A cross-dispersion principle-based echelle grating spectrometer and a preparation method thereof

Abstract

This invention discloses a mid-step grating spectrometer based on the principle of cross-dispersion and its fabrication method. The spectrometer includes a principal dispersive element, a transverse dispersive element, an area array detector, an optical fiber, and a slit. The principal dispersive element is a mid-step curved grating; the transverse dispersive element is a small-step curved grating. The mid-step curved grating and the small-step curved grating are used in combination to achieve spectral dispersion and point-to-point aberration elimination imaging. The area array detector is placed in the direction of the emitted light; the optical fiber is used to emit the light to be measured; the slit is located after the optical fiber and acts as an aperture stop. This invention uses a mid-step curved grating and a small-step curved grating to perform cross-dispersion, eliminating the need for collimating and focusing mirrors in traditional structures. The structure is compact, and high-resolution detection can be achieved, solving the problems of large number of components, high cost, and complex assembly in traditional cross-dispersion mid-step grating structures.

Description

Technical Field

[0001] This invention relates to the field of spectroscopic analysis instrument technology, and in particular to a mid-echelon grating spectrometer based on the principle of cross-dispersion and its preparation method. Background Technology

[0002] Existing miniature spectrometers are generally designed based on the Cherny-Turner structure or the Loland circular concave grating structure, which cannot simultaneously achieve high resolution and wide band detection.

[0003] Echeveria grating spectrometers achieve both high dispersion and a wide detection range. They utilize an echeveria grating as the primary dispersive element, employ low-dispersion prisms or small echeveria gratings for lateral dispersion, and use an area array detector to acquire a two-dimensional spectral image formed on the image plane. Finally, data processing yields complete spectral information. Existing technologies typically require numerous components, including collimating mirrors, focusing mirrors, primary dispersive elements, and lateral dispersive elements. The collimating and focusing mirrors increase the number of components, size, and cost, and also limit the possibility of integrating the echeveria grating structure onto a chip, thus hindering mass production.

[0004] Generally, existing cross-dispersive spectrometers mainly have two structures. The first type uses a zigzag grating as the primary dispersive element and a prism as the auxiliary dispersive element in a cross-dispersive optical path. When using a prism as the lateral dispersive element, there are no problems with blaze or order overlap, resulting in high efficiency. However, the prism is relatively large, which is not conducive to the miniaturization of the device. The second type uses a zigzag grating as the primary dispersive element and a low-line-density grating as the lateral dispersive element. Using a grating as the lateral dispersive element can achieve greater order separation and a wider operating wavelength range. However, it requires etching into a small step shape to increase diffraction efficiency. Both of these methods require collimating and focusing mirrors or lenses to achieve imaging, resulting in a large number of components, higher cost, and more complex assembly. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] Therefore, embodiments of the present invention propose a mid-echelon grating spectrometer based on the principle of cross-dispersion and its preparation method.

[0007] This invention proposes a mid-echelon grating spectrometer based on the principle of cross-dispersion, comprising:

[0008] The principal dispersive element is a mid-step curved grating;

[0009] A lateral dispersive element, wherein the lateral dispersive element is a small stepped curved grating, and the medium stepped curved grating is used in conjunction with the small stepped curved grating to achieve beam splitting and point-to-point aberration elimination imaging;

[0010] A planar detector, wherein the planar detector is positioned in the direction of the emitted light;

[0011] Optical fiber, used to emit the light to be measured;

[0012] A slit, located after the optical fiber, functions as an aperture stop.

[0013] In some embodiments, both the intermediate eddy curvature grating and the minor eddy curvature grating are planar gratings, the scribe line density of the intermediate eddy curvature grating is lower than that of the minor eddy curvature grating, and the diffraction order of the intermediate eddy curvature grating is higher than that of the minor eddy curvature grating.

[0014] In some embodiments, the scribe line distribution of the intermediate stepped curved grating and the small stepped curved grating is obtained through numerical simulation, and the scribe line distribution includes the spacing and curvature shape of the scribe lines.

[0015] In some embodiments, the principal dispersive element is placed in the direction of the incident light after passing through the slit, and the center of the principal dispersive element is at the same height as the center of the optical fiber and the slit. The transverse dispersive element is placed in the direction of the diffracted light, and the center height of the transverse dispersive element is at the same height as the optical axis of the diffracted light.

[0016] In some embodiments, the light to be tested emitted from the optical fiber passes through the slit and first illuminates the principal dispersive element, which disperses in the principal direction to separate different wavelengths. Then, it is dispersed in the lateral direction by the transverse dispersive element to separate different diffraction orders. The transverse dispersive element, together with the principal dispersive element, focuses the light in the meridional and sagittal directions onto the area array detector to obtain a two-dimensional dispersion spectrum of the light source to be tested.

[0017] In some embodiments, the transverse dispersion element is placed in the direction of the incident light after passing through the slit, and the center of the transverse dispersion element is at the same height as the center of the optical fiber and the slit. The principal dispersion element is placed in the direction of the diffracted light, and the center height of the principal dispersion element is at the same height as the optical axis of the diffracted light.

[0018] In some embodiments, the light to be tested emitted from the optical fiber passes through the slit and first illuminates the transverse dispersive element, which disperses in the transverse direction to separate different diffraction orders. Then, it is diffracted by the principal dispersive element to form a two-dimensional cross-dispersive beam. The principal dispersive element, together with the transverse dispersive element, focuses the light in the meridional and sagittal directions onto the area array detector to obtain a two-dimensional dispersion spectrum of the light source to be tested.

[0019] In some embodiments, the medium of the spectrometer is air or glass.

[0020] This invention proposes a method for fabricating a mid-echelon grating spectrometer based on the principle of cross-dispersion, comprising the following steps:

[0021] A curved grating mask pattern is obtained by homogenizing, exposing, and developing the substrate;

[0022] The curved grating mask pattern is transferred onto the substrate by etching, and metal is sputtered to form a metal reflective film, thus preparing a medium-step curved grating and a small-step curved grating respectively.

[0023] When the medium of the spectrometer is air, the intermediate stepped curved grating, the small stepped curved grating and the area array detector are fixed and finely adjusted using appropriate clamps.

[0024] When the medium of the spectrometer is glass, the medium-sized echelle grating and the small-sized echelle grating are respectively the same size as the corresponding surface of the glass block. The medium-sized echelle grating and the glass block are connected by UV adhesive curing. The small-sized echelle grating and the glass block are connected by UV adhesive curing.

[0025] When a spectrometer with a glass medium is fabricated into a chip, the thickness and area of ​​the glass chip are first determined. Then, the medium-sized stepped curved grating and the small stepped curved grating are designed on the same surface, and the two grating patterns are formed simultaneously through a single photolithography process.

[0026] In some embodiments, the exposure method is one of electron beam lithography, ultraviolet exposure, laser direct writing or nanoimprinting, the etching method is dry etching or wet etching, and the metal sputtering method is magnetron sputtering or electron beam evaporation.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention uses a combination of medium-sized and small-sized echelle gratings for cross-dispersion, resulting in a simple structure that eliminates the need for collimating and focusing mirrors found in traditional structures. This compact structure enables high-resolution detection and solves the problems of numerous components, high cost, and complex assembly in traditional cross-dispersion echelle grating structures.

[0029] The spectrometer of this invention requires only one principal dispersion bending grating and one transverse dispersion bending grating, in addition to the incident optical fiber and detector. Compared with traditional structures, it eliminates the need for collimating and focusing mirrors, thus resulting in a simpler structure, lower cost, and higher integration.

[0030] The beam-splitting elements used in this invention are all planar gratings, which can be realized through micro-nano fabrication, thus resulting in low cost and large-scale manufacturing.

[0031] This invention achieves aberration reduction and improved resolution by altering the grating line distribution of two curved gratings to make them work together.

[0032] This invention can be extended to an integrated structure of glass-medium micro-spectrometers and chip spectrometers. Attached Figure Description

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0034] Figure 1 This is a schematic diagram of a cross-dispersion high-resolution spectrometer that performs transverse dispersion first and then principal direction dispersion.

[0035] Figure 2 This is a schematic diagram of a cross-dispersion high-resolution spectrometer that performs dispersion in the main direction first and then in the transverse direction.

[0036] Figure 3 This is a schematic diagram of a glass-medium micro-spectrometer;

[0037] Figure 4 This is a schematic diagram of a high-resolution chip spectrometer with a double-curved grating cross-dispersion.

[0038] Figure 5 A schematic diagram of a stepped curved grating;

[0039] Figure 6 This is the overall optical path diagram of the simulated structure;

[0040] Figure 7 This is a simulated two-dimensional light spot pattern on the image plane.

[0041] Figure 8 For the simulation, two wavelengths spaced 80 pm apart;

[0042] Figure 9 The diffraction efficiency of the echelle grating as simulated in Rsoft;

[0043] Figure 10 The simulated area array CCD imaging effect for Zemax simulation.

[0044] Figure 11This is a comparative diagram of a standard straight-line grating and a curved-line grating. Detailed Implementation

[0045] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0046] The following description, with reference to the accompanying drawings, describes an echelle grating spectrometer based on the principle of cross-dispersion proposed according to an embodiment of the present invention and its preparation method.

[0047] like Figure 1-11 As shown, the echelle grating spectrometer based on the cross-dispersion principle of the present invention includes a principal dispersive element, a transverse dispersive element, an area array detector, an optical fiber, and a slit.

[0048] The principal dispersive element is a mid-step curved grating, and the transverse dispersive element is a small-step curved grating. Both the mid-step curved grating and the small-step curved grating are planar gratings. The combined use of the mid-step curved grating and the small-step curved grating achieves beam splitting and point-to-point aberration elimination imaging. Furthermore, the principal dispersive element is the same as the principal dispersive grating, and the transverse dispersive element is the same as the transverse dispersive grating. In this invention, the curved grating refers to a grating whose grating lines are curved, but which is itself planar.

[0049] A schematic diagram of a stepped curved grating is shown below. Figure 5 As shown, θ is measured from the normal N of the grating in the YZ plane. B The angle between the grating normal N and the scribed surface normal Z is called the flare angle of the grating, where α is the incident angle, β is the diffraction angle, and d is the grating period.

[0050] In this invention, both the principal dispersive element and the transverse dispersive element are curved gratings. Here, "curved" refers to the curvature of the grating lines; a curved grating is one where the fringes are arc-shaped, which can be considered part of a curve in a binary high-order equation, with the coefficients of the curve determined by calculation and simulation. Compared to curved gratings, ordinary gratings lack collimation and focusing capabilities; when divergent light is incident, the diffracted light remains divergent. In contrast, medium-step curved gratings and small-step curved gratings possess collimation and focusing capabilities; when divergent light is incident, the diffracted light can be directly focused. Therefore, ordinary gratings require collimating and focusing lenses to achieve imaging and focus into a dot pattern, while curved gratings do not. A comparative schematic diagram of ordinary straight-line gratings and curved gratings is shown below. Figure 11 As shown.

[0051] In principle, lens collimation and focusing work by altering the optical path of incident light through refraction, thereby changing the wavefront phase of the incident surface to meet the requirements of focusing or collimation. Ordinary equidistant straight gratings cannot arbitrarily change the phase distribution of incident light, but by changing the grating pitch and curvature at different points, a specific phase distribution can be achieved, thus collimating or focusing the light. Therefore, by calculating the grating line distribution at different positions, modulation of the light wavefront can be achieved, thereby changing the phase distribution of the light.

[0052] Furthermore, in the same optical path, the curvature of the medium-step curved grating and the small-step curved grating are different. It can be assumed that the more curved, the stronger the focusing effect on light. Therefore, the curvature of the two gratings is determined by the focusing in the meridional and sagittal directions.

[0053] This invention uses a mid-step curved grating, which has a high working order, resulting in a high dispersion rate and good spectral separation effect.

[0054] The "imaging" in "point-to-point aberration-correcting imaging" refers to the "focusing" function, which focuses the incident point light source into an outgoing point spot.

[0055] Explanation and principle analysis of "aberration correction" in "point-to-point aberration-corrected imaging":

[0056] Spectrometer aberrations generally include defocus, astigmatism, spherical aberration, coma, and other higher-order aberrations. Aberration correction aims to eliminate these aberrations as much as possible, thereby achieving the diffraction limit of the light spot on the image plane. The principle of aberration correction is to manipulate the wavefront by changing the grating pitch and curvature at various points on the grating to achieve a specific phase distribution.

[0057] The aberration correction method employs the optical path function method, which includes the following steps: Selecting the object point, image point, and the location of the curved grating, and expressing the grating equation as a function of two directional variables: horizontal (x) and meridional (y); representing the optical path from the object point to the grating surface and from the grating surface to the image point using variables x and y; performing a Taylor expansion to obtain expressions for various aberration coefficients such as meridional focusing, sagittal focusing, coma, spherical aberration, and astigmatism; selecting multiple aberrations and assigning different weights to combine them into an optimization function; using optimization algorithms such as genetic algorithms to obtain the result that minimizes the value of the optimization function; and finally obtaining the optimized curved grating structure parameters.

[0058] The scribe line distribution of the medium-step curved grating and the small-step curved grating was obtained through numerical simulation. The scribe line distribution includes the spacing and curvature of the scribe lines.

[0059] Curved gratings are specially designed to perform spectral splitting and aberration correction. Their grating lines are curved and arc-shaped, unlike ordinary gratings which are straight and parallel. The grating distribution of a curved grating can be calculated through numerical simulation. This distribution includes the grating spacing and the curvature shape, both of which are calculated and change with position. The grating spacing changes slowly.

[0060] The spectrometer of this invention uses two gratings, and the principal dispersion grating operates at a higher order. Therefore, ordinary rectangular gratings or sinusoidal gratings cannot obtain sufficient light intensity signals. Thus, the principal dispersion curved grating used needs to be made into an echelle grating with a large blaze angle to achieve higher diffraction efficiency.

[0061] The scribe line density of the medium-sized echelle grating is lower than that of the small-sized echelle grating, and the diffraction order of the medium-sized echelle grating is higher than that of the small-sized echelle grating.

[0062] Medium-sized echelle gratings are characterized by low line density (tens of line pairs), large blaze angle (tens of degrees), high diffraction order (tens to hundreds of orders), and narrow free spectral range (FSR). Small-sized echelle gratings, also known as "blazed gratings," are characterized by high line density (generally greater than 400 line pairs), low diffraction order, and a large free spectral range (FSR). The main differences between the two are in line density and blaze angle.

[0063] Compared to ordinary echelle gratings, curved echelle gratings share the following characteristics: both have lower line densities, typically less than 100 gr / mm, but offer larger blaze angles and higher working orders, generally ranging from tens to hundreds of orders, exhibiting high dispersion, high resolution, and full-wave blaze. The difference lies in the fact that ordinary echelle gratings have straight, parallel lines, while curved echelle gratings have curved, arc-shaped lines.

[0064] The area array detector is placed in the direction of the emitted light, the optical fiber is used to emit the light to be measured, and the slit is located after the optical fiber, which acts as an aperture stop.

[0065] There are two ways to place cross-dispersion elements: pre-dispersion and post-dispersion. In the pre-dispersion method, the lateral dispersion element is placed before the main dispersion element, while in the post-dispersion method, the lateral dispersion element is placed after the main dispersion element.

[0066] When the transverse dispersive element is placed before the principal dispersive element, transverse dispersion occurs first, followed by principal dispersion. In this case, the transverse dispersive element is positioned in the direction of the incident light after passing through the slit, with its center aligned with the height of the fiber and the slit center. The principal dispersive element is placed in the direction of the diffracted light, with its center height aligned with the optical axis of the diffracted light. The light to be tested emitted from the fiber, after passing through the slit, first illuminates the transverse dispersive element, where it disperses in the transverse direction, separating different diffraction orders. Then, it is diffracted by the principal dispersive element to form a two-dimensional cross-dispersive beam. The principal dispersive element, in conjunction with the transverse dispersive element, focuses the light in the meridional and sagittal directions onto the array detector to obtain the two-dimensional dispersion spectrum of the light source under test.

[0067] Specifically, the spectrometer consists only of a slit, a principal dispersive element, a transverse dispersive element, and an area array detector. The slit, located behind the optical fiber, acts as an aperture stop. The transverse dispersive element is placed in the direction of the incident light after passing through the slit, with its center aligned with the center of the optical fiber and the slit. The principal dispersive element is placed in the direction of the diffracted light, with its center at the same height as the optical axis of the diffracted light. Finally, the area array detector is placed in the direction of the outgoing light. The optical axis height of the diffracted light is the same as the optical axis height of the principal ray. The principal ray is the central ray emitted by the light source; for example, for optical fiber incident light, the principal ray is the ray that exits from the center of the fiber and is parallel to the fiber.

[0068] The light to be tested, emitted from the optical fiber, passes through a light-blocking slit and first illuminates the transverse dispersive element, where it disperses in the transverse direction, separating different diffraction orders. It then passes through a principal dispersive curved grating for diffraction. Because different wavelengths have different diffraction angles, they emerge in different directions, forming a two-dimensional cross-dispersive beam. The principal dispersive element, in conjunction with the transverse dispersive element, focuses the light in the meridional and sagittal directions onto an array detector to obtain a two-dimensional dispersion spectrum of the light source under test. In the spectrum, the principal dispersion direction is the dispersion direction of the echelle curved grating, and the transverse dispersion direction, which separates the diffraction orders, is perpendicular to the principal dispersion direction. A single wavelength spot is focused onto a single point on the array detector. The spectral information of the light under test can be obtained from the two-dimensional spectral image received by the array detector.

[0069] The transverse dispersive element is placed after the principal dispersive element, performing principal direction dispersion first, followed by transverse dispersion. The principal dispersive element is positioned in the direction of the incident light after passing through the slit, with its center aligned with the fiber and the center of the slit. The transverse dispersive element is placed in the direction of the diffracted light, with its center aligned with the optical axis of the diffracted light. The light to be tested emitted from the fiber, after passing through the slit, first illuminates the principal dispersive element, where it disperses in the principal direction to separate different wavelengths. Then, it is dispersed in the transverse direction by the transverse dispersive element, separating different diffraction orders. The transverse dispersive element, in conjunction with the principal dispersive element, focuses the light in the meridional and sagittal directions onto the area array detector to obtain the two-dimensional dispersion spectrum of the light source under test.

[0070] Specifically, the spectrometer consists only of a slit, a principal dispersive element, a transverse dispersive element, and an area array detector. The slit, located behind the light beam, acts as an aperture stop. The principal dispersive element is placed in the direction of the incident light beam after passing through the slit, with its center aligned with the height of the fiber and the slit center. The transverse dispersive element is placed in the direction of the diffracted light, with its center at the same height as the optical axis of the diffracted light. Finally, the area array detector is placed in the direction of the outgoing light. The optical axis height of the diffracted light is the same as the optical axis height of the principal ray. The principal ray is the central ray emitted by the light source; for example, for fiber optic incident light, the principal ray is the ray that exits from the center of the fiber and is parallel to the fiber.

[0071] The light to be tested emitted from the optical fiber passes through a slit and first illuminates the principal dispersive element. Dispersion in the principal direction separates different wavelengths. Then, it is diffracted by the transverse dispersive element. Because different wavelengths have different diffraction angles, they emerge in different directions, forming a two-dimensional cross-dispersive beam. The transverse dispersive element, in conjunction with the principal dispersive element, focuses the light in the meridional and sagittal directions onto an array detector to obtain a two-dimensional dispersion spectrum of the light source under test. In the spectrum, the principal dispersion direction is the dispersion direction of the echelle curved grating, and the transverse dispersion direction is the direction in which the diffraction orders separate, perpendicular to the principal dispersion direction. A single wavelength spot is focused onto a point on the array detector. The spectral information of the light under test can be obtained from the two-dimensional spectral image received by the array detector.

[0072] The fabrication method of the echelle grating spectrometer based on the principle of cross-dispersion includes homogenizing, exposing, and developing a curved grating mask pattern on a substrate; transferring the curved grating mask pattern onto the substrate by etching; and sputtering metal to form a metal reflective film, thereby fabricating a medium-sized curved grating and a small-sized curved grating, respectively.

[0073] The exposure method is one of electron beam lithography, ultraviolet exposure, laser direct writing or nanoimprinting; the etching method is dry etching or wet etching; and the metal sputtering method is magnetron sputtering or electron beam evaporation.

[0074] The medium of the spectrometer is either air or glass. When the medium is air, the components only need to be fixed in their designed positions. This involves using appropriate clamps to fix and fine-tune the eccentric grating, the small eccentric grating, and the area array detector. Specifically, the spectrometer casing is designed with interfaces for easy connection to optical fibers. Clamps are used to fix and fine-tune the two eccentric gratings and the area array detector. After fixing and adjusting, adhesive is used to firmly secure all components, preventing displacement.

[0075] When the medium of the spectrometer is glass, a polygonal glass block can be fabricated first. All surfaces of the glass block's sides are smooth. The fabricated gratings and other components are then fixed to the sides of the glass block using UV adhesive. The medium-sized and small-sized stepped curved gratings are sized to their respective surfaces on the glass block. The medium-sized stepped curved gratings and the small-sized stepped curved gratings are connected to the glass block using UV adhesive through a curing process.

[0076] Specifically, such as Figure 3 As shown, the principal dispersion bending grating and the transverse dispersion bending grating are respectively the same size as the corresponding surfaces of the glass blocks, and the patterns are fabricated at the center of the substrate. By perfectly aligning the substrate with the corresponding surfaces of the glass blocks, assembly can be easily performed and assembly errors can be reduced. The connection between the two is achieved by UV adhesive curing. UV lamp irradiation can both complete the curing and stabilize the optical performance. It is understandable that... Figure 3 When the first dispersion grating is a principal dispersion curved grating, the second dispersion grating is a transverse dispersion curved grating; when the first dispersion grating is a transverse dispersion curved grating, the second dispersion grating is a principal dispersion curved grating.

[0077] When fabricating a glass-based spectrometer into a chip, the thickness and area of ​​the glass chip are first determined. Then, a medium-sized stepped curved grating and a small stepped curved grating are designed on the same surface, and the two grating patterns are formed simultaneously in a single photolithography step. Specifically, as follows... Figure 4 As shown, two curved gratings are fabricated on the lower surface of a glass chip using photolithography. Light is reflected multiple times on both surfaces to increase the optical path, improve resolution, and reduce size. In this structure, the two curved gratings can be designed on the same surface, allowing for the simultaneous formation of both grating patterns in a single photolithography step, significantly reducing fabrication steps and alignment difficulties. This chip spectrometer has the potential for application in portable devices, achieving high spectral resolution. It is understandable that… Figure 4 When the first dispersion grating is a principal dispersion curved grating, the second dispersion grating is a transverse dispersion curved grating; when the first dispersion grating is a transverse dispersion curved grating, the second dispersion grating is a principal dispersion curved grating.

[0078] by Figure 2 The following is a Zemax simulation example using a miniature spectrometer. The spectrometer includes a slit, a principal dispersive element, a transverse dispersive element, and an area array detector. The slit is located behind the optical fiber and acts as an aperture stop; the principal dispersive element is placed in the direction of the incident light after passing through the slit, and its center is at the same height as the center of the optical fiber and the slit; in the direction of the diffracted light, a transverse dispersive element is placed, and its center height is the optical axis height of the diffracted light; finally, in the direction of the outgoing light, an area array detector is placed.

[0079] Figure 6 This is the simulated overall optical path diagram, with the spectral range set to 0.3014-0.3925 micrometers, corresponding to orders 70-90. The input light uses an aperture value NA = 0.11, a Gaussian apodization type, and an apodization factor of 1 to simulate a fiber optic source. The slit width is 25 micrometers, and the length is 2 millimeters, simulated using a rectangular aperture in the software. The center scribe line density of the echelle grating in the principal dispersion direction is 54.49 gv / mm, and the blaze angle is 48.0085 degrees. The transverse dispersive element is a low-density curved grating with a center pitch of 1.8 micrometers and an incident angle of 46.87 degrees. Both are simulated using a binary surface in Zemax.

[0080] After passing through the slit, the light emitted from the optical fiber is first incident on the transverse dispersion curved grating at an angle of 46.87 degrees. Then, the -1st order diffracted light is incident on the echelle grating in the curved scribe line of the principal dispersion direction at a diffraction angle of 48.3565 degrees. Finally, the diffracted light is focused onto the area array detector.

[0081] From the grating equation, we know that mλ = d(sinα + sinβ), therefore the center wavelength corresponding to each order is... The largest wavelength in this order for Minimum wavelength is

[0082] The wavelength range corresponding to different orders can be calculated using the above formula:

[0083] Level 70 …… 79 80 81 …… 90 center wavelength 0.3897 ….. 0.3453 0.3410 0.3368 ….. 0.3031 Maximum wavelength 0.3925 ….. 0.3475 0.3431 0.3389 ….. 0.3048 minimum wavelength 0.3869 ….. 0.3431 0.3389 0.3347 ….. 0.3014

[0084] The results can be obtained from the Zemax light trail map. By setting the light density to 45, selecting all structures, and setting the color display to wave, a two-dimensional light spot on the image plane can be obtained, such as... Figure 7 As shown, its two-dimensional spectral image is clearly visible, and light spots of different orders and wavelengths can be separated from each other. Figure 8 The two wavelengths, spaced 80 μm apart, were essentially resolvable. The diffraction efficiency for each wavelength segment was simulated using Rsoft software. Figure 9 It can be seen that it is between 40% and 80%.

[0085] Finally, the non-sequential mode in Zemax was used to simulate the signal received by an actual area array CCD. Figure 10 The simulation images of the 26th to 30th orders, in the range of 0.2906 to 0.3476 micrometers, are shown. As can be seen from the figure, the dots are arranged in order of order, with adjacent orders staggered in a step-like manner, and the two wavelengths separated by 80 pm are basically distinguishable.

[0086] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0087] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0088] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A cross-dispersed echelle grating spectrometer based on the principle of cross dispersion, characterized in that, include: The principal dispersive element is a mid-step curved grating; A transverse dispersive element, wherein the transverse dispersive element is a small stepped curved grating, is used in conjunction with a medium stepped curved grating to achieve beam splitting and point-to-point aberration elimination imaging. Both the medium stepped curved grating and the small stepped curved grating are planar gratings. The scribe line density of the medium stepped curved grating is lower than that of the small stepped curved grating. The diffraction order of the medium stepped curved grating is higher than that of the small stepped curved grating. The scribe line distribution of the medium stepped curved grating and the small stepped curved grating is obtained through numerical simulation. The scribe line distribution includes the spacing and curvature shape of the scribe lines. A planar detector, wherein the planar detector is positioned in the direction of the emitted light; Optical fiber, used to emit the light to be measured; A slit, located after the optical fiber, functions as an aperture stop.

2. The spectrometer as described in claim 1, characterized in that, The principal dispersive element is placed in the direction of the incident light after passing through the slit, and the center of the principal dispersive element is at the same height as the center of the optical fiber and the slit. The transverse dispersive element is placed in the direction of the diffracted light, and the center height of the transverse dispersive element is at the same height as the optical axis of the diffracted light.

3. The spectrometer as described in claim 2, characterized in that, The light to be tested emitted from the optical fiber passes through the slit and first illuminates the principal dispersive element, which disperses the light in the principal direction to separate different wavelengths. Then, the light is dispersed in the lateral direction by the transverse dispersive element to separate different diffraction orders. The transverse dispersive element, together with the principal dispersive element, focuses the light in the meridional and sagittal directions onto the area array detector to obtain a two-dimensional dispersion spectrum of the light source to be tested.

4. The spectrometer as described in claim 1, characterized in that, The transverse dispersive element is placed in the direction of the incident light after passing through the slit, and the center of the transverse dispersive element is at the same height as the center of the optical fiber and the slit. The principal dispersive element is placed in the direction of the diffracted light, and the center height of the principal dispersive element is at the same height as the optical axis of the diffracted light.

5. The spectrometer as described in claim 4, characterized in that, The light to be tested emitted from the optical fiber passes through the slit and first illuminates the transverse dispersive element. The light disperses in the transverse direction, causing different diffraction orders to separate. Then, it is diffracted by the principal dispersive element to form a two-dimensional cross-dispersive beam. The principal dispersive element, together with the transverse dispersive element, focuses the light in the meridional and sagittal directions onto the array detector to obtain a two-dimensional dispersive spectrum of the light source to be tested.

6. The spectrometer as described in claim 1, characterized in that, The medium of the spectrometer is either air or glass.

7. A method for fabricating a mid-echelon grating spectrometer based on the principle of cross-dispersion, characterized in that, The preparation of the spectrometer according to any one of claims 1-6 includes the following steps: A curved grating mask pattern is obtained by homogenizing, exposing, and developing the substrate; The curved grating mask pattern is transferred onto the substrate by etching, and metal is sputtered to form a metal reflective film, thereby preparing a medium-step curved grating and a small-step curved grating respectively. When the medium of the spectrometer is air, the intermediate stepped curved grating, the small stepped curved grating and the area array detector are fixed and finely adjusted using appropriate clamps. When the medium of the spectrometer is glass, the medium-sized echelle grating and the small-sized echelle grating are respectively the same size as the corresponding surface of the glass block. The medium-sized echelle grating and the glass block are connected by UV adhesive curing. The small-sized echelle grating and the glass block are connected by UV adhesive curing. When a spectrometer with a glass medium is fabricated into a chip, the thickness and area of ​​the glass chip are first determined. Then, the medium-sized stepped curved grating and the small stepped curved grating are designed on the same surface, and the two grating patterns are formed simultaneously through a single photolithography process.

8. The preparation method according to claim 7, characterized in that, The exposure method is one of electron beam lithography, ultraviolet exposure, laser direct writing or nanoimprinting, the etching method is dry etching or wet etching, and the metal sputtering method is magnetron sputtering or electron beam evaporation.

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