A grating diffraction efficiency measuring device

Abstract

The application discloses a grating diffraction efficiency measuring device, which comprises a laser light source, a Littrow collimation unit and a detection device; the Littrow collimation unit comprises a polarization beam splitting component, an alignment diaphragm, a collimation mirror, a light reflection diffraction component and a turntable; the light reflection diffraction component comprises a to-be-measured grating and a reference plane mirror; the turntable is used for carrying the to-be-measured grating or the reference plane mirror; the polarization beam splitting component is arranged in the light path of an outgoing light beam of the laser light source; and the alignment diaphragm, the collimation mirror and the light reflection diffraction component are sequentially arranged in the transmission light path of the polarization beam splitting component. The application realizes a light path structure of complete Littrow angle incidence in grating diffraction efficiency measurement, solves the problem that an incident light beam and a diffraction light beam do not coincide, and can accurately measure the diffraction efficiency measurement problem of the grating in the application of the Littrow structure.

Description

Technical Field

[0001] This application relates to the field of optical measurement for grating performance testing, and specifically to a grating diffraction efficiency measuring device. Background Technology

[0002] As an important diffraction element, gratings are widely used not only in spectral analysis but also in photolithography systems, astronomy, lasers, optical communications, precision measurement, and information processing in recent years. Diffraction efficiency, as one of its key performance indicators, makes a simple and accurate measurement method particularly important. One important application scenario for gratings is Littorh condition incidence, where the incident angle and diffraction angle are equal, meaning the incident beam and diffracted beam are completely coincident. However, in existing measurement techniques, the diffracted beam and the incident beam both have a certain angle, causing beam deviation and resulting in measurement results that deviate from the true value. To measure the diffracted light energy of a grating, current techniques adjust the diffracted beam to return along its original path and then rotate the grating under test to allow its beam to enter the receiving system. Current testing systems operate under quasi-Littorh condition, where the incident beam and diffracted beam are nearly coincident with a small angle, still resulting in some error compared to the true results in practical applications.

[0003] Therefore, it is necessary to solve the problem that the complete Litterow condition cannot be achieved in the measurement of grating diffraction efficiency, the incident beam and the diffracted beam do not coincide, and the measurement of the overall diffraction efficiency of the grating is inaccurate. Summary of the Invention

[0004] This application provides a grating diffraction efficiency testing device to solve the problem of measuring the overall diffraction efficiency of gratings under Litterow application conditions in the prior art.

[0005] This application provides a grating diffraction efficiency measuring device, comprising:;

[0006] Laser source, Littoral collimator, detection device;

[0007] The Littoral collimation unit includes: a polarization beam splitter assembly, an alignment stop, a collimating mirror, a light reflection and diffraction assembly, and a turntable;

[0008] The optical reflection diffraction assembly includes a grating to be tested and a reference plane mirror; the turntable is used to support the grating to be tested or the reference plane mirror.

[0009] The polarization beam splitter is disposed in the optical path of the emitted beam of the laser source, and the alignment stop, collimating lens and optical reflection diffraction component are disposed sequentially in the transmission optical path of the polarization beam splitter.

[0010] The detection device is disposed in the reflected optical path of the polarization beam splitter, and the light that has passed through the light reflection and diffraction component is reflected to the detection device by the polarization beam splitter.

[0011] Optionally, the polarization beam splitter assembly includes: a polarization beam splitter prism and a phase delay element;

[0012] A polarizing beam splitter polarizes the incident laser beam and decomposes the polarized beam into two components with mutually orthogonal polarization directions.

[0013] The phase delay element is a quarter-wave plate, and the angle between its fast axis direction and the X-axis direction is 45° or -45°.

[0014] The output beam becomes circularly polarized light after passing through the polarizing beam splitter and the phase delay element in sequence.

[0015] The alignment stop is located at the light outlet of the waveplate, and its aperture is consistent with the beam aperture. Adjusting the alignment stop allows the emitted beam from the waveplate to pass completely through.

[0016] Optionally, the collimating mirror and the turntable can be adjusted so that the diffracted beam or reflected beam completely coincides with the incident beam.

[0017] Optionally, the polarizing beam splitter is a Glan prism, a Lochtein prism, or a polarizing beam splitter cube. Optionally, the laser source is arbitrary polarized light.

[0018] Optionally, the detection device includes a photodetector and a data processing unit connected to the photodetector.

[0019] Optionally, the grating under test is made of the same substrate material as the reference plane mirror.

[0020] Optionally, the grating to be tested is a planar reflection grating.

[0021] Optionally, the photodetector is a silicon photodetector or a germanium photodetector.

[0022] Compared with the prior art, this application has the following advantages:

[0023] The grating diffraction efficiency measurement device provided in this application includes: a laser source, a Littoral collimating unit, and a detection device; the Littoral collimating unit includes: a polarization beam splitter assembly, an alignment stop, a collimating mirror, a light reflection diffraction assembly, and a turntable; the light reflection diffraction assembly includes a grating under test and a reference plane mirror; the turntable is used to support the grating under test or the reference plane mirror; the polarization beam splitter assembly is disposed in the optical path of the emitted beam from the laser source, and the alignment stop, collimating mirror, and light reflection diffraction assembly are sequentially disposed in the transmission optical path of the polarization beam splitter assembly; the detection device is disposed in the reflection optical path of the polarization beam splitter assembly, and the light passing through the light reflection diffraction assembly is reflected to the detection device by the polarization beam splitter assembly.

[0024] The polarization beam splitter structure used in this invention, under the condition of a fully collimated Littrow optical path, can effectively ensure polarization control of the incident measurement beam, making the P component and S component intensities consistent at the grating, thereby obtaining accurate measurements of the grating's overall diffraction efficiency. The polarization beam splitter can also perform polarization, greatly reducing the polarization requirements of the light source.

[0025] The grating diffraction efficiency measuring device provided in this application accurately measures the diffraction efficiency of the grating under Litterow application conditions by setting a fully collimated Litterow optical path structure so that the incident beam and the diffracted beam completely coincide. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the test optical path of a grating diffraction efficiency measuring device according to an embodiment of this application.

[0027] Figure 2 This is a schematic diagram illustrating the measurement principle of a grating diffraction efficiency measuring device with a reference plane mirror, according to an embodiment of this application.

[0028] Figure 3 This is an example diagram of a polarization beam splitter component in a grating diffraction efficiency measurement device according to an embodiment of this application.

[0029] Figure 4 This is a schematic diagram of the optical path polarization change in the measurement state of a grating diffraction efficiency measuring device provided in this application.

[0030] Figure 5 This is a schematic diagram of the optical path adjustment method for measuring the efficiency of different diffraction orders of a grating diffraction efficiency measuring device provided in this application.

[0031] Figure 6 This is a schematic diagram of the receiving module structure in a grating diffraction efficiency measurement device provided in this application. Detailed Implementation

[0032] Many specific details are set forth in the following description to provide a full understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of this application; therefore, this application is not limited to the specific embodiments disclosed below.

[0033] The embodiments of this application provide a grating diffraction efficiency measuring device, which will be described in detail below with reference to the accompanying drawings of the embodiments provided in this application.

[0034] This application provides a grating diffraction efficiency measurement device, such as... Figure 1 As shown. The grating diffraction efficiency measurement device includes a laser source 1, a Littoral collimation unit 7, and a detection device 8;

[0035] The Littoral collimation unit 7 includes: a polarization beam splitter 2, an alignment stop 3, a collimating mirror 4, a light reflection and diffraction assembly, and a turntable 6. The collimating mirror 4 is a concave mirror.

[0036] The light reflection diffraction assembly includes the grating under test 501 and the reference plane mirror 502 (e.g., Figure 2 (as shown in the diagram); Turntable 6 is used to support the grating 501 to be tested or the reference plane mirror 502;

[0037] The polarization beam splitter 2 is disposed in the optical path of the emitted beam of the laser source 1, and the alignment stop 3, collimating lens 4 and light reflection diffraction component are disposed in the transmission optical path of the polarization beam splitter 2 in sequence.

[0038] The detection device 8 is positioned in the reflected light path of the polarization beam splitter 2. The polarization beam splitter 2 reflects the light that has passed through the light reflection and diffraction component to the detection device 8. The collimating lens 4 and the turntable 6 are adjusted so that the diffracted beam or reflected beam completely coincides with the incident beam.

[0039] The working principle of the grating diffraction efficiency measuring device provided in the first embodiment of this application is described below:

[0040] The laser source 1 emits arbitrary polarized light, and the wavelength of the output beam is within the visible light range. The output beam passes sequentially through the polarization beam splitter 2, the alignment stop 3, and the collimating lens 4 before being incident on the grating 501 under test or the reference plane mirror 502. First, the grating 501 under test is mounted on the turntable 6. The turntable 6 and the collimating lens 4 are adjusted so that the diffracted beam returns along its original path, passing sequentially through the collimating lens 4, the alignment stop 3, and the polarization beam splitter 2 before being incident on the detection device 8. The result is recorded as the measured light flux I1. The aforementioned structure is a fully collimated Littoral optical path structure, in which the incident beam and the diffracted beam completely coincide, used to accurately measure the diffraction efficiency of the grating under Littoral application conditions.

[0041] In one implementation, the polarization beam splitter assembly 2 includes: a polarization beam splitter prism 201 and a phase retardation element; the polarization beam splitter prism is a Glan prism, and the phase retardation element is a quarter-wave plate, the fast axis of which makes an angle of 45° or -45° with the X-axis direction, such as... Figure 3As shown, the polarization beam splitter 2 has a Glan prism 201 and a wave plate 202. The Glan prism 201 operates in the 200-3500nm wavelength range, and the wave plate 202 is a quarter-wave plate. The laser output beam is converted into right-handed or left-handed circularly polarized light after passing through Glan prism 201 and waveplate 202. Specifically, the polarizing beam splitter polarizes the incident laser and decomposes the polarized beam into two components with mutually orthogonal polarization directions. The arbitrary polarized beam of the laser output becomes linearly polarized light after passing through Glan prism 201. Glan prism 201 almost completely transmits P-polarized light and almost completely reflects S-polarized light. The transmitted P-polarized light becomes circularly polarized light after being incident on waveplate 202. The polarization directions of the beam P and S components are consistent, so that the beam incident on the grating under test is circularly polarized light. Under the Littrow optical path structure, the diffracted beam and the incident beam completely coincide. In order to obtain the intensity result of the diffracted beam, the diffracted beam needs to be separated. After the beam returns along the original path, it passes through waveplate 202 and Glan prism 201 in sequence. Referring to the theoretical derivation below, the reflected beam incident on the detection device 8 is related to the overall efficiency of the grating.

[0042] Optionally, the polarizing beam splitter can be a Glan prism, a Lochon prism, or a polarizing beam splitter cube.

[0043] The laser source is arbitrary polarized light. In one embodiment, the alignment stop 3 is located at the exit port of the waveplate 202, and its aperture is consistent with the beam aperture. The alignment stop 3 is adjusted so that the emitted beam from the waveplate 202 passes completely. The collimating mirror 4 and the turntable are adjusted so that the diffracted or reflected beam completely coincides with the incident beam. Since the diffracted or reflected beam is not blocked after passing through the alignment stop 3, it is considered to completely coincide with the incident beam, i.e., the optical path structure is perfectly collimated.

[0044] refer to Figure 2 The light reflection and diffraction assembly also includes a reference plane mirror 502. After measuring I1, the grating to be measured is replaced with the reference plane mirror 502. The incident beam passes through the polarization beam splitter 2, the alignment stop 3, and the collimating mirror 4, and is reflected back through the reference plane mirror 502. It then passes through the collimating mirror 4, the alignment stop 3, and the polarization beam splitter 2 before being reflected again and incident on the detection device 8, where the result is recorded as the reference light flux I2. Figure 4This diagram illustrates the changes in optical polarization of a beam within its optical path. The separated beams in the diagram are only used to distinguish between the incident beam and the diffracted or reflected beams, and do not represent an actual situation. The laser beam output can be of arbitrary polarization. After passing through the Glan prism 201, it becomes linearly polarized light. The S component of the linearly polarized light is reflected out of the light path by the Glan prism. The P-polarized light transmitted through the Glan prism becomes right-handed / left-handed circularly polarized light after passing through the quarter-wave plate 202 arranged at 45° / -45°. It then passes through the alignment aperture 3 and collimating lens 4 and is incident on the grating under test 501 or the reference plane mirror 502. If its diffraction efficiency is affected by polarization, if it is incident on the grating under test 501, the diffracted beam becomes elliptically polarized light. If it is incident on the reference plane mirror 502, the reflected beam is still circularly polarized light. After the diffracted beam or reflected beam passes through the quarter-wave plate 202, the P-polarized light becomes S-polarized light, and the S-polarized light becomes P-polarized light. The final P-polarized light is transmitted through the Glan prism 201, and the final S-polarized light is reflected by the Glan prism 201 and enters the energy detector 8. Therefore, the intensity of the measured S-polarized light is related to the overall diffraction efficiency of the grating. The following analysis examines the beam changes through polarization analysis; that is, taking arbitrary polarized light as the initial beam, its optical path structure is as follows:

[0045] Arbitrarily polarized light - polarization beam splitter 2 (transmission) - P-polarized light - alignment stop 3 - collimating lens 4 - grating under test 501 / reference plane mirror 502 - collimating lens 4 - alignment stop 3 - polarization beam splitter 2 (reflection) - S-polarized light - detection device 8.

[0046] In the optical path structure, the alignment stop 3 and collimating lens 4 have no effect on the measurement results and can be ignored in polarization analysis.

[0047] Optionally, the grating under test is made of the same substrate material as the reference plane mirror.

[0048] Optionally, the grating to be tested is a planar reflection grating.

[0049] In one embodiment, the detection device 8 includes a photodetector 801 and a data processing unit 802 connected to the photodetector 801;

[0050] Optionally, the photodetector is a silicon photodetector or a germanium photodetector.

[0051] The photodetector 801 converts the measured and reference optical signals into electrical signals and transmits them to the data processing unit 802 to calculate the efficiency of the grating 501 under test. Let X represent the efficiency of the reference plane mirror 502, then the overall diffraction efficiency of the grating 501 under test is:

[0052] η=X·I1 / I2

[0053] Where I1 and I2 are the measured luminous flux (i.e., when the optical reflection diffraction component is grating 501) and the reference luminous flux (i.e., when the optical reflection diffraction component is reference plane mirror 502), respectively. Thus, the overall diffraction efficiency of the grating 501 under the condition of a fully Littoral optical path structure can be obtained.

[0054] Figure 5 The diagram illustrates the optical path adjustment method of the measuring device when measuring the efficiency of different diffraction orders of the grating. The turntable is adjusted so that the diffracted light of the grating test order returns along the original path and passes through the collimating lens 4, the alignment aperture 3, the quarter-wave plate 202, and the Glan prism 201 in sequence before entering the detection device 8. Then, the diffraction efficiency of each order is calculated.

[0055] The aforementioned Glan prism can also be replaced by a Lochon prism or a polarizing beam splitter cube, as long as it is a polarizing beam splitter prism that can polarize the incident laser and decompose the beam into two components with mutually orthogonal polarization directions.

[0056] refer to Figure 6 The diagram schematically shows the detection device 8, which includes a photodetector 801 and a data processing unit 802 connected to the photodetector 801. The measurement beam and the reference beam are incident on the photodetector 801 for photoelectric conversion, and the data processing unit 802 completes the calculation of the grating's overall diffraction efficiency.

[0057] against Figure 1 The grating diffraction efficiency measuring device shown in Figure 2 may include the following steps in its measurement process:

[0058] (1) According to Figure 1 Install laser light source 1, Littoral collimation unit 7, and detection device 8.

[0059] (2) Install the grating 501 to be tested onto the turntable 6.

[0060] (3) Turn on the laser source and wait for the laser source 1 to stabilize.

[0061] (4) Adjust the alignment aperture 3 so that the outgoing beam that has passed through the polarization beam splitter 2 can pass through completely.

[0062] (5) Adjust the collimating lens 4 and the turntable 6 so that the diffracted beam is not blocked after passing through the alignment aperture 3.

[0063] (6) The detection device 8 records and measures the light flux I1.

[0064] (7) Install the reference plane mirror 502 onto the turntable 6.

[0065] (8) Adjust the collimating lens 4 and the turntable 6 so that the reflected beam is not blocked after passing through the alignment aperture 3.

[0066] (9) The detection device 8 records the reference light flux I2.

[0067] (10) The detection device 8 automatically calculates the overall diffraction efficiency of the grating 501 under test based on I1 and I2.

[0068] The following analysis uses the theoretical Jones matrix to determine the light flux of the detector 8 and the derivation of the grating's overall diffraction efficiency η. When the grating 501 under test is installed on the turntable 6, the matrix representation of the light flux I1 at the detector 8 is as follows:

[0069] The laser beam incident from the laser source and emitted after passing through polarization beam splitter 2 is P-polarized. Normalizing this beam and ignoring the actual luminous flux, its matrix representation is as follows:

[0070]

[0071] The matrix representation of a typical waveplate is as follows:

[0072] Where δ is the phase difference between the slow and fast axes of the waveplate, and θ is the angle between the fast axis of waveplate 202 and the X-axis, then for the quarter-wave plate of this application, taking θ as 45° as an example, the matrix representation of waveplate 202 is as follows:

[0073]

[0074] Assume the diffraction efficiencies of the grating for P-polarization and S-polarization are respectively η p η s Then its matrix representation is:

[0075]

[0076] The beam diffracted by the grating becomes elliptically polarized light. After passing through the quarter-wave plate 202, the P-polarized light becomes S-polarized light, and the S-polarized light becomes P-polarized light. The final P-polarized light is transmitted through the Glan prism 201, while the final S-polarized light is reflected by the Glan prism 201 and enters the energy detector 8. The Glan prism almost completely reflects the S-polarized light and almost completely transmits the P-polarized light. The beam incident on the detection device 8 is the reflected portion of the polarization beam splitter component 2. Therefore, the reflected light portion incident on the control and measurement device 8 is only S-polarized light, and its matrix representation is as follows:

[0077]

[0078] Assuming the transmission efficiency of the optical path structure excluding the grating is T, the calculated beam polarization state at detector 8 is as follows:

[0079] Disregarding the phase factor, the polarization of the luminous flux I1 is obtained as follows:

[0080]

[0081] Normalized intensity I1=T(η) p +η s ) / 2.

[0082] When the reference plane mirror 502 is installed on the turntable 6, and the 501 grating is replaced with a reference plane mirror with efficiency X while the rest of the optical path remains unchanged, the matrix representation of the light flux I2 at the detection device 8 differs from that of I1 above in that its matrix representation is as follows:

[0083]

[0084] Assuming the above assumptions, the transmission efficiency in the optical path structure excluding the reference mirror is T. The calculated beam polarization at detector 8 is then:

[0085]

[0086] Disregarding the phase factor, the polarization expression of the luminous flux I2 is obtained as follows:

[0087]

[0088] Normalized intensity I2 = TX,

[0089] As mentioned above, the grating's overall diffraction efficiency η = X·I1 / I2I1 = T(η) p +η s ) / 2, I2 = TX

[0090] Substituting the calculated results of I1 and I2, we obtain the grating's overall diffraction efficiency η = (η p +η s The overall diffraction efficiency of the grating is η = (1 / 2) * (P-polarization and S-polarization diffraction efficiency). p η s The average value of the beam incident on the grating is such that if the P-polarized and S-polarized components in the beam are not of equal magnitude, the measurement accuracy of the grating's overall diffraction efficiency will be affected. The polarization beam splitter 2 of this invention ensures that the P-polarized and S-polarized components of the laser beam under test are of equal magnitude after polarization, thereby enabling accurate measurement of the grating's overall diffraction efficiency.

[0091] Preferably, the substrate material of the grating under test and the reference plane mirror is the same, so that the influence parameters on the beam are the same, which can improve the measurement accuracy of the grating diffraction efficiency.

[0092] Preferably, the above-mentioned photodetector can be a silicon photodetector with an applicable wavelength range of 200nm-1100nm or a germanium photodetector with an applicable wavelength range of 700nm-1800nm.

[0093] Photodetectors include silicon photodetectors suitable for wavelengths of 200nm-1100nm and germanium photodetectors suitable for wavelengths of 700nm-1800nm. Because these two photodetectors have different wavelength ranges, they can be freely switched between the two types of photodetectors according to the actual wavelength of the laser.

[0094] The above analysis serves as a reference for the overall diffraction efficiency of the grating. In actual measurements, the method described in the above embodiments shall prevail.

[0095] The test structure of the grating diffraction efficiency measuring device provided in this application is a fully collimated Littoral optical path structure, in which the incident beam and the diffracted beam are completely coincident, and it is used to accurately measure the diffraction efficiency of the grating under Littoral conditions.

[0096] Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A grating diffraction efficiency measuring device, characterized in that, include: Laser source, Littoral collimator, detection device; The Littoral collimation unit includes: a polarization beam splitter assembly, an alignment stop, a collimating mirror, a light reflection and diffraction assembly, and a turntable; The optical reflection diffraction assembly includes a grating to be tested and a reference plane mirror; the turntable is used to support the grating to be tested or the reference plane mirror. The polarization beam splitter is disposed in the optical path of the emitted beam of the laser source, and the alignment stop, collimating lens and optical reflection diffraction component are sequentially disposed in the transmission optical path of the polarization beam splitter. The polarization beam splitter includes a polarization beam splitter prism and a phase delay element. The polarization beam splitter polarizes the incident laser and decomposes the polarized beam into two components with mutually orthogonal polarization directions. The detection device is disposed in the reflection optical path of the polarization beam splitter, and the light that has passed through the light reflection diffraction component is reflected to the detection device by the polarization beam splitter; Adjust the collimating mirror and the turntable so that the diffracted beam or reflected beam completely coincides with the incident beam. The output beam then becomes circularly polarized light after passing through the polarizing beam splitter and the phase delay element in sequence.

2. The apparatus according to claim 1, characterized in that, The phase delay element is a quarter-wave plate, and the angle between its fast axis direction and the X-axis direction is 45° or -45°.

3. The apparatus according to claim 2, characterized in that, The alignment stop is located at the light outlet of the waveplate, and its aperture is consistent with the beam aperture. Adjusting the alignment stop allows the emitted beam from the waveplate to pass completely through.

4. The apparatus according to claim 2, characterized in that, The polarizing beam splitter is a Glan prism, a Lochon prism, or a polarizing beam splitter cube.

5. The apparatus according to claim 1, characterized in that, The laser source is arbitrary polarized light.

6. The apparatus according to claim 1, characterized in that, The detection device includes a photodetector and a data processing unit connected to the photodetector.

7. The apparatus according to claim 1, characterized in that, The grating under test is made of the same substrate material as the reference plane mirror.

8. The apparatus according to claim 1, characterized in that, The grating to be tested is a planar reflection grating.

9. The apparatus according to claim 6, characterized in that, The photodetector is a silicon photodetector or a germanium photodetector.

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