A method and apparatus for measuring the beam spreader ratio of an afocal optical system

Abstract

This invention discloses a method and apparatus for measuring the beam expansion ratio of a focalless optical system. The method involves constructing a test optical path and recording the initial position of the detector's centroid (X1, Y1); controlling the deflection angle of the light source's emission direction (α1, β1) and recording the position of the detector's centroid (X2, Y2); inserting the focalless optical system under test and recording the position of the detector's centroid (X3, Y3); controlling the deflection angle of the light source's emission direction (α2, β2) and recording the position of the detector's centroid (X4, Y4); and calculating the beam expansion ratio Γ. The measurement method is simple, low-cost, and can meet various measurement accuracy requirements.

Description

Technical Field

[0001] This invention belongs to the field of laser communication technology, and relates to a method and device for measuring the beam expansion ratio of a focalless optical system. Background Technology

[0002] In the field of free-space optical communication, reflective optical antenna designs are often used to meet the transmission and / or reception requirements of various operating wavelengths such as signal light and beacon light. The core specifications of an optical antenna include its beam spreader ratio (or amplification factor, compression ratio, etc.). An optical antenna is essentially a focusless beam spreader system, with two main functions: first, when used as a transmitting optical antenna, it compresses the beam divergence angle of the transmitted light; second, when used as a receiving optical antenna, it expands the receiving aperture.

[0003] Currently, beam spreader ratio control is mostly performed after the optical cold processing of the reflector and before the integration of the primary and secondary mirrors. This is done by measuring the R-values ​​or focal lengths of the primary and secondary mirrors, comparing them, and then theoretically calculating the beam spreader ratio of the optical antenna. However, this method cannot be used to measure the beam spreader ratio after the primary and secondary mirrors of the optical antenna have been integrated.

[0004] For integrated afocal optical systems, one approach is to directly test their actual function within the system, specifically their ability to compress the beam divergence angle or amplify the beam diameter. For methods that directly detect changes in the beam divergence angle, Gaussian laser beams are typically used. After compression, especially with large compression ratios (e.g., 10× or 20×), the data collected by the beam analyzer generally exhibits significant errors. For methods that detect changes in the beam diameter, it is difficult to distinguish the boundary using the human eye, and most methods rely on detecting the beam waist radius (see "Experimental Study on Laser Beam Expanding Ratio Measurement Based on Displacement Method" (Gao Hongyun, Wuhan University of Technology). The measurement accuracy of this method depends on many factors, including the stability of the laser output power, the accuracy of the optical power meter, the roundness of the beam spot, and the linearity of the light-blocking plate movement. Furthermore, it is susceptible to ambient light interference, and the measurement range is limited by the photosensitive surface of the optical power meter. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for measuring the beam expansion ratio of a focal-free optical system. The measurement method is simple, low in cost, and can meet various measurement accuracy requirements.

[0006] The technical solution to achieve the purpose of this invention is as follows:

[0007] A method for measuring the beam expansion ratio of an afocal optical system includes the following steps:

[0008] S100: Set up the test optical path and record the initial position (X1, Y1) of the detector's centroid;

[0009] S200: Controls the deflection angle (α1, β1) of the light source emission direction and records the position of the detector's centroid (X2, Y2);

[0010] S300: Insert the afocal optical system under test and record the centroid position (X3, Y3) of the detector;

[0011] S400: Controls the deflection angle of the light source emission direction (α2, β2) and records the position of the detector's centroid (X4, Y4);

[0012] S500: Calculate beam expansion ratio α1 and α2 are azimuth angles, and β1 and β2 are elevation angles.

[0013] In the preferred technical solution, step S100, which involves setting up the test optical path and recording the initial position (X1, Y1) of the detector's centroid, includes:

[0014] S110: The light source and detector are placed at opposite ends of the collimator's optical path, with the detector's photosensitive surface located at the collimator's focal plane.

[0015] S120: Adjust the emission direction of the light source so that it is converged by the collimator and incident on the detector, and record the initial position of the centroid (X1, Y1).

[0016] In the preferred embodiment, the light source is placed on an adjustment frame, and the emission direction of the light source is adjusted by adjusting the adjustment frame. The light source can be adjusted in at least two dimensions, azimuth and pitch, by the adjustment frame, and the corresponding detector center of mass performs two-dimensional motion.

[0017] In a preferred embodiment, the adjustment frame can also adjust its height and perform two-dimensional translation.

[0018] In a preferred embodiment, the afocal optical system under test is placed on an adjustment frame, and the position and orientation of the afocal optical system under test are adjusted by adjusting the adjustment frame.

[0019] In a preferred embodiment, the adjustment frame is used to adjust the afocal optical system under test to operate in an ideal state when inserted into the measurement optical path. The ideal state refers to the light beam entering and / or exiting from the center position of the effective aperture of the afocal optical system with zero field of view.

[0020] In the preferred technical solution, the emission direction of the light source is controlled to deflect in only one direction, namely β. 1＝ If β2 = 0, then the beam expansion ratio is...

[0021] In the preferred technical solution, if the deflection amount of the light source emission direction remains consistent in the two instances, the beam expansion ratio will be increased.

[0022] In a preferred embodiment, the light source includes an optical fiber laser and a reflective parabolic collimator for emitting stable Gaussian light.

[0023] The present invention also discloses a beam expansion ratio measuring device for afocal optical system, comprising a light source, a collimator and a detector, wherein the measuring device uses the above-described beam expansion ratio measuring method for afocal optical system to measure the beam expansion ratio.

[0024] Compared with the prior art, the significant advantages of this invention are:

[0025] 1. The measurement method is simple and low-cost, and can meet the requirements of various measurement accuracy.

[0026] 2. The measurement process has no subjective observation component; the entire process is recorded by objective instruments or tools, and the raw data is easy to preserve for future reference, meeting the current management requirements of the free-space optical communication industry, especially the aerospace field, for the production and manufacturing process.

[0027] 3. The measurement process does not require complex manual intervention and can be used for automated production lines, which is in line with the current trend and requirements of mass production in the field of free space optical communication. Attached Figure Description

[0028] Figure 1 This is a flowchart of the beam expansion ratio measurement method for the afocal optical system in this embodiment;

[0029] Figure 2 This is a schematic diagram of the test optical path in this embodiment;

[0030] Figure 3 This is a schematic diagram showing the addition of the unfocused optical system under test to the test optical path in this embodiment; Detailed Implementation

[0031] The principle of this invention is to utilize the angular magnification characteristics of a focalless optical system and, based on the principle of angle measurement, to achieve beam expansion ratio measurement. The measurement method is simple, low-cost, and can meet various measurement accuracy requirements.

[0032] Example 1:

[0033] like Figure 1 As shown, a method for measuring the beam expansion ratio of an afocal optical system includes the following steps:

[0034] S100: Set up the test optical path and record the initial position (X1, Y1) of the detector's centroid;

[0035] S200: Controls the deflection angle (α1, β1) of the light source emission direction and records the position of the detector's centroid (X2, Y2);

[0036] S300: Insert the afocal optical system under test and record the centroid position (X3, Y3) of the detector;

[0037] S400: Controls the deflection angle of the light source emission direction (α2, β2) and records the position of the detector's centroid (X4, Y4);

[0038] S500: Calculate beam expansion ratio α1 and α2 are azimuth angles, and β1 and β2 are elevation angles.

[0039] Generally, S100: Setting up the test optical path and recording the initial position (X1, Y1) of the detector's centroid includes:

[0040] S110: Construct the measurement optical path, with the light source and detector placed at opposite ends of the collimator's optical path, and the detector's photosensitive surface located at the collimator's focal plane; For example... Figure 2 As shown.

[0041] S120: Adjust the emission direction of the light source so that it is focused by the collimator and incident on the detector, and record the initial position of the centroid (X1, Y1);

[0042] Generally, the light source is placed on an adjustment frame, and the emission direction of the light source is adjusted by adjusting the adjustment frame.

[0043] Furthermore, the light source can be adjusted in at least two dimensions—azimuth and pitch—via the adjustment frame, causing the detector's center of mass to move in two dimensions. The azimuth angle is adjusted using a high-precision manual or electric rotary table, and the pitch angle is adjusted using a high-precision manual or electric arc-shaped stage. The adjustment angle can be read from both the manual and electric rotary table and the arc-shaped stage.

[0044] Furthermore, the adjustment frame can also adjust height, two-dimensional translation, and many other dimensions.

[0045] Generally, the initial position (X1, Y1) is the center of the available area of ​​the detector.

[0046] S300: Insert the afocal optical system under test and record the detector's centroid position (X3, Y3); For example... Figure 3 As shown.

[0047] Specifically, the afocal optical system can be an optical antenna, without any specific limitations.

[0048] Typically, the afocal optical system under test is placed on an adjustment frame, and its position and orientation are adjusted by adjusting the frame. The adjustment frame containing the afocal optical system under test and the adjustment frame containing the light source can be adjusted independently.

[0049] Furthermore, the afocal optical system under test can be adjusted in at least two dimensions—azimuth and elevation—on the adjustment frame, with the corresponding detector's center of mass undergoing two-dimensional motion. The azimuth angle is adjusted via a high-precision manual or electric rotary table, and the elevation angle is adjusted via a high-precision manual or electric arc stage. The adjustment angle can be read from both the manual or electric rotary table and the arc stage.

[0050] Furthermore, the adjustment frame can also adjust height, two-dimensional translation, and other dimensions to ensure that the afocal optical system under test works in an ideal state when inserted into the measurement optical path.

[0051] Ideally, a beam of light enters and / or exits from the center of the effective aperture (or the designed working position) of an afocal optical system with zero field of view (or central field of view, working field of view).

[0052] In the second aspect embodiment of the present invention, for the sake of simplification, only one direction is deflected in steps S200 and S400 of the above embodiment, namely β. 1＝ If β2 = 0, then:

[0053] S210: Control the deflection angle α1 of the light source emission direction and record the position of the detector's centroid (X2, Y2);

[0054] S410: Control the deflection angle α2 of the light source emission direction and record the position of the detector's centroid (X4, Y4);

[0055] S510: Calculate the beam expansion ratio

[0056] In the third aspect embodiment of the present invention, the deflection amount of the light source emission direction is kept consistent in two steps, i.e., α1 = α2, then:

[0057] S520: Calculate beam expansion ratio

[0058] In a preferred embodiment, the light source is used to emit stable Gaussian light.

[0059] In a preferred embodiment, the light source includes a fiber-optic output laser and a reflective parabolic collimator, the laser output wavelength being λ. 11 =1550nm, the output fiber is a 1550 single-mode fiber with a core diameter of 10μm and an NA of 0.24. The collimator has a reflection focal length of 33mm, the matching laser has an exit pupil diameter of 8mm, and the light source outputs a far-field beam divergence angle of 330μrad.

[0060] In a preferred embodiment, the method further includes determining the measurement accuracy, wherein the method for determining the measurement accuracy includes:

[0061] Calculate the effect of the error caused by the rotation angle on the detection accuracy ΔX a =θ 42*F 21 ;θ 42 For the repeatability accuracy of the rotary table, F 21 The focal length of the collimator;

[0062] Calculate the optical path stability ΔX b =X max -X min X max and X min These are the maximum and minimum values ​​of the system's centroid coordinates within time interval T;

[0063] Calculate the maximum systematic error γ = arctan((ΔX) a +ΔX b ) / F 21 ) / θ test Based on this, the measurement accuracy is judged, θ test For repeated rotation angles.

[0064] In another embodiment, a beam expansion ratio measuring device for an afocal optical system includes:

[0065] Light source, collimator, detector.

[0066] The light source includes: a light source assembly and a first adjustment frame.

[0067] Typically, a light source assembly includes a collimator and a laser. The laser emits light, which is collimated by an optical fiber connected to the collimator. The light source assembly can emit a stable beam of Gaussian light, with an exit pupil d. 11 Bundle divergence angle wavelength λ 11 .

[0068] The first adjustment frame includes an azimuth rotary table and a pitch arc swing table, which can adjust the two adjustment dimensions of azimuth and pitch in order to adjust the emission direction of the light source.

[0069] Furthermore, the first adjustment frame also includes a lifting platform and a two-dimensional translation platform.

[0070] A collimator can converge parallel light; the focal length of a collimator is F. 21 caliber D 21 .

[0071] Generally, the effective aperture of the collimator is required to be larger than the effective aperture of the afocal optical system under test.

[0072] Generally, reflective collimators are chosen. Specifically, a Newtonian reflector architecture can be selected.

[0073] Furthermore, the collimator can be selected as an off-axis reflective collimator.

[0074] To further reduce the requirements of the testing environment, the collimator can be replaced by other focused optical systems, such as lenses that are matched with the detector and adapted to the operating wavelengths of the light source and the unfocused optical system under test.

[0075] The detector can output the centroid coordinates of the imaging spot. The detector pixel size is d. 31 The response spectrum includes λ 11 The number of pixels in the array is m×n.

[0076] The afocal optical system under test is placed on the second adjustment frame.

[0077] The second adjustment frame includes an azimuth rotary table and a pitch arc swing table, which can adjust the two adjustment dimensions of azimuth and pitch in order to adjust the emission direction of the light source.

[0078] Furthermore, the second adjustment frame also includes a lifting platform and a two-dimensional translation platform.

[0079] Specifically, the working process of the beam expansion ratio measurement device for afocal optical system is described below using a preferred embodiment as an example:

[0080] The testing equipment includes: a light source, a collimator, a detector, and an adjustment frame.

[0081] The light source emits a stable beam of Gaussian light, with the exit pupil d 11 Bundle divergence angle wavelength λ 11 .

[0082] Collimator focal length F 21 caliber D 21 .

[0083] Detector pixel size d 31 The response spectrum includes λ 11 The number of pixels in the array is m×n.

[0084] Adjustment frame resolution θ 41 Repeatability θ 42 .

[0085] Test optical path as Figure 2 As shown, the light source is placed on the adjustment frame, and the detector is placed at the focal plane of the collimator (the center of the detector coincides with the focal point). The light source, collimator, and detector are placed at the same light height in sequence.

[0086] The testing method is as follows:

[0087] S1: As Figure 2 Set up the test optical path and preheat the light source and other test equipment;

[0088] S2: Adjust the direction of the light source so that it is focused by the collimator and incident on the detector, and record the initial position of the centroid (X1, Y1);

[0089] S3: Control the deflection angle of the light source emission direction (α1, β1) and record the position of the detector's centroid (X2, Y2);

[0090] S4: Insert the afocal optical system under test, adjust the pose of the afocal optical system, and record the position of the detector's centroid (X3, Y3); For example... Figure 3 As shown;

[0091] S5: Control the deflection angle of the light source emission direction (α2, β2) and record the position of the detector's centroid (X4, Y4);

[0092] S6: Calculate the beam expansion ratio

[0093] The systematic errors throughout the testing process mainly include the following factors: the repeatability of the rotary table is θ. 42 Optical path stability ΔX b .

[0094] Where, repeated rotation θ test The impact of angular error on detection accuracy is related to the focal length of the collimator, and is reflected as ΔX in the measurement. a =θ 42 *F 21 .

[0095] Where ΔX b It can be directly detected by a detector, that is, the maximum and minimum values ​​of the system's centroid coordinates X within time T are detected and recorded. max and X min Then ΔX b =X max -X min Generally, T = 5″ is taken.

[0096] Then the maximum systematic error γ=arctan((ΔX) a +ΔX b ) / F 21 ) / θ test The measurement accuracy can be judged accordingly. Of course, statistical judgments can also be made on the system based on the factors that contribute to the existence of systematic errors mentioned above.

[0097] In a feasible example of the above embodiments, the light source is implemented using a fiber-optic laser output paired with a reflective parabolic collimator. The laser output wavelength λ 11=1550nm, the output fiber is 1550 single-mode fiber with a core diameter of 10μm and an NA of 0.24. The collimator is a Thorlabs RC08APC-P01 with a reflection focal length of 33mm and a matching laser exit pupil diameter of 8mm. The light source outputs a far-field beam divergence of 330μrad.

[0098] In the example above, the collimator used is a self-developed off-axis reflective collimator with a focal length F. 21 =5m, caliber D 21 =500mm.

[0099] In the example above, the detector uses the CINOGY product CMOS-1203IR, with pixel d 31 =4.5μm, number of area array pixels 2048×2048.

[0100] In the example above, the adjustment frame uses Symiterie's BREVA product, with a resolution θ. 41 = 2.5 μrad, repeatability θ 42 = ±2.5μrad, corresponding to ΔX a =θ 42 *F 21 =12.5μm.

[0101] Furthermore, for testing requirements that do not require high precision, the testing method can be simplified to the following scheme:

[0102] In steps S200 and S400 of the above embodiment, only one direction is deflected, i.e., β1 = β2 = 0, then:

[0103] S210: Control the deflection angle α1 of the light source emission direction and record the position of the detector's centroid (X2, Y2);

[0104] S410: Control the deflection angle α2 of the light source emission direction and record the position of the detector's centroid (X4, Y4);

[0105] S510: Calculate the beam expansion ratio

[0106] In the third aspect embodiment of the present invention, the deflection amount of the light source emission direction is kept consistent in two instances, i.e., α1 = α2, then:

[0107] S520: Calculate beam expansion ratio

[0108] The beam expansion ratio of a certain type of afocal optical system was measured, and the results are shown in the table below:

[0109]

[0110]

[0111] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for measuring the beam expansion ratio of an afocal optical system, characterized in that, Includes the following steps: S100: Set up the test optical path, with the light source and detector placed at opposite ends of the collimator optical path, and the photosensitive surface of the detector located at the focal plane of the collimator; record the initial position of the detector's centroid (X1, Y1); the light source includes a collimator and a laser; S200: Controls the deflection angle (α1, β1) of the light source emission direction and records the position of the detector's centroid (X2, Y2); S300: Insert the afocal optical system under test between the light source and the collimator, and record the position of the detector's centroid (X3, Y3); S400: Controls the deflection angle of the light source emission direction (α2, β2) and records the position of the detector's centroid (X4, Y4); S500: Calculate beam expansion ratio α1 and α2 are azimuth angles, and β1 and β2 are elevation angles.

2. The method for measuring the beam expansion ratio of an afocal optical system according to claim 1, characterized in that, Step S100 involves setting up the test optical path and recording the initial position (X1, Y1) of the detector's centroid, including: Adjust the emission direction of the light source so that it is converged by the collimator and incident on the detector, and record the initial position of the centroid (X1, Y1).

3. The method for measuring the beam expansion ratio of an afocal optical system according to claim 2, characterized in that, The light source is placed on the adjustment frame. The emission direction of the light source can be adjusted by adjusting the adjustment frame. The light source can be adjusted in at least two dimensions, azimuth and pitch, through the adjustment frame, and the corresponding detector center of mass performs two-dimensional motion.

4. The method for measuring the beam expansion ratio of an afocal optical system according to claim 3, characterized in that, The adjustment frame can also adjust the height and two-dimensional translation.

5. The method for measuring the beam expansion ratio of an afocal optical system according to claim 1, characterized in that, The afocal optical system under test is placed on an adjustment frame, and the position and orientation of the afocal optical system under test are adjusted by adjusting the adjustment frame.

6. The method for measuring the beam expansion ratio of an afocal optical system according to claim 5, characterized in that, The adjustment frame is used to adjust the afocal optical system under test to work in an ideal state when it is inserted into the measurement optical path. The ideal state refers to the beam entering and / or exiting from the center position of the effective aperture of the afocal optical system with zero field of view.

7. The method for measuring the beam expansion ratio of an afocal optical system according to claim 1, characterized in that, The emission direction of the light source is controlled to deflect in only one direction, namely β. 1= If β2 = 0, then the beam expansion ratio is... .

8. The method for measuring the beam expansion ratio of an afocal optical system according to claim 1, characterized in that, If the deflection amount of the light source's emission direction remains consistent in both instances, the beam expansion ratio will be... .

9. The method for measuring the beam expansion ratio of an afocal optical system according to claim 1, characterized in that, The light source includes an optical fiber laser and a reflective parabolic collimator for emitting stable Gaussian light.

10. A device for measuring the beam expansion ratio of an afocal optical system, characterized in that, The measuring device includes a light source, a collimator, and a detector, and measures the beam expansion ratio using the beam expansion ratio measurement method for afocal optical system as described in any one of claims 1-9.

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