A Fourier spectrum interferometer

Abstract

The present application relates to the field of scientific research and teaching instruments, and specifically provides a Fourier spectrum interferometer, which comprises, in sequence along an optical path, a light source, a collimating lens, an object plane, an imaging lens, a spectrum plane, a spectrum imaging lens and a receiver. The imaging lens converges object plane information on the focal plane of the imaging lens by laser, forming the spectrum of the object plane information, i.e. the first Fourier transform of the object plane information. When the spectrum imaging lens is inserted into the optical path, the spectrum image of the spectrum plane is observed on the receiver. When the spectrum imaging lens is removed from the optical path, the light rays of the spectrum target plane or the gating sheet interfere at the receiver position, i.e. the second Fourier transform of the object plane information, displaying the optical image of the object plane. The present application can quickly switch the spectrum imaging lens to observe the two Fourier transforms of the optical system, and demonstrate the results of diffraction, interference and optical frequency multiplication through specific spectrum, facilitating a deep understanding of the principle of optical information transmission.

Description

Technical Field

[0001] This invention belongs to the field of scientific research and teaching instruments technology, and in particular relates to a Fourier spectrum interferometer. Background Technology

[0002] Information optics is the theoretical foundation of modern optical instruments and optical information processing, and is widely used in optical imaging, optical communication, optical measurement, optical encryption, and other fields. The Fourier transform has significant physical meaning in optics; optical Fourier transforms can be achieved through optical elements such as lenses, converting spatial domain information to the frequency domain, thereby enabling spectral analysis and modulation of light fields.

[0003] However, current scientific research and teaching practices lack systematic Fourier transform experimental equipment. Traditional textbooks often explain the Fourier transform process using group interference theory, which is extremely abstract and lacks intuitive optical experimental verification methods. Learners find it difficult to connect the abstract mathematical transformation with physical images, resulting in an understanding of Fourier optics that remains at the level of formula derivation. Furthermore, core concepts such as diffraction, interference, spectral analysis, and optical frequency doubling are usually scattered across different experimental setups, making it impossible to conduct systematic learning from basic to advanced levels on a single platform, which is detrimental to building a complete optical knowledge system.

[0004] Among existing optical experimental equipment, only the 4f system is an experimental setup for optical Fourier transform. Firstly, the 4f system is a device, not an instrument; the placement and adjustment of each component during experiments is time-consuming and labor-intensive. Secondly, the 4f system lacks a spectral target holder for mounting through-planes or spectral targets, making it impossible to quickly demonstrate the spectrum and perform comprehensive experiments on diffraction interference. Thirdly, the 4f system lacks an object plane holder for rapid object plane replacement. This makes it difficult to visually demonstrate spectral interference phenomena, limiting a deeper understanding of core concepts such as diagonal spectrum, spectrum, interference, diffraction, and optical frequency doubling.

[0005] Therefore, there is an urgent need for a teaching and research instrument that can intuitively demonstrate optical Fourier transform, interference, diffraction, and spectral analysis, so that students and researchers can directly observe optical phenomena through experiments and deeply understand the basic principles of Fourier optics. Summary of the Invention

[0006] In view of this, the present invention aims to provide a Fourier spectrum interferometer, which solves the technical problems of existing instruments such as limited functionality, inability to intuitively display spectrum interference, and disconnect between theory and experiment. It also realizes the function of flexibly switching between imaging observation mode and spectrum analysis mode on the same device, allowing for intuitive observation of two Fourier transforms and supporting optical frequency doubling experiments and successive signal analysis.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows: This invention provides a Fourier spectrum interferometer, comprising the following components arranged sequentially along the optical path: A light source, used to provide parallel laser light; The object surface, which is a one-dimensional grating or a two-dimensional orthogonal grating, is placed on the output light path of the parallel laser and is used to spatially modulate the parallel laser. The object surface is provided with an object surface holder, which is used to install a switchable object surface clip. The object surface is in a fixed position in the object surface clip. An imaging lens is positioned in the rear optical path of the object surface and is used to image the light field modulated by the object surface. The spectral plane is located at the back focal point of the imaging lens. Parallel laser light passing through the object plane passes through the imaging lens and undergoes the first Fourier transform on the spectral plane, forming the spectrum of the object plane. A spectral target holder is provided at the position of the spectral plane, which is used to install a switchable gating plate or spectral target. A spectrum imaging lens is located on the rear optical path of the spectrum plane. The object side of the spectrum imaging lens is on the spectrum plane. The spectrum imaging lens can be moved out of or into the optical path. The receiver is used to receive the first Fourier transform result of the imaging lens when the spectral imaging lens moves into the optical path; when the spectral imaging lens moves out of the optical path, the receiver is on the image plane of the imaging lens and is used to observe the second Fourier transform result of the imaging lens.

[0008] Preferably, the light source includes a laser and a collimating lens disposed at the laser emission end, the collimating lens being used to process the laser emitted by the laser into a parallel laser.

[0009] Preferably, the pattern on the object surface is a grating structure etched on transparent glass, and the grating structure adopts a one-dimensional grating or a two-dimensional orthogonal grating with different duty cycles.

[0010] Preferably, a surface support is provided at the position of the surface to position the surface; the surface is fixed to the surface support by a plug-in method, the surface support is used to replace the surface clip, and the glass with an etched grating structure is bonded to the surface clip to ensure that the center of the surface pattern on the glass is uniquely located in the surface clip.

[0011] One-dimensional or two-dimensional orthogonal gratings with different duty cycles are installed on the object plane to observe the amplitude changes of each spectrum on the spectral plane and analyze the amplitude information of each order spectrum in the spectrum of the first Fourier transform.

[0012] Preferably, the receiver is a CCD photoelectric receiver or a receiving screen.

[0013] Preferably, the receiver has a guiding and positioning mechanism at its front end, and the spectrum imaging lens is installed in a fixed position through the guiding and positioning mechanism.

[0014] Preferably, the gate is a pinhole glass plate with fixed-order characteristic spectral positions that allows light to pass through, enabling diffracted light of two specific orders to pass through. The diffracted light of the two orders interferes and forms interference fringes of a specific single spatial frequency, which is a multiple of the object plane's fundamental frequency, thus achieving optical frequency doubling. The gate is also used to allow diffracted light of more than two specific orders to pass through, using the interference of composite diffracted light of more than two specific orders to form a special fixed pattern. The spectral target is a glass plate with pinholes that allow light to pass through all spectral points. The spectral target has pinhole glass plates with fixed positions. The pinholes are transparent, and all spectral points generated by the spectral surface can pass through their corresponding pinholes. By programming the pinholes to block or black out useless pinholes, the functions of all gates can be realized on one spectral target, and one spectral target replaces all gates.

[0015] Preferably, parallel laser light irradiates the object surface and diffracts, and the diffraction angle of the diffracted light is the object-side aperture angle of the imaging lens.

[0016] Preferably, gating plates corresponding to different orders are sequentially placed into the optical path, and the corresponding harmonic information of each diffraction order is collected and observed for interference. By changing the amplitude of each diffraction order, its impact on the quality of harmonic information is observed, the order that causes the degradation of the interference image signal quality is identified, and correction is performed on the order that causes the degradation of the interference image signal quality.

[0017] Preferably, a light source holder is provided at the position of the light source, and the light source is screwed onto the light source holder through an interface to position the light source.

[0018] Compared with the prior art, the present invention can achieve the following beneficial effects: This invention designs a Fourier spectrum interferometer for teaching practice and scientific research. It interprets optical imaging as two Fourier transforms and allows for the separate observation of the results of each transform. By combining complex and abstract mathematical derivations with optical phenomena, learners can clearly understand the principles of the first and second Fourier transforms. Furthermore, the removable or insertable spectral imaging lens enables flexible switching between imaging observation mode and spectral analysis mode on the same device, offering multiple uses and avoiding the duplication of multiple instruments, thus significantly reducing the cost of teaching experimental equipment. The device allows for rapid observation of the first and second Fourier transforms of the optical system by switching the spectral imaging lens. By gating specific spectral effects on the spectral plane, it demonstrates diffraction, interference, and optical frequency doubling results, facilitating a deeper understanding of Fourier optics and the characteristics of the imaging lens, such as diffraction limit, optical resolution, and transfer function.

[0019] This invention starts with diffraction and interference, and supports progressive teaching from one-dimensional to two-dimensional, from diffraction to interference, and then to optical frequency doubling. It helps learners build a complete physical picture from the spatial-temporal domain to the frequency domain and then to the temporal domain, thus solving the problem of the disconnect between theory and experiment.

[0020] This invention sets a gating plate at the spectral plane position, realizing the gating and interference imaging of diffracted light of a specific order. It can clearly show the optical frequency doubling phenomenon where the spatial frequency of a single-order interference fringe is a multiple of the fundamental frequency, as well as the beat frequency and Fourier synthesis effect of multi-order composite interference fringes, making the abstract concept of spectral interference intuitive and visible. In addition, the gating plate can be replaced with a more automated spatial light modulator, which can dynamically generate arbitrary gating patterns, support user-defined filtering experiments, and expand the teaching and scientific research application scope of the equipment.

[0021] This invention sequentially places gating plates corresponding to different orders into the optical path, collects the frequency doubling signals corresponding to each diffraction order, and performs quality analysis on the frequency doubling signals of each diffraction order. It establishes a mapping relationship between the frequency doubling signals of each diffraction order and the interference image obtained without gating plates, thereby accurately identifying the key orders that cause degradation of the overall interference image signal quality and performing targeted corrections on these orders. This achieves closed-loop control from overall observation to order-by-order tracing and precise optimization. This order-by-order analysis and correction mechanism not only effectively improves the quality of high-order frequency doubling signals and optimizes the overall system performance, but also provides students with a complete experimental platform for signal quality analysis and system optimization, cultivating their problem diagnosis and solving abilities. It has significant research and teaching practice value. This invention's device can not only assist in understanding what the first and second Fourier transforms are, and what optical diffraction, diffractive interference, and optical frequency doubling are, in teaching and research, but also enable observation and understanding that the rectangular black-and-white grating of the object surface is composed of information of various spatial frequencies. Based on this understanding, the transfer function of the optical system can be designed, and the resolution limit of the optical system can be obtained. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the Fourier spectrum interferometer provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of different orders of spectrum passing through a one-dimensional grating provided according to an embodiment of the present invention; Figure 3 The embodiments of the present invention provide a corresponding Figure 2 A schematic diagram of the interference formed by different orders of the spectrum of a one-dimensional grating; Figure 4 This is a schematic diagram showing the passage of different orders of the spectrum of a two-dimensional grating according to an embodiment of the present invention; Figure 5 This is the corresponding embodiment provided according to the present invention. Figure 3 A schematic diagram of the interference formed by different orders of the spectrum of a two-dimensional grating; Figure 6 This is a schematic diagram of a specific order of multispectral transmission of a two-dimensional grating according to an embodiment of the present invention; Figure 7 The corresponding embodiment is provided according to the present invention. Figure 6 A schematic diagram of the "petals" formed by multispectral interference.

[0023] The reference numerals in the figures include: 1. Laser, 2. Collimating lens, 3. Object plane, 4. Imaging lens, 5. Spectral plane, 6. Spectral imaging lens, 7. Receiver. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and do not constitute a limitation thereof. Similar elements in different embodiments are referred to by associated similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the invention. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, some operations related to the invention are not shown or described in the specification. This is to avoid obscuring the core parts of the invention with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; the relevant operations can be fully understood based on the description in the specification and general technical knowledge in the art.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined to form various implementations. Furthermore, the order of the steps or actions in the method description can be changed or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various orders in the specification and drawings are merely for the clear description of a particular embodiment and do not imply a mandatory order, unless otherwise stated that a particular order must be followed.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0027] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] Please see Figure 1 In one embodiment of the present invention, a Fourier spectrum interferometer is provided, comprising the following components arranged sequentially along the optical path: A light source, used to provide parallel laser light; Object surface 3, which is a one-dimensional grating or a two-dimensional orthogonal grating, is set on the output light path of the parallel laser and is used to spatially modulate the parallel laser. Object surface 3 is provided with an object surface seat, which is used to install a switchable object surface clip, and the object surface 3 is fixed in a preset position by the object surface clip. Imaging lens 4 is located in the optical path at the rear end of object surface 3. Imaging lens 4 is used to image the light field modulated by object surface 3. The spectral surface 5 is located at the rear focal point of the imaging lens 4. The parallel laser light passing through the object surface 3 passes through the imaging lens 4 and undergoes the first Fourier transform on the spectral surface 5, forming the spectrum of the object surface 3 on the spectral surface 5. A spectral target holder is provided at the position of the spectral surface 5, which is used to install a switchable gating plate or a spectral target surface. The spectrum imaging lens 6 is located on the rear optical path of the spectrum plane 5. The object side of the spectrum imaging lens 6 is on the spectrum plane 5. The spectrum imaging lens 6 can be moved out of or into the optical path. Receiver 7 is used to receive the first Fourier transform result of imaging lens 4 when the spectrum imaging lens 6 moves into the optical path; when the spectrum imaging lens 6 moves out of the optical path, receiver 7 is located on the image plane of imaging lens 4 to observe the second Fourier transform result of imaging lens 4. Imaging lens 4, spectral plane 5, spectral plane 6, spectral plane 5, receiver 7. Imaging lens 4, spectral plane 6, spectral plane 6, receiver 7.

[0030] The light source provides the parallel laser light required for imaging and includes a laser 1 and a collimating lens 2. A common semiconductor laser can be used for the laser 1. Since the laser light emitted directly from the laser 1 has a certain divergence angle and cannot be used directly, a collimating lens 2 is placed at the rear end of the laser exit of the laser 1. The beam emitted by the laser 1 is processed by the collimating lens 2 to form a parallel laser beam. If a helium-neon laser is used, the collimating lens 2 is omitted.

[0031] The object plane 3 is positioned on the rear optical path of the collimating lens 2. To avoid on-site adjustment during each use, the object plane 3 in this embodiment of the invention uses an object plane holder. The object plane holder is designed to position the object plane 3. The object plane 3 is fixed to the object plane holder by a plug-in method, facilitating quick replacement of the object plane 3. The object plane holder is equipped with an object plane clip to fix the object plane 3 in a preset position. This ensures that the object plane 3 can be reset during replacement, preventing positional shifts caused by replacement and thus affecting subsequent imaging effects. One-dimensional or two-dimensional orthogonal gratings with different duty cycles can be installed on the object plane holder to observe the amplitude transformation of each spectrum on the spectral plane 5 and analyze the amplitude information of each order spectrum in the spectrum of the first Fourier transform. Therefore, as a teaching tool for students, the object surface 3 adopts a fixed-position design. An object surface holder is provided at the position of the object surface 3, which is used to install a switchable object surface clip. The object surface 3 remains in the fixed position of the object surface clip, while the object surface holder can replace the object surface clip. When replacing the object surface 3 on the object surface clip, it is necessary to ensure that the center of the object pattern on the object surface 3 remains uniquely fixed on the object surface clip. The object surface support is provided with a guide sliding slot to facilitate the installation and replacement of the object surface 3. The object surface 3 on the object surface support is preferably a one-dimensional grating or a two-dimensional orthogonal grating with switchable duty cycles, facilitating imaging and observation of diffraction, interference, and frequency doubling phenomena. After parallel laser light shines on the object surface 3, it is spatially modulated by the periodic structure of the object surface 3. The parallel laser light diffracts on the object surface 3, and the diffraction angle of the diffracted light is the object-side aperture angle of the imaging lens 4.

[0032] The parallel laser beam modulated by object plane 3 continues to propagate into imaging lens 4, which is used to image the light field modulated by object plane 3. Imaging lens 4 can be any existing optical imaging lens according to design requirements. After the modulated light field passes through imaging lens 4, it undergoes a first Fourier transform to form the Fourier spectrum of object plane 3 at its focal point. The plane containing the spectrum is called spectral plane 5. Placing a spectral target on this plane can receive the spectral pattern. In the laboratory, tracing paper or frosted glass can be placed on spectral plane 5 to observe the spectrum of object plane 3. This helps students understand the abstract concept of spectrum. Taking a one-dimensional grating as object plane 3 as an example, its spectrum is a series of light spots arranged at equal intervals along the direction perpendicular to the grating lines. The brightness changes of light spots of different diffraction orders can be observed, and the brightness of each spectrum is different. The phenomenon of "missing orders" can also be observed. Using spectral lens 6 on receiver 7 to observe the information of the spectral plane will be more convenient, faster, and clearer.

[0033] The parallel laser beam modulated by the object plane 3 undergoes a second Fourier transform after passing through the spectral plane 5, and optical imaging is achieved on the receiver 7. The receiver 7 can generally be a CCD photoelectric receiver or a receiving screen.

[0034] It should be noted that, in order to facilitate the demonstration of phenomena such as diffraction, interference, and optical frequency doubling to students, this embodiment of the invention also includes a removable or insertable spectrum imaging lens 6 in the optical path between the spectrum imaging lens 6 and the receiver 7. An existing spectrum lens can be used for the spectrum imaging lens 6. It is sufficient to ensure that the image planes of the imaging lens 4 and the spectrum imaging lens 6 are coplanar, and that the receiver 7 is fixed at the shared image plane position of the imaging lens 4 and the spectrum imaging lens 6; alternatively, they can be different.

[0035] Since the spectrum imaging lens 6 needs to be moved out and put in, to ensure that the position of the spectrum imaging lens 6 in the optical path is consistent each time, this embodiment of the invention mounts the spectrum imaging lens 6 on a lens bracket and provides a plug-in interface between the imaging lens 4 and the receiver 7. The spectrum imaging lens 6 is mounted on the plug-in interface through the lens bracket, ensuring that the position of the spectrum imaging lens 6 is fixed and avoiding the need for operators to adjust the position of the spectrum imaging lens 6 each time. In this embodiment of the invention, the light source, object plane 3, imaging lens 4, spectrum plane 5, spectrum imaging lens 6, and receiver 7 of the Fourier spectrum interferometer are all pre-modulated at the factory, and the position of each component is fixed. The light source is set on a fixed light source holder, and the light source is screwed onto the light source holder through an interface to locate the position of the light source. The object plane 3 is set on a fixed object plane holder, and the object plane is fixed to the object plane holder by a plug-in method to locate the position of the object plane 3. The imaging lens 4 is immovable and set in a fixed position. The object side of the imaging lens 4 is the object plane 3, and the image side of the imaging lens 4 is on the receiver 7. A spectral target mount is provided at position 5 on the spectral surface for mounting a gate chip or spectral target surface. The spectral imaging lens 6 is mounted on a lens support, and the position of the receiver 7 remains fixed. The object side of the spectral imaging lens 6 is on the spectral surface 5, and the image side is on the receiver 7. This invention eliminates the need for on-site assembly and adjustment by the user, improving ease of use.

[0036] In the process of learning Fourier optics, the Fourier spectrum interferometer provided in this embodiment of the invention can clearly demonstrate phenomena such as diffraction (first Fourier transform), interference (second Fourier transform), and optical frequency doubling. Students can use the Fourier spectrum interferometer to conduct related experiments and observe the spectrum of object plane 3 obtained after the first Fourier transform, the time-domain optical image obtained after the second Fourier transform, and the optical frequency doubling image, which facilitates understanding the abstract and complex mathematical derivation of Fourier optics.

[0037] First, for diffraction phenomena, it is necessary to observe the spectrum of object plane 3. There are two ways to observe the spectrum: one is to place sulfuric acid paper or frosted glass on the spectral plane 5 to directly observe the spectrum. However, this method cannot clearly and accurately capture the spectrum, nor is it conducive to subsequent optical research via computer. Therefore, this embodiment of the invention also provides another method, which not only allows observation of the spectrum but also allows for subsequent processing of the spectrum information via computer. Specifically, during the experiment, the spectral imaging lens 6 is placed in the optical path. At this time, the spectral imaging lens 6 images the spectrum on the spectral plane 5 onto the receiver 7, and a series of bright light spots can be observed. These photoelectric spots are the spectrum of object plane 3 obtained after the first Fourier transform. By comparing the spectrum when object plane 3 is a grating with different parameters (such as different spatial frequencies and different amplitudes), students can intuitively understand the relationship between spatial frequency and the spacing between spectral points, as well as the spectral differences between amplitude-type and phase-type objects. At this time, the spectral imaging lens 6 is actually using the spectrum of object plane 3 as the object source for imaging. If receiver 7 uses a receiving screen, the spectrum can be observed on the receiving screen; if receiver 7 uses a CCD photoelectric receiver, the CCD photoelectric receiver can be connected to a computer display screen, and not only can the spectrum be observed on the display screen, but the spectrum can also be analyzed and compared.

[0038] To observe the interference phenomenon, it is necessary to observe the optical temporal image of object plane 3. During the experiment, the spectral imaging lens 6 is moved out of the optical path. At this time, the receiver 7 receives the optical temporal image of object plane 3 after two Fourier transforms. Taking a one-dimensional grating as an example, the optical temporal image is a clear stripe of alternating bright and dark colors; a two-dimensional grating is a small square array.

[0039] For optical frequency doubling, diffraction transforms parallel laser light into multiple orders of diffracted light. Each order of diffracted light corresponds to a different spot on the spectrum. Taking object plane 3 as a one-dimensional grating as an example, its spectral plane 5 has diffracted spots of orders 0, ±1, ±2, etc. Current teaching methods typically explain the interference process of multi-order diffracted light using abstract mathematical derivations or direct physical phenomena, directly explaining the composite diffraction results of all orders. This explanation is too abstract and difficult to understand; students cannot grasp how each order of diffracted light participates in the interference, or what the final diffraction result is when some orders of diffracted light are blocked. To solve the above problems, this embodiment of the invention further sets up a spectral target at the position of spectral plane 5. The spectral target also adopts a fixed-position plug-and-play design. The spectral target facilitates the installation of a gating plate to block specific orders of diffracted light or allow only specific orders of diffracted light to pass through, thereby studying the optical frequency doubling phenomenon and gaining a deeper understanding of the diffraction and interference processes. The gating plate is the spectral aperture. The gating plate specifically employs a pinhole glass plate with fixed-order characteristic spectral positions, allowing light to pass through. This allows diffracted light of two specific orders to pass through, and the interference imaging of these two orders forms interference fringes at a specific single spatial frequency. This spatial frequency is a multiple of the object's fundamental frequency, enabling optical frequency doubling experiments. Furthermore, the gating plate can also allow diffracted light of more than two specific orders to pass through, utilizing the interference imaging of composite diffracted light of two or more specific orders to form a special fixed pattern. The spectral target holder can also mount a spectral target surface, which is a glass plate with pinholes at fixed positions. These pinholes are transparent, allowing all spectral points generated by the spectral surface to pass through their corresponding pinholes. By programming the pinholes—that is, by blocking or blacking out useless pinholes—the function of all the gating plates can be achieved on a single spectral target surface, with one spectral target surface replacing all the gating plates.

[0040] In studying optical frequency doubling experiments involving single-order interference, a gating plate can be selected that allows only specific orders of diffracted light to pass through, while physically blocking other orders. For example, by installing a gating plate on a spectral target that only allows the +1st and -1st order diffracted light to pass through, while blocking all other orders, and then moving the spectral imaging lens 6 out of the optical path, the receiver 7 will receive an image formed solely by the interference of the +1st and -1st order lights. Since the +1st and -1st order diffracted lights correspond to twice the fundamental frequency, the spatial frequency of the resulting interference fringes is twice the spatial frequency of the object plane 3, thus achieving optical frequency doubling. Taking a 25-line one-dimensional grating as the object plane 3 as an example, if a gating plate is installed on the spectral target... Figure 2 Figure a shows a gate that allows only +1st and 0th order diffracted light to pass through. The interference pattern received at receiver 7 is as follows. Figure 2 As shown in Figure a, it represents 25 lines; if a target is mounted on the spectral target holder as shown in Figure a... Figure 2Figure b shows a gate that allows only +1st and -1st order diffracted light to pass through. The interference pattern received at receiver 7 is as follows. Figure 3 As shown in b, this represents 50 lines. Similarly, if a target is mounted on a spectral target holder as shown... Figure 2 The interference pattern received at receiver 7 by a gate that only allows +1st and -2nd order diffracted light to pass through, while blocking all other orders, is shown in Figure c. Figure 3 As shown in Figure c, this represents 75 lines. If only +2nd and -2nd order diffracted light are allowed to pass through, the spatial frequency of the interference fringes is four times the original fundamental frequency. Taking a two-dimensional grating with 25 lines in each row and column as object plane 3 as an example, if a grating with 25 lines in each row and column is installed on the spectral target... Figure 4 Figure a shows a gate that allows only diffracted light of orders (0, 0), (0, +1), (-1, 0), and (-1, -1) to pass through. The interference pattern received at receiver 7 is as follows. Figure 5 As shown in Figure a, it is a 25×25 square matrix; if a spectral target is mounted as shown in Figure a... Figure 4 Figure b shows a gate that allows only (+1, -1), (+1, +1), (-1, +1), and (-1, -1) order diffracted light to pass through. The interference pattern received at receiver 7 is as follows. Figure 5 As shown in Figure b, this is a 50×50 grid matrix. Similarly, if a spectral target is mounted on a grid like... Figure 2 The interference pattern received at receiver 7 by a gated plate shown in Figure c, which allows only diffracted light of orders (+1, +2), (+1, -1), (-2, +2), and (-2, -1) to pass through while blocking all other orders, is as follows. Figure 5 As shown in c, this is a 75×75 grid matrix. Furthermore, irregular order diffracted light can be selected to pass through, such as... Figure 6 As shown, the receiver 7 can receive the following: Figure 7 The image shown is a frequency mixing interferometer of a specific shape.

[0041] This helps students understand that any image can be decomposed into spectral components of different frequencies; and that selecting specific frequency components and superimposing them for interference can reconstruct fringes of the corresponding frequency. By comparing full-spectrum imaging and single-order imaging through imaging lens 4, students can intuitively understand the contribution of different frequency components to the details of the final image.

[0042] When studying optical interference experiments involving the blocking of specific orders of diffracted light, a gating plate that allows multiple specific orders of diffracted light to pass through can be used. For example, a gating plate can be installed on a spectral target holder that blocks only the +1st and -1st order diffracted light while allowing all other orders of diffracted light to pass through. In this case, if the spectral imaging lens 6 is moved out of the optical path, the receiver 7 will receive multi-order composite interference fringes formed by the lack of interference from the +1st and -1st order light. Students would usually think that the fringes corresponding to the +1st and -1st order light would become darker in this situation. However, according to actual experimental observations, the positions corresponding to the blocked orders do not become darker, but instead present a set of interference fringes with higher density and lower contrast, that is, interference fringes of higher-order diffracted light are leaking out.

[0043] As an optional embodiment, a spatial light modulator is positioned at the spectral plane 5, replacing the gating plate. The spatial light modulator is electrically connected to a controller and can dynamically change its optical properties according to the electrical signal, thereby generating a gating pattern of arbitrary shape on the spectral plane 5. The gating pattern includes one or more light-transmitting regions, the positions of which correspond to the spatial positions of preset diffraction orders on the spectral plane 5. It can selectively allow one or more specific orders of diffracted light to pass through, realizing programmable optical frequency doubling experiments. The spatial light modulator can instantaneously switch gating patterns, achieving rapid switching between different filtering modes without the need for manual replacement of the gating plate, making operation more convenient and supporting an unlimited number of gating and filtering modes from simple to complex.

[0044] As an optional embodiment, the Fourier spectrum interferometer of this invention can be used for signal analysis. Since the light field distribution on the image plane is the result of the coherent superposition of each diffraction order on the image plane, to study which orders affect the signal quality of the full-spectrum interferometric image, a full-spectrum interferometric image with all orders of light can be acquired first. Then, gating plates corresponding to different orders are sequentially placed into the optical path. Here, gating plates corresponding to different orders refer to gating plates that allow only one pair of diffracted light of a specific order to pass through. After sequentially placing gating plates corresponding to different diffraction orders (such as ±1st, ±2nd, ±3rd...±Kth orders) into the spectral target at position 5 on the spectral plane, for each gating plate, the corresponding single-order harmonic signal image is acquired. Quantitative quality analysis is performed on each harmonic signal image. By changing the amplitude of each diffraction order, its impact on the quality of the harmonic information is observed, identifying the orders that cause signal quality degradation in the interferometric image. Targeted correction is then performed on the problematic orders, thus realizing a closed-loop process of signal acquisition, analysis, and correction. The process of sequentially replacing different levels of gating chips described above can also be achieved using an coded spatial light modulator, enabling rapid and automated acquisition without the need for manual gating chip replacement.

[0045] The Fourier spectrum interferometer proposed in this invention can effectively demonstrate diffraction, interference, and optical frequency doubling results, making it easier for students to deeply understand Fourier optics. It solves the problem that existing teaching methods rely solely on abstract mathematical derivations. This Fourier spectrum interferometer can be used as a teaching tool and experimental instrument, and has extremely high application value for basic teaching and research.

[0046] In summary, the above description is merely a preferred embodiment of this specification and is not intended to limit the scope of protection of this specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this specification should be included within the scope of protection of this specification.

[0047] The systems, apparatuses, modules, or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, a computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0048] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0049] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

Claims

1. A Fourier spectrum interferometer, characterized in that, Including those arranged sequentially along the optical path: A light source, used to provide parallel laser light; The object surface, which is a one-dimensional grating or a two-dimensional orthogonal grating, is placed on the output light path of the parallel laser and is used to spatially modulate the parallel laser. The object surface is provided with an object surface seat, which is used to install a switchable object surface clip to fix the object surface in a preset position. An imaging lens is disposed on the rear optical path of the object surface, and the imaging lens is used to image the light field modulated by the object surface. The spectral surface is located at the rear focal point of the imaging lens. Parallel laser light passing through the object surface undergoes a first Fourier transform on the spectral surface after passing through the imaging lens, forming the spectrum of the object surface. A spectral target holder is provided at the position of the spectral surface, which is used to install a switchable gating plate or a spectral target surface. A spectrum imaging lens is located in the rear optical path of the spectrum plane, the object side of the spectrum imaging lens is on the spectrum plane, and the spectrum imaging lens can be moved out of or into the optical path. The receiver is used to receive the first Fourier transform result of the imaging lens when the spectral imaging lens moves into the optical path; and to observe the second Fourier transform result of the imaging lens on the image plane when the spectral imaging lens moves out of the optical path.

2. The Fourier spectrum interferometer according to claim 1, characterized in that, The light source includes a laser and a collimating lens disposed at the laser emission end, the collimating lens being used to process the laser emitted by the laser into a parallel laser.

3. The Fourier spectrum interferometer according to claim 1, characterized in that, The pattern on the surface is a grating structure etched on transparent glass, and the grating structure adopts a one-dimensional grating or a two-dimensional orthogonal grating with different duty cycles.

4. The Fourier spectrum interferometer according to claim 3, characterized in that, The object surface is fixed to the object surface holder by a plug-in method. One-dimensional gratings or two-dimensional orthogonal gratings with different duty cycles are installed on the object surface holder to observe the amplitude changes of each spectrum on the spectral surface and analyze the amplitude information of each order spectrum in the spectrum of the first Fourier transform.

5. The Fourier spectrum interferometer according to claim 1, characterized in that, The receiver is a CCD photoelectric receiver or a receiving screen.

6. The Fourier spectrum interferometer according to claim 4, characterized in that, The receiver is equipped with a guiding and positioning mechanism at its front end, and the spectrum imaging lens is installed in a fixed position through the guiding and positioning mechanism.

7. The Fourier spectrum interferometer according to claim 1 or 6, characterized in that, The gate is a glass plate with a fixed-position light-passing pinhole. The gate allows diffracted light of two specific orders to pass through. The interference of the two orders of diffracted light forms an interference fringe with a specific single spatial frequency, which is a multiple of the fundamental frequency of the object plane, thus achieving optical frequency doubling. The gate also allows diffracted light of more than two specific orders to pass through. The interference of the composite diffracted light of more than two specific orders forms a special fixed pattern. The Fourier spectrum interferometer is further characterized by a spectral target surface being a glass plate with a fixed-position light-passing pinhole. All spectral points generated by the spectral surface can pass through their corresponding pinholes on the spectral target surface. By programming the pinholes to block or black out useless pinholes, the functions of all gates can be realized on a single spectral target surface.

8. The Fourier spectrum interferometer according to claim 1 or 6, characterized in that, When a parallel laser beam is irradiated onto the object surface, diffraction occurs, and the diffraction angle of the diffracted light is the object-side aperture angle of the imaging lens.

9. The Fourier spectrum interferometer according to claim 6, characterized in that, Gating plates of different orders are sequentially placed into the optical path, and the corresponding harmonic information of each diffraction order is collected and observed for interference. By changing the amplitude of each diffraction order, its impact on the quality of harmonic information is observed, the order that causes the degradation of the interference image signal quality is identified, and correction is performed on the order that causes the degradation of the interference image signal quality.

10. The Fourier spectrum interferometer according to claim 1, characterized in that, The light source is positioned on a light source holder, and the light source is screwed onto the light source holder via an interface to position the light source.

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