Patent Description:
The concave diffraction grating is an optical element used in an optical device such as a spectrophotometer and has a function of dispersing and condensing light for each wavelength. In the optical device including the concave diffraction grating, the number of components of the device can be reduced, and the configuration of the device can be simplified.

In a conventional diffraction grating, a reflection film on which a grating groove is formed is affixed to a substrate. Examples of a conventional diffraction grating are described in PTLs <NUM> to <NUM>.

PTL <NUM> describes that a grating surface of a diffraction grating is formed by forming a reflection film (aluminum film) in a mold (master diffraction grating) in which grating grooves are formed, affixing the reflection film to a glass substrate with a resin adhesive, peeling the glass substrate from the mold, and inversely bonding the reflection film to the substrate.

PTL <NUM> describes that a diffraction grating is manufactured by forming sawtooth-shaped grating grooves on a flat plate-shaped substrate such as quartz or glass by holographic exposure and ion beam etching, and coating the surface of the grating grooves with a metal film such as aluminum or gold.

PTL <NUM> describes that a load is applied to a planar diffraction grating placed on a curved surface affixing substrate to form a mold of a curved surface diffraction grating. A concave diffraction grating is produced by transferring the shape of the mold of the curved diffraction grating to a reflection film (metal or resin) and disposing a curable resin and an affixing substrate on the reflection film.

<CIT> describes another concave diffraction grating manufactured differently.

The diffraction gratings described in PTLs <NUM> and <NUM> are produced by transferring the shape of a diffraction grating mold to a reflection film (forming a reflection film in the diffraction grating mold), and the reflection film is affixed to a substrate with a resin. In these diffraction gratings, since the reflection film is disposed on a resin, there is a problem that when the resin expands and contracts due to an influence of temperature, humidity, or the like, the reflection film deforms to affect optical characteristics of the diffraction grating.

In the diffraction grating described in PTL <NUM>, since the surface of the grating grooves formed on a substrate such as quartz or glass is coated with a metal film (reflection film), the reflection film is hardly affected by temperature, humidity, and the like. However, since the reflection film is formed by coating the surface of the grating grooves, there is a problem that the top of each grating groove (the top of the protrusion constituting the grating groove) of the reflection film is rounded, and the optical characteristics of the diffraction grating may deteriorate.

An object of the present invention is to provide a concave diffraction grating that can prevent deformation of a reflection film due to an influence of temperature and can prevent deterioration of optical characteristics due to temperature, and an optical device including the concave diffraction grating.

A concave diffraction grating according to the present invention includes a reflection film including a plurality of grating grooves, a holding film formed of metal and having one surface provided with the reflection film, a concave substrate including a concave surface, and an affixing layer that is provided between the concave surface and the other surface of the holding film and affixes the holding film and the reflection film to the concave substrate.

The present invention can provide a concave diffraction grating that can prevent deformation of a reflection film due to an influence of temperature and can prevent deterioration of optical characteristics due to temperature, and an optical device including the concave diffraction grating.

The concave diffraction grating according to the present invention includes a holding film between a reflection film including grating grooves and a concave substrate, and includes an affixing layer that affixes the holding film and the reflection film to the concave substrate. The concave diffraction grating according to the present invention can prevent deformation of the grating grooves with the holding film, and can prevent deterioration of optical characteristics even when the affixing layer deforms due to the influence of temperature or humidity or the temperature of the reflection film rises due to light irradiation. The holding film inhibits deformation of the reflection film and prevents deterioration of optical characteristics due to an influence of the temperature of the concave diffraction grating. When the concave diffraction grating according to the present invention includes the concave substrate, the affixing layer, and the holding film each formed of a material having high thermal conductivity, heat is easily released from the concave diffraction grating, and therefore, the concave diffraction grating can inhibit a temperature rise due to heat and can have a stable spectral performance even when it is irradiated with light having high energy. The concave diffraction grating according to the present invention has a small variation in the shape of grating grooves of the reflection film and is excellent in optical characteristics.

Hereinafter, a concave diffraction grating and an optical device according to an embodiment of the present invention will be described with reference to the drawings.

<FIG> is a diagram illustrating an optical device according to a first embodiment of the present invention. The optical device <NUM> is used for concentration measurement and substance identification of a sample (for example, a chemical substance or a biological substance) by utilizing a fact that light having a wavelength specific to chemical bonding of a substance contained in the sample is selectively absorbed when the sample is irradiated with light.

The optical device <NUM> includes a white light source <NUM>, condenser lenses 12a, 12b, a sample chamber <NUM>, a slit <NUM>, a concave diffraction grating <NUM>, and a plurality of detectors <NUM>. The optical device <NUM> preferably includes a cooling device <NUM>.

The white light source <NUM> emits light to irradiate the sample.

The condenser lens 12a condenses the light emitted from the white light source <NUM> and irradiates the sample in the sample chamber <NUM> with the light.

The sample chamber <NUM> stores the sample to be measured.

The condenser lens 12b condenses the light transmitted through the sample on the slit <NUM>.

The slit <NUM> allows the light condensed by the condenser lens 12b to pass therethrough and irradiates the concave diffraction grating <NUM> with the light.

The concave diffraction grating <NUM> disperses the light passing through the slit <NUM> for each wavelength to form spectra.

The plurality of detectors <NUM> are provided according to the wavelengths to be detected and are disposed linearly. The plurality of detectors <NUM> detect the formed spectra and measure the intensity of light for each wavelength.

The cooling device <NUM> can be configured using, for example, a radiator or a Peltier element, and cools the concave diffraction grating <NUM>. When the concave diffraction grating <NUM> is irradiated with light having high energy, the temperature of the concave diffraction grating <NUM> rises, and the reflection film may deform to deteriorate optical characteristics (spectral performance). It is preferable to install the cooling device <NUM> in such a manner as to be in contact with the concave diffraction grating <NUM> to prevent a decrease in optical characteristics due to a temperature rise. The concave diffraction grating <NUM> is cooled by the cooling device <NUM>, and a temperature rise is inhibited. Alternatively, the housing constituting the optical device <NUM> may be regarded as the cooling device <NUM>, and the concave diffraction grating <NUM> may be placed in contact with the housing.

The concave diffraction grating <NUM> according to the first embodiment of the present invention will be described with reference to <FIG> is a perspective view illustrating the concave diffraction grating <NUM> according to the present embodiment. <FIG> is a sectional view of the concave diffraction grating <NUM> taken along the line A-A in <FIG>.

The concave diffraction grating <NUM> according to the present embodiment includes a concave substrate <NUM>, an affixing layer <NUM>, a holding film <NUM>, and a reflection film <NUM>. The affixing layer <NUM>, the holding film <NUM>, and the reflection film <NUM> have a concave shape that is concave toward the concave substrate <NUM>.

The concave substrate <NUM> may be formed of metal such as copper or aluminum, silicon, or glass. On the concave substrate <NUM>, the affixing layer <NUM>, the holding film <NUM>, and the reflection film <NUM> are provided in this order. The concave substrate <NUM> includes a concave surface 24a, and the affixing layer <NUM> is provided on the concave surface 24a. The concave surface 24a has any curvature.

The affixing layer <NUM> is formed of resin or metal, is provided between the concave substrate <NUM> and the holding film <NUM> and serves as an adhesive material for affixing the holding film <NUM> and the reflection film <NUM> to the concave substrate <NUM>. The affixing layer <NUM> may be formed of, for example, thermosetting resin such as epoxy, or metal for adhesion such as solder, tin, or indium. The affixing layer <NUM> may be formed of thermosetting resin containing metal particles (for example, particles of copper or aluminum). The metal particles increase the thermal conductivity of the affixing layer <NUM>.

The holding film <NUM> is formed of metal and is a member for maintaining the shape of the reflection film <NUM>. The holding film <NUM> is affixed to the concave substrate <NUM> by the affixing layer <NUM>. The reflection film <NUM> is provided on one surface of the holding film <NUM>. The affixing layer <NUM> is provided on the other surface (that is, the surface facing the concave substrate <NUM>) of the holding film <NUM>. The holding film <NUM> is preferably formed of metal having high thermal conductivity such as copper or nickel.

The reflection film <NUM> includes a plurality of grating grooves <NUM> and reflects light with the grating grooves <NUM>. The reflection film <NUM> may be formed of a material having high reflectance such as aluminum or gold. The reflection film <NUM> formed of a material having high thermal conductivity such as aluminum or gold can effectively release heat and prevent deformation due to a temperature rise.

The grating grooves <NUM> may have any shape, and examples of the shape include a sawtooth shape, a corrugated shape (for example, a sinusoidal waveform shape), and a rectangular shape (for example, a pulse waveform shape). The grating grooves <NUM> having a sawtooth shape have an advantage that they are easily produced in the method for manufacturing the concave diffraction grating <NUM> according to the present embodiment described later.

The holding film <NUM> is a member for preventing deformation of the grating grooves <NUM> of the reflection film <NUM> due to temperature or humidity and maintaining the shape of the reflection film <NUM>. The other surface (that is, the surface affixed to the concave substrate <NUM>) of the holding film <NUM> is a flat concave surface. As illustrated in <FIG>, it is preferable that the holding film <NUM> be also present between the grating grooves <NUM> of the reflection film <NUM>. When the holding film <NUM> is also present between the grating grooves <NUM>, one surface (that is, the surface on which the reflection film <NUM> is provided) of the holding film <NUM> has the same shape (for example, a sawtooth shape, a corrugated shape, or a rectangular shape) as the grating grooves <NUM>.

The reflection film <NUM> deforms when heat is accumulated by light and the temperature rises. It is necessary to release heat from reflection film <NUM> to prevent deformation of reflection film <NUM> due to a temperature rise. It is therefore preferable that the concave substrate <NUM>, the affixing layer <NUM>, and the holding film <NUM> be formed of a material having high thermal conductivity in the concave diffraction grating <NUM> according to the present embodiment.

Here, a configuration of a conventional concave diffraction grating will be described.

<FIG> is a sectional view of a conventional concave diffraction grating <NUM>. <FIG> corresponds to <FIG>. In the conventional concave diffraction grating <NUM>, the affixing layer <NUM> and the reflection film <NUM> are provided on the concave substrate <NUM> having the concave surface 24a. The affixing layer <NUM> is a member that is formed of resin and affixes the reflection film <NUM> to the concave substrate <NUM>. The reflection film <NUM> includes a plurality of grating grooves <NUM>.

The affixing layer <NUM> is also present between the grating grooves <NUM> of the reflection film <NUM>. Consequently, when the affixing layer <NUM> deforms due to the influence of temperature or humidity, the reflection film <NUM> deforms, the grating grooves <NUM> lose their shape, and the optical characteristics of the concave diffraction grating <NUM> may deteriorate.

In the concave diffraction grating <NUM> (<FIG>) according to the present embodiment having the above-described configuration, the holding film <NUM> inhibits deformation of the reflection film <NUM>, and it is possible to prevent deterioration of optical characteristics of the concave diffraction grating <NUM> even when the affixing layer <NUM> deforms (for example, expands and contracts) due to the influence of temperature or humidity.

In addition, when the affixing layer <NUM> and the concave substrate <NUM> are formed of a material having high thermal conductivity, it is possible to effectively inhibit the temperature from rising due to accumulation of heat in the concave diffraction grating <NUM>.

The holding film <NUM> preferably has a linear expansion coefficient with which the shape of the holding film <NUM> changes in the same manner as the reflection film <NUM> due to a temperature change. That is, the linear expansion coefficient of the holding film <NUM> is preferably a value substantially equal to or close to the linear expansion coefficient of the reflection film <NUM>. The holding film <NUM> and the reflection film <NUM> having substantially the same linear expansion coefficient value deform together when they deform due to a temperature rise, and therefore, the grating grooves <NUM> of the reflection film <NUM> stretch but can maintain its shape.

In the conventional concave diffraction grating <NUM> (<FIG>), the linear expansion coefficient of the affixing layer <NUM> is larger than the linear expansion coefficient of the reflection film <NUM>. Consequently, in the conventional concave diffraction grating <NUM>, when the affixing layer <NUM> deforms due to a temperature rise, the grating grooves <NUM> of the reflection film <NUM> deform and lose their shape.

Note that, as described with reference to <FIG> and <FIG> and <FIG>, a seed film <NUM> is provided between the reflection film <NUM> and the holding film <NUM>. The seed film <NUM> is not illustrated in <FIG>. The seed film <NUM> will be described later.

Next, an example of a method for manufacturing the concave diffraction grating <NUM> according to the present embodiment will be described.

<FIG> are diagrams illustrating first to eighth steps of the method for manufacturing the concave diffraction grating <NUM> according to the present embodiment. A part of a planar substrate <NUM> and a planar diffraction grating <NUM> is illustrated in <FIG>.

First, as illustrated in <FIG>, grating grooves <NUM> are formed on the planar substrate <NUM>. The planar substrate <NUM> may be formed of metal such as copper or aluminum, silicon, or glass. The grating grooves <NUM> may be formed on the planar substrate <NUM> by providing protrusions 31a on a surface of the planar substrate <NUM> by, for example, photolithography, etching, or the like used in a manufacturing process of a semiconductor element. the protrusions 31a may have any shape similarly to the grating grooves <NUM> of the concave diffraction grating <NUM>, and examples of the shape include a sawtooth shape, a wave shape, and a rectangular shape.

Next, as illustrated in <FIG>, the reflection film <NUM> is formed on the grating grooves <NUM> (protrusions 31a) by vapor deposition or sputtering. The reflection film <NUM> is formed to have unevenness along the protrusions 31a.

Next, as illustrated in <FIG>, the seed film <NUM> is formed on the reflection film <NUM> by vapor deposition or sputtering, and the holding film <NUM> is formed on the seed film <NUM> by plating.

The seed film <NUM> is used to allow a current to easily flow and grow the holding film <NUM> when the holding film <NUM> is formed by plating and is particularly effective when the reflection film <NUM> is formed of aluminum. The seed film <NUM> prevents diffusion (for example, diffusion of aluminum constituting the reflection film <NUM> into the holding film <NUM>) between the reflection film <NUM> and the holding film <NUM>. The seed film <NUM> may be formed of a plurality of kinds of metal films. For example, the seed film <NUM> may be formed by forming a film of a metal (for example, titanium) having a large adhesion force with the reflection film <NUM>, a film of a metal (for example, platinum) that prevents diffusion due to a temperature rise of the reflection film <NUM>, and a film of a metal (for example, gold or platinum) that is hardly oxidized in this order on the reflection film <NUM>.

Next, as illustrated in <FIG>, the planar substrate <NUM> on which the grating grooves <NUM> (protrusions 31a) are formed is peeled off from a stacked body of the reflection film <NUM>, the seed film <NUM>, and the holding film <NUM>, whereby the planar diffraction grating <NUM> is produced. The planar diffraction grating <NUM> is a planar stacked body in which the reflection film <NUM>, the seed film <NUM>, and the holding film <NUM> are disposed in this order. In the reflection film <NUM>, the grating grooves <NUM> are formed by the protrusions 31a. The planar diffraction grating <NUM> is produced by, for example, dissolving and removing the protrusions 31a to peel off the planar substrate <NUM>.

Next, as illustrated in <FIG>, the affixing layer <NUM> is disposed on the opposite surface of the planar diffraction grating <NUM> from the surface provided with the grating grooves <NUM>. Then, a convex substrate <NUM> is disposed to face the surface of the planar diffraction grating <NUM> on which the grating grooves <NUM> are provided, and the concave substrate <NUM> is disposed to face the surface of the planar diffraction grating <NUM> on which the affixing layer <NUM> is disposed. The convex substrate <NUM> is a substrate having a convex surface 27a and is disposed such that the convex surface 27a faces the planar diffraction grating <NUM>. The concave substrate <NUM> is a substrate having the concave surface 24a and is disposed such that the concave surface 24a faces the planar diffraction grating <NUM>.

Next, as illustrated in <FIG>, under a vacuum atmosphere, a load <NUM> is applied to the convex substrate <NUM> at a temperature equal to or higher than the adhesion temperature or eutectic point of the affixing layer <NUM>, and the planar diffraction grating <NUM> is sandwiched between the convex substrate <NUM> and the concave substrate <NUM>. By this heating and pressurization, the shape of the planar diffraction grating <NUM> is deformed to follow the shapes of the convex surface 27a of the convex substrate <NUM> and the concave surface 24a of the concave substrate <NUM>, and the planar diffraction grating <NUM> is adhered to the concave substrate <NUM>. The affixing layer <NUM> is cooled and cured in a state where the load <NUM> is applied to the convex substrate <NUM> to deform the planar diffraction grating <NUM>. When the affixing layer <NUM> is cured, the planar diffraction grating <NUM> is affixed to the concave substrate <NUM>.

Note that the grating grooves <NUM> do not deform even when the load <NUM> is applied to the convex substrate <NUM> and the planar diffraction grating <NUM> is sandwiched between the convex substrate <NUM> and the concave substrate <NUM>. It has been verified by experiments that, even when a force is applied to the top of each grating groove <NUM> (top of the protrusion constituting the grating groove <NUM>), the grating grooves <NUM> do not deform because the force disperses to the sides sandwiching the top of the grating groove <NUM>.

Next, as illustrated in <FIG>, after the affixing layer <NUM> is cured and the planar diffraction grating <NUM> is affixed to the concave substrate <NUM>, the convex substrate <NUM> is removed.

Next, as illustrated in <FIG>, a portion of the planar diffraction grating <NUM> overflowing from the concave substrate <NUM> is removed, whereby the concave diffraction grating <NUM> can be manufactured.

The concave diffraction grating <NUM> according to the present embodiment can also be manufactured by a method described below.

<FIG> are diagrams corresponding to <FIG>, illustrating first to fourth steps of another method for manufacturing the concave diffraction grating <NUM> according to the present embodiment. The concave diffraction grating <NUM> according to the present embodiment can also be manufactured by performing the steps illustrated in <FIG> instead of the steps illustrated in <FIG>.

First, as illustrated in <FIG>, the grating grooves <NUM> are formed in the planar substrate <NUM> by providing the protrusions 31a on a surface of the planar substrate <NUM> by machining (for example, imprint using a mechanical device).

Next, as illustrated in <FIG>, the reflection film <NUM> is formed on the grating grooves <NUM> (protrusions 31a) by vapor deposition or sputtering. The reflection film <NUM> is formed to have unevenness along the protrusions 31a. The step illustrated in <FIG> is the same as the step illustrated in <FIG>.

Next, as illustrated in <FIG>, the seed film <NUM> is formed on the reflection film <NUM> by vapor deposition or sputtering, and the holding film <NUM> is formed on the seed film <NUM> by plating. The step illustrated in <FIG> is the same as the step illustrated in <FIG>.

Next, as illustrated in <FIG>, the planar substrate <NUM> on which the grating grooves <NUM> (protrusions 31a) are formed is peeled off from a stacked body of the reflection film <NUM>, the seed film <NUM>, and the holding film <NUM>, whereby the planar diffraction grating <NUM> is produced. The planar diffraction grating <NUM> is produced by peeling and removing the planar substrate <NUM> from the stacked body.

Next, the steps illustrated in <FIG> are performed, whereby the concave diffraction grating <NUM> according to the present embodiment can be manufactured.

In the concave diffraction grating <NUM> according to the present embodiment, the shape of the grating grooves <NUM> of the reflection film <NUM> reflects the shape of the grating grooves <NUM> formed in the planar substrate <NUM>, and the shape of the top of each grating groove <NUM> (top of the protrusion constituting the grating groove <NUM>) reflects the shape of the bottom of each grating groove <NUM>. The concave diffraction grating <NUM> according to the present embodiment therefore has a small variation in the shape of the grating grooves <NUM>, can reduce noise (stray light), and is excellent in optical characteristics.

Claim 1:
A method for manufacturing a concave diffraction grating (<NUM>),
the concave diffraction grating including:
a reflection film (<NUM>) including a plurality of grating grooves (<NUM>);
a holding film (<NUM>) formed of metal and having one surface provided with the reflection film;
a concave substrate (<NUM>) including a concave surface; and
an affixing layer (<NUM>) that is provided between the concave surface and the other surface of the holding film and affixes the holding film and the reflection film to the concave substrate,
the holding film having a linear expansion coefficient with which a shape of the holding film changes in the same manner as the reflection film due to a temperature change,
the method comprising:
forming grating grooves (<NUM>) on a planar substrate (<NUM>);
forming the reflection film on the grating grooves of the planar substrate;
forming the holding film on the reflection film;
producing a planar diffraction grating in which the grating grooves are formed in the reflection film by peeling the planar substrate from a stacked body of the reflection film and the holding film;
disposing the affixing layer on an opposite surface of the planar diffraction grating from the surface provided with the grating grooves and disposing the concave substrate to face the surface of the planar diffraction grating on which the affixing layer is disposed; and
deforming a shape of the planar diffraction grating to follow a shape of the concave surface of the concave substrate to form the concave diffraction grating.