JPWO2004111693A1 - Diffraction grating and manufacturing method thereof - Google Patents

Abstract

Provided is a high-dispersion and high diffraction efficiency and inexpensive diffraction grating and a method for manufacturing the same, and a diffraction grating incident surface on which light from the outside is incident, and the diffraction grating incident surface facing the diffraction grating incident surface. Light that is formed between the diffraction grating exit surface from which light incident inside from the diffraction grating entrance surface exits, and the diffraction grating entrance surface and the diffraction grating exit surface, and is incident from the diffraction grating entrance surface to the inside. And a plurality of reflecting surfaces that reflect the incident light. In addition, the diffraction grating entrance surface and the diffraction grating exit surface are each formed in a substantially rectangular shape, and are positioned substantially parallel to each other with a predetermined distance therebetween, and the plurality of reflection surfaces include the diffraction surface. It is arranged at equal intervals substantially perpendicular to the grating incident surface and the diffraction grating exit surface, and is configured as a transmission type planar diffraction grating.

Description

  The present invention relates to a diffraction grating, and more specifically, various observation apparatuses such as astronomy, earth and planetary science, meteorology, environmental hygiene, various spectroscopic analysis apparatuses such as physics and chemistry, minerals, organisms, pathology, foods, pharmaceuticals, The present invention relates to a diffraction grating suitable for use in various apparatuses such as a chemical product manufacturing apparatus, a quality control apparatus, and an all-optical routing apparatus that forms the basis of WDM (Wavelength Division Multiplexing).

Conventionally, diffraction gratings are used in various apparatuses. For example, a grism is known as a diffraction grating used in an astronomical spectroscopic observation apparatus.
This grism is a transmissive dispersion element that combines a transmissive diffraction grating and a prism so that light of an arbitrary order and an arbitrary wavelength travels straight or in an arbitrary direction.

  High-dispersion spectroscopic observation devices for astronomy use high-dispersion elements (echelle type) such as diffraction gratings and grisms that use high-order diffracted light, and vertical dispersive elements (prisms, etc.) for measuring a wide wavelength range at the same time. In combination with a low dispersion diffraction grating). Therefore, it has been desired that the dispersion element has high diffraction efficiency.

  In general, the chromatic dispersion of the grism is proportional to the optical path difference generated by the prism portion of the grism. For this reason, in order to obtain high wavelength dispersion, it is necessary to use a high-refractive prism having a large apex angle as a prism constituting the grism.

  However, in the SR grism that combines a conventional surface relief (SR) diffraction grating with a stepped groove shape on the surface and a prism, the refractive index of the prism is set to obtain high dispersion. If the apex angle is increased by increasing the value, the apex angle of the prism is limited by the critical angle at the interface between the prism and the diffraction grating. For this reason, in order to obtain higher dispersion, the effective diameter of the SR grism and the size of the optical system must be increased.

Therefore, in addition to the SR grism in which the apex angle of the prism is limited as described above, a VPH grism has also been proposed. This VPH grism is formed by combining a VHP (Volume Phase Holographic) grating whose refractive index is periodically modulated and a prism.
Such a VPH grism has a lower limit on the apex angle of the prism due to the critical angle than the conventional SR grism. Therefore, the apex angle of the prism can be made larger than that of the conventional SR grism, and higher wavelength dispersion can be achieved. .
However, this VPH grism has a lower diffraction efficiency at a higher order than an SR grism configured using a conventional SR type diffraction grating.

A diffraction grating such as an arrayed waveguide grating (AWG) used as a path switching element in WDM has also been put into practical use.
However, the unit price of the arrayed waveguide diffraction grating is currently several tens of thousands to several hundreds of thousands of yen, and there is a problem that the manufacturing cost cannot be reduced and it is not suitable for mass production.

  The present invention has been made in view of the problems of the conventional techniques as described above, and an object of the present invention is to provide a high-dispersion and high diffraction efficiency and an inexpensive diffraction grating and a method for manufacturing the same. It is something to be offered.

In order to achieve the above object, the present invention provides a diffraction grating incident surface on which light from the outside is incident, and light incident on the diffraction grating incident surface facing the diffraction grating is emitted to the outside. A plurality of reflections that are formed between the diffraction grating exit surface, the diffraction grating entrance surface, and the diffraction grating exit surface, and in which light incident on the inside from the diffraction grating entrance surface is incident and reflects the incident light And a surface.
In the present invention, the diffraction grating entrance surface and the diffraction grating exit surface are each formed in a substantially rectangular shape, and are positioned substantially parallel to each other with a predetermined distance therebetween, and the plurality of reflection surfaces Are arranged at equal intervals substantially perpendicular to the diffraction grating entrance surface and the diffraction grating exit surface, and are configured as transmissive planar diffraction gratings.
Further, according to the present invention, an angle formed by the light incident on the reflection surface and entering the reflection surface from the diffraction grating incident surface and the reflection surface is “θ ₂ ”, and the grating interval is “d”. Assuming that the thickness of the reflective surface is “w” and the height of the reflective surface is “t”, the reflective surface is dimensioned so as to satisfy tan θ ₂ = (d−w) / t. It is a thing.
Further, the present invention provides a base portion of a substantially plate-like body that is formed in a comb shape as a whole and has a planar end surface that is substantially rectangular, and a protrusion projecting at a predetermined interval on the back side of the end surface of the base portion. A first stage of forming a reflective film on the back side of the base, and a second stage of removing a part of the reflective film formed in the first stage; And a third step of filling a predetermined material with the base on which the reflective film is left only in a predetermined region by the second step.
The present invention also provides a first high-refractive index prism having a prism incident surface on which light from the outside is incident, and light incident on the inside from the prism incident surface of the first prism is emitted to the outside. A second prism having a high refractive index having a prism exit surface, and an apex angle of the first prism and an apex angle of the second prism so as to face each other. And is formed as a transmission type plane diffraction grating sandwiched between the prisms of the first prism, and has a substantially rectangular shape in which the light incident from the prism incident surface of the first prism and transmitted through the first prism enters the interior. A substantially rectangular shape in which the formed diffraction grating incident surface is opposed to the diffraction grating incident surface in a substantially parallel manner and has a predetermined interval, and light incident on the inside from the diffraction grating incident surface is emitted to the second prism. Shape Formed between the diffraction grating exit surface, the diffraction grating entrance surface and the diffraction grating exit surface, and located at substantially equal intervals with respect to the diffraction grating entrance surface and the diffraction grating exit surface, The light incident on the inside from the diffraction grating incident surface is incident, and has a diffraction grating region having a plurality of reflection surfaces for reflecting the incident light.
In the present invention, the angle formed by the light incident on the reflection surface and entering the reflection surface from the diffraction grating incident surface of the diffraction grating region and the reflection surface is “θ ₂ ”, and the grating interval Is “d”, the thickness of the reflecting surface is “w”, and the height of the reflecting surface is “t”, the tan θ ₂ = (d−w) / t is satisfied in the diffraction grating region. The reflecting surface is dimensioned.

  Since the present invention is configured as described above, it has an excellent effect of providing a diffraction grating having high dispersion, high diffraction efficiency, and low cost.

FIG. 1 is a conceptual structural explanatory view showing a first embodiment of a diffraction grating according to the present invention.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is an explanatory view showing the main part of the first embodiment of the diffraction grating according to the present invention.
[FIG. 4] FIG. 4 is an explanatory diagram showing a case where the condition of tan θ ₂ = (d−w) / t is satisfied in the diffraction grating shown in FIG.
FIG. 5 is an explanatory diagram showing a case where tan θ ₂ > (d−w) / t in the diffraction grating shown in FIG.
FIG. 6 is an explanatory diagram showing a case where tan θ ₂ <(d−w) / t in the diffraction grating shown in FIG.
[FIG. 7] FIGS. 7 (a), (b), (c), (d), and (e) are explanatory views showing an example of a method of manufacturing the diffraction grating shown in FIG.
[FIG. 8] FIG. 8 is a conceptual structural perspective view showing a second embodiment of a diffraction grating according to the present invention.
FIG. 9 is a schematic configuration explanatory view showing a second embodiment of a diffraction grating according to the present invention.
FIGS. 10 (a) and 10 (b) are explanatory views showing an example of the size of each component part of the diffraction grating according to the present invention.
[FIG. 11] FIG. 11 (a) is a schematic configuration explanatory view showing an example of a conventional arrayed waveguide diffraction grating (AWG), and FIG. 11 (b) functions as the diffraction grating of FIG. 11 (a). FIG. 11 (c) is a waveguide type wavelength discrimination optical circuit using a diffraction grating according to the present invention, and FIG. 11 (d) is a cross-sectional view of FIG. It is sectional drawing in B line, FIG.11 (e) is explanatory drawing which showed typically an example of the manufacturing process of the diffraction grating shown by FIG.11 (c).
[FIG. 12] FIG. 12 is a conceptual structural explanatory view showing another example of the embodiment of the diffraction grating according to the present invention.
[FIG. 13] FIGS. 13A and 13B are conceptual structural explanatory views showing another example of the embodiment of the diffraction grating according to the present invention.
FIG. 14 is a graph showing an example of diffraction efficiency when the Bragg angle is about 20 ° in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Diffraction grating 10a Diffraction grating entrance surface 10b Diffraction grating exit surface 10c Reflection surface 20 Grism 22, 24 Prism 22a Prism incidence surface 24a Prism exit surface 100 Base 100a End surface 100b Base 100c Protrusion 100d Upper end surface 100e, 100f Side surface 100g Bottom surface 102 Reflective film

  Hereinafter, an example of an embodiment of a 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.

  FIG. 1 is a conceptual diagram illustrating a first embodiment of a diffraction grating according to the present invention, and FIG. 2 is a cross-sectional view taken along line AA of FIG.

The diffraction grating 10 according to the first embodiment is entirely formed in a plate-like body, and has a substantially rectangular diffraction grating incident surface 10a and a substantially rectangular diffraction grating output facing the diffraction grating incident surface 10a. The surface 10b includes a plurality of reflecting surfaces 10c formed between the diffraction grating incident surface 10a and the diffraction grating exit surface 10b.
The diffraction grating 10 is a transmissive diffraction grating and is designed as a planar diffraction grating.
More specifically, with reference to the coordinate systems shown in FIGS. 1 and 2, the diffraction grating entrance surface 10a and the diffraction grating exit surface 10b are respectively along XY planes located at different heights in the Z-axis direction. The diffraction grating entrance surface 10a and the diffraction grating exit surface 10b are substantially parallel to each other with a predetermined distance therebetween.
On the other hand, the reflecting surface 10c is formed at every predetermined interval in the X-axis direction, substantially coincides with a plane extended along the Z-axis direction, and Y on the diffraction grating entrance surface 10a and the diffraction grating exit surface 10b. It extends over the entire length in the axial direction. That is, the extending direction of the reflecting surface 10c is substantially orthogonal to the extending directions of the diffraction grating incident surface 10a and the diffraction grating exit surface 10b. Accordingly, the diffraction grating 10 includes a plurality of reflecting surfaces 10c formed at equal intervals substantially perpendicular to the diffraction grating entrance surface 10a and the diffraction grating exit surface 10b.

  In the above-described configuration, in the diffraction grating 10, light is incident from the diffraction grating incident surface 10 a of the diffraction grating 10, and the light incident in the diffraction grating 10 passes through the diffraction grating 10 to be output from the diffraction grating. 10b.

Then, as shown in FIG. 3, the refractive index of the diffraction grating 10 is “n ₂ ”, the diffraction order is “m”, the wavelength is “λ”, the grating interval is “d”, and the diffraction grating entrance surface 10a. When the angle formed by the incident light from the light source, that is, the light incident on the reflecting surface 10c and the reflecting surface 10c is “θ ₂ ”, the relationship of the following formula (1) holds for the diffraction grating 10 become.
At this time, the magnitude of the angle theta ₂ formed by the light incident on the reflecting surface 10c and the reflecting surface 10c is consistent with the size of the angle formed by the reflecting surface 10c and the light reflected by the reflecting surface 10c Is. Further, in the conventional diffraction grating, the grating interval d indicates the interval between grooves formed in the diffraction grating. However, in the diffraction grating 10 according to the present invention, no grooves are formed. This shows the interval between the reflection surfaces 10c.
mλ = 2n ₂ dsin θ ₂ (1)
Here, Formula (1) is expressed by the same formula as the Bragg diffraction formula, and θ ₂ corresponds to the Bragg angle.
The thickness of the reflecting surface 10c (the length of the reflecting surface 10c along the X-axis direction of the coordinate system shown in FIG. 3) is “w”, and the height of the reflecting surface 10c (the coordinates of the reflecting surface 10c shown in FIG. 3). If the length of the system along the Z-axis direction) is “t”,
tan θ ₂ = (d−w) / t (2)
4, most of the light beam incident from the diffraction grating incident surface 10a and passing through the diffraction grating 10 is reflected once by the reflecting surface 10c and contributes to the diffraction, as shown in FIG. Since it can be used as light, the diffraction efficiency is the highest.
The following formula (3) is referred to as the aspect ratio of the diffraction grating 10.
t / (d−w) = 1 / tan θ ₂ Formula (3)
On the other hand, when the condition of the above equation (2) is not satisfied, that is, when tan θ ₂ > (d−w) / t (see FIG. 5), or when tan θ ₂ <(d−w) / t (see FIG. 5). 6), the incident light is distributed in directions other than the direction that contributes to the diffracted light, so that the diffraction efficiency is lowered.
More specifically, as shown in FIG. 5, in the case of tan θ ₂ > (d−w) / t, out of the light flux that enters from the diffraction grating incident surface 10 a and passes through the diffraction grating 10, it is reflected by the reflecting surface 10 c. Since the light beam reflected twice travels in the same direction as the incident light from the diffraction grating incident surface 10a, vignetting occurs (see the shaded area in FIG. 5), and the diffraction efficiency decreases.
As shown in FIG. 6, in the case of tan θ ₂ <(d−w) / t, the speed of light that does not strike the reflecting surface 10 c out of the light flux that enters from the diffraction grating incident surface 10 a and passes through the diffraction grating 10. However, since the light travels straight and travels in the same direction as the incident light from the diffraction grating incident surface 10a, vignetting occurs (see the shaded area in FIG. 6), and the diffraction efficiency decreases.
Then, the light beam incident from the outside of the diffraction grating incident surface 10a of the diffraction grating 10 and reflected by the reflection surface 10c spreads with a diffraction distribution defined by the wavelength λ and the grating interval d.
In particular, when high-order diffracted light is used, it has the highest diffraction efficiency for the light beams of the respective orders satisfying the interference condition in the direction of regular reflection with respect to the reflecting surface 10c, and the highest A light beam having a wavelength before and after the wavelength of the diffraction efficiency exhibits an efficiency proportional to the diffraction intensity distribution in a direction satisfying the interference condition.

Therefore, according to the diffraction grating 10 of the first embodiment of the present invention, high dispersion and high diffraction efficiency can be realized, and the diffraction efficiency can be increased even with a high order such as high-order diffracted light. Can do.
In addition, in the conventional SR type diffraction grating described in the above-mentioned section “Prior Art”, since the groove shape is formed on the surface, the groove shape is easily damaged and damaged. Since the reflecting surface 10c of the diffraction grating 10 according to the present invention is formed inside the diffraction grating, there is no fear that the reflecting surface 10c is damaged and damaged, and a good operating state can be maintained.

Here, a manufacturing method of the diffraction grating 10 will be described with reference to FIG.
First, when the diffraction grating 10 is manufactured, a base 100 (see FIG. 7A) that is formed in a comb shape as a whole is used. More specifically, the base 100 has a flat plate-like base portion 100b having a flat and substantially rectangular end surface 100a, and a protrusion 100c formed to protrude from the back surface side of the end surface 100a of the base portion 100b at a predetermined interval. And is configured.
The end face 100 a of the base 100 forms the diffraction grating exit surface 10 b of the diffraction grating 10. And the back side of the end surface 100a of the base 100 is comprised from the upper end surface 100d of the protrusion 100c, the side surfaces 100e and 100f of the protrusion 100c, and the bottom face 100g formed between the adjacent protrusions 100c.
The base 100 is made of a dielectric material, and is dimensioned according to the overall size of the diffraction grating 10, the grating interval d, the height t of the reflective film 10c, and the like. As a dielectric material forming the base 100, for example, a glass material such as quartz or BK-7, a resin such as PMMA or polyimide, crystal, magnesium fluoride, or various crystal materials can be used.
Then, the reflective film 102 is formed on the back surface side of the end surface 100a of the base 100 by ion sputtering or the like (see FIG. 7B). That is, the reflective film 102 is formed with a predetermined film thickness on the upper end surface 100d, the side surface 100e, the side surface 100f, and the bottom surface 100g of the protrusion 100c of the base 100. As the material of the reflective film 102, for example, aluminum, gold, silver, silicon, germanium, or the like can be used.
After the reflection film 102 is formed in this way, the reflection film formed on the upper end surface 100d and the bottom surface 100g of the protrusion 100c of the base 100 by perpendicular incident anisotropic etching (see the arrow shown in FIG. 7B). Only 102 is removed (see FIG. 7C).
Thereafter, only the reflective film 102 formed on the side surface 100e of the protrusion 100c of the base 100 is removed by oblique incidence anisotropic etching (see the arrow shown in FIG. 7C).
When the base 100 (see FIG. 7D) where the reflective film 102 is left only on the side surface 100f of the protrusion 100c is filled with PMMA resin or silicon resin, the diffraction grating 10 is formed (FIG. 7). (See (e)). That is, the diffraction grating entrance surface 10a of the diffraction grating 10 is formed by the filled PMMA resin or silicon resin.

Note that the material filled in the base 100 (see FIG. 7D) in which the reflective film 102 is left only on the side surface 100f of the protrusion 100c is not limited to resin, and may be transparent at the wavelength used, for example. For example, a vapor deposition material such as SiO ₂ , MgF ₂ , Al ₂ O ₃ , ZrO, ITO (transparent electrode), or low melting point glass may be used. At this time, a material having the same refractive index as that of the material forming the base 100 is used as a material for filling the base 100 in which the reflective film 102 is left only on the side surface 100f of the protrusion 100c. Is desirable.
Further, instead of filling the base 100 where the reflective film 102 is left only on the side surface 100f of the protrusion 100c with a deposition material such as SiO ₂ , MgF ₂ , Al ₂ O ₃ , ZrO, or ITO (transparent electrode). Then, it may be grown by a sol-gel method or a CVD method.
That is, the diffraction grating 10 can be manufactured as described above. However, the present invention is not limited to this, and depending on the overall size of the diffraction grating 10 required by the application, photo diffraction Various methods such as a semiconductor process using light such as lithography, laser ablation, X-ray ablation, ion etching, or plasma etching can be used.

  Next, a second embodiment of the diffraction grating according to the present invention will be described with reference to FIGS.

FIG. 8 is a perspective view of a conceptual configuration showing a second embodiment of the diffraction grating according to the present invention. Here, the second embodiment of the diffraction grating according to the present invention is configured as a direct-view transmission type diffraction grating, and is a so-called grism.
The grism 20 shown in FIG. 8 is configured such that the diffraction grating 10 is sandwiched between the prism 22 and the prism 24.
Here, the diffraction grating 10 of the grism 20 shown in FIG. 8 has the same configuration as the diffraction grating 10 of the first embodiment shown in FIG. 1 to FIG. Detailed description of the configuration and operation will be omitted. The diffraction grating 10 constitutes the diffraction grating region of the grism 20.
On the other hand, the prism 22 and the prism 24 are both made of a common material and have the same refractive index. Specifically, the prism 22 and the prism 24 are high refractive index prisms, for example, having a refractive index of 1.5 to 4. As a material constituting these prisms 22 and 24, for example, a dielectric such as zinc sulfide (ZnS) or lithium niobate (LiNbO ₃ ) or a semiconductor can be used, and the refractive index is as high as about 2.3. Refractive index.
The diffraction grating 10 is sandwiched so that the apex angle α of the prism 22 (see FIG. 9) and the apex angle of the prism 24 are opposed to each other. At this time, the side surface including the apex angle α of the prism 22 (corresponding to the surface of the prism 22 showing the region of the substantially right triangle shape in FIG. 9) and the side surface including the apex angle of the prism 24 (substantially right triangle shape in FIG. 9). The diffraction grating 10 is disposed substantially orthogonally to the surface of the prism 24 indicating the region (1).

In the above configuration, in the grism 20, light is incident from the outside through the surface of the prism 22, that is, from the prism incident surface 22 a of the prism 22, and the light incident on the prism 22 is transmitted through the prism 22. Then, the light enters the diffraction grating 10 from the diffraction grating incident surface 10a. The light transmitted through the diffraction grating 10 exits from the diffraction grating exit surface 10 b and enters the prism 24. The light incident on the prism 24 passes through the prism 24 and is emitted to the outside through the surface of the prism 24, that is, from the prism exit surface 24 a of the prism 24.
Here, the refraction formula at the prism incident surface 22a, which is the light incident surface of the prism 22 of the grism 20, is “n ₀ ” as the refractive index of the external medium of the grism 20, and “n ₁ ” as the refractive index of the prism 22. Then, it is the following formula (4).
n ₀ sin α = n ₁ sin θ ₁ (4)
The refraction formula at the interface between the prism 22 and the diffraction grating 10 is:
n ₁ sin (α−θ ₁ ) = n ₂ sin θ ₂ (5)
It is. Here, when substituting equation (5) into equation (1) above,
mλ = 2n ₁ dsin (α−θ ₁ ) (6)
Is obtained.

For example, if the refractive index n ₀ of the external medium is 1.0, the apex angle α of the prism 22 is 20 °, the refractive index n ₁ of the prism 22 is 2.3, the diffraction order m is 10, and the wavelength λ is 600 nm. (4) and (6), the lattice spacing d = 11.0 μm is obtained.
Further, when the refractive index n ₂ of the diffraction grating 10 is 1.5, the angle θ formed by the light incident on the reflection surface 10c of the diffraction grating 10 and the reflection surface 10c according to the equations (4) and (5). ₂ = 10.5. Therefore, when the thickness w of the reflecting surface 10c is sufficiently small with respect to the grating interval d of the diffraction grating 10, the height t = 11 / tan10.5 = 59. The aspect ratio of the grating in which 4 μm is obtained and no vignetting occurs is t / d = 5.4 from the equation (3).
That is, when the refractive index n ₀ = 1.0 of the external medium, the diffraction order m = 10, and the wavelength λ = 600 nm, the prism 22 has an apex angle α = 20 ° and the prism 22 has a refractive index n ₁ = 2.3. 22 and the refractive index n ₂ = 1.5, and the thickness w of the reflecting surface 10c is made sufficiently small with respect to the grating interval d = 11.0 μm, and the height t of the reflecting surface 10c is 59.4 μm. In the grism 20 configured using the diffraction grating 10 that satisfies the aspect ratio 5.4, the angle θ ₂ = 10.5 formed by the light incident on the reflection surface 10c of the diffraction grating 10 and the reflection surface 10c. Then, the condition of the above equation (2) is satisfied (see FIG. 4).
As a result, in the grism 20, a light beam that enters from the outside via the prism incident surface 22 a of the prism 22, passes through the prism 22, enters the diffraction grating 10 from the diffraction grating incident surface 10 a, and passes through the diffraction grating 10. Most of the light is reflected once by the reflecting surface 10c, contributes to diffraction, and can be used as diffracted light, so that the diffraction efficiency is highest.

Here, the effect of the grism 20 using the diffraction grating 10 according to the present invention will be described in comparison with the conventional SR grism and VHP grism described in the above-mentioned section “Prior Art”.
The VPH grism VHP grating can obtain high diffraction efficiency in a wide wavelength range by adjusting the incident and outgoing angles so as to satisfy the Bragg condition. For this reason, in the case of the VHP grism, by making the apex angle of the prism and the angle of the VHP grating variable so as to satisfy the Bragg condition, it is possible to perform high-dispersion spectroscopic measurement with a wide wavelength while maintaining high efficiency.
The grism 20 (see FIGS. 8 and 9) using the diffraction grating 10 according to the present invention is configured by sandwiching the diffraction grating 10 between the two prisms 22 and 24, so that the VPH grating is composed of two prisms. It has the same configuration as the conventional VPH grism configured to be sandwiched. For this reason, the grism 20 using the diffraction grating 10 according to the present invention, like the VPH grism, has less restriction on the prism apex angle due to the critical angle than the conventional SR grism, and the apex angle of the prism is larger than that of the conventional SR grism. Therefore, higher chromatic dispersion can be realized (see, for example, patent applications “Japanese Patent Application Laid-Open No. 2002-14209” and “Japanese Patent Application Laid-Open No. 2004-13080” by the present applicant).
Further, the grism 20 using the diffraction grating 10 according to the present invention is a diffraction grating having high dispersion and high diffraction efficiency, so that the diffraction efficiency of the high-order diffracted light is high as in the conventional SR grism. realizable.
Thus, the grism 20 using the diffraction grating 10 according to the present invention has the advantages of both SR grism and VHP grism, and in particular, the refraction of the prism 22 with respect to the refractive index n ₂ of the diffraction grating 10. This is very effective when the ratio n ₁ is high and the diffraction order m is high.

For example, specifically in FIG. 3, the reflecting surface 10c of the diffraction grating 10 is made of aluminum, the height t = 15.3 μm of the reflecting surface 10c, the grating interval d = 5.7 μm, and the thickness w = 0 of the reflecting surface 10c. When the refractive index n ₂ = 1.50 of the diffraction grating 10 and the Bragg angle θ ₂ = 20.5 °, the maximum efficiency wavelength of each order is 1000 nm as clearly shown in FIG. The 7th order diffracted light is 875 nm, the 8th order diffracted light is 750 nm, the 9th order diffracted light is 667 nm, the 10th order diffracted light is 600 nm, the 11th order diffracted light is 545 nm, and the 12th order diffracted light is 500 nm. The 13th order diffracted light is 462 nm, the 14th order diffracted light is 428 nm, and the 15th order diffracted light is 400 nm.
Specifically, as described above, the refractive index n ₀ = 1.0 of the external medium, the apex angle α = 20 ° of the prism 22, the refractive index n ₁ = 2.3 of the prism 22, and the diffraction order m = 10. , Wavelength λ = 600 nm, grating spacing d = 11.0 μm, refractive index n ₂ = 1.5 of diffraction grating 10, angle θ ₂ formed by light incident on reflection surface 10 c of diffraction grating 10 and reflection surface 10 c. = 10.5, and when the thickness w of the reflecting surface 10c is sufficiently small with respect to the grating interval d of the diffraction grating 10, the height t of the reflecting surface 10c is 59.4 μm, and the aspect of the grating in which no vignetting occurs When the ratio t / d = 5.4, according to the grism 20 using the diffraction grating 10 according to the present invention, a diffraction efficiency of about 80% or more can be achieved for the 10th-order diffracted light.
The diffraction efficiency of the 10th-order diffracted light is about 20% or less in the case of the VHP grism, and the diffraction efficiency of about 80% or more realized by the grism 20 of the present invention is very high. In addition, if the SR grism is used, it is possible to achieve a diffraction efficiency of about 80% or more for the 10th-order diffracted light. However, in the SR grism, the apex angle of the prism can be increased as in the grism 20 of the present invention. This results in a problem that high chromatic dispersion cannot be obtained.
In SR grism, since the SR type diffraction grating is arranged on the surface of the prism, the groove shape of the SR type diffraction grating is easily damaged and damaged, and the stable operation state as the grism is obtained. There is a risk that it cannot be maintained. On the other hand, in the grism 20 according to the present invention, since the diffraction grating 10 is sandwiched between the two prisms 22 and 24, the reflection surface 10c of the diffraction grating is not damaged and is not damaged. Can maintain a stable operating state.
Furthermore, in the SR-type transmission diffraction grating constituting the SR grism, the traveling direction of light is changed by refraction and diffraction on the exit surface of the stepped groove shape. Further, the refractive index of the VHP grating constituting the VPH grism is periodically modulated, and the traveling direction of light is converted by Bragg diffraction. On the other hand, the diffraction grating 10 constituting the grism 20 of the present invention uses the reflecting surface 10c and diffraction, and is physically close to the SR type using refraction and diffraction on the exit surface (incident surface), and has Bragg diffraction. Are physically different.

Here, in the diffraction grating 10 according to the first embodiment of the present invention, vignetting occurs by setting the height t of the reflecting surface 10c and the like so as to satisfy the condition of the above-described formula (2). In this case, most of the light beam entering from the diffraction grating incident surface 10a and passing through the diffraction grating 10 can be emitted from the diffraction grating output surface 10b as diffracted light (see FIG. 4), so that it functions as a so-called waveguide. It is also possible to provide a high versatility in various fields, such as arranging the diffraction grating 10 according to the present invention between optical waveguides for use in optical communication.
For example, the size of the diffraction grating 10 (see FIG. 1) according to the first embodiment of the present invention can be dimensioned as shown in FIGS. 10 (a) and 10 (b). For this reason, when the diffraction grating according to the first embodiment of the present invention is formed in a size as shown in FIG. 10B (see FIG. 11E) and used as a diffraction grating in the waveguide (FIG. 11). (See (c) and (d)), the loss can be reduced as compared with the conventional case where a surface relief (SR) type diffraction grating is used by providing an air layer or the like in the waveguide.
In addition, as described in the above section “Prior Art”, an arrayed waveguide diffraction grating (AWG) used for WDM is tens of thousands to hundreds of thousands of yen, which is expensive due to the manufacturing cost. (See FIGS. 11 (a) and 11 (b)). On the other hand, since the diffraction grating 10 according to the present invention is manufactured as shown in FIG. 7, the cost is low. For example, the diffraction grating 10 can be manufactured at several hundred yen to several thousand yen, so it is very inexpensive. Therefore, it is suitable for mass production.
The AWG must be directly processed into a waveguide having a large area by ion exchange or etching which takes time one by one, but the diffraction grating of the present invention is shown in FIGS. As shown in e), a process of forming a metal reflecting surface grating on the side surface of the replica grating by a simple semiconductor process, and embedding it in a groove dug in a waveguide in advance by a dicing saw or the like As a result, the cost can be greatly reduced.

The above-described embodiment can be modified as shown in the following (1) to (6).
(1) In the first and second embodiments described above, several materials constituting the diffraction grating 10 and the prisms 22 and 24 of the grism 20 are exemplified, but it is needless to say that the present invention is not limited to this. Yes, the material may be appropriately changed according to the manufacturing method and application.
For example, in the manufacturing method of the diffraction grating 10 shown in FIG. 7, for example, aluminum, gold, silver, silicon, germanium, or the like can be used as the material of the reflective film 102, but compared with the base 100. The reflective film 102 may be configured by using a material having a small refractive index or by forming a void so as to be used under conditions of total reflection.
Also, the size of the diffraction grating 10 may be set to various dimensions such as 10 mm × 10 mm and 100 mm × 100 mm, for example, depending on the space where the diffraction grating 10 is disposed and the size of the grism 20 as a whole.
(2) In the above-described second embodiment, the grism 20 is constituted by the two prisms 22 and 24. However, the present invention is not limited to this, and the diffraction grating according to the present invention. The grism may be configured using 10 and one prism, or the type of prism used may be changed.
(3) In the above-described embodiment, when the diffraction grating 10 is manufactured (see FIG. 7), it is formed on the upper end surface 100d and the bottom surface 100g of the protrusion 100c of the base 100 by vertical incident anisotropic etching. After removing the reflective film 102, the reflective film 102 formed on the side surface 100e of the protrusion 100c of the base 100 is removed by oblique incidence anisotropic etching. However, the present invention is not limited to this. Needless to say, the reflective film 102 formed on the side surface 100e of the protrusion 100c of the base 100 is removed by oblique incidence anisotropic etching, and then the base 100 is etched by normal incidence anisotropic etching. The reflective film 102 formed on the upper end surface 100d and the bottom surface 100g of the protrusion 100c may be removed.
Further, the reflection film 102 formed on the side surface 100e of the protrusion 100c of the base 100 is removed by the oblique incidence anisotropic etching, but without performing the oblique incidence anisotropic etching, FIG. As shown in (c), the base 100 in which the reflective film 102 is left on the side surface 100e and the side surface 100f of the protrusion 100c may be filled with a PMMA resin or a silicon resin. Thereby, many reflective surfaces 10c can be formed at a time, and various dimension settings such as the interval between the reflective films 10c may be appropriately changed.
Further, the base 100 is formed by controlling the error of the interval between the protrusions 100c to a value sufficiently smaller than the wavelength, or the metal film process is changed from an isotropic method to an anisotropic oblique incidence method. By changing to, the step of oblique incidence anisotropic etching can be omitted.
(4) In the first embodiment described above, both ends of the reflecting surface 10c of the diffraction grating 10 in the Z-axis direction have a predetermined distance from the diffraction grating entrance surface 10a and the diffraction grating exit surface 10b. Of course, the present invention is not limited to this (see FIG. 2), and as shown in FIG. 12, the reflecting surface may be extended over the entire length in the Z-axis direction of the diffraction grating.
(5) In the first embodiment described above, the diffraction grating 10 is a transmission type diffraction grating and is designed as a planar diffraction grating, but it is of course not limited to this. The diffraction grating according to the first embodiment of the present invention is designed as a concave diffraction grating, a convex diffraction grating, or a diffractive optical element (DOE) such as a holographic optical element (HOE). May be.
For example, FIGS. 13A and 13B show an explanatory diagram of an example of the diffraction grating according to the present invention designed as a concave diffraction grating. FIG. 13A shows an example of a concave diffraction grating of the type that converts a parallel light beam into convergent light. The reflecting surface is not positioned perpendicular to the diffraction grating incident surface, and the interval between the reflecting surfaces is the Fresnel zone plate. Thus, the outer peripheral side is narrower and the reflecting surface is inclined toward the outer peripheral side. On the other hand, FIG. 13B is an example of a concave diffraction grating of the type of 1: 1 imaging (the distance between the object side and the image side is the same), and the reflecting surface is perpendicular to the diffraction grating incident surface. The distance between the reflecting surfaces is narrower toward the outer periphery as in the Fresnel zone plate. In any of FIGS. 13A and 13B, the diffraction grating entrance surface and the diffraction grating exit surface are not limited to planes, and can be appropriately spherical or aspherical.
Thus, when the diffraction grating according to the present invention is designed as a concave diffraction grating or a holographic element, it is not necessary to form the reflecting surfaces at equal intervals perpendicular to the diffraction grating entrance surface and the diffraction grating exit surface. That is, a plurality of reflecting surfaces may be formed at unequal intervals, and may be inclined at a predetermined angle without being perpendicular to the diffraction grating entrance surface and the diffraction grating exit surface.
Furthermore, due to such changes, the diffraction grating according to the present invention can be used for non-uniformly spaced diffraction gratings used for measurement and analysis, beam distribution / mixers used in optical communication and laser related equipment, wavelength discriminators, lenses, etc. It is also effective as various diffractive optical elements.
In addition, when manufacturing the diffraction grating by this invention as a holographic optical element, it is good to form a pattern by methods, such as CGH (Computer Generated Hologram).
(6) You may make it combine the above-mentioned embodiment and the modification shown in above-mentioned (1)-(5) suitably.

  High-dispersion, high diffraction efficiency, and inexpensive diffraction gratings can be obtained, so a wide variety of devices such as various observation devices, various spectroscopic analyzers, manufacturing equipment for chemical products, quality control devices, all-optical routing devices, etc. Can be used.

Claims (6)

A diffraction grating incident surface on which light from the outside is incident;
A diffraction grating exit surface from which the light incident on the inside from the diffraction grating entrance surface is opposed to the diffraction grating entrance surface;
A diffraction grating formed between the diffraction grating incident surface and the diffraction grating exit surface, and having a plurality of reflecting surfaces on which light incident from the diffraction grating incident surface enters and reflects the incident light. The diffraction grating according to claim 1, wherein
The diffraction grating entrance surface and the diffraction grating exit surface are each formed in a substantially rectangular shape, and are positioned substantially parallel to each other with a predetermined interval therebetween,
The plurality of reflecting surfaces are located at substantially equal intervals with respect to the diffraction grating incident surface and the diffraction grating exit surface,
A diffraction grating that is configured as a transmission type planar diffraction grating. The diffraction grating of claim 2, further comprising:
The angle formed by the light entering the diffraction grating incident surface and entering the reflective surface and the reflective surface is “θ ₂ ”, the grating interval is “d”, and the thickness of the reflective surface is “ w ”and the height of the reflecting surface is“ t ”.
tan θ ₂ = (d−w) / t
A diffraction grating in which the reflective surface is dimensioned to satisfy A base having a substantially plate-like body having a generally rectangular end face that is formed in a comb shape and a protrusion formed at a predetermined interval on the back side of the end face of the base. And a first step of forming a reflective film on the back side of the base;
A second step of removing a part of the reflective film formed in the first step;
And a third step of filling a predetermined material in the base on which the reflective film is left only in a predetermined region by the second step. A high-refractive index first prism having a prism incident surface on which light from the outside is incident;
A high-refractive-index second prism having a prism exit surface from which light incident inside from the prism entrance surface of the first prism exits;
It is configured as a transmission type plane diffraction grating sandwiched between the first prism and the second prism so that the apex angle of the first prism and the apex angle of the second prism are opposed to each other. A diffraction grating incident surface formed in a substantially rectangular shape into which light incident from the prism incident surface of the first prism and transmitted through the first prism is incident, and the diffraction grating incident surface A diffraction grating exit surface formed in a substantially rectangular shape that is substantially parallel to each other and is opposed in parallel with each other and is incident on the inside from the diffraction grating entrance surface; and the diffraction grating entrance surface, It is formed between the diffraction grating exit surface, is located at substantially equal intervals with respect to the diffraction grating entrance surface and the diffraction grating exit surface, and light incident on the inside from the diffraction grating entrance surface is incident thereon, The incident light Direct view transmissive diffraction grating as a diffraction grating having a diffraction grating region having a plurality of reflecting surfaces for reflecting. The diffraction grating of claim 5, further comprising:
The angle formed by the light incident on the reflection surface from the diffraction grating incident surface of the diffraction grating region and the reflection surface and the reflection surface is “θ ₂ ”, the grating interval is “d”, and the reflection When the thickness of the surface is “w” and the height of the reflecting surface is “t”,
tan θ ₂ = (d−w) / t
A diffraction grating in which the reflection surface of the diffraction grating region is dimensioned so as to satisfy

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