JPH10307203A - Diffraction grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent stray light from being made incident on a photodetector and to eliminate the influence of the stray light caused by the reflection of a glass plate by inclining and sticking the glass plate at a fixed angle to a direction perpendicular to a diffraction direction. SOLUTION: A resin layer 2 is formed on glass base material 1 and further grooves (a) are plurally formed in parallel with each other on the resin layer 2. The glass plate 4 is stuck to the surface side of the layer 2 through adhesive 3a. The plate 4 is kept parallel in terms of attaching accuracy to the layer 2 with respect to the direction (diffraction direction) orthogonally crossed with the grooves (a) and stuck to be somewhat inclined (b) by the fixed angle θwith respect to the direction along the groove (a) (direction perpendicular to the diffraction direction). Thus, the stray light 103a is emitted with a fixed angle difference not only in the diffraction direction of the diffraction grating to 1st order diffracted light 101a but also in the direction perpendicular to the diffraction direction. As a result, the stray light 103a is prevented from being made incident on the photodetector and the influence of the stray light caused by the reflection of the plate 4 is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a diffraction grating which is a spectral component such as an optical spectrum analyzer, and more particularly to a diffraction grating capable of eliminating the influence of stray light generated on the structure of the diffraction grating.

[0002]

2. Description of the Related Art A conventional diffraction grating forms a groove in a resin layer on a glass base material and separates incident light by diffraction at different angles caused by the wavelength of the light incident on the groove.

FIG. 3 is a sectional view showing an example of such a conventional diffraction grating. In FIG. 3, 1 is a glass base material and 2 is a resin layer. 1 and 2 constitute a diffraction grating 50.

A resin layer 2 is formed on a glass base material 1,
Further, a plurality of grooves as shown by "A" in FIG. 3 are formed in the resin layer 2 in parallel with each other.

[0005] However, since the resin layer 2 is in contact with the surrounding atmosphere, there is a problem that the resin layer 2 is easily affected by the deterioration of the resin layer 2 due to the ambient temperature and humidity, and the environmental resistance is poor.

For this reason, a quartz crystal or a glass plate, which is an optically transparent substance, is adhered to the surface of the resin layer 2 so as to adhere to the resin layer 2.
Is used to protect the surface of the device.

FIG. 4 is a sectional view showing an example of a diffraction grating in which such a resin layer 2 is protected. 4, 1, 2, and 50 are denoted by the same reference numerals as in FIG.
Denotes a glass plate, 100 denotes incident light, and 101 denotes first-order diffracted light.

A resin layer 2 is formed on a glass base material 1,
Further, a plurality of grooves as shown by "a" in FIG. 4 are formed in the resin layer 2 in parallel with each other. Further, a glass plate 4 is adhered to the surface side of the resin layer 2 in parallel with the diffraction grating 50 via an adhesive 3.

Now, the operation of the diffraction grating shown in FIG. 4 will be described. In FIG. 4, the density of the groove indicated by “a” is set to “500 grooves / mm”.
(Pitch d = 2 μm) ”and the wavelength of the incident light is“ λ = 150
0 nm ", and the refractive indices of the adhesive 3 and the glass plate 4 are set to" 1.
5 ", the incident angle indicated by" b "in FIG.
The emission angle indicated by the middle “c” is “b”, and the angles of the light propagating in the adhesive 3 and the glass plate 4 are “b ′” and “a ′”.

At this time, from the Snell's formula, n × {sin (a ′)} = sin (a) (1) holds, so that 1.5 × {sin (a ′)} = sin (10 °) b '= Sin ^-1 {sin (10 °) /1.5} = 6.648 ° (2)

Further, since λ = {sin (b ′) − sin (a ′)} × n · d (3) holds according to the equation of diffraction, sin (b ′) = 0.5 + sin (6.648 °) B) = sin ⁻¹ {0.5 + sin (6.648 °)} = 38.0078 ° (4)

Further, since n × {sin (b ′)} = sin (b) (5) holds from the Snell equation, 1.5 × {sin (38.0078 °)} = sin (b) b = sin ^-1 {1.5 × sin (38.0078 °)} = 67.467 ° (6)

As a result, by forming a resin layer 2 having a plurality of grooves formed on the glass base material 1 and bonding the glass plate 4 to the surface side of the resin layer 2, the resistance of the diffraction grating is improved. Environmental characteristics can be improved.

[0014]

However, the glass plate 4 for protecting the resin layer 2 is not in a completely parallel state, but has a slight inclination in terms of mounting accuracy, and the reflection of the surface of the glass plate 4 on the "F" side. There is a problem that stray light is generated due to the above.

FIG. 5 is an explanatory diagram for explaining the generation of such stray light. Reference numerals 1 to 4, 50, 100 and 101 have the same reference numerals as in FIG. Reference numerals 102 and 103 denote stray light.

For example, the zero-order diffracted light (reflected light) on the resin layer 2 is reflected toward the resin layer 2 at a point indicated by "A" in FIG.
The light is diffracted by the resin layer 2 and emitted as stray light 102.

Further, for example, the first-order diffracted light indicated by "b" in FIG. 5 is reflected toward the resin layer 2 at the point indicated by "c" in FIG.
The light is reflected by the resin layer 2 and emitted as stray light 103.

In this state, if the glass plate 4 is attached to the diffraction grating 50 at an inclination of "0.01 °" with respect to the mounting accuracy, the 0th-order diffracted light (reflected light) on the resin layer 2 is shown in FIG. Since it is reflected on the surface of the glass plate 4 shown in the middle “d”
The angle again incident on the resin layer 2 becomes “6.668 °” by adding “0.01 ° × 2” to the angle shown in Expression (2).

Since this light is diffracted by the resin layer 2, if the diffraction angle is “c ′”, then sin (c ′) = 0.5 + sin (6.668 °) c ′ = sin ^{−1 according to} the equation of diffraction. {0.5 + sin (6.668 °)} = 38.033 ° (7)

Further, assuming that the exit angle of the stray light 102 is "c", from the Snell's equation, 1.5 × {sin (38.033 °)} = sin (c) c = sin ^-1 ｛1.5 × sin (38.033 °)｝ = 67.543 ° (8)

Accordingly, the difference between the equations (6) and (8) is 67.543-67.467 = 0.076 ≒ 0.08 (9)

Similarly, the angle at which the first-order diffracted light indicated by “b” in FIG. 5 is reflected toward the resin layer 2 at the point indicated by “c” in FIG. 01 ° × 2 ”is added to“ 38.0278 ° ”.

Since this light is reflected by the resin layer 2, FIG.
The incident angle on the surface of the glass plate 4 shown in the middle “e” is “3”.
8.0278 ° ”.

If the exit angle of the stray light 103 is "d", then from Snell's equation, 1.5 * {sin (38.0278 °)} = sin (d) d = sin ^-1 << 1.5 * sin (38.0278 °)｝ = 67.528 ° (10)

Therefore, the difference between the equations (6) and (10) is 67.528−67.467 = 0.061 ≒ 0.06 (11)

That is, the stray light 10
2 has an angle difference of “about 0.08 °” and stray light 103 has “
An angle difference of about 0.06 ° "is produced in each case.

Since the stray lights 102 and 103 are emitted in the diffraction direction of the diffraction grating 50, it can be said that the photodetector side (not shown) erroneously recognizes that light of another wavelength exists. Problems arise.

These stray lights 102 and 103 are applied to the glass plate 4
Can be prevented by forming an anti-reflection film on the surface of the diffraction grating 50, but when the wavelength of light incident on the diffraction grating 50 is wide, it is difficult to prevent reflection in all wavelength regions. .

Even when the range of the incident wavelength is limited, since the incident angle of the incident light and the exit angle of the diffracted light are different from each other, an antireflection film for preventing reflection of both the incident light and the diffracted light is formed. It is difficult.

Of course, when the parallel and sufficiently flat glass plate 4 is mounted in parallel with the diffraction grating 50, the above-mentioned problem does not occur even if there is reflection on the surface of the glass plate 4, It is difficult and, if possible, would be very costly. Therefore, an object to be solved by the present invention is to realize a diffraction grating that can remove the influence of stray light generated by reflection of a glass plate.

[0031]

In order to achieve the above object, according to a first aspect of the present invention, a groove is formed in a resin layer on a glass base material, and different grooves are formed depending on the wavelength of light incident on the groove. In a diffraction grating that separates incident light by diffraction at an angle, a glass base material, a resin layer formed on the glass base material and formed with a plurality of parallel grooves, and a surface side of the resin layer. And a glass plate bonded at a predetermined angle with respect to the direction along the groove.

In order to achieve the above object, according to a second aspect of the present invention, a groove is formed in a resin layer on a glass base material, and incident light is diffracted at different angles caused by the wavelength of light incident on the groove. In a diffraction grating that performs spectroscopy, a glass base material, a resin layer formed on the glass base material and having a plurality of grooves parallel to each other, and a direction along the grooves on the surface side of the resin layer And a wedge plate adhered so as to be inclined at a certain angle with respect to (1).

In order to achieve the above object, a third aspect of the present invention is characterized in that the first or second diffraction grating of the present invention is used for an optical spectrum analyzer.

In order to achieve such an object, a fourth aspect of the present invention is characterized in that the first or second diffraction grating of the present invention is used in a spectroscope.

In order to achieve the above object, a fifth aspect of the present invention is characterized in that the first or second diffraction grating of the present invention is used for a variable wavelength light source.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the diffraction grating according to the present invention. Here, 1, 2, and 4 are denoted by the same reference numerals as in FIG. 4, 3a is an adhesive, 100a is incident light,
01a is first-order diffracted light, and 103a is stray light. FIG. 1A is a plan view, and FIG. 1B is a side view.

A resin layer 2 is formed on a glass base material 1,
Further, a plurality of grooves as shown by "a" in FIG. 1 are formed in the resin layer 2 in parallel with each other. Further, a glass plate 4 is bonded to the surface side of the resin layer 2 via an adhesive 3a.

The glass plate 4 is parallel to the resin layer 2 in the direction perpendicular to the groove indicated by "a" in FIG. 1 (hereinafter referred to as "diffraction direction" for simplicity of description). The direction along the groove (hereinafter referred to as “direction perpendicular to the diffraction direction” for simplicity of description) is “b” in FIG.
As shown in FIG. 7, the adhesive is slightly inclined by a fixed angle “θ”.

Here, the operation of the embodiment shown in FIG. 1 will be described. However, the plan view shown in FIG. 1A, that is, the incident light 100a, the first-order diffracted light 101a and the stray light 1 in the diffraction direction
The relationship of 03a is 100, 101 and 103 in FIG.
And the description is omitted.

In the side view shown in FIG.
00a is a resin layer 2 that has passed through the glass plate 4 and the adhesive 3a.
, And the diffracted light from the resin layer 2 passes through the adhesive 3a and the glass plate 4 again and is emitted as the first-order diffracted light 101a.

On the other hand, of the diffracted light, the light reflected by the glass plate 4 at the point "C" in FIG. 1 is further reflected by the resin layer 2 and emitted as stray light 103a.

Therefore, the first-order diffracted light 101a and the stray light 10a
3a in the direction perpendicular to the diffraction direction in FIG.
An angle difference as shown in FIG.

For example, if the inclination with respect to the direction perpendicular to the diffraction direction is “θ = 0.1 °”, the diffracted light is transmitted to the wedge plate 5.
Is reflected on the surface of the resin layer 2, and “0.1 ° × 2 = 0.2 °” is added to the angle of incidence on the resin layer 2 again.

That is, in the direction perpendicular to the diffraction direction, the stray light 103a is "about 0.
It will be emitted with a 2 ° "angle difference.

The stray light 103a is 1 in the diffraction direction.
As described above, the second-order diffracted light 101a is emitted with an angle difference of “about 0.06 °” for each inclination “0.001 °” of the glass plate 4.

Therefore, the stray light 103a is converted to the first-order diffracted light 101.
The light is emitted with a constant angle difference not only in the diffraction direction of the diffraction grating 50 but also in the direction perpendicular to the diffraction direction with respect to a. A similar angle difference also occurs for the stray light 102 shown in FIG.

In this state, by installing the photodetector (not shown) at an appropriate position perpendicular to the diffraction direction, it is possible to prevent the stray light 103a and the like from being incident on the photodetector. Can be.

As a result, by adhering the glass plate 4 at a fixed angle with respect to the direction perpendicular to the diffraction direction, it is possible to prevent the stray light 103a and the like from entering the photodetector. Can be eliminated.

In the embodiment shown in FIG. 1, the glass plate 4 is fixed at a certain angle in a direction perpendicular to the diffraction direction by the adhesive 3a.
Although they are slightly inclined by θ ″ and bonded, a wedge plate in which the surfaces of the glass plates are not parallel to each other but inclined at a fixed angle (wedge degree) may be used.

FIG. 2 is a configuration diagram showing an embodiment of a diffraction grating using a wedge plate. In FIG. 2, 1 and 2 have the same reference numerals as in FIG. 1, 3b is an adhesive, 5 is a wedge plate, 100b is incident light, 101b is first-order diffracted light, 103
b is stray light. Further, the plan view is the same as the plan view shown in FIG.

A resin layer 2 is formed on a glass base material 1,
Further, a plurality of grooves are formed in the resin layer 2 in parallel with each other. A wedge plate 5 is adhered to the surface of the resin layer 2 via an adhesive 3b.

However, one surface of the wedge plate 5 is adhered in parallel with not only the diffraction direction but also a direction perpendicular to the diffraction direction in terms of mounting accuracy, and the other surface of the wedge plate 5 is oriented in the diffraction direction. Adhere so that it is inclined at a certain angle in the vertical direction.

Here, the operation of the embodiment shown in FIG. 2 will be described. The other surface of the wedge plate 5 is slightly inclined by a certain angle "Θ" as shown by "A" in FIG.

Therefore, similarly to the embodiment shown in FIG. 1, the stray light 103b and the like generated by the reflection of the surface of the wedge plate 5 are not only directed in the diffraction direction of the diffraction grating 50 but also in the direction perpendicular to the diffraction direction with respect to the primary diffraction light 101b. Is also emitted with a certain angle difference.

As a result, by inclining the surface of the wedge plate 5 at a certain angle with respect to the direction perpendicular to the diffraction direction, it is possible to prevent the stray light 103b and the like from entering the photodetector. The effect can be eliminated.

The above-mentioned diffraction grating can be used not only for an optical spectrum analyzer but also for a spectroscope, a multiplexer for wavelength multiplex communication, a demultiplexer for wavelength multiplex communication, a variable wavelength light source, and the like.

In addition to the protection of the resin tank 2, it can also be used to protect the surface coating of the diffraction grating having grooves formed directly on the glass with aluminum or the like.

[0058]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. By gluing the glass plate at a fixed angle to the direction perpendicular to the diffraction direction, it is possible to prevent stray light from entering the photodetector, thus eliminating the effects of stray light caused by reflection from the glass plate. A grid can be realized.

By inclining the surface of the wedge plate at a certain angle with respect to the direction perpendicular to the diffraction direction, it is possible to prevent the stray light from entering the photodetector, so that the influence of the stray light generated by the reflection of the wedge plate can be eliminated. Diffraction grating can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a diffraction grating according to the present invention.

FIG. 2 is a configuration diagram showing an embodiment of a diffraction grating using a wedge plate.

FIG. 3 is a cross-sectional view illustrating an example of a conventional diffraction grating.

FIG. 4 is a cross-sectional view illustrating an example of a diffraction grating that protects a resin layer.

FIG. 5 is an explanatory diagram for explaining generation of stray light.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass base material 2 Resin layer 3,3a, 3b Adhesive 4 Glass plate 5 Wedge plate 50 Diffraction grating 100,100a, 100b Incident light 101,101a, 101b Primary diffracted light 102,103,103a, 103b Stray light

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuyuki Suzuki 2-9-132 Nakamachi, Musashino City, Tokyo Inside Yokogawa Electric Corporation (72) Inventor Yasuyuki Minagawa 2-9-132 Nakamachi, Musashino City, Tokyo Side Kawa Electric Co., Ltd.

Claims (5)

[Claims] 1. A diffraction grating which forms a groove in a resin layer on a glass base material and separates incident light by diffraction at different angles caused by the wavelength of light incident on the groove, comprising: a glass base material; A resin layer formed on the base material and having a plurality of mutually parallel grooves formed thereon; and a glass plate bonded to the surface of the resin layer at a predetermined angle with respect to a direction along the grooves. A diffraction grating. 2. A diffraction grating which forms a groove in a resin layer on a glass base material and separates incident light by diffraction at different angles caused by the wavelength of light incident on the groove, comprising: a glass base material; A resin layer formed on the base material and having a plurality of mutually parallel grooves formed thereon; and a wedge plate bonded to the surface of the resin layer so as to be inclined at a predetermined angle with respect to a direction along the grooves. A diffraction grating, characterized in that: 3. An optical spectrum analyzer using the diffraction grating according to claim 1 or 2. 4. A spectroscope using the diffraction grating according to claim 1 or 2. 5. A variable wavelength light source using the diffraction grating according to claim 1 or 2.