JP5050594B2 - Spectrometer - Google Patents

Description

  The present invention relates to a diffraction grating and an optical device that use a plurality of wavelengths, and more specifically, is used for wavelength division multiplexing optical communication, spectroscopic measurement, and the like. The present invention relates to a reflective diffraction grating to be changed and a spectroscopic device using the same.

  A diffractive optical element represented by a diffraction grating is widely used for analyzing an optical spectrum in a spectroscopic analysis instrument. In spectroscopic analysis, high light utilization efficiency is required over a wide wavelength range. A reflection-type blazed diffraction grating consisting of fine grooves with a sawtooth cross-section, straight lines in the depth direction, and equidistant spacing provides a relatively high diffraction efficiency for a specific diffraction order in a specific wavelength range, and a wavelength Since the wavelength angle dispersion, which is the change rate of the diffraction angle with respect to, is large, it is widely used in spectroscopic analyzers.

  An example of a sectional view of a conventional reflective diffraction grating is shown in FIG. Using a mold in which the cross section is sawtooth, straight in the depth direction and formed with a blazed grating consisting of fine grooves at equal intervals, the blazed grating shape is transferred to the resin layer applied to the surface of the substrate 41 and replicated A grating 42 is prepared, and a metal reflection film 43 is formed on the surface thereof to form a reflective blazed diffraction grating 200.

Here, when the groove inclination θ _B is called a blaze angle and the number of grooves per 1 mm is N, a high + 1st order diffraction efficiency is obtained in the vicinity of the blaze wavelength λ _B = 2 × sin (θ _B ) / N. . The incident angle i and the + 1st-order diffraction angle θ at this time are almost equal to the blaze angle θ _B and are called a Littrow arrangement.

However, in the conventional reflective blazed diffraction grating, + 1st order diffraction is high in the wavelength region near the blaze wavelength λ _B for S-polarized light (TE wave) in which the groove direction of the diffraction grating and the electric field vibration direction of incident light are parallel. Although efficiency can be obtained, there is a problem that the wavelength dependence of the + 1st order diffraction efficiency is large and the wavelength loss characteristic is not stable for P-polarized light (TM wave) in which the groove direction of the diffraction grating and the electric field oscillation direction of incident light are perpendicular. there were. As a result, a reflective diffraction grating capable of realizing a high + 1st order diffraction efficiency with little polarization dependent loss (PDL) has not been obtained.

N = 1000 (that is, the lattice spacing 1 / N = 1 μm), the surface of the replica grating 42 having a blaze angle θ _B = 50 °, a refractive index n = 0.188 as an optical reflecting surface, and an attenuation coefficient k = 11.1. FIG. 10 shows the calculation result of the + 1st order diffraction efficiency in the wavelength range of 1460 to 1620 nm for the reflective blazed diffraction grating 200 on which the gold (Au) reflective film 43 represented by 218 is formed. The diffraction efficiency in the region where the grating interval is equal to or smaller than the wavelength needs to strictly solve the Maxwell equation in consideration of the electromagnetic field vector component which is the polarization direction. For example, the exact coupled wave theory (RCWA) described in Non-Patent Document 1 ) To calculate.

  The S-polarized light has a high + 1st order diffraction efficiency over a wide wavelength range, but the P-polarized light has a low diffraction efficiency of 20% or less.

  Also, it is difficult to accurately manufacture a mold having a blazed grating as shown in FIG. 9, and the shape of the convex and concave portions of the sawtooth cross section is likely to occur, which causes a decrease in + 1st order diffraction efficiency and generation of stray light. Cheap.

  Further, the replica grating 42 and the metal reflective film 43 made of resin are likely to cause a change in characteristics over time at high temperatures, high temperatures and high humidity, and have a problem in reliability. Therefore, they can be used only in a limited environment.

  In addition, when a metal reflection film is formed on the surface of a replica grating produced by transferring a blazed grating shape, the film thickness should be 0.1 μm or more in order to ensure a high reflectance of the metal reflection film in the operating wavelength range. It is preferable to form a metal reflective film. However, since it is difficult to form a uniform film on a blazed inclined surface, the film thickness distribution of the metal reflective film is likely to occur, and the precisely formed replica grating deviates from the optimum shape, resulting in deterioration of diffraction efficiency performance. There was a fear.

MGMoharam, DAPommet, EBGrann, and TKGayload, “Stable implementation of the rigorous coupled-wave analysis for surface relief gratings: enhanced transmittance matrix approach” Journal of the Optical Society of America A, vol.12, no.5, PP.1077-1086 (May 1995)

  The present invention has been made to solve such problems, and it is also an object of the present invention to provide a reflective diffraction grating that is excellent in mass productivity and stable in optical characteristics by a simple process. It is another object of the present invention to provide a reflection type diffraction grating that realizes high diffraction efficiency and a large wavelength angle separation effect in a wide wavelength range and is excellent in reliability.

  In the present invention, since the cross-section formed on the optical reflecting surface is uneven, the upper surface of the convex portion is substantially flat, and the convex portion is made of a light-transmitting material that is symmetrical, it is widely used as a planar micromachining technique. A stable lattice shape can be produced by using typical photolithography and isotropic dry etching, and stable optical characteristics can be easily obtained. Even when a replica grating is transferred using a mold whose surface is processed with a grating shape, a precise mold can be processed, and stable optical characteristics are easily obtained.

  Further, the optical reflecting surface is composed of a dielectric multilayer film in which the optical reflecting surface is alternately laminated with a transparent dielectric film having a relatively large refractive index and a transparent dielectric film having a relatively small refractive index. A reflective diffraction grating is provided. The reflection type diffraction grating having such a configuration can be used as a reflection type diffraction grating having high + 1st order diffraction efficiency and a large wavelength angle separation effect in a wide wavelength range as compared with a conventional reflection type blazed diffraction grating.

Further, the grid projection or translucent material of the optical reflecting surface and the front Symbol grating _{protrusions, TiO 2, SiO 2, Ta} 2 O 5, Nb 2 O 5, Al 2 O 3, Si 3 N 4 There is provided the above reflection type diffraction grating, which is at least one selected from the group consisting of SiON and Si.

  By adopting such a configuration, a reflective diffraction grating having high reliability and high stability under high temperature, high temperature and high humidity can be obtained without causing a change in optical characteristics over time with environmental changes.

In addition, in a method of using a reflection type diffraction grating formed on a substrate having an optical reflection surface on its surface and having a grating made of a translucent material having a concavo-convex cross section and a substantially flat top surface of the convex portion, The ratio P / λ of the grating interval P of the reflection type diffraction grating to the wavelength λ of light is 0.55 or more and 1.45 or less, and the reflection type diffraction grating is formed on the light reflection surface of the reflection type diffraction grating. In contrast, it is used as a spectroscopic element in an arrangement where light is incident obliquely, the incident angle to the reflective diffraction grating is i, the average refractive index of the translucent material of the grating convex portion is n, When T a is, to provide a (formula 1), or the use of reflection type diffraction grating you and satisfies the equation (5).

0.80 ≦ n × T / {λ × cos (i ′)} ≦ 1.25 (Formula 1)
However, the angle i ′ satisfies sin (i) = n × sin (i ′).
0.97 ≦ n × T / {λ × cos (i ′)} ≦ 1.21 (Formula 5)

  By adopting such a configuration, a reflective diffraction grating having high + 1st order diffraction efficiency in a wider wavelength range can be obtained.

  In addition, an optical reflecting surface made of a dielectric multilayer film and a light-transmitting material layer to be a convex portion of the lattice are formed on the substrate, and the light-transmitting material layer has an uneven cross section and substantially has an upper surface of the convex portion. The present invention provides a method for manufacturing a reflection type diffraction grating, which is processed so as to be a flat grating.

  By adopting such a manufacturing method, the optical reflecting surface and the grating convex portion can be formed with high accuracy by the film forming process and the microfabrication process, so that stable optical characteristics can be obtained.

  Furthermore, the optical reflection surface made of a dielectric multilayer film and the grating convex portion made of a light-transmitting material are produced by the same film forming process, thereby simplifying the process of forming a reflective diffraction grating and improving mass productivity. Stable optical characteristics can be obtained.

In addition, in a spectroscopic device including a reflective diffraction grating having a grating made of a light-transmitting material having a concavo-convex cross section and a substantially flat top surface of a convex portion, formed on a substrate having an optical reflective surface on the surface. The ratio P / λ of the grating interval P of the reflective diffraction grating to the wavelength λ of incident light is 0.55 or more and 1.45 or less, and the reflective diffraction grating is a light reflecting surface of the reflective diffraction grating. The optical reflection surface is a transparent dielectric film having a relatively high refractive index and a transparent dielectric film having a relatively low refractive index. It is composed of dielectric multilayer films laminated alternately, and the translucent material of the lattice convex portions is TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , Si ₃ N _4. And at least one selected from the group consisting of Si and The incident angle to the reflection type diffraction grating i, an average refractive index of the translucent material of the grid convex portion n, when the height is T, providing a spectroscopic apparatus characterized by satisfying the equation (5) To do.
0.97 ≦ n × T / {λ × cos (i ′)} ≦ 1.21 (Formula 5)
However, the angle i ′ satisfies sin (i) = n × sin (i ′).

  By using such a spectroscopic device, a spectroscopic device having a wavelength angle separation effect corresponding to the wavelength resolution and high light utilization efficiency can be obtained.

  By adopting the configuration of the present invention, the optical reflecting surface can be stably formed with a uniform film thickness on the flat surface of the substrate, and there is no restriction on the film thickness, and a film that can secure a sufficiently high reflectance in the operating wavelength range. A film can be formed with a thickness.

  In addition, it is possible to provide a reflective diffraction grating having excellent mass productivity with a simple process, realizing high diffraction efficiency and a large wavelength angle separation effect in a wide wavelength range, and having excellent reliability.

  Further, by optimizing the configuration of the dielectric multilayer film and the grating convex portion on the optical reflecting surface, it is possible to provide a reflective diffraction grating with less polarization dependent loss (PDL).

  In addition, the metal reflective film has poor adhesion to the replica grating and is easy to peel off, and the material itself is soft, so the surface is prone to scratches, and the optical performance deteriorates when dirt is attached to the metal reflective film surface. However, in the embodiment in which the dielectric multilayer film is used for the optical reflecting surface, such a problem can be solved.

  A cross-sectional view of an example of the configuration of the reflective diffraction grating of the present invention is shown in FIG. 1, and a perspective view is shown in FIG.

  An optical reflecting surface 12 is formed on the substrate 11, and a light transmissive material layer is further formed thereon. Next, a convex portion having a cross section of the translucent material layer and an upper surface of the convex portion being substantially flat and having line symmetry with respect to a straight line perpendicular to the substrate is formed into a lattice 13 having a lattice interval P. The reflection type diffraction grating 100 is processed. A ratio D / P of the width D of the convex portion to the lattice interval P is referred to as a duty ratio.

  Here, the substrate 11 on which the optical reflecting surface 12 is formed may be a transparent material such as quartz glass, white plate glass, silicone, or polycarbonate, or an opaque material such as ceramics or metal. The lattice spacing P of the lattice 13 formed on the optical reflecting surface 12 changes due to the thermal expansion of the substrate according to the environmental temperature change. Therefore, it is preferable to use a low expansion substrate such as quartz glass or crystallized glass having a low coefficient of thermal expansion in order to suppress fluctuations in the lattice spacing P due to temperature changes.

In addition, the optical reflecting surface 12 alternately includes a transparent dielectric film having a relatively large refractive index and a transparent dielectric film having a relatively small refractive index in order to obtain a stable high reflectance in the wavelength range of use. It is preferable to use a laminated dielectric multilayer film. Specifically, TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , Si ₃ N ₄ , SiON, Si, etc. are used as the high refractive index transparent dielectric film, and the low refractive index transparent dielectric is used. For the film, SiO ₂ , SiON, or the like is used. Here, SiON indicates a film having a mixed composition of SiO ₂ and Si ₃ N ₄ , and the refractive index of the SiON film can be adjusted by adjusting the ratio of O and N. The film thickness configuration of each dielectric film necessary for obtaining a high reflectivity with respect to the wavelength range of incident light having a predetermined incident angle i and wavelength λ can be realized by using a known multilayer film design technique, and thus description thereof is omitted. To do.

  Although the reliability is inferior in terms of change in reflectance with time and mechanical strength as compared with the dielectric multilayer film, a metal reflective film such as Au, Ag, Al or the like is formed on the substrate as the optical reflecting surface 12 and used. Also good. In this case, a metal film such as Cr or Ni is preferably formed in advance on the substrate in order to improve the adhesion between the substrate 11 and the metal reflective film.

  The grating 13 on the optical reflection surface 12 is obtained by processing a light-transmitting material layer formed on the optical reflection surface.

In order to achieve high reliability, a light-transmitting material layer that is a lattice material is mainly composed of SiO ₂ , TiO ₂ , Ta ₂ O ₅ , Si ₃ N ₄ , SiON, Si, etc. It is preferable to use a mixed film or a multilayer film. In order to process the translucent material layer into the lattice 13 having an uneven cross section by photolithography and dry etching, it is preferable to use a translucent material having excellent etching characteristics.

  Although the reliability is inferior to that of the lattice 13 made of an inorganic material, a mold having a concave and convex cross section, a straight lattice in the depth direction, and a linear lattice made of fine grooves at equal intervals is used on the surface. Then, the resin layer coated on the optical reflection surface may be released after curing by heating or ultraviolet irradiation to form the convex grating 13 made of resin.

  Using the same material or a part thereof as the optical reflective surface 12 made of the transparent dielectric multilayer film described above, a multilayer film for the optical reflective surface and a translucent material layer for forming the lattice are formed on the substrate by the same film forming apparatus. By continuously forming the film, the reflection type diffraction grating can be efficiently manufactured without contamination of the interface between the optical reflection surface 12 and the grating 13. As a result, stabilization and reliability of optical characteristics are improved.

  For example, using a vacuum deposition method, a sputtering method, a chemical vapor deposition (CVD) method, or the like, a dielectric multilayer film on the optical reflecting surface and a light-transmitting material layer for forming a lattice are continuously formed. Further, after patterning a photosensitive resist coated on a light-transmitting material layer for forming a lattice formed on the optical reflecting surface by photolithography using a photomask corresponding to the lattice pattern, reactive ions are formed. The translucent material layer is processed into a lattice shape with an uneven cross section by etching.

  The light of wavelength λ incident at an angle i formed with the normal direction to the optical reflecting surface 12 of the grating 13 given by the grating interval P is m-order diffracted light in the direction of the diffraction angle θ defined by (Equation 2). (M = ± 1, ± 2,...) Is generated.

sin (θ) + sin (i) = m × λ / P (Formula 2)
From (Equation 2), when the light is incident perpendicularly to the optical reflection surface of the reflective diffraction grating 100 (i = 0 °), there is no diffracted light of the reflective diffraction grating having a grating interval P smaller than the wavelength λ. However, when light is incident from an oblique direction, that is, when 0 ° <i <90 °, diffracted light having an order m can exist even when the grating interval P is smaller than the wavelength λ. For this reason, even if the cross section of a grating convex part has a symmetrical shape, it turns out that asymmetrical diffraction characteristics are shown.

  By utilizing the effect of the oblique incidence, a sufficiently high diffraction efficiency and a large wavelength angle separation effect can be obtained even with a diffraction grating having a symmetrical cross-sectional shape that is easy to manufacture. In addition, it is preferable to use a reflection type diffraction grating that maximizes the + 1st order diffraction efficiency because the height of the grating convex portion can be reduced, and manufacturing becomes easy.

  By adopting such a configuration of the reflective diffraction grating 100, it is possible to realize a reflective diffraction grating that is excellent in mass productivity while having a simple process, has high diffraction efficiency, and has a large wavelength angle separation effect. Since it has a large wavelength angle separation effect, it can be used as a diffraction grating for spectroscopy.

  Here, the ratio P / λ of the grating interval P of the reflective diffraction grating to the wavelength λ of the incident light is set in the range of 0.55 or more and 1.45 or less, and the incident angle i with respect to the optical reflection surface is appropriately selected to be +1. Since only the second order diffracted light is generated, high + 1st order diffraction efficiency can be realized.

  When the ratio P / λ is 0.5 or less, since there is no diffraction angle at which diffracted light is generated from (Equation 2), the diffraction phenomenon does not occur and only regular reflected light is generated. If the ratio P / λ is larger than 0.5, diffracted light is generated, but if it is smaller than 0.55, the wavelength range in which high diffraction efficiency can be obtained may be limited. When the ratio P / λ is 1.45 to 1.50, the wavelength range in which only the + 1st order diffracted light is generated may be limited. In particular, when the ratio P / λ is 1.50 or more, other than the + 1st order diffracted light. Diffracted light is generated, causing a decrease in the + 1st order diffracted light rate and causing stray light.

  In addition, incident obliquely with respect to the optical reflecting surface means that the incident angle i in the grating cross section shown in FIG. 1 is 15 to 80 ° with respect to the normal line of the optical reflecting surface 12 of the reflective diffraction grating 100. In particular, in the incident angle range of 25 to 65 °, the effect of the present invention can be sufficiently achieved.

  If the cross section of the grating 13 of the reflective diffraction grating 100 is concave and convex and the top surface of the convex portion is substantially flat, the effect of the present invention can be obtained even if the cross sectional shape is a trapezoidal shape in addition to the rectangular shape, but the convex portion is perpendicular to the substrate. Those having a line symmetry with respect to a straight line are more preferable in terms of production.

  FIG. 3 shows a sectional view of the reflective diffraction grating 110 in which the sectional shape of the grating convex portion is trapezoidal. By adjusting the angle α (hereinafter referred to as taper angle) of the wall surface of the grating convex portion 23 with respect to the normal line of the optical reflecting surface 12, the wavelength dependency and polarization dependency of the + 1st order diffraction efficiency can be adjusted. Here, the taper angle α is preferably 10 degrees or less. The width D of the convex portion in this case can be defined as the width of the convex portion at a point where the height is half of the height of the convex portion, and the pitch P of the diffraction grating is equal to half the height of each convex portion. It can be defined as the interval between each convex part of the point.

  By adopting such a configuration of the reflective diffraction grating 100, it is possible to realize a reflective diffraction grating that is excellent in mass productivity while having a simple process, has high diffraction efficiency, and has a large wavelength angle separation effect. Since it has a large wavelength angle separation effect, it is preferably used as a diffraction grating for spectroscopy.

  Hereinafter, the present invention will be described based on specific design results with reference to FIG. 1 showing a sectional view of the reflective diffraction grating 100 assuming that the shape of the convex portion is rectangular.

[Example 1]
In the reflective diffraction grating 100 of FIG. 1, Ta ₂ O ₅ having a refractive index n _H = 2.11 and SiO ₂ having a refractive index n _L = 1.44 are alternately stacked on the surface of the quartz glass substrate 11, and a wavelength 1525 is obtained. The optical reflection surface 12 is formed of a dielectric multilayer film having a reflectance of 99% or more with respect to incident light having a wavelength of ˜1565 nm and an incident angle i = 50 °. Note that n _H represents the refractive index of a transparent dielectric film having a relatively large refractive index, and n _L represents the refractive index of a transparent dielectric film having a relatively small refractive index.

In order to obtain a high reflectance with a small number of layers and a total film thickness, it is desirable that the Ta ₂ O ₅ film thickness d _H and the SiO ₂ film thickness d _{L be set} as follows.

_{n H × d H × cos (} i H) = n L × d L × cos (i L) = λ / 4 ( Equation 3)
However, i _H and i _L are the refractive angle in the film which satisfies the Snell law (Equation 4).

_{n H × sin (i H)} = n L × sin (i L) = sin (i) ( Equation 4)
Specifically, when i = 50 °, i _H = 21.3 °, i _L = 32.1 °, and when λ = 1545 nm, d _H = 195 nm and d _L = 317 nm. When 26 layers are alternately laminated in the order of Ta ₂ O ₅ and SiO ₂ from the quartz glass substrate side, the optical reflecting surface 12 having a reflectance of 99% or more in the wavelength range of 1460 to 1630 nm is obtained.

Further, Ta ₂ O ₅ , which is a high refractive index material, is formed on the SiO ₂ film, which is the surface layer of the optical reflecting surface 12, so as to have a film thickness T, and the convex section has a rectangular shape with a height T. Then, it is processed into a lattice 13.

  For a reflective diffraction grating with P = 1 μm, D = 0.5 μm (duty ratio D / P = 0.5), T = 780 nm, and a rectangular cross-section, the + 1st order diffracted light rate at an incident angle i = 50 ° The wavelength dependence calculation results are shown in FIG.

  In a wide wavelength range of 1495 to 1585 nm, high + 1st order diffraction efficiency of 95% or more is realized with respect to incident light of P-polarized light and S-polarized light. Further, the polarization dependent loss (PDL) defined by the difference of the + 1st order diffracted light rate with respect to the incident light of P-polarized light and S-polarized light is 3% or less.

The calculated results are shown in FIG. 5, where the horizontal axis is n _H × T / {λ × cos (i ′)}, and the vertical axis is the average + 1st-order diffraction efficiency in the C-band wavelength band 1525 to 1565 nm in wavelength division multiplexing optical communication. . When n _H × T / {λ × cos (i ′)} is in the range of 0.80 to 1.25 shown in (Equation 1), at least the first-order diffraction efficiency average value of P-polarized light is 90% or more. In the range from 97 to 1.21, the + 1st-order diffraction efficiency of S-polarized light and P-polarized light is 90% or more. That is, a reflective diffraction grating with high efficiency and low PDL is realized by setting the film thickness T of Ta ₂ O ₅ of the grating convex to 660 to 820 nm.

[Example 2]
On the SiO ₂ film, which is the surface layer of the optical reflective surface 12 made of the same dielectric multilayer film as in Example 1, a low refractive index material, SiO ₂ , is formed to a film thickness T, and the cross-sectional shape of the convex portion Is processed into a lattice 13 so as to be rectangular. Here, in order to obtain a reflective diffraction grating having high + 1st order diffraction efficiency, the film thickness T is set to T = 1200 nm so that n _L × T / {λ × cos (i ′)} is approximately 1. . FIG. 6 shows the wavelength dependence calculation result of the + 1st order diffracted light rate in this case.

  In a wide wavelength range from 1495 to 1595 nm, a high + 1st order diffraction efficiency of 95% or more is realized with respect to S-polarized incident light. On the other hand, for P-polarized light, the + 1st-order diffracted light rate has a low efficiency of 35% or less, and the PDL has a large value. That is, the wavelength dependency and polarization dependency of the + 1st order diffracted light rate change depending on the difference between the refractive index of the surface layer material of the optical reflecting surface 12 and the refractive index of the convex material of the diffraction grating.

The lattice convex portion 13 may have a structure in which materials having a refractive index other than Ta ₂ O ₅ or SiO ₂ or film materials having different refractive indexes are laminated. By the configuration of the optical reflecting surface 12 and the grating 13, high + 1st order diffraction efficiency can be obtained in a wide wavelength range. Also, the PDL can be adjusted.

[Example 3]
FIG. 7 shows a cross-sectional view of a reflective diffraction grating 120 in which the grating convex portion is formed of a two-layer film having a different refractive index.

On the SiO ₂ film, which is the surface layer of the optical reflective surface 12 made of the same dielectric multilayer film as in Example 1, Ta ₂ O ₅ 33a, which is a high refractive index material, has a film thickness of 530 nm, and further, a low refractive index material. SiO ₂ 33b is formed to a film thickness of 760 nm, and the two-layer portion of the surface of Ta ₂ O ₅ and SiO ₂ is processed into a lattice 33 so that the cross-sectional shape of the convex portion is rectangular.

  FIG. 8 shows the wavelength dependence calculation result of the + 1st order diffracted light rate in this case. In the wide wavelength range of 1495 to 1625 nm, the + 1st order diffraction efficiency is 5% or less lower than the incident light of P-polarized light, and in the wide wavelength range of 1470 to 1570 nm, it is higher than 95% higher than the incident light of S-polarized light. + 1st order diffraction efficiency. That is, a reflection type diffraction grating having a large polarization dependency is obtained.

  Further, by setting the duty ratio D / P, which is the ratio of the convex portion in one period of the grating, to a value other than 0.5, the wavelength dependency and polarization dependency of the + 1st order diffraction efficiency can be adjusted. The duty ratio D / P is preferably in the range of 0.45 to 0.55.

[Example 4]
FIG. 11 shows a sectional view of a reflective diffraction grating 300 in which the optical reflection film is made of a metal film.

On the surface of the optical reflecting surface 42 consisting of an Au film having a refractive index 0.188, the _Ta 2 _O 5 43 is a high refractive index material with a thickness of 604nm deposition, so that the cross-sectional shape of the convex portion is a rectangular Ta The surface of ₂ O ₅ is processed into a lattice 43. The reflectance becomes 99% or more by forming the Au film to a thickness of 0.1 μm or more. FIG. 12 shows the wavelength dependence calculation result of the + 1st order diffracted light rate in this case.

  Since the grating pattern on the optical reflection surface in the diffraction grating of the present invention can be produced using a photomask or the like, the grating pattern is not limited to a linear shape, and for example, the grating pattern can be processed into a curved shape. By adopting this curved shape, it is possible to add a lens function so that the diffracted light is condensed on the photodetector.

  Various optical devices can be constructed using the reflection type diffraction grating of the present invention. This optical apparatus may be any optical apparatus as long as it uses characteristics such as spectral diffraction of the reflective diffraction grating of the present invention.

  As the spectroscopic device of the present invention, for example, there is a multiplexer / demultiplexer for wavelength multiplexing optical communication. When signal light having different wavelengths from 1520 nm to 1620 nm propagates through a single optical fiber, it is necessary to demultiplex into each wavelength channel and detect the signal light or switch to another optical fiber for propagation. The light emitted from the optical fiber is diffracted and propagated in different directions according to the wavelength by the reflective diffraction grating of the present invention, and is incident on a light receiving element composed of a plurality of light detection units or a plurality of optical fibers. Channel signal detection or optical path switching transmission is possible.

  The reflective diffraction grating of the present invention is used for diffraction gratings using a plurality of wavelengths and optical devices, particularly spectroscopic devices. In particular, in the case of a diffraction grating having a small PDL, in a wavelength division multiplexing optical communication, etc., a demultiplexer that splits the light for each wavelength channel by splitting the incident light composed of a plurality of wavelength channels by changing the emission direction by reflection diffraction. In addition, it can be used in a multiplexer in which light of each wavelength channel having different incident angles is aligned at the same angle by reflection diffraction. In the case of a diffraction grating with a large PDL, the laser medium is placed in a resonator composed of a diffraction grating and an output mirror, and the wavelength light returning to the resonance optical path is defined by setting the incident angle of the diffraction grating, thereby oscillating. A tunable laser can be constructed.

Sectional drawing which shows an example of a structure of the reflection type diffraction grating of this invention The perspective view which shows an example of a structure of the reflection type diffraction grating of this invention Sectional drawing which shows an example of the other structure of the reflection type diffraction grating of this invention The graph which shows the wavelength dependence calculation result of the + 1st order diffracted light rate in Example 1 of the reflection type diffraction grating of this invention The graph which shows the calculation result of the relationship between the grating | lattice convex part film thickness and + 1st order diffracted light rate in Example 1 of the reflection type diffraction grating of this invention The graph which shows the wavelength dependence calculation result of the + 1st order diffracted light rate in Example 2 of the reflection type diffraction grating of this invention Sectional drawing which shows an example of the other structure of the reflection type diffraction grating of this invention The graph which shows the wavelength dependence calculation result of the + 1st order diffracted light rate in Example 3 of the reflective diffraction grating of this invention Sectional drawing which shows an example of a structure of the conventional reflection type diffraction grating The graph which shows the wavelength dependence calculation result of the + 1st order diffracted light rate in an example of the conventional reflection type diffraction grating Sectional drawing which shows an example of the other structure of the reflection type diffraction grating of this invention The graph which shows the wavelength dependence calculation result of the + 1st order diffracted light rate in Example 4 of the reflection type diffraction grating of this invention

Explanation of symbols

11, 41: Substrate 12: Optical reflecting surface 13, 23, 33: Lattice convex portion 33a: Ta ₂ O ₅
33b: SiO ₂
42: Replica grating 43: Metal reflective film 100, 110, 120, 300: Reflective diffraction grating 200: Reflective blaze diffraction grating

Claims (1)

In a spectroscopic device including a reflective diffraction grating formed on a substrate having an optical reflective surface on its surface and having a grating made of a light-transmitting material having a concavo-convex cross section and a substantially flat upper surface of the convex portion,
The ratio P / λ of the grating interval P of the reflective diffraction grating to the wavelength λ of incident light is 0.55 or more and 1.45 or less,
The reflective diffraction grating is used as a spectroscopic element in an arrangement in which light is incident obliquely with respect to the light reflection surface of the reflective diffraction grating,
The optical reflecting surface is composed of a dielectric multilayer film in which transparent dielectric films having a relatively large refractive index and transparent dielectric films having a relatively small refractive index are alternately laminated,
The light-transmitting material of the lattice protrusion is at least one selected from the group consisting of TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , Si ₃ N ₄ and Si,
A spectroscopic device satisfying (Equation 5), where i is an incident angle to the reflective diffraction grating, n is an average refractive index of the translucent material of the grating convex portion, and T is a height.
0.97 ≦ n × T / {λ × cos (i ′)} ≦ 1.21 (Formula 5)
However, the angle i ′ satisfies sin (i) = n × sin (i ′).

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