JP2003084114A - Reflection diffraction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reflection diffraction device exhibiting high wavelength dependence of the diffraction efficiency while hardly depending on the polarization direction of incident light and having excellent reliability and productivity. SOLUTION: A pseudo-sawtooth diffraction grating 102 which is a diffraction grating having a rugged cross-sectional pattern is formed on one surface of a transparent substrate 101, and a high reflecting layer 104 as a light reflective film is formed on the rugged pattern. A low reflecting film 103 as a light transmissive (antireflection) film is formed on the opposite side of the transparent substrate 101 to the face where the rugged pattern is formed. A protective substrate 106 is laminated with an adhesive layer 105 interposed on the side where the high reflecting layer 104 is formed to constitute the reflection diffraction device 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type diffractive element, and more particularly to a reflection type diffractive element used in devices such as optical multiplex communication and spectroscopic measurement.

[0002]

2. Description of the Related Art Light of various wavelengths contained in incident light is measured by diffracting light of various wavelengths in different directions to separate the light according to wavelength and measuring the intensity of each of the separated light. There is a method to measure the intensity of. As a method of wavelength separation, there is known a method of using a reflection type diffraction element having a grating having a sawtooth cross section.

FIG. 4 shows an example of the structure of a conventional reflection type diffraction element using a resin. In this element, a die in which a linear sawtooth diffraction grating of 250 to 1600 lines / mm is precisely formed is pressure-bonded to a resin formed on the surface of the glass substrate 401, and the sawtooth diffraction grating is transferred to form a sawtooth shape. The diffraction grating 402 is produced, and then the high reflection layer 403 is coated to form the reflection type diffraction element 40 using resin.

As a diffraction grating having a similar function, there is a pseudo-sawtooth diffraction grating in which a sawtooth shape is approximated by steps.
This element is manufactured by using the technique of photolithography and dry etching. A reflection type diffraction element manufactured by this technique is shown in FIG. Similar to that shown in FIG. 4, the pseudo sawtooth diffraction grating 50 is formed on the glass substrate 501.
2 is processed, and the reflection layer 503 is applied on it to form a pseudo sawtooth reflection type diffraction element 50. Further, in FIGS. 4 and 5, solid arrows represent incident light, dashed lines represent reflected light, and broken lines represent first-order diffracted light.

As a material for forming the diffraction grating, a glass substrate, an inorganic film or the like can be used in addition to the resin as in the case of FIG. Since these elements are reflective diffractive elements, they diffract and separate incident light by reflection. Due to the arrangement, the diffraction grating diffracts the grating surface from the top of the reflective diffractive element toward the pseudo sawtooth or sawtooth diffraction grating. The incident angle θ to the line is often used at an incident angle of 30 to 45 °. As an example, the wavelength dependence of the diffraction efficiency of the reflection type diffraction element including a sawtooth diffraction grating using a resin and a pseudo sawtooth diffraction grating using an inorganic film is shown in FIG. It shows in FIG. Here, in both figures, a white circle represents S-polarized light and a black circle represents P-polarized light.

[0006]

When a resin having excellent transferability is used as a diffraction grating material, as shown in FIG. 6, the wavelength dependence of the diffraction efficiency does not change significantly and the reflection direction is not significantly affected by the polarization direction. Type diffractive element can be realized. However, when a resin is used, durability is not sufficient such as deterioration of the element due to high temperature or high temperature and high humidity, and there is a problem that it can be used only under limited environmental conditions. Further, since the precision transfer process is used, there is a problem that the productivity is low and the inexpensive and high-performance elements cannot be mass-produced.

On the other hand, a reflection type diffraction element in which a substrate made of an inorganic material or an inorganic film formed on the substrate is stepwise processed is excellent in reliability and productivity, and a large number of inexpensive elements are provided. Can be produced. However, as shown in FIG. 7, the wavelength dependence of the diffraction efficiency greatly depends on the polarization direction, so that practically, a large variation occurs in the spectral signal. In addition, in order to secure good incident polarization dependence and wavelength dependence, it is necessary to make the incident angle small, and there are restrictions on the layout design of the spectroscopic system, such as a large separation angle between the incident light and the diffracted light. I had it together.

Further, in any element using a resin film or an inorganic film, the high reflection layer formed on the surface is scratched,
There is a problem that the optical characteristics are significantly deteriorated when stains and the like occur. In addition, when a highly reflective layer with sufficient reflection characteristics is formed, a deviation from the original lattice shape may occur depending on the adhesion state of the layer, and the characteristic may deteriorate with respect to the design value of the lattice. I had it together.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a reflection type diffraction element which has a small change in diffraction efficiency depending on an incident polarization direction and an incident wavelength and which is excellent in mass productivity and reliability. To aim.

[0010]

The present invention provides a reflective diffraction element having a light-reflecting film formed on the concavo-convex portion of a diffraction grating having a concavo-convex cross-section formed on the surface of a transparent substrate. A reflection-type diffractive element characterized in that a light reflection preventing film is formed on the surface opposite to the surface where the concavo-convex portion is formed, and light is incident from the light reflection preventing film side for use.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a reflection type diffractive element in which a light-reflecting film is formed on an uneven portion of a diffraction grating having an uneven cross section formed on the surface of a transparent substrate.
Then, a light reflection preventing film is formed on the surface of the transparent substrate opposite to the surface on which the concavo-convex portion is formed, and light is incident from the light reflection preventing film side to be used.

By constructing the reflection type diffractive element in this way, it is possible to suppress an efficiency change in the wavelength dependence of the diffraction efficiency and also suppress a difference in polarization direction. The concavo-convex portion may have a rectangular shape, a sawtooth shape, a pseudo sawtooth shape, or the like, and any of them has the effect of the present invention. In the case of the sawtooth shape or the pseudo sawtooth shape, the wavelength and the angle of the incident light In a wide range, or in a wide range of the grating period, the diffraction efficiency of diffracted light in a specific direction can be increased.
Hereinafter, the present invention will be described with reference to the drawings by taking a sawtooth shape or a pseudo sawtooth shape as an example.

FIG. 2 is a side view showing an example of the structure of the reflection type diffraction element of the present invention. A low reflection film 203, which is a light reflection preventing film, is provided on the transparent substrate 201, and this film forms a light incident surface. Transparent substrate 2 without low reflection film 203
By repeating photolithography and dry etching on the back surface of 01, a pseudo sawtooth diffraction grating 202 having a grating pitch P that approximates the sawtooth unevenness in a four-level (3 steps) step shape is formed. A high reflection layer 204, which is a light-reflecting film made of metal, is formed on the diffraction grating.

Further, the protective substrate 2 for protecting the high reflection layer 204 by the adhesive layer 205 applied on the high reflection layer 204.
The reflective diffraction element 20 is formed by laminating 06. Light having a wavelength λ, which is incident on the low reflection film 203 of the reflective diffraction element 20 at an external incident angle θ ₁ which is a normal line, is refracted by the transparent substrate 201 having a refractive index n, so Snell's law,
It propagates in the transparent substrate 201 at an internal incident angle θ ₂ that satisfies sin (θ ₂ ) = sin (θ ₁ ) / n.

The propagated light is a pseudo sawtooth diffraction grating 202.
, The internal incident angle θ_TwoIncident at
The whole sign, either + or-
Most of the propagated light is concentrated and reflected at a specific diffraction order of
Diffracts. If the diffracted light is concentrated in the -1st order,
The diffracted light is the diffraction angle φ formed by the normal defined by the following formula_TwoThrough
The low-reflectivity film 203 propagates through the bright substrate 201 and interacts with the air.
Refraction again on the surface and diffraction angle φ ₁Detector not shown in the air
Propagate toward. Here, the solid arrow indicates the incident light,
The dashed line represents reflected light and the broken line represents first-order diffracted light.

[0016]

[Equation 1]

Here, φ ₁ is consequently equal to the diffraction direction of the reflection type diffraction element having the diffraction grating on the surface of the transparent substrate.

In FIG. 3, about 6 is formed on the back surface (the surface on which the low reflection film is not formed) of the quartz glass substrate having the refractive index of 1.44.
When a pseudo sawtooth diffraction grating of 00 lines / mm is formed,
The wavelength dependence of the diffraction efficiency due to the difference in the polarization direction at the external incident angle θ ₁ = 40 ° is shown. Here, the white circle is S-polarized light and the black circle is P-polarized light. It can be seen that the wavelength dependence of the diffraction efficiency due to the difference in the polarization direction is improved in FIG. 3 compared to the pseudo sawtooth reflection type diffraction element used at the same incident angle shown in FIG.

By using the configuration of the present invention, even if light is incident on the reflection type diffraction element at a large external incident angle, it can be incident on the pseudo sawtooth diffraction grating at a small internal incident angle in the transparent substrate, resulting in polarization. The wavelength dependence of the diffraction efficiency due to the difference in direction can be reduced. With this configuration, it is possible to realize a reflective diffraction element having excellent reliability and mass productivity, and it is possible to realize an inexpensive spectroscopic system. Further, in order to secure the diffraction efficiency that does not depend so much on the polarization direction or wavelength of the incident light, it is not necessary to make the external incident angle to the reflection type diffractive element particularly small, so that there is a great freedom in designing the spectroscopic system. Have

In the reflection type diffraction element of the present invention, the diffraction grating pattern seen in a plan view can be produced by using a photomask or the like, and therefore the diffraction grating pattern is not limited to a linear shape and may be a curved shape, for example. With this curved shape, a lens function can be added so that the diffracted light is condensed on the detector. Further, by using a large-area wafer process, an optical layer having other functions such as a phase plate can be laminated on the reflection type diffraction element, and further higher functionality and compounding can be performed.

The diffraction grating in the present invention is preferably produced by processing the glass substrate itself or an inorganic material formed on the glass substrate. In particular, it is extremely preferable to directly process a quartz glass substrate having a high-speed and uniform etching property from the viewpoint that the film-forming cost does not occur, and the interface between the film-forming and the substrate does not exist.
It is also preferable in terms of mass productivity. Further, in order to suppress changes in the diffraction direction due to temperature changes, it is effective to form an inorganic material having excellent etching characteristics as a film on a quartz glass substrate having a thermal expansion coefficient smaller than that of the material,
Such a configuration is also preferable in order to obtain an element having excellent temperature characteristics.

In the high reflection film, only the interface with the saw-toothed diffraction grating optically functions, so that there is no limitation on the thickness of the high reflection film. Therefore, it is not necessary to consider the shape deterioration (deformation) of the high reflection film due to the increase in the film thickness, and the film can be formed to have a sufficient film thickness to secure the reflectance of the high reflection film. Further, since it is not necessary to form a thin film with high precision, it is not always necessary to use a vacuum film forming method such as a vacuum vapor deposition method or a sputtering method, and a plating method or the like can be used.

Since the protection means for protecting the high reflection film on the back surface of the reflection type diffraction element does not function optically, it does not need to be transparent and its thickness is not limited, and it is made of an inorganic material or an organic material. It is preferable that the protection means is provided on the high reflection film side. Also, an organic material made of resin,
Although a wide variety of inorganic materials capable of forming a vacuum film can be used, it is particularly preferable to use an organic resin material that can be prepared by coating and curing.

When the reflection type diffractive element is installed in a specific device, for example, when the back surface of the reflection type diffractive element is required to be used as a reference at the time of accuracy, or when a stronger protective property is required, a high level is required. It is preferable to bond a flat and strong transparent substrate or the like using an adhesive applied on the reflective film.

At this time, a glass substrate, a silicon substrate or the like can be used, but it is preferable to use a material having substantially the same thermal expansion coefficient as that of the transparent substrate in order to suppress the characteristic change at high temperature caused by the difference in expansion coefficient. . INDUSTRIAL APPLICABILITY The present invention has a remarkable effect as long as it is a narrow-pitch diffraction grating that improves wavelength resolution by increasing the diffraction angle in particular. In particular, the pitch of the diffraction grating is almost equal to the center wavelength, or the pitch is the center. The effect is large in the range smaller than the wavelength.

[0026]

EXAMPLE FIG. 1 is a side view showing the structure of a reflective diffraction element of this example. In this example, a quartz glass substrate having a thickness of 0.5 mm was used as the transparent substrate 101, and a pseudo sawtooth diffraction grating was formed on one surface of the substrate by using photolithography and dry etching techniques. That is,
Etching is carried out twice with 0.36 μm and 0.18 μm, respectively, and there are 4 levels (3 steps) with a step of 0.18 μm and a total depth (total step) of 0.54 μm.
A pseudo sawtooth diffraction grating 102 having

Next, a wavelength of 1.55 is formed on the surface of the transparent substrate 101 opposite to the surface on which the pseudo sawtooth diffraction grating 102 is formed.
Low reflection film 10 which is an antireflection film having a center wavelength of μm
3 was applied. On the pseudo sawtooth diffraction grating 102, a thickness of 0.
A film of gold having a thickness of 8 μm was formed by a vacuum evaporation method to form a highly reflective layer 104 which is a light reflective film. An epoxy adhesive serving as the adhesive layer 105 was applied on the high reflection layer 104, and a 0.5 mm-thick quartz glass substrate (protecting means) serving as the protective substrate 106 was stacked on the epoxy adhesive.

Thereafter, by rotating the quartz glass substrate, the epoxy adhesive is formed into a thin and uniform adhesive layer 105, and the transparent substrate 101 and the protective substrate 106 are adhered to each other.
To form a laminated substrate. The produced laminated board,
It was cut into a rectangle of 10 mm × 7 mm with a dicing saw to obtain a reflective diffraction element 10.

When light having a wavelength of 1.55 μm is incident from the low reflection film 103 side of the reflection type diffraction element 10 at an external incident angle θ ₁ = 40 °, light in the polarization direction parallel to the grating longitudinal direction (S polarization) ) And light in the vertical polarization direction (P-polarized light), the diffraction efficiencies were 73% and 70%, respectively. These diffraction efficiencies are almost equal. Also, even if the wavelength of the incident light is changed from 1.5 μm to 1.6 μm,
The amount of change in diffraction efficiency was a small value of about ± 5%. In FIG. 1, the solid arrow indicates the incident light, and the alternate long and short dash line indicates the reflected light.
The broken lines represent the first-order diffracted light, respectively.

[0030]

As described above, in the reflection type diffraction element of the present invention, compared with the conventional reflection type diffraction element which is incident from the diffraction grating side even at a large incident angle to the reflection type diffraction element. , Shows good wavelength dependence of diffraction efficiency that does not depend much on the difference in polarization direction. Further, it is possible to realize a reflection type diffraction element excellent in mass productivity and reliability.

[Brief description of drawings]

FIG. 1 is a side view showing a configuration of a reflective diffraction element according to an example.

FIG. 2 is a side view showing an example of the configuration of a reflective diffraction element of the present invention.

FIG. 3 is a graph showing an example of diffraction characteristics of the reflective diffraction element of the present invention.

FIG. 4 is a side view showing an example of the configuration of a conventional reflective diffraction element.

FIG. 5 is a side view showing another example of the configuration of a conventional reflective diffraction element.

FIG. 6 is a graph showing an example of diffraction characteristics of a conventional reflective diffraction element.

FIG. 7 is a graph showing another example of diffraction characteristics of a conventional reflective diffraction element.

[Explanation of symbols]

10, 20, 40, 50: Reflective diffraction element 101, 102: transparent substrate 401, 501: glass substrate 402: Sawtooth diffraction grating 102, 202, 502: pseudo sawtooth diffraction grating 103, 202: low reflection film 104, 204, 403, 503: high reflection layer 105, 205: Adhesive layer 106, 206: protective substrate

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H042 DA05 DA12 DA17                 2H049 AA07 AA33 AA37 AA45 AA58                       AA59 AA63 AA64                 2K009 AA02 BB02 DD12                 4G059 AA08 AA11 AB01 AB09 AB11                       AC01 AC04 AC05 AC06 BB01                       GA01 GA04 GA15

Claims (4)

[Claims] 1. A reflection type diffraction element having a light-reflecting film formed on an uneven portion of a diffraction grating having a concave-convex cross-section formed on the surface of a transparent substrate, which is opposite to the surface on which the uneven portion of the transparent substrate is formed. A reflection type diffractive element characterized in that a light reflection preventing film is formed on the surface of the side and light is incident from the light reflection preventing film side for use. 2. The reflection type diffraction element according to claim 1, wherein protective means made of an inorganic material or an organic material for protecting the light reflecting film is provided on the light reflecting film side. 3. The transparent substrate is made of a glass substrate, and the uneven portion is formed directly on the surface of the glass substrate, or is formed of an inorganic material deposited on the surface of the glass substrate. Alternatively, the reflective diffraction element according to the item 2. 4. The cross-sectional shape of the concavo-convex portion is a sawtooth or a sawtooth-like shape which is approximated by steps.
The reflective diffractive element described.