A dual view off-axis digital holographic measuring device, system and phase measurement method

Abstract

The application relates to the technical field of off-axis digital holography, and discloses a double-view-field off-axis digital holographic measuring device, a system and a phase recovery method, wherein an optical system comprises, in sequence along the propagation direction of a light beam, a light source, a first beam splitter for splitting the light beam into object light and reference light, a to-be-measured object, a collimating system and a sampling optical system arranged in sequence along the direction of the object light, the sampling optical system being used for splitting the light beam emitted by the collimating system into first sampling channel object light and second sampling channel object light, a mirror arranged along the direction of the reference light, a second beam splitter and a CCD camera used for generating an interference pattern of the reference light, the first sampling channel object light and the second sampling channel object light. The application realizes accurate control of an off-axis angle and acquisition of a double view field through the micro-mirror angle of a digital micromirror device in an electrically-controlled 4f optical system, reduces the complexity of the system and is convenient for integration.

Description

Technical Field

[0001] This invention relates to the field of off-axis digital holography, and more specifically, to a dual-field-of-view off-axis digital holographic measurement device, system, and phase measurement method. Background Technology

[0002] Digital holography, due to its advantages of being non-destructive, non-contact, and fast in measurement, is widely used in fields such as micro-nano device detection and biological cell detection. Based on whether there is an angle between the object beam and the reference beam, digital holography is divided into coaxial digital holography and off-axis digital holography. Unlike coaxial digital holography, off-axis digital holography has attracted much attention from scholars due to its lower reconstruction complexity.

[0003] One existing technology is a two-step phase-shifting diffraction interferometry measurement device based on a cubic beam splitter. This device splits the object beam in two using a 45° tilted cubic beam splitter: one beam is filtered by a pinhole on its Fourier plane to become the reference beam, while the other beam remains unchanged and is still the object beam. A second cubic beam splitter separates the object beam and reference beam into two different channels, and two parallel phase-shifting interferograms are obtained with the aid of polarization elements. This device improves the bandwidth utilization of off-axis digital holography, but the field of view becomes half of the original field of view, and the device complexity is relatively high.

[0004] Another existing technology proposes a multi-image region interferometry device. This device, when using off-axis interferometric imaging, can collect multiple times the quantitative information in a single camera exposure, multiple off-axis interferograms can be multiplexed on a single camera sensor, and temporal and spatial resolutions are not lost without altering the system's imaging characteristics. However, using pinhole diffraction to generate reference light leads to a loss of object morphology information, and the integrity of the object information cannot be guaranteed.

[0005] It is known that existing off-axis digital holography technology is limited by the size of the CCD target area, resulting in a small information throughput per acquisition and low bandwidth utilization. Summary of the Invention

[0006] The purpose of this 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 aforementioned technical problems. The specific solution is as follows:

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

[0008] A holographic measurement device includes: components arranged sequentially along the beam propagation direction.

[0009] light source;

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

[0011] The first beam splitter is used to split the beam into an object beam and a reference beam, forming an object beam optical path and a reference beam optical path;

[0012] The object-optical path includes: the object to be measured, a collimation system, and a sampling optical system. The sampling optical system is used to divide the light beam emitted through the collimation system into: a first sampling channel object beam and a second sampling channel object beam. The first sampling channel object beam and the second sampling channel object beam have the same transmission direction, both perpendicular to the direction of the light beam emitted by the collimation system.

[0013] The reference light path includes: a reflector, which is disposed on the conjugate back focal plane of the beam shaping system;

[0014] The object beam, the object beam from the first sampling channel, and the object beam from the second sampling channel are combined on the second beam splitter.

[0015] The combined beam of light from a CCD camera interferes with the CCD camera to form an interference pattern.

[0016] Preferably, the beam shaping system includes:

[0017] A first microscope objective is used to focus the light beam;

[0018] A pinhole is placed at the focal point of the first microscope objective to increase the quality of the light beam.

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

[0020] Preferably, the collimation system includes:

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

[0022] Preferably, the sampling optical system includes: 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 positioned at the Fourier focal plane of the 4f optical system;

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

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

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

[0028] The attenuator is positioned between the second beam splitter and the CCD camera to adjust 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 specific embodiments disclosed in this invention, a second aspect of this invention discloses a dual-field-of-view off-axis digital holographic measurement system, comprising: the aforementioned dual-field-of-view off-axis digital holographic measurement device and a computer.

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

[0033] Off-axis digital holograms measured using the aforementioned dual-field-of-view off-axis digital holographic measurement system;

[0034] The complex amplitude distribution of the object under test is calculated based on the off-axis digital hologram.

[0035] The phase information of the object under test is calculated using the complex amplitude division algorithm based on the complex amplitude distribution.

[0036] Compared with the prior art, the solutions disclosed in this invention have at least the following beneficial effects:

[0037] This invention eliminates the need for multiple reflective optical devices. It achieves precise control of the off-axis angle and double the field of view simply by controlling the micromirror angle of the digital micromirror device in the electronically controlled 4f optical system. This reduces the use of reflective devices, lowers the system complexity, and facilitates integration. Attached Figure Description

[0038] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the disclosure of this invention and, together with the description, serve to explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

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

[0040] Figure label:

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

[0042] 3. First beam splitter; 4. Object under test; 5. Collimation system; 51. Second microscope objective; 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 Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the following will describe in further detail, with reference to the accompanying drawings, an off-axis digital holographic imaging optical system, measuring device, and phase retrieval method disclosed in this invention.

[0046] The described embodiments are clearly only a part of the embodiments disclosed in this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the disclosed embodiments without inventive effort are within the scope of protection of this invention.

[0047] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the article or device that includes said element.

[0048] The following is in conjunction with the appendix Figure 1 Detailed description of optional embodiments of the present invention.

[0049] Example 1

[0050] In the data acquisition process of off-axis digital holography, the fixed CCD target area and issues such as partial optical path overlap and insufficient beam splitting efficiency during imaging prevent the field of view from being fully covered and utilized, resulting in a reduced imaging area. Therefore, the information throughput acquired by an off-axis digital holographic device in a single operation is limited, making it impossible to acquire all the information of the sample in a single session. Methods involving multiple movements or stitching increase operational difficulty and time costs. Furthermore, existing off-axis digital holographic devices have high structural complexity, hindering the integration of off-axis digital holographic systems.

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

[0052] Light source 1;

[0053] Beam shaping system 2 is used to improve the beam quality emitted by the light source 1;

[0054] The first beam splitter 3 is used to split the beam into an object beam and a reference beam, forming an object beam optical path and a reference beam optical path;

[0055] The object light path includes: the object under test 4, the collimation system 5, and the sampling optical system 6. The sampling optical system 6 is used to divide the light beam emitted through the collimation system 5 into: the object light of the first sampling channel and the object light of the second sampling channel. The propagation directions of the object light of the first sampling channel and the object light of the second sampling channel are the same and are both perpendicular to the direction of the light beam emitted by the collimation system 5.

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

[0057] The second beam splitter 8, the object beam, the object beam of the first sampling channel and the object beam of the second sampling channel are combined on the second beam splitter;

[0058] The combined beam of light from the CCD camera 9 interferes with the CCD camera to form an interference pattern.

[0059] This invention utilizes the high-precision beam control characteristics of digital micromirror devices (DMDs) to achieve off-axis dual-field-of-view holographic multiplexing imaging. This embodiment uses a DMD as the core optical path distribution element, leveraging the flexible rotation of the micromirrors...

[0060] By controlling the angle of the reflected beam, two independent off-axis fields of view are constructed. Each field of view acquires a holographic interferogram at a specific angle, enabling the simultaneous capture of information from different sides of the sample under test, resulting in richer three-dimensional structural information during reconstruction.

[0061] In a preferred embodiment of the present invention, a beam shaping system 2 is used to improve beam quality. Specifically, the beam shaping system 2 includes, in sequence along the optical axis, a first microscope objective 21, a pinhole 22, and a first collimating lens 23. The beam emitted by the light source is first focused by the first microscope objective 21, then passed through the pinhole 22 located at the focal point, and finally collimated by the first collimating lens 23, thus transforming the focused beam into parallel light.

[0062] Focusing using a microscope objective avoids introducing phase aberrations. The aperture D of pinhole 22 is the same as the diameter d of the Airy disk generated by the wavelength of light source 1 on the Fourier plane, i.e., d < 1.22λf1 / D; f1 is the focal length of the first microscope objective 21. By introducing pinhole 22, higher-order distortions and noise can be filtered out, retaining only the fundamental mode of the light spot, thereby improving beam quality and facilitating high-quality phase recovery of the object under test.

[0063] Furthermore, the shaped beam is split into two by the first beam splitter 3. One beam, without carrying information about the object under test, passes through the reflector 7, which is placed at a 45° angle, and then enters the second beam splitter 8 as a reference beam. The reflector 7 is positioned on the conjugate back focal plane of the first collimating lens 23.

[0064] Another beam of light continues to propagate in a straight line, passing through the object under test 4 and carrying the object information into object light. After being expanded and collimated by the collimation system 5 composed of the second microscope objective 51 and the second collimating lens 52, it enters the sampling optical system 6.

[0065] In a preferred embodiment of the present invention, the sampling optical system 6 includes: 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 from the image plane of the collimation 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 disposed 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 undergoes a Fourier transform via the first Fourier lens 61 to form a spectral plane. After the optical Fourier transform via the first Fourier lens 61, the light beam is incident on the digital micromirror device 62. The circuit control system adjusts the angle of each micromirror to split it into two independent sampling channel object beams, namely the first sampling channel object beam and the second sampling channel object beam. The two object beams then undergo an inverse optical Fourier transform via the second Fourier lens 63 and are incident on the second beam splitter 8 to obtain a clear image.

[0067] In this embodiment, precise control of the micromirror array on the digital micromirror device enables the reflected incident light to form multiple diffracted beams. Each micromirror can be tilted independently to control the direction of the reflected light. The digital micromirror device generates two or more diffracted beams through rapid tilt control of the micromirrors, as follows:

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

[0069] An incident light beam is projected onto a 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, digital micromirror devices can precisely control the diffraction angle of the reflected beam, generating diffracted beams of different orders. For example, a micromirror array arranged at a specific angle can form diffracted beams of ±1 orders, suitable for applications such as spectral separation and phase modulation.

[0071] Therefore, this invention uses a digital micromirror device to guide a light beam to different optical channels at different angles, thereby achieving multi-channel analysis and processing of optical signals.

[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 plane after passing through the second beam splitter 8, adjusting the light intensity. Interference occurs on the sensor target surface of the CCD camera 9, forming an interference pattern which is recorded by the CCD camera.

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

[0074] In summary, the off-axis digital holographic imaging optical system of this invention can achieve precise control of the off-axis angle and double the field of view acquisition using only digital micromirror devices, eliminating the need for multiple reflective optical components. This results in lower system complexity and easier integration. By generating and precisely controlling the micromirror angle of the electronically controlled digital micromirror device, two different channels are generated and precisely adjusted. These channels then interfere with the reference light at the CCD camera target surface, providing the advantage of a double field of view. This reduces the need for reflective components and lowers system complexity.

[0075] The off-axis digital holographic imaging optical system of the present invention does not require sparsity in the fabrication of the sample under test, has high light energy utilization, and while ensuring full field-of-view utilization, it reuses two interference channels on a single CCD camera sensor through an off-axis multiplexing system, effectively utilizing the bandwidth of the interferogram and achieving higher bandwidth utilization on the same detector. Moreover, it realizes scanning-free quantitative optical imaging without affecting spatial bandwidth and acquisition rate, and has high measurement accuracy, high stability, compact structure, and good repeatability.

[0076] The second embodiment of the present invention provides a system embodiment that follows the above embodiments. The interpretation of the same names is the same as that of the above embodiments, and it has the same technical effects as the above embodiments. It will not be repeated here.

[0077] This invention discloses a dual-field-of-view off-axis digital holographic measurement system, comprising: a dual-field-of-view off-axis digital holographic measurement device and a computer for processing interferograms.

[0078] In this embodiment, the interferogram recorded by the CCD camera is uploaded to the computer, and the phase recovery of the sample under test 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 this invention utilizes a digital micromirror device within a dual-field-of-view off-axis digital holographic measurement apparatus. This device distributes the light beam into two independent optical paths according to a preset field-of-view angle. In each optical path, the object beam reflected from the sample and the reference beam interfere with each other. These interference images are recorded by a high-resolution imaging system, forming holographic images of the two fields of view. This acquisition of multi-field-of-view information significantly improves the integrity of sample surface information and the accuracy of depth measurement. Compared to traditional single-field-of-view off-axis holographic imaging devices, it not only solves the problem of low field-of-view utilization but also improves the utilization of spatial bandwidth. By rapidly switching different micromirror angles, the optical path can be flexibly adjusted to achieve optimal bandwidth allocation, thereby effectively avoiding the limitations of zero-order noise interference in traditional off-axis holographic images and improving the spatial resolution of the imaging.

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

[0081] Step S1: Obtain an off-axis digital hologram using a dual-field-of-view off-axis digital holographic measurement system;

[0082] Step S2: Calculate the complex amplitude distribution of the object under test based on the off-axis digital hologram;

[0083] Step S3: Calculate the phase information of the object under test using the complex amplitude division algorithm based on the complex amplitude distribution.

[0084] Specifically, in step S2, the interferogram captured by the CCD camera sensor is subjected to a two-dimensional Fourier transform to obtain its spectrum. The +1 level spectrum is then selected and centered using a filter, and finally subjected to a two-dimensional inverse Fourier transform to obtain a complex amplitude image. The complex amplitude distribution of the object under test can be calculated as follows:

[0085] c(x,y)=IFT{C{FT[I(x,y)]·F}};

[0086] Where F represents the filter, FT represents the two-dimensional Fourier transform, IFT represents the inverse two-dimensional Fourier transform, and C represents the spectrum centering operation.

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

[0088]

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

[0090] The method in this embodiment avoids the problem of low spectral utilization caused by the loss of a lot of spectral information 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, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0092] The above embodiments are only used to illustrate the technical solutions disclosed in this invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments disclosed in this invention.

Claims

1. A dual view off-axis digital holographic measurement apparatus, characterized in that, Comprising: sequentially arranged in the direction of light beam propagation, a light source; a light beam shaping system for improving the quality of the light beam emitted by the light source; a first beam splitter for splitting the light beam into object light and reference light, forming an object light path and a reference light path; the object light path comprising: an object to be measured, a collimating system, and a sampling optical system, the sampling optical system for splitting the light beam emitted by the collimating system into first sampling channel object light and second sampling channel object light, the first sampling channel object light and the second sampling channel object light having the same transmission direction, both perpendicular to the direction of the light beam emitted by the collimating system; the reference light path comprising: a mirror, the mirror being arranged on the conjugate back focal plane of the light beam shaping system; a second beam splitter, the reference light, the first sampling channel object light, and the second sampling channel object light being combined on the second beam splitter; a CCD camera, the combined light beam being interfered on the CCD camera to form an interference pattern; the collimating system comprising: a second microscope objective and a second collimating lens for expanding and collimating the object light after the object to be measured.

2. The apparatus of claim 1, wherein, the light beam shaping system comprising: a first microscope objective for focusing the light beam; a pinhole arranged at the focal point of the first microscope objective for increasing the quality of the light beam; a first collimating lens for changing the focused light beam into parallel light.

3. The apparatus of claim 1, wherein, the sampling optical system comprising: a first Fourier lens, a second Fourier lens, and a digital micromirror device; the first Fourier lens and the second Fourier lens constituting a 4f optical system; the digital micromirror device being arranged at the Fourier focal plane of the 4f optical system; independent first sampling channel object light and second sampling channel object light being formed by adjusting the micromirror angle of the digital micromirror device.

4. The apparatus of claim 2, wherein, the pinhole has the same diameter as the Airy disk produced by the wavelength of the light source on the Fourier plane.

5. The apparatus of claim 1, wherein, further comprising: an attenuator; the attenuator being arranged between the second beam splitter and the CCD camera for adjusting the light intensity.

6. The apparatus of claim 1, wherein, the first beam splitter and the second beam splitter are cubic beam splitters.

7. The apparatus of claim 5, wherein, the attenuator is a polarizer.

8. A double view off-axis digital holographic imaging measurement system, characterized in that, Comprising: the two-view off-axis digital holographic measurement device and computer of any one of claims 1-7.

9. A method of phase measurement in two-view off-axis digital holography, characterized in that, Comprising: obtaining an off-axis digital hologram by the two-view off-axis digital holographic imaging measurement system of claim 8; calculating the complex amplitude distribution of the object to be measured according to the off-axis digital hologram; calculating the phase information of the object to be measured by complex amplitude division algorithm according to the complex amplitude distribution.

Images