A method for detecting and calibrating the parallelism of FP etalon

Abstract

The invention belongs to the field of optics and discloses a method for detecting and calibrating the parallelism of an F‑P etalon. Specifically, a mask with sub-apertures is used to segment the clear aperture of a Fabry-Perot etalon, spectral curves of different regions of the Fabry-Perot etalon are simultaneously acquired by a spectrometer, and the relative offset of spectral curves of local regions of the etalon is compared to accurately measure the difference in plate spacings in each local region, thereby realizing detection and real-time calibration of the parallelism of the Fabry-Perot etalon. The method does not require a precise moving mechanism and is not affected by the stability of a light source and a detection environment, and the measurement and calibration accuracy can reach nanometer level.

Description

Technical Field

[0001] The invention belongs to the field of optics, and in particular relates to a FP standard tool parallelism detection and calibration method. Background Art

[0002] The FP (Fabry-Perot) etalon is mainly composed of two parallel fused quartz plates, with a high reflectivity film on the inner side of the plates. The medium between the plates is air, and the distance between the plates is fixed by a gasket (or spacer). The Fabry-Perot etalon is based on the principle of multi-beam interference. When light enters the Fabry-Perot cavity, it is reflected multiple times between the two plates to form multi-beam interference. Due to the advantages of high spectral resolution, accurate measurement, good stability and easy integration, the Fabry-Perot standard is widely used in spectroscopy, laser technology, optical communication, astronomy, biomedicine and industrial detection.

[0003] The parallelism of the two plates of the Fabry-Perot etalon determines the half-width of the spectral lines and the intensity of transmitted light, and is a key parameter for evaluating the performance of the etalon. At present, the main methods for measuring parallelism are: mechanical measurement method, which uses a mechanical device to directly measure the change in the spacing between the two plates. This type of method belongs to contact measurement and will cause physical damage or contamination to the reflective surface of the plate. At the same time, the measurement accuracy is low and can only reach the micron level; autocollimation method, this method uses the principle of autocollimation, the light beam emitted by the laser is reflected by the two working surfaces respectively, and then imaged on the focal plane, and the parallelism of the two plates is calculated according to the relative position of the image point. Although this measurement method does not cause physical damage to the reflective surface, the measurement accuracy is also low, also in the micron level; interference measurement method, by changing the phase difference of the interference beam, analyzing the counting, uniformity and change of the interference fringes, to obtain The parallelism between the two plates. The traditional interference measurement method is limited by human experience and imaging system resolution, so the measurement accuracy can only reach λ / 10-λ / 20. Later, the measurement accuracy was improved to λ / 50 by adopting a precise phase-shifting mechanical structure and a data processing system. Later, by using a wavelength-adjustable laser for phase shifting, the measurement accuracy in the short term can reach 0.3nm. However, this method judges the parallelism based on the change in the interference fringes caused by changing the phase difference. It has high requirements on the accuracy of the phase-shifting mechanism, the stability of the laser light source, and the measurement environment. Once these conditions cannot be guaranteed, the measurement accuracy will be affected, which greatly increases the complexity and cost of the detection system. Summary of the invention

[0004] The present invention provides a method for detecting and calibrating the parallelism of a Fabry-Perot etalon, and aims to solve the technical problem of dividing the clear aperture of the Fabry-Perot etalon by using a mask with sub-apertures, and generating corresponding spectral curves after the light beam passes through the local areas of the Fabry-Perot etalon corresponding to each sub-aperture. By comparing the relative offsets of the spectral curves, the difference in the spacing between the plates in each local area is accurately measured.

[0005] A method for detecting and calibrating the parallelism of a FP (Fabry-Perot) etalon, wherein the Fabry-Perot etalon is composed of two parallel plates, the plates are made of fused quartz and are provided with a light-clearing aperture, and specifically comprises the following steps:

[0006] Step 1: Place a mask on the clear aperture of the FP etalon. n clear subapertures are distributed in pairs around the edge of the mask. Each subaperture matches the area of ​​the FP etalon, and the plate spacing of the corresponding area is h. n ;

[0007] Step 2: The light emitted by the broadband continuous spectrum light source is collimated to form a collimated beam, which is respectively incident on the n sub-apertures on the mask and their corresponding Fabry-Perot etalon regions, and then converged onto the focal plane through the imaging mirror;

[0008] Step 3: Block the sub-apertures on the mask, leaving only a pair of sub-apertures corresponding to the direction through which light passes, and use a spectrometer to measure the spectral curve of the image point on the focal plane;

[0009] When the two plates of the Fabry-Perot etalon are not parallel, the distance between the plates corresponding to the two subapertures is h. n Inconsistent, in this case, two sub-apertures obtain two spectral curves;

[0010] Step 4: Compare the offset Δλ of the above two spectral curves.

[0011] (1)

[0012] Where h is the spacing and λ is the wavelength

[0013] And the difference Δh between the plate spacings corresponding to the two sub-apertures is calculated according to formula (1);

[0014] Step 5: The center distance between the two sub-apertures is L,

[0015] (2)

[0016] According to formula (2) and the direction of the pair of sub-apertures, the relative tilt Δθ of the two plates of the Fabry-Perot etalon in this direction is obtained;

[0017] Step 6: According to the tilt amount Δθ and tilt direction of the plate, adjust the spacer (or spacer) between the two plates of the Fabry-Perot etalon, and observe the translation of the two spectral curves at the same time. When the two spectral curves completely overlap, it means that the Fabry-Perot etalon is parallel in this direction.

[0018] Step 7: Replace the photon aperture on the mask and repeat steps 3 to 6;

[0019] Step 8: Allow all sub-apertures on the mask to pass light. When the spectral curves of all sub-apertures overlap, the two plates of the FP etalon are completely parallel.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention simultaneously obtains spectral curves of different regions of the FP (Fabry-Perot) etalon, and detects and calibrates the parallelism of the Fabry-Perot etalon by comparing the relative offset of the spectral curves. It does not require a precise moving mechanism, is not affected by the stability of the light source and the detection environment, and has better measurement and calibration effects.

[0022] (2) The present invention measures the spectral curve of the local area of ​​the Fabry-Perot etalon by a spectrometer, so the detection and calibration accuracy depends on the spectrometer used. Since the spectrometer has a high spectral resolution, the detection and calibration accuracy of the present invention is high and can reach the nanometer level.

[0023] (3) The present invention can determine the tilt direction of the Fabry-Perot etalon plate according to the orientation of the sub-aperture on the mask, and can perform real-time calibration of the parallelism of the Fabry-Perot etalon by observing the spectral curve. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the FP (Fabry-Perot) etalon parallelism detection and calibration system provided by the present invention;

[0025] Figure 2 is a schematic diagram of a mask and a subaperture provided by the present invention;

[0026] Figure 3 Schematic diagram of the plate spacing difference in a local area of ​​the Fabry-Perot etalon corresponding to the sub-aperture provided by the present invention;

[0027] Figure 4 It is a spectrum curve formed after the light beam provided by the present invention passes through sub-apertures 1 and 3;

[0028] Figure 5 It is a spectrum curve formed after the light beam provided by the present invention passes through sub-apertures 2 and 4;

[0029] Figure 6 It is a spectrum curve formed after the light beam provided by the present invention passes through all sub-apertures.

[0030] in, Figures 4 to 6 The vertical coordinate it / li is the ratio of the electron current to the intensity of the incident light. DETAILED DESCRIPTION

[0031] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0032] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0033] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0034] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0035] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0036] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0037] In a possible implementation, this embodiment provides a FP (Fabry-Perot) etalon parallelism detection and calibration method, such as Figure 1As shown, the specific steps include:

[0038] Step 1: Place a mask on the clear aperture of the Fabry-Perot etalon, and distribute n sub-clear apertures in pairs in different directions on the edge of the mask;

[0039] like Figure 2 As shown;

[0040] Different subapertures correspond to different regions of the FP etalon, and the distance between the plates in each region is h. n ,like Figure 3 As shown;

[0041] Step 2: The light emitted by the wide-band continuous spectrum light source is collimated to form a collimated beam, which is respectively injected into the n sub-apertures of the mask and their corresponding Fabry-Perot etalon areas, and then converged onto the focal plane through the imaging mirror;

[0042] Step 3: Block the sub-apertures on the mask so that only a pair of sub-apertures corresponding to the direction of light are left. Use a spectrometer to measure the spectral curve of the image point on the focal plane. When the two plates of the Fabry-Perot etalon are not parallel, the distance h between the two plates corresponding to the sub-apertures is n Inconsistent, in this case, two sub-apertures can obtain two spectral curves;

[0043] like Figure 4-Figure 5 As shown;

[0044] Step 4: Compare the offset Δλ of the two spectral curves, and calculate the difference Δh between the plate spacings corresponding to the two sub-apertures according to formula (1);

[0045] (1)

[0046] like Figure 3 As shown, h is the spacing and λ is the wavelength

[0047] Step 5: The center distance between the two sub-apertures is L. According to formula (2) and the direction of the pair of sub-apertures, the relative tilt Δθ of the two plates of the FP etalon in this direction can be obtained;

[0048] (2)

[0049] Step 6: According to the tilt amount and tilt direction of the plates, adjust the spacer (or spacer) between the two plates of the Fabry-Perot etalon, and observe the translation of the two spectral curves at the same time. When the two spectral curves completely overlap, it means that the Fabry-Perot etalon is parallel in this direction.

[0050] Step 7: Replace the photon aperture on the mask and repeat steps 3 to 6;

[0051] Step 8: Let all sub-apertures on the mask pass light. When the spectral curves of all sub-apertures overlap, the two plates of the FP etalon are completely parallel.

[0052] like Figure 6 shown.

[0053] In another embodiment, the spacing between the plates of the Fabry-Perot etalon to be detected is 100.0827 μm, the central wavelength is 656.28 nm, and the clear aperture is 30 mm;

[0054] The outer diameter of the mask is 30 mm, and 4 subapertures are evenly distributed on the edge of the mask. Subapertures 1 and 3 correspond to the y direction of the Fabry-Perot etalon, and subapertures 2 and 4 correspond to the x direction of the Fabry-Perot etalon. The diameter of the subaperture is 4 mm, and the subaperture center distance L is 22 mm.

[0055] The light source uses a halogen lamp, and the spectrometer uses an Ocean Optics high-resolution fiber optic spectrometer with a spectral resolution of 0.08nm;

[0056] Sub-apertures 2 and 4 are blocked, and the light beam converges to the focal plane after passing through sub-apertures 1 and 3. Two spectral curves are obtained after measuring the image point with a spectrometer. The offset Δλ of the two spectral curves near the wavelength of 656.28nm is 0.38nm. The difference Δh of the plate spacing corresponding to sub-apertures 1 and 3 is calculated using formula (1): y 57.95nm;

[0057] The center distance L between subapertures 1 and 3 is 22 mm. The relative tilt Δθ of the two plates of the Fabry-Perot etalon in the y direction is calculated using formula (2): y 0.54”;

[0058] According to the tilt amount and tilt direction of the plate, adjust the spacer between the two plates of the Fabry-Perot etalon, and observe the translation of the two spectral curves at the same time. When the two spectral curves completely overlap, it means that the Fabry-Perot etalon is parallel in the y direction.

[0059] Block sub-apertures 1 and 3, and the light beam converges to the focal plane after passing through sub-apertures 2 and 4. Using a spectrometer to measure the image point, two spectral curves can also be obtained. The offset Δλ of the two spectral curves near the wavelength of 656.28nm is 0.41nm. The difference in the plate spacing Δh corresponding to sub-apertures 2 and 4 is calculated using formula (1): x 62.525nm;

[0060] The center distance L of sub-apertures 2 and 4 is also 22 mm. The relative tilt Δθ of the two plates of the Fabry-Perot etalon in the x direction is calculated using formula (2): x 0.59”;

[0061] According to the tilt amount and tilt direction of the plate, adjust the spacer between the two plates of the Fabry-Perot etalon and observe the translation of the two spectral curves at the same time.

[0062] When the two spectral curves completely overlap, it means that the Fabry-Perot etalon is parallel in the x-direction;

[0063] Do not block the subaperture, e.g. Figure 2 In the example, subapertures 1, 2, 3 and 4 are all allowed to pass light. When the four spectral curves of the four subapertures coincide, the two plates of the Fabry-Perot etalon are completely parallel.

[0064] The detection and calibration accuracy of the present invention depends on the spectral resolution of the spectrometer. The resolution of the Ocean Optics high-resolution fiber optic spectrometer is 0.08 nm. According to formula (1), the measurement accuracy of the plate spacing difference in the local area of ​​the Fabry-Perot etalon is calculated to be 12.2 nm. According to formula (2), the parallelism detection and calibration accuracy of the Fabry-Perot etalon is calculated to be 0.11".

[0065] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0066] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for detecting and calibrating the parallelism of an FP etalon, wherein the FP etalon is composed of two parallel plates, the plates are made of fused quartz and are provided with a clear aperture, characterized in that: The specific steps include: Step 1: Place a mask on the clear aperture of the FP etalon. n clear subapertures are distributed in pairs around the edge of the mask. Each subaperture matches the area of ​​the FP etalon, and the plate spacing of the corresponding area is h. n ; Step 2: The light emitted by the wide-band continuous spectrum light source is collimated to form a collimated beam, which is respectively injected into the n sub-apertures on the mask and their corresponding Fabry-Perot etalon areas, and then converged to the focal plane through the imaging mirror; Step 3: Block the sub-apertures on the mask, leaving only a pair of sub-apertures corresponding to the direction through which light passes, and use a spectrometer to measure the spectral curve of the image point on the focal plane; When the two plates of the Fabry-Perot etalon are not parallel, the distance between the plates corresponding to the two subapertures is h. n Inconsistent, in this case, two sub-apertures obtain two spectral curves; Step 4: Compare the offset Δλ of the above two spectral curves. Δh=(h / λ)Δλ (1) And according to formula (1), the difference Δh between the plate spacings corresponding to the two sub-apertures is calculated, where h is the spacing and λ is the wavelength; Step 5: The center distance between the two sub-apertures is L, Δθ=arctan(Δh / L) (2) According to formula (2) and the direction of the pair of sub-apertures, the relative tilt Δθ of the two plates of the Fabry-Perot etalon in this direction is obtained; Step 6: According to the tilt amount Δθ and tilt direction of the plate, adjust the spacer between the two plates of the Fabry-Perot etalon, and observe the translation of the two spectral curves at the same time. When the two spectral curves completely overlap, it means that the Fabry-Perot etalon is parallel in this direction. Step 7: Replace the photon aperture on the mask and repeat steps 3 to 6; Step 8: Allow all sub-apertures on the mask to pass light. When the spectral curves of all sub-apertures overlap, the two plates of the Fabry-Perot etalon are completely parallel.

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