CN111220283A - Light field complex amplitude measuring device and method based on multi-step phase modulation - Google Patents
Light field complex amplitude measuring device and method based on multi-step phase modulation Download PDFInfo
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Abstract
The invention relates to a phase recovery technology, provides a light field complex amplitude measuring device and method based on multi-step phase modulation, and solves the problems that the existing phase recovery technology needs a complex scanning process to obtain a plurality of diffraction intensities, and displacement errors and light path inclination introduced in the scanning process influence the convergence speed and precision of phase recovery. The device comprises a modulation system, a detector and a data processing unit; the modulation system is used for loading n modulation phases and modulating the light field to be detected to obtain n diffraction light intensities of the light field to be detected, wherein n is an integer greater than or equal to 4; the n modulation phases are matched with the phases of different frequency bands of the light field to be detected; the detector is used for receiving the modulated n diffracted light intensities; the data processing unit comprises a memory and a processor, wherein the memory is stored with a computer program for processing n modulation phases and n diffraction light intensities, and the computer program realizes a phase recovery method to calculate the complex amplitude of the light field to be measured when being executed by the processor.
Description
Technical Field
The invention relates to a phase recovery technology, in particular to a light field complex amplitude measuring device and method based on multi-step phase modulation.
Background
The light field complex amplitude information comprises light intensity and phase information, the light intensity information can be directly detected and obtained by a detector, and the phase information is generally obtained by adopting a phase recovery technology. However, recovering phase information is a vital part of various imaging systems and plays an important role in many technical and scientific applications, such as in the fields of biological tissue imaging, x-ray crystallography, microwave holography, fringe pattern analysis, astronomy imaging, antenna detection, and adaptive optics.
Currently, methods for measuring phase can be divided into two main categories: one type uses a reference beam, i.e., interferometry, and the other type does not use a reference beam, also known as phase recovery techniques. Interferometric measurement, while the most suitable method for quantitatively measuring phase, requires ideal reference light, and for some imaging systems, interferometric methods are no longer applicable. The phase recovery technology does not need a reference beam, and the complex amplitude of the measured optical field is obtained through iterative calculation of a phase recovery algorithm by utilizing diffraction field intensity information acquired by a detector.
The phase recovery technology is essentially a mathematical optimization problem, and the difficulty is how to obtain the complex amplitude information of the measured optical field with high precision and fast convergence. The initial assumed value is usually given by using a priori knowledge, and then the high precision and fast convergence of the phase recovery technology are realized by constraint through various mathematical means or physical means. A common mathematical approach is the GS constraint which replaces the calculated diffracted intensity with the actual detected intensity while preserving phase, but this constraint method is not easily converged. In order to further improve the convergence of phase recovery, constraints such as Error Reduction (ER), Hybrid Input Output (HIO), and the like are successively proposed in mathematical terms. These mathematical constraints can speed up convergence to some extent compared to the GS constraint, but are still susceptible to the initial assumptions. In terms of physical means, the constraint applied by utilizing a plurality of diffracted light intensities is also the most convenient and effective constraint means. The constraint means is applied to the PIE (Ptycholographic Iterative Engine) technology, the SBMIR (Single-Beam Multiple integrity Reconstruction) technology and the improvement technology thereof, and has good effect. However, the above-mentioned techniques require one-dimensional or two-dimensional complicated scanning process to obtain multiple diffraction intensities, and displacement errors and optical path tilt errors introduced during the scanning process also affect the convergence speed and accuracy of phase recovery.
Disclosure of Invention
The invention provides a light field complex amplitude measuring device and method based on multi-step phase modulation, and aims to solve the technical problems that the existing phase recovery technology needs a one-dimensional or two-dimensional complex scanning process to obtain a plurality of diffraction intensities, and the phase recovery convergence speed and precision are also influenced by displacement errors and light path inclination introduced in the scanning process.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
a light field complex amplitude measuring device based on multi-step phase modulation is characterized in that: the system comprises a modulation system, a detector and a data processing unit;
the modulation system is used for loading n modulation phases and modulating the light field to be detected to obtain n diffraction light intensities of the light field to be detected, wherein n is an integer greater than or equal to 4; the n modulation phases are matched with the phases of different frequency bands of the light field to be detected;
the detector is used for receiving the modulated n diffracted light intensities;
the data processing unit comprises a memory and a processor, the memory is stored with a computer program for processing n modulation phases and n diffracted light intensities, and the n modulation phases are set to form a modulation phase set phi (x)m,ym)，φ(xm,ym)＝[φ1(xm,ym),φ2(xm,ym)…,φt(xm,ym),…φn(xm,ym)](ii) a Let n diffraction light intensities constitute a diffraction light intensity set I (x)d,yd)，I(xd,yd)＝[I1(xd,yd),I2(xd,yd)…,It(xd,yd),…In(xd,yd)]；
Wherein t is an integer greater than 1 and less than n; (x)m,ym) As modulation plane coordinates, (x)d,yd) Is a diffraction plane coordinate;
the computer program when executed by a processor implementing the steps of:
1) setting the complex amplitude of the light field to be measured as O (x)o,yo)，O(xo,yo)＝exp[iφo(xo,yo)](ii) a The initial iteration number num is 1;
wherein phi iso(xo,yo) Is an assumed initial value of phase;
2) the complex amplitude O (x) of the light field to be measuredo,yo) Transmitting the wave to a modulation surface of a modulation system to obtain an incident wavefront P before the j modulation phasej(xm,ym)，Pj(xm,ym)＝ρAS[O(xo,yo)]；
Where ρ isASFor the forward angular spectrum calculation, j ═ 1,2 … … n;
3) incident wavefront Pj(xm,ym) J-th modulation phase phi of modulated surfacej(xm,ym) Modulating to obtain modulated emergent wavefront Sj(xm,ym)，Sj(xm,ym)＝Pj(xm,ym)exp[iφj(xm,ym)]；
4) Wave front S of emergencej(xm,ym) Transmitted to the diffraction surface to obtain the detection wave front D of the diffraction surfacej(xd,yd)，Dj(xd,yd)＝ρAS[Sj(xm,ym)]；
Wherein, the diffraction surface is a plane where the detector is located;
5) at the diffraction plane with the detected light intensity Ij(xd,yd) Calculating an updated diffraction surface wavefront Dj'(xd,yd)，
6) Updated diffraction surface wavefront Dj'(xd,yd) Reversely transmitting to the modulation surface to obtain an updated modulation surface emergent wave front S'j(xm,ym)，
Wherein the content of the first and second substances,
calculating a reverse angle spectrum;
7) removing modulation effect of j modulation phase to obtain updated modulation surface incident wavefront P'j(xm,ym)，P′j(xm,ym)＝S'j(xm,ym)/exp[iφj(xm,ym)]；
8) Judging whether j is equal to n, if so, completing one-time modulation of all modulation phases, and executing the step 9); if not, making j equal to j +1, and repeatedly executing the steps 3) to 8);
9) updated modulation plane incident wavefront Pj'(xm,ym) Reversely transmitting to the surface to be measured to obtain the complex amplitude O' (x) of the updated light field to be measured of the surface to be measuredo,yo)，
The iteration number num is num + 1;
the surface to be detected is a plane where the light field to be detected is located;
10) if num reaches the set iteration number, executing step 11); if not, returning to the step 2);
11) outputting complex amplitude distribution O' (x) of light field to be measuredo,yo)。
Further, the number of iterations is set to 200.
Further, the modulation system comprises a phase-only spatial light modulator and a computer for controlling the phase-only spatial light modulator.
Further, the modulation system comprises an electric rotating wheel mechanism, a motor and n phase plates;
the n phase plates are arranged on the electric rotating wheel mechanism;
the motor is used for driving the electric rotating wheel mechanism to rotate, and replacement of modulation phases is achieved.
Further, the electric rotating wheel mechanism is a disc;
the n-8, 8 phase plates are uniformly distributed on the disk along the circumferential direction.
Meanwhile, the invention provides a light field complex amplitude measuring method based on multi-step phase modulation, which is characterized by comprising the following steps of:
1) obtaining different diffracted light intensities using multi-step phase modulation
1.1) the modulation system inputs n modulation phases, the n modulation phases form a modulation phase set phi (x)m,ym)，φ(xm,ym)＝[φ1(xm,ym),φ2(xm,ym)…,φt(xm,ym),…φn(xm,ym)]N is an integer of 4 or more;
1.2) the modulation system loads n modulation phases respectively to modulate the light field to be detected, the detector obtains n diffraction light intensities of the light field to be detected, and the n diffraction light intensities form a diffraction light intensity set I (x)d,yd)，I(xd,yd)＝[I1(xd,yd),I2(xd,yd)…,It(xd,yd),…In(xd,yd)]；
Wherein t is an integer greater than 1 and less than n; (x)m,ym) As modulation plane coordinates, (x)d,yd) Is a diffraction plane coordinate;
2) calculating complex amplitude of light field to be measured
2.1) setting the complex amplitude of the light field to be measured as O (x)o,yo)，O(xo,yo)＝exp[iφo(xo,yo)](ii) a The initial iteration number num is 1;
wherein phi iso(xo,yo) Is an assumed initial value of phase;
2.2) measuring the complex amplitude O (x) of the light field to be measuredo,yo) Transmitting the wave to a modulation surface of a modulation system to obtain an incident wavefront P before the j modulation phasej(xm,ym)，Pj(xm,ym)＝ρAS[O(xo,yo)]；
Where ρ isASFor the forward angular spectrum calculation, j ═ 1,2 … … n;
2.3) incident wavefront Pj(xm,ym) J-th modulation phase phi of modulated surfacej(xm,ym) Modulating to obtain modulated emergent wavefront Sj(xm,ym)，Sj(xm,ym)＝Pj(xm,ym)exp[iφj(xm,ym)]；
2.4) emergent wavefront Sj(xm,ym) Transmitted to the diffraction surface to obtain the detection wave front D of the diffraction surfacej(xd,yd)，Dj(xd,yd)＝ρAS[Sj(xm,ym)]；
Wherein, the diffraction surface is a plane where the detector is located;
2.5) detection of the intensity I at the diffraction planej(xd,yd) Calculating an updated diffraction surface wavefront Dj'(xd,yd)，
2.6) updated diffraction surface Probe wavefront Dj'(xd,yd) Reversely transmitting to the modulation surface to obtain an updated modulation surface emergent wave front S'j(xm,ym)，
Wherein the content of the first and second substances,
calculating a reverse angle spectrum;
2.7) removing the modulation effect of the j-th modulation phase to obtain an updated modulation surface incident wavefront P'j(xm,ym)，P′j(xm,ym)＝S'j(xm,ym)/exp[iφj(xm,ym)]；
2.8) judging whether j is equal to n, if so, completing one modulation of all modulation phases, and executing the step 2.9); if not, making j equal to j +1, and repeatedly executing the steps 2.3) to 2.8);
2.9) updated modulation surface incident wavefront P'j(xm,ym) Reversely transmitting to the surface to be measured to obtain the complex amplitude O' (x) of the updated light field to be measured of the surface to be measuredo,yo)，
The iteration number num is num + 1;
the surface to be detected is a plane where the light field to be detected is located;
2.10) if num reaches the set iteration number, executing the step 2.11); if not, returning to the step 2.2);
2.11) outputting complex amplitude distribution O' (x) of the light field to be measuredo,yo)。
Further, in the step 1), the modulation system comprises a pure phase spatial light modulator and a computer, and the computer controls the pure phase spatial light modulator to input n modulation phases;
in the step 2), the modulation surface is a plane where the pure phase spatial light modulator is located.
Further, in the step 1), the modulation system comprises an electric rotating wheel mechanism, a motor and n phase plates; the n phase plates are arranged on the electric rotating wheel mechanism, and the motor is used for driving the electric rotating wheel mechanism to rotate so as to realize the replacement of the modulation phase;
in the step 2), the modulation surface is a plane where the electric rotating wheel mechanism is located.
Further, the electric rotating wheel mechanism is a disc;
the n-8, 8 phase plates are uniformly distributed on the disk along the circumferential direction.
Further, in step 2.1), phio(xo,yo) Is a set of constants or a set of random numbers;
in step 2.10), the number of iterations is set to 200.
Compared with the prior art, the invention has the advantages that:
1. the device and the method load a plurality of modulation phases through a modulation system, modulate the light field to be measured and obtain a plurality of diffraction light intensities, and the existing complex scanning process is cancelled, so that corresponding displacement errors and light path inclination errors cannot be introduced; the device and the method of the invention modulate the light field to be measured by utilizing a plurality of modulation phases after the complex amplitude of the light field to be measured, and can respectively obtain different diffraction light intensities after the complex amplitude of the light field to be measured is modulated. Finally, the complex amplitude distribution of the unknown light field can be obtained by utilizing the modulation phase and the plurality of diffracted light intensities and then through a phase recovery method.
2. In the device and the method, n can be selected to be an integer more than or equal to 4, so that the precision requirement of the complex amplitude measurement result of the light field to be measured can be met; generally, the larger n is, the higher the measurement precision is, the faster the iteration speed is, and the calculation time is reduced; however, when n is 8, the measurement accuracy is already high, the complex amplitude measurement result of the light field to be measured is not greatly affected with the increase of n, but experimental operation steps are increased, so that n is preferably 8, the convergence speed and accuracy of phase recovery can be improved, and unnecessary calculation processes are avoided.
Drawings
FIG. 1 is a schematic working diagram of a first embodiment of the optical field complex amplitude measuring device based on multi-step phase modulation according to the present invention;
FIG. 2 is a flow chart of calculating complex amplitude of a light field to be measured in the light field complex amplitude measuring method based on multi-step phase modulation according to the present invention;
FIG. 3 is a schematic working diagram of a second embodiment of the optical field complex amplitude measuring device based on multi-step phase modulation according to the present invention;
wherein the reference numbers are as follows:
1-pure phase spatial light modulator, 2-computer, 3-electric rotating wheel mechanism, 4-phase plate, 5-motor and 6-detector.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments.
According to the measuring device and method, after the complex amplitude of the unknown light field is modulated, the unknown light field is modulated by a series of modulation phases with specific distribution, and different diffraction light intensities of the modulated complex amplitude of the unknown light field can be respectively obtained. Finally, the complex amplitude distribution of the unknown light field can be obtained by utilizing the modulation phase and a plurality of diffraction light intensities and a phase recovery method.
Example one
As shown in fig. 1, a light field complex amplitude measuring device based on multi-step phase modulation includes a modulation system, a detector 6 and a data processing unit; the modulation system can be composed of a pure-phase spatial light modulator 1 and a computer 2, wherein the pure-phase spatial light modulator 1 is controlled by the computer 2 and is used for loading n modulation phases and modulating the light field to be measured to obtain n diffraction light intensities of the light field to be measured; the n modulation phases are a series of modulation phases with specific distribution and are matched with the phases of different frequency bands of the light field to be detected; n is preferably an integer greater than or equal to 4, and the precision requirement of the complex amplitude measurement result of the light field to be measured can be met. Generally, the larger n is, the higher the measurement precision is, the faster the iteration speed is, and the calculation time is reduced; however, when n is 8, the measurement precision is already high, the complex amplitude measurement result of the light field to be measured is not greatly influenced along with the increase of n, and experimental operation steps are added, so that n is preferably 8, the convergence speed and precision of phase recovery can be improved, and unnecessary calculation process is avoided
The detector 6 is used for receiving the modulated n diffracted light intensities and finally substituting the n diffracted light intensities into a phase recovery method to obtain the wavefront to be measured;
the data processing unit comprises a memory and a processor, the memory having stored thereon a computer program for processing n modulation phases and n diffracted light intensities, the n modulation phases being arranged to form a set of modulation phases phi (x)m,ym)，φ(xm,ym)＝[φ1(xm,ym),φ2(xm,ym)…,φt(xm,ym),…φn(xm,ym)](ii) a Let n diffraction light intensities constitute a diffraction light intensity set I (x)d,yd)，I(xd,yd)＝[I1(xd,yd),I2(xd,yd)…,It(xd,yd),…In(xd,yd)](ii) a When the computer program is executed by a processor, the complex amplitude of the light field to be detected is calculated by a phase recovery method;
wherein t is an integer greater than 1 and less than n; (x)m,ym) As modulation plane coordinates, (x)d,yd) Is a diffraction plane coordinate; .
The embodiment provides a light field complex amplitude measuring method based on multi-step phase modulation, which comprises the following steps:
1) obtaining different diffraction light intensities by adopting multi-step phase modulation technology
1.1) pure phase spatial light modulator 1 is controlled by computer 2 to input n modulation phases, and the n modulation phases form a modulation phase set phi (x)m,ym)，φ(xm,ym)＝[φ1(xm,ym),φ2(xm,ym)…,φt(xm,ym),…φn(xm,ym)]N is an integer of 4 or more;
1.2) when a modulation phase is loaded every time, the detector 6 obtains the diffraction light intensity once, the modulation system loads n modulation phases respectively to modulate the light field to be detected, n diffraction light intensities of the light field to be detected are obtained, and the n diffraction light intensities form a corresponding diffraction light intensity set I (x)d,yd)，I(xd,yd)＝[I1(xd,yd),I2(xd,yd)…,It(xd,yd),…In(xd,yd)]；
2) Phase recovery method for calculating complex amplitude of light field to be measured
By modulating the phase phi (x)m,ym) And the obtained diffracted light intensity I (x)d,yd) And the complex amplitude of the light field to be measured is obtained by a phase recovery method. The specific steps of the phase recovery method for obtaining the complex amplitude of the light field to be detected are as follows, and the corresponding algorithm flow is shown in fig. 2:
2.1) initially assuming that the complex amplitude of the light field to be measured is O (x)o,yo)，O(xo,yo)＝exp[iφo(xo,yo)](ii) a The initial iteration number num is 1.
Wherein phi iso(xo,yo) Is an assumed initial value of phase, which is a set of constants or a set of random numbers; the group of constants means that all values of the initial phase value are equal; the random numbers refer to that all values of the initial phase values are arbitrary values, and no correlation exists among all values;
2.2) measuring the complex amplitude O (x) of the light field to be measuredo,yo) Transmitting to the modulation surface to obtain the incident wavefront P before the j modulation phasej(xm,ym)，Pj(xm,ym)＝ρAS[O(xo,yo)]；
Where ρ isASFor the calculation of the forward angle spectrum, j is 1,2 … … n, and the modulation surface is the plane where the pure phase spatial light modulator 1 is located;
2.3) incident wavefront Pj(xm,ym) J-th modulation phase phi of modulated surfacej(xm,ym) Modulating to obtain modulated emergent wavefront Sj(xm,ym)，Sj(xm,ym)＝Pj(xm,ym)exp[iφj(xm,ym)]；
2.4) emergent wavefront Sj(xm,ym) Transmitted to the diffraction surface to obtain the detection wave front D of the diffraction surfacej(xd,yd)，Dj(xd,yd)＝ρAS[Sj(xm,ym)]；
Wherein, the diffraction surface is a plane where the detector 6 is located;
2.5) detection of the intensity I at the diffraction planej(xd,yd) Calculating an updated diffraction surface wavefront Dj'(xd,yd)，
2.6) updated diffraction surface Probe wavefront Dj'(xd,yd) Reversely transmitting to the modulation surface to obtain an updated modulation surface emergent wave front S'j(xm,ym)，
Wherein the content of the first and second substances,
calculating a reverse angle spectrum;
2.7) removing the modulation effect of the j-th modulation phase to obtain an updated modulation surface incident wavefront P'j(xm,ym)，P′j(xm,ym)＝S'j(xm,ym)/exp[iφj(xm,ym)]；
2.8) judging whether j is equal to n, if so, completing one modulation of all modulation phases, and executing the step 2.9); if not, making j equal to j +1, and repeatedly executing the steps 2.3) to 2.8);
2.9) updated modulation surface incident wavefront P'j(xm,ym) Reversely transmitting to the surface to be measured to obtain the complex amplitude O' (x) of the updated light field to be measured of the surface to be measuredo,yo)，
The iteration number num is num + 1;
the surface to be detected is a plane where the light field to be detected is located;
2.10) checking the convergence of the recovery result, and if num reaches a set iteration number, generally num is more than or equal to 200, executing the step 2.11); if not, returning to the step 2.2);
2.11) outputting complex amplitude distribution O' (x) of the light field to be measuredo,yo)。
Example two
The difference from the first embodiment is that:
1) as shown in fig. 3, the modulation system in the optical field complex amplitude measuring device can be composed of an electric rotating wheel mechanism 3, a motor 5, n phase plates 4; the n phase plates 4 are arranged on the electric rotating wheel mechanism 3; the motor 5 is used for driving the electric rotating wheel mechanism 3 to rotate, and the modulation phase is replaced. The electric rotating wheel mechanism 3 is usually a disc; and n is 8, and 8 phase plates 4 are uniformly distributed on the disk along the circumferential direction.
2) In the light field complex amplitude measuring method: in the step 1), the modulation system comprises an electric rotating wheel mechanism 3, a motor 5 and n phase plates 4; the n phase plates 4 are arranged on the electric rotating wheel mechanism 3, and the electric rotating wheel mechanism 3 is driven to rotate through the motor 5, so that the modulation phase is replaced;
in step 2), the modulation surface is a plane where the electric rotating mechanism 3 is located.
The above description is only for the purpose of describing the preferred embodiments of the present invention and does not limit the technical solutions of the present invention, and any known modifications made by those skilled in the art based on the main technical concepts of the present invention fall within the technical scope of the present invention.
Claims (10)
1. A light field complex amplitude measuring device based on multi-step phase modulation is characterized in that: comprises a modulation system, a detector (6) and a data processing unit;
the modulation system is used for loading n modulation phases and modulating the light field to be detected to obtain n diffraction light intensities of the light field to be detected, wherein n is an integer greater than or equal to 4; the n modulation phases are matched with the phases of different frequency bands of the light field to be detected;
the detector (6) is used for receiving the modulated n diffracted light intensities;
the data processing unit comprises a memory and a processor, the memory is stored with a computer program for processing n modulation phases and n diffracted light intensities, and the n modulation phases are set to form a modulation phase set phi (x)m,ym)，φ(xm,ym)＝[φ1(xm,ym),φ2(xm,ym)…,φt(xm,ym),…φn(xm,ym)](ii) a Let n diffraction light intensities constitute a diffraction light intensity set I (x)d,yd)，I(xd,yd)＝[I1(xd,yd),I2(xd,yd)…,It(xd,yd),…In(xd,yd)]；
Wherein t is an integer greater than 1 and less than n; (x)m,ym) As modulation plane coordinates, (x)d,yd) Is a diffraction plane coordinate;
the computer program when executed by a processor implementing the steps of:
1) setting the complex amplitude of the light field to be measured as O (x)o,yo)，O(xo,yo)＝exp[iφo(xo,yo)](ii) a The initial iteration number num is 1;
wherein phi iso(xo,yo) Is an assumed initial value of phase;
2) the complex amplitude O (x) of the light field to be measuredo,yo) Transmitting the wave to a modulation surface of a modulation system to obtain an incident wavefront P before the j modulation phasej(xm,ym)，Pj(xm,ym)＝ρAS[O(xo,yo)]；
Where ρ isASFor the forward angular spectrum calculation, j ═ 1,2 … … n;
3) incident wavefront Pj(xm,ym) J-th modulation phase phi of modulated surfacej(xm,ym) Modulating to obtain modulated emergent wavefront Sj(xm,ym)，Sj(xm,ym)＝Pj(xm,ym)exp[iφj(xm,ym)]；
4) Wave front S of emergencej(xm,ym) Transmitted to the diffraction surface to obtain the detection wave front D of the diffraction surfacej(xd,yd)，Dj(xd,yd)＝ρAS[Sj(xm,ym)]；
Wherein the diffraction surface is a plane where the detector (6) is located;
5) at the diffraction plane with the detected light intensity Ij(xd,yd) Calculating an updated diffraction surface wavefront Dj'(xd,yd)，
6) Updated diffraction surface wavefront Dj'(xd,yd) Reversely transmitting to the modulation surface to obtain an updated modulation surface emergent wave front S'j(xm,ym)，
Wherein the content of the first and second substances,
calculating a reverse angle spectrum;
7) removing modulation effect of j modulation phase to obtain updated modulation surface incident wavefront P'j(xm,ym)，P′j(xm,ym)＝S'j(xm,ym)/exp[iφj(xm,ym)]；
8) Judging whether j is equal to n, if so, completing one-time modulation of all modulation phases, and executing the step 9); if not, making j equal to j +1, and repeatedly executing the steps 3) to 8);
9) furthermore, the utility modelNew modulation surface incident wavefront P'j(xm,ym) Reversely transmitting to the surface to be measured to obtain the complex amplitude O' (x) of the updated light field to be measured of the surface to be measuredo,yo)，
The iteration number num is num + 1;
the surface to be detected is a plane where the light field to be detected is located;
10) if num reaches the set iteration number, executing step 11); if not, returning to the step 2);
11) outputting complex amplitude distribution O' (x) of light field to be measuredo,yo)。
2. The light field complex amplitude measuring device based on multi-step phase modulation according to claim 1, characterized in that: the number of iterations was set to 200.
3. The light field complex amplitude measuring device based on multi-step phase modulation according to claim 2, characterized in that: the modulation system comprises a phase-only spatial light modulator (1) and a computer (2) for controlling the phase-only spatial light modulator (1).
4. The light field complex amplitude measuring device based on multi-step phase modulation according to claim 2, characterized in that: the modulation system comprises an electric rotating wheel mechanism (3), a motor (5) and n phase plates (4);
the n phase plates (4) are arranged on the electric rotating wheel mechanism (3);
the motor (5) is used for driving the electric rotating wheel mechanism (3) to rotate, and the modulation phase is replaced.
5. The light field complex amplitude measuring device based on multi-step phase modulation according to claim 4, wherein: the electric rotating wheel mechanism (3) is a disc;
the n-8 and 8 phase plates (4) are uniformly distributed on the disc along the circumferential direction.
6. A light field complex amplitude measuring method based on multi-step phase modulation is characterized by comprising the following steps:
1) obtaining different diffracted light intensities using multi-step phase modulation
1.1) the modulation system inputs n modulation phases, the n modulation phases form a modulation phase set phi (x)m,ym)，φ(xm,ym)＝[φ1(xm,ym),φ2(xm,ym)…,φt(xm,ym),…φn(xm,ym)]N is an integer of 4 or more;
1.2) the modulation system loads n modulation phases respectively to modulate the light field to be detected, the detector (6) obtains n diffraction light intensities of the light field to be detected, and the n diffraction light intensities form a diffraction light intensity set I (x)d,yd)，I(xd,yd)＝[I1(xd,yd),I2(xd,yd)…,It(xd,yd),…In(xd,yd)]；
Wherein t is an integer greater than 1 and less than n; (x)m,ym) As modulation plane coordinates, (x)d,yd) Is a diffraction plane coordinate;
2) calculating complex amplitude of light field to be measured
2.1) setting the complex amplitude of the light field to be measured as O (x)o,yo)，O(xo,yo)＝exp[iφo(xo,yo)](ii) a The initial iteration number num is 1;
wherein phi iso(xo,yo) Is an assumed initial value of phase;
2.2) measuring the complex amplitude O (x) of the light field to be measuredo,yo) Transmitting the wave to a modulation surface of a modulation system to obtain an incident wavefront P before the j modulation phasej(xm,ym)，Pj(xm,ym)＝ρAS[O(xo,yo)]；
Where ρ isASFor the forward angular spectrum calculation, j ═ 1,2 … … n;
2.3) incident wavefront Pj(xm,ym) J-th modulation phase phi of modulated surfacej(xm,ym) Modulating to obtain modulated emergent wavefront Sj(xm,ym)，Sj(xm,ym)＝Pj(xm,ym)exp[iφj(xm,ym)]；
2.4) emergent wavefront Sj(xm,ym) Transmitted to the diffraction surface to obtain the detection wave front D of the diffraction surfacej(xd,yd)，Dj(xd,yd)＝ρAS[Sj(xm,ym)]；
Wherein the diffraction surface is a plane where the detector (6) is located;
2.5) detection of the intensity I at the diffraction planej(xd,yd) Calculating an updated diffraction surface wavefront Dj'(xd,yd)，
2.6) updated diffraction surface Probe wavefront Dj'(xd,yd) Reversely transmitting to the modulation surface to obtain an updated modulation surface emergent wave front S'j(xm,ym)，
Wherein the content of the first and second substances,
calculating a reverse angle spectrum;
2.7) removing the modulation effect of the j-th modulation phase to obtain an updated modulation surface incident wavefront P'j(xm,ym)，P′j(xm,ym)＝S'j(xm,ym)/exp[iφj(xm,ym)]；
2.8) judging whether j is equal to n, if so, completing one modulation of all modulation phases, and executing the step 2.9); if not, making j equal to j +1, and repeatedly executing the steps 2.3) to 2.8);
2.9) updated modulation surface incident wavefront P'j(xm,ym) Reversely transmitting to the surface to be measured to obtain the complex amplitude O' (x) of the updated light field to be measured of the surface to be measuredo,yo)，
The iteration number num is num + 1;
the surface to be detected is a plane where the light field to be detected is located;
2.10) if num reaches the set iteration number, executing the step 2.11); if not, returning to the step 2.2);
2.11) outputting complex amplitude distribution O' (x) of the light field to be measuredo,yo)。
7. The light field complex amplitude measurement method based on multi-step phase modulation according to claim 6, characterized in that: in the step 1), the modulation system comprises a pure phase spatial light modulator (1) and a computer (2), wherein the computer (2) controls the pure phase spatial light modulator (1) to input n modulation phases;
in the step 2), the modulation surface is a plane where the pure-phase spatial light modulator (1) is located.
8. The light field complex amplitude measurement method based on multi-step phase modulation according to claim 6, characterized in that: in the step 1), the modulation system comprises an electric rotating wheel mechanism (3), a motor (5) and n phase plates (4); the n phase plates (4) are arranged on the electric rotating wheel mechanism (3), and the motor (5) is used for driving the electric rotating wheel mechanism (3) to rotate so as to realize the replacement of modulation phases;
in the step 2), the modulation surface is a plane where the electric rotating wheel mechanism (3) is located.
9. The light field complex amplitude measurement method based on multi-step phase modulation according to claim 8, characterized in that: the electric rotating wheel mechanism (3) is a disc;
the n-8 and 8 phase plates (4) are uniformly distributed on the disc along the circumferential direction.
10. The light field complex amplitude measuring method based on multi-step phase modulation according to any one of claims 6 to 9, characterized in that: in step 2.1), phio(xo,yo) Is a set of constants or a set of random numbers;
in step 2.10), the number of iterations is set to 200.
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