A collimated beam divergence angle detection device and a divergence angle detection method

Abstract

The application discloses a collimated light beam divergence angle detection device and a divergence angle detection method. The device can focus the measured light through a lens group, and then the light is incident on the surface of a photonic crystal through a prism. The light beam is reflected and emitted after exciting a Love surface wave on the photonic crystal. A CCD collects and records the emitted light from the direction of the prism. The device can monitor and judge whether the incident light is collimated by the bending degree of the image formed in the CCD, and calculate the divergence angle of the incident light. The device provides a new type of collimated light beam judgment and divergence angle detection method, which is economical, convenient, fast in response and accurate in detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of precision measurement and the field of collimated beam collimation and detection, and particularly relates to a collimated beam divergence angle detection device and a divergence angle detection method. BACKGROUND

[0002] A collimated beam generally represents a beam with a very small divergence angle; the beam radius does not change significantly within a certain propagation distance. Collimated beams are indispensable light sources in many fields such as optical applications, communication engineering, and mechanical production and manufacturing; they have different application scenarios in specific engineering applications such as fiber communication, laser welding, laser marking, laser cutting and engraving, mechanical part shaft hole coaxiality and concentricity measurement. In traditional collimated beam judgment and divergence angle detection, a Shack-Hartmann sensor, knife-edge shadow method, or a specific interferometer is generally used to measure the change of the beam radius within a certain distance of propagation in free space, so as to verify whether the beam is collimated. In fiber optics, a fiber collimator is usually used, which is a device suitable for detecting bare optical fibers and optical fibers that need to be connected. Obviously, the fiber collimator is only suitable for optical fiber equipment that needs to be connected with an optical fiber connector. If a traditional Shack-Hartmann sensor is used to detect beam collimation by detecting the wave surface of the beam, the device has a relatively high cost and is complex to operate. If the knife-edge shadow method is used for detection, although the basic principle is also to detect the wave surface, and the cost is low and the environmental requirements are not high, the precision is relatively low and is very dependent on the experience of the user, so that the results for different users have large errors. In summary, the specific problems can be summarized as follows: (1) The experience of the user is required to be high, and the results obtained by different users have large errors. Most detection devices can obtain relatively accurate results, but the precision is quite different. (2) The use scene is limited. Most devices can obtain the required results in a specific material or situation facing the device, but lack of versatility. (3) The precision is not ideal. Some instruments can only give a rough result with insufficient precision. (4) The cost is high, the operation is complex, and the operation personnel are required to be high. In addition, under certain special working conditions, collimated beam judgment and divergence angle detection of light beams from multiple light sources are required. SUMMARY

[0003] To solve the above problems, the present application provides a collimated beam divergence angle detection device and a divergence angle detection method.

[0004] The technical solutions for achieving the above-mentioned purposes are as follows:

[0005] A collimated light beam divergence angle detection device, the device comprising a light source mounting frame, a polarizer, a cylindrical lens, a cylindrical prism, a photonic crystal, a CCD,

[0006] The polarizer, cylindrical lens and cylindrical prism are arranged along the main optical axis in sequence, the photonic crystal is deposited on the hypotenuse upper surface of the rear end of the cylindrical prism, the CCD is arranged on the main optical axis of the light beam emitted below the cylindrical prism and perpendicular to the main optical axis, the light source mounting frame is arranged with the light source to be measured, the emitted light is focused by the polarizer and the cylindrical lens, and is incident on the cylindrical prism and the photonic crystal, and can excite a Bloch surface wave on the photonic crystal, and the coupled reflected light is recorded by the CCD after being emitted.

[0007] Further, the light source mounting frame comprises a frame body, a transverse straight guide rail and a longitudinal straight guide rail, the frame body can move horizontally along the transverse straight guide rail and the longitudinal straight guide rail, and the frame body can also rotate in the plane formed by the transverse straight guide rail and the longitudinal straight guide rail.

[0008] Further, the cylindrical lens is close to one side of the front end surface of the cylindrical prism, and the focusing direction is the horizontal direction.

[0009] Further, the polarization direction of the polarizer is the transverse electric direction, i.e. the TE polarization direction, so that the emitted polarized light can excite a Bloch surface wave on the photonic crystal.

[0010] Further, the intersection interface between the cylindrical prism and the photonic crystal is located at the rear focal plane position of the cylindrical lens.

[0011] Further, the cylindrical prism is an isosceles right prism.

[0012] Further, the photonic crystal is deposited on the hypotenuse of the cylindrical prism and is closely connected.

[0013] Further, the photonic crystal comprises 14 layers of Si3N4 with a thickness of about 90 nm and SiO2 with a thickness of about 135 nm alternately deposited from bottom to top on the hypotenuse of the cylindrical prism, wherein the bottom layer of Si3N4 is attached to the cylindrical prism, and then a layer of Si3N4 with a thickness of about 90 nm and a layer of SiO2 with a thickness of 185 nm are sequentially deposited.

[0014] Further, the light source to be measured on the light source mounting frame is a helium-neon laser.

[0015] According to the divergence angle detection method of the above-mentioned collimated light beam divergence angle detection device, the method comprises the following steps:

[0016] Step one: put the light source to be measured into the light source mounting frame and turn it on, adjust the position of the light source mounting frame, so that the main optical axis of the light emitted by the light source is perpendicular to the polarizer and the column lens, and is focused by the column lens, so that part of the incident light can excite Bloch surface waves at the air interface after the column lens;

[0017] Step two: adjust the position of the CCD in the horizontal direction, so that the light emitted from the column prism is imaged on the CCD; record the picture taken by the CCD at this time;

[0018] Step three: observe and analyze the image formed by the CCD, record the bending degree of the dark line in the image, and express it as the maximum bending offset distance Δl of the dark line; then complete the detection of the beam divergence angle according to the complementary angle α of the Bloch surface wave excitation angle of the device photonic crystal, the focal length f of the column lens, the distance L of the CCD from the surface of the photonic crystal, the refractive index n1 of the column prism and the refractive index n2 of the air outside; the divergence angle θ of the light beam is obtained according to the following calculation formula:

[0019]

[0020] If the divergence angle θ is 0°, it means that the light source emits a collimated light beam, if the divergence angle θ is not 0°, it means that the light source emits a non-collimated light beam and the angle value of the light beam divergence angle is θ.

[0021] Compared with the prior art, the advantages of the present application include:

[0022] (1) wide application scene and high measurement accuracy: the device described in the present application can be applied to single-color LED, laser and other light sources, and the precision of the detection instrument is almost not affected by the environment, and has high measurement accuracy;

[0023] (2) high measurement sensitivity and rapid response: the device described in the present application can detect the small changes of the beam divergence angle, and has rapid response, which can realize real-time monitoring.

[0024] (3) low cost and easy to build: the device described in the present application does not need expensive optical devices, compared with the same precision detection instrument, it does not need precise adjustment, and the operation difficulty is low.

[0025] (4) convenient measurement: only by knowing the conditions and the results of the image on the CCD, the divergence angle of the light beam can be calculated without multiple measurements, which is convenient for calibration and reduces measurement error.

[0026] In addition to the above-described features and advantages, the principles and other features and advantages of the present application. The present application will be further described in detail with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1A schematic diagram of the light beam collimation detection device of the present application.

[0028] Figure 2 A schematic diagram of the imaging results of the light source with different divergence angles on the CCD.

[0029] Figure 3 A schematic diagram when the collimated light is incident.

[0030] Figure 4 A schematic diagram when the divergent light is incident.

[0031] Figure 5 A schematic diagram of the incident light from the cylindrical lens to the photonic crystal and reflected to the CCD.

[0032] Figure 6 A schematic diagram for deriving the divergence angle. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. The implementation of the present application is described in detail below in combination with specific examples.

[0034] As shown in Figure 1 A light beam divergence angle detection device, the device comprises a light source mounting frame 1, a transverse guide rail 1-1, a longitudinal guide rail 1-2, a polarizer 2, a cylindrical lens 3, a cylindrical prism 4, a photonic crystal 5, a CCD 6.

[0035] Further, on the hypotenuse of the cylindrical prism 4, from bottom to top, 14 layers of Si3N4 with a thickness of about 90 nm and SiO2 with a thickness of about 135 nm are deposited alternately, wherein the bottom layer of Si3N4 is attached to the cylindrical prism, and then a layer of Si3N4 with a thickness of about 90 nm and a layer of SiO2 with a thickness of 185 nm are deposited in sequence as the photonic crystal 5.

[0036] Further, the measured light emitted by the light source on the light source mounting frame 1 passes through the polarizer 2 and the cylindrical lens 3, is incident on the cylindrical prism 4, and excites a localized surface wave at the interface between the photonic crystal 5 and the air, and is finally reflected on the CCD 6.

[0037] Further, the light source on the light source mounting frame 1 is a helium-neon laser, and the wavelength of the light source is 633 nm.

[0038] Further, the CCD 6 is arranged to be adjustable in position to allow better imaging results.

[0039] Further, the polarization direction of the polarizer 2 is set to be along the normal direction of the plane defined by the transverse straight rail 1-1 and the longitudinal straight rail 1-2, so that the emergent light is linearly polarized light, and the polarization direction is the transverse electric (TE) direction.

[0040] Further, the cylindrical lens 3 is vertically placed, and the focusing direction is the horizontal direction.

[0041] Further, the focal length f of the cylindrical lens 3 is about 3 cm, and the intersection of the upper surface of the prismatic lens 4 and the photonic crystal 5 is located on the back focal plane of the cylindrical lens 3, and the incident light is focused by the cylindrical lens 3 to the upper surface of the prismatic lens 4.

[0042] Further, the refractive index n1 of the prismatic lens 4 is 1.515, and the refractive index n2 of air at normal temperature is 1.0.

[0043] According to the above light beam collimation detection device, the operation can include the following steps:

[0044] Step one: turn on the laser with a wavelength of 633 nm, adjust the position of the light source, and make the optical axis of the light emitted by the light source perpendicular to the polarizer 2 and the cylindrical lens 3, and focus the incident light by the cylindrical lens 3. Make part of the incident light be able to excite Bloch surface waves at the photonic crystal 5 after being incident on the prismatic lens 4.

[0045] Step two: adjust the position of the CCD 6 so that the light emitted from the prismatic lens 4 is imaged on the CCD 6; record the picture taken by the CCD 6 at this time.

[0046] Step three: observe the bending of the dark lines on the image and record the bending offset distance Δl of the dark lines; since the complementary angle α of the excitation angle required by the Bloch surface wave of the photonic crystal used is 45.55°, the focal length f of the cylindrical lens 3 is 3 cm, and the distance L from the surface of the photonic crystal 5 to the CCD 6 is 10 cm, as shown in Figure 5 .

[0047] Step four: according to the following calculation formula, substitute the above data to obtain the divergence angle θ of the light:

[0048]

[0049] When three beams of divergent light with different divergence angles are incident, the corresponding dark line distribution on the CCD 6 at this time is recorded, as shown from left to right Figure 2 , and the bending degrees are 0.1842, 0.3245, and 0.1969 cm, respectively. According to the method of the present application, the divergence angles of the above three beams are calculated to be 10.76°, 14.16°, and 11.12°, respectively, without the need for multiple measurements.

[0050] The related principles of the technical scheme of the present application are as follows:

[0051] Once the thickness of each layer of the photonic crystal is determined and deposited on the prism, given the structure and surrounding environment, the excitation angle of the Bloch surface wave at a specific wavelength is uniquely determined.

[0052] like Figure 3 As shown, the light emitted from the light source is converted into linearly polarized light in TE mode after passing through polarizer 2. This linearly polarized light is then focused at the interface between prism 4 and photonic crystal 5 after passing through cylindrical lens 3 and reflected to CCD 6. If the incident light is a collimated beam, the collimated beam will be focused at aa' when it passes through the cylindrical lens and enters the prism at different angles. According to the excitation condition of Bloch surface waves, only one specific angle among the polarized light rays incident on photonic crystal 5 can satisfy the excitation condition of Bloch surface waves. Figure 3 As shown in dd', light rays along this direction can just excite Bloch surface waves, so angle dao is the complementary angle α of the excitation angle. At this time, a perpendicular line is drawn from point d to the hypotenuse of the prism and intersects at point o. After the Bloch surface waves are excited, the incident light in this direction will couple to the surface of the photonic crystal without being reflected. Therefore, the CCD6 used to collect the reflected light will not collect the reflected light in the corresponding reflection direction, that is, a vertical dark line will appear in the collected beam.

[0053] When the light emitted by the light source is divergent, the beam no longer focuses at aa', but at ba', as shown below. Figure 4 As shown. The initial ray da will be incident at point b on the hypotenuse of the prism. At this point, the incident angle dbo of this ray is less than α, meaning it does not satisfy the excitation condition for Bloch surface waves. However, there must exist a deflection point e in the same plane as point d such that the angle ebc between the ray eb and the photonic crystal is equal to α, thus satisfying the excitation condition for Bloch surface waves, where c is the projection of point e onto the hypotenuse of the prism. Therefore, the ray eb incident from point e will excite Bloch surface waves on the photonic crystal 5, and thus will not be collected by the CCD. Similarly, each ray incident from dd' cannot excite Bloch waves due to beam divergence, and the corresponding rays that can excite Bloch surface waves are all deflected, i.e. Figure 4 The curved curve in the image indicates the position of the beam on d'e. Therefore, at this point, the beam collected on the CCD will appear as a curved dark line. To calculate the divergence angle of the beam, projections are made through points a and b onto the principal surface of the cylindrical lens, intersecting at point x. The angle axb is then the divergence angle of the beam, denoted as θ.

[0054] The diverging beam at the curved position, after being reflected by the photonic crystal, is spatially magnified into dark lines that are collected by CCD6 due to the distance it has traveled. The specific degree of magnification depends on the relationship between the focal length f of the prism and the position L of the CCD, such as... Figure 5The length of the line segment de and the curved offset distance Δ1 of the dark line measured on the CCD 6 satisfy the following relationship according to the geometric relationship between the isosceles right-angle prism prisms:

[0055]

[0056] In order to calculate the divergence angle of the light beam, the divergence angle derivation schematic diagram is shown in FIG. 4. Figure 6 Since the cylindrical lens 4 is close to one side of the cylindrical prism 4, the following relationship is obtained:

[0057] f = l ax = l ad cos (α-45)

[0058]

[0059] Since the cylindrical prism is an isosceles right-angle prism, the following relationship is obtained:

[0060] l ce = l od + l oc

[0061] and the angle o-a-d is equal to the angle c-b-e which is the complementary angle α of the excitation angle, according to the similarity theorem of right-angle triangles, the triangle oad is similar to the triangle cbe. The lengths of the line segment oa, the line segment cb, and the line segment od and the focal length f of the cylindrical lens satisfy the following relationship:

[0062]

[0063]

[0064]

[0065] In the right-angle triangle cab, the right-angle side ab satisfies the following relationship:

[0066]

[0067] After simplification, the expression of the length of the right-angle side ab is obtained as follows:

[0068]

[0069] According to the definition of the divergence angle above,

[0070]

[0071] Substituting the expression of ab above, the following relationship is obtained:

[0072]

[0073] According to the above formula, the relevant data are substituted to obtain the light divergence angle θ.

[0074] The foregoing is considered as illustrative only of the principles of the application. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the application to the exact construction and practice described. Accordingly, all such variations and modifications are intended to be included within the scope of the application as defined in the following claims and the equivalents thereof.

Claims

1. A collimated beam divergence angle detection device, characterized in that, The device comprises a light source mounting rack (1), a polarizer (2), a cylindrical lens (3), a cylindrical prism (4), a photonic crystal (5), a CCD (6), The polarizer (2), the cylindrical lens (3) and the cylindrical prism (4) are sequentially arranged along the main optical axis, the photonic crystal (5) is deposited on the hypotenuse upper surface of the rear end of the cylindrical prism (4), the CCD (6) is arranged on the main optical axis of the light beam emitted below the cylindrical prism (4) and is perpendicular to the main optical axis, the light source to be measured is arranged on the light source mounting rack (1), the emitted light is focused by the polarizer (2) and the cylindrical lens (3) and is incident on the cylindrical prism (4) and the photonic crystal (5), and the photonic crystal (5) can generate a Bloch surface wave, and the coupled and reflected light is recorded by the CCD (6) after being emitted.

2. The collimated beam divergence angle detection apparatus of claim 1, wherein, The light source mounting rack (1) comprises a rack body, a transverse straight guide rail (1-1) and a longitudinal straight guide rail (1-2), the rack body can move horizontally along the transverse straight guide rail (1-1) and the longitudinal straight guide rail (1-2), and the rack body can also rotate in the plane formed by the transverse straight guide rail (1-1) and the longitudinal straight guide rail (1-2).

3. The collimated beam divergence angle detection apparatus of claim 1, wherein, The cylindrical lens (3) is tightly attached to one side of the front end surface of the cylindrical prism (4), and the focusing direction is the horizontal direction.

4. The collimated beam divergence angle detection apparatus of claim 1, wherein, The polarization direction of the polarizer (2) is the transverse electric direction, that is, the TE polarization direction, so that the emitted polarized light can generate a Bloch surface wave on the photonic crystal (5).

5. The collimated beam divergence angle detection apparatus of claim 1, wherein, The intersection interface between the cylindrical prism (4) and the photonic crystal (5) is located at the rear focal plane of the cylindrical lens (3).

6. The collimated beam divergence angle detection apparatus of claim 1, wherein, The cylindrical prism (4) is an isosceles right prism.

7. The collimated beam divergence angle detection apparatus of claim 6, wherein, The photonic crystal (5) is deposited on the hypotenuse of the cylindrical prism (4) and is tightly connected to the cylindrical prism (4).

8. The collimated beam divergence angle detection apparatus of claim 7, wherein, The photonic crystal (5) comprises 14 layers of Si3N4 with a thickness of about 90 nm and SiO2 with a thickness of about 135 nm alternately deposited from bottom to top on the hypotenuse of the cylindrical prism (4), wherein the bottom layer of Si3N4 is attached to the cylindrical prism (4), and then a layer of Si3N4 with a thickness of about 90 nm and a layer of SiO2 with a thickness of 185 nm are sequentially deposited.

9. The collimated beam divergence angle detection apparatus of claim 1, wherein, The light source to be measured on the light source mounting rack (1) is a helium-neon laser.

10. The divergence angle detection method of the collimated beam divergence angle detection apparatus according to any one of claims 1 to 9, characterized in that, The method comprises the following steps: Step one: place the light source to be measured in the light source mounting rack (1) and turn it on, adjust the position of the light source mounting rack (1) so that the main optical axis of the emitted light of the light source is perpendicular to the polarizer (2) and the cylindrical lens (3) and is focused by the cylindrical lens (3) to be incident, so that part of the incident light can generate a Bloch surface wave at the interface between the photonic crystal (5) and air after being incident on the cylindrical lens (3); Step two: adjust the position of the CCD (6) in the horizontal direction so that the light emitted from the cylindrical prism (4) is imaged on the CCD (6); record the picture taken by the CCD (6) at this time. Step three: observing and analyzing the image formed by the CCD (6), recording the bending degree of the dark line in the image, and expressing it as the maximum bending offset distance Δl; and then detecting the beam divergence angle according to the complementary angle α of the excitation angle of the Bloch surface wave of the device photonic crystal, the focal length f of the cylindrical lens (3), the distance L of the CCD (6) from the surface of the photonic crystal (5), the refractive index n1 of the cylindrical prism (4), and the refractive index n2 of the air outside, and obtaining the divergence angle θ of the light beam according to the following calculation formula: If the divergence angle θ is 0°, it means that the light source emits a collimated light beam; if the divergence angle θ is not 0°, it means that the light source emits a non-collimated light beam, and the angle value of the light beam divergence angle is θ.

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