Method for determining the amount of phase modulation of a spatial light modulator

Abstract

The application relates to a method for determining the phase modulation amount of a spatial light modulator, comprising the following steps: setting up a small-angle light path, wherein the small-angle light path comprises a laser, a beam expander, a polarizer, a spatial light modulator, an analyzer and a power meter arranged along the light path; the spatial light modulator is connected to a computer through a video line, the power meter is connected to the computer through a data line, and the computer is installed with spatial light modulator control software and power meter software; the computer is used to load a 0-255 pure grayscale image through the spatial light modulator control software; the computer is used to collect the light power size reflected by the spatial light modulator under different grayscale images through the power meter software, and grayscale-power curve data are obtained; and the obtained grayscale-power data curve is processed to determine the phase modulation amount of the spatial light modulator. The application improves the accuracy of the obtained phase modulation amount, and the light path is simple to set up.

Description

Technical Field

[0001] This invention relates to a method for determining the phase modulation amount of a spatial light modulator. Background Technology

[0002] With the development of digital optics technology, spatial light modulators are used in various fields such as optical field manipulation, wavefront correction, computational holography, optical tweezers, optical microscopy, and adaptive optics. Phase modulation, as one of the important parameters of spatial light modulators, is a measure of their phase modulation characteristics. Obtaining accurate phase modulation parameters is crucial for the design and calculation of phase diagrams in experiments.

[0003] The working principle of a spatial light modulator is to independently control each pixel by changing the addressing voltage. Current technology maps the device's driving voltage to grayscale values ​​displayed on a computer. Users load a two-dimensional grayscale image with the same pixel resolution as the spatial light modulator into the modulator's driving software. The grayscale image typically ranges from 0 to 255, and each grayscale value corresponds one-to-one with the driving voltage applied to the pixel unit of the spatial light modulator. By changing the grayscale values ​​of the image, users can control the voltage.

[0004] Most existing methods obtain the phase modulation amount by analyzing the positions of bright and dark interference fringes in the acquired diffraction pattern. However, since the interference fringes have a certain width, a large error is introduced when calibrating the position of the interference fringes, resulting in a large deviation in the results. Users cannot obtain a relatively accurate phase modulation amount parameter, which affects subsequent experiments. Summary of the Invention

[0005] In view of this, it is necessary to provide a method for determining the phase modulation amount of a spatial light modulator, which can improve the accuracy of the obtained phase modulation amount and simplify the optical path setup.

[0006] This invention provides a method for determining the phase modulation amount of a spatial light modulator, the method comprising the following steps: a. constructing a small-angle optical path, the small-angle optical path comprising: a laser, a beam expander, a polarizer, a spatial light modulator, an analyzer, and a power meter arranged along the optical path; the spatial light modulator is connected to a computer via a video cable, the power meter is connected to the computer via a data cable, and the computer is equipped with spatial light modulator control software and power meter software; b. loading a 0-255 pure grayscale image using the computer and the spatial light modulator control software; collecting the light power reflected by the spatial light modulator under different grayscale images using the computer and the power meter software, obtaining grayscale-power curve data; c. processing the obtained grayscale-power data curve to determine the phase modulation amount of the spatial light modulator.

[0007] Specifically, the power meter measures the optical power of the 0th-order light diffracted by the spatial light modulator; the spatial light modulator is adjusted to operate in amplitude mode; and the angle between the polarizer and the analyzer is orthogonal.

[0008] Specifically, step b includes:

[0009] The time interval for playing grayscale images is set through the spatial light modulator control software;

[0010] The data collection time period is set using the power meter software.

[0011] Specifically, step c includes:

[0012] Step S31: Extract the valid data range from the obtained grayscale-power curve data;

[0013] Step S32: Normalize the selected valid data using the normalization formula to obtain normalized data;

[0014] Step S33: Subtract the normalized data to obtain the subtracted data;

[0015] Step S34: Calculate the phase modulation amount data using the subtracted data;

[0016] Step S35: Obtain multiple curve data using phase modulation data;

[0017] Step S36: Use multiple curve data to draw multiple curves, and select a portion of data from each curve to combine them according to the curve trend.

[0018] Specifically, the normalization formula is: (each data value - the minimum value in the data) / (the maximum value in the data - the minimum value in the data).

[0019] Specifically, subtracting the normalized data means subtracting each normalized data point from 1 and then flipping the data.

[0020] Specifically, step S34 includes:

[0021] The phase modulation data is calculated according to Formula 2:

[0022] Formula 2: 2-ASIN(SQRT(each subtracted data))*2 / π

[0023] Specifically, the multiple curve data correspond to the multiple flips of the phase modulation amount data curve.

[0024] Specifically, step S36 includes:

[0025] Select 2 to 3 data segments from each curve.

[0026] This invention utilizes power data to calculate the phase modulation amount, which helps improve the accuracy of the obtained phase modulation amount. At the same time, it can obtain the light utilization rate of the spatial light modulator when different gray values ​​are loaded. Furthermore, it can also obtain the correspondence between gray values ​​and light utilization rate, such as linearity.

[0027] Furthermore, traditional interference typically requires two beams of light, and the two beams need to be adjusted to produce interference. The positions of the interference fringes collected in the interference experiment also need to be calibrated. The optical path is complex and difficult to adjust, making it not easy to learn. Moreover, the position calibration of the interference fringes is relatively rough and has a large error. In contrast, this invention only requires measuring the optical power of the zero-order light emitted from the spatial light modulator, which is easier to detect. The optical path is simple to build, requiring only one beam, making it very easy to learn and improving measurement accuracy. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method for determining the phase modulation amount of a spatial light modulator according to the present invention;

[0029] Figure 2 A schematic diagram of a small-angle optical path provided in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram illustrating the correspondence between gray levels and grayscale images provided in an embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram illustrating the acquisition of multiple curve data using phase modulation data, provided in an embodiment of the present invention.

[0032] Figure 5 This is a schematic diagram illustrating the correspondence between grayscale and phase modulation amounts provided in an embodiment of the present invention. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0034] Please see Figure 1 This is a flowchart of a preferred embodiment of the method for determining the phase modulation amount of a spatial light modulator according to the present invention.

[0035] Step S1, build as follows Figure 2 The small-angle optical path shown includes: a laser, a beam expander, a polarizer, a spatial light modulator, an analyzer, and a power meter arranged along the optical path. Wherein:

[0036] The video cable of the spatial light modulator is connected to the computer, and the power cord of the spatial light modulator is powered on (not shown in the figure); the data cable of the power meter is connected to the computer, and the power meter measures the optical power of the 0th-order light diffracted by the spatial light modulator. The computer has spatial light modulator control software and power meter software installed.

[0037] The spatial light modulator is adjusted to operate in amplitude mode, and the angle relationship between the polarizer and the analyzer is orthogonal;

[0038] For example, for a phase-type spatial light modulator, when the alignment angle of the spatial light modulator is 0°, in amplitude operation mode, the angle of the polarizer is generally adjusted to 45° and the angle of the analyzer is generally adjusted to -45°.

[0039] For example, for an amplitude-phase type spatial light modulator, the angle of the polarizer is generally adjusted to 0° and the angle of the analyzer is generally adjusted to 90°. At this time, the spatial light modulator is in amplitude working mode.

[0040] Step S2 involves using a computer to load a 0-255 pure grayscale image via spatial light modulator control software; and using a computer to collect the light power reflected by the spatial light modulator under different grayscale images via power meter software, thus obtaining grayscale-power curve data. Specifically, this includes:

[0041] Using a computer and spatial light modulator control software, a pure grayscale image ranging from 0 to 255 (256 levels) is loaded. Each grayscale level corresponds to one grayscale image. Please refer to [reference needed]. Figure 3 A total of 256 images were collected. The power of light reflected by the spatial light modulator under different grayscale images was collected using a computer and power meter software to obtain grayscale-power curve data.

[0042] Among them: the time interval for grayscale image playback is set by the spatial light modulator control software: in this embodiment, the playback interval is set to 100ms;

[0043] The power meter software sets the acquisition time period. In this embodiment, the acquisition time period is greater than or equal to the playback time of 256 grayscale images, for example, 35 seconds. The power meter software acquisition rate is once per second. In this embodiment, power data is acquired every 10 grayscale levels to obtain grayscale-power curve data.

[0044] Step S3 involves processing the obtained grayscale-power data curve to determine the phase modulation amount of the spatial light modulator. Specifically, this includes:

[0045] Step S31: Extract the valid data range from the obtained grayscale-power curve data;

[0046] Step S32: Normalize the selected valid data using a normalization formula to obtain normalized data; wherein, the normalization formula is: (each data value - minimum value in the data) / (maximum value in the data - minimum value in the data);

[0047] Step S33: Subtract the normalized data to obtain the subtracted data; that is: 1 - each normalized data, and then flip the data.

[0048] Step S34: Using the subtracted data, calculate the phase modulation amount data according to Formula 2.

[0049] 2-ASIN(SQRT(each subtracted data))*2 / π; Formula 2

[0050] Step S35: Obtain multiple curve data using phase modulation data;

[0051] Among them, multiple curve data correspond to multiple flips of the phase modulation amount data curve, such as... Figure 4 As shown;

[0052] Step S36: Multiple curves are plotted using the data from multiple curves, and a subset of data is selected from each curve and combined according to the curve trend. In this embodiment, 2-3 data segments are selected from each curve:

[0053] For example, for Figure 4 The acquired data is divided into three segments, which are then combined. The combined data is then calibrated to ensure the phase modulation data changes from 0, resulting in a new data curve, i.e., the phase modulation curve, and the corresponding phase modulation value. The three selected data segments are: data before the intersection of series 2 and series 1 + intermediate data between the intersection of series 1 and series 2 before the intersection of series 1 and series 3 + data after the intersection of series 1 and series 3. The extracted data is integrated and subjected to coordinate transformation to obtain the correspondence between grayscale and phase modulation value, as shown below. Figure 5 As shown.

[0054] Although the present invention has been described with reference to the present preferred embodiments, those skilled in the art should understand that the above preferred embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the amount of phase modulation of a spatial light modulator, characterized by, The method comprises the following steps: a. Build a small-angle light path, which comprises a laser, a beam expander, a polarizer, a spatial light modulator, a power meter and a power meter along the light path; the spatial light modulator is connected to a computer through a video line, and the power meter is connected to the computer through a data line; the computer is installed with spatial light modulator control software and power meter software; b. Load 0-255 pure gray scale images into the computer through the spatial light modulator control software; collect the light power reflected by the spatial light modulator under different gray scale images through the power meter software, and obtain the gray power curve data; c. Process the obtained gray power data curve to determine the phase modulation amount of the spatial light modulator; The step c comprises: Step S31, cut the effective data range from the obtained gray power curve data; Step S32, normalize the selected effective data using a normalization formula to obtain normalized data; Step S33, subtract the normalized data to obtain subtracted data; Step S34, calculate the phase modulation amount data using the subtracted data; Step S35, obtain multiple curve data using the phase modulation amount data; Step S36, draw multiple curves using the multiple curve data, and select part of the data from each curve according to the curve trend for combination; wherein: The subtraction of the normalized data is that 1 minus each normalized data, and the data is flipped.

2. The method of claim 1, wherein: The power meter measures the light power of the 0th order light diffracted by the spatial light modulator; the spatial light modulator is adjusted to work in amplitude mode; and the angle relationship between the polarizer and the analyzer is orthogonal.

3. The method of claim 2, wherein, The step b comprises: Set the time interval of gray scale image playback through the spatial light modulator control software; Set the acquisition time period through the power meter software.

4. The method of claim 3, wherein, The normalization formula is: (each data value - minimum value in the data) / (maximum value in the data - minimum value in the data).

5. The method of claim 4, wherein, The step S34 comprises: Calculate the phase modulation amount data according to the following formula: 2-ASIN(SQRT(each subtracted data))*2 / π.

6. The method of claim 5, wherein, The multiple curve data corresponds to multiple flipped data of the phase modulation amount data curve.

7. The method of claim 6, wherein, The step S36 comprises: Select 2-3 segments of data from each curve.

Images