JP2006259439A - Demultiplexing element and demultiplexing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when part of signal light is demultiplexed from an optical path, it is difficult for a conventionally used demultiplexing element to put positions where incident light and projection light are made incident and projected respectively and a position where demultiplexed light is taken out away from each other and it is difficult to make the demultiplexing element small-sized. <P>SOLUTION: Provided is the demultiplexing element having a diffraction grating formation surface having a diffraction grating where uneven structures extending in one direction are periodically formed, a transmitted light projection surface, and a demultiplexed light projection surface, the demultiplexing element being characterized in that the light incident on the diffraction grating formation surface is transmitted straight and projected from the transmitted light projection surface and part of the incident light is diffracted, totally reflected by the transmitted light projection surface in a transparent base body, and guided to the demultiplexed light projection surface to be projected as demultiplexed light from the demultiplexed light projection surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a branching element.

  Conventionally, when a part of signal light is taken out from the optical path by optical communication or the like and the intensity or wavelength distribution is measured, a part of the incident light is demultiplexed using a prism or a diffraction grating, which is different from the outgoing light. It was taken out in the direction. However, it is difficult to reduce the size of the prism, and the diffraction grating has a problem that it is difficult to separate the position where incident light and outgoing light are incident and output from the position where the demultiplexed light is extracted.

Japanese Patent Laid-Open No. 2003-307606

  The present invention has been made in view of the above-described circumstances, and provides a small-sized demultiplexing element that can extract transmitted light, outgoing light, and demultiplexed light from a sufficiently separated position.

In order to solve the above-mentioned problems, the present invention is a demultiplexing element including a transparent substrate having a diffraction grating forming surface, a transmitted light emitting surface, and a demultiplexed light emitting surface, and the diffraction grating forming surface Includes a diffraction grating in which a concavo-convex structure extending in one direction is periodically formed, and the demultiplexing element transmits the incident light incident on the diffraction grating formation surface in a straight line and emits it from the transmitted light emission surface. And diffracting a part of the incident light, totally reflecting the diffracted diffracted light by the transmitted light exit surface within the transparent substrate, and guiding the light to the demultiplexed light exit surface. The present invention provides a demultiplexing element that emits as:
At this time, the diffracted light is preferably first-order diffracted light.
The transparent substrate is a flat substrate, and one of the opposing substrate surfaces is the diffraction grating forming surface, the other is the transmitted light exit surface, and one of the end surfaces is flat and the diffraction grating is It is preferable that the branched light exit surface is disposed substantially perpendicular to the periodic direction of the concavo-convex structure.

The concavo-convex structure is preferably formed by forming a transparent material layer on the diffraction grating forming surface of the transparent substrate and processing the layer, and the transparent material includes silicon nitride, silicon oxide, titanium oxide, and oxide. The main component is preferably one selected from tantalum, niobium oxide, and zinc oxide.
The concavo-convex structure preferably has a cross-sectional shape of a rectangular convex portion and a rectangular concave portion, or a saw-tooth cross-sectional shape. Alternatively, it is preferable that the concavo-convex structure has a cross-sectional shape that approximates a desired sawtooth shape in a step shape.

  In the branching element of the present invention, the diffracted light diffracted by the diffraction grating is totally reflected once by the transmitted light exit surface and then further reflected by the diffraction grating forming surface and the transmitted light exit surface. It is preferable that the light is emitted from the demultiplexed light exit surface.

  Furthermore, the present invention provides a demultiplexing method in which incident light is incident on a demultiplexing element to be transmitted in a straight line and a part of the incident light is extracted as demultiplexed light by changing an optical path, and the demultiplexing element is a flat plate made of a transparent material. A diffraction grating forming surface provided with a diffraction grating formed using a substrate and periodically formed with a concavo-convex structure in which one surface of one of the opposing substrate surfaces of the flat substrate extends in one direction; And the other surface is a transmitted light exit surface, and one of the end faces is flat and is disposed substantially perpendicular to the periodic direction of the concavo-convex structure of the diffraction grating and is used as the split light exit surface. The incident light incident on the diffraction grating forming surface of the demultiplexing element is diffracted at a diffraction angle larger than the total reflection angle of the transparent substrate, and the inside of the transparent substrate is directed to the demultiplexed light exit surface. And the demultiplexed light from the demultiplexed light exit surface Be emitted Te provides a demultiplexing method comprising.

  Although the demultiplexing element of the present invention is small, the demultiplexed light obtained by demultiplexing a part of the incident light is emitted from a position sufficiently separated from the emission position of the incident light and the transmitted light through which the incident light is linearly transmitted. be able to. Further, the demultiplexed light can be emitted at different emission angles depending on the wavelength of the incident light. By using the branching element of the present invention, an apparatus for detecting characteristics such as the intensity of incident light can be realized with a compact configuration.

  Hereinafter, although the detail of the branching element of this invention is demonstrated using drawing, this invention is not limited to the following description at all.

A demultiplexing element 1 according to an embodiment of the present invention shown in FIG. 1 is formed using a transparent flat substrate 1a. One of the opposing substrate surfaces is provided with a diffraction grating 1b in which a concavo-convex structure extending in one direction is periodically formed to be a diffraction grating forming surface 1c, and the other substrate surface is a transmitted light emitting surface 1d. It is said that. One of the end surfaces of the transparent substrate 1a is a demultiplexed light exit surface 1e. The demultiplexed light exit surface 1e is preferably smoothed by polishing or the like in order to prevent loss due to variation in the exit angle or scattering. Furthermore, if a low-reflection coating is formed for light having a wavelength of incident light, the amount of light emitted from the demultiplexed light can be increased, so that it is not diffracted by the diffraction grating 1b out of the incident light 2 incident on the diffraction grating forming surface 1c. The light diffracted by the diffraction grating 1b is totally reflected by the transmitted light emission surface 1d and the diffraction grating forming surface 1c and emitted as a demultiplexed light. It is guided to the surface 1e and emitted as demultiplexed light 6. With respect to the emitted demultiplexed light 6, it is possible to measure characteristics such as intensity using the photodetector 13.

  The flat substrate only needs to be made of a material that is substantially transparent to the wavelength at which the branching element of the present invention is used. Glass material such as quartz glass and optical glass, silicon, polycarbonate, polymethyl Although resin materials, such as a methacrylate (PMMA), are illustrated, it is preferable to be attacked by quartz glass and optical glass from viewpoints, such as durability.

  The concavo-convex structure may be produced by processing the surface of the transparent substrate itself, or by forming a layer made of a transparent material on the surface of the transparent substrate and processing the layer. Examples of such processing methods include cutting, pressing, molding, photolithography and etching.

  When the concavo-convex structure is formed by forming and processing a layer made of a transparent material, the transparent material preferably has excellent workability for the processing described above, and the processing described above is performed by photolithography and etching. In some cases, a material mainly containing one kind selected from silicon nitride, silicon oxide, titanium oxide, tantalum oxide, niobium oxide, zinc oxide, and silicon is preferable.

  In addition, it is preferable to use a high refractive index material as the transparent material, because a diffraction grating with high diffraction efficiency can be obtained, and the depth of the concavo-convex portion can be reduced, which facilitates processing. Examples of such a high refractive index transparent material include a material mainly composed of one selected from silicon nitride, titanium oxide, tantalum oxide, niobium oxide, zinc oxide, and silicon.

The behavior of light incident on the branching element of the present invention will be described with reference to FIG. Incident light 2 having a wavelength λ is incident on the diffraction grating forming surface 1c of the branching element 1 of the present invention in a plane that includes the normal line of the diffraction grating forming surface 1c and is orthogonal to the extending direction of the concavo-convex structure of the diffraction grating 1b. The incident light is incident at an angle α (that is, an angle formed with the normal direction of the diffraction grating forming surface 1c and denoted by reference numeral 7 in FIG. 2). When the grating period of the diffraction grating 1b is P, the incident light 2 is expressed by the formula (1) in a substrate having a refractive index n:
sin φ + sin α = m · λ / (n · P) (1)
The mth-order diffracted light 4 is generated in the direction of the internal diffraction angle φ (symbol 8 in FIG. 2) that satisfies the following relationship. Here, m is a natural number, and the internal diffraction angle φ is an angle formed by light diffracted by the diffraction grating 1b and emitted into the transparent substrate 1a with the normal direction of the diffraction grating forming surface 1c.

In the branching element of this embodiment, since the diffraction grating forming surface 1c and the transmitted light emitting surface 1d are parallel, the diffracted light 4 diffracted on the diffraction grating forming surface 1c with the internal diffraction angle φ travels in the transparent substrate. Then, the light enters the transmitted light exit surface 1d at an incident angle equal to the internal diffraction angle φ. The outgoing angle when the diffracted light 4 incident on the transmitted light exit surface 1d is refracted and emitted at the transparent substrate-air interface, that is, the angle θ with respect to the normal direction of the transmitted light exit surface is the internal diffraction angle φ and (2 )formula:
sin θ = n · sin φ (2)
When sin θ ≧ 1, the diffracted light 4 cannot be transmitted through the transmitted light exit surface 1d and is totally reflected. The diffracted light 4 totally reflected by the transmitted light exit surface 1d enters the diffraction grating forming surface 1c at an angle equal to the internal refraction angle φ, but is totally reflected except that it is partially diffracted and transmitted. In this way, the diffracted light 4 cannot pass through either the diffraction grating forming surface 1c or the transmitted light exit surface 1d, is totally reflected, travels through the substrate, and reaches the demultiplexed light exit surface 1e. .

The light that has been reflected an even number of times inside the substrate and has reached the demultiplexed light exit surface is expressed by equation (3), and the light that has been reflected an odd number of times and has reached the demultiplexed light exit surface 1e For (4),
sinψ = n · sin (β−φ) (3)
sinψ = n · sin (β + φ) (4)
Are emitted in the direction of the angle satisfying the above, that is, the emission angle ψ (represented by reference numeral 11 in FIG. 2). In both equations, β is an angle formed by the demultiplexed light exit surface 1e and the diffraction grating forming surface on which the diffraction grating 1b is formed. At this time, if sinψ ≧ 1, the demultiplexed light 6 is totally reflected by the demultiplexed light exit surface 1e, and therefore it is necessary to satisfy sinψ <1 in order to extract the demultiplexed light 6 from the demultiplexed light exit surface 1e.
If the angle β is 90 degrees, the transparent substrate 1a can be cut perpendicularly to the parallel substrate surface to form the demultiplexed light emission surface 1e, which is easy to manufacture and is preferable. However, the transparent substrate 1a is inclined obliquely within a range where sinψ <1 is satisfied. In this case, it is preferable that the extraction angle of the demultiplexed light 6 with respect to the direction of the incident light 2 or the transmitted light 3 can be adjusted.

  If the periodic direction of the concavo-convex structure of the diffraction grating is not substantially perpendicular to the demultiplexed light output surface 1e, the incident angle of the demultiplexed light 5 to the demultiplexed light output surface 1e is β-φ or β + φ which is the incident angle, The extension direction of the concavo-convex structure and the angle formed by the demultiplexed light output surface 1e are combined angles, and the incident angle is larger than when the periodic direction of the concavo-convex structure is substantially perpendicular to the demultiplexed light output surface 1e. Restrictions for emitting the light without causing total reflection at the demultiplexed light emitting surface 1e are severe. That is, it is preferable that the periodic direction of the concavo-convex structure is substantially perpendicular to the demultiplexed light exit surface 1e because the selection range of the diffraction grating 1b and the angle β is widened.

  In the branching element of the present invention, the ratio of the width of the convex portion to the concave portion of the diffraction grating, the repetition period of the diffraction grating 1b, and the concave and convex portions so that the following a), b), and c) are satisfied: The values of parameters such as the depth, the angle β formed between the diffraction grating forming surface 1c and the diffraction grating forming surface 1c represented by reference numeral 12 in FIG. 2, and the angle of incidence on the diffraction grating 1b are determined. As a result, the incident light 2 incident on the diffraction grating forming surface 1c is linearly transmitted by the diffraction grating 1b provided on the diffraction grating forming surface 1a to be emitted as the transmitted light 3 from the transmitted light emitting surface 1d. A part is diffracted by the diffraction grating 1 b, the diffracted diffracted light 4 is totally reflected by the transmitted light exit surface 1 d, guided to the demultiplexed light exit surface 1 e, and emitted as the demultiplexed light 6. If necessary, the diffracted light 4 diffracted by the diffraction grating 1b is totally reflected by the transmitted light emitting surface 1d and the diffraction grating forming surface 1c and guided to the demultiplexed light emitting surface 1e.

a) Since incident light incident on the demultiplexing element 1 is diffracted and emitted into the transparent substrate, sin φ <1 in equation (1).
b) Since the diffracted light 4 is totally reflected by the transmitted light exit surface 1d, sin θ ≧ 1 in the equation (2).
c) sin ψ <1 in the expression (3) or (4) so that the demultiplexed light 5 is emitted without being totally reflected by the demultiplexed light exit surface 1e.

  In the formula (1), m is preferably +1 or -1. That is, in the demultiplexing element 1 of the present invention, + 2nd order or higher order or −2nd order or lower high-order diffracted light among the light diffracted by the diffraction grating 1b can be used. When folded light is used, a higher diffraction intensity than that of higher-order diffracted light can be obtained, so that the intensity of transmitted light 3 and demultiplexed light 6 can be increased with respect to incident light 2.

  For example, when a transparent substrate made of quartz glass is used as the transparent substrate 1a and light having a wavelength band of 1580 to 1620 nm is perpendicularly incident on the diffraction grating forming surface 1c as the incident light 2, the parallel and periodicity of the diffraction grating 1b. The period of the concavo-convex structure formed is set to 1122 nm to 1580 nm. That is, in order to make the internal refraction angle φ less than 90 degrees so that the diffracted light is diffracted into the transparent substrate, the period of the concavo-convex structure is 1122 nm or more. Further, in order to make the internal diffraction angle φ larger than the total reflection angle 44 degrees of the quartz glass so that the diffracted light is totally reflected in the transparent substrate, it is set to 1580 nm or less. With this configuration, the vertically incident light can be totally reflected by the transmitted light emitting surface 1d and the diffraction grating forming surface 1a and guided to the demultiplexed light emitting surface 1e.

  Further, in the branching element 1 of the present invention, the diffracted light 4 diffracted by the diffraction grating 1b provided on the diffraction grating forming surface 1c is transmitted light emitting surface 1d, or the diffraction grating forming surface 1c and transmitted light emitting surface. If it is configured to be totally reflected by 1d and guided to and output from the demultiplexed light output surface 1e, instead of using the transparent flat substrate as the transparent substrate, the diffraction grating forming surface 1c and the transmitted light output It is also possible to use a substrate whose surface 1d is not parallel.

  The diffracted light 4 diffracted by the diffraction grating is totally reflected once by the transmitted light exit surface 1d, and then is not further reflected by the diffraction grating forming surface 1c and the transmitted light exit surface 1d. It is preferable that the light is emitted from the demultiplexing light exit surface 1e because the loss in the demultiplexing element 1 can be reduced. The diffracted light 3 is displaced by a distance corresponding to the diffraction angle and the substrate thickness in the periodic direction of the concavo-convex structure while traveling through the transparent substrate 1a from the diffraction grating forming surface 1c to the transmitted light emitting surface 1d. This configuration can be achieved by adjusting the substrate thickness and the distance between the position where the incident light is incident on the demultiplexing element and the demultiplexed light exit surface. For example, when incident light having a wavelength of 1580 to 1620 nm and a beam diameter of 1 mm is perpendicularly incident on a demultiplexing element made of a quartz glass substrate having a thickness of 2 mm on which a diffraction grating having a grating period of 1500 nm is formed, Since the first-order diffraction angle is 47 to 48 degrees and is larger than the total reflection angle 44 degrees of quartz glass, the first-order diffracted light with respect to the incident light that is vertically incident is totally reflected by the transmitted light exit surface. Further, when the incident light is made incident at a point at a distance of 2.8 mm to 3.8 mm from the end surface of the parallel substrate surface serving as the demultiplexed light output surface, the diffracted light diffracted by the diffraction grating is emitted from the transmitted light. After being totally reflected once by the surface, it is emitted from the demultiplexed light emitting surface without being further reflected by the and transmitted light emitting surfaces.

  Further, when the incident light 2 is tilted from the normal direction of the diffraction grating formation surface to the periodic direction of the concavo-convex structure and further inclined to the extension direction of the concavo-convex structure, the incident light 2 is inclined with respect to the diffraction grating formation surface. As compared with the case where the incident light is vertically incident, the incident angle when the diffracted light 4 is incident on the transmitted light exit surface 1d can be increased. This can alleviate the conditions for total reflection at the transparent substrate-air interface, which is preferable because the grating period of the diffraction grating can be increased.

  As an example, a case where light having a wavelength of 1600 nm is incident will be described. When the incident light 2 is incident perpendicular to the diffraction grating forming surface 1c, the grating period of the diffraction grating 1b must be 1600 nm or less in order to totally reflect the diffracted light 4 by the transmitted light emitting surface 1d. When the incident light is incident at an angle of 10 degrees from the normal direction of the diffraction grating forming surface 1c to the extending direction of the concavo-convex structure, that is, the direction perpendicular to the paper surface of FIG. That is, since the grating period can be increased, the production of the diffraction grating is facilitated, which is preferable. Incident light 2 is tilted from the normal direction of the grating plane in a plane perpendicular to the extending direction of the concavo-convex structure of the diffraction grating 1b, and incident from the normal direction of the grating plane in a plane perpendicular to the periodic direction of the grating. In this case, it is more preferable because the condition that the diffracted light is totally reflected at the interface between the transparent substrate and air can be further relaxed and the grating period of the diffraction grating can be further increased.

The cross-sectional shape of the concavo-convex structure of the diffraction grating 1b is preferably rectangular or trapezoidal, and any of these has the effect of the present invention, but a shape close to a rectangle is preferable because it is easy to manufacture. Various combinations can be used for the ratio of the width between the concave portion and the convex portion in this cross-sectional structure, the repetition period of the concave-convex structure, and the depth of the concave-convex portion. When the surface of a quartz glass substrate having a refractive index of 1.444 is processed to form a diffraction grating having a cross-sectional shape with a ratio of the width of the convex portion to the concave portion of 2: 1 and a grating period of 1500 nm, the depth of the concave and convex portion is set. A structure of 1000 nm or 3400 nm is preferable because high diffraction efficiency can be obtained regardless of the polarization direction of incident light, but applicable depth of the uneven portion and grating period are not limited to this example. Further, a Ta ₂ O ₅ film, which is a high refractive index transparent material, is formed on a quartz glass substrate, and this is processed so that the ratio of the width of the convex portion to the concave portion is 2: 1 and the repetition period of the concave and convex structure is 1500 nm. When a diffraction grating having a cross-sectional shape is formed, a configuration in which the depth of the concavo-convex portion is 800 nm is exemplified. According to this configuration, it is preferable that a high diffraction efficiency can be obtained with a shallow concave-convex portion depth for linearly polarized light in any of the polarization direction parallel to and perpendicular to the periodic direction of the grating. However, the present invention is not limited to this.

  Further, when the cross-sectional shape of the concavo-convex structure is changed to a rectangular cross section and is asymmetric in the plane perpendicular to the extending direction of the concavo-convex structure, the diffraction efficiency of either the + 1st order diffracted light or the −1st order diffracted light is increased. Can do. At this time, it is preferable to increase the diffraction efficiency toward the demultiplexed light exit surface, since the intensity of the demultiplexed light emitted from the demultiplexed light exit surface 1e can be increased. The left-right asymmetric cross-sectional shape is preferably a sawtooth shape or a cross-sectional shape that approximates a desired sawtooth shape to a step shape. The concavo-convex structure having a sawtooth cross-sectional structure can be formed by photolithography using a gray scale mask. A cross-sectional shape approximating a desired sawtooth shape like a step shape can be formed by repeating photolithography processing of 3 to 8 steps, and is preferable because it is easier to manufacture than a sawtooth cross-sectional shape.

  In addition, it is preferable to form a mirror that reflects light having the wavelength of the incident light on the end surface opposite to the demultiplexed light exit surface 1e, because the amount of light emitted to the demultiplexed light exit surface 1e can be increased.

  Hereinafter, Examples 1 and 2 which are embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

[Example 1]
The branching element 1 of Example 1 is formed by using a transparent substrate 1a made of a quartz glass flat substrate, and has a configuration shown in a schematic sectional view in FIG. First, a linear groove having a rectangular cross section is periodically formed on one surface of a transparent substrate 1a made of quartz glass having a diameter of 125 mm, a thickness of 2.0 mm, and a refractive index of 1.444 by photolithography and etching. A diffraction grating 1b is formed. The groove having a rectangular cross section has a width of 500 nm and a depth of 3400 nm, a pitch of 1500 nm parallel to each other, and a ratio of the width of the convex portion to the concave portion is 2: 1. The surface on which the diffraction grating 1b is formed is referred to as a diffraction grating forming surface 1c, and the surface facing this surface is referred to as a transmitted light emitting surface 1d.
Next, the transparent substrate is cut into a 10 mm × 6 mm rectangle by a dicing saw so that the end face is perpendicular to the surface. At this time, the short side of the diffraction element 10 is orthogonal to the periodic direction of the diffraction grating, the end surface of the short side is polished smoothly, and a low reflection coating for the wavelength of the light is applied to obtain a demultiplexed light exit surface 1e. . The branching element 1 of this example is obtained by the above process.

  The linearly polarized incident light 2 obtained by combining the light of the three wavelengths of 1580 nm, 1600 nm, and 1620 nm is vertically incident on the center of the diffraction grating forming surface 1 c of the branching element 10 of the present example obtained in this way. . Here, the polarization direction of the linearly polarized light is a direction parallel or orthogonal to the periodic direction of the diffraction grating 1b. The incident light travels straight through the diffraction grating and is emitted as transmitted light from the transmitted light exit surface, and a part of the incident light is 47 degrees by the diffraction grating according to wavelengths of 1580 nm, 1600 nm, and 1620 nm, respectively. Diffracted at 48 degrees and 48 degrees. The diffracted light 4 of each wavelength is incident on the opposite transmitted light exit surface 1d at an incident angle that is the same as the internal diffraction angle of each wavelength. These incident angles are all the total reflection angles of quartz glass. Since it is larger than 44 degrees, it is totally reflected. The light totally reflected by the transmitted light exit surface 1d then enters the diffraction grating forming surface at an incident angle equal to the internal diffraction angle, and is totally reflected in the same manner. The diffracted light thus demultiplexed is sequentially totally reflected by the transmitted light emitting surface and the diffraction grating forming surface, and is emitted as demultiplexed light from the demultiplexed light emitting surface 1e.

  When the polarization direction of the incident light beam is parallel and orthogonal to the periodic direction of the diffraction grating, the intensity and emission angle of the demultiplexed light emitted from the left and right side surfaces of the transparent substrate and the transmitted light for each wavelength. The strength measurement results are summarized in Tables 1 and 2. Here, the intensity of the demultiplexed light refers to the intensity ratio of the demultiplexed light to the incident light, and the emission angle of the demultiplexed light refers to an angle formed by the emission direction of the demultiplexed light and the incident direction of the incident light.

  As can be seen from Tables 1 and 2, by using the demultiplexing element 1 of the present example, the incident light is transmitted and a part thereof is demultiplexed and taken out from the demultiplexed light emitting surface 1e which is one of the end faces of the flat substrate. be able to. Further, the demultiplexed light can be separated and extracted for each wavelength.

[Example 2]
As shown in the schematic cross-sectional view of FIG. 4, the branching element of this example was formed by sputtering on one surface of a transparent substrate 1a made of a quartz glass flat substrate having a thickness of 2.0 mm. A Ta ₂ O ₅ film having a refractive index of 2.107 and a thickness of 800 nm is formed into a diffraction grating 1b in which grating-like grooves are periodically arranged by photolithography and dry etching. That is, the diffraction grating 1b of this example has a structure in which convex portions having a refractive index of 2.107, a width of 1000 nm, and a height of 800 nm are arranged with a period of 1500 nm.
Next, the transparent substrate is cut into a 6 mm × 6 mm square by a dicing saw so that the end surface is perpendicular to the parallel substrate surface. At this time, one side of the diffractive element 1 is parallel to the longitudinal direction of the diffraction grating, the end surface of this side is polished smoothly, and a low reflection coating for the wavelength of the light is applied to form a demultiplexed light exit surface 1e. . The branching element 1 of this example is obtained by the above process.

  When linearly polarized incident light 2 obtained by combining the three wavelengths of light is vertically incident, the incident light 2 is transmitted straight as transmitted light 3 as in Example 1, and a part thereof is caused by the diffraction grating. Diffraction is performed at internal diffraction angles of 47 degrees, 48 degrees, and 48 degrees, respectively, according to wavelengths of 1580 nm, 1600 nm, and 1620 nm. Although the diffracted light is incident at the same angle with respect to the opposite transmitted light exit surface, both are totally reflected because the total reflection angle of the quartz glass is greater than 44 degrees, and is emitted from the demultiplexed light exit surface 1e as demultiplexed light.

  Tables 3 and 4 summarize the measurement results of the intensity and emission angle of the demultiplexed light and the intensity of the transmitted light when the polarization direction of the incident light beam is parallel and orthogonal to the periodic direction of the diffraction grating. Here, the intensity of the demultiplexed light refers to the intensity ratio of the demultiplexed light to the incident light, and the emission angle of the demultiplexed light refers to an angle formed by the emission direction of the demultiplexed light and the incident direction of the incident light.

  As can be seen from Tables 3 and 4, by using the demultiplexing element 1 of this example, the incident light is transmitted and a part thereof is demultiplexed and taken out from the demultiplexed light emitting surface 1e which is one of the end faces of the flat substrate. be able to. Further, the demultiplexed light can be separated and extracted for each wavelength.

  Since the demultiplexing element of the present invention is small and can emit demultiplexed light from a position away from the incident position of incident light and the output position of transmitted light, light detection that measures characteristics such as intensity and wavelength of demultiplexed light There are few restrictions on the container and its arrangement. Therefore, it is possible to realize a measurement system that monitors while transmitting the characteristics of incident light with a compact configuration.

The schematic block diagram of the measuring apparatus which demultiplexes incident light and measures the characteristic of incident light using the branching element of this invention. The path diagram of the light demultiplexed by the demultiplexing element of the present invention. 1 is a schematic cross-sectional view of a branching element of the present invention formed by processing a transparent substrate surface. 1 is a schematic cross-sectional view of a branching element of the present invention formed by processing a transparent material layer. The schematic block diagram of the measuring apparatus which demultiplexes incident light and measures the characteristic of incident light using the branching element using the diffraction grating of a prior art.

Explanation of symbols

1: Demultiplexing element 1a: Transparent flat substrate 1b: Diffraction grating 1c: Diffraction grating forming surface 1d: Transmitted light exit surface 1e: Demultiplexed light exit surface 2: Incident light 3: Transmitted light 4: Diffracted light 5: Transmitted light exit Diffracted light totally reflected by the surface 6: Photo detector 7: Incident angle of incident light to diffraction grating surface 8: Internal diffraction angle 9: Incident angle of diffracted light to transmitted light exit surface 10: Minute of diffracted light Incident angle to wave light exit surface 11: Exit angle of split light from split light exit surface 12: Extraction angle of demultiplexed light with respect to direction of incident light 13: Photo detector 23: Low reflection coating

Claims (11)

A demultiplexing device comprising a transparent substrate having a diffraction grating forming surface, a transmitted light emitting surface, and a demultiplexed light emitting surface,
The diffraction grating forming surface includes a diffraction grating in which a concavo-convex structure extending in one direction is periodically formed,
The demultiplexing element causes the incident light incident on the diffraction grating forming surface to pass straight through and be emitted from the transmitted light exit surface, diffracts a part of the incident light, and causes the diffracted diffracted light to pass through the transparent substrate. The demultiplexing element according to claim 1, wherein the demultiplexing element is totally reflected by the transmitted light exit surface, guided to the demultiplexed light exit surface, and emitted as demultiplexed light from the demultiplexed light exit surface.   The branching element according to claim 1, wherein the diffracted light is first-order diffracted light.   The transparent substrate is a flat substrate, and one of the opposing substrate surfaces is the diffraction grating forming surface, the other is the transmitted light emitting surface, and one of the end surfaces is flat and the concavo-convex structure of the diffraction grating The demultiplexing element according to claim 1, wherein the demultiplexing element is disposed substantially perpendicular to the periodic direction of the first and second demultiplexed light and serves as the demultiplexed light output surface.   4. The branching element according to claim 1, wherein the uneven structure is formed by processing a surface of the transparent substrate.   4. The branching element according to claim 1, wherein the concavo-convex structure is formed by forming a transparent material layer on a diffraction grating forming surface of the transparent substrate and processing the layer.   6. The branching element according to claim 5, wherein the transparent material is mainly composed of one kind selected from silicon nitride, silicon oxide, titanium oxide, tantalum oxide, niobium oxide, and zinc oxide.   The branching element according to any one of claims 1 to 6, wherein the concavo-convex structure has a cross-sectional shape of a rectangular convex portion and a rectangular concave portion.   The branching element according to any one of claims 1 to 6, wherein the uneven structure has a sawtooth cross-sectional shape.   The branching element according to any one of claims 1 to 6, wherein the lattice-shaped concavo-convex structure has a cross-sectional shape that approximates a desired sawtooth shape in a step shape.   The diffracted light diffracted by the diffraction grating is totally reflected once by the transmitted light exit surface, and then is not further reflected by the diffraction grating forming surface and the transmitted light exit surface from the demultiplexed light exit surface. The branching element according to any one of claims 1 to 9, which is emitted. In a demultiplexing method in which incident light is incident on a demultiplexing element to be transmitted in a straight line and a part of the incident light is changed as a demultiplexed light by changing the optical path.
The branching element is
It is formed using a flat substrate made of a transparent material,
One of the opposing substrate surfaces of the flat substrate is a diffraction grating forming surface provided with a diffraction grating in which an uneven structure with one surface extending in one direction is periodically formed, and the other surface is a transmitted light emitting surface. A demultiplexing element in which one of the end faces is flat and is disposed substantially perpendicular to the periodic direction of the concavo-convex structure of the diffraction grating and serves as the demultiplexed light exit surface,
The incident light incident on the diffraction grating forming surface of the demultiplexing element is diffracted at a diffraction angle larger than the total reflection angle of the transparent substrate to guide the inside of the transparent substrate to the demultiplexed light exit surface, and the demultiplexed light A demultiplexing method characterized by emitting light as demultiplexed light from an emission surface.

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