Mach-Zehnder type optical path phase shift digital holographic microscopic imaging system based on optical fiber

Abstract

The invention discloses a Mach-Zehnder type optical path phase-shift digital holographic microscopic imaging system based on optical fibers, relates to the technical field of digital holography, and solves the problems that an existing phase-shift digital holographic microscopic imaging system is small in application range and is difficult to completely eliminate the influence of a phase-shift error on a reproduced image. Comprising an optical fiber coupling laser, an optical fiber polarization beam splitter, a first optical fiber collimator, a second optical fiber collimator (lens type or reflection type collimator), a beam combining prism, a quarter-wave plate, a polarization imaging camera and a reflector. The optical fiber polarization beam splitter can split light beams into S polarized light and P polarized light, the beam combining prism can combine light beams which are reflected by the first optical fiber collimator and collimated by the second optical fiber collimator, and the first optical fiber collimator, the beam splitting prism, the quarter-wave plate and the polarization imaging camera are sequentially arranged. Miniaturized, high-robustness and high-precision real-time measurement is realized.

Description

Technical Field

[0001] The invention relates to the technical field of digital holography, and in particular to an optical fiber-based Mach-Zehnder optical path phase-shift digital holographic microscopic imaging system. Background Art

[0002] With the rapid development of optical instruments, the demand for miniaturization and dynamic measurement of optical instruments is getting higher and higher. Digital holography refers to the technology of obtaining and processing interference patterns through CCD and CMOS cameras, and using computers to process digital interference patterns to achieve image drawing or target reconstruction. Digital holography technology can measure optical phase information and reconstruct the three-dimensional surface or depth image of the target. Based on digital holography, a variety of accurate measurement methods based on amplitude, phase, and polarization optical properties have been developed. Digital holography has become an important non-contact three-dimensional measurement and display technology;

[0003] Existing digital holographic devices are usually based on volume optical elements, using spatial filters to filter light beams and changing the trajectory of light beams through reflectors, beam splitters, etc. This design not only increases the weight of the system, but also increases the volume of the system, limiting the application of digital holography in various aspects.

[0004] Digital holography usually uses a coaxial method to measure holograms, but the coaxial method will be interfered by factors such as DC components and twin images. In order to achieve accurate measurement, phase shift technology is often used. Phase shift technology is usually divided into time phase shift or time domain phase shift, that is, changing the phase of the reference light in the time or space dimension and recording the corresponding hologram, that is, recording multiple phase shift interference patterns at different times;

[0005] The optical path structure of the traditional phase-shift digital holographic imaging system can be found in Figure 1 , where L1, L2 and L3 all represent lenses, PH represents aperture stop, BS1, BS2 and BS3 all represent beam splitters, M1 and M2 all represent reflectors, MO represents microscope objective, and Sample represents sample;

[0006] Traditional distributed phase shift mainly includes three commonly used phase shift methods: piezoelectric ceramic drive method, polarization phase shift method and grating phase shift method. Their structures are relatively simple, but they are only applicable to static or slow-changing processes and cannot achieve dynamic measurement. Since the more phase shift operations are performed, the greater the error may be. In the process of introducing the reference light into the phase shift amount of the distributed phase shift method, it is often difficult to match the recorded light beam phase change value with the theoretical design value due to objective factors such as the inaccuracy of the actual phase shift device, experimental operation errors, and vibration of the experimental table. To address this type of problem, most literatures propose an average method of repeated phase shifting and repeated recording, or find an algorithm that is less sensitive to phase shift errors or can compensate for phase shift errors to eliminate phase shift deviations. However, these methods have relatively large computational complexity and a small scope of application, and it is difficult to completely eliminate the influence of phase shift errors on the reproduced image. Summary of the invention

[0007] In order to solve the problems of large relative calculation amount, small application scope and difficulty in completely eliminating the influence of phase shift error on reproduced image in existing phase-shift digital holographic imaging systems, the present invention provides a parallel phase-shift digital holographic microscopic imaging system interconnected by optical fibers.

[0008] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0009] The invention discloses a Mach-Zehnder optical path phase-shift digital holographic microscopy imaging system based on optical fiber, which is characterized by: an optical fiber coupled laser, an optical fiber polarization beam splitter, a first optical fiber collimator, a second optical fiber collimator, a beam combining prism, a quarter wave plate, a polarization imaging camera and a reflector. The optical fiber polarization beam splitter can split a light beam into S-polarized light and P-polarized light. The beam combining prism can combine the light beam collimated by the first optical fiber collimator and the second optical fiber collimator reflected by the reflector. The first optical fiber collimator, the beam splitting prism, the quarter wave plate and the polarization imaging camera are arranged in sequence. The invention has a wide range of applications and realizes miniaturization, high robustness and high-precision real-time measurement.

[0010] The beneficial effects of the present invention are as follows: the present invention is a fiber-based Mach-Zehnder optical path phase-shift digital holographic microscopy imaging system, which can be miniaturized and realize high robustness and high precision real-time measurement. The amount of calculation required for calculating the interference pattern obtained by the present invention to realize image drawing or target reconstruction is relatively small. The present invention is suitable for dynamic measurement in extreme environments: it can measure quickly and is insensitive to vibration. The present invention is suitable for integration in various detection equipment. The system's unique small-size optical elements and systems and simple and stable optical path structure allow it to be carried on various detection equipment to complete a variety of detection tasks. The present invention is suitable for highly difficult dynamic tests: motion and resonance detection, detection in a production environment, ultrafast process detection, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1Schematic diagram of the optical path structure of the traditional phase-shifting digital holographic imaging system.

[0012] Figure 2 The present invention is a schematic structural diagram of a Mach-Zehnder optical path phase-shifting digital holographic microscopy imaging system based on optical fiber.

[0013] Figure 3 The figure is a schematic diagram of the output light spot after the beam splitting prism combines the beams of the optical fiber interconnected parallel phase-shift digital holographic microscopic imaging system of the present invention.

[0014] Figure 4 The micro-polarization array structure schematic diagram of the polarization imaging camera of the optical fiber-based Mach-Zehnder optical path phase-shifting digital holographic microscopy imaging system of the present invention.

[0015] In the figure: 1. fiber-coupled laser, 2. fiber polarization beam splitter, 3. first fiber collimator, 4. second fiber collimator (lens-type or reflective collimator), 5. beam splitting prism, 6. quarter-wave plate, 7. polarization imaging camera, 8. reflector. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0017] A fiber-based Mach-Zehnder optical path phase-shifting digital holographic microscopy imaging system, such as Figure 2 As shown, it includes a fiber-coupled laser 1, a fiber polarization beam splitter 2, a first fiber collimator 3, a second fiber collimator 4, a beam combining prism 5, a quarter-wave plate 6, a polarization imaging camera 7 and a reflector 8.

[0018] a) The light beam emitted by the fiber-coupled laser 1 is transmitted to the fiber polarization beam splitter 2, and is divided into S polarized light and P polarized light with perpendicular polarization states by the fiber polarization beam splitter 2. The S polarized light enters the first fiber collimator 3, and is incident on the beam-combining prism 5 after being collimated by the first fiber collimator 3. The P polarized light enters the second fiber collimator 4, and is incident on the reflector 8 after being collimated by the second fiber collimator 4. The output light of the reflector 8 reaches the beam-combining prism 5. The S polarized light and the P polarized light are combined by the beam-combining prism 5 (S is transmitted and P is reflected) and are incident on the quarter-wave plate 6. After being modulated by the quarter-wave plate 6, two beams of circularly polarized light with opposite rotation directions, namely left-handed circularly polarized light and right-handed circularly polarized light, are obtained. The left-handed circularly polarized light and the right-handed circularly polarized light enter the polarization imaging camera 7 to generate interference, and the interference fringes are imaged on the target surface of the polarization imaging camera 7, and the polarization imaging camera 7 obtains an interference image.

[0019] b) The light beam emitted by the fiber-coupled laser 1 is transmitted to the fiber polarization beam splitter 2, and is divided into S polarized light and P polarized light with perpendicular polarization states by the fiber polarization beam splitter 2. The S polarized light enters the first fiber collimator 3, and is incident on the beam-combining prism 5 after being collimated by the first fiber collimator 3. The P polarized light enters the second fiber collimator 4 and is incident on the beam-combining prism 5. The S polarized light and the P polarized light are combined by the beam-combining prism 5 (S is transmitted and P is reflected) and are incident on the quarter-wave plate 6. After being modulated by the quarter-wave plate 6, two beams of circularly polarized light with opposite rotation directions, namely left-handed circularly polarized light and right-handed circularly polarized light, are obtained. The left-handed circularly polarized light and the right-handed circularly polarized light enter the polarization imaging camera 7 to generate interference, and the interference fringes are imaged on the target surface of the polarization imaging camera 7, and the polarization imaging camera 7 obtains an interference image.

[0020] The S polarized light passes through the first fiber collimator 3 and the P polarized light passes through the second fiber collimator 4 and serves as the object light and the reference light respectively. Since the polarization directions are perpendicular and no interference occurs, the S polarized light and the P polarized light are combined by the beam splitter prism 5 to obtain the light spot of the combined light. Figure 3 As shown, after the quarter wave plate 6 is modulated, the left-handed circularly polarized light and the right-handed circularly polarized light are incident on the polarization imaging camera 7 with a micro-polarization array structure, and the formed interference pattern is captured and recorded by the polarization imaging camera 7. All phase shift diagrams are obtained at the same time, that is, the polarization imaging camera 7 obtains interference diagrams with different phase shifts (also called phase shift diagrams), thereby achieving high-precision three-dimensional measurement.

[0021] The schematic diagram of the micro-polarization array structure of the polarization imaging camera 7 is as follows: Figure 4 As shown, it includes multiple 2×2 micro-polarizer units, each of which includes a 0° polarizer, a 45° polarizer, a 135° polarizer and a 90° polarizer arranged in the same plane and tightly combined. Each micro-polarizer unit includes a 0° polarizer, a 45° polarizer, a 135° polarizer and a 90° polarizer starting from the upper left corner clockwise.

[0022] The fiber-coupled laser 1 of this embodiment is produced by Haoran Optoelectronics Co., Ltd. and has a wavelength of 780nm; the fiber polarization beam splitter 2 is the PBC780-APC product of Thorlabs; the first fiber collimator 3 and the second fiber collimator 4 are both COL6-550-APC products of Shanghai Wenyi Optoelectronics Co., Ltd.; the beam-combining prism 5 is the CCM1-PBS014 product of Thorlabs; the quarter-wave plate 6 is the WPQ10ME-780 product of Thorlabs; the polarization imaging camera 7 uses the BFS-U3-51S5P product of FLIR Corporation; and the reflector 8 is the BB1-E02 product of Thorlabs.

[0023] The optical fiber-based Mach-Zehnder optical path includes an optical fiber polarization beam splitter 2, a first optical fiber collimator 3 and a second optical fiber collimator 4. The function of the optical fiber-based Mach-Zehnder optical path is to use optical fibers to complete the filtering, polarization splitting and transmission of light beams, thereby realizing the miniaturization of the system. The present invention adopts a combination of an optical fiber polarization beam splitter 2 and a parallel phase-shifted digital hologram, and cooperates with a quarter-wave plate 6 to obtain two circularly polarized lights with different rotation directions and appropriate light intensities, thereby realizing interference on a rear-end polarization imaging camera 7.

[0024] The present invention discloses a Mach-Zehnder phase-shift digital holographic microscopy imaging system based on optical fiber, which can be miniaturized and meet the requirements of high robustness and high precision real-time measurement. The amount of calculation required for calculating the interference pattern obtained by the polarization imaging camera 7 of the present invention to achieve image rendering or target reconstruction is relatively small. The present invention is suitable for dynamic measurement in extreme environments: it can measure quickly and is insensitive to vibration; the present invention is suitable for integration in various detection equipment. The system's unique small-size optical elements and systems and simple and stable optical path structure allow it to be carried on various detection equipment to complete a variety of detection tasks. The present invention is suitable for highly difficult dynamic tests, motion and resonance detection, detection in production environments, ultrafast process detection, etc.

[0025] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An optical fiber-based Mach-Zehnder optical path phase-shift digital holographic microscopy imaging system, comprising an optical fiber-coupled laser (1), an optical fiber polarization beam splitter (2), a first optical fiber collimator (3), a second optical fiber collimator (4), a beam combining prism (5), a quarter-wave plate (6), a polarization imaging camera (7) and a reflector (8), characterized in that: The optical fiber polarization beam splitter (2) is capable of splitting a light beam into S-polarized light and P-polarized light, the beam combining prism (5) is capable of combining the light beams collimated by the first optical fiber collimator (3) and the second optical fiber collimator (4), and the first optical fiber collimator (3), the beam combining prism (5), the quarter wave plate (6) and the polarization imaging camera (7) are arranged in sequence.

2. The optical fiber-based Mach-Zehnder optical path phase-shifting digital holographic microscopy imaging system according to claim 1, characterized in that: The light beam emitted by the fiber-coupled laser (1) is split into S-polarized light and P-polarized light by the fiber polarization beam splitter (2); the S-polarized light is collimated by the first fiber collimator (3) and then incident on the beam-combining prism (5); the P-polarized light is collimated by the second fiber collimator (4) and then incident on the beam-combining prism (5); the S-polarized light and the P-polarized light are combined by the beam-combining prism (5) and then incident on the quarter-wave plate (6); two beams of circularly polarized light with opposite rotation directions are modulated by the quarter-wave plate (6); the two beams of circularly polarized light with opposite rotation directions enter the polarization imaging camera (7) to generate interference, and interference fringes are imaged on a target surface of the polarization imaging camera (7).

3. The optical fiber-based Mach-Zehnder optical path phase-shifting digital holographic microscopy imaging system according to claim 1, characterized in that: The P polarized light of the optical fiber polarization beam splitter (2) can be collimated and rotated 90° through a lens-type collimator and the reflector (8) to collimate the light path, or collimate and rotate the light path 90° through a reflective collimator.

4. The optical fiber-based Mach-Zehnder optical path phase-shifting digital holographic microscopy imaging system according to claim 1, characterized in that: The polarization imaging camera (7) has a micro-polarization array structure.

5. The optical fiber-based Mach-Zehnder optical path phase-shifting digital holographic microscopy imaging system according to claim 4, characterized in that: The micro-polarization array structure comprises a plurality of micro-polarizer units of a size of 2×2, and each micro-polarizer unit comprises a 0° polarizer, a 45° polarizer, a 135° polarizer and a 90° polarizer which are arranged in the same plane and closely combined.

6. The optical fiber-based Mach-Zehnder optical path phase-shifting digital holographic microscopy imaging system according to claim 5, characterized in that: Each of the micro polarizer units includes a 0° polarizer, a 45° polarizer, a 135° polarizer, and a 90° polarizer, starting from the upper left corner clockwise.

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