CN110186563A - Light splitting light guide module and integrated spectrometer and production method based on cylindrical grating - Google Patents

Abstract

The invention discloses an integrated spectrometer based on cylindrical gratings and a manufacturing method thereof. The spectrometer includes an incident slit arranged in a box, a light splitting waveguide module and a linear array detector. The light splitting waveguide module includes a slab waveguide, a cylindrical entrance and exit end, and a cylindrical grating. The spectroscopic waveguide module based on the cylindrical grating is processed as a whole by combining the mechanical processing method and the 3D grayscale exposure photolithography method based on the electron beam. The slab waveguide adopts high-refractive-index materials, which can effectively reduce the overall thickness of the spectrometer, increase the numerical aperture of the spectrometer, and have higher luminous flux. Using 3D grayscale exposure lithography and etching technology to make cylindrical gratings, gratings with a line width of tens of nanometers can be made, with high processing precision and smooth surface after etching, which is easy to make micro spectrometers. The invention has the advantages of high luminous flux, thinness, high resolution, more compact system, more stable performance and the like.

Description

Spectroscopic waveguide module and integrated spectrometer based on cylindrical grating and manufacturing method

technical field

The invention relates to a spectroscopic waveguide module based on a cylindrical grating, an integrated spectrometer and a manufacturing method thereof, in particular to a miniaturized and highly integrated spectrometer and a manufacturing method thereof, and belongs to the technical field of spectroscopy.

Background technique

Spectrometers have important applications in many fields such as environmental detection, food safety, and real-time security inspection. Among them, the grating dispersion spectrometer has attracted extensive attention because of its advantages of uniform dispersion and high spectral resolution.

At present, grating dispersion spectroscopic analysis instruments on the market are developing towards miniaturization and integration, usually by reducing the size of optical components and optimizing the space of traditional structures, resulting in more difficult assembly and rapid performance degradation.

Some scholars have proposed to use waveguides to compress light beams for better miniaturization. For example, the ZnSe waveguide infrared spectrometer developed by Foster-Miller uses a Rowland structure, the waveguide is a ZnSe wedge-shaped waveguide, the concave grating is glued to one end of the waveguide, and the linear array detector is placed at the other end of the waveguide. The light is introduced by the incident optical fiber, and is imaged on the detector after being split and converged by the concave grating. The radius of curvature of the concave holographic grating is the same in both directions, so it is not easy to match the aberration when designing the optical path, and the grating is glued to the ZnSe waveguide, so positioning deviation cannot be avoided.

Contents of the invention

The present invention aims to provide a spectroscopic waveguide module based on a cylindrical grating, an integrated spectrometer and a manufacturing method. A piece of solid light-guiding medium is used to complete the preparation of optical waveguides, lenses, gratings, etc. on it, and the integral formation does not require splicing and Adjustment, with the characteristics of stable and reliable effect and miniature.

The present invention is realized through the following technical solutions:

The light splitting waveguide module based on the cylindrical grating includes an optical waveguide unit and a grating light splitting unit. The output and incident ends are respectively arranged at both ends of the slab waveguide, and are integrated with the slab waveguide; the surface of the cylindrical grating is coated with a high reflection film.

In the above technical solution, the slab waveguide is made of high-refractive-index material, and the high-refractive-index material includes SiO ₂ , ZnSe or glass.

In the above technical solution, the high reflection film is made of gold film.

In the above technical solution, the cylindrical grating includes several continuous grooves, which are generally in the shape of an arc columnar structure, and its curvature radius in the horizontal direction is R, and 20mm≤R≤120mm.

An integrated spectrometer based on a cylindrical grating, including an incident slit, a light-splitting waveguide module and a linear array detector; the incident slit is used to receive an external light signal and inject the light signal into the inside of the spectrometer; the light-splitting waveguide module It includes an optical waveguide unit and a grating light splitting unit, the light waveguide unit includes a slab waveguide and a cylindrical entrance and exit end, the grating light separation unit includes a cylindrical grating, and the cylindrical entrance and exit end is used to split the optical signal in the vertical direction compress to limit transmission in the waveguide, and focus the optical signal reflected on it to the line array detector; the cylindrical grating is used to split the incident light and reflect it to the cylindrical exit and entrance; the incident The slit and the linear array detector are arranged close to the cylindrical entrance and exit end of the light splitting waveguide module.

A method for manufacturing a spectroscopic waveguide module based on a cylindrical grating, the method adopts a mechanical processing method to make a module outline structure, and makes a cylindrical grating based on an electron beam 3D grayscale exposure photolithography method; the method includes:

Choose a high refractive index material with a suitable size as the slab waveguide substrate;

The slab waveguide substrate is processed into a module profile structure by machining, and the module profile structure is a plate structure with one end straight and the other end forming an arc surface, and the plate structure includes the above-mentioned slab waveguide and cylindrical out The incident end, and the arc cylinder used to make the cylindrical grating;

Clean and dry the arc cylinder, and make the surface of the arc cylinder hydrophobic by HMDS (hexamethyldisilamine) vapor deposition;

According to the etching ratio, an appropriate amount of photoresist is spin-coated on the arc cylinder; and the arc cylinder is soft-baked using a vacuum hot plate, and the photoresist on the edge of the arc cylinder is removed;

Align the electron beam with the arc cylinder and precisely position it, and perform electron beam exposure according to the BMP grayscale file, and the BMP grayscale file includes the exposure energy and focal length data of the cylindrical grating corresponding to the photoresist; After electron beam exposure, the circular arc cylindrical surface is immersed in a developing solvent to develop the cylindrical grating structure, and then baked on a hot plate at 110~300°C to remove the unexposed photoresist to obtain the crude product of the spectroscopic waveguide module;

Hard-bake the rough product of the splitting waveguide module through a hot plate at 100-130°C for 1-2 minutes, and use dry etching technology to perform ICP (inductively coupled plasma) on the cylindrical grating structure of the rough product of the splitting waveguide module after hard-baking etching, and removing the photoresist exposed by the electron beam grayscale from the cylindrical grating structure, and obtaining the cylindrical grating after cleaning.

The spectroscopic waveguide module is obtained by coating the surface of the cylindrical grating with a high reflection film.

In the above technical solution, the cylindrical grating includes a grating formed by several continuous grooves, and the line width of the grating can reach tens of nanometers.

In the above technical solution, the size of the slab waveguide base is 20mm×15mm×2mm~120mm×100mm×10 mm.

The present invention has the following advantages and beneficial effects:

1) The optical signal propagates in the solid slab waveguide without the influence of stray light, and the structure is simple. The larger the refractive index of the slab waveguide material, the smaller the divergence angle, the smaller the beam size, and the smaller the overall size, and the cylindrical structure at the incident end can further The beams are converged, thereby reducing the size of the spectrometer. Smaller divergence angle improves signal strength while ensuring resolution;

2) Realize on-chip integration in the true sense, rather than assembling optical components by sticking. Various apertures in the spectrometer are reduced, and there are no moving parts, which improves the stability of the entire system. The resolution is improved while reducing the size of the spectrometer, and can be applied in various fields, especially the fields requiring high resolution.

Description of drawings

FIG. 1 is a schematic diagram of the optical path of an integrated spectrometer based on cylindrical gratings involved in the present invention.

FIG. 2 is a schematic structural diagram of a cylindrical grating-based optical splitting waveguide module involved in the present invention.

FIG. 3 is a schematic diagram of the manufacturing steps of the optical splitting waveguide module based on cylindrical gratings involved in the present invention.

FIG. 4 is a schematic diagram of a structure of a cylindrical grating involved in the present invention.

Fig. 5 is a schematic diagram of the dimensions of Example 1: (a) top view; (b) side view.

In the figure: 1—incident light; 2—cylindrical entrance and exit facet; 3—incident light; 4—cylindrical grating; 5—exit light; 6—linear array detector; 7—slab waveguide; 8—entrance slit.

Detailed ways

The specific embodiment of the present invention and working process will be further described below in conjunction with accompanying drawing.

The orientation terms such as up, down, left, right, front and rear in this application document are established based on the positional relationship shown in the drawings. If the drawings are different, the corresponding positional relationship may also change accordingly, so this should not be understood as limiting the scope of protection.

As shown in FIG. 1 , an integrated spectrometer based on a cylindrical grating includes an incident slit 8 , a light splitting waveguide module and a linear array detector 6 . The spectrometer structure described in the present invention is actually an internal structure arranged in the instrument case of the spectrometer, which can be understood and imagined by those skilled in the art. One side of the instrument box is provided with an optical signal entrance, and the optical signal entrance is the incident slit 8 described in the present invention. The specific position of the linear array detector 6 in the instrument box needs to be calibrated according to the specific parameters of the spectrometer. The incident slit 8 is used to receive external optical signals and inject the optical signals into the inside of the spectrometer (light-splitting waveguide module).

As shown in FIG. 2 , the optical splitting waveguide module includes an optical waveguide unit and a grating splitting unit. The optical waveguide unit includes a slab waveguide 7 and a cylindrical incident end 2 . The slab waveguide is a straight rectangular parallelepiped structure, and high refractive index materials are selected, including SiO ₂ , ZnSe or glass, which can effectively reduce the overall height of the system, increase the numerical aperture of the system, obtain higher luminous flux, and more It is suitable for weak signal detection fields such as Raman spectroscopy.

The grating light splitting unit includes a cylindrical grating 4, and the cylindrical grating used in the present invention is a reflective grating. The cylindrical grating 4 has an arc-shaped columnar structure, the arc-shaped columnar structure is equal in height to the slab waveguide and the upper and lower planes are horizontally parallel, and the grating surface is arc-shaped in a horizontal plan view direction. The radius of curvature of the cylindrical grating 4 in the horizontal direction is R, and 20mm≤R≤120mm. The cylindrical grating 4 includes several continuous grooves, and these grooves are gratings. The blaze angle of the grating is fixed and the line width is the same, as shown in Figure 4. The blaze angle of the cylindrical grating is determined by the wavelength of the spectrometer, usually 5°~40°. The grating line width of the present invention can reach the order of tens of nanometers. The cylindrical grating 4 and the cylindrical incident and exit ports 2 are respectively arranged at both ends of the slab waveguide 7 , and are integrated with the slab waveguide 7 . The cylindrical entrance and exit end 2 is a cylindrical lens, as shown in the side views of Fig. 2 and Fig. 5b, and its curvature is often the thickness of the slab waveguide. The cylindrical input and output end 2 is used to compress the optical signal in the vertical direction so that it is limited to be transmitted in the waveguide, and to focus the optical signal reflected thereon to the linear array detector 6 . The surface of the cylindrical grating 4 (the side opposite to the cylindrical entrance-exit end) is coated with a high-reflection film, and the high-reflection film is gold (Au) film, which is used to split the incident light and reflect it to the cylindrical entrance-exit end 2 .

The incident slit 8 and the linear array detector 6 are arranged close to the cylindrical entrance and exit end 2 of the light splitting waveguide module.

The manufacturing method of the spectroscopic waveguide module based on the cylindrical grating adopts the mechanical processing method to manufacture the module outline structure, and the cylindrical grating is manufactured based on the electron beam 3D grayscale exposure photolithography method.

A high-refractive-index material with a suitable size is selected as the flat waveguide substrate, and the high-refractive-index material includes SiO ₂ , ZnSe or glass. The size of the slab waveguide substrate is 20mm×15mm×2mm~120mm×100mm×10mm.

The slab waveguide substrate is processed into a module profile structure by machining. The module profile structure is a plate structure with one end straight and the other end arc-shaped (as shown in Figure 3a). The plate structure includes a slab waveguide 7 and a cylindrical incident End 2 and the arc cylinder used to make the cylinder grating.

Clean and dry the arc cylindrical surface to remove surface pollutants and water vapor, change the surface of the substrate from hydrophilic to hydrophobic, and enhance the adhesion of the surface; through HMDS (hexamethyldisilamine) vapor deposition , forming a base film in the vapor phase, making the surface of the arc cylindrical surface hydrophobic, and enhancing the adhesion between the arc cylindrical surface and the photoresist.

According to the etching ratio, an appropriate amount of photoresist is spin-coated onto the arc cylinder, as shown in Figure 3b. And use a vacuum hot plate to soft bake the arc cylinder to remove the solvent (4-7%), enhance the adhesion, release the stress in the photoresist film, and prevent the photoresist from contaminating the equipment; photoresist removal.

The electron beam is aimed at the arc cylinder and positioned precisely. Alignment mainly includes pre-alignment by laser automatic alignment function and precise positioning by alignment marks, as shown in Figure 3c. And perform electron beam exposure according to the BMP grayscale file, as shown in Figure 3d. The BMP grayscale file includes the exposure energy and focal length data of the cylindrical grating corresponding to the photoresist, which is obtained through experiments.

The dotted line in Figure 3 is the principle of electron beam lithography. Under vacuum conditions, the low-energy density electrons generated in the electron gun are used to accelerate and focus the polymer material to irradiate the polymer material, so that the molecular chain of the material is cut or recombined, causing the molecular weight to change. The change creates a latent image, which is then developed by immersing it in a solvent.

And post-baking it through a hot plate at 110~300°C to reduce the standing wave effect, stimulate the acid generated by the PAG of the chemically amplified photoresist to react with the protective group on the photoresist and remove the group so that it can be dissolved in developer. Develop to make the photoresist have a cylindrical grating structure, remove the unexposed photoresist on it, and obtain the crude product of the splitting waveguide module, as shown in Figure 3e.

The crude product of the optical splitter waveguide module is hard-baked on a hot plate at 100°C-130°C for 1-2min, and the solvent in the photoresist is completely evaporated, so as to improve the ability of the photoresist to protect the lower surface during ion implantation or etching, and further Enhances the adhesion between the photoresist and the substrate surface and reduces the standing wave effect. Use dry etching technology to perform ICP etching on the cylindrical grating structure of the hard-baked spectroscopic waveguide module rough product, and remove the photoresist exposed by the electron beam gray scale from the cylindrical grating structure, after cleaning A cylindrical grating is obtained, as shown in Figure 3f. Cylindrical gratings include several vertical grooves, which are called gratings. The blaze angle of the grating is fixed and the line width is the same, as shown in Figure 4. Moreover, the line width of the cylindrical grating fabricated by this method can reach tens of nanometers.

The surface of the cylindrical grating is coated with a high-reflection film to obtain a splitting waveguide module.

The grating is the core component of the spectrometer, and the selection of a cylindrical grating has the following significant advantages:

1) Compared with the planar blazed grating, it is more conducive to integration, so as to realize its miniaturization. This is because when using a planar grating, it is necessary to add collimating and focusing lenses at the same time, which increases the difficulty of integration. At the same time, due to the divergence of the light, if it is only collimated in one direction, such as the cylindrical structure of the light incident and exit, the final size of the spectrometer is much larger than the size of the present invention. If the cylindrical structure at the light incident and exit is changed to a spherical structure, the processing difficulty will be increased.

2) Compared with the holographic concave grating, the cylindrical grating can reduce aberrations such as spherical aberration in the spectrum, because the curvature radius of the holographic concave grating is the same in both directions, it is not easy to match the aberration when designing the optical path, and the design and production requirements are higher. .

At present, the main way to manufacture cylindrical gratings is machining, so it is often limited by the precision of machining and the overall size of spectrometer design. The machining accuracy of general machining is difficult to be higher than 1 μm, and the grating produced by it is difficult to be used for high-precision spectral spectroscopy.

Laser processing is a very commonly used processing method at present. The femtosecond laser processing accuracy can reach 100nm, but its processing depth is generally only 10μm, and it is impossible to process a grating with a depth of 4mm perpendicular to the upper surface. High-precision alignment cannot be achieved if it is machined perpendicular to the sides. Moreover, the laser will generate heat during processing, which limits the types of processed materials. The surface of the structure after laser processing is rougher than that of etching.

Using 3D grayscale exposure lithography and etching technology to produce cylindrical gratings, gratings with a line width of tens of nanometers can be produced, with high processing precision and smooth surface after etching.

Embodiment one:

The selected high-refractive index slab waveguide K9 glass with a suitable size has a refractive index of about 1.517, which can make the resolution of the spectrometer higher than that of air transmission (refractive index 1). As shown in Figure 5, after machining, the outline size of the slab waveguide is 70mm × 60mm × 4mm. The incident slit 8 has a width of 0.05 mm and a height of 0.5 mm, which can ensure sufficient light intensity in the slab waveguide. The thickness of the slab waveguide 7 is 4 mm, and the radius of curvature of the cylindrical entrance and exit end 2 is about 4 mm, which can make the light divergence angle small, ensure that the light propagates horizontally in the slab waveguide, and reduce aberrations. The distance from the slit 8 to the cylindrical incident end 2 is 6 mm, the distance from the cylindrical incident end 2 to the cylindrical grating 4 is 70 mm, and the distance from the cylindrical grating 4 to the cylindrical incident end 2 is 69 mm. The distance from the cylindrical incident end 2 to the linear array detector 6 is 8mm.

The radius of curvature of the cylindrical grating produced by 3D grayscale exposure lithography technology is 87mm, the number of grooves is 600/mm, and the blaze angle β is 14.7°. The final grating has a line width of 1.66 μm and a height of 0.4 μm. The upper and lower surfaces of the flat-panel spectrometer are parallel, and the cylindrical grating is perpendicular to the two surfaces at the same time, and the vertical height is 4mm. After the grating is etched, the outer surface is coated with a highly reflective film-Au film, so that the signal detected by the linear array detector is stronger. The angle between the vertical line and the horizontal line of the cylindrical grating 4 is 13°, the angle between the vertical line and the horizontal line of the cylindrical incident end 2 is 6.5°, and the angle between the linear array detector 6 and the horizontal line is 3°. The linear array detector 6 is a CCD (Charged Coupled Device) image sensor, and the size of a single pixel is 14 μm×14 μm. The optical path diagram is shown in Figure 1, the spectral range is 800-900nm, and the spectral resolution is 0.6nm.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. the light splitting light guide module based on cylindrical grating, which is characterized in that the light splitting light guide module include optical waveguide unit and Grating beam splitting unit, the optical waveguide unit include that planar waveguide (7) and cylindricality go out incidence end (2), the grating beam splitting unit Including cylindrical grating (4), the cylindrical grating (4) and cylindricality go out incidence end (2) is separately positioned on the planar waveguide (7) two End, and be an integral structure with the planar waveguide (7)；The surface of the cylindrical grating (4) is coated with high-reflecting film.

2. the light splitting light guide module according to claim 1 based on cylindrical grating, which is characterized in that the planar waveguide choosing With high-index material, the high-index material includes SiO₂, ZnSe or glass.

3. the light splitting light guide module according to claim 1 based on cylindrical grating, which is characterized in that the high-reflecting film is selected Golden film.

4. the light splitting light guide module according to claim 1 based on cylindrical grating, which is characterized in that the cylindrical grating (4) include several continuous cuttings, be in circular arc column structure, in the horizontal direction the radius of curvature in face be R, 20mm≤R≤ 120mm。

5. the integrated spectrometer based on cylindrical grating comprising be divided light guide module as described in claim 1, feature exists In the spectrometer includes entrance slit (8), light splitting light guide module and linear array detector (6)；The entrance slit (8) is used for It receives external optical signals and the optical signal is incident on inside the spectrometer；The light splitting light guide module includes optical waveguide unit With grating beam splitting unit, the optical waveguide unit includes that planar waveguide (7) and cylindricality go out incidence end (2), the grating beam splitting list Member includes cylindrical grating (4), and the cylindricality goes out incidence end (2) makes it be limited in wave for compressing optical signal in vertical direction Interior transmission is led, and the optical signal that will be reflected to thereon focuses on the linear array detector (6)；The cylindrical grating (4) is used for will Incident ray, which is divided and is reflected into cylindricality, goes out incidence end (2)；The entrance slit (8) and the linear array detector (6) are close to institute The cylindricality for stating light splitting light guide module goes out incidence end (2) setting.

6. the integrated spectrometer according to claim 5 based on cylindrical grating, which is characterized in that the planar waveguide is selected High-index material, the high-index material include SiO₂, ZnSe or glass.

7. the integrated spectrometer according to claim 5 based on cylindrical grating, which is characterized in that the cylindrical grating (4) It is in circular arc column structure including several continuous cuttings, the radius of curvature in face is R, 20mm≤R≤120mm in the horizontal direction.

8. the production method of the light splitting light guide module based on cylindrical grating is used to prepare light splitting wave as described in claim 1 Guide module, which is characterized in that the method makes module profile structure using mechanical processing method, and is exposed based on electron beam 3D gray scale Light photoetching process makes cylindrical grating；The described method includes:

Select the high-index material of suitable size as planar waveguide substrate；

The planar waveguide substrate is processed into module profile structure by being machined, the module profile structure is in for one end The device of shifting block type structure of arc surface, the plank frame includes the planar waveguide (7) and the cylindricality goes out incidence end (2) and uses In the circular arc cylinder of production cylindrical grating；

Circular arc cylinder is cleaned and dried, makes circular arc spherocylindrical surface that there is hydrophobicity by HMDS vapor deposition；

Appropriate photoresist is spun to the circular arc cylinder according to etching ratio；And the circular arc cylinder is carried out using vacuum hot plate Soft baking, and the photoresist at circular arc cylinder edge is removed；

Make circular arc cylinder described in electron beam alignment and precise positioning, and electron beam exposure is carried out according to BMP gray-scale document, it is described BMP gray-scale document includes the exposure energy and focal length data of cylindrical grating corresponding with photoresist；It will be after electron beam exposure Circular arc cylinder immerse developer solution its cylindrical grating structure made to develop, and by its by dried after 110 ~ 300 DEG C of hot plates removal its Upper unexposed photoresist obtains light splitting light guide module crude product；

The light splitting light guide module crude product is dried firmly by hot plate, using dry etching technology to the light splitting wave guide mode after hard dry The cylindrical grating structure of block crude product carries out ICP etching, and by by the photoresist of electron beam gradation exposure from the cylinder light It is removed in grid structure, cylindrical grating is obtained after cleaning；

The cylindrical grating surface is plated into high-reflecting film to get the light splitting light guide module is arrived.

9. the production method of the light splitting light guide module according to claim 8 based on cylindrical grating, which is characterized in that described Cylindrical grating includes the grating that several continuous cuttings are formed, and the grating line width can reach tens nanometers；The high-reflecting film choosing Use golden film.

10. the production method of the light splitting light guide module according to claim 8 based on cylindrical grating, which is characterized in that institute The size for stating planar waveguide substrate is 20mm × 15mm × 2mm ~ 120mm × 100mm × 10mm.