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Research progress of computational microspectrometer based on speckle inspection
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Abstract
Fast, accurate and nondestructive spectral analysis technique is important and widely used in the fields of scientific research, information, biomedical, pharmaceutical detection, agriculture, environment, and security. However, the existing spectroscopic analysis equipments are usually bulky and complex, which are difficult to adapt to portable application scenarios such as on-site rapid detection, light-load platform, etc. In recent years, miniature spectroscopic detection technology and equipment have received extensive attention, and have been rapidly developed, with significant advantages in size, weight, and power consumption. In particular, the computational spectral analysis technology based on the speckle detection can obtain high-precision spectral information by recording and analyzing the speckle pattern formed by the scattering element on the measured light. This paper will first introduce the related technical principles and technological developments, then analyze the existing techniques including the advantages and disadvantages, and finally discuss and summarize the future development direction and application prospects.-
Keywords:
- spectrum /
- speckle /
- microspectrometer /
- compressive sensing
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References
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Overview
Overview: Fast, accurate and nondestructive spectral analysis technique is important to differentiate matters and widely used in the fields of scientific research, information, biomedical, pharmaceutical detection, agriculture, environment, and security. The existing spectroscopic analysis equipments usually use individual optical elements such as gratings, prisms and interferometer to obtain spectral information, and therefore the whole system is usually bulky, complex and expensive, which are difficult to adapt to portable application scenarios such as on-site rapid detection, point-of-care diagnostics, and light-load platform in low-resource settings. It is not straight forward to minimize the conventional spectrometer without a loss of performance because the spectral resolution is usually associated with the length of light path. Novel mechanisms and advanced techniques are required to tackle this issue. With the rapid developments of the novel nanophotonic techniques and micro-nano fabrication methods, spectral analysis has been achieved on a single chip with decent spectral resolution, for example, quantum dot microspectrometer, photonic crystal microspectrometer, and so on, which shows great advantages in volume, weight, integration, cost, etc. In addition, combining such minimized spectrometers together with the cloud technology and big data technology is expected to significantly improve the efficiency of spectral information in collection, distribution and analysis, which is important for timely, accurate and portable applications. In particular, the computational spectral technology based on the speckle inspection can obtain high-resolution spectral information by recording and analyzing the speckle patterns formed by the light scattering process. In general, the speckle detection-based spectral analysis techniques are divided into two categories: the waveguide types and the normal incidence types. The waveguide types include multimode fibers, multimode waveguides, and in-plane scatters. Different modes have different propagation constants and thus different phase delay. Different scattering paths also result in different phase delay. The light interference therefore induces the generation of the wavelength-dependent speckles. The normal incidence type usually includes disordered micro-nano structures such as nanoparticles, micro-holes, and frosted glass. Similar optical interference phenomenon occurs and generates wavelength-dependent speckles. By initially calibrating the speckle generation structures by a series of monochromatic light and dealing the speckle with the compressive sensing algorithm, the spectral information of the target spectrum can be reconstructed. This paper will introduce the relevant technical principles and technical development status, analyze the existing technical performance, advantages and disadvantages, discuss and summarize the future development direction and application prospects.
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Figure 1.
Schematic diagram of micro-computing spectrometer for speckle detection. (a) Schematic of speckle pattern distribution on the detector array after the incident light passing through the dispersive component; (b) Schematic diagram of spectral reconstruction measured based on mapping matrix
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Figure 2.
Diagram of miniature spectrometer with multimode fiber. (a) Speckle pattern intensity distribution at the end of a 5 m long multimode fiber with varying input wavelength, spectral correlation function of the different length multimode fiber, and 5 m long multimode fiber spectrometer can resolve narrow-band laser spectral lines[45]; (b) Fiber spectrometer with wavelength division multiplexers and a 1-to-7 fan-out fiber bundle, reconstructed spectrum test results in the 100 nm bandwidth[48]; (c) Miniature multimode fiber spectrometer using optical switch space-division multiplexing, spectral correlation function, reconstructed narrow spectral lines test results[59]; (d) Miniature spectrometer using multimode tapered optical fibre, speckle pattern intensity distribution with varying input wavelength, and reconstructed narrow spectral lines test results[60]
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Figure 3.
Diagram of a miniature spectrometer with a planar strip optical waveguide. (a) Schematic of a spiral spectrometer, speckle pattern intensity distribution with varying input wavelength, spectral correlation function, and reconstructed narrow laser spectral lines test results[46]; (b) Schematic of input switch matrix silicon multimode waveguide spectrometer, and reconstructed test results[63]
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Figure 4.
Diagram of miniature spectrometer with planar photonic crystal and micro-ring optical waveguide. (a) Schematic of integrated photonic crystal spectrometers, and speckle distribution with different wavelengths at the output waveguide[65]; (b) Micro-spectrometer based on miniaturized microdonut resonators array, out-of-plane speckle pattern intensity distribution with varying input wavelength, and reconstructed spectral test results[69]; (c) Schematic of an integrated digital plane hologram spectrometer, speckle pattern intensity distribution, and reconstructed spectral test results[71]
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Figure 5.
Miniature spectrometer with plane scatter light guide structure. (a) SEM image of the disordered photonic spectrometer, the bottom area is an enlarged image with a scale of 1 μm, the right area is numerical simulation and experimental results at 1500 nm[47]; (b) Calibration matrix of disordered photonic structure[47]; (c) The spectral correlation function based on the average intensity of all detection channels[47]; (d) Disordered photonic spectrometer can resolve narrow-band laser spectral lines[47]
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Figure 6.
Part of spatial type spectrometer. (a) Schematic of miniature spectrometer based on inhomogeneous and self-assembled disordered photonic crystals, speckle pattern distribution, and spectral test results[74]; (b) SEM image and far-field speckle pattern of alumina particles[75]
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Figure 7.
Space scattering structure type spectrometer. (a) Schematic of miniature spectrometer based on hole array, speckle distribution and spectrum test results[49]; (b) Schematic of a miniature spectrometer based on frosted glass, and the spectrum test results in the visible and ultraviolet bands[14]; (c) The frosted glass spectrometer using up conversion and down conversion materials spectral test results in the three bands of ultraviolet, visible and infrared[77]
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Figure 8.
Polychromats, grating, and nanoparticles structure type spectrometer. (a) Spectral analysis based on the polychromats: the groove depth distribution, speckle pattern distribution and correlation function of the two types of polychromats[33]; (b) Schematic diagram of the random grating array speckle spectrometer[79]; (c) Schematic of nanoparticles speckle-enhanced prism spectrometer[80]
