CN113281901B - Method for designing diffractive optical element for suppressing regular noise - Google Patents
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Abstract
The application discloses a method for designing a diffractive optical element for suppressing regular noise, comprising: a. determining a first target light field having a particular pattern to be projected by the diffractive optical element; b. adding background noise into the first target light field to obtain a second target light field; deriving a phase distribution of the diffractive optical element from the second target light field design. According to the present invention, by adding background noise to a first target light field having a specific pattern to be projected by a diffractive optical element and designing a phase distribution of the diffractive optical element based on a second target light field including the first target light field and the added background noise, a diffractive optical element capable of projecting the specific pattern accurately, clearly, and with high contrast is obtained. Thus, under the condition of not requiring higher requirements on the design theory and the processing precision of the diffraction optical element, the regular noise in the specific pattern when the diffraction optical element for projecting the specific pattern is designed in the prior art can be eliminated, and the design purpose is realized.
Description
Technical Field
The present invention relates generally to the field of precision optics, and more particularly, to a method for designing a diffractive optical element.
Background
Diffractive Optical Elements (DOE) can be used for laser beam shaping, such as homogenizing, collimating, focusing, and patterning.
When designing a diffractive optical element that forms a specific pattern, the specific pattern formed by the diffractive optical element is generally required to be clear, high in contrast, and accurate in angle of view. However, neither scalar design theory nor vector design theory of light propagation can completely simulate the propagation mode of light waves in real situations. Furthermore, due to the limitations of the processing technology, deviations between the actually processed diffractive optical elements and the results of the theoretical design always exist. Therefore, in the actual design and manufacturing process, some non-uniform regular noise related to the specific pattern often occurs in the specific pattern obtained by the designed diffractive optical element. These regular noises have a certain intensity, affect the display of a specific pattern, and are difficult to remove by the existing design method or improvement of the processing accuracy.
Disclosure of Invention
The invention aims to provide a design method of a diffraction optical element, which can eliminate regular noise in a specific pattern obtained by the designed diffraction optical element, obtain the specific pattern with clear pattern, high contrast and accurate view angle, and overcome the defects in the prior art.
According to an aspect of the present invention, there is provided a diffractive optical element design method for suppressing regular noise, including:
a. determining a first target light field having a first specific pattern to be projected by the diffractive optical element;
b. adding background noise to said first target light field, thereby obtaining a second target light field having a second specific pattern consisting of the first specific pattern of the first target light field and the background noise; and
c. deriving a phase distribution of the diffractive optical element from the second target light field design,
wherein the background noise is added for displaying a first target light field having a first specific pattern when projected using the diffractive optical element having the phase distribution, thereby suppressing regular noise having an intensity and associated with the first specific pattern contained in the pattern projected by the diffractive optical element.
Preferably, the method further comprises:
d. simulating based on the designed phase distribution of the diffractive optical element to obtain a simulated light field, evaluating the effect of the simulated light field, and adjusting the background noise according to the evaluation result; and
e. and repeating the steps b-d until the effect of the simulated light field meets the design requirement.
Preferably, in step d, the adjusting the background noise according to the evaluation result includes adjusting at least one of the intensity of the background noise and the distribution area of the background noise.
Preferably, step d comprises: increasing at least one of a strength of the background noise and a distribution area of the background noise if the simulated light field is in presence of regular noise associated with the first target light field in addition to the background noise as compared to the first target light field.
Preferably, step d comprises: reducing at least one of an intensity of the background noise and a distribution area of the background noise if the simulated light field is free of regular noise associated with the first target light field other than the background noise as compared to the first target light field, but an efficiency of the simulated light field is less than a design requirement.
Preferably, the background noise is distributed in a global sense of the first target light field.
Preferably, the background noise is distributed in a locally continuous area of the first target light field, and the locally continuous area covers the first specific pattern.
Preferably, the background noise is uniform noise.
Preferably, the background noise is random intensity noise.
Preferably, the intensity of the background noise is gradually decreased from the first specific pattern to a blank region.
Preferably, the step c further includes assigning a gray value to the second target light field according to the light intensity, where the gray value is the maximum max when the light intensity is maximum, and the gray value is 0 when the light intensity is not maximum, and the gray value g corresponding to the background noise satisfies: 0< -g/max ≦ 0.05, and calculating a phase distribution of the diffractive optical element from the second target light field represented by the gray scale values.
According to the present invention, by adding background noise to a first target light field having a specific pattern to be projected by a diffractive optical element and designing a phase distribution of the diffractive optical element based on a second target light field including the first target light field and the added background noise, a diffractive optical element capable of projecting the specific pattern accurately, clearly, and with high contrast is obtained. Thus, under the condition of not requiring higher requirements on the design theory and the processing precision of the diffractive optical element, the regular noise in the specific pattern when the diffractive optical element for projecting the specific pattern is designed in the prior art can be eliminated, and the design purpose is realized.
Drawings
FIG. 1 is a schematic diagram of a target light field with a particular pattern being a straight line segment;
FIG. 2 is a prior art view of an actual light field obtained by light projection from a diffractive optical element derived as the target light field of FIG. 1;
FIG. 3 is a schematic diagram of an 8-point circle as the target light field for a particular pattern;
FIG. 4 is a prior art view of a simulated light field of a diffractive optical element taken with FIG. 3 as the target light field;
FIG. 5 is a prior art view of an actual light field obtained by light projection from a diffractive optical element derived using FIG. 3 as the target light field;
FIG. 6 is a flow chart of a diffractive optical element design method according to the present invention;
FIG. 7 is a flow chart of a preferred embodiment of a diffractive optical element design method according to the present invention;
FIG. 8 is a schematic diagram of a second target light field in accordance with the first embodiment of the diffractive optical element design method of the present invention resulting from the addition of background noise to the target light field shown in FIG. 1;
FIG. 9 is a view of a simulated light field of a diffractive optical element taken from FIG. 8 as a second target light field in accordance with a first embodiment of a diffractive optical element design method according to the present invention;
FIGS. 10, 11 and 12 are schematic illustrations of a second target light field for various arrangements of a second embodiment of a method of designing a diffractive optical element according to the invention resulting from the addition of background noise to the target light field shown in FIG. 3;
FIG. 13 is a view of a simulated light field of a diffractive optical element taken from FIG. 10 as a second target light field in accordance with a second embodiment of the diffractive optical element design method according to the present invention;
FIG. 14 is a view of an actual light field obtained by light projection by the diffractive optical element obtained as the second target light field in FIG. 10 according to the second embodiment of the diffractive optical element design method according to the present invention;
FIG. 15 is a schematic illustration of a target light field with an I-shaped pattern as the specific pattern;
FIG. 16 is a diagram of a second target light field resulting from the addition of background noise to the target light field shown in FIG. 15 for a third embodiment of a method of designing a diffractive optical element according to the present invention;
FIG. 17 is a prior art illustration of a simulated light field of a diffractive optical element obtained with the target light field of FIG. 15;
FIG. 18 is a prior art view of an actual light field obtained by light projection from a diffractive optical element derived using FIG. 15 as the target light field;
FIG. 19 is a view of a simulated light field of the diffractive optical element resulting from FIG. 16 as a second target light field in accordance with the third embodiment of the diffractive optical element design method according to the present invention;
FIG. 20 is a view of an actual light field obtained by light projection by the diffractive optical element obtained as the second target light field in FIG. 16 according to the third embodiment of the diffractive optical element designing method according to the present invention;
FIG. 21 is a schematic diagram of a target light field with two straight line segments as the specific pattern;
FIG. 22 is a schematic illustration of a second target light field in accordance with a fourth embodiment of a method of designing a diffractive optical element according to the invention resulting from the addition of background noise to the target light field illustrated in FIG. 21;
FIG. 23 is a prior art view of a simulated light field for a diffractive optical element obtained with the target light field of FIG. 21;
FIG. 24 is a prior art view of an actual light field obtained by light projection from a diffractive optical element derived using FIG. 21 as the target light field;
FIG. 25 is a view of a simulated light field of a diffractive optical element taken from FIG. 22 as a second target light field in accordance with a fourth embodiment of a diffractive optical element design method according to the present invention; and
fig. 26 is a view of an actual light field obtained by light projection by the diffractive optical element obtained with fig. 22 as the second target light field according to the fourth embodiment of the diffractive optical element designing method according to the present invention.
Detailed Description
The present application will be described in further detail with reference to the following drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention. It should be noted that, for convenience of description, only the portions related to the present invention are shown in the drawings.
The diffractive optical element design method in the present invention is suitable for projecting a diffractive optical element having a specific pattern in order to eliminate regular noise other than the specific pattern contained in the pattern projected by the diffractive optical element. So-called regular noise is non-uniform noise, has a certain intensity, and is associated with a specific pattern, affecting accurate, clear display of the specific pattern.
Fig. 1 is a schematic diagram of a target light field, indicated generally at 101, having a straight line segment 111 as a particular pattern, with the straight line segment as the particular pattern. Fig. 2 is a view of an actual light field obtained by light projection by the diffractive optical element obtained by taking fig. 1 as a target light field in the prior art, wherein the actual light field is generally indicated by 104, and the actual light field 104 includes a straight line segment 141 corresponding to a specific pattern, and regular noises 142 and 143 associated with the straight line segment 141, and the regular noises 142 and 143 are extended line segments of the straight line segment 141, and have strong luminance, so that the field angle of the straight line segment 111 in the target light field 101 shown in fig. 1 deviates from the design. Fig. 3 is a schematic diagram of an 8-point circle as the target light field of the particular pattern, where the target light field is generally indicated at 201, and the target light field 201 has an 8-point circle 211 as the particular pattern. FIG. 4 is a prior art view of a simulated light field of a diffractive optical element taken from FIG. 3 as the target light field, generally indicated at 203, as seen in simulated light field 203, including distinct regular point noise 232 in addition to the 8-point annular pattern comprising target light field 231. Fig. 5 is a prior art view of an actual light field obtained by light projection from a diffractive optical element derived as the target light field from fig. 3, the actual light field shown in fig. 5 being indicated generally at 204 and comprising, as seen from the actual light field 204, distinct regular point noise 242 in addition to the 8-point annular pattern comprising the target light field 241.
Such regular noise shown in fig. 2, 4 and 5 is also difficult to eliminate by improving the design algorithm of the diffractive optical element or improving the machining accuracy of the diffractive optical element. However, the inventors have found that, in designing a diffractive optical element, regular noise can be effectively suppressed by adding background noise to a target light field, and a specific target pattern can be obtained more clearly.
Fig. 6 is a flow chart of the general principles of a diffractive optical element design method according to the present invention. A diffractive optical element design method according to the present invention, generally designated by reference numeral 100, includes three steps S110, S120 and S130. In step S110, a first target light field with a specific pattern to be projected by the diffractive optical element is determined. In step S120, a background noise is added to the first target light field to obtain a second target light field. In step S130, a phase distribution of the diffractive optical element is designed according to the second target light field. In step S130, the phase distribution of the diffractive optical element is calculated by using computer-aided software according to the input optical field distribution (e.g., the light source-related parameter) and the output optical field distribution (i.e., the second target optical field obtained in step S120) in the known optical system through an iterative optimization Algorithm, etc., wherein the iterative optimization Algorithm includes a geschberg-Saxton Algorithm (GS), a Simulated Annealing Algorithm (SA), a Genetic Algorithm (GA), and a Yang-guest Algorithm (YG), etc.
The inventors have also found that in the design of diffractive optical elements, the suppression of regular noise in the simulation or actual projection results of the designed diffractive optical element is more pronounced as the intensity of the background noise added in the target light field increases, but if the intensity of the background noise continues to increase, this can result in too much energy in the projected light being distributed to the background noise, thereby reducing the effective energy fraction of the particular pattern. Therefore, when a diffractive optical element capable of eliminating the regular noise is actually designed, it is preferable to evaluate the effect of the simulated light field of the diffractive optical element obtained after the noise is added, so as to obtain a diffractive optical element that not only eliminates the regular noise but also realizes a target light field with a good effective energy ratio. A preferred embodiment of the diffractive optical element designing method according to the present invention will be described in detail below with reference to fig. 7.
Fig. 7 is a flowchart of a preferred embodiment of a diffractive optical element design method according to the present invention. A diffractive optical element design method according to a preferred embodiment of the present invention, generally designated by reference numeral 200, first determines a first target light field having a particular pattern to be projected by the diffractive optical element in step S210. In step S220, a background noise is added to the first target light field to obtain a second target light field. In step S230, a phase distribution of the diffractive optical element is obtained according to the second target light field design. In step S240, a simulated light field is obtained by simulating based on the designed phase distribution of the diffractive optical element, and the effect of the simulated light field is evaluated. Next, in step S250, if the effect of the simulated light field meets the design requirement, the design method ends, and step S270 is performed to determine the phase distribution of the diffractive optical element meeting the design requirement; if the effect of the simulated light field in the step 250 does not meet the design requirement, adjusting the background noise in the step S260, and then repeating the steps S220, S230, and S240 until the effect of the simulated light field meets the design requirement, ending the design method, and performing the step S270 to determine the phase distribution of the diffractive optical element meeting the design requirement.
In a preferred embodiment of the method of designing a diffractive optical element according to the present invention, although the simulated light field is estimated by simulating the phase distribution of the diffractive optical element obtained by the design, the present invention does not exclude manufacturing the diffractive optical element to be designed, obtaining the actual light field by projecting light using the diffractive optical element obtained by the manufacture, and estimating the actual light field to optimize the design of the diffractive optical element.
It should be understood that although the addition of the background noise can effectively suppress the regular noise, since the energy of the projected light is constant, the effective light energy for forming the specific pattern decreases as the added background noise increases, so if the background noise light energy increases too high, the light energy of the specific pattern may be too low, and the signal-to-noise ratio of the projection system decreases, which affects the display effect of the projected target light field.
The adjusting of the background noise may be performed by adjusting at least one of an intensity of the background noise and a distribution area of the background noise. If the simulated light field is in the presence of regular noise associated with the first target light field in addition to the background noise as compared to the first target light field, at least one of the intensity of the background noise and the area of distribution of the background noise is increased. If the simulated light field is free of regular noise associated with the first target light field in addition to the background noise as compared to the first target light field, but the efficiency of the simulated light field is less than design requirements, at least one of the intensity of the background noise and the area of distribution of the background noise is reduced.
Therefore, the addition of the background noise needs to consider not only the intensity of each point in the background noise but also the distribution area of the background noise.
The distribution area is usually determined by the distribution mode. The most common background noise distribution mode is global noise, that is, noise is distributed in the whole first target light field region, and may be distributed over all pixel points of the target light field, or may be distributed at a certain duty ratio.
The background noise may also be selected to be a local distribution, i.e. local noise, in case a global distribution of the background noise is not needed or desired. So-called local distribution, i.e. the area of the background noise distribution is smaller than the area of the first target light field. In theory, the background noise may be distributed in a locally continuous region at any position of the first light field. It is preferred that the background noise is distributed in a locally continuous area of the first target light field and that the locally continuous area covers the specific pattern. Thus, the distribution position of the background noise can be overlapped with the occurrence position of the regular noise, and the regular noise is more favorably eliminated by the background noise with lower intensity. Similarly, the local noise may be distributed over all the pixel points in the local region of the target light field, or may be distributed in the local region of the target light field at a certain duty ratio.
The intensity of the background noise, whether globally or locally distributed, at each pixel point in the global or local range can be set in a variety of ways. For example, the intensities may be identical, vary randomly or gradually from the center of the target light field outward, from one side of the target light field to the other, etc. The gradual intensity change may be that the distribution of the background noise is uniform (the duty ratio is constant) but the intensity of the noise points changes gradually, that the intensity of the noise points is consistent but the duty ratio changes gradually, or that both the intensities change.
The preferred way of gradually changing the background noise intensity is to gradually decrease from the specific pattern to the blank area, so that the background noise is more distributed at the position where the regular noise associated with the specific pattern may exist, and the effective elimination of the regular noise is more favorable under the condition of adding lower background noise.
The background noise, whether distributed globally or locally, may be randomly located within a global or local area, and the intensity of the background noise may also be random.
In the method of designing a diffractive optical element according to the present invention, the background noise is preferably uniform noise or random intensity noise. The uniform noise refers to that the intensities of all noise points are consistent, and the uniform noise can be all pixel points which are fully distributed in a target light field or can be uniformly distributed at a certain duty ratio. The random intensity noise means that the intensities of all noise points are random, and the random intensity noise may be all pixel points that are fully distributed in the target light field, or may be distributed at a certain duty ratio.
In the method for designing a diffractive optical element according to the present invention, a background noise is added to a first target light field of the diffractive optical element, a specific pattern of the first target light field and the added background noise constitute a second target light field, the pattern of the specific pattern and the background noise can be represented by setting the pattern as a pattern having a certain gray value, the gray value of a pixel without the specific pattern and the background noise is 0, and the gray value is set as 1 or a maximum value max when the light intensity is maximum, then the gray value g corresponding to the background noise preferably satisfies: 0 woven fabric g/max is less than or equal to 0.05. The method for designing a diffractive optical element of the present invention calculates the phase distribution of the diffractive optical element based on the light intensity distribution of the second target light field represented by the gray scale values.
Specific embodiments of the present invention will be described in detail below with reference to fig. 8 to 26.
Fig. 8 is a schematic diagram of a second target light field of the first embodiment of the design method of the diffractive optical element according to the present invention obtained by adding background noise to the target light field shown in fig. 1, which includes the specific pattern 421 and the globally uniform background noise 422, in this embodiment, the gray-scale value of the pixels of the specific pattern 421 is set to 1 or Max, the gray-scale value of the pixels of the background noise 422 is changed from 0 to 0.0002 or 0.0002Max, and then the diffractive optical element is designed according to the second target light field 402 in a simulation manner. FIG. 9 is a view of a simulated light field of a diffractive optical element according to a first embodiment of the method for designing a diffractive optical element according to the invention, taken from FIG. 8 as a second target light field, showing that the simulated light field 403 includes a specific pattern 431 without apparent regular noise in the simulated light field 403. The signal-to-noise ratio at the extension of the specific pattern 431 and the end thereof is measured to be 54821, 1331 ≈ 41, which is improved by about 23 times compared with the specific pattern without adding background noise.
Fig. 10 to 12 are schematic diagrams of a second object light field for various arrangements of the second embodiment of the diffractive optical element design method according to the invention resulting from the addition of background noise to the object light field shown in fig. 3. Fig. 10 shows a second target light field 502 with global random position background noise added, which includes an 8-point circular ring specific pattern 521 and global random position background noise 522. In this embodiment, the grayscale value of the 8-point annular specific pattern pixel in the second target light field 502 is set to 1 or Max, the grayscale value of the global random position background noise 522 is changed to 0.003 or 0.003Max, and then the simulation design and processing of the diffractive optical element are performed according to the second target light field 502 after the background noise is added.
FIG. 13 is a view of a simulated light field of the diffractive optical element obtained as the second target light field of FIG. 10 in accordance with the second embodiment of the diffractive optical element design method according to the present invention; fig. 14 is a view of an actual light field obtained by light projection with the diffractive optical element obtained as the second target light field in fig. 10 according to the second embodiment of the diffractive optical element design method according to the present invention. In contrast, referring back to fig. 4 and 5, which show the results of simulation and actual measurement of the diffractive optical element of the 8-point ring to which no background noise is added, it is apparent that there are a large number of noise points around the 8-point ring, which have a correspondence relationship with the 8-point ring as the specific pattern in the target map, so-called regular noise. By contrast, as is apparent from fig. 13 and 14, in the simulation and actual measurement results after adding the background noise shown in the figures, the pattern of the 8-point circular ring is clear, and there is no regular noise around the 8 points.
Regarding the selection of the random position, random background noise can be generated in matlab by generating a random logic matrix, and the specific additional expression is as follows:
intensity*imbinarize(weight*rand(m,n),0.5)。
where m and n are the longitudinal and transverse dimensions of the background noise region, respectively, and if the dimensions of m and n are consistent with the dimensions of the second target light field, the added background noise is global background noise, as shown in fig. 10. If m, n is smaller than the size of the target map, the added background noise is local background noise, as shown in fig. 11 and 12, fig. 11 is a second target light field 602 including an 8-point circular ring specific pattern 621 and local random background noise 622; fig. 12 is a second target light field 702 comprising an 8-point circular ring specific pattern 721 and local random background noise 722.
weight represents added weight and is used for controlling the area proportion of the added background noise, the value range of the weight is [0.5, ∞ ], when the weight =1, the total area of random background noise occupies half of the added area, if the weight is less than 0.5, no background noise is represented, and the larger the value of the weight is, the larger the proportion of the added background noise is; the immiarize is a binarization function of matlab, and the binarization threshold value is 0.5; the intensity represents the intensity of the background noise, and if the intensity is a random matrix of m × n, the operation mode is changed to ". Times.e", that is, the intensity is an intensity estimate (m, n), 0.5), and the background noise with random intensity is obtained.
Fig. 15 is a schematic diagram of a target light field with an i-shaped pattern as a specific pattern, wherein the target light field is generally indicated by reference numeral 801 and comprises an i-shaped specific pattern 811. Fig. 16 is a schematic diagram of a second target light field of the third embodiment of the diffractive optical element design method according to the present invention resulting from the addition of background noise to the target light field shown in fig. 15, which second target light field is generally indicated by reference numeral 802 in fig. 16 and includes an i-shaped specific pattern 821 and random position background noise 822. In the third embodiment of the diffractive optical element design method according to the present invention, the gradation value of the specific pattern 821 is set to 1 or Max, the gradation value of the background noise 822 is set to 0.004 or 0.004Max, and then the diffractive optical element simulation design and machining are performed according to the second target light field 802 to which the background noise is added.
FIG. 17 is a view of a simulated light field of the diffractive optical element derived as the target light field of FIG. 15; FIG. 18 is a view of an actual light field obtained by light projection from the diffractive optical element obtained as the target light field in FIG. 15; FIG. 19 is a view of a simulated light field of the diffractive optical element resulting from FIG. 16 as a second target light field in accordance with the third embodiment of the diffractive optical element design method according to the present invention; fig. 20 is a view of an actual light field obtained by light projection by the diffractive optical element obtained as the second target light field in fig. 16 according to the third embodiment of the diffractive optical element designing method according to the present invention. By comparing fig. 17, 18, 19 and 20, it is apparent from fig. 19 and 20 that, after the background noise is added according to the method for designing a diffractive optical element of the present invention, the extension lines of the left and right ends and the upper and lower sides of the i-shaped line are substantially eliminated, the pattern is clear, and the lines and the background can be clearly distinguished.
Fig. 21 is a schematic diagram of a target light field with two straight line segments as a specific pattern, wherein the target light field is denoted by reference numeral 901, and the target light field 901 comprises the specific pattern 911 with two straight line segments. Fig. 22 is a schematic diagram of a second object light field according to the fourth embodiment of the diffractive optical element design method of the present invention obtained by adding background noise to the object light field shown in fig. 21, wherein the second object light field is denoted by reference numeral 902, and includes a specific pattern 921 having two straight line segments and added local uniform noise 922. The background noise region 922 covers 50 ° x30 °. In the present embodiment, the gray value of the local uniform noise 922 is set to 0.04, and the gray values other than the local uniform noise 922 are set to 0.
FIG. 23 is a prior art view of a simulated light field for a diffractive optical element obtained with the target light field of FIG. 21; FIG. 24 is a prior art view of an actual light field obtained by light projection from the diffractive optical element obtained with the target light field of FIG. 21; FIG. 25 is a view of a simulated light field of a diffractive optical element taken from FIG. 22 as a second target light field in accordance with a fourth embodiment of a diffractive optical element design method according to the present invention; fig. 26 is a view of an actual light field obtained by light projection by the diffractive optical element obtained with fig. 22 as the second target light field according to the fourth embodiment of the diffractive optical element designing method according to the present invention. As is apparent from a comparison of fig. 23, 24, 25, and 26, in fig. 25 and 26, the diffractive optical element design method according to the present invention adds background noise, and the extension line noise is well controlled. Under the illumination of 50lux environment, neither extension line nor background noise is visible.
The manner of adding the background noise in the embodiments is only exemplary, and is used to illustrate the implementation process and the obtained effect of the design method of the present invention, and not to limit the present invention.
The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the invention herein disclosed is not limited to the particular combination of features described above, but also encompasses other arrangements formed by any combination of the above features or their equivalents without departing from the spirit of the invention. For example, the above features may be replaced with (but not limited to) features having similar functions disclosed in the present application.
Claims (11)
1. A diffractive optical element design method for suppressing regular noise, comprising:
a. determining a first target light field having a first specific pattern to be projected by the diffractive optical element;
b. adding background noise to said first target light field, thereby obtaining a second target light field having a second specific pattern consisting of the first specific pattern of the first target light field and the background noise; and
c. deriving a phase distribution of the diffractive optical element from the second target light field design,
wherein the background noise is added for displaying a first target light field having a first specific pattern when projected using the diffractive optical element having the phase distribution, thereby suppressing regular noise having an intensity and being associated with the first specific pattern contained in the pattern projected by the diffractive optical element.
2. The diffractive optical element design method according to claim 1, wherein the method further comprises:
d. simulating based on the designed phase distribution of the diffractive optical element to obtain a simulated light field, evaluating the effect of the simulated light field, and adjusting the background noise according to the evaluation result; and
e. and repeating the steps b-d until the effect of the simulated light field meets the design requirement.
3. The diffractive optical element design method according to claim 2, wherein the adjusting of the background noise according to the evaluation result in the step d includes adjusting at least one of an intensity of the background noise and a distribution area of the background noise.
4. The diffractive optical element design method according to claim 3, wherein step d includes: increasing at least one of an intensity of the background noise and an area of distribution of the background noise if the simulated light field is in presence of regular noise associated with the first target light field in addition to the background noise as compared to the first target light field.
5. The diffractive optical element design method according to claim 3, wherein step d includes: reducing at least one of an intensity of the background noise and an area of distribution of the background noise if the simulated light field is absent regular noise associated with the first target light field in addition to the background noise as compared to the first target light field, but an efficiency of the simulated light field is less than a design requirement.
6. The diffractive optical element design method according to any one of claims 1-5, wherein the background noise is distributed in a global sense of the first target light field.
7. The diffractive optical element design method according to any one of claims 1 to 5, wherein the background noise is distributed in a locally continuous area of the first target light field and the locally continuous area covers the first specific pattern.
8. The diffractive optical element design method according to any one of claims 1 to 5, wherein the background noise is uniform noise.
9. The diffractive optical element design method according to any one of claims 1 to 5, wherein the background noise is random intensity noise.
10. The diffractive optical element design method according to any one of claims 1 to 5, wherein the intensity of the background noise is gradually decreased from the first specific pattern toward a blank region.
11. The diffractive optical element design method according to any one of claims 1 to 5, wherein the step c further includes assigning the second target light field to a gray value according to light intensity, where the gray value is maximum max when the light intensity is maximum, and 0 when the light intensity is not maximum, and the gray value g corresponding to the background noise satisfies: 0< -g/max ≦ 0.05, and calculating a phase distribution of the diffractive optical element from the second target light field represented by the gray scale values.
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