Phase-shift digital holographic measurement device and method based on electro-optical modulation

Abstract

The present invention discloses a phase-shift digital holographic measurement device and method based on electro-optical modulation. The device consists of two parts: a phase-shift digital holographic interference optical path and an orthogonal detection single-frequency interference optical path. The electro-optical phase modulator is placed in the common arm of the two sets of interference optical paths. A DC voltage is applied to the electro-optical phase modulator to perform the same phase modulation on the two sets of interference optical paths. The orthogonal detection single-frequency interference optical path is used to accurately measure and control the phase modulation amount, that is, the phase shift amount, to achieve accurate phase shift of multiple holographic interference patterns and improve the measurement accuracy of digital holography. The present invention does not require mechanical phase shifting, has a fast phase shifting speed, high measurement efficiency, and high phase shifting accuracy, and can be widely used in the field of phase-shift interference measurement technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase-shift digital holographic measurement and relates to a holographic measurement device and method, and in particular relates to a phase-shift digital holographic measurement device and method based on electro-optical modulation. Background Art

[0002] Phase-shift digital holography introduces phase-shift technology into digital holography. It not only makes full use of the spatial bandwidth product of the image sensor, but also has the advantages of high resolution, non-contact, and label-free quantitative phase imaging. It is widely used in technical fields such as three-dimensional surface morphology measurement and biological detection.

[0003] The measurement accuracy of phase-shift digital holography is limited by the phase shift accuracy of the phase shifter. Commonly used time phase shift methods include piezoelectric ceramic drive method, polarization phase shift method and acousto-optic modulation phase shift method. The piezoelectric ceramic drive method uses a piezoelectric ceramic driver to drive the reflector in the reference light path to achieve phase shift. It has the advantages of high step accuracy and convenient operation. However, the hysteresis nonlinearity of the piezoelectric drive will lead to a large phase shift error. In addition, the piezoelectric drive phase shift will cause the obliquely incident reference beam to produce lateral movement, thereby affecting the consistency of the multi-step phase shift hologram. The polarization phase shift method uses a combination of polarizers and wave plates to change the polarization state of the light beam by rotating the polarizer or wave plate to achieve phase shift. It has the advantages of simple structure and low cost, but the limited rotation accuracy of the polarizer or wave plate will make it impossible to achieve high-precision phase shift. The acousto-optic modulation phase shift method achieves phase shift by controlling the frequency difference of the two acousto-optic modulators and the CCD frame rate. It has the advantages of high phase shift accuracy and fast speed, but it requires precise control of the CCD exposure time, phase shift device and adjustment control are relatively complex. Summary of the invention

[0004] In view of the shortcomings of the existing methods, the purpose of the present invention is to provide a phase-shift digital holographic measurement device and method based on electro-optical modulation, in which a phase-shift digital holographic interference optical path and an orthogonal detection single-frequency interference optical path are simultaneously constructed in the optical path, an electro-optical phase modulator is placed in the common arm of the two sets of interference optical paths to modulate the phase, the orthogonal interference signal is collected and processed in real time to obtain the phase value, the interference signal phase is compared with the phase value of the phase-shift digital hologram target, and the driving voltage of the electro-optical phase modulator is adjusted in real time according to the error signal to achieve precise control of the phase shift amount and improve the measurement accuracy of the phase-shift digital hologram.

[0005] The specific technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0006] 1. A phase-shift digital holographic measurement device based on electro-optical modulation:

[0007] The device comprises a single-frequency laser, a first polarizer, a first beam splitter, a second beam splitter, an electro-optic phase modulator EOM, a third beam splitter, a first plane reflector, a fourth beam splitter, a charge coupled device CCD, a second plane reflector, a half-wave plate, a polarization beam splitter, a fifth beam splitter, a quarter-wave plate, a second polarizer, a first photodetector, a third polarizer and a second photodetector; a light beam with a wavelength λ output by the single-frequency laser is converted into an s-polarized light beam with a polarization direction perpendicular to the paper surface after passing through the first polarizer, and then transmitted and reflected through the first beam splitter, a transmitted output light beam of the first beam splitter is directed to the second beam splitter to be transmitted and reflected, a reflected output light beam of the second beam splitter is modulated by the electro-optic phase modulator and directed to the third beam splitter to be transmitted and reflected, and a transmitted output light beam of the second beam splitter is transmitted and reflected through the first After reflection by the plane reflector, the light is irradiated on the object to be measured and transmitted through the object to be measured. The transmitted output light beam of the object to be measured and the reflected output light beam of the third beam splitter are combined at the fourth beam splitter to form holographic interference, and the holographic interference pattern is obtained by collecting through the charge coupled device CCD; the transmitted output light beam of the third beam splitter passes through the second plane reflector and the half wave plate in sequence to become a p-polarized light beam with a polarization direction parallel to the paper surface and is emitted to the polarization beam splitter, and is combined with the reflected output light beam of the first beam splitter at the polarization beam splitter to form a beam of orthogonal linear polarized light, and the orthogonal linear polarized light is incident on the fifth beam splitter for transmission and reflection, the transmitted output light beam of the fifth beam splitter passes through the quarter wave plate and the second polarizer in sequence and is received by the first photodetector, and the reflected output light beam of the fifth beam splitter passes through the third polarizer and is received by the second photodetector.

[0008] It also includes a signal processing system and a high-voltage amplifier HVA. The first photodetector, the second photodetector and the charge-coupled device CCD are all connected to the signal processing system. The signal processing system is connected to the electro-optic phase modulator via the high-voltage amplifier HVA.

[0009] The signal processing system comprises an analog-to-digital conversion module AD, a digital-to-analog conversion module DA, a programmable logic gate array FPGA and a computer; the first photodetector and the second photodetector are both connected to the input end of the analog-to-digital conversion module AD, the output end of the digital-to-analog conversion module DA is connected to the input end of the electro-optical phase modulator via a high-voltage amplifier HVA, the output end of the digital-to-analog conversion module DA and the input end of the digital-to-analog conversion module DA are both connected to the programmable logic gate array FPGA, and the programmable logic gate array FPGA is connected to the computer; and the charge coupled device CCD is connected to the computer.

[0010] A pair of orthogonal interference signals output by the first photodetector and the second photodetector are collected by the analog-to-digital conversion module AD and input into the programmable logic gate array FPGA, which calculates the phase of the interference signal; at the same time, the programmable logic gate array FPGA sends a trigger signal to the computer, and the computer controls the charge-coupled device CCD to collect the holographic interference pattern; and the modulation signal output by the programmable logic gate array FPGA is converted by the digital-to-analog conversion module DA and amplified by the high-voltage amplifier HVA, and then applied to the electro-optical phase modulator EOM for phase modulation.

[0011] The fast axis of the half wave plate is 45° to the polarization direction of the incident s-polarized light beam, the fast axis of the quarter wave plate is 45° to the polarization direction of the incident s-polarized light beam, the transmission direction of the first polarizer is along the s-polarization direction, the transmission direction of the third polarizer is 45° to the incident s-polarized light beam and the p-polarized light beam, and the transmission direction of the second polarizer is 90° to the transmission direction of the third polarizer.

[0012] The object to be measured is specifically a light-transmitting object.

[0013] 2. A phase-shift digital holographic measurement method based on electro-optical modulation:

[0014] 1) The single-frequency laser outputs a light beam with a wavelength of λ, which is converted into an s-polarized light beam by the first polarizer. The first photodetector and the second photodetector detect the interference signal of the orthogonal detection single-frequency interference optical path, and the charge coupled device CCD detects the interference signal of the phase-shifted digital holographic interference optical path. The modulation signal V output by the signal processing system m Apply to the electro-optic phase modulator EOM for phase modulation;

[0015] 2) The interference signal of the orthogonal detection single-frequency interference optical path enters the signal processing system and calculates the phase of the interference signal in real time The phase of the interference signal Target phase shift value with phase-shift digital holography Compare them one by one to obtain the error phase signal

[0016]

[0017] Where k is the ordinal number of the phase shift step, k = 1, 2, ... N, N represents the total number of phase shift steps, is the phase shift value for each step;

[0018] 3) The signal processing system uses the error phase signal Real-time adjustment of the modulation signal V m size;

[0019] At the same time, for the error phase signal Make a judgment:

[0020] when When , the signal processing system controls the charge coupled device CCD to perform N phase shift holographic interference patterns. The collection of Indicates that the spatial coordinates are (x, y) and the phase shift value is The kth phase-shifted hologram.

[0021] when When the signal V is modulated, no acquisition is performed and the process returns to step 2). m Regulation;

[0022] 4) Calculate the complex amplitude distribution of the object light wave of the measured object on the imaging surface of the charge coupled device (CCD) based on the collected N phase-shifted holographic interferograms;

[0023] 5) A digital reference light C(x, y) is autonomously generated in a computer of the signal processing system, and the complex amplitude distribution U(x, y) of the reproduced object light wave is obtained based on the digital reference light C(x, y) and the complex amplitude distribution of the object light wave on the imaging surface of the charge coupled device CCD;

[0024] 6) Finally, the wrapped phase of the object under test is obtained according to the complex amplitude distribution U(x, y) of the reconstructed object light wave, and the wrapped phase is processed using the phase unwrapping algorithm to obtain the three-dimensional morphology of the object under test.

[0025] In the above 4), the complex amplitude distribution of the object light wave of the measured object on the imaging surface of the charge coupled device CCD is calculated by the following formula:

[0026]

[0027] Among them, k1, k2…k N is the phase shift intensity coefficient, O(x, y) and R(x, y) are the complex amplitudes of the object light wave and the reference light wave in the phase-shifted digital holographic interference optical path, respectively, and * represents the conjugate of the complex number.

[0028] In 5), the complex amplitude distribution U(x,y) of the reconstructed object light wave is obtained by the following angular spectrum diffraction formula:

[0029]

[0030] Among them, F and F -1 Represents the symbol of Fourier transform and inverse Fourier transform; f x and f yis the spatial frequency domain coordinate; λ is the laser wavelength of the single-frequency laser; z0 is the distance along the optical axis from the object to be measured to the charge-coupled device CCD; U(x,y) represents the complex amplitude distribution of the reconstructed object light wave corresponding to the coordinate (x,y) on the plane perpendicular to the optical axis of the object to be measured; i represents the imaginary unit.

[0031] The device consists of two parts: a phase-shifted digital holographic interference optical path and an orthogonal detection single-frequency interference optical path. The electro-optical phase modulator (EOM) is placed in the common arm of the two sets of interference optical paths. A DC voltage is applied to the EOM to perform the same phase modulation on the two sets of interference optical paths. The orthogonal detection single-frequency interference optical path is used to accurately measure and control the phase modulation amount, that is, the phase shift amount, to achieve precise phase shifting of multiple holographic interference patterns and improve the measurement accuracy of digital holography.

[0032] The present invention has the following beneficial effects:

[0033] (1) The present invention uses electro-optic modulation technology to achieve phase shift of digital holographic interference, and uses orthogonal detection single-frequency interference optical path to accurately measure and control the phase shift, with high phase shift accuracy;

[0034] (2) The present invention can achieve a change in the phase shift amount by only changing the driving voltage of the electro-optic phase modulator, without the need for mechanical movement or mechanical phase shifting. The phase shift speed is fast and the measurement efficiency is high, and the invention can be widely used in the field of phase shift interferometry measurement technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the apparatus and method of the present invention.

[0036] Figure 2 It is a schematic diagram of phase shift interference of the present invention.

[0037] Figure 3 It is a schematic diagram of the three-dimensional morphology of the measured transmission step sample of the present invention.

[0038] In the figure: 1, single-frequency laser, 2, first polarizer, 3, first beam splitter, 4, second beam splitter, 5, electro-optic phase modulator (EOM), 6, third beam splitter, 7, first plane reflector, 8, object to be measured, 9, fourth beam splitter, 10, charge coupled device (CCD), 11, second plane reflector, 12, half wave plate, 13, polarization beam splitter, 14, fifth beam splitter, 15, quarter wave plate, 16, second polarizer, 17, first photodetector, 18, third polarizer, 19, second photodetector, 20, signal processing system, 21, high voltage amplifier (HVA). DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0040] like Figure 1 As shown, the specific implementation of the present invention includes a single-frequency laser 1, a first polarizer 2, a first beam splitter 3, a second beam splitter 4, an electro-optical phase modulator EOM5, a third beam splitter 6, a first plane reflector 7, a fourth beam splitter 9, a charge coupled device CCD10, a second plane reflector 11, a half wave plate 12, a polarization beam splitter 13, a fifth beam splitter 14, a quarter wave plate 15, a second polarizer 16, a first photodetector 17, a third polarizer 18 and a second photodetector 19.

[0041] The single-frequency laser 1 outputs a light beam with a wavelength of λ, which is converted into an s-polarized light beam with a polarization direction perpendicular to the paper surface after passing through the first polarizer 2, and then passes through the first beam splitter 3 for transmission and reflection. The transmission output light beam of the first beam splitter 3 is emitted to the second beam splitter 4 for transmission and reflection. The reflection output light beam of the second beam splitter 4 is modulated by the electro-optical phase modulator 5 and then emitted to the third beam splitter 6 for transmission and reflection. The transmission output light beam of the second beam splitter 4 is reflected by the first plane reflector 7 and then irradiated on the object to be measured 8 and transmitted through the object to be measured 8. The transmission output light beam of the object to be measured 8 and the reflection output light beam of the third beam splitter 6 are combined at the fourth beam splitter 9 to form holographic interference, and the holographic interference pattern is obtained by collecting the holographic interference pattern through the charge coupled device CCD10.

[0042] The transmitted output light beam of the third beam splitter 6 passes through the second plane reflector 11 and the half wave plate 12 in sequence, becomes a p-polarized light beam with a polarization direction parallel to the paper surface, and is emitted to the polarization beam splitter 13, and merges with the s-polarized light beam reflected by the first beam splitter 3 at the polarization beam splitter 3 to form a beam of orthogonal linear polarized light. The orthogonal linear polarized light is incident on the fifth beam splitter 14 for transmission and reflection. The transmitted output light beam of the fifth beam splitter 14 passes through the quarter wave plate 15 and the second polarizer 16 in sequence, and is received by the first photodetector 17. The reflected output light beam of the fifth beam splitter 14 passes through the third polarizer 18 and is received by the second photodetector 19.

[0043] The specific implementation also includes a signal processing system 20 and a high-voltage amplifier HVA21. The first photodetector 17, the second photodetector 19 and the charge-coupled device CCD10 are all connected to the signal processing system 20, and the signal processing system 20 is connected to the electro-optic phase modulator 5 via the high-voltage amplifier HVA21.

[0044] The signal processing system 20 includes an analog-to-digital conversion module AD, a digital-to-analog conversion module DA, a programmable logic gate array FPGA development board and a computer; the first photodetector 17 and the second photodetector 19 are both connected to the input end of the analog-to-digital conversion module AD, the output end of the digital-to-analog conversion module DA is connected to the input end of the electro-optical phase modulator 5 via a high-voltage amplifier HVA21, the output end of the digital-to-analog conversion module DA and the input end of the digital-to-analog conversion module DA are both connected to the programmable logic gate array FPGA, and the programmable logic gate array FPGA is connected to the computer; the charge coupled device CCD10 is connected to the computer.

[0045] A pair of orthogonal interference signals output by the first photodetector 17 and the second photodetector 19 are collected by the analog-to-digital conversion module AD and input into the programmable logic gate array FPGA, which calculates the phase of the interference signal; at the same time, the programmable logic gate array FPGA sends a trigger signal to the computer, and the computer controls the charge-coupled device CCD10 to collect the holographic interference pattern; and the modulation signal output by the programmable logic gate array FPGA is converted by the digital-to-analog conversion module DA, amplified by the high-voltage amplifier HVA21, and then applied to the electro-optical phase modulator EOM5 for phase modulation.

[0046] The fast axis of the half wave plate 12 is 45° to the polarization direction of the incident s-polarized light beam, the fast axis of the quarter wave plate 15 is 45° to the polarization direction of the incident s-polarized light beam, and the transmission direction of the first polarizer 2 is along the s-polarization direction, i.e., perpendicular to the polarization direction of the incident s-polarized light beam. Figure 1 As shown in the paper, the polarization transmission direction of the third polarizer 18 is 45° to the incident s-polarized light beam and p-polarized light beam, and the transmission direction of the second polarizer 16 is 90° to the transmission direction of the third polarizer 18 .

[0047] The second beam splitter 4, the first plane reflector 7, the object to be measured 8, the electro-optic phase modulator 5, the third beam splitter 6, the fourth beam splitter 9 and the charge coupled device CCD 10 form a phase-shifted digital holographic interference optical path; the first beam splitter 3, the second beam splitter 4, the electro-optic phase modulator 5, the third beam splitter 6, the second plane reflector 11, the half wave plate 12, the polarization beam splitter 13, the fifth beam splitter 14, the quarter wave plate 15, the second polarizer 16, the third polarizer 18, the first photodetector 17 and the second photodetector 19 form an orthogonal detection single-frequency interference optical path. The second beam splitter 4, the electro-optic phase modulator 5, the third beam splitter 6 and the second plane reflector 11 form a common arm of the phase-shifted digital holographic interference optical path and the orthogonal detection single-frequency interference optical path.

[0048] The electro-optic phase modulator 5 is placed in the common arm of the phase-shift digital holographic interference optical path and the orthogonal detection single-frequency interference optical path, and modulates the s-polarized light beam reflected by the second beam splitter. The electric field application direction of the electro-optic phase modulator is consistent with the polarization direction of the s-polarized light beam.

[0049] The specific implementation process of the present invention is as follows:

[0050] 1) The single-frequency laser 1 outputs a light beam with a wavelength of λ, which is converted into s-polarized light by the first polarizer 2. The electro-optic phase modulator 5 is placed in the common arm of the phase-shift digital holographic interference optical path and the orthogonal detection single-frequency interference optical path. The modulation signal V output by the FPGA development board m After DA conversion and high-voltage amplifier amplification, it is applied to the electro-optic phase modulator 5 to perform the same phase modulation on the two sets of interference light paths. for:

[0051]

[0052] Wherein, K is the gain factor of the high voltage amplifier 21, V π is the phase modulation half-wave voltage of the electro-optic phase modulator 5 corresponding to the input s-polarized light.

[0053] Specifically, the s-polarized light beam enters the phase-shifted digital holographic interference optical path and the orthogonal detection single-frequency interference optical path, the electro-optical phase modulator is placed in the common arm of the two sets of interference optical paths, and the FPGA of the signal processing system 20 outputs the modulated signal V m After being converted by the digital-to-analog conversion module DA and amplified by the high-voltage amplifier HVA21, it is applied to the electro-optical phase modulator EOM5 for phase modulation, thereby performing the same phase modulation on the two sets of interference optical paths.

[0054] 2) The interference signal of the orthogonal detection single-frequency interference optical path enters the signal processing system 20, and is specifically input into the programmable logic gate array FPGA after being collected by the analog-to-digital conversion module AD. The programmable logic gate array FPGA calculates the phase of the interference signal in real time. The phase of the interference signal The target phase shift value of the phase shift digital hologram is set to Compare them one by one to obtain the error phase signal

[0055]

[0056] 3) The programmable logic gate array FPGA of the signal processing system 20 generates an error phase signal according to the error phase signal. Use PID control method to adjust the modulation signal V in real time mThe size of , and then the same phase modulation (i.e. the same phase shift adjustment) is performed on the phase-shift digital holographic interference optical path and the orthogonal detection single-frequency interference optical path;

[0057] At the same time, for the error phase signal Make a judgment:

[0058] when When , the signal processing system 20 controls the charge coupled device CCD10 to collect N phase-shifted holographic interference patterns.

[0059] when When the signal V is modulated, no acquisition is performed and the process returns to step 2). m Regulation;

[0060] In the specific implementation, the programmable logic gate array FPGA sends a trigger signal to the computer, and the computer controls the charge coupled device CCD10 to complete the collection of N phase-shifted holographic interferograms.

[0061] 4) Based on the collected N phase-shift holographic interference patterns, the complex amplitude distribution of the object light wave of the measured object 8 on the imaging surface of the charge coupled device CCD is calculated by the following formula:

[0062]

[0063] The object light wave refers to the light wave of the optical path from the second beam splitter 4 to the charge coupled device CCD 10 through the first plane reflector 7, the object to be measured 8, and the fourth beam splitter 9 in sequence.

[0064] The reference light wave refers to the light wave of the optical path from the second beam splitter 4 to the charge coupled device CCD 10 after passing through the electro-optic phase modulator 5, the third beam splitter 6, and the fourth beam splitter 9 in sequence.

[0065] 5) Generate digital reference light C(x,y) in the computer, and obtain the complex amplitude distribution U(x,y) of the reconstructed object light wave through the following angular spectrum diffraction formula:

[0066]

[0067] In the embodiment, the single-frequency laser 1 adopts the HRS015B stable helium-neon laser of Thorlabs, USA, and the wavelength of the output linear polarized light is λ=632.992nm; the electro-optic phase modulator (EOM) 5 adopts the EO-PM-NR-C1 electro-optic phase modulator of Thorlabs, USA; the CCD 10 adopts the acA2040-90um black and white area array camera of Basler, Germany; the high-voltage amplifier 21 adopts the ATA-2161 high-voltage amplifier of Xi'an Antai Electronic Technology Co., Ltd., with a maximum amplification factor of 240, a voltage output range of ±800V and a bandwidth range of DC to 150kHz; the photodetector (17, 19) adopts the PDA36A-EC photodetector of Thorlabs, USA, with a bandwidth of 10MHz; the object to be measured 8 is a transmission step sample.

[0068] When the phase shift step number N = 4, the phase shift amounts are When , the four phase-shifted interference patterns recorded by CCD 10 are as follows Figure 2 As shown, the light intensity distribution is expressed as:

[0069]

[0070] In the formula, A O , A R They represent the amplitude distribution of the object light wave O(x,y) and the reference light wave R(x,y), respectively, O ,φ R Represent the phase distribution of object light and reference light respectively, and O(x,y)=A O exp(iφ O ),R(x,y)=A R exp(iφ R ), A O , A R and φ O ,φ R They are all functions of the spatial coordinates (x, y).

[0071] From equation (5), the complex amplitude distribution of the object light wave can be obtained as:

[0072]

[0073] Among them, R * =A R exp(-iφ R ) represents the conjugate of the reference light wave, A R represents the amplitude distribution of the reference light wave R(x,y), and i represents the imaginary unit.

[0074] The digital reference light C(x,y) is generated in the computer, and the complex amplitude function U(x,y) of the object light is numerically reproduced by the angular spectrum method. The wrapped phase of the transmission step sample is further obtained as:

[0075]

[0076] Among them, φ O (x,y) represents the wrapped phase, Im[] represents the operation of taking the imaginary part, and Re[] represents the operation of taking the real part.

[0077] The phase unwrapping algorithm is further used to solve the wrapped phase to obtain the three-dimensional morphology of the measured transmission step sample, such as Figure 3 shown.

[0078] It can be seen from the above embodiments that the present invention simultaneously constructs a phase-shifting digital holographic interference optical path and an orthogonal detection single-frequency interference optical path in the optical path, places an electro-optical phase modulator in the common arm of the two sets of interference optical paths to modulate the phase, and adopts electro-optical modulation technology to realize the phase shift of digital holographic interference. No mechanical movement is required, the phase shift speed is fast, and the measurement efficiency is high. The orthogonal detection single-frequency interference optical path is used to accurately measure and control the phase shift amount, and the phase shift accuracy is high, which improves the phase-shift digital holographic measurement accuracy, and has its outstanding and significant technical effects.

[0079] The above specific implementation modes are used to explain the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A phase-shift digital holographic measurement device based on electro-optical modulation, characterized in that: The invention comprises a single-frequency laser (1), a first polarizing plate (2), a first beam splitter (3), a second beam splitter (4), an electro-optic phase modulator (5), a third beam splitter (6), a first plane reflector (7), a fourth beam splitter (9), a charge coupled device (CCD) (10), a second plane reflector (11), a half-wave plate (12), a polarizing beam splitter (13), a fifth beam splitter (14), a quarter-wave plate (15), a second polarizing plate (16), a first photodetector (17), a third polarizing plate ( 18) and a second photodetector (19); a light beam with a wavelength of λ output by a single-frequency laser (1) is converted into an s-polarized light beam with a polarization direction perpendicular to the paper surface after passing through a first polarizer (2), and then transmitted and reflected through a first beam splitter (3); a transmitted light beam output by the first beam splitter (3) is directed to a second beam splitter (4) for transmission and reflection; a reflected light beam output by the second beam splitter (4) is modulated by an electro-optic phase modulator (5) and then directed to a third beam splitter (6) for transmission and reflection; a transmitted light beam output by the second beam splitter (4) is transmitted and reflected. The light beam is reflected by the first plane reflector (7) and then irradiated on the object to be measured (8) and transmitted through the object to be measured (8); the transmitted output light beam of the object to be measured (8) and the reflected output light beam of the third beam splitter (6) are combined at the fourth beam splitter (9) to form a holographic interference, and the holographic interference pattern is obtained by collecting the light beam through a charge coupled device (CCD) (10); the transmitted output light beam of the third beam splitter (6) is transformed into a p-polarized light beam with a polarization direction parallel to the paper surface after passing through the second plane reflector (11) and the half wave plate (12) in sequence. The light beam is incident on a polarizing beam splitter (13) and is combined with the reflected output light beam of the first beam splitter (3) at the polarizing beam splitter (13) to form a beam of orthogonal linear polarized light. The orthogonal linear polarized light is incident on a fifth beam splitter (14) to be transmitted and reflected. The transmitted output light beam of the fifth beam splitter (14) is sequentially passed through a quarter wave plate (15) and a second polarizing plate (16) and then received by a first photodetector (17). The reflected output light beam of the fifth beam splitter (14) is passed through a third polarizing plate (18) and then received by a second photodetector (19).

2. The phase shift digital holographic measurement device based on electro-optical modulation according to claim 1, characterized in that: The invention also comprises a signal processing system (20) and a high-voltage amplifier HVA (21); the first photodetector (17), the second photodetector (19) and the charge coupled device CCD (10) are all connected to the signal processing system (20); and the signal processing system (20) is connected to the electro-optic phase modulator (5) via the high-voltage amplifier HVA (21).

3. The phase shift digital holographic measurement device based on electro-optical modulation according to claim 2, characterized in that: The signal processing system (20) comprises an analog-to-digital conversion module AD, a digital-to-analog conversion module DA, a programmable logic gate array FPGA and a computer; the first photodetector (17) and the second photodetector (19) are both connected to the input end of the analog-to-digital conversion module AD, the output end of the digital-to-analog conversion module DA is connected to the input end of the electro-optical phase modulator (5) via a high-voltage amplifier HVA (21), the output end of the digital-to-analog conversion module DA and the input end of the digital-to-analog conversion module DA are both connected to the programmable logic gate array FPGA, and the programmable logic gate array FPGA is connected to the computer; and the charge coupled device CCD (10) is connected to the computer.

4. The phase shift digital holographic measurement device based on electro-optical modulation according to claim 3, characterized in that: A pair of orthogonal interference signals output by the first photodetector (17) and the second photodetector (19) are collected by an analog-to-digital conversion module AD and input into a programmable logic gate array FPGA, which calculates the phase of the interference signal; at the same time, the programmable logic gate array FPGA sends a trigger signal to a computer, which controls a charge coupled device CCD (10) to collect a holographic interference pattern; and a modulation signal output by the programmable logic gate array FPGA is converted by a digital-to-analog conversion module DA, amplified by a high-voltage amplifier HVA (21), and applied to an electro-optical phase modulator (5) for phase modulation.

5. The phase shift digital holographic measurement device based on electro-optical modulation according to claim 1, characterized in that: The fast axis of the half wave plate (12) is 45° to the polarization direction of the incident s-polarized light beam, the fast axis of the quarter wave plate (15) is 45° to the polarization direction of the incident s-polarized light beam, the transmission direction of the first polarizer (2) is along the s-polarization direction, the transmission direction of the third polarizer (18) is 45° to the incident s-polarized light beam and the p-polarized light beam, and the transmission direction of the second polarizer (16) is 90° to the transmission direction of the third polarizer (18).

6. A phase shift digital holographic measurement method based on electro-optical modulation applied to the device of any one of claims 1 to 5, characterized in that: 1) A single-frequency laser (1) outputs a light beam with a wavelength of λ, which is converted into an s-polarized light beam by a first polarizer (2); a first photodetector (17) and a second photodetector (19) detect and obtain an interference signal of an orthogonal detection single-frequency interference optical path; a charge coupled device (CCD) (10) detects and obtains an interference signal of a phase-shifted digital holographic interference optical path; a signal processing system (20) outputs a modulation signal V m Applying to an electro-optical phase modulator (5) for phase modulation; 2) The interference signal of the orthogonal detection single-frequency interference optical path enters the signal processing system (20), and the phase of the interference signal is calculated in real time The phase of the interference signal Target phase shift value with phase-shift digital holography Compare them one by one to obtain the error phase signal Where k is the ordinal number of the phase shift step, k = 1, 2, ... N, N represents the total number of phase shift steps, is the phase shift value for each step; 3) The signal processing system (20) processes the error phase signal Real-time adjustment of the modulation signal V m size; At the same time, for the error phase signal Make a judgment: when When , the signal processing system (20) controls the charge coupled device CCD (10) to perform N phase shift holographic interference patterns. The collection of Indicates that the spatial coordinates are (x, y) and the phase shift value is The kth phase-shifted hologram; when When the signal V is modulated, no acquisition is performed and the process returns to step 2). m Regulation; 4) calculating the complex amplitude distribution of the object light wave of the measured object (8) on the imaging surface of the charge coupled device (CCD) according to the collected N phase-shifted holographic interference patterns; 5) generating a digital reference light C(x, y) in the signal processing system (20), and obtaining a complex amplitude distribution U(x, y) of the reconstructed object light wave according to the digital reference light C(x, y) and the complex amplitude distribution of the object light wave on the imaging surface of the charge coupled device (CCD); 6) Finally, the wrapped phase of the object (8) is obtained based on the complex amplitude distribution U(x, y) of the reconstructed object light wave, and the wrapped phase is processed using a phase unwrapping algorithm to obtain the three-dimensional morphology of the object (8) being measured.

7. The phase shift digital holographic measurement method based on electro-optical modulation according to claim 6, characterized in that: In the above 4), the complex amplitude distribution of the object light wave of the measured object (8) on the imaging surface of the charge coupled device CCD is calculated by the following formula: Among them, k1, k2…k N is the phase shift intensity coefficient, O(x, y) and R(x, y) are the complex amplitudes of the object light wave and the reference light wave in the phase-shifted digital holographic interference optical path, respectively, and * represents the conjugate of the complex number.

8. The phase shift digital holographic measurement method based on electro-optical modulation according to claim 7, characterized in that: In 5), the complex amplitude distribution U(x,y) of the reconstructed object light wave is obtained by the following formula: Among them, F and F -1 Represents the symbol of Fourier transform and inverse Fourier transform; f x and f y is the spatial frequency domain coordinate; λ is the laser wavelength of the single-frequency laser (1); z0 is the distance along the optical axis from the object to be measured (8) to the charge coupled device CCD (10); U(x, y) represents the complex amplitude distribution of the reconstructed object light wave corresponding to the coordinate (x, y) on the plane perpendicular to the optical axis of the object to be measured (8); i represents an imaginary unit.

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