CN114488513B - Full-vector modulation single-fiber high-signal-to-noise-ratio three-dimensional imaging method and device - Google Patents

Full-vector modulation single-fiber high-signal-to-noise-ratio three-dimensional imaging method and device Download PDF

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CN114488513B
CN114488513B CN202210130711.5A CN202210130711A CN114488513B CN 114488513 B CN114488513 B CN 114488513B CN 202210130711 A CN202210130711 A CN 202210130711A CN 114488513 B CN114488513 B CN 114488513B
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polarization
full
noise ratio
optical fiber
high signal
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CN114488513A (en
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杨青
文仲
董振宇
邓启林
刘旭
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Zhejiang Lab
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Zhejiang Lab
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/24Instruments or systems for viewing the inside of hollow bodies, e.g. fibrescopes
    • G02B23/2407Optical details
    • G02B23/2461Illumination
    • G02B23/2469Illumination using optical fibres
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/24Instruments or systems for viewing the inside of hollow bodies, e.g. fibrescopes
    • G02B23/2407Optical details
    • G02B23/2415Stereoscopic endoscopes
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/24Instruments or systems for viewing the inside of hollow bodies, e.g. fibrescopes
    • G02B23/2476Non-optical details, e.g. housings, mountings, supports
    • G02B23/2484Arrangements in relation to a camera or imaging device

Abstract

The invention discloses a full-vector modulation single-fiber high signal-to-noise ratio three-dimensional imaging method and device. The excitation light generated by the laser realizes an optical field with randomly controllable phase, polarization and amplitude after passing through the spatial light modulator and the polarization modulation module. After the optical fiber is incident, a full vector transmission matrix is obtained through reconstruction by an orthogonal polarization microscopic module. The transmission matrix values are processed to compensate for mode coupling, mode loss, and polarization dispersion in long-haul large-curvature multimode fibers. And the axial scanning with high signal-to-noise ratio is obtained by adding a propagation factor in the virtual frequency domain of the optical fiber emergent end, and the imaging device has high signal-to-noise ratio, high resolution and large depth imaging, so that the imaging device can be widely applied to biomedicine.

Description

Full-vector modulation single-fiber high-signal-to-noise-ratio three-dimensional imaging method and device
Technical Field
The invention belongs to the technical field of optical fiber microscopy, and particularly relates to a single-optical-fiber high-signal-to-noise-ratio three-dimensional imaging method and device with full vector modulation.
Background
In recent years, the development of science and technology has been accompanied. It is highly desirable to be able to study the mechanisms of biological processes directly in complex organisms. Such applications require high spatial-temporal resolution, enabling imaging in three dimensions, capturing critical depth-resolved tissue structures in the human body in real time. Multimode fiber optic endoscopes can provide high resolution three-dimensional imaging, and are of great interest both in research and commerce.
However, in long or large-curvature fiber optic transmission, there are varying degrees of fiber radius of curvature, imperfections, and the like. Mode coupling and mode dependent loss due to mode dispersion and polarization mode dispersion are further enhanced, thereby greatly reducing the signal to noise ratio of the image, especially for deep three-dimensional images. The application range of the optical fiber as a microscopic tool with low cost and high spatial bandwidth product in the fields of biology, medicine and materials is limited.
Disclosure of Invention
Aiming at the problems existing in the current optical fiber endoscope field, the invention provides a full vector modulation single optical fiber high signal-to-noise ratio three-dimensional imaging method and device. Meanwhile, the depth is expanded, and three-dimensional endoscopic microscopic observation with high signal to noise ratio is realized.
In order to achieve the above purpose, the invention provides a single-fiber high signal-to-noise ratio three-dimensional imaging method of full vector modulation, which comprises the following steps:
s1: performing full vector transmission matrix measurement on the optical fiber;
s2: processing the transmission matrix value to compensate mode coupling, mode loss and polarization dispersion in the long-distance large-curvature multimode fiber;
s3: the axial scanning is realized by adding a propagation factor in the virtual frequency domain of the optical fiber emergent end, and finally, the three-dimensional image with high signal to noise ratio is obtained by reconstruction.
Preferably, the step S1 is to measure the corresponding conversion relationship of the phase, polarization and amplitude of the incident light and the emergent light of the optical fiber by using wavefront modulation and holographic interferometry.
Preferably, the step S2 is to implement redistribution of pattern energy according to matrix information by regularization and various optimization algorithms, so as to reduce the influence of loss. And decompose the incident mode corresponding to the emergent mode onto incident wave fronts with different polarizations.
Preferably, the step S3 is to construct the corresponding frequency distribution by using the complete property values of the full vector transmission matrix to realize the frequency domain reconstruction.
The invention also provides a full-vector-modulation single-fiber high signal-to-noise ratio three-dimensional imaging device, which comprises a laser, a spatial light modulator, a polarization modulation module, a multimode fiber, a polarization microscopic module and a server which are sequentially arranged along the direction of a light path, wherein a calibration module is arranged between the laser and the spatial light modulator, the laser is connected with the calibration module through a first fiber, a beam splitter and an objective lens are arranged between the polarization modulation module and the multimode fiber, a collecting module is arranged in the other direction of the beam splitter, the laser is connected with the polarization modulation module through a second fiber, and the collecting module is electrically connected with the server.
Preferably, the calibration module comprises a collimating mirror and a first quarter wave plate, the collimating mirror is connected with the first optical fiber, and the first quarter wave plate is connected with the spatial light modulator.
Preferably, a beam shrinking module is further arranged between the spatial light modulator and the polarization modulation module, the beam shrinking module comprises a first lens and a second lens, and the first lens and the second lens shrink light from the spatial light modulator and transmit the light to the polarization modulation module.
Preferably, the polarization modulation module comprises a polarization beam splitter, wherein the S light direction of the polarization beam splitter is provided with a second quarter wave plate and a first reflecting mirror, and the P light direction of the polarization beam splitter is provided with a third quarter wave plate and a second reflecting mirror.
Preferably, the polarization microscope module comprises a sample and a polarization microscope, the polarization microscope is connected with the second optical fiber and the server, the collecting module comprises a third lens and a photoelectric detector, and the photoelectric detector is electrically connected with the server.
Preferably, the multimode optical fiber includes a step-index optical fiber, a graded-index optical fiber, and an arbitrary refractive index distribution optical fiber; the spatial light modulator is used for controlling the phase and amplitude of incident light and comprises a digital micro mirror array, a liquid crystal spatial light modulator and a deformable mirror; the polarization modulation module realizes the polarization regulation and control of the pixel level by overlapping two holograms with orthogonal polarization and changing relative phase distribution.
According to the full-vector modulated remote single-fiber high signal-to-noise ratio three-dimensional imaging method and device, excitation light generated by a laser is modulated by a spatial light modulator to have complex amplitude, and then can be coupled into an optical fiber in any polarization state through a polarization modulation module. The imaging system composed of the objective lens and the lens focuses the light spot at the outgoing end of the optical fiber on the camera and interferes with the reference light, the complex amplitude and polarization of the incident light are changed, the complex amplitude of the interference light spot collected by the camera is extracted in a holographic mode, and the polarization before the interference light spot enters the camera is rotated through the polarization rotation regulator. And establishing a linear corresponding relation between the incident/emergent light complex amplitude and the polarization, and finally calculating to obtain a full vector transmission matrix. And reversely calculating the incident polarization and the complex amplitude distribution according to the phase and the polarization distribution corresponding to the emergent scanning point, and decomposing the incident polarization and the complex amplitude distribution into two polarization holograms of the space light. Imaging at different depths in a sample can be realized by adding propagation factors to the virtual frequency plane of the optical fiber emergent end.
The invention adopts full vector modulation and full vector transmission matrix to compensate mode coupling, mode loss and polarization dispersion in long-distance large-curvature multimode fiber. And the axial scanning with high signal-to-noise ratio is obtained by adding a propagation factor to the virtual frequency plane of the optical fiber emergent end. Finally, three-dimensional scanning imaging with high signal to noise ratio can be realized under the condition of no mechanical movement, and the application range of the optical fiber endoscope microscopy is enlarged.
Drawings
FIG. 1 is a schematic view of the apparatus of the present invention;
FIG. 2 is a schematic diagram of the modulation scheme of the polarization module of FIG. 1;
FIG. 3 is a schematic diagram of arbitrary polarization and phase modulation at the exit end of an optical fiber;
FIG. 4 is a schematic diagram of a multimode fiber high signal-to-noise ratio three-dimensional imaging in accordance with the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments.
Firstly, the system is based on the principle of conventional complex amplitude modulation, and in order to perform full vector modulation in the axial direction of the optical fiber emergent end with high signal-to-noise ratio, a wavefront with completely controllable phase, amplitude and polarization needs to be generated at the optical fiber incident end. And then adding a propagation factor to the virtual frequency domain surface of the emergent end for axial modulation. The process is subdivided into a full vector transmission matrix measurement link for generating a required light spot, and a scanning reconstruction imaging link for calculating a hologram required by axial modulation and a sample by the light spot, which comprises the following steps:
(1) Matrix measurement link: a pair of orthogonal complex amplitude wavefronts are generated and combined. The polarization distribution is adjusted at the pixel level by correcting the corresponding phase of the coincident light fields. And changing the phase, amplitude and polarization to generate a group of measurement basis vectors, and entering the optical fiber, and reconstructing a full vector transmission matrix through the complex amplitude and polarization of the emergent light spots.
(2) Hologram calculation step: and adding propagation factors into the virtual frequency plane of the optical fiber emergent end to obtain transmission matrixes at different axial positions. And returning the three-dimensional focusing light spots required to be output through a regularized transmission matrix to obtain corresponding incident complex amplitude and polarization, and then calculating and decomposing the corresponding incident complex amplitude and polarization to holograms with two polarizations.
(3) Imaging: the full vector adjustment is realized by loading the corresponding phase modulation and the polarization module through the spatial light modulator, the reflected light or fluorescence of the excitation light spot excitation sample is synchronously collected, and the purpose of high signal-to-noise ratio and high resolution three-dimensional imaging is achieved by reconstructing according to a preset scanning sequence.
The specific equipment is as shown in fig. 1:
the optical fiber comprises a laser 1, a first optical fiber 2, a second optical fiber 3, a collimating lens 4, a first quarter wave plate 5, a spatial light modulator 6, a first lens 7, a second lens 8, a polarization beam splitter 9, a second quarter wave plate 10, a first reflecting mirror 11, a third quarter wave plate 12, a second reflecting mirror 13, a beam splitter 14, an objective lens 15, a multimode optical fiber 16, a polarization microscope 17, a server 19, a third lens 20 and a photodetector 21, which are arranged along the optical path direction.
In this embodiment, in the matrix measurement procedure:
(1) First, an incident light of an arbitrary wavefront needs to be generated, and the laser 1 emits object light and reference light. One path of object light is transmitted through the first optical fiber 2, collimated and expanded by the collimating lens 4, modulated into circularly polarized light by the first quarter wave plate 5, and then enters the spatial light modulator 6 for phase and complex amplitude modulation, and the modulated light is reduced in beam diameter by the first lens 7 and the second lens 8 and split by the polarization beam splitter 9. Wherein the S light is reflected back through the second quarter wave plate 10 and the first reflecting mirror 11, and the P light is reflected through the third quarter wave plate 12 and the second reflecting mirror 13 and combined with the S light. Wherein the first mirror 11 and the second mirror 13 are used for adjusting angles to ensure that the 1 st diffraction order of S light coincides with the-1 diffraction order of P light (as shown in fig. 2), and the combined light is coupled to the multimode optical fiber 16 via the objective lens 15. The relative phase of the two coincident diffraction orders incident to the multimode optical fiber 16 can be adjusted to achieve arbitrary control of phase, amplitude, polarization.
(2) A set of orthogonal polarization, phase, amplitude measurement basis vectors is generated for incidence on the multimode optical fiber 16. The polarizing microscope 17 digitally records the outgoing light spot with the reference light. The polarization microscope is turned to the orthogonal polarization direction, and the process (2) is repeated.
Through the process, a corresponding relation is established between complex amplitudes corresponding to the incident basic vector and the emergent interference pattern, and a full vector transmission matrix is obtained:
in this specific embodiment, the hologram calculation procedure: to eliminate mode coupling and mode loss along the length of the fiber, the transmission matrix is regularized and then multiplied by a vector representing the superposition of the desired output modes and a propagation factor H to obtain a corresponding dual-polarization mode coefficient vectorThe vector must be transmitted over the spatial light modulator to produce the desired output (as shown in fig. 3).
In this embodiment, the imaging procedure is as follows: as shown in fig. 1, the module shown in dashed black lines may be removed and then a sample 18 placed at the exit end of the multimode optical fiber 16. And the optical fiber emergent end face realizes random access point scanning in a three-dimensional space through the calculated hologram. The reflected light or stimulated fluorescence emitted from the scanned sample 18 is collected by the multimode optical fiber 16, passes through the objective lens 15 and the third lens 20, and is collected by the photodetector 21. The photodetector 21 converts the light intensity information into a voltage signal to be transmitted to the server 19, and reconstructs a high signal-to-noise ratio three-dimensional image (as shown in fig. 4) through a preset scanning path.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.

Claims (9)

1. A single-fiber high signal-to-noise ratio three-dimensional imaging method of full vector modulation comprises the following steps:
s1: performing full vector transmission matrix measurement on the multimode optical fiber;
s2: the full vector transmission matrix value is processed to compensate mode coupling, mode loss and polarization dispersion in the long-distance large-curvature multimode fiber;
s3: axial scanning is realized by adding a propagation factor in a virtual frequency domain of an emergent end of the multimode optical fiber, and a three-dimensional image with high signal to noise ratio is finally reconstructed;
the device for realizing the steps comprises a laser, a spatial light modulator, a polarization modulation module, a multimode optical fiber, a polarization microscopic module and a server which are sequentially arranged along the direction of a light path, wherein a calibration module is arranged between the laser and the spatial light modulator, the laser is connected with the calibration module through a first optical fiber, a beam splitter and an objective lens are arranged between the polarization modulation module and the multimode optical fiber, one side of the beam splitter is provided with a collecting module, and the collecting module is electrically connected with the server.
2. The full-vector modulated single-fiber high signal-to-noise ratio three-dimensional imaging method according to claim 1, wherein the method comprises the following steps of: the step S1 is to measure the corresponding conversion relation of the phase, polarization and amplitude of the incident light and the emergent light of the multimode fiber by utilizing a wavefront modulation and holographic interferometry.
3. The full-vector modulated single-fiber high signal-to-noise ratio three-dimensional imaging method according to claim 1, wherein the method comprises the following steps of: step S2 is to realize redistribution of mode energy through regularization and various optimization algorithms according to the full vector transmission matrix value, reduce the influence of loss, and decompose the incident mode corresponding to the emergent mode onto incident wave fronts with different polarizations.
4. The full-vector modulated single-fiber high signal-to-noise ratio three-dimensional imaging method according to claim 1, wherein the method comprises the following steps of: the step S3 is to construct the frequency distribution corresponding to the emergent light by using the complete property value of the full vector transmission matrix to realize the reconstruction of the virtual frequency domain.
5. The full-vector modulated single-fiber high signal-to-noise ratio three-dimensional imaging method according to claim 1, wherein the method comprises the following steps of: the calibration module comprises a collimating mirror and a first quarter wave plate, wherein the collimating mirror is connected with the first optical fiber, and the first quarter wave plate is connected with the spatial light modulator.
6. The full-vector modulated single-fiber high signal-to-noise ratio three-dimensional imaging method according to claim 1, wherein the method comprises the following steps of: and a beam shrinking module is further arranged between the spatial light modulator and the polarization modulation module, the beam shrinking module comprises a first lens and a second lens, and the first lens and the second lens shrink light from the spatial light modulator and transmit the light to the polarization modulation module.
7. The full-vector modulated single-fiber high signal-to-noise ratio three-dimensional imaging method according to claim 1, wherein the method comprises the following steps of: the polarization modulation module comprises a polarization beam splitter, wherein a second quarter wave plate and a first reflecting mirror are arranged in the S light direction of the polarization beam splitter, and a third quarter wave plate and a second reflecting mirror are arranged in the P light direction of the polarization beam splitter.
8. The full vector modulated single fiber high signal to noise ratio three dimensional imaging method of claim 5, wherein: the polarization microscope module comprises a sample and a polarization microscope, the polarization microscope is connected with the second optical fiber and the server, the collecting module comprises a third lens and a photoelectric detector, and the photoelectric detector is electrically connected with the server.
9. The full-vector modulated single-fiber high signal-to-noise ratio three-dimensional imaging method according to claim 1, wherein the method comprises the following steps of: the multimode optical fiber comprises any refractive index distribution optical fiber; the spatial light modulator is used for controlling the phase and amplitude of incident light and comprises a digital micro mirror array, a liquid crystal spatial light modulator and a deformable mirror; the polarization modulation module realizes the polarization regulation and control of the pixel level by overlapping two holograms with orthogonal polarization and changing relative phase distribution.
CN202210130711.5A 2022-02-12 2022-02-12 Full-vector modulation single-fiber high-signal-to-noise-ratio three-dimensional imaging method and device Active CN114488513B (en)

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