Double-view-field off-axis digital holographic measurement device and system and phase measurement method

Abstract

The invention relates to the technical field of off-axis digital holography, and discloses a double-view-field off-axis digital holography measuring device and system and a phase recovery method. The first beam splitter is used for splitting a light beam into object light and reference light, an object to be measured, a collimation system and a sampling optical system are sequentially arranged in the direction of the object light, and the sampling optical system is used for splitting the light beam emitted by the collimation system into first sampling channel object light and second sampling channel object light; the reflecting mirror is arranged along the direction of the reference light; and the second beam splitter and the CCD camera are used for generating an interference pattern from the reference light, the first sampling channel object light and the second sampling channel object light. According to the invention, a plurality of optical devices with reflection performance are not needed, accurate control of an off-axis angle and collection of a double view field are realized only through the micro-mirror angle of the digital micro-mirror device in the electrically-controlled 4f optical system, the complexity of the system is reduced, and integration is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of off-axis digital holography, and in particular to a dual-field-of-view off-axis digital holography measurement device, system and phase measurement method. Background Art

[0002] Digital holography is widely used in the fields of micro-nano device detection, biological cell detection, etc. due to its advantages of non-destructive, non-contact, and fast measurement. According to whether there is an angle between the object light and the reference light, digital holography is divided into on-axis digital holography and off-axis digital holography. Different from on-axis digital holography, off-axis digital holography has attracted the attention of many scholars due to its low reconstruction complexity.

[0003] One of the existing technologies is a two-step phase-shift diffraction interferometry device based on a cubic beam splitter. The device splits the object light into two through a 45° inclined cubic beam splitter: one beam of light is filtered by a pinhole on its Fourier plane as a reference light, and the other beam of light remains unchanged and is still the object light. The second cubic beam splitter is used to separate the object light and the reference light into two different channels, and two parallel phase-shift interference patterns are obtained with the help of a polarization element. The device improves the bandwidth utilization of the off-axis digital holographic device, but the field of view becomes 1 / 2 of the original field of view, and the device complexity is relatively high.

[0004] Another prior art proposes a multiple imaging area interferometry device, which can collect multiple times of quantitative information in a single camera exposure when using off-axis interferometric imaging, and multiplex multiple off-axis interferograms on a single camera sensor, without changing the imaging characteristics of the system, and without losing time resolution and spatial resolution. However, the use of pinhole point diffraction to generate reference light leads to the loss of object morphology information, and the integrity of object information cannot be guaranteed.

[0005] It can be seen that the existing off-axis digital holography technology is limited by the size of the CCD target surface, resulting in a small amount of information flux acquired in a single time and low bandwidth utilization. Summary of the invention

[0006] The purpose of the present invention is to provide a dual-field-of-view off-axis digital holographic measurement device, system and phase measurement method, which can solve at least one of the above-mentioned technical problems. The specific solution is as follows:

[0007] According to the specific embodiments disclosed in the present invention, the first aspect of the present invention discloses a dual-field off-axis digital

[0008] The holographic measuring device comprises: arranged in sequence along the propagation direction of the light beam,

[0009] light source;

[0010] A beam shaping system for improving the quality of the beam emitted by the light source;

[0011] A first beam splitter is used to split the light beam into an object light and a reference light, so as to form an object light path and a reference light path;

[0012] The object light path includes: an object to be measured, a collimation system and a sampling optical system, wherein the sampling optical system is used to divide the light beam emitted from the collimation system into: a first sampling channel object light and a second sampling channel object light, wherein the transmission directions of the first sampling channel object light and the second sampling channel object light are the same and are both perpendicular to the direction of the light beam emitted from the collimation system;

[0013] The reference light path comprises: a reflector, wherein the reflector is arranged on a conjugate back focal plane of the beam shaping system;

[0014] a second beam splitter, on which the object light, the object light of the first sampling channel and the object light of the second sampling channel are combined;

[0015] The combined light beams interfere with each other on the CCD camera to form an interference pattern.

[0016] Preferably, the beam shaping system comprises:

[0017] A first microscope objective lens, used for focusing the light beam;

[0018] A pinhole is arranged at the focus of the first microscope objective lens to increase the quality of the light beam.

[0019] The first collimating lens converts the focused light beam into parallel light.

[0020] Preferably, the collimation system comprises:

[0021] The second microscope objective lens and the second collimating lens are used to expand and collimate the object light after passing through the object to be measured.

[0022] Preferably, the sampling optical system comprises: a first Fourier lens, a second Fourier lens and a digital micromirror device;

[0023] The first Fourier lens and the second Fourier lens constitute a 4f optical system;

[0024] The digital micromirror device is arranged at the Fourier focal plane of the 4f optical system;

[0025] By adjusting the micromirror angle of the digital micromirror device, independent object light of the first sampling channel and object light of the second sampling channel are formed.

[0026] Preferably, the clear aperture of the pinhole is the same as the diameter of the Airy disk generated by the wavelength of the light source on the Fourier plane.

[0027] Preferably, it also includes: an attenuator;

[0028] The attenuator is arranged between the second beam splitter and the CCD camera, and is used for adjusting the light intensity.

[0029] Preferably, the first beam splitter and the second beam splitter are cubic beam splitters.

[0030] Preferably, the attenuator is a polarizer.

[0031] According to the specific embodiment disclosed in the present invention, the second aspect of the present invention discloses a dual-viewing field off-axis digital holographic measurement system, comprising: the above-mentioned dual-viewing field off-axis digital holographic measurement device and a computer

[0032] According to the specific implementation mode disclosed in the present invention, the third aspect of the present invention discloses a dual-field-of-view off-axis digital holographic phase measurement method, comprising:

[0033] An off-axis digital hologram measured by the above dual-field-of-view off-axis digital holography measurement system;

[0034] Calculating the complex amplitude distribution of the object to be measured according to the off-axis digital hologram;

[0035] The phase information of the object to be measured is calculated according to the complex amplitude distribution using a complex amplitude division algorithm.

[0036] Compared with the prior art, the above solution of the embodiment disclosed in the present invention has at least the following beneficial effects:

[0037] The present invention does not require multiple optical devices with reflective properties. The precise control of off-axis angles and the acquisition of double fields of view can be achieved only by electrically controlling the micromirror angles of the digital micromirror device in the 4f optical system, thereby reducing the use of devices with reflective properties, reducing the complexity of the system, and facilitating integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the disclosure of the present invention, and together with the specification, are used to explain the principles disclosed in the present invention. Obviously, the drawings described below are only some embodiments disclosed in the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0039] Figure 1 A schematic structural diagram of a dual-field-of-view off-axis digital holographic measurement system provided in an embodiment of the present invention.

[0040] Reference numerals:

[0041] 1. Light source; 2. Beam shaping system; 21. First microscope objective lens; 22. Pinhole; 23. First collimating lens;

[0042] 3. first beam splitter; 4. object to be measured; 5. collimation system; 51 second microscope objective lens; 52 second collimating lens;

[0043] 6. Sampling system; 61. First Fourier lens; 62. Digital micromirror device; 63. Second Fourier lens;

[0044] 7. Reflector; 8. Second beam splitter; 9. CCD camera; 10. Attenuator. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages disclosed in the present invention clearer, the following will further describe in detail an off-axis digital holographic imaging optical system, a measuring device and a phase recovery method disclosed in the present invention in conjunction with the accompanying drawings.

[0046] It is obvious that the described embodiments are only part of the embodiments disclosed in the present invention, rather than all the embodiments. Based on the embodiments disclosed in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection disclosed in the present invention.

[0047] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such product or device. In the absence of more restrictions, the elements defined by the sentence "comprises a" do not exclude the presence of other identical elements in the product or device including the elements.

[0048] The following is combined with Figure 1 Alternative embodiments of the present invention are described in detail.

[0049] Example 1

[0050] In the data acquisition process of off-axis digital holography, since the CCD target surface area is fixed and there are problems of partial optical path overlap and insufficient splitting efficiency during the imaging process, the field of view cannot be fully covered and utilized, resulting in a reduction in the imaging area. Therefore, the information flux obtained by the off-axis digital holographic device at a time is limited, making it impossible to collect all the information of the sample in a single time. The method of multiple movement or splicing increases the difficulty of operation and time cost. In addition, the existing off-axis digital holographic device has a high structural complexity, which is not conducive to the integration of the off-axis digital holographic system.

[0051] Therefore, the first embodiment of the present invention provides a dual-field off-axis digital holographic measurement device, such as Figure 1 As shown, it includes: arranged in sequence along the propagation direction of the light beam,

[0052] Light source 1;

[0053] A beam shaping system 2, used to improve the quality of the beam emitted by the light source 1;

[0054] A first beam splitter 3, used for dividing the light beam into an object light and a reference light, forming an object light path and a reference light path;

[0055] The object light path includes: an object to be measured 4, a collimation system 5 and a sampling optical system 6, wherein the sampling optical system 6 is used to divide the light beam emitted from the collimation system 5 into: a first sampling channel object light and a second sampling channel object light, wherein the propagation directions of the first sampling channel object light and the second sampling channel object light are the same and are both perpendicular to the direction of the light beam emitted from the collimation system 5;

[0056] The reference light path comprises: a reflector 7, which is arranged on a conjugate back focal plane of the beam shaping system;

[0057] A second beam splitter 8, on which the object light, the first sampling channel object light and the second sampling channel object light are combined;

[0058] CCD camera 9, on which the combined light beams interfere to form an interference pattern.

[0059] The present invention utilizes the high-precision beam control characteristics of digital micromirror devices to achieve off-axis dual-field holographic multiplexing imaging. This embodiment uses digital micromirror devices as the core optical path distribution element, and the rotation of the micromirror can flexibly control the beam control characteristics of the digital micromirror device.

[0060] The angle of the reflected light beam can be flexibly controlled to construct two independent off-axis fields of view. Each field of view obtains a holographic interference pattern at a specific angle, which can simultaneously capture different side information of the sample to be tested, and generate richer three-dimensional structural information during the reconstruction process.

[0061] In a preferred embodiment of the present invention, a beam shaping system 2 is used to improve the beam quality. Specifically, the beam shaping system 2 includes: a first microscope objective lens 21, a pinhole 22, and a first collimating lens 23, which are arranged in sequence along the optical axis. The light beam emitted by the light source is first focused by the first microscope objective lens 21, passes through the pinhole 22 arranged at the focus, and is collimated by the first collimating lens 23, so that the focused light beam becomes parallel light.

[0062] Among them, focusing with a microscope objective lens can avoid introducing phase difference; the aperture D of the pinhole 22 is the same as the diameter d of the Airy disk generated by the wavelength of the light source 1 on the Fourier plane, that is, d<1.22λf1 / D; f1 is the focal length of the first microscope objective lens 21. By introducing the pinhole 22, high-order distortion and noise can be filtered out, and only the fundamental mode part of the light spot is retained, thereby improving the beam quality, which is conducive to subsequent high-quality phase recovery of the object to be measured.

[0063] Furthermore, the shaped light beam is split into two after passing through the first beam splitter 3, and one beam does not carry the information of the object to be measured, passes through the reflector 7 placed at an angle of 45°, and then enters the second beam splitter 8 as a reference light. The reflector 7 is arranged on the conjugate back focal plane of the first collimating lens 23.

[0064] The other light beam continues to propagate in a straight line, passes through the object 4 to carry the object information and becomes object light, and then enters the sampling optical system 6 after being expanded and collimated by the collimation system 5 composed of the second microscope objective lens 51 and the second collimating lens 52 .

[0065] In a preferred embodiment of the present invention, the sampling optical system 6 comprises: a first Fourier lens 61, a second Fourier lens 63 and a digital micromirror device 62. The first Fourier lens 61 is located at a focal length away from the image plane of the collimating system 5, and the first Fourier lens 61 and the second Fourier lens 63 constitute a 4f optical system; the digital micromirror device 62 is arranged at the Fourier focal plane of the 4f optical system.

[0066] In the sampling optical system 6, the light beam emitted from the second collimating lens 52 is Fourier transformed by the first Fourier lens 61 to form a spectrum surface. After the light beam is optically Fourier transformed by the first Fourier lens 61, it is incident on the digital micromirror device 62. The angle of each micromirror is adjusted by the circuit control system to divide it into two independent sampling channel object lights, namely the first sampling channel object light and the second sampling channel object light. The two object lights are then optically Fourier inverse transformed by the second Fourier lens 63 and incident on the second beam splitter 8 to obtain a clear image.

[0067] In this embodiment, the reflected incident light is formed into multiple diffracted light beams by precisely controlling the micromirror array on the digital micromirror device. Each micromirror can be tilted independently to control the direction of the reflected light. The digital micromirror device achieves the generation of two or more diffracted light beams by fast tilt control of the micromirrors, and the process is as follows:

[0068] 1. Micromirror array structure: Each micromirror can be tilted in two directions (e.g. ±10° or ±12°) under voltage drive. The two tilt states of each micromirror correspond to different paths of the reflected light beam.

[0069] The incident light beam is projected onto the micromirror at a certain angle. By precisely controlling the tilt angle of the micromirror, diffracted light beams in different directions can be reflected;

[0070] 2. By controlling the switching frequency and tilt angle of the micromirror array, the digital micromirror device can accurately control the diffraction angle of the reflected light beam and generate diffraction beams of different orders. For example, a micromirror array arranged at a specific angle can form a ±1-order diffraction beam, which is suitable for applications such as spectral separation and phase modulation.

[0071] Therefore, the present invention guides the light beam to different optical channels at different angles through a digital micromirror device, thereby realizing multi-channel analysis and processing of the optical signal.

[0072] In a preferred embodiment of the present invention, an attenuator 10 is placed in front of the CCD camera 9 to adjust the light intensity, preferably a polarizer. At this time, the reference light, the object light of the first sampling channel and the object light of the second sampling channel are incident on the polarizer at the same imaging surface after passing through the second beam splitter 8 to adjust the light intensity, and interference occurs on the sensor target surface of the CCD camera 9 to form an interference pattern and is recorded by the CCD camera.

[0073] Preferably, the first beam splitter 3 and the second beam splitter 8 are cubic beam splitters.

[0074] In summary, the off-axis digital holographic imaging optical system of the present invention can achieve precise control of off-axis angles and acquisition of double fields of view only through digital micromirror devices, without the need for multiple optical devices with reflective properties, with low system complexity and easy integration. Two different channels are generated and precisely regulated by the micromirror angle of the electrically controlled digital micromirror device, and then interfere with the reference light on the target surface of the CCD camera respectively, which has the advantage of double fields of view, reduces the use of devices with reflective properties, and reduces the complexity of the system.

[0075] The off-axis digital holographic imaging optical system of the present invention has no sparseness requirements for the production of the measured sample, has a high light energy utilization rate, and while ensuring the utilization rate of the entire field of view, multiplexes two interference channels on a single CCD camera sensor through an off-axis multiplexing system, effectively utilizes the bandwidth of the interference pattern, and achieves higher bandwidth utilization on the same detector. In addition, without affecting the spatial bandwidth and the acquisition rate, non-scanning quantitative optical imaging is achieved, and the measurement accuracy is high, the stability is high, the structure is compact, and the repeatability is good.

[0076] The second embodiment of the present invention provides a system embodiment that is consistent with the above embodiment. The explanation based on the same name meaning is the same as that of the above embodiment, and has the same technical effect as the above embodiment, which will not be repeated here.

[0077] The invention discloses a dual-viewing-field off-axis digital holographic measurement system, comprising: a dual-viewing-field off-axis digital holographic measurement device and a computer for processing interference patterns.

[0078] In this embodiment, the interference pattern recorded by the CCD camera is uploaded to a computer, and the phase recovery of the sample to be tested can be completed using a phase recovery algorithm based on Fourier transform.

[0079] The dual-field-of-view off-axis digital holographic measurement system of the present invention uses a digital micromirror device in a dual-field-of-view off-axis digital holographic measurement device to distribute the light beam to two independent optical paths according to a preset field-of-view angle. In each optical path, the object light and the reference light reflected by the sample interfere with each other, and these interference images are recorded by a high-resolution imaging system to form holographic images of the two fields of view respectively. The acquisition of this multi-field-of-view information greatly improves the integrity of the sample surface information and the accuracy of depth measurement. Compared with the traditional single-field-of-view off-axis holographic imaging device, it not only solves the problem of low field-of-view utilization, but also improves the utilization of spatial bandwidth. By quickly switching different micromirror angles and flexibly adjusting the optical path, the optimal bandwidth allocation can be achieved, thereby effectively avoiding the limitation of zero-order noise interference in traditional off-axis holographic images and improving the spatial resolution of imaging.

[0080] A third embodiment of the present invention provides a method for phase measurement using the above dual-field-of-view off-axis digital holographic measurement system, comprising:

[0081] Step S1, obtaining an off-axis digital hologram through a dual-field-of-view off-axis digital holographic measurement system;

[0082] Step S2, calculating the complex amplitude distribution of the object to be measured according to the off-axis digital hologram;

[0083] Step S3: Calculate the phase information of the object to be measured by using a complex amplitude division algorithm according to the complex amplitude distribution.

[0084] Specifically, in step S2, the interference pattern captured by the CCD camera sensor is subjected to a two-dimensional Fourier transform to obtain its spectrum, the +1-level spectrum is selected through a filter for centering, and then a two-dimensional inverse Fourier transform is performed on it to obtain a complex amplitude image, and the complex amplitude distribution of the object to be measured is calculated to obtain:

[0085] c(x,y)=IFT{C{FT[I(x,y)]·F}};

[0086] Among them, F represents a filter, FT represents a two-dimensional Fourier transform, IFT represents an inverse two-dimensional Fourier transform, and C represents a spectrum centering operation.

[0087] In step S3, the phase information of the object to be measured is calculated according to the complex amplitude division algorithm:

[0088]

[0089] Among them, I m Represents the imaginary part of a complex number, R e Represents the real part of a complex number.

[0090] The method of this embodiment avoids the problem of more spectrum information loss and low spectrum utilization due to interference from the zero-order image during off-axis digital holographic reconstruction.

[0091] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the system or device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0092] The above embodiments are only used to illustrate the technical solutions disclosed in the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments disclosed in the present invention.

Claims

1. A dual-field-of-view off-axis digital holographic measurement device, characterized in that: include: Set in sequence along the beam propagation direction, light source; A beam shaping system for improving the quality of the beam emitted by the light source; A first beam splitter is used to split the light beam into an object light and a reference light, so as to form an object light path and a reference light path; The object light path includes: an object to be measured, a collimation system and a sampling optical system, wherein the sampling optical system is used to divide the light beam emitted from the collimation system into: a first sampling channel object light and a second sampling channel object light, wherein the transmission directions of the first sampling channel object light and the second sampling channel object light are the same and are both perpendicular to the direction of the light beam emitted from the collimation system; The reference light path comprises: a reflector, wherein the reflector is arranged on a conjugate back focal plane of the beam shaping system; a second beam splitter, on which the object light, the object light of the first sampling channel and the object light of the second sampling channel are combined; The combined light beams interfere with each other on the CCD camera to form an interference pattern.

2. The device according to claim 1, characterized in that The beam shaping system comprises: A first microscope objective lens, used for focusing the light beam; A pinhole, disposed at the focus of the first microscope objective lens, to increase the quality of the light beam; The first collimating lens converts the focused light beam into parallel light.

3. The device according to claim 1, characterized in that The collimation system comprises: The second microscope objective lens and the second collimating lens are used to expand and collimate the object light after passing through the object to be measured.

4. The device according to claim 1, characterized in that The sampling optical system comprises: a first Fourier lens, a second Fourier lens and a digital micromirror device; The first Fourier lens and the second Fourier lens constitute a 4f optical system; The digital micromirror device is arranged at the Fourier focal plane of the 4f optical system; By adjusting the micromirror angle of the digital micromirror device, independent object light of the first sampling channel and object light of the second sampling channel are formed.

5. The device according to claim 2, characterized in that The clear aperture of the pinhole is the same as the diameter of the Airy disk generated by the wavelength of the light source on the Fourier plane.

6. The device according to claim 1, characterized in that Also includes: Attenuator; The attenuator is arranged between the second beam splitter and the CCD camera, and is used for adjusting the light intensity.

7. The device according to claim 1, characterized in that The first beam splitter and the second beam splitter are: cube beam splitters.

8. The device according to claim 6, characterized in that The attenuator is a polarizing plate.

9. A dual-field-of-view off-axis digital holographic imaging measurement system, characterized in that: include: A dual-field-of-view off-axis digital holographic measurement device and a computer as described in any one of claims 1 to 9.

10. A dual-field-of-view off-axis digital holographic phase measurement method, characterized in that: include: Obtaining an off-axis digital hologram by the dual-field-of-view off-axis digital holographic measurement system as claimed in claim 9; Calculating the complex amplitude distribution of the object to be measured according to the off-axis digital hologram; The phase information of the object to be measured is calculated according to the complex amplitude distribution using a complex amplitude division algorithm.

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