DMD-based time division multiplexing common-path dual-wavelength digital holographic imaging system and method

Abstract

The invention discloses a DMD-based time division multiplexing common-path dual-wavelength digital holographic imaging system and a DMD-based time division multiplexing common-path dual-wavelength digital holographic imaging method, and relates to the field of dual-wavelength digital holographic imaging. The invention solves the problems of environmental sensitivity and coherent noise influence on measurement precision caused by lengthy dynamic measurement record and complex interference structure in dual-wavelength digital holographic imaging, and adopts the technical scheme that a digital micro-mirror device is used for rapid overturning, and two paths of light sources with different wavelengths irradiated on the digital micro-mirror device are rapidly switched, so that the measurement precision is greatly improved. An interference image is obtained through a polaroid, an objective table, a microscopic imaging system, a transmission type diffraction grating and a confocal spatial filtering system; according to the invention, high-speed acquisition of two-wavelength interferograms is ensured, the time resolution of measurement is remarkably improved, the problem that phase recovery data is difficult to separate when dual-wavelength illumination is carried out simultaneously is avoided, and common-path interference and partial coherent light illumination are combined, so that the space-time phase sensitivity of measurement is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of dual-wavelength digital holographic imaging technology, specifically to a time-division multiplexing common-path dual-wavelength digital holographic imaging system and method based on DMD. Background Technology

[0002] Digital holographic microscopy, as a label-free, highly sensitive, and high-precision full-field microscopic imaging method, has been widely used in biomedical detection, materials characterization, and advanced manufacturing of semiconductors and micro / nano functional structures. While single-wavelength digital holographic microscopy can achieve high-precision quantitative phase imaging when measuring smooth, continuous samples with a height greater than the illumination wavelength, it suffers from limitations when the sample contains a step structure with a height difference greater than half a wavelength. This severely restricts its application. To address this, researchers have proposed a dual-wavelength digital holographic imaging method. This method uses two light sources of different wavelengths for illumination to acquire the encapsulation phase information of the sample at the corresponding illumination wavelengths. Then, the dual-wavelength unwrapping method enables high-precision reconstruction of the phase distribution of step samples. This method not only combines the inherent advantages of single-wavelength digital holography but also, through the rational selection of wavelength combinations, forms an equivalent composite wavelength much larger than a single wavelength, thus significantly expanding the longitudinal measurement range.

[0003] However, traditional dual-wavelength digital holography based on phase-shifting interferometry typically requires acquiring multiple phase-shifting interferograms to obtain phase retrieval data under two wavelengths of illumination. This lengthy recording process severely limits the application of this method in high-speed real-time detection scenarios. To significantly improve imaging efficiency, carrier frequency interferometry schemes based on simultaneous dual-wavelength illumination, supplemented with filters or similar optical elements to achieve interference multiplexing, have been developed to simultaneously acquire and separate phase retrieval data from the two wavelengths. However, these non-common-path interferometry methods not only lead to complex interference structures but also reduce system stability. Although constructing a common-path interferometry structure can address the extreme sensitivity of the above methods to environmental disturbances and improve the temporal phase sensitivity of the measurement, it also presents difficulties for separating phase retrieval data under dual-wavelength illumination. On the other hand, in dual-wavelength digital holographic imaging research, higher spatial phase sensitivity is always pursued to achieve observation of more detailed spatial structures of samples. However, many currently developed methods still struggle to be compatible with partially coherent illumination, and the parasitic interference and speckle noise introduced by laser illumination, which are difficult to eliminate, severely affect the system's spatial phase sensitivity, further deteriorating imaging quality, measurement accuracy, and reliability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the existing defects and provide a time-division multiplexing common-path dual-wavelength digital holographic imaging system and method based on DMD, which can effectively solve the problems in the background technology.

[0005] To achieve the above objectives, this invention discloses a time-division multiplexing common-path dual-wavelength digital holographic imaging system based on a digital micromirror device (DMD). The technical solution includes a light source and a DMD. The light source has two intersecting optical paths, and the DMD is located at the intersection of the two optical paths. The angles between the transmission directions of the two light sources and the reflected optical path of the DMD are respectively... and The digital micromirror device (DMD) has a polarizer in its reflected light path. Downstream of the polarizer are a stage, a microscopic imaging system, a transmission diffraction grating, a confocal spatial filter system, and an image acquisition device. The two light sources emit light with different wavelengths and spectral bandwidths. The transmission diffraction grating is located at the back focal plane of the microscopic imaging system. The image acquisition device is located at the conjugate plane of the confocal spatial filter system. By rapidly flipping the DMD, the image acquisition device and the DMD are time-coordinated to acquire images, enabling the acquisition of two carrier frequency interferograms at different illumination wavelengths. This system has a simple structure and good stability. By acquiring images of different wavelengths through time-controlled acquisition, it facilitates the separation of phase recovery data later. The image acquisition device can be a common acquisition device from an image sensor or camera.

[0006] As a preferred embodiment of the present invention, the light source includes a first superluminescent diode and a second superluminescent diode, and a first beam-expanding collimating lens and a second beam-expanding collimating lens are respectively provided between the two and the digital micromirror device.

[0007] As a preferred embodiment of the present invention, the microscopic imaging system includes an infinity imaging objective and a tube lens, wherein the tube lens is located downstream of the infinity imaging objective; and the transmission diffraction grating is located at the back focal plane of the tube lens.

[0008] As a preferred embodiment of the present invention, the confocal spatial filtering system includes a 4f system and a pinhole filter. The 4f system includes a first lens and a second lens. The front focal plane of the first lens coincides with the rear focal plane of the tube lens. The rear focal plane of the second lens is the conjugate plane of the 4f system, which is also the conjugate plane of the confocal spatial filtering system. The pinhole filter is located at the spectral plane of the 4f system.

[0009] In a preferred embodiment of the present invention, the main body of the pinhole filter is a circular spatial filter. The spatial filter has a light-transmitting aperture and a filtering pinhole. The filtering pinhole is located at the center of the spatial filter, and the light-transmitting aperture is located vertically in the direction of the filtering pinhole. The filtering pinhole performs strict spatial low-pass filtering on the 0th-order light diffracted by the transmission-type diffraction grating, filtering out high-frequency components carrying sample information and allowing only the DC component (zero-frequency component) to pass through, thereby generating a plane wave with uniform amplitude as the reference light. The vertical light-transmitting aperture allows the full spectrum of the +1st-order diffracted light to pass through without loss, thus preserving the complete complex amplitude information of the sample as the object light.

[0010] As a preferred embodiment of the present invention, the image acquisition device is a monochrome black and white image sensor.

[0011] This invention further discloses an imaging method based on the above-mentioned time-division multiplexing common-path dual-wavelength digital holographic imaging system, the technical solution of which includes the following steps:

[0012] Step 1: Place the sample to be tested onto the stage, turn on the light source, and illuminate the target surface of the digital micromirror device with different wavelengths emitted by the two light sources. Use a synchronous trigger signal to control the micromirror assembly of the digital micromirror device. and The two mechanical limit states alternately flip to achieve time-division multiplexing output of dual-wavelength illumination light; during the flipping process of the micromirror assembly, different wavelengths of illumination light are obtained alternately, and the acquisition sequence of the illumination light corresponds to the flipping sequence of the micromirror assembly.

[0013] Step 2: The light reflected by the digital micromirror device illuminates the polarizer to obtain linearly polarized illumination light, which then illuminates the sample to be tested on the stage. After being scattered by the sample, the object light wave passes through the microscopic imaging system and is imaged onto the intermediate imaging plane where the transmission diffraction grating is located, forming different diffraction orders of 0th order and ±1st order.

[0014] Step 3: After filtering out redundant orders using a confocal spatial filtering system and separating the reference light and object light, the two beams are superimposed on the image acquisition device to generate interference, thereby obtaining an interference fringe image with carrier frequency modulation. By controlling the acquisition timing of the image acquisition device to correspond with the flipping timing of the micromirror components of the digital micromirror device, the alternating acquisition of two carrier frequency interference patterns at different wavelengths is achieved.

[0015] Step 4: The complex amplitude information of the sample under test is reconstructed using the Fourier transform algorithm, and finally, the phase information of the sample under test is reconstructed with high precision by combining the dual-wavelength unwrapping algorithm.

[0016] In a preferred embodiment of the present invention, in step 1, the light source is a combination of a superluminescent diode and a beam expander collimating lens. The two light sources emit collimated illumination light with center wavelengths of 636 nm and 510 nm, respectively. The angles between the optical paths generated by the two light sources and the reflected optical path of the digital micromirror device are respectively... and .

[0017] As a preferred embodiment of the present invention, in step 1, the two mechanically limiting states of the alternating flipping of the micromirror assembly are as follows: In the first timing sequence, the micromirror assembly flips to Location, will The incident 636nm light beam is reflected into the reflected light path of the digital micromirror device; in the second time sequence, the micromirror flips to... Location, will The incident 510nm light beam is reflected into the reflected light path of the digital micromirror device.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention introduces the light into the imaging system through two-way light-guided digital micromirror devices, which are then reflected by the digital micromirror devices. Utilizing the high-speed flipping characteristic of the digital micromirror devices, which have no mechanical inertia, rapid alternation of dual-wavelength illumination beams can be achieved. Combined with the synchronous acquisition of a high-speed image acquisition device, this not only effectively improves imaging efficiency but also avoids the coupling of dual-wavelength phase recovery data, significantly simplifying the separation operation of phase recovery data.

[0019] Furthermore, by employing a common-path off-axis interference structure constructed with a transmission-type diffraction grating, the object light and reference light follow almost the same optical path, effectively canceling out the effects of air disturbances, mechanical vibrations, and temperature drift, thus significantly improving the temporal phase stability of the measurement. In addition, the system operates well under partially coherent illumination, significantly suppressing the influence of coherent noise on the measurement results, thereby effectively improving the signal-to-noise ratio of the reconstructed phase image and the spatial phase sensitivity of the system. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the time-division multiplexing common-path dual-wavelength digital holographic imaging system of the present invention;

[0021] Figure 2 This is a carrier frequency interference fringe pattern of polystyrene microspheres at a wavelength of 636nm, acquired by the monochrome black and white image sensor of this invention;

[0022] Figure 3 This is a carrier frequency interference fringe pattern of polystyrene microspheres at a wavelength of 510 nm, acquired by the monochrome black and white image sensor of this invention;

[0023] Figure 4The image shows the phase distribution of polystyrene microspheres encapsulated at a wavelength of 636 nm, reconstructed using the Fourier transform algorithm.

[0024] Figure 5 The image shows the phase distribution of polystyrene microspheres encapsulated at a wavelength of 510 nm, reconstructed using the Fourier transform algorithm.

[0025] Figure 6 The phase distribution diagram of polystyrene microspheres at the synthetic wavelength obtained by using the dual-wavelength unwrapping algorithm;

[0026] Figure 7 The image shows the phase distribution of polystyrene microspheres unwrapped at a 510 nm illumination wavelength, obtained using a single-wavelength unwrapping method guided by the synthetic wavelength.

[0027] Figure 8 For along Figure 7 Phase cross-section of polystyrene microspheres (white dashed line);

[0028] Figure 9 This is a carrier frequency interference fringe pattern of a polydimethylsiloxane (PDMS) stepped microstructure sample at a wavelength of 636 nm, acquired by the monochrome black and white image sensor of this invention.

[0029] Figure 10 This is a carrier frequency interference fringe pattern of a PDMS stepped microstructure sample at a wavelength of 510 nm, acquired by the monochrome black and white image sensor of this invention.

[0030] Figure 11 The image shows the phase distribution of a PDMS stepped microstructure sample at 636 nm wavelength, reconstructed using the Fourier transform algorithm.

[0031] Figure 12 The image shows the phase distribution of a PDMS stepped microstructure sample at 510 nm wavelength, reconstructed using the Fourier transform algorithm.

[0032] Figure 13 The image shows the phase distribution of the PDMS stepped microstructure sample at the synthesized wavelength, calculated using a dual-wavelength unwrapping algorithm.

[0033] Figure 14 For along Figure 13 Phase profile of the PDMS step microstructure sample with white dashed lines.

[0034] In the figure: 1. First superluminescent diode; 2. Second superluminescent diode; 3. First beam expander collimating lens; 4. Second beam expander collimating lens; 5. Digital micromirror device; 6. Polarizer; 7. Stage; 8. Infinity imaging objective; 9. Tubular lens; 10. Transmission diffraction grating; 11. First lens; 12. Pinhole filter; 13. Second lens; 14. Monochrome black and white image sensor. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] like Figure 1 As shown, this invention first discloses a time-division multiplexing common-path dual-wavelength digital holographic imaging system based on DMD. The technical solution adopted includes a first superluminescent diode 1, a second superluminescent diode 2, and a digital micromirror device 5. When placing the digital micromirror device 5, its normal direction extends along the positive x-axis. A first beam-expanding collimating lens 3 and a second beam-expanding collimating lens 4 are respectively set downstream of the first superluminescent diode 1 and the second superluminescent diode 2 to obtain collimated illumination light. The two collimated illumination lights are located in the xy plane and are perpendicular to the x-axis, respectively. The included angle. Downstream of the digital micromirror device 5 is a polarizer 6, which can adjust the polarization direction of the beam reflected by the digital micromirror device 5 to the yz plane, obtaining linearly polarized light extending along the z-axis. The digital micromirror device 5 is a high-speed adjustable reflective switch. By flipping the micromirror assembly, the light source reflected onto the polarizer 6 can be changed. Specifically, it switches between the first superluminescent diode 1 and the first beam expander collimating lens 3, and the second superluminescent diode 2 and the second beam expander collimating lens 4.

[0038] Downstream of polarizer 6 is stage 7, on which the sample to be tested can be mounted. Linearly polarized light irradiates the sample to obtain the object light wave. Downstream of stage 7 is a microscopic imaging system consisting of an infinity imaging objective lens 8 and a tube lens 9. After passing through the microscopic imaging system, the object light wave becomes the imaging light carrying sample information. At the back focal plane of tube lens 9 is a transmission diffraction grating 10, which diffracts the imaging light carrying sample information into different diffraction orders of 0th order and ±1st order. A confocal spatial filter system is disposed downstream of the transmissive diffraction grating 10. The confocal spatial filter system includes a first lens 11, a second lens 13, and a pinhole filter 12. The front focal plane of the first lens 11 coincides with the rear focal plane of the tube lens 9. The first lens 11 and the second lens 13 together form a 4f imaging system with magnification of 1x. The pinhole filter 12 is located on the spectral plane of the 4f imaging system. Its main body is a circular spatial filter with a filter pinhole at its center. There is a light-transmitting hole vertically above the filter pinhole, which filters the spectra of the 0th order and +1st order diffracted light, respectively. The light-transmitting hole in the vertical direction does not change the spectrum of the +1st order diffracted light (used as the object light). The filter pinhole in the center performs low-pass filtering on the 0th order diffracted light diffracted by the transmissive diffraction grating 10 to form a reference light without object light information. The subsequently generated object light and reference light are coherently superimposed on the rear focal plane of the second lens 13 to form a carrier frequency interferogram. A monochrome image sensor 14 is positioned at the back focal plane of the second lens 13 (the conjugate plane of the 4f imaging system) to acquire a carrier frequency interferogram. The digital micromirror device 5 and the monochrome image sensor 14 are connected to an external computer for controlling the flipping timing of the digital micromirror device 5, the image acquisition timing of the monochrome image sensor 14, and for exporting, processing, and analyzing the images output by the monochrome image sensor 14.

[0039] This invention also discloses an imaging method based on the above-mentioned time-division multiplexing common-path dual-wavelength digital holographic imaging system, the technical solution of which includes the following steps:

[0040] Step 1: Connect the digital micromirror device 5 and the monochrome image sensor 14 to an external computer;

[0041] Step 2: Turn on the superluminescent diodes 1 and 2. The light emitted by these two diodes is collimated by the first beam-expanding collimating lens 3 and the second beam-expanding collimating lens 4, respectively, and then illuminates the target surface of the digital micromirror device 5. A synchronous trigger signal is sent to the digital micromirror device 5 via a computer to apply binarized timing encoding to its micromirror components, controlling the micromirror components to alternately flip between two mechanical limit states of ±12°: In the first timing sequence, the micromirror components flip to the +12° position, reflecting the collimated illumination beam (emitted by the second superluminescent diode 2 and the second beam-expanding collimating lens 4) with a wavelength of 636nm and a spectral bandwidth incident at +24° to the x-direction for emission; in the second timing sequence, the micromirror components flip to the -12° position, reflecting the collimated illumination beam (emitted by the first superluminescent diode 1 and the first beam-expanding collimating lens 3) with a wavelength of 510nm and a spectral bandwidth incident at -24° to the x-direction for emission. Through the high-speed flipping action of the micromirror components described above, time-division multiplexing output of dual-wavelength illumination light is achieved.

[0042] Step 3: The illumination beam alternately reflected by the digital micromirror device 5 is polarized by the polarizer 6 to generate linearly polarized illumination light with a polarization direction parallel to the z-axis. This linearly polarized light is imaged onto the intermediate imaging plane where the transmission diffraction grating 10 is located after passing through the microscopic imaging system composed of the infinity imaging objective 8 and the tube lens 9. The light is then superimposed on the target surface of the monochrome black and white image sensor 14 by the confocal spatial filtering system to generate interference. Sample-free interferograms at illumination wavelengths of 636 nm and 510 nm are collected for system aberration correction. The wrapping phase distribution of the sample-free interferogram is extracted using the Fourier transform algorithm.

[0043] Step 4: Turn off superluminescent diodes 1 and 2, clamp the sample to be tested on stage 7, and turn on superluminescent diodes 1 and 2 again. The linearly polarized light generated by polarizer 6 illuminates the sample to be tested on stage 7. The object light wave scattered by the sample passes through the microscopic imaging system composed of infinity imaging objective 8 and tube lens 9 and is imaged onto the intermediate imaging plane where the transmission diffraction grating 10 is located. The imaging light carrying sample information forms 0th and ±1st order diffraction orders after being diffracted by the transmission diffraction grating 10. The pinhole filter 12 located at the 4f imaging system spectrum plane filters out the redundant orders and separates the 0th order reference light and the +1st order object light. The filtered object light and reference light pass through the second lens 13 and are superimposed on the target surface of monochrome black and white image sensor 14 to produce interference, thereby obtaining an interference fringe image with carrier frequency modulation.

[0044] Step 5: The micromirror assembly of the digital micromirror device 5 is switched at high speed to switch the illumination wavelength, and two carrier frequency interferograms of the sample under test are recorded simultaneously at illumination wavelengths of 636nm and 510nm. The phase distribution of the sample interferogram is extracted by using the Fourier transform algorithm, and the system aberration is eliminated by using background subtraction. Finally, the phase distribution of the sample under test is reconstructed by combining the dual-wavelength unwrapping algorithm, thereby obtaining quantitative information on its three-dimensional morphology.

[0045] Verification test

[0046] To verify the accuracy of the DMD-based time-division multiplexing common-path dual-wavelength digital holographic imaging system and method in quantitative phase measurement, polystyrene microspheres with a diameter of 4 micrometers were selected as standard test samples for experimental verification.

[0047] Before the experiment, the polystyrene microspheres were immersed in objective oil with a refractive index of 1.518 to prepare the observation sample. The measurement process is as follows:

[0048] First, without a sample, two carrier frequency interferograms corresponding to illumination wavelengths of 636 nm and 510 nm were simultaneously acquired. Then, the prepared polystyrene microsphere sample was placed on the stage 7, and under the same timing control and illumination conditions, dual-wavelength carrier frequency interferograms carrying the phase information of the sample were acquired. The acquired interferograms are shown below. Figure 2 and Figure 3 As shown.

[0049] During the data processing stage, the encapsulated phase distribution of the test sample without systematic aberrations at wavelengths of 636 nm and 510 nm was extracted using the Fourier transform algorithm. Figure 4 and Figure 5 The phase distributions of polystyrene microsphere encapsulation under illumination at 636 nm and 510 nm wavelengths are shown, respectively. Subsequently, the phase distribution at the composite wavelength was calculated using a dual-wavelength unwrapping algorithm, and the results are as follows: Figure 6 As shown. To further reduce phase noise, this embodiment employs a dual-wavelength-guided single-wavelength phase unwrapping algorithm for noise cancellation. Specifically, utilizing the large unambiguous range characteristic of the synthesized wavelength generated by the dual wavelengths, the phase order information is determined, thereby guiding the unwrapping process of the single-wavelength wrapped phase under 510nm wavelength illumination. The final result is a low-noise, high-precision two-dimensional quantitative phase distribution of polystyrene microspheres, as shown. Figure 7 As shown.

[0050] To further conduct quantitative analysis of the measurement results, along Figure 7 The white dashed line depicts the phase profile of the central section of the polystyrene microspheres, and the result is as follows: Figure 8As shown, using a wavelength of 510 nm as the measurement reference, the experimentally measured phase height at the center of the microsphere was 3.54885 radians; while the theoretical phase height calculated based on the nominal diameter and refractive index parameters of the microsphere was 3.546 radians. Comparative analysis shows that the experimentally measured value and the theoretically calculated value are in good agreement. This result fully demonstrates that the dual-wavelength digital holographic imaging system and method proposed in this embodiment have extremely high accuracy and reliability in quantitative phase imaging.

[0051] To verify the applicability of the system and method described in this embodiment in the advanced manufacturing and testing of micro / nano functional structures, a polydimethylsiloxane (PDMS) stepped microstructure prepared by two-photon polymerization was selected as the standard test sample. The measurement process is as follows:

[0052] First, without a sample, two carrier frequency interferograms were simultaneously acquired at illumination wavelengths of 636 nm and 510 nm, respectively. Then, the step sample to be tested was placed on stage 7, and under the same timing control and illumination conditions, dual-wavelength carrier frequency interferograms carrying the phase information of the sample to be tested were acquired. The acquired interferograms are shown below. Figure 9 and Figure 10 As shown.

[0053] In the data processing stage, the encapsulation phase distribution of the PDMS stepped microstructure samples at wavelengths of 636 nm and 510 nm was extracted using the Fourier transform algorithm, and the results are as follows: Figure 11 and Figure 12 As shown in the figure. Subsequently, the spatial height distribution of the PDMS stepped microstructure sample was reconstructed using a dual-wavelength unwrapping algorithm.

[0054] Specifically, the nominal height of the PDMS stepped microstructure is 1.699 μm, and the refractive indices of PDMS material at illumination wavelengths of 510 nm and 636 nm are 1.42 and 1.414, respectively. Theoretical calculations show that the theoretical phase heights of the stepped sample at 510 nm and 636 nm wavelengths are 8.8 rad and 6.95 rad, respectively, while the theoretical phase height at the synthesized wavelength is 1.84 rad. Since the phase abrupt change at the step edge far exceeds the unambiguous range of a single wavelength, traditional single-wavelength holographic detection would induce aliasing and phase ambiguity. However, the synthesized wavelength generated in this embodiment effectively extends the unambiguous measurement range of the system from the submicron scale to the micron scale, and its range is sufficient to completely cover the physical depth of the sample. The final reconstructed two-dimensional quantitative phase distribution result of the PDMS stepped sample is as follows: Figure 13 As shown, the results indicate that the morphology obtained by the dual-wavelength unwrapping algorithm accurately reconstructs the step profile of the step, and no artifacts caused by step transitions appear at the edges.

[0055] To further quantitatively analyze the accuracy of the measurement results, along Figure 13 The white dashed line plots the phase profile at the center of the PDMS stepped microstructure sample, as shown in the figure. Figure 14 As shown in the figure, the dashed line represents the theoretical phase height value of 1.84 rad, and the solid line represents the experimental measurement data. The comparison shows that the phase distribution measured in the experiment matches the theoretical height, and the steep vertical boundary of the steps is accurately reconstructed without any shape distortion caused by phase blurring.

[0056] In summary, the present invention provides a time-division multiplexing common-path dual-wavelength digital holographic imaging system and method based on DMD, which achieves high-precision quantitative phase imaging of step samples through dual-wavelength synthesized phase technology. Unlike traditional dual-wavelength interferometry, this method utilizes a digital micromirror device (DMD) to achieve microsecond-level wavelength switching without mechanical inertia, significantly improving the measurement speed. Furthermore, it combines the high temporal phase stability provided by a grating diffraction common-path off-axis interference structure with the advantages of suppressing coherent noise from partially coherent illumination, thereby significantly improving the accuracy and signal-to-noise ratio of phase measurement. This has significant practical value in the fields of micro / nano functional structure detection and precision manufacturing quality monitoring.

[0057] Components not described in detail in this article are existing technologies.

[0058] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A DMD-based time-multiplexed common-path dual-wavelength digital holographic imaging system, characterized in that: The application relates to a light source and a digital micro-mirror device (5), the light source has two paths and the light paths intersect, the digital micro-mirror device (5) is located at the intersection of the two light paths, the transmission directions of the two light sources and the reflection light path of the digital micro-mirror device (5) form angles of and respectively, a polarizer (6) is arranged on the reflection light path of the digital micro-mirror device (5), downstream of the polarizer (6) are sequentially arranged a stage (7), a microscopic imaging system, a transmission diffraction grating (10), a confocal spatial filtering system and an image acquisition device; the wavelengths and spectral bandwidths of the light emitted by the two light sources are different; the transmission diffraction grating (10) is located at the back focal plane of the microscopic imaging system; and the image acquisition device is located at the conjugate plane of the confocal spatial filtering system.

2. The DMD-based time multiplexed common-path dual-wavelength digital holographic imaging system according to claim 1, wherein: The light source comprises a first super-radiation light emitting diode (1) and a second super-radiation light emitting diode (2), and a first beam expansion collimating lens (3) and a second beam expansion collimating lens (4) are arranged between the two and the digital micro-mirror device (5) respectively.

3. The DMD-based time multiplexed common-path two-wavelength digital holographic imaging system of claim 1, wherein: The microscopic imaging system comprises an infinite imaging objective (8) and a tube lens (9), the tube lens (9) is located downstream of the infinite imaging objective (8); the transmission type diffraction grating (10) is located at the back focal plane of the tube lens (9).

4. The DMD-based time multiplexed common-path two-wavelength digital holographic imaging system of claim 3, wherein: The confocal spatial filter system comprises a 4f system and a pinhole filter (12), the 4f system comprises a first lens (11) and a second lens (13), the front focal plane of the first lens (11) coincides with the back focal plane of the tube lens (9), the back focal plane of the second lens (13) is the conjugate plane of the 4f system, that is, the conjugate plane of the confocal spatial filter system; the pinhole filter (12) is located at the spectral plane of the 4f system.

5. The DMD-based time multiplexed common-path two-wavelength digital holographic imaging system of claim 4, wherein: The main body of the pinhole filter (12) is a circular spatial filter, and the spatial filter has a light transmission hole and a filter pinhole, the filter pinhole is located at the center of the spatial filter, and the light transmission hole is located in the vertical direction of the filter pinhole.

6. The DMD-based time multiplexed common path dual-wavelength digital holographic imaging system of claim 1 or 4, wherein: The image acquisition device is a monochrome black and white image sensor (14).

7. An imaging method based on the time division multiplexing common path dual- wavelength digital holographic imaging system of claim 1, characterized in that, The method comprises the following steps: Step 1, load the sample to be tested on the stage (7), turn on the light source, the different wavelengths of illumination light emitted by the two light sources are irradiated on the target surface of the digital micromirror device (5), the micro-mirror assembly of the digital micromirror device (5) is controlled by using a synchronous trigger signal to realize the time division multiplexing output of the double-wavelength illumination light and Alternating between the two mechanical limiting states, the time division multiplexing output of the double-wavelength illumination light is realized. Step 2, the light reflected by the digital micro-mirror device (5) is irradiated on the polarizer (6) to obtain linearly polarized illumination light, and the object light wave scattered by the sample on the object table (7) is imaged to the intermediate imaging plane where the transmission type diffraction grating (10) is located, forming different diffraction orders; Step 3, the confocal spatial filter system is used to filter out the redundant orders, separate the reference light and the object light, and then superimpose and interfere on the image acquisition device to obtain an interference fringe image with a carrier frequency modulation; by controlling the acquisition time sequence of the image acquisition device to correspond to the micro-mirror component flipping time sequence of the digital micro-mirror device (5), the alternate acquisition of two different wavelength carrier interference images is realized; Step 4, the complex amplitude information of the sample to be measured is reconstructed by using the Fourier transform algorithm, and finally the high-precision reconstruction of the phase information of the sample to be measured is realized by combining the double-wavelength unwrapping algorithm.

8. The imaging method of claim 7, wherein: In step 1, the light source is a super radiation light emitting diode combined with a beam expander collimator, two light sources respectively emit collimated illumination light with center wavelengths of 636 nm and 510 nm, the angles between the light paths generated by the two light sources and the reflected light path of the digital micromirror device (5) are respectively and .

9. The imaging method of claim 8, wherein: In step 1, the two mechanically limiting states of the alternating flipping of the micromirror assembly are as follows: In the first timing sequence, the micromirror assembly flips to Location, will The incident 636nm light beam is reflected into the reflected light path of the digital micromirror device (5); in the second time sequence, the micromirror flips to Location, will The incident 510nm beam is reflected into the reflected light path of the digital micromirror device (5).

Images