JP4643431B2 - Reflective diffraction grating and method of manufacturing the same - Google Patents

Description

  The present invention relates to a reflective diffraction grating and a method for manufacturing the same, and more specifically, various spectroscopic measurement devices and spectroscopic analysis devices in atmospheric environment, astronomy, earth and planetary science, meteorology, chemistry, biology, medicine, etc. The present invention relates to a reflection diffraction grating suitable for use in a quality control apparatus in the chemical industry, food manufacturing or hygiene related product manufacturing, communication information fields such as optical communication and laser related equipment, and a manufacturing method thereof.

  In recent years, in the fields of atmospheric environment science, astronomy, earth and planetary science, or meteorology, with the advancement of two-dimensional detectors, many observation devices having both imaging functions and spectroscopic functions have been developed. In such an observation apparatus, an immersion grating, which is a reflective diffraction grating filled with a transparent medium in the optical path, is used as a diffraction grating having high accuracy and high efficiency.

FIG. 1 shows an explanatory diagram of a conceptual configuration of a conventional immersion diffraction grating. This immersion diffraction grating 100 is made of a solid transparent medium, and the overall shape thereof is a triangular prism shape whose cross section forms a right triangle. I have. A staircase-like lattice is formed on the slope 100a forming the hypotenuse of a right triangle.

  In such conventional immersion diffraction grating 100, for example, a high refractive index crystal or glass material is used as a solid transparent medium, and this is ground or polished to form a staircase-shaped grating.

  By the way, the above-described immersion diffraction grating 100 is used in a vacuum or a transparent medium (gas, liquid or solid). When the wavelength of incident light is shortened, a staircase shape is formed by grinding or polishing. It has been pointed out that the loss due to the scattering of the surface of the lattice, which is the processed surface, increases.

For this reason, in order to obtain the immersion diffraction grating 100 having a grating shape that can satisfy optical performance and the surface roughness of the reflecting surface, many processes such as roughing, intermediate finishing, and precision finishing are required. There was a problem that it required a lot of time and labor.

International Publication No. 2004/116163 Pamphlet JP 2001-246561 A A New Generation of High-Performance Diffraction Grafting; http: // www-cms. llnl. gov / st / diff gratings. html (Lawrence Livermore National Laboratory HP, patent, literature available) Demultiplexing waveguide; http: // unit. aist. go. jp / photonics / optglass / # theme (AIST HP, patents, literature information available) Ultraviolet laser ablation microfabrication technology; http: // unit. aist. go. jp / photonics / group / laserimp. html (AIST HP, patents, literature information available) K. Oka, N .; Ebizuka, K .; Kodate, “Optimal design of the grafting with reflective plate of combo type for astronomical using RCWA”, Proc. SPIE, 5290, 168-178, 2004. N. Ebizuka, K .; Oka, A.A. Yamada, M .; Ishikawa, M .; Kashiwagi, K .; Kodate, Y. et al. Hirahara, S.H. Sato, K .; S. Kawabata, M .; Wakaki, S .; Morita, T .; Shimizu, S .; Yin, H.C. Omori and M.M. Iye, “Grism and Immersion Grafting for Space Telescope”, The 5th International Conference on Space Optics (ICSO 2004), ESA, SP-554, 743-749, 2004.

  The present invention has been made in view of the problems of the conventional techniques as described above, and the object of the present invention is to have a simple structure and easily without enormous time and labor. It is an object of the present invention to provide a reflective diffraction grating that can be manufactured and that has high accuracy and high efficiency, and a method for manufacturing the same.

  In order to achieve the above-mentioned object, the present invention is simplified by using the reflection on the side surface of the groove and the regular reflection on the inclined surface so as to form a deep groove grating instead of the conventional step-shaped grating. Although it is a structure, it is intended to obtain high accuracy and high efficiency.

  Such a reflection type diffraction grating according to the present invention is suitable for use as a dispersion element of a high dispersion spectroscopic device.

That is, the present invention is an immersion diffraction grating made of a solid transparent medium on which light is incident, and the overall shape is a triangular prism shape whose section forms a triangle, and the inclined surface forming the hypotenuse of the triangle is A lattice is formed by engraving a plurality of grooves in parallel along the extending direction of the triangular prism shape, the slope is a mirror surface, and the surface of the groove is a total reflection surface or a mirror surface. The incident light is set so as to be reflected on the side surface of the groove, further reflected on the slope, and reflected again on the side surface of the groove .

In the present invention, the light incident on the transparent medium is reflected on the side surface of the groove where the angle between the two side surfaces of the groove and the inclined surface is an acute angle, and further on the inclined surface where the groove is formed. The half value of the sum of the first reflection angle and the second reflection angle on the side surface is determined by the side surface and the slope so that the light is reflected and reflected again on the side surface of the groove having an acute angle with the slope. It is set to be equal to the angle formed .

In the present invention, a plurality of the grooves are carved in parallel on the slope by a dicer .

In the present invention, a plurality of the grooves are engraved on the slope by laser ablation .

  According to the present invention, since it has a simple structure, it can be easily manufactured without requiring enormous time and labor, and an excellent effect is achieved in that it can be realized with high accuracy and high efficiency. .

  Hereinafter, an example of an embodiment of a reflective diffraction grating and a method for manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings.

First, FIG. 2 is a perspective view illustrating a conceptual configuration of an example of an embodiment of a reflective diffraction grating according to the present invention, and FIG. 3 is a conceptual diagram illustrating a conceptual configuration as viewed in the direction of arrow A in FIG. 4 is a partially enlarged configuration explanatory view of FIG.

  The reflection diffraction grating 10 is a so-called immersion diffraction grating made of a solid transparent medium, and has an overall shape of a triangular prism whose cross section forms a right triangle. The reflective diffraction grating 10 is used in a vacuum or a transparent medium (gas, liquid or solid).

  On the slope 10a forming the hypotenuse of a right triangle, a lattice is formed by cutting a plurality of deep grooves 10b in parallel along the axial direction (extension direction) of the triangular prism shape. As the solid transparent medium, for example, a high refractive index crystal or glass material can be used.

  Here, the surface of the inclined surface 10a is processed as a mirror surface, and the surface of the groove 10b is processed as a total reflection surface or a mirror surface.

  The depth D of the groove 10b is, for example, about several hundred to several thousand μm, and the width W of the groove 10b is, for example, about several to several tens of μm. Furthermore, a pitch P that is an interval between a certain groove 10b and the groove 10b adjacent to the groove 10b is set to, for example, several hundred to several thousand μm.

  Further, the angle formed by the groove 10b and the inclined surface 10a is set so that incident light is reflected on the side surface 10ba of the groove 10b and reflected substantially vertically on the inclined surface 10a of the grating. Since the side surface 10ba of the groove 10b is obliquely reflected, loss due to scattering is small even if it is a rough surface.

  Further, since the slope 10a of the grating is mirror-finished, the scattering loss can be substantially ignored.

Next, the angle formed by the groove 10b and the inclined surface 10a will be described in detail with reference to FIG.

That is, in FIG. 5, paying attention to the quadrangle formed by the apex angle α, the two right angles RA1, RA2, and the obtuse angle OA, if the incident angle (= reflection angle) θ is γ, then α = 2γ. Formula (1)
It turns out that it is.

When attention is paid to the triangle formed by the additional angle γ, the angle β formed by the groove 10b and the inclined surface 10a, and the right angle RA2, β = R−γ.
Therefore, from equation (1),
β = R−α / 2 Formula (2)
Thus, the angle β, which is the angle formed by the groove 10b and the slope 10a, may be set appropriately.

Further, regarding the loss due to the scattering on the inclined surface 10a, the loss Ls due to the scattering is represented by σ [rms] as the surface roughness.
Ls = 1−exp {− (4πσ cos θ / λ)}
Given in.

  Here, θ is an incident angle, and λ is a wavelength of incident light (in addition, “JM Bennet and L. Mattson,“ Introduction to surface roughness and scattering ”, Optical Society of America, Amer. 1989. ").

  Therefore, for example, when “σ = 0.2 μm” and “λ = 10 μm”, the relationship between the incident angle θ and the loss Ls is as shown in FIG.

Thus, the reflection type diffraction grating 10, if the incident angle θ is 45 ° or more over, for example, if the incident angle θ is used such that 60 °, the conventional immersion diffraction grating 100 shown in FIG. 1 Compared to the case, the scattering loss is greatly reduced.

  That is, even if the reflection by the rough surface of the conventional immersion diffraction grating 100 shown in FIG. 1 is one time and the reflection by the reflection type diffraction grating 10 is two times, for example, when the incident angle θ is 60 °, In the diffraction grating 10, the loss due to scattering is about 1/4 with respect to the normal incidence, and the scattering loss is about half even if the reflection by the rough surface is twice.

In the above configuration, when light is incident on the reflection type diffraction grating 10 described above, the angle β formed by the groove 10b and the inclined surface 10a reflects the incident light on the side surface 10ba of the groove 10b, and is generally perpendicular to the inclined surface 10a of the grating. Therefore, the incident light is obliquely incident on the side surface of the groove 10b and reflected by the side surface 10ba, and the loss due to scattering is extremely small.

  In addition, since the slope 10a of the grating is mirror finished as a mirror surface, the scattering loss on the slope 10a can be ignored.

Here, in the conventional immersion diffraction grating 100 shown in FIG. 1, for example, when processing a step grating having a period of 600 μm in the range of “30 mm × 75 mm” of the inclined surface 100a, optical performance is satisfied at a wavelength of 8 μm. In order to achieve this, a processing time of 300 to 500 hours is required by the latest nano-precision grinding apparatus. Furthermore, when the processing range is “120 mm × 300 mm”, it is estimated that man-hours of about 1000 to 1500 hours are required.

  On the other hand, the groove 10b of the reflective diffraction grating 10 according to the present invention can be easily formed by using, for example, a dicer or a laser ablation device used when cutting an IC chip from a silicon wafer.

  A grindstone having a width of 10 μm or less has also been developed for dicers, and the grinding surface is relatively smooth because grinding is performed at high speed.

  The dicer also has an apparatus (dual spindle) in which grindstones having different widths and roughnesses are arranged in series, and roughing and finishing can be performed in one step.

  Therefore, in manufacturing the diffraction grating 10 according to the present invention, the number of man-hours can be reduced to about several tenths compared to the conventional immersion diffraction grating 100 shown in FIG.

  On the other hand, fine processing by ultraviolet laser ablation using a laser ablation apparatus can obtain a good processed surface when the energy of the laser wavelength is higher than the work function of the medium, and is thus extremely effective for forming the groove 10b. It is.

  Note that fine processing by ultraviolet laser ablation using a laser ablation apparatus is difficult to control in the depth direction, but the depth of the groove can also be limited by an SOI substrate or the like.

In the conventional immersion diffraction grating 100 shown in FIG. 1, the surface roughness at which scattering is not a practical problem is, for example, about λ / 100 rms or less when the transparent medium is germanium (n = 4). The surface roughness of 100 nm rms when the wavelength is 10 μm is a value that can be achieved by grinding, but the surface roughness of 20 nm rms when the wavelength is 2 μm is difficult to achieve. On the other hand, in the reflection type diffraction grating 10 according to the present invention, the surface roughness at which scattering does not become a practical problem is, for example, the transparent medium is germanium (n = 4), and the incident angle (= reflection angle) θ on the side surface 10ba of the groove 10b. Is about λ / 30 rms or less when the angle is 70 ° (vertical is 0 °). A surface roughness of 60 nm rms at a wavelength of 2 μm can be sufficiently achieved by grinding a dicer.

The above-described embodiment can be modified as shown in the following (1) to (4).

  (1) In the above-described embodiment, the case where the reflective diffraction grating 10 is formed of a solid transparent medium has been described. However, the present invention is not limited to this. That is, the reflection type diffraction grating 10 only needs to be filled with a vacuum or a transparent medium in the optical path, and the transparent medium is not limited to a solid, and a liquid or a gas can be used. When the optical path of the reflective diffraction grating 10 is filled with vacuum or liquid or gas, the reflective diffraction grating 10 is used in a solid, and the reflective diffraction grating 10 and the solid The solid may be processed so that a plurality of grooves 10b are formed in parallel at the interface.

(2) In the above-described embodiments, the shape of the bottom portion 10bb of the groove 10b, a detailed description is omitted, the bottom 10bb of the groove 10b may be a curved surface as shown in FIG. 4, the planar shape It may be.

  (3) Although the detailed description of the number of the grooves 10b is omitted in the above-described embodiment, the number of the grooves 10b may be appropriately selected according to the design.

  (4) You may make it combine suitably the embodiment shown above and the modification shown in said (1)-(3).

  The present invention relates to a dispersive element used in a spectroscopic measurement apparatus or a spectroscopic analysis apparatus, a diffractive optical element used in a beam distributor, a beam mixer or a wavelength discriminator used in optical communication or laser optics, etc. Can be used as

FIG. 1 is an explanatory diagram of a conceptual configuration of a conventional immersion diffraction grating. FIG. 2 is a perspective view of a conceptual configuration showing an example of an embodiment of a reflective diffraction grating according to the present invention. FIG. 3 is an explanatory diagram of a conceptual configuration as viewed in the direction of arrow A in FIG. 2. FIG. 4 is a partially enlarged configuration explanatory view of FIG. FIG. 5 is a partially enlarged configuration explanatory view for explaining the angle formed by the groove and the inclined surface in the reflection type diffraction grating according to the present invention. FIG. 6 is a chart showing the relationship between the incident angle θ and the loss Ls when the surface roughness σ is 0.2 μm and the incident angle wavelength λ is 10 μm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Reflective diffraction grating 10a Slope 10b Groove 10ba Side surface 10bb Bottom part 100 Immersion diffraction grating 100a Slope

Claims (4)

An immersion diffraction grating composed of a solid transparent medium on which light is incident,
The overall shape is a triangular prism shape whose section forms a triangle,
On the slope forming the hypotenuse of the triangle, a lattice is formed by engraving a plurality of grooves in parallel along the extending direction of the triangular prism shape,
The slope is a mirror surface;
The surface of the groove is a total reflection surface or a mirror surface,
The reflection type diffraction grating is set so that light incident on the transparent medium is reflected on the side surface of the groove, further reflected on the inclined surface, and reflected again on the side surface of the groove . The reflective diffraction grating according to claim 1,
The light incident on the transparent medium is reflected at the side surface of the groove, wherein the beveled surface and the angle is an acute angle of the two sides of the groove, reflected in yet the slopes the grooves are formed, and wherein the beveled surface The half value of the sum of the first reflection angle and the second reflection angle on the side surface is equal to the angle formed by the side surface and the inclined surface so that the reflection is reflected again on the side surface of the groove having an acute angle. Reflective diffraction grating characterized by being set to. It is a manufacturing method of the reflection type diffraction grating given in any 1 paragraph of Claim 1 or 2,
A plurality of the grooves are engraved on the slope by a dicer.
A method for producing a reflective diffraction grating. It is a manufacturing method of the reflection type diffraction grating given in any 1 paragraph of Claim 1 or 2,
A plurality of the grooves are engraved on the slope by laser ablation.
A method for producing a reflective diffraction grating.

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