci@metu.edu.tr

arXiv:2210.13292v1 [physics.optics] 24 Oct 2022

Introduction

Spectrometers achieve spectral-to-spatial mapping which allows spectral decomposition of

the input light. Conventional spectrometers use dispersive media such as gratings or prisms,

and they can achieve resolving powers around R < 104, and can reach up to R < 105only

with the installation of complex triple-grating systems (the spectral resolution is δλ =λ0/R,

where λ0is the operating wavelength). However, such spectrometers generally require moving

parts (grating, mirrors) and a line array detector for scanning whole wavelengths of interest.

Moreover, inverse proportionality between spectral resolution and optical path length leads to

bulky systems when high-resolution is demanded. The fundamental need for high resolution

spectral analysis in various lines of research and applications triggers new concepts that are

built on the basis of holography [1], scattering of light by a photonic crystal [2, 3], a random

scattering medium [4], or a multimode ﬁber (MMF) [5, 6, 7, 8] to form a complex spatial

intensity distribution (a speckle pattern) on a multipixel detector such as a charged couple

device (CCD) or a focal plane array (FPA). In such systems, wavelengths experience diﬀerent

propagation constants inside the scattering medium, thus forming distinct spatial intensity

proﬁles on the detector, which provides the required one-to-one spectral-to-spatial mapping.

Before the use of spectrometer, a calibration matrix is measured by scanning all wavelengths

in the operational range and it stores the corresponding speckle patterns. The calibration

matrix is then utilized to reconstruct an arbitrary input spectrum based on the measured

intensity distribution. However, the increased cost of CCD and FPA sensors especially in

infrared regime limits the deployment of high-resolution spectral analysis tools.

Among all scattering-based systems, the multimode ﬁber spectrometers have been particu-

larly attractive by oﬀering high-resolutions with reduced scattering losses (keeping the light

collimated inside the ﬁber and preventing scattering to higher angles). Since ﬁbers can be

wrapped, higher spectral resolution can be achieved without enlarging the system. It was

shown in [7] that high resolving powers R > 106in near-infrared regime is possible with

ﬁbers of 100 m long. Yet the signal-to-noise ratio (SNR) is the main limiting factor for the

resolution at low signal levels and increased ﬁber length [9].

Single pixel detection together with compressed sensing [10, 11, 12] have been revolutionizing

imaging methods. Surprisingly, the penetration of this methods in spectroscopy have been

very limited due to mechanical resolution limits. The single-pixel imaging (SPI) systems are

based on the use of a spatial light modulator (SLM) and a single-pixel detector. Employing

the SPI method is particularly useful when working in the infrared regime since FPAs get

extremely expensive at longer wavelengths [13].

In this paper, we develop a high-resolution single-pixel multimode ﬁber spectrometer and

demonstrate its ability to reconstruct arbitrary spectra. The single-pixel detection is achieved

by focusing light on a selected target region of a focal plane array which is employed as

a bucket detector. The input wavefronts are structured using a spatial light modulator

which provides distinct output intensities at the detector [14, 15, 16, 17, 18]. The intensity

variations at the target position as a function of input wavelength are used to reconstruct the

spectra at a resolution of 20 pm. The increased intensity at the focused point also increases

SNR which removes low signal barrier in reaching high resolutions at low signal levels. This,

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摘要：

Single-PixelMultimodeFiberSpectrometerviaWavefrontShapingSahinKurekci*1,2,S.SuleymanKahraman1,3,andEmreYuce1,21ProgrammablePhotonicsGroup,DepartmentofPhysics,MiddleEastTechnicalUniversity,Ankara,Turkey2TheCenterforSolarEnergyResearchandApplications(ODTU-GUNAM),MiddleEastTechnicalUniversity,Ank...

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Single-Pixel Multimode Fiber Spectrometer via Wavefront Shaping S ahin K urekci1 2 S. S uleyman Kahraman1 3 and Emre Y uce1 2

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