JP2008032931A - Optical coupling element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical coupling element that imparts input/output of light such as a highly efficient laser to an optical waveguide with a high refractive index difference, in an optical coupling element between optical waveguides and between a waveguide and other optical systems, for example. <P>SOLUTION: The optical coupling element is composed of an optical waveguide having a core 2 and a clad 3 formed on a substrate 1 and having an end face of the core that provides a numerical aperture NA<SB>1</SB>and a lens having an optical axis not in parallel with the light guide direction of the optical waveguide and having a lens that provides a numerical aperture NA<SB>2</SB>. In this element, the lens 6 is arranged in the manner that the sum of the maximum light receiving angle at which the optical waveguide provides the numerical aperture NA<SB>1</SB>and the similar angle at NA<SB>2</SB>is ≥90° and that the converging position of the lens is in proximity to the end face. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical coupling device, and more particularly to a highly efficient optical coupling device having an optical waveguide having a large refractive index difference between a core and a clad.

  Conventionally, various methods for optical coupling to an optical waveguide have been proposed. There are various cases such as coupling of a light emitting element or a light receiving element and an optical waveguide, coupling of optical waveguides, and the like. In general, these elements and the waveguide are arranged in the same straight line in the waveguide direction of the optical waveguide so as to be directly connected or connected via a medium.

  In the case of an optical waveguide having the same size of the light propagation region of the optical waveguide composed of the core and the clad, the optical waveguides can be coupled with low loss even if the central axes of the optical waveguides are aligned and directly connected. In order to connect to a lower loss, the coupling portion is filled with a refractive index matching solvent to reduce scattering loss at the interface due to direct connection, or the connection portion is fused to change the refractive index at the interface. The method to lose is taken.

  However, in these methods, unless the optical waveguides have substantially the same size, the mode shape of light propagating through the respective optical waveguides is different, so that scattering loss increases in direct connection. As a typical example, in a Fabry-Perot type semiconductor laser, the photoactive layer portion serving as an optical waveguide is extremely thin with a submicron width, so that the mode shape at the emission end face is large and flat. When this light is coupled to the optical fiber (when it is input to the optical fiber), the mode shape at the laser emission end face and the shape of the propagation mode of the optical fiber are very different, so the coupling efficiency is extremely low just by connecting the end face directly. Become. Therefore, it is necessary to convert the mode shape between the connected optical waveguides.

  One method of this conversion is a mode conversion method using a lens. By providing a lens between the semiconductor laser and the optical fiber, the mode shape can be deformed and the coupling efficiency can be increased. Similarly to this method, when the light from the optical fiber is coupled to the light receiving element, the coupling efficiency can be increased by condensing the light using a lens.

  As described above, when the mode shape is different at the emission end face, the optical coupling efficiency between the elements is greatly deteriorated, so that a mode conversion structure is required.

  On the other hand, an optical waveguide with a large refractive index difference between the core and the clad (high refractive index difference optical waveguide) can have a radius of curvature as small as a micron, which dramatically improves the optical wiring integration and wiring flexibility. Can be made. When such an optical wiring technology is used, it is expected that the optical integrated device can be miniaturized.

  However, when this optical waveguide is connected to a conventional waveguide having a small refractive index difference between the core and the clad (low refractive index difference optical waveguide), the cross-sectional area of the core is smaller than that of the optical refractive index. The connection loss is expected to be extremely large because it is different from several tens of times.

  As such a technique, an invention is disclosed in which the size of the core of the optical waveguide is gradually changed to convert and connect the mode field size (for example, Patent Document 1).

In Patent Document 1, the spot size of the waveguide mode is converted by using a reverse taper structure in which the tip of the high refractive index difference optical waveguide is gradually narrowed and the reverse taper portion is connected to the low refractive index difference optical waveguide. With this structure, the low refractive index optical waveguide and the high refractive index optical waveguide having greatly different mode shapes can be coupled with low loss (see FIG. 1 of Patent Document 1 and the first embodiment).
JP 2004-184986 A

  The invention disclosed in Patent Document 1 is effective for coupling light propagating through an optical fiber to a high refractive index optical waveguide. However, in order to couple the light emitted from the light source to the high refractive index difference optical waveguide or to couple the light from the high refractive index difference optical waveguide to the light receiving element, it is necessary to change the optical waveguide structure step by step. Yes, it requires complex optical waveguide combinations.

  To connect light that has not propagated through the optical fiber, for example, spatially propagated light, to the optical waveguide, the light from the direct light source is narrowed by the lens, and the optical axis of the optical waveguide and lens are aligned and input to the end face of the optical waveguide. However, accurate alignment is necessary to collect the light with the lens on the sub-micron core end face. Furthermore, it may be possible to integrate a spot size converter by forming a lens with the optical axis aligned with the core end face, but it is extremely difficult to create such a structure on the end face of the waveguide. It is.

  As an optical coupling method that does not require the optical axes to be aligned, an optical coupling method using a prism coupler is also used in the low refractive index difference optical waveguide. However, since the core size of a high refractive index difference optical waveguide is submicron, it is necessary to reduce the prism shape in accordance with the size, and it is extremely difficult to couple light into this optical waveguide. There is also.

Accordingly, in order to solve the above-described problems, the present invention provides a maximum light receiving angle at which an optical waveguide having a core end face that provides a numerical aperture NA ₁ and a core formed on a substrate has a numerical aperture NA _1. And the maximum light receiving angle that gives the numerical aperture NA ₂ is 90 degrees or more, so that the optical waveguide having the end face of the core that gives the numerical aperture NA ₁ and the condensing position of the lens in the vicinity of the end face of the optical waveguide An object of the present invention is to provide an optical coupling element in which a lens is arranged.

In order to solve the above-mentioned problems, an invention according to claim 1 includes a substrate, an optical waveguide having a core and a clad formed on the substrate, and having an end face of the core that provides a numerical aperture NA _1. An optical coupling element having an optical axis that is not parallel to the light guiding direction of the light in the optical waveguide and having a lens with a numerical aperture NA ₂ , wherein the optical waveguide has a maximum light receiving angle that gives the numerical aperture NA ₁ And the maximum light receiving angle that gives the numerical aperture NA ₂ is 90 degrees or more, and the optical coupling element has the lens arranged so that the condensing position of the lens is in the vicinity of the end face. And

  According to a second aspect of the present invention, in the optical coupling element according to the first aspect, the optical axis of the lens is substantially orthogonal to the waveguide direction of the optical waveguide.

  According to a third aspect of the present invention, in the optical coupling element according to the first or second aspect, the lens is formed on a clad of the optical waveguide provided on the substrate when the substrate is the lower side. It is characterized by being.

  According to a fourth aspect of the present invention, in the optical coupling element according to any one of the first to third aspects, a light scatterer is provided in the vicinity of the end face of the core condensed by the lens on the optical waveguide. It is characterized by that.

  According to a fifth aspect of the present invention, in the optical coupling element according to any one of the first to fourth aspects, the clad forming the optical waveguide is composed of a plurality of portions having different refractive indexes. It is characterized by.

  According to a sixth aspect of the present invention, in the optical coupling element according to the fifth aspect, at least one of the plurality of refractive index portions of the clad forming the optical waveguide is formed of a continuously changing material. It is characterized by.

  According to a seventh aspect of the present invention, in the optical coupling element according to any one of the first to sixth aspects, a reflective region is provided between the optical waveguide and the substrate.

  The invention according to claim 8 is the optical coupling element according to any one of claims 1 to 7, wherein a photoelectric conversion element is provided on the layer having the lens on the side of the optical waveguide or on the side opposite to the optical waveguide. It is characterized by that.

  The invention according to claim 9 is the photonic crystal according to any one of claims 1 to 8, wherein the core of the optical waveguide has a line defect structure and the cladding has a photonic crystal array. It is an optical waveguide.

  According to a tenth aspect of the present invention, in the optical coupling element according to any one of the first to ninth aspects, the optical coupling element has an array structure.

  According to an eleventh aspect of the present invention, in the optical coupling element according to any one of the first to tenth aspects, the optical coupling element has a stacked array structure.

Up according to the present invention consists of a core and a clad formed on a substrate, an optical waveguide having an end face of the core to provide a numerical aperture NA ₁ is, giving the maximum light receiving angle and the numerical aperture NA ₂ which gives the numerical aperture NA ₁ An optical waveguide having an end face of the core that gives a numerical aperture NA ₁ when the sum of the light receiving angles is 90 degrees or more, and light in which the lens is disposed so that the condensing position of the lens is in the vicinity of the end face of the optical waveguide A coupling element can be provided.

  The present embodiment has been made in consideration of the above-described circumstances, and an object thereof is to provide an optical coupling element capable of inputting and outputting light with high efficiency to and from a high refractive index difference optical waveguide.

  More specifically, the problem of the first to third embodiments is to appropriately arrange the lens in an optical system in which the waveguide direction of the high refractive index difference optical waveguide and the optical axis of the lens do not coincide with each other. Accordingly, an object of the present invention is to provide an optical coupling element that provides a high refractive index difference optical waveguide capable of optical coupling with high efficiency.

  An object of the fourth to seventh embodiments is to provide a more efficient optical coupling element by providing a simple structure in the core or cladding of the high refractive index difference optical waveguide.

  An object of an eighth aspect of the present invention is to provide an optical coupling element that can be integrated with a photoelectric conversion element.

  The ninth embodiment of the present invention aims to provide an optical coupling element with a photonic crystal optical waveguide.

  An object of the tenth and eleventh embodiments is to provide an optical coupling element array structure

  The first to third problems are: an optical waveguide that forms an end surface in a high refractive index difference optical waveguide, and that provides a refractive index difference in which the sum of the numerical aperture and the maximum acceptance angle that gives the numerical aperture of the lens is 90 ° or more; This can be solved by placing a lens.

  The fourth to seventh problems are to provide a light scatterer in a high refractive index difference optical waveguide, to provide a clad made of a plurality of materials, to provide a clad having a continuous refractive index change, or to reflect on the clad It is solved by providing a region.

  The eighth problem is solved by disposing the photoelectric conversion element on the side opposite to the optical waveguide with respect to the lens.

  The ninth problem is solved by forming an end face in the photonic crystal optical waveguide and making the condensing position of the lens near the end face.

  The tenth and eleventh problems are solved by arranging the optical coupling element in a planar arrangement or a laminated structure.

  Hereinafter, embodiments of an optical coupling element of the present invention will be described in detail with reference to the drawings.

[First and Second Embodiments]
The optical coupling elements of the first and second embodiments will be described with reference to FIGS.

  1A and 1B are views showing a first embodiment, wherein FIG. 1A is a top view of an optical coupling element, FIG. 1B is a side view of the optical coupling element, and FIG. 1C is a front view of the optical coupling element. It is. Fig.1 (a) is sectional drawing in the straight line AB of FIG.1 (b).

(High refractive index difference optical waveguide and relative refractive index difference)
An optical waveguide 4 including a core 2 and a clad 3 is formed on a substrate 1 shown in FIG. 1B, and the core 2 has an end face 5. The difference in refractive index between the core 2 and the clad 3 is a waveguide that takes a refractive index difference where the NA becomes extremely large as described below. The relative refractive index difference Δ is used as an index indicating the magnitude of the refractive index difference between the core 2 and the clad 3. When the refractive index of the core 2 is n ₁ and the refractive index of the cladding 3 is n ₂ , the relative refractive index difference Δ [%] is Δ [%] = [(n ₁ ² −n ₂ ² ) / 2n ₁ ² ] defined by x100.

  The high refractive index difference optical waveguide preferably has a relative refractive index difference of 5% or more, more preferably 10% or more. If such an optical waveguide is, for example, an optical waveguide having silicon as the core 2 and silicon dioxide as the cladding 3, the refractive index of silicon is 3.5 and the refractive index of silicon dioxide is relative to the infrared wavelength of the optical communication band. Since it is 1.45, the relative refractive index difference is about 41%, which is a very large value. If an optical waveguide having an optical crystal such as lithium niobate as the core 2 and silicon dioxide as the cladding 3 is formed, the refractive index of lithium niobate is 2.2 and the refractive index of silicon dioxide is 1. When 45 is set, the relative refractive index difference is 28%, and a large value of 10% or more is obtained.

(Characteristics of high refractive index difference optical waveguide: NA)
Generally, when the refractive index of the core 2 is n ₁ and the refractive index of the cladding 3 is n ₂ , the numerical aperture NA ₁ of the optical waveguide is NA ₁ = sqrt (n ₁ ² −n ₂ ² ) (= (n ₁ ² −n ₂ ² ) ^1/2 ) (1). That is, the numerical aperture NA ₁ the maximum acceptance angle theta _max when inputted from the refractive index n ₃ in the waveguide is defined by NA ₁ = n ₃ sin [theta _max, entered at this maximum acceptance angle theta _max light, to progresses in the waveguide from Snell's law when the critical angle and _{θ c, n 1 sin (90} ° -θ c) (= n 1 cosθ c) = n 2 sin90 ° = n ₂ (where n ₁ and n ₂ represent the refractive indexes of the core 2 and the clad 3, respectively), and sin θ _c = sqrt (1−n ₂ ² / n ₁ ² ) is obtained. Therefore, the numerical aperture of the optical waveguide NA ₁ from the above _{equation, NA 1 = n 3 sinθ max} = n 1 than sin [theta _c, and substituting _{sinθ c NA 1 = n 1 sqrt} (1-n 2 2 / n 1 2 Thus, the above equation (1) is obtained.

  Thus, the numerical aperture of the waveguide is a value determined by the refractive indexes of the core 2 and the clad 3.

  Here, light from the waveguide to the air is radiated with respect to a generally used optical waveguide such as an optical fiber (low refractive index difference optical waveguide) and a high refractive index difference optical waveguide that is a feature of the present invention. Consider the numerical aperture if

  As a typical optical waveguide of the low refractive index difference waveguide, there is a quartz optical waveguide. The numerical aperture of this waveguide is when the refractive index of the core is 1.45 and the refractive index of the cladding is 1.44. Further, the relative refractive index difference is about 0.7% and the numerical aperture is about 0.17, which can be calculated from the respective definition equations. At this time, the maximum light receiving angle calculated from the numerical aperture is about 17 °, and it can be seen that light is emitted substantially parallel to the light guiding direction.

  On the other hand, when considering an optical waveguide having silicon as a core and silicon dioxide as a cladding as a high refractive index difference optical waveguide, if the refractive index of the core is 1.5 and the refractive index of the cladding is 1.45, the numerical aperture Is a very large value of about 3.2. When the core is an optical crystal such as lithium niobate (refractive index 2.2) and the cladding is silicon dioxide (refractive index 1.45), the numerical aperture is 1.65.

The numerical aperture of 1 or more in this way means that the maximum light receiving angle θ _{1 of} light has a large radiation angle of 90 ° or more. That is, the light propagating through the optical waveguide is emitted in a direction substantially perpendicular to the waveguide direction. This can be considered that the light reaching the end face is reflected by the end face and radiates upward because the difference in refractive index at the end face is large.

A lens 6 having an optical axis in a direction not parallel to the waveguide direction (z direction) of the optical waveguide is formed on the lens layer 7. The lens formed in the lens layer lens having a numerical aperture NA ₂ is formed. The numerical aperture NA ₂ is the maximum receiving angle is taken as theta _2, is a value defined by _{NA 2 = n 3 sin ((} 2). Here, n ₃ is the refractive index of the medium, FIG. 1 In the following description, the refractive index of the medium on the side where the optical waveguide is present is assumed to be the same value as the refractive index n ₃ of the lens layer other than the lens and the refractive index n _{2 of the} cladding. According to the law, it is derived by the following equation: n ₃ sin θ ₂ = n ₂ sin (90 ° −θ ₁ ) (however, θ ₁ and θ ₂ are shown in FIG. 1).

  In FIG. 1, the optical axis of the lens 6 is in the direction perpendicular to the waveguide direction (z direction) of the optical waveguide (z direction), but is not necessarily perpendicular as shown in FIG. For example, as shown in FIG. 2A, the structure may be inclined, and the present invention is characterized in that the optical axis of the lens and the waveguide direction of the waveguide are not parallel. The angle formed by the optical axis may be a value larger than 0 °. However, in order to take advantage of the effects of the present invention, it is preferably 75 ° or more and more preferably in the vicinity of 90 °.

  In the example shown in FIG. 2A, an example in which the optical axis of the lens 6 is tilted is shown, but in FIG. 2B, an example in which the end face is not 90 ° is shown. The core of the optical waveguide is characterized in that the end face 5 is formed so as to have an angle with respect to the x axis, and the shape of the end face is not a right angle in FIG. In FIG. 4, the angle is set to be oblique.

  When the shape of the end face 5 of the core is oblique, more light can be emitted to the lens side. Since the amount of light emitted with respect to the radiation angle from the end face of the core is not necessarily the maximum in the vertical direction, the light that has propagated through the core by such a shape increases the amount of light emitted upward at the end face.

  Such a structure of the oblique end face can be adjusted by etching when forming the core of the optical waveguide. For example, by adjusting the thickness of the resist at the end face when forming the core by lithography and dry etching, a difference in the etching amount at the time of etching occurs, and etching for manufacturing an oblique end face using this difference is performed. It becomes possible.

  In addition, it is possible to form an oblique end surface by applying a technique capable of forming the side surface obliquely by adjusting the etching conditions of the dry etching itself. Further, when the end face is exposed to protect other portions and anisotropic wet etching is performed, an oblique end face can be formed.

The shape of the lens used in the optical coupling element of the present invention is mainly a spherical biconvex lens, but may be a planoconvex lens, a convex meniscus lens, or a concave lens depending on the case, and may be an aspherical lens. In addition, an element having a lens effect (condensing or diverging performance) by multiple reflection using the super lens effect of a photonic crystal may be used, and a lens according to the application can be used. However, NA _{2 at} this time is a numerical aperture converted to a refractive optical system.

Here, since the NA of the high refractive index difference optical waveguide is extremely large, the following formula θ ₁ > is set between the maximum light receiving angle θ ₁ that gives the NA of the optical waveguide and the maximum light receiving angle θ ₂ that gives the NA of the lens. It is also possible to configure an optical coupling element that satisfies 90 ° −θ ₂ (1). In the case of a normal low refractive index optical waveguide, it is necessary to make the optical axis of the lens and the central axis of the optical waveguide substantially parallel because the light receiving angle that satisfies the formula (1) cannot be given. In the case of a rate difference optical waveguide, if the condensing position of the lens is in the vicinity of the end face of the optical waveguide, the light propagating through the optical waveguide can be received by using the structure of the present invention. Conversely, it is also possible to couple the light collected by the lens to the optical waveguide.

  For example, when a lens having a numerical aperture NA of 0.25 is used as the lens 6, the maximum light receiving angle is 14.5 °. Therefore, if the maximum light receiving angle giving the NA of the waveguide is 75.5 degrees or more. It is possible to receive light with a lens. This is the case where the lens is arranged substantially perpendicular to the light guiding direction (light traveling direction). If the optical axis of the lens is tilted in the direction without the core, the angle of the waveguide decreases accordingly. To do.

  An optical waveguide that gives such a maximum acceptance angle has a maximum acceptance angle of 75 ° or more by setting the refractive index of the clad to 3.36 when silicon having a refractive index of 3.5 is used as a core, for example. It is possible. Further, when the refractive index of the core is 2.0, by setting the refractive index of the cladding to 1.75 or less, it is possible to receive light emission in a right angle direction only by forming the end face. If the numerical aperture NA of the lens is large, more light from the waveguide can be received. Therefore, it is preferable that the numerical aperture NA of the lens is large. In this structure, since the relationship between the arrangement of light input and output is reversible, it is possible to adopt a configuration in which light is coupled from the lens side to the waveguide.

  The present embodiment is an optical coupling element that utilizes light radiation unique to a high refractive index difference optical waveguide. Therefore, in a normal low refractive index difference optical waveguide, in order to emit light in a direction perpendicular to the light guiding direction, a complicated structure needs to be added to the waveguide itself. On the other hand, the high refractive index difference waveguide used in the optical coupling element of the present invention can realize light emission in the direction perpendicular to the waveguide direction only by forming the end face. Furthermore, by adopting such a configuration of the present invention, it becomes possible to combine more light.

[Third Embodiment]
FIG. 3 shows a configuration example of the optical coupling element of the present embodiment in the third embodiment. FIG. 3 is a side view similar to FIG. The other top view and front view are the same as FIGS. 1 (a) and 1 (c), and are omitted. The same elements as those in FIG. 1 are given the same numbers (symbols). The same applies to other embodiments.

  A high refractive index difference optical waveguide 4 including a core 2 and a clad 3 is formed on a substrate 1. An end face 5 is formed on the core 2, and the end face of the optical waveguide is terminated or started (starting end). The lens 6 is formed on the clad 3, and the refractive index of the lens 6 and the film thickness of the clad 3 are adjusted so that the condensing position of the lens 6 is on or near the end face 5 of the core 2. In FIG. 3, a lens layer is formed by filling a portion where the lens 6 is formed with a medium 7. The lens layer only needs to be formed of a medium having a refractive index smaller than that of the lens except for the lens in contact with the cladding. For example, the lens layer other than the lens can adopt an air layer having the lowest refractive index, which can be paraphrased as a structure in which the lens is exposed to the air.

  The film thickness of the clad can be adjusted relatively easily by adjusting the film formation conditions, and the film thickness can be adjusted with a nanometer size, and a clad with a highly accurate film thickness can be configured. . Further, the lens 6 on the clad 3 can be formed by forming a lens material by lithography and dry etching. It is also possible to print a medium using an ink jet to form a lens shape. In this embodiment, it is easier to form compared to the structure shown in FIG.

[Fourth Embodiment]
A configuration example of the optical coupling element of the fourth embodiment is shown in FIG. FIG. 4 shows a side view similar to the above embodiment. Others are the same as those in the top view and the front view of FIG.

  An optical waveguide 2 is formed on a substrate 1 and a lens layer in which a lens 6 is configured is provided. The core 2 of the optical waveguide has an end face 5, and the condensing position of the lens is set on or near the core end face 5. Here, the vicinity of the end surface 5 means not only the end surface but also a region other than the end surface of the region where the end surface of the core is included in the beam spot size collected by the lens.

  A light scatterer 8 that scatters light is formed in the vicinity of the core end face. With this light scatterer, the light confined in the waveguide by total reflection at the interface between the core and the clad can be emitted to the lens side outside the core, or the light can enter the waveguide from the lens side. . By forming such a structure, the light coupling efficiency to the lens or the light coupling efficiency from the lens side to the waveguide can be improved.

  The light scatterer may have a structure formed by patterning on the core, or may be scattered with a scattering material such as silica sphere. Furthermore, a photonic crystal pattern is formed to increase the light extraction efficiency to the top. Or, conversely, a method of increasing the light extraction efficiency from the lens to the waveguide may be used, and a structure in which a structure is formed in the cladding may be used.

[Fifth Embodiment]
The optical coupling element of 5th Embodiment is demonstrated using FIG.

  An optical waveguide layer 2 is formed on the substrate 1, and a lens layer on which a lens 6 is formed is disposed thereon. The optical waveguide is formed of a core 4, a lower clad 9, and an upper clad 10. The core 4 has an end face 5, and the end face 5 is covered with an upper clad 10. The lower clad 9 is formed on the side opposite to the surface on which the lens 6 is formed with respect to the upper clad 10. The upper clad 10 and the lower clad 9 are materials lower than the refractive index of the core 2, and these two clads are formed of materials having different refractive indexes.

  Thus, by providing the clad 4 with a refractive index difference, it is possible to increase the coupling efficiency between the light emitted from the end face 5 and the lens 6. That is, the light emitted from the end face 5 and emitted in the direction opposite to the lens 6 has a refractive index difference between the upper cladding 10 and the lower cladding 9, and is reflected by the interface between the two claddings. The light is emitted from the upper clad to the lens side. By forming such an interface, the radiation efficiency to the upper part is increased, and the optical coupling efficiency to the lens 6 is increased.

  Such a shape (layer configuration) can be manufactured by changing the film forming material. That is, in order to form an optical waveguide, the lower cladding layer 9 is formed by a film forming apparatus, the core layer 2 is formed, and patterning is performed by lithography. Thereafter, the upper clad 10 can be formed in layers by using different materials. Forming films of different materials can be obtained by sputtering using a sputtering apparatus or the like. Even with the same material, the refractive index can be adjusted by doping, and this can also be achieved by adjusting the film formation of the cladding portion.

[Sixth Embodiment]
A configuration example of the sixth embodiment of the optical coupling element of the present invention is shown in FIG.

  Similar to FIG. 5, an upper clad 10 and a lower clad 9 are formed and cover the core 3. It is characterized in that the refractive index of at least one of the two upper and lower clads (that is, the upper and / or lower or both) continuously changes. FIG. 6 illustrates an example in which the lower cladding has a configuration in which the refractive index gradually decreases. With such a structure, the light is reflected to the lens side, and the optical coupling efficiency at the lens can be increased.

  Such a layer whose refractive index continuously changes can be formed by a method similar to that for a gradient index optical waveguide. For example, a glass or plastic layer is provided on a substrate, a dopant that changes the refractive index is selectively diffused, or a material capable of causing a refractive index change by ultraviolet rays is formed on the substrate. By adjusting the irradiation time, the refractive index can be continuously changed by forming the lower clad layer (upper clad) having the refractive index continuously changed.

[Seventh Embodiment]
A configuration example of the seventh embodiment of the optical coupling element of the present invention is shown in FIG.

  In the configuration example shown in FIG. 7A, the light reflecting layer 11 is formed between the substrate 1 and the optical waveguide layer 4 composed of the core 2 and the clad 3. A lens layer 12 in which a lens is formed on the surface opposite to the substrate with respect to the optical waveguide layer 4 is provided. An end face 5 is formed on the core 2 of the optical waveguide, and the light emitted from the optical waveguide and the light incident on the end face have a large NA, and the optical axis of the lens is perpendicular to the waveguide direction of the waveguide. Even it can be combined with light.

  With such a structure, the light emitted from the end face is also emitted to the side opposite to the lens. For this reason, the light reflecting layer 11 is formed on the side opposite to the lens layer, and the light scattered to the side opposite to the lens is reflected to the lens side. By adopting this structure, the reflected light is again reflected in the lens. The light coupling efficiency can be increased. In the example shown in FIG. 7A, the reflective layer is configured at a position away from the core 2, but may be positioned close to the core 2, and is not formed on the entire surface of the optical waveguide, but near the end surface. An area for reflecting light (light reflecting portion) may be provided.

  FIG. 7A shows an example in which the light reflecting layer 11 is formed between the substrate and the lens layer. In the present embodiment, the lens layer 7 and the light reflecting layer 11 may be configured with the optical waveguide layer 4 interposed therebetween, and the position of the substrate 1 may be on the lens forming layer 7 side. 7B, the asymmetric cladding as illustrated in the fifth embodiment in which the optical waveguide 4 is formed of the core 2, the lower cladding 9 and the upper cladding 10 having different refractive indexes in FIG. 7A. The example of a structure which is a structure is employ | adopted. By combining the reflection at the interface with the dielectric according to this configuration, light scattering on the side opposite to the lens layer 7 can be suppressed, and the coupling with the optical waveguide can be increased.

  The light reflecting layer (light reflecting portion) 11 employed in the present embodiment can be selected from a metal, a multilayer film, a photonic crystal structure, and the like, and has a high reflectance with respect to the wavelength of light propagating through the optical waveguide. Any reflective layer having a thickness may be used.

[Eighth Embodiment]
An example of the eighth embodiment of the optical coupling element of the present invention is shown in FIG.

  In the configuration example shown in FIG. 8A, the optical waveguide 4 is formed on the substrate 1, and the lens layer 7 on which the lens 6 is formed is formed thereon. A photoelectric conversion layer 14 is formed on the side opposite to the optical waveguide layer 4 with the lens layer 7 interposed therebetween. A photoelectric conversion element 13 is formed on the photoelectric conversion layer 14. The photoelectric conversion element 13 is an element that converts light into an electric signal, and indicates a light emitting element or a light receiving element. The light emitting element is an element such as a laser diode, LED (light emitting diode) or VCSEL (vertical cavity surface emitting laser), and the light receiving element is a PD (Photo detector), APD (avalanche photo diode) or CCD ( charge coupled device). These elements are made of an inorganic material or an organic material, and form a semiconductor structure.

  With such a configuration, it is possible to integrate an element that converts an optical signal output from the optical waveguide into an electric signal or vice versa.

  Further, as shown in FIG. 8B, a semiconductor material is used for the substrate, a photoelectric conversion element is formed in that portion, and the lens layer and the optical waveguide layer are laminated, thereby integrating the photoelectric conversion element and the optical waveguide. Can be realized. If a semiconductor substrate is used, connection (coupling) with an electronic circuit is possible, and such a structure can be used for optical interconnection between integrated circuits, and a highly efficient optical coupling element is configured with a simple structure. Is possible.

[Ninth Embodiment]
An example of the ninth embodiment of the present invention is shown in FIG.

  FIG. 9A is a side view, and FIG. 9B is a lateral cross-sectional view taken along the line CC in FIG.

  FIG. 9A has the same configuration as the side view of FIG. 1B, but as shown in FIG. 9A showing a cross-sectional view along the line C-C, an optical waveguide is formed. A slab type photonic crystal line defect optical waveguide is used. This waveguide has a structure in which a photonic crystal array portion 14 composed of circular holes is formed on a thin film 15, and a portion where light propagates is composed of a line defect 15 having no photonic crystal array. . That is, it is a waveguide in which the core 2 is the line defect portion 17 and the cladding is the photonic crystal array 16. The photonic crystal array part 14 is at least configured to surround the core up to the end of the core 2 of the waveguide layer, and the remaining part of the cladding is configured with the photonic crystal array part 14. Alternatively, the same configuration as the cladding layer of the above-described embodiment may be used.

  A photonic crystal is a crystal in which a dielectric periodic structure having an optical frequency is artificially formed. A band structure for photons is formed, and light transmission characteristics called a photonic band gap can be suppressed.

  In FIG. 9, by using the strong optical confinement effect of the photonic crystal 16 as the cladding 3 of the optical waveguide, the same effect as that of the optical waveguide having a large refractive index difference can be exhibited. As the optical waveguide, the core 2 can be quasi-three-dimensionally confined to realize the optical confinement structure in three dimensions and the upper and lower confinement by total reflection. FIG. 9 shows a structure for realizing the latter pseudo three-dimensional optical confinement.

  In this photonic crystal waveguide, three layers having significantly different refractive index differences are stacked, and the photonic crystal is formed in the layer where the core 2 is formed. Therefore, the upper and lower confinement is the same as the high refractive index difference optical waveguide. The structure is used. Further, by forming the end face 5 and forming the lens 6 whose portion is the light collecting position, the same effect as described above can be obtained. In other words, the NA of the optical waveguide can be as large as that of the conventional optical waveguide. Therefore, the sum of the angle given by the NA and the angle given by the NA of the lens is 90 ° or more, so that highly efficient light can be obtained. Achieving a bond is possible.

[Tenth embodiment]
(Optical coupling element array structure)
An example of the tenth embodiment of the optical coupling element (array structure) of the present invention is shown in FIG. FIG. 10A shows a top view, and FIG. 10B shows a side view.

  In the lens layer 7, a group of lenses 6 is formed on the optical waveguide layer 4. An optical waveguide 4 composed of a core 2 and a clad 3 is formed in the optical waveguide layer, and has a plurality of end faces 5. The core 2 of the optical waveguide 4 is formed on the same plane, and the clad 2 is made of a common material (same material). The lenses 6 are formed so that the condensing position of the lens 6 is in the vicinity of the end face 5 of the core, and the lenses 6 are arranged so as to be coupled (in other words, having a lens coupling portion). Here, the lenses 6 are densely arranged, whereas the end face 5 of the optical waveguide is arranged at the condensing position of each lens.

  By adopting such a structure, it is possible to form a structure having a plurality of sets of optical coupling elements that output the light transmitted through each optical waveguide in a concentrated manner. Further, by expanding the beam radius of light, it is possible to input to the optical waveguide at the same time. Further, since the optical waveguide is a high refractive index difference optical waveguide, it can have a radius of curvature on the order of microns, so that it is possible to form a free optical coupling element wiring even if lenses are integrated at high density. . In addition, since strong optical confinement is possible, if the respective optical waveguides are separated by about 10 times the width of the core, light can be coupled without interaction.

  For example, in the case of an optical waveguide having a relative refractive index difference of about 20%, the size of the core cross section is about 1 μm on a side when in single mode operation. It is possible to arrange them at a sufficient distance so as not to interact even if they are integrated with a lens radius of 10 μm when the lenses are constituted by the microlenses 6. In the present embodiment, in an array structure having a plurality of waveguide structures, the refractive index of the upper portion 10 and the lower portion 9 of the core 2 portion of the waveguide cladding portion is different as in the fifth or sixth embodiment, or The structure shown in the seventh embodiment in which a reflective layer (reflecting part) is provided between the waveguide and the substrate may be provided, and the lens layer 7 (the lens 6) is the structure of the third embodiment. May be adopted.

  Similarly to the eighth embodiment, a set of a waveguide 4, a lens 6, and a photoelectric conversion unit (a light receiving element or a light emitting element, a lens and a waveguide), and a reflection unit, a waveguide, a lens, and a photoelectric conversion unit are included. An array structure in which at least one set selected from a set, a set of a waveguide and a lens is combined, or a combination of two or more types is selected, or the waveguide 4 is selected from any of Embodiments 4 to 6 or 9. Thus, an array structure can be formed.

  Further, for example, the lens layer 7 can be formed using a photonic crystal employed in the waveguide shown in the ninth embodiment.

[Eleventh embodiment]
Examples of the optical coupling element (array structure) of the eleventh embodiment are shown in FIGS.

  As shown in FIG. 11A, a lens layer in which a plurality of optical waveguides 3-1, 3-2, 3-3... Are formed on a substrate 1 in a layered manner, and a lens 6 is formed thereon. 7 is provided. Here, the number of optical waveguides that are typically laminated is three, but the number of layers may be two or more, and the number of lens layers is not limited. The end faces 5-1, 5-2, 5-3,... Are formed on the cores of the optical waveguides formed in the respective waveguide layers so that the condensing position of the lens is on each end face. , Corresponding lenses 61, 62, 63,.

  The width in the thickness direction is about 1 μm in the case of a high refractive index difference optical waveguide, so if it is about three layers, the misalignment of the condensing point can be covered even if the shape of the lens is substantially the same. In order to further increase the optical coupling efficiency, the condensing efficiency decreases when the focal length of the lens is the same, so the focal position of the lens is adjusted by adjusting the radius of curvature and refractive index of the lens. By adjusting, light can be coupled with high efficiency.

  Further, as shown in FIG. 11B, the focal position can be adjusted by adjusting the position of the same lens 6-1. The manufacturing method of the array structure shown in FIG. 2 repeats the process of forming the lens 6-1 after forming the core 2 and the clad 3 on the substrate, embedding with the clad material, forming the core again, and embedding with the clad material. It is possible to form a laminated structure by returning and forming it stepwise.

  Furthermore, in order to increase the coupling efficiency in the depth direction, a structure in which a coupling lens 6-2 is combined as shown in the figure may be used. With the structure as shown in FIG. 11B, the light between the lens 6-1 and the coupling lens 6-2 can be converted into parallel light, so that the coupling efficiency can be increased.

  Even in the array structure of this embodiment, the clad layer constituting the waveguide is configured as in the fifth embodiment in which the upper and lower portions of different refractive indexes are formed, or at least one of the upper and lower portions is continuously provided. In the fourth embodiment, the light scattering portion 8 is provided in the vicinity of at least one end of each of the end portions 5-1, 5-2,. As in the seventh embodiment, a light reflecting portion is provided in an area including a portion between the substrate and the first waveguide layer or at least a portion where each optical waveguide layer intersects with the optical axis. It can be configured as in the eighth embodiment in which the photoelectric conversion layer is formed on the lens layer 7.

  Furthermore, the optical coupling element array structure of the present invention can also be configured by configuring at least one of the waveguide layers as in the ninth embodiment or appropriately configuring it. These structures can be manufactured by the manufacturing method described above or described later.

(Production method)
An example of a manufacturing method is shown below. Here, a manufacturing method of the structure of FIG. 1 is shown.

First, a substrate is prepared. As the substrate, a substrate having a flat surface such as quartz glass or silicon is prepared. The substrate may be an optical crystal such as lithium niobate or a ceramic such as PLZT {(Pb, La) (Zr, Ti) O ₃ }.

Next, in forming an optical waveguide on such a substrate, first, a cladding material is formed on the substrate. For this film formation, glass (SiO ₂ ) or the like is formed using a film forming apparatus capable of performing vapor deposition, sputtering, PVD, CVD, or the like.

  After forming the clad, the core is formed. The method of forming the core material in the same manner as the cladding is adopted, or the substrate on which the cladding is formed is flattened by polishing or the like, and the core material substrate is joined and thinned by polishing or the like. be able to. Furthermore, it is also possible to take a method in which ions are implanted, heated, and separated from the implantation interface. By these methods, a core layer having a thickness of submicron to several microns is formed.

  A core pattern is formed on the thin film by lithography and etching. For lithography, methods such as photolithography, electron beam lithography, and laser beam lithography can be employed. Furthermore, it is possible to use nanoimprint technology. The size of the core of the high refractive index difference optical waveguide may be about the wavelength of the light to be propagated, so that the size is about 1 micron and can be patterned by using these lithography techniques.

  After the core is formed, a clad material is formed again so as to cover the formed core pattern, and the formed substrate is flattened, and then a lens layer is formed. After the lens layer is formed as a lens material, a lens portion is formed by lithography and etching. At this time, alignment of the core end face and the lens is also performed at the same time. The alignment has a positional accuracy of about 100 nm to several microns, which can be sufficiently realized by patterning technology.

  Finally, the optical coupling element structure is completed by embedding a lens. For forming the lens, a method of forming a microlens by applying a solvent by an inkjet technique can also be used. In addition, the light diffusing element, the reflective portion (reflective layer), and the like can be formed and patterned as described above.

  According to the present embodiment, in the optical system of the high refractive index difference optical waveguide and the lens that is not on the optical axis, by arranging the high refractive index difference optical waveguide and the lens, a direction that is impossible with the conventional optical waveguide An optical coupling element capable of realizing optical coupling to can be provided. By forming the lens on the upper surface of the core, the optical coupling element can be formed more easily. Furthermore, coupling efficiency can be improved by providing a light scatterer in the core or clad of the optical waveguide. By forming the clad from a plurality of materials, changing the refractive index continuously, and further providing a reflection region, it is possible to couple light that has come to the opposite side of the lens to the lens. Further, by integrating the photoelectric conversion elements, it is possible to realize high functionality of the elements. By forming an array, it is possible to detect a plurality of optical signals at a time, and to combine light with an expanded beam spot size into a plurality of optical waveguides at a time.

  By using this technique, it is possible to reduce the size of the element, and it can be applied to an optical writing structure for a laser printer, an optical pickup for an optical disk, an optical integrated circuit for optical transmission, and the like.

It is a figure which shows the structure of the high refractive index difference optical coupling element of this embodiment, (a) is a top view, (b) is side sectional drawing (front view) which shows the cross-sectional structure in the surface containing a core. (C) is a front sectional view of a line including the optical axis of (b). It is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows the structure of the optical coupling element of this embodiment, (a) shows the case where an optical axis and the waveguide direction of a waveguide are not parallel. FIG. 4B is a side cross-sectional view showing the configuration of the optical coupling element when the end face of the waveguide is not 90 °. It is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows the structure of the optical coupling element of this embodiment, and the light in case the material which coat | covers a lens may have a low refractive index It is side surface sectional drawing which shows a coupling element. It is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows the structure of the optical coupling element of this embodiment, and is a side surface sectional view of an optical coupling element in the case of having a light-scattering body in a core end surface. . It is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows the structure of the optical coupling element of this embodiment, and is a side sectional view of the optical coupling element in case a lower clad has a low refractive index. It is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows the structure of the optical coupling element of this embodiment, and the refractive index of the upper clad of the clad which comprises a waveguide, or the lower clad is continuous It is side surface sectional drawing of the optical coupling element in the case of changing. It is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows the structure of the optical coupling element of this embodiment, and includes the layer structure by which the light reflection layer (or light reflection part) was installed in the board | substrate. It is side surface sectional drawing of the optical coupling element in a case. It is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows the structure of the optical coupling element of this embodiment, and sectional drawing of the optical coupling element in the case of including the layer structure in which the photoelectric conversion element was installed It is. (a) is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows the structure of the optical coupling element of this embodiment, and is sectional drawing of the coupling element using the optical confinement effect with the photonic crystal (B) is a cross-sectional view of a portion including a core cut in the horizontal direction along line CC in (a). It is a figure which shows the structural example of the array structure of the high refractive index difference optical coupling element of this embodiment, (a) is a top view, (b) is a core which shows the structure of the optical coupling element array structure of this invention. It is side surface sectional drawing of the coupling element which formed the lens group which shows the cross-sectional structure in the surface to include. It is sectional drawing of the array structure (coupling element array structure which installed the lens group and several optical waveguide) of the high refractive index difference optical coupling element of this embodiment, (a) is in the surface containing the core which shows the example It is side surface sectional drawing (front view) which shows a cross-sectional structure, (b) is side surface sectional drawing (front view) which shows the cross-sectional structure in the surface containing the core which shows another example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Core 3 Clad 4, 4-1, 4-2, 4-3 Optical waveguide layer 5, 5-1, 5-2, 5-3 End face 6, 61, 62, 63 Lens 6-2 Coupling lens 7 Lens layer 8 Light scatterer 9 Lower clad 10 Upper clad 11 Light reflecting layer 12 Photoelectric conversion element 13 Photoelectric conversion layer 14 Photonic crystal array part 15 Line defect

Claims (11)

Yes: a substrate having a core and a clad formed on said substrate, an optical waveguide having an end face of said core to provide a numerical aperture NA _1, the optical axis is not parallel to the light propagation direction of said optical waveguide An optical coupling element having a lens with a numerical aperture NA ₂ ,
The optical waveguide has a sum of a maximum light receiving angle that gives the numerical aperture NA ₁ and a maximum light receiving angle that gives the numerical aperture NA ₂ is 90 degrees or more, and has the condensing position of the lens in the vicinity of the end face. An optical coupling element characterized in that the lens is arranged on the optical coupling element.   The optical coupling element according to claim 1, wherein an optical axis of the lens is substantially orthogonal to a waveguide direction of the optical waveguide.   3. The optical coupling element according to claim 1, wherein the lens is formed on a clad of the optical waveguide provided on the substrate when the substrate is faced down. 4.   4. The optical coupling element according to claim 1, wherein a light scatterer is provided in the vicinity of an end face of the core condensed by the lens on the optical waveguide. 5.   5. The optical coupling element according to claim 1, wherein the clad forming the optical waveguide is composed of a plurality of portions having different refractive indexes.   6. The optical coupling element according to claim 5, wherein at least one of a plurality of refractive index portions of the clad forming the optical waveguide is made of a continuously changing material.   The optical coupling element according to claim 1, wherein a reflective region is provided between the optical waveguide and the substrate.   8. The optical coupling element according to claim 1, wherein a photoelectric conversion element is provided on a layer having the lens on a side in contact with the optical waveguide or on an opposite layer side.   9. The optical coupling element according to claim 1, wherein the core of the optical waveguide has a line defect structure, and the cladding is a photonic crystal optical waveguide having a photonic crystal array.   The optical coupling element according to claim 1, wherein the optical coupling element has an array structure.   The optical coupling element according to any one of claims 1 to 10, wherein the optical coupling element has a stacked array structure.

Images