A wavelength division multiplexing optical fiber communication system

Abstract

The application discloses a kind of based on Wollaston prism carrier frequency interference detection device and method, utilize Wollaston prism and test light with reference light produce small angle separation to realize carrier frequency, to avoid the method of introducing carrier frequency by the object to be measured to tilt a certain angle to generate return error, realize high-precision carrier frequency interference detection.Through high-precision displacement table, Wollaston prism is moved, so that the detection device can be compatible with carrier frequency interference detection and normal Fizeau interference detection.The application further reduces the return error in the interference detection optical path by designing a relay lens with ultra-low return error, ensuring the detection accuracy.Using the application, dynamic carrier frequency interference detection of the surface shape of the object to be measured can be effectively and accurately realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical precision detection, and particularly relates to a carrier frequency interference detection device and method based on a Wollaston prism. BACKGROUND

[0002] Carrier frequency interference utilizes test light and reference light with a certain included angle to interfere, and realizes phase modulation by introducing a linear carrier frequency, so that only one carrier frequency interference image is needed to realize phase extraction and obtain surface shape information of a measured surface, and is suitable for real-time dynamic detection.

[0003] A Chinese patent document with publication number CN107560565A discloses a surface shape detection device and method based on dynamic time-sharing tilt carrier frequency interference. According to the surface shape of a detected element, a required spatial interference point source array position is calculated, a Tip / Tilt mirror is used to generate a time-sharing spatial interference point source array, and the spatial posture of the Tip / Tilt mirror is adjusted once to realize the arrangement of one spatial point source. Through a designed posture adjustment position, the scanning of the planned spatial point source is sequentially completed. The interference fringes are solved, and the surface shape reconstruction of the detected element is completed, so that the surface shape measurement of the high-precision surface shape element of the present application is realized.

[0004] The current common method is to tilt the reference surface or the measured surface to make the test light and the reference light have a certain included angle. In order to ensure that the low-frequency noise can be separated from the phase information through filtering and spectrum analysis technology, the reference surface or the measured surface needs to be tilted by a large angle. However, because of the tilt of the reference surface or the measured surface, the path of the test light returning from the measured surface to the imaging surface is not exactly the same as the path of the reference light returning from the reference surface to the imaging surface, and each lens passed in the path will introduce different aberrations in the test light and the reference light, which is called return error. The existence of the return error will have a certain influence on the detection accuracy of the surface shape. When the tilt angle is small, the influence of the return error is relatively small, and when the tilt angle is large, the influence of the return error on the detection result of the surface shape cannot be ignored. Especially when the system structure is relatively complex, the increase in the number of lenses will make the return error larger.

[0005] Therefore, a design is needed to avoid the influence of the return error caused by the separation of the test light and the reference light. SUMMARY

[0006] The present application provides a carrier frequency interference detection device and method based on a Wollaston prism, which can realize low-return-error high-precision dynamic surface shape measurement.

[0007] A carrier frequency interference detection device based on a Wollaston prism, comprising an interference measurement system and a computer processing module.

[0008] The light emitted by the fiber laser is converted into linearly polarized light after the first polarizer, and is separated into S-polarized light and P-polarized light after the polarization beam splitter prism; the S-polarized light emitted by the polarization beam splitter prism passes through the first quarter-wave plate, is reflected by the first plane mirror, and then passes through the first quarter-wave plate again to be converted into P-polarized light, and then enters the third plane mirror; the P-polarized light and the S-polarized light reflected by the third plane mirror pass through the beam expander and the first depolarization beam splitter prism, and then pass through the focusing lens, the second depolarization beam splitter prism and the collimator to be expanded into parallel light, and then pass through the standard mirror and the sample to be measured;

[0009] The light reflected by the standard mirror serves as reference light, and the light reflected by the sample to be measured serves as test light; the two beams of light pass through the collimator and the second depolarization beam splitter prism again, and then a part of the light passes through the second imaging lens to enter the Wollaston prism, and is emitted as two beams of light at a certain angle, and then passes through the 1× relay lens group and the second polarizer to be imaged on the imaging camera; another part of the light passes through the focusing lens and the first depolarization beam splitter prism, and then passes through the first imaging lens to be imaged on the alignment camera;

[0010] The Wollaston prism is installed on the high-precision displacement stage;

[0011] The computer processing module comprises a displacement control module, an image acquisition module and an interferogram data analysis processing module; the displacement control module is used to control the high-precision displacement stage to move, the image acquisition module is connected with the imaging camera, transmits data to the interferogram data analysis processing module for analysis and processing, and the surface shape information of the sample to be measured is obtained.

[0012] Further, the fiber laser adopts 532nm short coherence light.

[0013] Further, the separation angle of the Wollaston prism is below 2°.

[0014] Further, the Wollaston prism is moved transversely by the high-precision displacement stage to realize the compatibility of the Fizeau interference detection and the carrier frequency interference detection.

[0015] When the high-precision displacement stage moves the Wollaston prism between the second imaging lens and the 1× relay lens group, the function of the carrier frequency interference detection is realized; when the high-precision displacement stage moves the Wollaston prism out of the carrier frequency interference light path, the function of the Fizeau interference detection is realized.

[0016] Further, the 1× relay lens group comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are sequentially arranged on the same optical axis along the light propagation direction.

[0017] The first lens, the second lens, the third lens and the fifth lens, the sixth lens, the seventh lens are symmetrically distributed with the fourth lens as the center.

[0018] Further, the first lens and the seventh lens are both plano-convex lenses with positive focal power; the second lens and the sixth lens are both meniscus lenses with positive focal power; the third lens and the fifth lens are both double-concave lenses with negative focal power; and the fourth lens is a double-convex lens with positive focal power.

[0019] Further, the 1x relay lens group has a nearly consistent optical path difference at 1° field of view, 2° field of view and 3° field of view, and has ultra-low return error.

[0020] Further, the first lens has a material refractive index of 1.80-1.85, a front surface curvature radius of 34-35 mm, a flat back surface, and a thickness of 1-2 mm.

[0021] The second lens has a material refractive index of 1.80-1.85, a front surface curvature radius of 22-23 mm, a back surface curvature radius of 45-46 mm, and a thickness of 2-3 mm.

[0022] The third lens has a material refractive index of 1.45-1.50, a front surface curvature radius of -117 to -118 mm, a back surface curvature radius of 3-4 mm, and a thickness of 12-13 mm.

[0023] The fourth lens has a material refractive index of 1.50-1.55, a front surface curvature radius of 4-5 mm, a back surface curvature radius of -4 to -5 mm, and a thickness of 6-7 mm.

[0024] The fifth lens has a material refractive index of 1.45-1.50, a front surface curvature radius of -3 to -4 mm, a back surface curvature radius of 117-118 mm, and a thickness of 12-13 mm.

[0025] The sixth lens has a material refractive index of 1.80-1.85, a front surface curvature radius of -45 to -46 mm, a back surface curvature radius of -22 to -23 mm, and a thickness of 2-3 mm.

[0026] The material refractive index of the seventh lens is 1.80-1.85; the front surface of the seventh lens is a plane; the radius of curvature of the rear surface of the seventh lens is -34mm to -35mm; and the thickness of the seventh lens is 1mm-2mm.

[0027] A carrier frequency interference detection method based on a Wollaston prism, using the carrier frequency interference detection method based on the Wollaston prism, comprising the following steps:

[0028] Step 1, adjust the pose of the standard mirror and the sample to be measured until the light spot reflected by the standard mirror and the sample to be measured in the alignment camera is located at the center and the light spot is the smallest;

[0029] Step 2, adjust the distance d1 between the polarization beam splitter prism and the first plane mirror, the distance d2 between the polarization beam splitter prism and the second plane mirror, and the distance d3 between the standard mirror and the sample to be measured, so that d1+d3=d2;

[0030] Step 3, adjust the position of the 1x relay lens to ensure that the two beams of light exiting the Wollaston prism at a certain angle can enter the 1x relay lens completely; at the same time, adjust the position of the second polarizer and the imaging camera until the interference pattern appears on the imaging camera.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] 1. The present application uses the Wollaston prism to produce a small angle separation of the reference light and the test light to realize the carrier frequency, thereby avoiding the return error generated by the method of introducing the carrier frequency by tilting the object to be measured at a certain angle, and realizing high-precision carrier frequency interference detection.

[0033] 2. The present application moves the Wollaston prism through a high-precision displacement table, so that the detection device can be compatible with carrier frequency interference detection and normal Fizeau interference detection.

[0034] 3. The present application further reduces the return error in the interference detection light path by designing a relay lens with ultra-low return error, thereby ensuring the detection accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 A structure diagram of a carrier frequency interference detection device based on a Wollaston prism is provided for an embodiment of the present application.

[0036] Figure 2 A structure diagram of one of the embodiments of the 1x relay lens group provided by the present application.

[0037] Figure 3 An optical path difference diagram of the 1x relay lens group provided by the present application under 0°, 1° and 2° field of view.

[0038] Figure 4Interference diagrams of the 1× relay lens assembly provided by the present invention under 0° and 2° fields of view. DETAILED DESCRIPTION

[0039] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0040] like Figure 1 As shown, a carrier frequency interference detection device based on Wollaston prism includes an interference measurement system and a computer processing module.

[0041] In the interferometry system, a fiber laser 1 serves as the light source, using 532nm short-coherent light to ensure that only two beams of light can ultimately interfere and form an image. The laser light emitted by the light source is converted into linearly polarized light after passing through the first polarizer 2. It is then split into two beams, P light and S light, after passing through the polarization beam splitter prism 3. The S light is reflected by the first quarter-wave plate 4 before passing through the first plane mirror 5 again. At this point, the S light emitted from the polarization beam splitter prism 3 is converted into P light. The P light emitted from the polarization beam splitter prism 3 is reflected by the second quarter-wave plate 6 before passing through the second plane mirror 7 again. At this point, the P light emitted from the polarization beam splitter prism 3 is converted into S light. By adjusting the spacing d1 between the polarization beam splitter prism 3 and the first plane mirror 5, and the spacing d2 between the polarization beam splitter prism 3 and the second plane mirror 7, a certain phase deviation is achieved between the P light and the S light when they exit the polarization beam splitter prism 3 and reach the third plane mirror 8. The P and S light beams are expanded into wide beams by the beam expander 9, then converge into spherical waves after passing through the first depolarizing beam splitter prism 10 and the focusing lens 13. The spherical waves then pass through the second depolarizing beam splitter prism 14 and are incident on the collimator 15, becoming parallel light. The parallel light beams strike the standard mirror 16 and the sample 17, then reflect through the collimator 15 and the second depolarizing beam splitter prism 14, before being deflected and converted back into parallel light by the second imaging lens 18. The light beams incident on the standard mirror 16 and the sample 17 contain P light and S light with phase differences. After these two beams are reflected by the standard mirror 16 and the sample 17, four beams of light with different phases are returned: the P light reflected from the standard mirror 16, the P light reflected from the sample 17, the S light reflected from the standard mirror 16, and the S light reflected from the sample 17. By adjusting the distance d3 between standard mirror 16 and sample 17 so that d1 + d3 = d2, interference occurs between the P-light reflected from sample 17 and the S-light reflected from standard mirror 16. The four beams of light are imaged on imaging camera 23 via Wollaston prism 19, 1× relay lens assembly 21, and second polarizer 22.

[0042] The light reflected from the standard mirror 16 and the sample 17 to be measured is imaged on the alignment camera 12 through the first imaging mirror 11, and the pose of the standard mirror 16 and the sample 17 to be measured can be adjusted according to the pattern on the alignment camera, facilitating subsequent interference measurement.

[0043] The high-precision displacement table 20 can be used to remove the Wollaston prism 19 from the interference light path, and the original light path can be used as a Fizeau interference detection function, realizing the compatibility of Fizeau interference detection and carrier frequency interference detection.

[0044] The computer processing module includes a displacement control module, an image acquisition module, and an interference pattern data analysis processing module; wherein the displacement control module is used to control the high-precision displacement table 20 to move, the image acquisition module is connected with the imaging camera 23, and after obtaining the carrier frequency interference pattern image of the interference imaging of the sample 17 to be measured and the standard mirror 16, the data is transmitted to the interference pattern data analysis processing module for analysis and processing to obtain the surface shape information of the sample 17 to be measured.

[0045] The method for carrier frequency interference detection using the above device is as follows:

[0046] Step 1, adjust the pose of the standard mirror 16 and the sample 17 to be measured until the light spot reflected from the standard mirror 16 and the sample 17 to be measured in the alignment camera 12 is located at the center and the light spot is smallest.

[0047] Step 2, adjust the distance d1 between the polarization beam splitter prism 3 and the first plane mirror 5, the distance d2 between the polarization beam splitter prism 3 and the second plane mirror 7, and the distance d3 between the standard mirror 16 and the sample 17 to be measured, so that d1, d2, d3 satisfy the following relationship:

[0048] d1+d3=d2

[0049] Step 3, adjust the position of the 1× relay lens (21) to ensure that the two beams of light exiting the Wollaston prism 19 at a certain angle can enter the 1× relay lens group 21 completely. At the same time, adjust the position of the second polarizer 22 and the imaging camera 23 until the interference pattern appears on the imaging camera 23.

[0050] Figure 2 The design scheme of the 1× relay lens group 21 in the device of the application is shown. The design includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens arranged in sequence on the same optical axis. The first lens, the second lens, the third lens, and the fifth lens, the sixth lens, and the seventh lens are symmetrically distributed around the fourth lens as the center.

[0051] The first lens and the seventh lens are both plano-convex lenses with positive refractive power; the second lens and the sixth lens are both meniscus lenses with positive refractive power; the third lens and the fifth lens are both double-concave lenses with negative refractive power; and the fourth lens is a double-convex lens with positive refractive power.

[0052] Specifically, the material refractive index of the first lens of the 1x relay lens group is 1.80-1.85; the curvature radius of the front surface of the first lens is 34mm-35mm; the back surface of the first lens is a plane; the thickness of the first lens is 1mm-2mm; the material refractive index of the second lens is 1.80-1.85; the curvature radius of the front surface of the second lens is 22mm-23mm; the curvature radius of the back surface of the second lens is 45mm-46mm; the thickness of the second lens is 2mm-3mm; the material refractive index of the third lens is 1.45-1.50; the curvature radius of the front surface of the third lens is -117mm--118mm; the curvature radius of the back surface of the third lens is 3mm-4mm; the thickness of the third lens is 12mm-13mm; the material refractive index of the fourth lens is 1.50-1.55; the curvature radius of the front surface of the fourth lens is 4mm-5mm; the curvature radius of the back surface of the fourth lens is -4mm--5mm; the thickness of the fourth lens is 6mm-7mm; the material refractive index of the fifth lens is 1.45-1.50; the curvature radius of the front surface of the fifth lens is -3mm--4mm; the curvature radius of the back surface of the fifth lens is 117mm--118mm; the thickness of the fifth lens is 12mm-13mm; the material refractive index of the sixth lens is 1.80-1.85; the curvature radius of the front surface of the sixth lens is -45mm--46mm; the curvature radius of the back surface of the sixth lens is -22mm--23mm; the thickness of the sixth lens is 2mm-3mm; the material refractive index of the seventh lens is 1.80-1.85; the front surface of the seventh lens is a plane; the curvature radius of the back surface of the seventh lens is -34mm--35mm; and the thickness of the seventh lens is 1mm-2mm.

[0053] Figure 3 The optical path difference diagrams of the 1x relay lens group at 0°, 1° and 2° fields of view are shown. The optical path difference diagrams at the three fields of view are basically consistent, which shows that the designed 1x relay lens group has ultra-low return error.

[0054] Figure 4 The interference diagrams of the 1x relay lens group at 0° field of view and 2° field of view are shown. The PV value of the interference diagrams of the designed 1x relay lens group at 0° field of view and 2° field of view is only 0.0041 wavelengths, which specifically shows that the designed 1x relay lens group has ultra-low return error.

[0055] The above-described embodiments have described the technical solutions and beneficial effects of the present application in detail, and it should be understood that the above-described is only a specific embodiment of the present application and is not used to limit the present application, and any modification, supplement and equivalent replacement made within the principle range of the present application should be included in the protection range of the present application.

Claims

1. A Wollaston prism based carrier frequency interference detection apparatus, characterized in that, It comprises an interferometric system and a computer processing module; In the interferometric system, the light emitted by the fiber laser (1) is converted into linearly polarized light after passing through the first polarizer (2), and is separated into S-polarized light and P-polarized light after passing through the polarization beam splitter prism (3); the S-polarized light emitted by the polarization beam splitter prism (3) passes through the first quarter-wave plate (4) again, is reflected by the first plane mirror (5), passes through the first quarter-wave plate (4) again to be converted into P-polarized light, and then is incident on the third plane mirror (8); the P-polarized light emitted by the polarization beam splitter prism (3) passes through the second quarter-wave plate (6) again, is reflected by the second plane mirror (7), passes through the second quarter-wave plate (6) again to be converted into S-polarized light, and then is incident on the third plane mirror (8); the P-polarized light and the S-polarized light reflected by the third plane mirror (8) pass through the beam expander (9) and the first depolarization beam splitter prism (10) again, pass through the focusing lens (13), the second depolarization beam splitter prism (14) and the collimating lens (15) to be expanded into parallel light, and then pass through the standard mirror (16) and the sample (17) to be measured; The light reflected by the standard mirror (16) serves as reference light, and the light reflected by the sample (17) to be measured serves as test light; the two beams of light pass through the collimating lens (15) and the second depolarization beam splitter prism (14) again, a part of the two beams of light passes through the second imaging lens (18) to be incident on the Wollaston prism (19), and is emitted as two beams of light at a certain angle, passes through the 1× relay lens group (21) and the second polarizer (22) to be imaged on the imaging camera (23); the other part of the two beams of light passes through the focusing lens (13) and the first depolarization beam splitter prism (10), and is imaged on the alignment camera (12) through the first imaging lens (11); The Wollaston prism (19) is installed on the high-precision displacement stage (20); The computer processing module comprises a displacement control module, an image acquisition module and an interferogram data analysis processing module; the displacement control module is used for controlling the high-precision displacement stage (20) to move, the image acquisition module is connected with the imaging camera (23) to transmit data to the interferogram data analysis processing module for analysis and processing, and the surface shape information of the sample (17) to be measured is obtained.

2. The Wollaston prism based carrier frequency interference detection apparatus of claim 1, wherein, The fiber laser (1) adopts 532nm short coherence light.

3. The Wollaston prism based carrier frequency interference detection apparatus of claim 1, wherein, The separation angle of the Wollaston prism (19) is below 2°.

4. The Wollaston prism based carrier frequency interference detection apparatus of claim 1, wherein, The Wollaston prism (19) is moved laterally by the high-precision displacement stage (20) to realize the compatibility of the Fizeau interference detection and the carrier frequency interference detection; When the Wollaston prism (19) is moved by the high-precision displacement stage (20) to be between the second imaging lens (18) and the 1× relay lens group (21), the function of the carrier frequency interference detection is realized; when the Wollaston prism (19) is moved out of the carrier frequency interference light path by the high-precision displacement stage (20), the function of the Fizeau interference detection is realized.

5. The Wollaston prism based carrier frequency interference detection apparatus of claim 1, wherein, The 1× relay lens group (21) comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are arranged in sequence on the same optical axis along the light propagation direction; The first lens, the second lens, the third lens and the fifth lens are symmetrically distributed around the fourth lens.

6. A Wollaston prism based carrier frequency interference detection apparatus as claimed in claim 5, wherein, The first lens and the seventh lens are both plano-convex lenses with positive focal length; the second lens and the sixth lens are both meniscus lenses with positive focal length; the third lens and the fifth lens are both double-concave lenses with negative focal length; and the fourth lens is a double-convex lens with positive focal length.

7. The Wollaston prism based carrier frequency interference detection apparatus of claim 5, wherein, The 1x relay lens group (21) has a consistent optical path difference at 1° field of view, 2° field of view and 3° field of view, and has ultra-low return error.

8. The Wollaston prism based carrier frequency interference detection apparatus of claim 5, wherein, The material refractive index of the first lens is 1.80-1.85; the curvature radius of the front surface of the first lens is 34-35 mm; the back surface of the first lens is a plane; and the thickness of the first lens is 1-2 mm. The material refractive index of the second lens is 1.80-1.85; the curvature radius of the front surface of the second lens is 22-23 mm; the curvature radius of the back surface of the second lens is 45-46 mm; and the thickness of the second lens is 2-3 mm. The material refractive index of the third lens is 1.45-1.50; the curvature radius of the front surface of the third lens is -117--118 mm; the curvature radius of the back surface of the third lens is 3-4 mm; and the thickness of the third lens is 12-13 mm. The material refractive index of the fourth lens is 1.50-1.55; the curvature radius of the front surface of the fourth lens is 4-5 mm; the curvature radius of the back surface of the fourth lens is -4--5 mm; and the thickness of the fourth lens is 6-7 mm. The material refractive index of the fifth lens is 1.45-1.50; the curvature radius of the front surface of the fifth lens is -3--4 mm; the curvature radius of the back surface of the fifth lens is 117-118 mm; and the thickness of the fifth lens is 12-13 mm. The material refractive index of the sixth lens is 1.80-1.85; the curvature radius of the front surface of the sixth lens is -45--46 mm; the curvature radius of the back surface of the sixth lens is -22--23 mm; and the thickness of the sixth lens is 2-3 mm. The material refractive index of the seventh lens is 1.80-1.85; the front surface of the seventh lens is a plane; the curvature radius of the back surface of the seventh lens is -34--35 mm; and the thickness of the seventh lens is 1-2 mm.

9. A Wollaston prism based carrier frequency interference detection method, characterized in that, The method for detecting the carrier frequency interference based on the Wollaston prism according to any one of claims 1-8 comprises the following steps: Step 1: adjusting the positions of the standard mirror (16) and the sample (17) until the light spot reflected by the standard mirror (16) and the sample (17) is located at the center of the camera (12) and the light spot is smallest; Step 2: adjusting the distance d1 between the polarization beam splitter (3) and the first plane mirror (5), the distance d2 between the polarization beam splitter (3) and the second plane mirror (7), and the distance d3 between the standard mirror (16) and the sample (17) so that d1+d3=d2. Step 3, adjust the position of the 1x relay lens group (21) to make sure that the two beams of light exiting the Wollaston prism (19) at an angle can enter the 1x relay lens group (21) completely; at the same time, adjust the position of the second polarizer (22) and the imaging camera (23) until the interference pattern appears on the imaging camera (23).

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