JP2005037872A - Optical element, and optical circuit and optical demultiplexer having same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element having a high flexibility in a periodical structure and to provide an optical demultiplexer which has high wavelength resolution and little dependence on polarization and which can be made small in size. <P>SOLUTION: A planar optical circuit type optical demultiplexer having a diffraction grating 30 and concave mirrors 33, 35 fabricated on one substrate 38 is provided. The grating 30 is formed by periodically arranging a solid ridge part and a space of a groove part, and is embedded in a solid material to have an optical waveguide structure. The planar optical circuit can be easily manufactured usually by lithography, etching and film deposition techniques. The optical demultiplexer to be used for low-density wavelength multiplex system for optical communication is small-sized, requires a small space for installation, and satisfies the conditions that it has high durability against temperature or humidity and excellent stability and that it can be mass produced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element, an optical circuit including the optical element, and an optical demultiplexer.

  With the rapid spread of the Internet, there is a strong demand for an increase in information transmission capacity of optical fiber communication networks, and the development of wavelength division multiplexing (WDM) systems has been rapidly advanced. The WDM system is a communication technique that multiplexes and transmits independent information using light having different wavelengths. In this technique, an optical demultiplexer with good wavelength selectivity is required to separate multiplexed signals.

  By the way, in recent years, optical communication by the WDM system is being applied not only to the trunk line system so far but also to middle and short distance systems such as in cities. In this case, not a high-density wavelength division multiplexing (DWDM) system such as a trunk line system but a low-density wavelength multiplexing (CWDM) system having a relatively wide channel width becomes mainstream.

  Unlike the DWDM system, optical demultiplexers in the CWDM system require performance such as small installation space (miniaturization), high resistance to temperature and humidity (high stability), and mass production is possible. (Low cost).

  One means for realizing such a requirement is to make the optical demultiplexer a planar circuit type using an optical waveguide. The greatest advantage of the planar circuit type is that the substrate can be processed in large quantities for each wafer by lithography and dry etching techniques, as a matter of course. An optical waveguide using silica glass is highly practical because it has a good refractive index matching with an optical fiber and a small connection loss.

  As such an optical demultiplexer, an arrayed waveguide grating (AWG) is known. An AWG is an element that propagates light containing a plurality of wavelength components to a plurality of optical waveguides (optical waveguide arrays) having different optical path lengths little by little, and performs wavelength separation using a diffraction phenomenon caused by a phase shift that occurs. .

  However, since AWG is an optical demultiplexer originally developed for the DWDM system, even if designed for CWDM, the effects of cost reduction and miniaturization are small, and application to the CWDM system is not appropriate.

  On the other hand, an optical demultiplexer that performs wavelength separation using a reflection type or transmission type diffraction grating is well known. Although these are configured by a combination of optical components, a spectroscopic device in which this optical system is integrated in a planar optical circuit has also been developed (see Non-Patent Documents 1 and 2). A planar circuit using a reflective blazed diffraction grating can be reduced in size by several tens of percent or more with respect to AWG, and an optical demultiplexer in which the diffraction grating is integrated in a planar optical circuit is promising for CWDM.

  In recent years, photonic crystals have been actively studied as optical integrated circuits. A photonic crystal is a material in which a material with a large difference in refractive index is regularly arranged with a period of the order of the wavelength of light, and can exhibit characteristics not found in conventional homogeneous materials, such as sharp bending of light and complete confinement. Is possible.

  In order to form a photonic crystal, for example, in the optical communication field, a microfabrication technique for forming a periodic structure on a micron to submicron scale is required. A slab type two-dimensional photonic crystal in which fine holes and columnar structures are arranged on a substrate surface is generally produced using a fine patterning device such as electron beam drawing and a dry etching device. Forming a fine periodic structure on the substrate surface in this way has become relatively easy with the development of semiconductor microfabrication technology.

  Furthermore, a photonic crystal having a periodic structure in the vertical direction of the substrate has been proposed. Such a two-dimensional or three-dimensional photonic crystal having periodicity in the vertical direction makes it possible to form a polarization separation element or an optical resonance element using a complete band gap. Specifically, the photosensitive polymer resin is irradiated with a laser from three directions to form a periodic structure using light interference, or a silica microsphere is closely packed on a substrate. Various proposals have been made such as forming a multilayer film while maintaining a regular uneven shape on the surface of the substrate. However, many of such forming methods have a low degree of structural freedom such as introducing a point or line defect at a specific position.

  On the other hand, a highly flexible three-dimensional photonic crystal having a periodic structure in the vertical direction of the substrate has been reported (Non-patent Document 3). This is a process of laminating periodic structures of lines and spaces formed on a pair of substrates and peeling only one of the substrates to obtain a laminated periodic structure (called a woodpile type). ing. In this formation method, it is possible to form a structure in which a part of the period is removed for each layer or the period is modulated. As a result, for example, a defect waveguide that bends light at a right angle and a reflection mirror with a three-dimensional complete band gap have been reported.

S. Janz, 13 others, "Proceedings of OFC 2002", (USA), 2002, TuK2 Christopher. N. Morgan and 4 others, “IEEE Photonics Technology letters, (USA), 2002, Vol. 14, No. 9, p. 1303− 1305 Susumu Noda, Katsuhiro Tomoda, Noritsugu Yamamoto, Alongkarn Chutian, SCIENCE, vol.289, p.604-606, 2000.

  However, a reflective diffraction grating integrated in a planar optical circuit needs to form a minute and vertical diffraction grating surface with a height of several μm from the substrate, and further, a metal component as a reflection surface is formed on the diffraction grating surface. A membrane is required. In order to produce such a structure, a complicated and advanced processing technique is required.

  Further, it is well known that the wavelength resolution by a diffraction grating is proportional to the product of the order of diffraction light and the number of gratings. If the order and the size of the diffraction grating are constant, the grating period must be reduced in order to improve the resolution. In the blaze diffraction grating, when the grating period becomes about the wavelength, the difference in efficiency depending on the polarization direction (TE polarization and TM polarization), that is, polarization dependent loss (PDL) becomes remarkable. Conversely, if the period is increased to alleviate PDL, the number of gratings must be increased, making it difficult to reduce the size of the duplexer. In addition, when the diffraction order is increased, the higher-order unnecessary light has to be removed by another device, so that the efficiency naturally decreases.

  On the other hand, in a planar optical circuit using a transmission type diffraction grating, it is necessary to create a space for forming the diffraction grating in the slab waveguide. However, in order to construct an optical waveguide, it is necessary to form a clad layer on the upper portion, and it is difficult to maintain a space during the formation. In general, in an optical waveguide having an air layer as a clad, the propagation mode becomes multimode, and the dependence due to polarization becomes very significant.

  Next, attention is paid to the formation technique of the periodic structure. As explained in the prior art, in order to form a periodic structure in the direction perpendicular to the substrate, it is desirable to form a defect or the like in each layer and stack the structure because the degree of freedom of the structure is high. . In the above-described “formation of a periodic structure by bonding”, a pattern of a new layer is overlaid on a pattern serving as a base. Therefore, any pattern is not overlaid, and there are restrictions on the pattern to be used. In other words, the degree of freedom of structure is not so high.

  Further, in order to perform bonding, for example, when a semiconductor is used as a substrate material, the structures are fused with a nano-level positional accuracy in a furnace at 500 ° C., and these are repeated for the number of layers. A process is required. Of course, the materials used are also limited to those that can be fused. Also, it is not easy to increase the area.

  The present invention has been made paying attention to such conventional problems. The object is to provide an optical element having a high degree of freedom in the periodic structure. Another object of the present invention is to provide an optical demultiplexer that has high wavelength resolution, is less dependent on polarization, and can be miniaturized.

In order to achieve the above object, according to the first aspect of the present invention, a structure including a convex portion and a concave portion provided around the convex portion is embedded in a solid with a space by the concave portion. In the optical element,
The gist is that the solid in which the structure is embedded is a film formed by a film forming method.

  According to a second aspect of the present invention, in the optical element according to the first aspect, the structure is provided on a substrate or a solid layer laminated on the substrate, and the structure is formed at a top portion by a film forming method. The gist is that the film is covered with the formed film.

  In such an optical element, since the structure is embedded with a film formed by a film formation method, the structure can be covered with a thin film. That is, another optical element can be laminated on the optical element. Further, when an optical component such as a lens array is provided on the optical element, the distance between the structure and the optical component is the thickness of the thin film, so that the structure and the optical component can be brought close to each other.

  Further, such an optical element can be manufactured only by general lithography, etching, and film formation techniques. For this reason, it can manufacture easily compared with the case where a structure is embedded by bonding. Further, it is easy to form the structure in the optical waveguide, and the fine structure can be protected from damage and contamination, and durability can be improved.

The gist of the invention described in claim 3 is that, in the optical element according to claim 1 or 2, at least one of the convex portion or the concave portion of the structure has a periodic structure.
At least the convex part has a periodic structure, or the space by the concave part has a periodic structure, so that the optical characteristics can be controlled by this periodic structure. This periodic structure is a repeated pattern, and the patterns may be provided connected to each other or the patterns may be provided isolated from each other. Moreover, both the convex part and the recessed part may have a periodic structure.

According to a fourth aspect of the present invention, in the optical element according to any one of the first to third aspects, at least one of the convex portion and the concave portion of the structure is periodically arranged in one dimension. It is characterized by.
At least, the convex portions are periodically arranged one-dimensionally, or the spaces formed by the concave portions are periodically arranged one-dimensionally, so that the optical characteristics can be controlled by the periodic arrangement of the convex portions or concave portions. Moreover, both the convex part and the concave part may be periodically arranged one-dimensionally.

According to a fifth aspect of the present invention, in the optical element according to any one of the first to third aspects, at least one of the convex portion and the concave portion of the structure is periodically arranged in two dimensions. It is characterized by.
At least the convex portions are periodically arranged in a two-dimensional manner, or the spaces formed by the concave portions are two-dimensionally arranged periodically, so that the optical characteristics can be controlled by the periodic arrangement of the convex portions or the concave portions. Moreover, both the convex part and the concave part may be periodically arranged two-dimensionally.

The gist of the invention described in claim 6 is that, in the optical element according to any one of claims 1 to 5, the convex portion of the structure is a laminated film.
Since the convex portion is provided by a laminated film, the optical characteristics can be controlled by the laminated film.

The gist of the invention according to claim 7 is that, in the optical element according to any one of claims 1 to 5, the recess of the structure is a recess provided in the laminated film.
Since the concave portion is provided in the laminated film, the optical characteristics can be controlled also by this laminated film.

The gist of the invention described in claim 8 is that the optical element according to any one of claims 1 to 7 is laminated.
Since the optical elements according to any one of claims 1 to 7 are laminated with optical elements having the same structure or are laminated with optical elements having different structures, the optical characteristics can be further improved.

The gist of the invention according to claim 9 is that the optical element according to any one of claims 1 to 8 is provided with an optical component.
As described above, the optical element according to any one of claims 1 to 8 may be provided with an optical component such as a condensing unit or an optical waveguide.

  For example, when a condensing part such as a lens is provided in the optical element, when the condensing part is provided on the light incident side of the optical element, parallel light can be condensed by the lens and incident on the optical element. Further, the divergent light can be converted into parallel light by a lens and incident on the optical element. On the other hand, when a condensing part is provided on the light emitting side of the optical element, when parallel light is emitted from the optical element, it can be condensed and emitted by the lens. When divergent light is emitted from the optical element, it can be emitted as parallel light by a lens.

Further, when an arrayed lens is provided on the light incident side of the optical element, for example, a plurality of incident lights having different incident positions on the optical element can be condensed by the individual lenses and incident on the optical element. In addition, when an arrayed lens is provided on the light emitting side of the optical element, for example, a plurality of emitted lights having different emission positions can be condensed and emitted by each lens.
For example, when the optical element includes an optical waveguide, light emitted from the optical element can be incident on the optical waveguide.

  The invention according to claim 10 is the optical element according to any one of claims 1 to 9, wherein the structure is a periodic structure in which convex portions and concave portions are periodically arranged, The ratio of the depth and width (depth / width) of the recess is greater than 0.5, and the ratio of the period of the periodic structure to the wavelength used is in the range of 1/20 or more and 20 or less. And

Since the concave portion is formed so that the ratio of depth to width (depth / width) is larger than 0.5, the periodic structure having such a shape is not concave even if a coating film is formed on the upper portion. Is not buried, and the space of the concave portion constituting the periodic structure can be maintained.
In addition, since the ratio of the period to the wavelength used is in the range of 1/20 or more and 20 or less, the periodic structure can be applied to, for example, a diffraction grating, a photonic crystal, a polarization separation element, a non-reflective structure, and the like. it can. In particular, by using a periodic structure made of solid and gas (or vacuum), the difference in refractive index can be increased, so that the performance of each of the above elements can be improved.

The gist of the invention described in claim 11 is that, in the optical element according to claim 10, the ratio (depth / width) between the depth and the width of the concave portion of the periodic structure is 2 or more.
Since the recesses are formed deeply in this way, the periodic structure can be suppressed from being filled even if a coating film is formed on the upper portion, and the space of the recesses constituting the periodic structure can be further maintained.

A twelfth aspect of the present invention is the optical element according to any one of the first to eleventh aspects, wherein the periodic structure includes a substrate or a lower clad layer laminated on the substrate and an upper portion of the periodic structure. It is formed in a core layer between the upper cladding layer and the upper cladding layer, and the refractive index of the core layer is larger than the refractive indexes of the upper and lower cladding layers.
Since the optical element having such a structure has an optical waveguide structure, it can propagate in a single mode, can reduce polarization dependence, and can reduce a coupling loss with an optical fiber. It becomes.

The invention according to claim 13 is the optical element A according to claim 12, wherein the periodic structure is a diffraction grating that first-order diffracts at least incident light.
An optical element B provided in the core layer in which the optical element A is formed and having a function of controlling the spread angle of propagating light and entering the optical element A;
An optical element C that collects light beams having a plurality of different wavelength components demultiplexed by the optical element A;
The gist is that at least one of each is provided.
By providing the optical element as an element, a planar optical circuit that functions as an optical demultiplexer can be provided.

The invention according to claim 14 is the optical circuit according to claim 13, wherein a channel optical waveguide for entering light into the optical element B;
A channel optical waveguide array coupled to each of the light beams demultiplexed for each wavelength emitted from the optical element C;
The main point is that
By arranging the channel optical waveguide and the waveguide array in the optical circuit, it is possible to facilitate the incidence of light to the optical circuit and the extraction of the emitted light from the optical circuit.

  The gist of the invention according to claim 15 is the optical circuit according to claim 13 or 14, wherein at least one of the optical elements B and C is a concave mirror.

  The invention according to claim 16 is the optical circuit according to claim 15, wherein the concave mirror uses total reflection at the interface between the core layer in which the concave mirror is formed and the space.

  According to a seventeenth aspect of the present invention, in the optical circuit of the sixteenth aspect, the optical elements B and C are both concave mirrors, and the interface between the core layer in which the concave mirror is formed and the space is a paraboloid. It consists of a part of.

  The concave mirror as described above can be easily provided in the planar optical circuit by a process common to the periodic structure. Further, since total reflection is used, it is not necessary to provide a metal film on the reflection surface. Further, by making the concave mirror parabolic, it is possible to obtain light collecting characteristics without aberration.

The gist of the invention according to claim 18 is that, in the optical circuit according to claim 17, the dimensions of each part satisfy the following conditions (1) to (2).
(1) The width capable of diffracting the light of the diffraction grating which is the optical element A is
2a (λ ₀ / Δλ) / m
That's it.
(2) The width capable of reflecting the light of the concave mirror which is the optical element B is
2a · cos β ₁ · (λ ₀ / Δλ) / (m · cos α ₁ )
The width that can reflect the light of the concave mirror that is the optical element C is as described above.
2a · cos β ₂ · (λ ₀ / Δλ) / (m · cos α ₂ )
That's it.
However,
α ₁ : Incident angle to the concave mirror that is the optical element B α ₂ : Incident angle to the concave mirror that is the optical element C β ₁ : Incident angle of the incident light beam to the diffraction grating that is the optical element A β ₂ : Output angle of light beam emitted from diffraction grating as optical element A a: Lattice period of diffraction grating as optical element A Δλ: predetermined minimum wavelength interval λ ₀ : predetermined center wavelength m: diffraction order.

  By following the above conditions, an optical circuit having a desired optical demultiplexing performance can be realized with a minimum size.

The invention according to claim 19 is an optical circuit according to claim 13,
A light input portion arranged to make light incident on the optical element B;
A light output unit disposed so as to be coupled to a light beam demultiplexed for each wavelength emitted from the optical element C;
The main point is that

The invention according to claim 20 is the optical circuit according to claim 14,
A light input portion arranged to allow light to enter the channel optical waveguide;
An optical output disposed to couple to the channel optical waveguide array;
The main point is that

  Since it is configured in this way, a planar optical circuit type optical demultiplexer is provided by providing an optical fiber or the like that allows light to enter the optical circuit of the present invention from the outside and extract light emitted from the optical circuit. Can be provided.

The invention according to claim 21 is a method of manufacturing an optical element in which a structure having a convex portion and a concave portion provided around the convex portion is embedded in a solid while having a space by the concave portion.
The gist is to embed the structure with a film formed by a film formation method.

  According to a twenty-second aspect of the present invention, in the optical element manufacturing method according to the twenty-first aspect, the structure is provided on a substrate or a solid layer laminated on the substrate, and the upper portion of the structure is formed by a film forming method. The gist is to cover with the formed film.

  According to a twenty-third aspect of the present invention, in the optical element manufacturing method according to the twenty-first or twenty-second aspect, at least one of a chemical vapor deposition method, a physical vapor deposition method, and a flame deposition method is used as the film embedded with the structure. The gist is to do it.

  The gist of a twenty-fourth aspect of the invention is the method for manufacturing an optical element according to any one of the twenty-first to twenty-third aspects, wherein the convex portion or the concave portion is formed by photolithography and etching.

  According to the present invention, a periodic structure having a large refractive index difference can be embedded in a solid, and a multifunctional optical element can be formed. In particular, it is possible to reduce the size of an optical demultiplexer that separates light of a plurality of wavelengths using a diffraction grating, and to enable wavelength separation with high efficiency and little polarization dependence.

Hereinafter, embodiments of the present invention will be specifically described.
FIG. 1 is a diagram schematically showing the configuration of an optical element 1 having a periodic structure that is the basis of the present invention. FIG. 1A is a cross-sectional view, and FIG. A periodic structure 10 in which ridges 11 and grooves 12 are periodically arranged is formed on a substrate 18, and a coating layer 14 is further formed thereon.

  The term “periodic structure” as used herein refers to a structure in which two kinds of materials having different refractive indexes are periodically arranged. Specific applications of the periodic structure include diffraction gratings, photonic crystals, polarization separation elements, and the like.

  A periodic structure whose period is sufficiently larger than the wavelength or about the wavelength functions as a diffraction grating in which incident light is diffracted. If the period is similar to the wavelength and has a sufficient length in the propagation direction, it functions as a photonic crystal.

  When the period is sufficiently smaller than the wavelength, the periodic structure functions only as a medium having an average refractive index. However, when the structure has anisotropy, the periodic structure functions as a polarization separation element, and when there is no anisotropy in the structure, the refractive index is designed to have a continuous gradient from the surface to the substrate. By doing so, a non-reflective structure can be realized.

Summing up the above quantitatively, it is desirable to use the period a of the periodic structure in the following range with respect to the wavelength λ to be used.
.Lamda. / 20.ltoreq.a.ltoreq..lamda. / 10: polarization separation element, non-reflective structure, etc. .lamda. / 10.ltoreq.a.ltoreq.5.lamda .: photonic crystal, etc. .lamda. / 10.ltoreq.a.ltoreq.20.lamda. The structure preferably has a value (= a / λ) obtained by normalizing the period a with the wavelength λ in a range from 1/20 to 20.

In the present invention, an optical element in which a periodic structure made of a solid material and gas (or vacuum) is embedded in the solid material is manufactured. By burying the periodic structure inside the solid material, durability and antifouling properties can be improved. In addition, an optical waveguide structure capable of single mode propagation can be taken. In addition, the polarization dependency can be reduced, and the coupling loss with the optical fiber can be reduced.
Moreover, a periodic structure having a large refractive index difference can be realized by using a periodic structure made of a solid and a gas (or vacuum).

  In order to embed the periodic structure inside the solid material, a method of forming a layer covering the periodic structure on the substrate can be considered. However, when a gas layer is used for the periodic structure, there is a possibility that a groove for forming the gas layer is filled by film formation, and it is necessary to prevent this.

  Therefore, the inventors investigated the relationship between the film penetration into the groove and the shape of the periodic structure during film formation on the periodic structure. For the test, a one-dimensional periodic structure in which linear grooves having different groove depth / groove width ratios (aspect ratios) were arranged at equal intervals was used. Lithography and dry etching techniques were used for the formation. As a film forming means, a plasma chemical vapor deposition (plasma CVD) method widely used for forming a dielectric film such as silica or silicon nitride was used. As a result, it was found that the penetration of the film into the groove generally depends greatly on the aspect ratio. Their relational expressions are shown below.

The aspect ratio AR is defined by the following equation.
AR = d / w
Here, d is the groove depth perpendicular to the substrate surface, and w is the groove width in the direction parallel to the substrate surface at the top of the groove. At this time, depending on the value of AR, the penetration of the film into the groove changed as follows.
When AR ≦ 0.5: The groove is completely filled.
・ When 0.5 <AR <2: Some of the film has entered, but pores remain.
When 2 ≦ AR: The groove shape before film formation is maintained as it is.

  That is, in order to form a groove made of gas, it is necessary to form a groove with a high aspect ratio. It was found that a gas layer (hole) reflecting the groove shape and the aspect ratio can be formed in the groove having an aspect ratio larger than 0.5, although the film is formed on the groove side wall or bottom. Furthermore, by forming a groove with an aspect ratio of 2 or more, it is possible to form a structure in which the film does not substantially enter the groove and the initial shape is maintained. Therefore, it is more preferable that the aspect ratio is 2 or more in view of the production accuracy of the periodic structure. The larger the aspect ratio is, the more the film can be prevented from entering the groove, so that the initial groove shape is more easily maintained. For example, when the aspect ratio is 100, the initial groove shape can be easily maintained.

An example in which a one-dimensional periodic structure is embedded will be described below.
[Example 1]
The embedded one-dimensional periodic structure was manufactured by the following procedure. After forming line-shaped metal masks on the quartz glass substrate at equal intervals, grooves were formed by dry etching. The manufactured periodic structure has a period of 3 μm, a groove depth of 4 μm, and an aspect ratio of 3. Silica was deposited on the surface of the periodic structure by plasma CVD. An electron micrograph of a cross section of the periodic structure after film formation is shown in FIG. As is apparent from the figure, it can be seen that the periodic structure is buried under the coating layer made of silica. Further, no penetration of the film into the groove was confirmed, and it was proved that a buried periodic structure could be formed.

  As can be seen from the photograph, since the upper surface of the periodic structure is flat, various applications such as forming various functional elements on the periodic structure and repeatedly stacking and integrating them are possible.

  In the above embodiment, the production of a one-dimensional periodic structure by forming grooves with a constant period on a homogeneous substrate has been described. However, a two-dimensional or three-dimensional periodic structure can also be produced. Two-dimensional periodic structure in which grooves orthogonal to a homogeneous substrate are formed using orthogonal linear masks, two-dimensional in a substrate vertical plane in which grooves are formed on a multilayer film instead of a homogeneous substrate, or 3 A three-dimensional periodic structure can also be produced.

  In the present invention, it is desirable to use a general chemical vapor deposition (CVD) method (including a plasma CVD method) as a method for forming an optical film. In addition, a physical vapor deposition (PVD) method, a flame deposition (FHD) method, or the like can also be used. Basically, it is desirable to adopt a method or condition that has no directionality in film formation and a relatively high film formation speed. It is desirable to use a silica-based material for the reason that the film forming material is highly stable and has a low refractive index. In the case of forming a multilayer film in a direction perpendicular to the substrate surface, it is preferable to use a material suitable for each application in consideration of the refractive index and transmittance.

  When it is necessary to suppress the burying amount as much as possible, it is preferable to use a general sputtering method in the PVD method. The sputtering method is roughly classified into a plasma method and an ion beam method, and the plasma method is more preferable in that the film forming component does not have directionality. Further, the plasma method has an advantage that a large area film can be formed at a high speed.

  Moreover, although classified into a physical sputtering method, a chemical sputtering method, and a reactive sputtering method according to the reaction mechanism of sputtering, it is not specifically limited. Moreover, although there exist a direct current | flow type, RF type, a magnetron type etc. as a plasma generation method, there is no limitation in particular also about this. What is necessary is just to use properly according to the kind of coating layer to form, and an optical characteristic, respectively.

[Example 2]
A highly functional diffraction grating will be described as an optical element of the second embodiment. The diffraction grating was fabricated by dry etching by ICP-RIE after forming a mask pattern on a quartz glass substrate by electron beam drawing and Ni lift-off. For embedding film formation, opposed RF sputtering using silica as a target was used. FIG. 3 shows an electron micrograph of a cross section of the embedded diffraction grating produced. It can be seen that there is almost no reduction in the groove width, and it is possible to cover the film while preventing the film from entering the groove. This diffraction grating showed good characteristics of a first-order diffraction efficiency of 90% or more and a loss due to polarization of 5% or less. In addition, the mechanical strength of the diffraction grating is increased by embedding.
Opposite sputtering film formation is effective for the embedding in which the film formation in the groove is suppressed, and it is possible to reduce the structural deviation from the design value due to the embedding.

  On the other hand, the CVD method includes a thermal CVD method and a plasma CVD method. The CVD method can obtain a wide variety of films from semiconductors such as amorphous silicon, silicon oxide, and silicon nitride to insulators and even metals. Further, it has characteristics such as a film forming speed and a large film forming area.

  In particular, in optical communication, a CVD method is applied to form a silica-based film doped with various impurities. For example, it is possible to increase the refractive index by doping germanium to function as an optical waveguide, or to decrease the refractive index by doping fluorine. Further, if boron or phosphorus is doped, the softening point can be lowered. As described above, the CVD method has a feature that film physical properties can be controlled by doping various elements.

  In addition, in the CVD method, the amount of film formation components entering the grooves varies depending on the material to be formed and the film formation conditions. Therefore, it is preferable to actively use this phenomenon. That is, the shape of the periodic structure can be controlled by embedding with a material having a softening point lower than that of the periodic structure and then performing heat treatment. This will be described in the next embodiment.

[Example 3]
As a third embodiment, an example in which the shape of the embedded periodic structure is controlled will be described. In the same manner as in the above-described embodiment, first, periodic grooves were formed on a quartz glass substrate, and then a silica film to which 14 mol% of boron was added for the purpose of lowering the glass transition point was formed by plasma CVD. Thereafter, heat treatment was performed in the air at 800 ° C. for 1 hour to expand the gas contained in the space of the periodic structure, thereby controlling the shape of the periodic structure.

  FIG. 4 shows an electron micrograph of a cross section of the periodic structure after the heat treatment. The embedded diffraction grating of Example 2 (see FIG. 3) described above has a shape in which the tip of the groove is pointed by film formation, but in this example, the cross-sectional shape of the groove is made elliptic by heat treatment. We were able to. This is considered to be due to only the silica doped with boron being compressed by the thermal expansion of the gas in the space of the periodic structure. Thus, by controlling the depth and width of the periodic grooves, the film forming components, and the heat treatment conditions, it is possible to form a periodic structure that has been difficult in the prior art, for example, in which spherical spaces are arranged.

  In the present invention, the material for forming the periodic structure is not particularly limited, and a dielectric, a semiconductor, a metal, an organic material, or the like can be used. However, it is desirable to use a thermally stable inorganic material because a film forming method having a relatively high temperature is used for forming the coating layer as described above.

Specific examples of materials are given below.
Examples of the substrate material include oxide glass such as soda lime glass and borosilicate glass, non-oxide glass such as chalcogenide glass and halide glass, and mixed glass such as oxynitride glass and chalcogenide glass. . Materials that can be formed by vacuum film formation, such as silica doped with silica, silicon, silicon nitride, silicon carbide, silica doped with B, P, Ge, F, Ti, and semiconductors such as InP and GaAs, can also be used as the substrate material. It is. In some cases, a polymer such as PMMA, a film formed by a sol-gel method, or the like is also applicable.

A multilayer film can also be used as a substrate material. Specific examples include optical multilayer films made of silica, titania, tantalum oxide, silicon, silicon nitride, alumina oxide, magnesium fluoride, and the like.
Of course, the above materials can also be used as a material for forming a periodic structure. In addition, a material that can be formed by vacuum film formation typified by silica or a semiconductor can be applied to the coating layer.

  In addition, it is desirable to apply a semiconductor microfabrication technique for processing, and therefore, a dielectric material such as silica, silicon nitride, and titania, or a material with high processing accuracy such as a semiconductor such as silicon or InP is desirable.

  Since the periodic structure in the present invention is a periodic arrangement of a solid material and a gas, the difference in refractive index is as large as 30% or more. Therefore, when manufacturing an optical element that requires a large difference in refractive index or has an advantage in performance when the difference in refractive index is large (for example, a photonic crystal, a polarizing beam splitter, a high-efficiency transmission type diffraction grating) This structure is very suitable. Further, if a high refractive index material such as silicon nitride or a semiconductor is used, the refractive index difference can be further increased. In contrast, a sufficiently large refractive index difference can be secured even in silica having a low refractive index, and therefore, it is suitable for the production of a silica-based optical element that is very chemically and physically stable.

[Example 4]
The optical element of the fourth embodiment has an optical waveguide structure, and a diffraction grating which is a periodic structure is embedded in the optical waveguide. FIG. 5 shows a cross-sectional view (a) and a plan view (b) of the optical element 1. A lower clad layer 28 and a core layer 26 are provided on a substrate (not shown), and an upper clad layer 24 covers the lower clad layer 28 and the core layer 26. A diffraction grating 20 is formed in a part of the core layer. The periodic structure of the diffraction grating 20 is constituted by a periodic arrangement of a solid ridge layer 21 and an air layer composed of grooves 22. The lower clad layer 28 can be substituted by a substrate.

  By increasing the refractive index of the core layer 26 relative to the refractive indexes of the upper and lower cladding layers 24 and 28, an optical waveguide structure is formed, and the light introduced into the core layer 26 is confined in the core layer and propagates. When incident light 92 parallel to the diffraction grating 20 formed in the optical waveguide is incident, the light is emitted with a diffraction angle determined by the wavelength, the period of the diffraction grating, and the refractive index of the core layer, and this diffracted light 93 is again emitted from the core layer. To propagate. According to this configuration, light can be propagated in the in-plane direction instead of the direction perpendicular to the substrate surface as in an optical system using a conventional diffraction grating, and the optical circuit can be integrated and miniaturized.

In this example, an optical waveguide structure capable of single mode propagation was manufactured under the following conditions.
・ Wavelength: 1.55μm
Upper clad layer: silica (refractive index 1.455)
Lower clad layer (substrate): silica (refractive index 1.455)
-Core layer: Ge-doped silica (refractive index 1.460),
Thickness 5μm

  If the upper cladding layer is not formed, the thickness of the core layer for obtaining a single mode is 1 μm or less, which not only makes it difficult to couple input / output light from the outside, but also has a large refractive index difference or distortion. Naturally, the polarization dependence and the propagation loss at the interface also increase. That is, by forming the upper cladding layer, propagation in a single mode in which the wavefront can be easily controlled can be realized with realistic design values. Needless to say, the formation of the upper cladding layer is preferable from the viewpoint of protection of the diffraction grating, durability, and contamination resistance.

Here, the transmission type diffraction grating whose period is about the wavelength causes a volume effect by providing a thickness in the light propagation direction. In the case of a rectangular grooved diffraction grating made of silica, according to simulation, polarization dependent loss PDL (= 10 × log ₁₀ (first-order diffraction efficiency in TE-polarized light / first-order diffraction efficiency in TM-polarized light) at wavelengths of 1.46 to 1.58 μm. ) Is 0.1 dB or less and the first-order diffraction efficiency is 94% or more. (The calculation is based on the RCWA (Rigorous Coupled Wave Analysis) method (GSOLVER ver4.20b manufactured by Grating Solver Development). used).

The conditions used for the calculation are as follows.
Ridge refractive index: 1.46 (value at 1.55 μm wavelength)
-Refractive index of groove: 1.00 (value at a wavelength of 1.55 μm)
・ Ridge width: 0.85μm
・ Width of groove: 0.60 μm
・ Width in light propagation direction: 3.15 μm
-Incident angle: 20 °

  For example, when the application field is directed to optical communication, the light guided from the optical fiber has various polarization states depending on the state of the optical fiber, and it is difficult to predict the polarization state realistically. Therefore, a component for controlling the polarization direction must be added to the system, which naturally increases the cost. Therefore, by using such a diffraction grating, loss depending on polarization can be suppressed, which is very advantageous for system construction. Here, a rectangular diffraction grating was used as an example, but excellent characteristics were obtained with various shapes such as a triangular shape and a pointed shape, and the shape is not particularly limited (Jiro Koyama, Hiroshi Nishihara “ Lightwave Electro-Optics ", Corona, 1978, Chapter 4).

  Since the above-described performance of the diffraction grating can be realized by a periodic structure having a refractive index of 1.46 and 1.00, a technique for embedding the groove portion in the air as it is is necessary. In the case of the optical communication wavelength band (wavelength of 1.3 to 1.5 μm), since the thickness of the silica-based waveguide is about 5 μm, the aspect ratio of the grating groove is about 8, and as described in the first embodiment. An embedded transmission diffraction grating having a periodic structure of a core material and air can be formed.

  This configuration is not particularly limited to the core material, and can be formed not only from general Ge-doped silica but also from silicon nitride or silicon having a high refractive index. However, when used as an optical demultiplexer for optical communication, it is preferable to use a silica / Ge-doped silica type optical waveguide with a core thickness of about 5 μm, which is advantageous in terms of performance and connection with the outside.

  As described above, by using a transmission type diffraction grating whose period is about the wavelength and having a volume effect, a diffraction grating can be fabricated in an embedded optical waveguide that is advantageous for polarization dependence, connection to an optical fiber, etc. It turns out that the thing with the very excellent characteristic is obtained.

[Example 5]
FIG. 6 shows a schematic plan view of the optical demultiplexer 50 of this embodiment. A slab optical waveguide is formed on the substrate 38, and light demultiplexing is performed by the transmission type diffraction grating 30 embedded in the optical waveguide described in the fourth embodiment. In the optical waveguide on the same substrate, a concave mirror 33 for entering light into the diffraction grating and a concave mirror 35 for emitting light transmitted through the diffraction grating are also formed, and a planar optical circuit 50a is formed. The planar optical circuit 50a is provided with a light input unit 37 composed of an optical fiber for entering light and a light output unit 39 for outputting light to each wavelength, and the optical demultiplexer 50 as a whole. Is configured.

  Next, in order to describe the operation of the optical demultiplexer 50, FIG. 7 shows a conceptual diagram of an optical system showing the components and optical parameters. The light 51 entering the core layer (slab waveguide) from the light input portion 37 propagates while spreading in a fan shape according to the numerical aperture (NA) of the optical waveguide. This light is converted into a parallel light beam 52 having a small divergence angle by the concave mirror 33 and is incident on the diffraction grating 30 at a predetermined incident angle. Incident light becomes a light beam 53 having a different direction for each wavelength component by the diffraction grating 30, and each light is condensed at a different point by the concave mirror 35 and coupled to the light output unit 39.

Here, the incident wavelengths of the minimum wavelength interval to be separated by the optical demultiplexer are λ ₁ and λ ₂ , and the average wavelength is λ ₀ (= (λ ₁ + λ ₂ ) / 2). At this time, the difference between the angles at which the light beams having the wavelengths λ ₁ and λ ₂ are diffracted by the diffraction grating 30 is represented by Δψ (unit: radians).

The NA of the optical waveguide is defined by the following equation.
NA = (n ₁ ² −n ₀ ² ) ^0.5 = n ₁ · sin θ
Here, n ₁ is the refractive index of the core layer, and n ₀ is the refractive index of the cladding layer. Here, for the sake of simplicity, it is assumed that the upper and lower clad layers have the same refractive index and that the refractive index difference (n ₁ −n ₀ ) is about 0.01. Light incident on the core layer from the optical fiber propagates with a spread angle of approximately θ.

Here, as shown in FIG. 7, the parameters of the optical demultiplexer are defined as follows.
Effective diameter of incident side concave mirror: D ₁
Effective diameter of exit side concave mirror: D ₂
Incident side parallel light flux width: P ₁
The width of the parallel light beam on the exit side: P ₂
Diffraction order: m
Total number of grooves in diffraction grating: N
Groove period of diffraction grating: a
Angle between mirror normal and optical axis at intersection of optical axis and incident side mirror surface: α ₁
Angle between mirror normal and optical axis at the intersection of optical axis and output side mirror surface: α ₂
Angle of incidence on diffraction grating: β ₁
Output angle from diffraction grating: β ₂
Refractive index of the waveguide portion: n

The wavelength resolution in the diffraction grating is determined by the product of the diffraction order m and the total number N of grooves as shown in the following equation.
λ ₀ / Δλ = m · N
However, the above formula adopts the radius of the Airy disk as the wavelength interval in the far field. In order to clearly separate the two wavelengths, an interval of about the diameter of the Airy disk is required.
λ ₀ / Δλ = mN / 2 (1)
Is the resolution of the diffraction grating.

From equation (1), the width D _{0 of the} diffraction grating is
D ₀ = a · N = 2a (λ ₀ / Δλ) / m
The width P ₁ of the light beam incident on the diffraction grating is
P ₁ = D ₀ · cos β ₁ = 2a · cos β ₁ · (λ ₀ / Δλ) / m
The effective diameter D ₁ of the entrance-side concave mirror is
D ₁ = P ₁ / cos α ₁ = 2a · cos β ₁ · (λ ₀ / Δλ) / (m · cos α ₁ )
It becomes. Similarly, the exit side
D ₂ = 2a · cos β ₂ · (λ ₀ / Δλ) / (m · cos α ₂ )
It is. Based on the relationship described above, the minimum size of each element of the optical demultiplexer shown in FIG. 7 is determined.

In addition, it is necessary to select the curvature of the concave mirror so that the numerical aperture NA ₁ of the incident-side concave mirror corresponding to D ₁ covers the numerical aperture of the incident portion 37.
Since the focal distance S of the exit portion is the Airy disk diameter on the exit side, the numerical aperture NA ₂ of the exit-side concave mirror is used, and S = 1.22λ ₀ / NA ₂
It is represented by If the lower limit of the value of S is set by the method of manufacturing the waveguide portion, it may be necessary to increase S by decreasing the numerical aperture NA ₂ on the output side.

The design values described above are for the case where the entire optical demultiplexer is minimized while ensuring the wavelength resolving power. Therefore, for example, the total number of grooves and the width of the luminous flux can be made larger than the above values so as to provide a margin. By doing so,
-The value of S is made larger than the above-mentioned value to reduce the crosstalk.-There is an effect that the loss of the light flux at the concave mirror is reduced and the loss is reduced.

Further, the concave mirror can be easily manufactured by a groove processing step common to the periodic structure by utilizing the interface between the space and the material of the core layer. Here, it is well known that when light propagates from a medium having a high refractive index to a medium having a low refractive index, the light is not emitted to the medium having a low refractive index but totally reflected at the interface in a certain angle range. The angle γ is called a critical angle and is expressed by the following equation.
sin γ = n _air / n ₁ = 1 / n ₁
Here, n _air is the refractive index of air.

  Therefore, by designing so that the light incident on the concave mirror satisfies the critical angle condition, it is not necessary to form a metal film on the surface of the concave mirror, and the reflection loss is theoretically almost zero. Further, in this configuration, the concave mirror has a function of converting light from the condensing point into parallel light (or vice versa). Therefore, by making the concave curve part of the parabola, a perfect condensing point or parallel light without aberration can be obtained. Therefore, an optimum concave mirror with a minimum loss can be obtained by the above-mentioned total reflection condition and a shape that satisfies the parabolic condition.

  Although a pair of concave mirrors are used here for condensing or collimating, other optical elements that exhibit the same function, for example, an optical waveguide type lens may be disposed. However, it is preferable to use a concave mirror from the viewpoint of ease of manufacture. Further, the propagating light may be collected by one concave mirror or lens. In this case, a diffraction grating may be arranged somewhere in the optical path.

  The optical demultiplexer having the above-described configuration is extremely low in polarization dependence for both the diffraction grating and the optical waveguide. Therefore, the polarization compensator is unnecessary, and it is a planar optical circuit type and ultra-small. It has features such as being capable of being manufactured in large quantities on a substrate, and is very suitable in a field where low cost and space saving are required.

[Example 6]
A schematic plan view of the optical demultiplexer 50 of this embodiment is shown in FIG. In this optical demultiplexer 50, the optical input / output portions are channel optical waveguides 47 and 49, and are integrated with other elements (diffraction grating 40, concave mirrors 43 and 45) in the optical circuit. In this case as well, an optical fiber coupled to each channel optical waveguide is required, but the illustration is omitted. Thus, in the structure of the fifth embodiment in which light is directly incident from an optical fiber or the like, it is necessary to adjust the incident angle and the focal length. However, in the optical circuit of the present embodiment, only the optical fiber or the like is coupled to each channel optical waveguide. This eliminates the need for complicated adjustment work. Further, if an optical waveguide is used, the condensing points at the emitting portion can be set at an interval of about 10 μm, and further miniaturization is possible.

  Next, a specific configuration example of the optical system of the planar optical circuit type optical demultiplexer 50 of the present embodiment is shown in FIGS. FIG. 9 schematically shows an optical path of propagating light. The light 51 incident from the channel optical waveguide of the light input unit is converted into parallel light 52 by the concave mirror 43 and enters the diffraction grating 40. The demultiplexed light 53 transmitted through the diffraction grating 40 is condensed by the concave mirror 45 onto the end face of the channel optical waveguide array of the light output unit.

The concave mirrors 43 and 45 are both parabolic mirrors. Each parameter is as follows.
-Incident wavelength: 1.51, 1.53, 1.55, 1.57 μm
-NA of optical waveguide: 0.17
・ Diffraction grating period a: 1.45 μm
・ Diffraction grating width D: 1 mm
・ Focal distance f of concave mirror: 1.68 mm
-Curvature radius of concave mirror: 1mm
・ Distance S between light output points and condensing points: 17.4 μm

  With the above configuration, light having a wavelength interval of 20 nm can be demultiplexed. Further, the focal plane P of the light output unit is inclined with respect to the parabolic axis C of the concave mirror 45 by the angle of emission from the diffraction grating 40 (angle between the grating normal and the emitted light), thereby providing a more optimal spot diameter. Is obtained.

  FIG. 10 shows an example of a specific shape of the planar optical circuit type optical demultiplexer according to the present invention manufactured according to the optical design described above. In order to make the light incident end face PI and the light exit end face PO into parallel planes, a part of the channel optical waveguide 47 of the light input portion is a bent waveguide. The size of the element is about 5 mm × 8 mm, and it can be seen that a very small optical demultiplexer can be obtained.

  Naturally, it is also possible to input light having different wavelengths from the optical waveguide array of the light output unit, combine them, and output the light from the input-side waveguide. Furthermore, although four-wavelength multiplexing / demultiplexing is shown here, the number of channels can naturally be increased and the wavelength width can be narrowed.

  The circuit arrangement of the optical circuit is not limited as long as the above conditions are satisfied, and various arrangements as shown in FIG. 11 are conceivable. The optical circuit 50a can be arranged in a line-symmetric type as shown in FIGS. 11B and 11C in addition to the point-symmetric type as in the above embodiment (FIG. 11A). Further, it is possible to arrange such that the light paths cross each other or the light input part and the light output part are on the same end face as shown in FIG.

  The production procedure for the fifth or sixth embodiment will be described below. Fabrication of this optical demultiplexer uses patterning by photolithography and groove processing by dry etching. The manufacturing procedure will be described with reference to FIG. A lower cladding layer 68 is formed on the substrate 78 as necessary. Further, a core layer 66 is formed thereon (FIG. 12A). As a film formation method, it is known that a CVD method, a flame deposition method, or the like can produce a good quality film with low loss, but is not particularly limited.

  Next, a metal mask for producing the constituent elements of the optical circuit type optical demultiplexer is produced by a so-called lift-off method. First, a material that is sensitized by energy irradiation such as ultraviolet rays, electron beams, and X-rays (hereinafter referred to as a resist) is spin-coated on the surface of the core layer 66, and then a pattern of a desired component is formed by an appropriate exposure technique. Next, a metal film is formed on the resist pattern. As a film formation method, a sputtering method, a vacuum evaporation method, or the like can be used. For the metal film, chromium, tungsten silicide, nickel, or the like can be used. In particular, when the lift-off method is used, it is desirable to use a vacuum evaporation method or a directional sputtering method from the viewpoint of damage to the photoresist and improvement of patterning accuracy.

  By removing the unnecessary metal film together with the resist pattern, the pattern of the metal mask 69 is formed (FIG. 12B). Of course, a method of forming the pattern of the metal mask 69 by etching by changing the order of the resist and the metal film formation is also possible. In this case, however, it is desirable to select a material that can be easily etched as a metal.

  Next, the core layer 66 is grooved using an ion etching apparatus to form a periodic structure (diffraction grating) 60 in which the ridge portions 21 and the groove portions 22 are periodically arranged. In addition, components of the optical demultiplexer such as other optical elements and optical waveguides are manufactured. An etching apparatus should be selected suitable for the material to be processed, but in order to efficiently process a large area, a high density plasma such as inductively coupled plasma (ICP) or magnetic neutral line discharge (NLD) is used. It is desirable to use reactive ion etching. The remaining metal mask may be removed with a corrosive solution, dry etching, or the like (FIG. 12C).

Finally, the upper clad layer 64 is formed by CVD (FIG. 12D). As described above, conditions are set so that the film does not enter the groove of the diffraction grating.
As described above, the optical waveguide type optical demultiplexer of the present invention can be easily produced by conventional lithography processing.

  It goes without saying that the optical demultiplexer of the present invention can be used as an optical multiplexer that sends light of a plurality of wavelengths into a single optical fiber if the direction of the light beam is reversed.

  Further, in the present invention, a plurality of diffraction gratings may be arranged. As a result, the chromatic dispersion increases in proportion to the number. When the wavelength interval is very narrow as in the DWDM system, the wavelength resolution can be increased and the element size can be kept small. At this time, since the waveguide portion and the diffraction grating portion are integrally formed by lithography, there is an advantage that there is no increase in the process and almost no increase in cost.

  On the other hand, in the optical recording field, in recent years, development of recording devices aiming at large capacity, such as DVD, has been underway. It is obvious that the recording / reading speed must be increased with the increase in the capacity of the recording information. One of them is simultaneous recording / reading by multiple wavelengths. In this system, light multiplexed with a plurality of wavelengths is guided to an optical head and demultiplexed there to perform writing or reading with light of a plurality of wavelengths to enable parallel processing of information. In this case, it is essential that the optical head is small in consideration of scanning over the disk, and the present invention is suitable for incorporation into such a system.

In addition, although Example 1 to Example 3 mainly shows an example of a rectangular periodic groove, other shapes can be applied to the periodic structure. A specific example will be described below.
Periodic structures are classified into one, two, and three dimensions according to the axial direction having a period.

  First, FIG. 13 shows a plan view of a one-dimensional periodic structure as an example. A periodic structure 100 shown in FIG. 13A is embedded in a solid 101 in which a cylindrical groove 102 is periodically arranged in a one-dimensional manner with a space. In FIG. 13B, a triangular prism groove 103 is embedded in the solid 101, and in FIG. 13C, a rectangular prism groove is embedded with a space. The Y axis in the figure is an axis having a period. The groove may be a pentagon or more polygon, an ellipse, or any other irregular shape.

  A periodic structure 110 shown in FIG. 14 is an example in which patterns 110 </ b> A are periodically arranged in a solid 101. In the pattern 110A, the interval and width of the groove 111 may change with respect to the Y-axis direction, and the length of the structure 111 may change in the Z-axis direction. The periodic structure 110 shown in FIG. 14 has a two-dimensional structure, but the direction of periodic arrangement is one-dimensional.

  In the one-dimensional periodic structure, the case where the periodic structure is not formed when the groove portions or the ridge portions are in close contact with each other, such as when square grooves are arranged on an axis perpendicular to a certain side, is excluded.

  13 and 14 illustrate the case where the groove portions as the concave portions are periodically arranged, a structure in which the convex portions formed of the ridge portions are periodically arranged may be used, and both the concave portions and the convex portions are periodically arranged. It may be a structure.

  The cross section of the groove or ridge in the direction perpendicular to the substrate surface (X-axis direction) may not be rectangular. For example, it may have a barrel shape, or may be a cone, a pyramid, or a taper shape or a reverse taper shape. Further, oblique groove portions inclined from a direction perpendicular to the substrate surface may be formed in parallel to each other. Thus, the groove or ridge does not necessarily have to be provided perpendicular to the substrate surface, and the groove or ridge may be provided irregularly or asymmetrically. The above-described high-functional diffraction grating is an application example of a one-dimensional periodic structure having a square groove.

Next, an example of a two-dimensional periodic structure will be described. The two-dimensional periodic structure may basically be a two-dimensional arrangement of the one-dimensional periodic structure.
FIG. 15 shows a plan view of a two-dimensional periodic structure as an example. In the periodic structure 120 shown in FIG. 15A, the rectangular columnar grooves 121 are embedded in the solid 101 while being arranged in a lattice shape with a space. FIG. 15B shows the triangular prism grooves 122 arranged in a triangular lattice.

FIG. 15C shows the cylindrical groove portions 123 arranged in a square lattice so as to be in contact with each other. Since the groove portions are in contact with each other, convex portions 101a isolated from the solid 101 are formed, and the convex portions 101a are also arranged in a square lattice pattern.
FIG. 15D shows the triangular prism grooves arranged in a triangular lattice pattern so that their vertices are in contact with each other. Since the groove portions are in contact with each other, convex portions 101b isolated from the solid 101 are formed, and the convex portions 101b are also arranged in a triangular lattice pattern.

  Thus, the two-dimensional array has an array shape such as a square lattice, a triangular lattice, a polygonal lattice, or a concentric circle, and the array period may be modulated. For example, if a single row of defect portions (regions in which holes are not formed) are introduced into a photonic crystal in which circular holes are squarely arranged, a buried photonic crystal defect waveguide can be realized. In addition, when concentric circular line grooves are arranged with their periods appropriately modulated, an embedded binary blazed grating lens can be formed.

  Further, if the multilayer film is processed into a rectangular groove in a one-dimensional arrangement, a two-dimensional periodic structure is obtained. For example, if a square groove (line & space groove) is formed in a multilayer film having a large refractive index difference such as silica / silicon, the function as a polarization separation element can be exhibited.

  In addition, although FIG. 15 demonstrated the case where the groove part as a recessed part was periodically arranged, the structure which the convex part which consists of a ridge part arranged periodically may be sufficient.

  If the multilayer film is processed in a two-dimensional array, a three-dimensional periodic structure is obtained. FIG. 16 shows an example of a three-dimensional periodic structure in which convex portions of a quadrangular prism made of a multilayer film are squarely arranged. This three-dimensional periodic structure 130 is formed by squarely arranging a multilayer film 130A in which a film 131 and a film 132 are stacked.

  In addition, although FIG. 16 demonstrated the case where the convex part which consists of laminated films was periodically arranged, the recessed part provided in the laminated film may be periodically arranged.

  Since the optical element of the present invention has a flat surface, the optical element can be further laminated. For example, FIG. 17 shows an optical element 150 having two embedded periodic structures. In this optical element 150, a periodic structure 140 in which ridge portions 141 and groove portions 142 are periodically arranged is formed on the covering layer 14 of the optical element 1 shown in FIG. 1, and the structure 140 is covered with the covering layer 151. This is a case where another optical element made of is laminated.

  Thus, since the coating layer of the optical element of the present invention is flat, it is possible to form not only a simple planar layer but also a multilayer film or another periodic structure. For example, a flat coating layer can be used as a surface-mount laser or a platform for mounting a light receiving element. In addition, when the periodic structure as described above is formed, a coating layer can be further formed. Therefore, in principle, the periodic structure can be laminated without limitation.

  Further, not only the periodic structure but also a spherical uneven shape such as a lens, a lens array obtained by arraying them, a triangular prism shape, a prism array, and the like may be laminated on the optical element. In particular, the structure that cannot be embedded is preferably formed on the uppermost surface. Moreover, when forming a structure in a coating layer, it is not necessary to form in a lower layer structure, and you may form in a free position.

  FIG. 18 shows an optical element 160 provided with a plurality of lenses as optical components as an example. In this optical element 160, lenses 161 are arranged in an array on the coating layer 14 of the optical element 1 shown in FIG. Light incident on the periodic structure 10 or light emitted from the periodic structure 10 can be condensed by the lens 161 or converted into parallel light.

FIG. 19 shows an optical element 170 provided with an optical waveguide as an optical component as an example. This optical element 170 is an example in which an optical waveguide 171 is provided on the coating layer 14 of the optical element 1 shown in FIG. Light emitted from the periodic structure 10 can be incident on the optical waveguide 171.
Thus, since the optical element of the present invention can be provided with a lens array or an optical waveguide, a more integrated optical element can be provided.

  In the present invention, not only the optical demultiplexer but also other elements such as a photonic crystal and a polarization separation element can be manufactured as described in the first embodiment. The light propagation direction can function not only in the substrate surface (in the optical waveguide) but also in the direction perpendicular to the substrate surface. In the optical waveguide, optical functional integrated circuits such as optical multiplexing / demultiplexing, polarization separation, and delay elements can be integrally formed. On the other hand, the surface of the uppermost coating layer is flat in the direction perpendicular to the substrate surface, forming a lens array. An optical integrated device in a direction perpendicular to the substrate surface can be produced.

  INDUSTRIAL APPLICABILITY The present invention can be used for an apparatus for separating light having different wavelengths used in an optical communication system or an optical disk pickup device.

The schematic diagram of the optical element which has an embedded type | mold periodic structure of this invention. The electron micrograph of the embedded type periodic structure of this invention. The electron micrograph of the embedded type diffraction grating of this invention. The electron micrograph of the embedded type periodic structure of this invention. The schematic diagram of the optical waveguide type optical element provided with the diffraction grating of this invention. The schematic diagram which shows the structure of the planar optical circuit type | mold optical demultiplexer of this invention. The figure explaining the optical arrangement | positioning of the planar optical circuit type | mold optical demultiplexer of this invention. The schematic diagram which shows the other structure of the planar optical circuit type | mold optical demultiplexer of this invention. The figure which shows the example of the optical arrangement | positioning of the planar optical circuit type | mold optical demultiplexer of this invention. The figure which shows the example of the optical arrangement | positioning of the planar optical circuit type | mold optical demultiplexer of this invention. The figure which shows the modification of the optical arrangement | positioning of the planar optical circuit type | mold optical demultiplexer of this invention. The figure which shows the manufacturing process of the planar optical circuit of this invention. The schematic diagram of the one-dimensional periodic structure of this invention. The schematic diagram of the one-dimensional periodic structure of this invention. The schematic diagram of the two-dimensional periodic structure of this invention. The schematic diagram of the three-dimensional periodic structure of this invention. The schematic diagram of the optical element which has an embedded type | mold periodic structure of this invention. The schematic diagram of the optical element which has the lens array of this invention. The schematic diagram of the optical element which has the optical waveguide of this invention.

Explanation of symbols

1, 150, 160, 170 Optical element 10, 100, 110, 120, 130, 140 Periodic structure 11, 141 Ridge part 12, 142 Groove part 14, 151 Cover layer 18, 38, 78 Substrate 20, 30, 40, 60 Diffraction gratings 24, 64 Upper clad layers 26, 66 Core layers 28, 68 Lower clad layers 33, 35, 43, 45 Concave mirror 37 Optical input part 39 Optical output part 47 Channel optical waveguide 49 Channel optical waveguide array 50 Optical demultiplexer 69 Metal mask 161 Lens 171 Optical waveguide

Claims (24)

In an optical element in which a structure including a convex portion and a concave portion provided around the convex portion is embedded in a solid while having a space by the concave portion,
An optical element, wherein the solid in which the structure is embedded is a film formed by a film forming method.   2. The structure according to claim 1, wherein the structure is provided on a substrate or a solid layer laminated on the substrate, and the structure is covered with a film formed by a film formation method on an upper portion thereof. Optical elements.   The optical element according to claim 1, wherein at least one of the convex portion or the concave portion of the structure has a periodic structure.   The optical element according to claim 1, wherein at least one of the convex portion and the concave portion of the structure is periodically arranged in one dimension.   The optical element according to claim 1, wherein at least one of the convex portion or the concave portion of the structure is periodically arranged in two dimensions.   The optical element according to claim 1, wherein the convex portion of the structure is a laminated film.   The optical element according to claim 1, wherein the concave portion of the structure is a concave portion provided in the laminated film.   The optical element as described in any one of Claims 1-7 is laminated | stacked, The optical element characterized by the above-mentioned.   The optical element as described in any one of Claims 1-8 is equipped with the optical component, The optical element characterized by the above-mentioned.   The structure is a periodic structure in which convex portions and concave portions are periodically arranged, and the ratio (depth / width) of the depth and width of the concave portion is larger than 0.5, and the periodic structure body 10. The optical element according to claim 1, wherein the ratio of the period to the wavelength to be used is in the range of 1/20 or more and 20 or less.   The optical element according to claim 10, wherein a ratio (depth / width) between a depth and a width of the concave portion of the periodic structure is 2 or more.   The periodic structure is formed in a core layer between a substrate or a lower clad layer laminated on the substrate and an upper clad layer covering the upper portion of the periodic structure, and the refractive index of the core layer is The optical element according to claim 1, wherein the optical element has a refractive index greater than that of the lower cladding layer. The optical element A according to claim 12, wherein the periodic structure is a diffraction grating that firstly diffracts incident light.
An optical element B provided in the core layer in which the optical element A is formed and having a function of controlling the spread angle of propagating light and entering the optical element A;
An optical element C that collects light beams having a plurality of different wavelength components demultiplexed by the optical element A;
An optical circuit having at least one of each. A channel optical waveguide for entering light into the optical element B;
A channel optical waveguide array coupled to each of the light beams demultiplexed for each wavelength emitted from the optical element C;
The optical circuit according to claim 13, comprising:   The optical circuit according to claim 13 or 14, wherein at least one of the optical elements B and C is a concave mirror.   16. The optical circuit according to claim 15, wherein the concave mirror uses total reflection at the interface between the core layer in which the concave mirror is formed and the space.   The optical circuit according to claim 16, wherein the optical elements B and C are both concave mirrors, and an interface between the core layer and the space where the concave mirrors are formed is a part of a paraboloid. 18. The optical circuit according to claim 17, wherein the dimensions of each part satisfy the following conditions (1) to (2).
(1) The width capable of diffracting the light of the diffraction grating which is the optical element A is
2a (λ ₀ / Δλ) / m
That's it.
(2) The width capable of reflecting the light of the concave mirror which is the optical element B is
2a · cos β ₁ · (λ ₀ / Δλ) / (m · cos α ₁ )
The width that can reflect the light of the concave mirror that is the optical element C is as described above.
2a · cos β ₂ · (λ ₀ / Δλ) / (m · cos α ₂ )
That's it.
However,
α ₁ : Incident angle to the concave mirror that is the optical element B α ₂ : Incident angle to the concave mirror that is the optical element C β ₁ : Incident angle of the incident light beam to the diffraction grating that is the optical element A β ₂ : Output angle of light beam emitted from diffraction grating as optical element A a: Lattice period of diffraction grating as optical element A Δλ: predetermined minimum wavelength interval λ ₀ : predetermined center wavelength m: diffraction order. An optical circuit according to claim 13;
A light input portion arranged to make light incident on the optical element B;
A light output unit disposed so as to be coupled to a light beam demultiplexed for each wavelength emitted from the optical element C;
An optical demultiplexer characterized by comprising: An optical circuit according to claim 14,
A light input portion arranged to allow light to enter the channel optical waveguide;
An optical output disposed to couple to the channel optical waveguide array;
An optical demultiplexer characterized by comprising: In the method of manufacturing an optical element in which a structure having a convex portion and a concave portion provided around the convex portion is embedded in a solid while having a space by the concave portion,
A method of manufacturing an optical element, wherein the structure is embedded with a film formed by a film forming method.   The method for manufacturing an optical element according to claim 21, wherein the structure is provided on a substrate or a solid layer laminated on the substrate, and an upper portion of the structure is covered with a film formed by a film formation method.   23. The method of manufacturing an optical element according to claim 21, wherein the film for embedding the structure is formed by at least one of a chemical vapor deposition method, a physical vapor deposition method, and a flame deposition method. The method for manufacturing an optical element according to any one of claims 21 to 23, wherein the convex portion or the concave portion is formed by photolithography and etching.

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