JP2007047694A - Optical transmission line and optical element possessing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission line that has low loss and high efficiency and also to provide an optical element using the optical transmission line. <P>SOLUTION: The optical transmission line is provided with a light guiding optical transmitter composed of a first optical transmission medium and a second optical transmission medium which is made of a material having a refractive index lower than that of the first, which is arranged in the periphery of the first, and which projects in the direction horizontal and vertical relative to the first. This optical transmission line is characterized in that the part projecting in two vertical directions of the second optical transmission medium is each provided with a prescribed width to form a light confinement part and that the first optical transmission medium is provided with a first waveguide in which the cross section of a surface vertical to the light traveling direction is formed in a manner continuously increasing or decreasing in that traveling direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical transmission line in an optical member such as an optical fiber or an optical element.

  In recent years, an increase in information processing speed accompanying an increase in the amount of content transmitted in optical communication has further increased the necessity of speeding up optical information processing technology. Accordingly, an optical element that responds at high speed is required. ing.

  By the way, when the optical waveguide in the optical element has a plurality of transverse modes, the time width of the optical pulse traveling in the optical waveguide is widened due to the difference in propagation speed for each mode. As a result, the front and rear light pulses overlap on the time axis, causing crosstalk.

  Accordingly, an optical element used in high-speed optical communication is configured to include a single mode optical waveguide having only one transverse mode.

By the way, the mode field of such a single mode optical transmission line is generally very small. For example, the wavelength dispersion correcting element described in Japanese Patent Application No. 2004-315167 (patent application before publication) filed by the inventors. In this case, the cross-sectional area of the optical transmission line is about 0.5 μm × 1.0 μm. On the other hand, the cross-sectional area of the core in the single mode optical fiber is about 64 μm ² (= 4.5 × 4.5 × π).

  That is, the mode field of the single-mode optical transmission line is about 1/128 of the cross-sectional area of the optical fiber core. For this reason, when the optical fiber and the single mode optical transmission line are simply coupled, the optical energy is largely lost at the coupling portion. Therefore, increasing the optical coupling efficiency between the optical fiber and the single mode optical waveguide is an important issue in terms of reducing power consumption in optical communication.

  To deal with such a problem, for example, Patent Document 1 discloses that a low refractive index light transmission portion made of SiN having a reverse-tapered tip portion and a rectangular low shape made of SiON surrounding the high refractive index light transmission portion. A technique relating to an optical transmission line that effectively takes in light from an optical fiber by a coupling portion including a rectangular clad portion surrounding the optical transmission portion having a refractive index optical transmission portion is disclosed.

With such a structure, light taken from an optical fiber or the like can be converted from a large mode field in the optical fiber to a small mode field in a SiN waveguide having a high refractive index along the propagation direction.
International Publication No. 2004/038459 Pamphlet

  By the way, in high-speed optical communication, as described above, a single mode optical waveguide is used in order to avoid the spread of the time waveform of an optical pulse. At this time, light energy is efficiently transferred from the optical fiber to the single mode optical waveguide. In order to propagate, it is important to design the input and output to the single mode optical waveguide so that the mode conversion is such that only the fundamental mode exists in the single mode optical waveguide.

  However, in the optical transmission line disclosed in Patent Document 1 described above, as much optical energy as possible cannot be propagated to the fundamental mode in the single mode optical waveguide, and when taking in light from the optical fiber (or When connecting light to an optical fiber, the connection loss is large.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a low-loss and high-efficiency optical transmission line and an optical element using the optical transmission line.

  In order to solve the above-mentioned problem, the invention described in claim 1 is composed of a first optical transmission medium and a material having a refractive index lower than that of the first optical transmission medium. In an optical transmission line having an optical transmission unit for guiding light, which is configured by a second optical transmission medium arranged around and protruding in a horizontal direction and a vertical direction with respect to the first optical transmission medium The portions projecting in the two perpendicular directions of the second optical transmission medium each have a predetermined width to form a light confinement portion, and the first optical transmission medium is in the light traveling direction. The first waveguide section is formed so that the cross-sectional area of the vertical plane continuously increases or decreases in the light traveling direction.

  According to this, the second optical transmission medium prevents both the diffusion (loss) of light in the horizontal direction as well as the vertical direction with respect to the first optical transmission medium. Since the optical confinement of the axis can be realized, light with an ideal mode profile can be detected with a simple and compact structure, approximating the Gaussian profile, and a low loss and high efficiency optical transmission line Can be provided.

  In order to solve the above-described problem, according to a second aspect of the present invention, in the optical transmission line according to the first aspect, the first transmission medium is a second waveguide that is continuous with the first waveguide section. The second waveguide section is formed so that a cross-sectional area of a plane perpendicular to the light traveling direction is constant.

  According to this, the focusing of light can be stably focused by the second waveguide section, and light can be propagated more efficiently.

  In order to solve the above-described problem, a third aspect of the present invention is the optical transmission line according to the first aspect, wherein the first transmission medium is a third waveguide continuous with the first waveguide section. And the first waveguide section is formed such that a cross-sectional area of a plane perpendicular to the light traveling direction continuously increases in the light traveling direction, The third waveguide is formed such that a cross-sectional area of a plane perpendicular to the light traveling direction is continuously reduced in the light traveling direction, and the first waveguide is When the cross-sectional area of the surface perpendicular to the traveling direction is formed so as to continuously decrease in the light traveling direction, the third waveguide section is perpendicular to the light traveling direction. The cross-sectional area of a smooth surface is formed so as to continuously increase in the traveling direction of the light.

  According to this, the change in the effective refractive index can be reduced, and the wave can be guided with lower loss and higher efficiency.

  In order to solve the above-mentioned problem, an invention according to claim 4 is an optical element having an optical transmission line according to any one of claims 1 to 3, wherein the refractive index is higher than that of the first optical transmission medium. A fourth waveguide portion made of a material having a cross-sectional area of a plane perpendicular to the traveling direction of the light continuously increasing or decreasing in the traveling direction of the light. The second or third waveguide section of the first optical transmission medium is formed by being laminated on the fourth waveguide section.

  According to this, the change in the effective refractive index can be moderated, and light can be taken into the optical element more efficiently or can be emitted out of the optical element.

  In order to solve the above-mentioned problem, the invention according to claim 5 is the optical element according to claim 4, further comprising a photonic crystal layer that imparts chromatic dispersion fluctuation having predetermined dispersion characteristics to incident light. A part of the first optical transmission medium is partially stacked on the photonic crystal layer, and the photonic crystal layer includes a first material and a second material having different refractive indexes. The first substance is arranged in a plane in the second substance with a predetermined size and a predetermined arrangement interval, and the fourth waveguide section is formed of the second waveguide. It is characterized by being molded with a substance.

  According to this, the change in the effective refractive index can be reduced, and light can be taken into or taken out of the photonic crystal layer with much lower loss and higher efficiency.

  In order to solve the above-mentioned problem, the invention according to claim 6 is the optical element according to claim 5, wherein the fourth waveguide portion has the first substance having a predetermined size and a predetermined arrangement interval. The second material is formed in a planar shape.

  According to this, the change in the effective refractive index can be reduced, and light can be taken into or taken out of the photonic crystal layer with much lower loss and higher efficiency.

  In order to solve the above-mentioned problem, the invention according to claim 7 is the optical element according to claim 5 or 6, wherein the photonic crystal layer has a boundary surface between the photonic crystal layer and the optical transmission line. The first substance and the second substance are alternately arranged, and the first substance is made of a material having a lower refractive index than that of the first optical transmission medium.

  According to this, light entering the photonic crystal layer is prevented from being reflected by the end face of the photonic crystal layer, and light can be taken into the photonic crystal layer with even lower loss and higher efficiency. it can.

  In order to solve the above-mentioned problems, an invention according to claim 8 is the optical element according to any one of claims 4 to 7, wherein the optical element is made of a material having a refractive index lower than that of the second optical transmission medium. The light confinement portion of one of the second optical transmission media is stacked on the first clad portion, and the photonic crystal layer includes the first clad portion and the second clad portion. The first clad portion and the second clad portion are stacked on a second clad portion, and are formed on the substrate.

  According to this, the optical element according to any one of claims 4 to 8 can be formed by being laminated on the substrate.

  In order to solve the above-mentioned problem, the invention according to claim 9 is the optical element according to claim 8, wherein the fourth waveguide section is stacked on the second cladding section, and the second cladding section is provided. A part of the substrate on which the fourth waveguide part is laminated and a part of the substrate on which the second cladding part that laminates the fourth waveguide are laminated with respect to the light traveling direction. The cross-sectional area of a vertical surface is formed to continuously increase or decrease in the light traveling direction.

  According to this, the change in the effective refractive index can be reduced, and light can be taken into or taken out of the photonic crystal layer with much lower loss and higher efficiency.

  According to the present invention, the low-refractive-index optical transmission unit prevents both light diffusion (loss) in the horizontal direction as well as the vertical direction with respect to the high-refractive-index optical transmission unit. Therefore, it is possible to provide a low-loss and high-efficiency optical transmission line with a simple and compact structure.

  Hereinafter, the best embodiment of the present application will be described with reference to the drawings. The embodiment described below is an embodiment in the case where the optical transmission path of the present application and the optical element having the optical transmission path are applied to an optical element composed of a photonic crystal layer or the like.

<1. Configuration and function of optical element>
The configuration and function of the optical element according to this embodiment will be described.

  FIG. 1 is an explanatory view of an optical element according to the present embodiment, which has an optical transmission line as an input interface when light is input from an optical fiber to a single mode waveguide portion provided therein. is there.

  As shown in FIG. 1, the optical element 1 in the present embodiment is configured to have a coupling portion including a single mode waveguide portion and a beam focusing portion A and a beam focusing portion B as an optical transmission path. The optical pulse output from the optical fiber is first input to the coupling unit and propagates from the beam converging unit A to the beam converging unit B. The light is converged while suppressing the loss of light, and has the function of an optical element. It is propagated (input) to the single mode waveguide section. When an optical transmission path is configured as an output interface when outputting light from the optical element to the optical fiber, for example, the optical element is propagated in the reverse order. That is, light is propagated from the single mode waveguide section to the beam focusing section A via the beam focusing section B and input to the optical fiber.

  2 is an xz plane in FIG. 1 and is a cross-sectional view on the input side connected to the optical fiber of the optical element 1, and FIG. 3 is an xz plane in FIG. FIG. 4 is a cross-sectional view at the boundary surface of the beam converging part B, and FIG. 4 is a cross-sectional view at the xz plane in FIG.

  The optical element 1 includes a substrate 2, a clad portion 3 disposed on the substrate, a silicon layer 4 made of SOI (Silicon On Insulator) which is a base material of a photonic crystal layer described later, a ridge portion 5a, a slab A low refractive index optical transmission section (second optical transmission medium) 5 comprising a portion 5b and a trench section 5c, and a high refractive index optical transmission section functioning together with the low refractive index optical transmission section 5 as an optical transmission section in the present invention ( A first optical transmission medium) 6 and a photonic crystal layer 7 as constituent members.

  Hereinafter, specific configurations and functions of the respective constituent members in the coupling portion and the single mode waveguide portion of the optical element 1 will be described in detail.

  The substrate 2 is made of, for example, silicon having a refractive index of about 3.4.

  The clad part 3 functions as a first clad part and a second clad part in the present invention and has a lower refractive index than the low refractive index optical transmission part 5, for example, silicon oxide (having a refractive index of about 1.. 45) to be laminated on the substrate 2.

  The silicon layer 4 is composed of silicon layers 4a and 4b and is a base material of the photonic crystal layer 7. The silicon layer 4 is a material having a higher refractive index than the high refractive index optical transmission unit 6, for example, a refractive index of about 3. 4 is a thin film formed of silicon or the like.

  The photonic crystal layer 7 will be described more specifically with reference to FIG. FIG. 5A is a cross-sectional view of the optical element 1 in FIG. 1 taken along the xy plane, in which a ridge portion 5a and a slab portion 5b of the low refractive index optical transmission portion 5 described later are omitted. 5B is a cross-sectional view of the zy plane at the center of the high-refractive-index optical transmission unit 6 of the optical element 1 in FIG. 1, and is illustrated by a one-dot chain line when described with reference to FIG. It is sectional drawing in the DD section. In FIG. 5 (B), the clad part functioning as the first clad part in the present invention is shown as the clad part 3A in the clad part 3, and the clad part functioning as the second clad part in the present invention. Is shown as a cladding part 3B.

As shown in the figure, the photonic crystal layer 7 is laminated on the clad portion 3A as the second clad portion in the present invention. The photonic crystal layer 7 has a plurality of holes formed in a planar shape in a base material formed of silicon as a second material, and a refractive index (dielectric constant) different from the refractive index (dielectric constant) of the base material in the hole. Is filled with a silicon oxide film (SiO ₂ ) or the like as a first substance having a predetermined size and a predetermined arrangement interval to form a plane in silicon. The base material made of silicon is continuously formed with the silicon layers 4a and 4b. The planar shape means a planar shape or the like arranged in a two-dimensional direction in the photonic crystal layer 7 and has an effect as a photonic crystal that imparts chromatic dispersion fluctuation to the optical pulse. In the case of exhibiting, when the photonic crystal layer 7 has a curved surface or a shape in which a flat surface and a curved surface are combined in the manufacturing process, the arrangement along the shape is also included. It should be noted that the applicant has filed a patent application (Japanese Patent Application No. 2004-315167) regarding a dispersion compensation element relating to a photonic crystal layer using silicon as a base material.

  The silicon layer 4b formed of silicon which is the base material of the photonic crystal layer 7 functions as an example of the fourth waveguide portion in the present invention, and reliably guides light into the single mode waveguide. Therefore, the cross-sectional area (xz plane in FIG. 1) of the plane perpendicular to the light traveling direction has an inversely tapered shape that gradually and gradually increases in the light traveling direction (y direction in FIG. 1) ( In other words, it is formed protruding from the beam converging part B of the coupling part, and functions as an example of the fourth waveguide part in the present invention.

  Specifically, the silicon layer 4b has a small cross-sectional area of the silicon layer 4b at the boundary surface as shown in the sectional view of the boundary surface between the beam focusing portion A and the beam focusing portion B in FIG. However, as shown in FIG. 1 and FIG. 5A, the cross-sectional area gradually increases, and finally, at the interface between the beam converging part B of the coupling part and the single mode waveguide part of FIG. As shown in the cross-sectional view, it can be seen that the photonic crystal layer 7 of the single mode waveguide portion is integrated.

  On the output side, if the silicon layer 4b, which is the base material of the single mode waveguide, is formed so that the cross-sectional area has a forward tapered shape that gradually and gradually decreases in the light traveling direction. Good.

  The low refractive index optical transmission unit 5 functions as an optical transmission unit in the present invention together with the high refractive index optical transmission unit 6 and has a lower refractive index than the high refractive index optical transmission unit 6, for example, a refractive index of about 1. 2 is formed around the high refractive index light transmission section 6 in the beam focusing section A of the coupling section, and is shown in FIG. Thus, the ridge portion 5a, the slab portion 5b, and the trench portion 5c project in the horizontal direction (x direction in FIG. 1) and the vertical direction (z direction in FIG. 1). Then, the trench portion 5c is laminated on the cladding portion 3 (illustrated as the cladding portion 3B in FIG. 5B) as the first cladding portion in the present invention.

  Further, the ridge portion 5a and the trench portion 5c, which are portions protruding in two directions perpendicular to the high refractive index optical transmission portion 6 (z direction in FIG. 1), each have a predetermined width to confine light. Configured to function as a light confinement section.

  That is, for example, when the light input to the optical element 1 is an optical pulse output from a single mode fiber having a core diameter of 8 μm (micrometer), a cladding diameter of 125 μm, and a relative refractive index difference of 0.34%, As shown in FIG. 2, the width of the ridge portion 5a is preferably about 6.5 μm, and the width of the trench portion 5c is preferably about 12.5 μm. This makes it possible to confine light simultaneously in the x and z directions in FIG.

  FIG. 2 shows a design example of each component when guiding the light pulse output from the single mode fiber into the single mode waveguide with low loss and high efficiency. The size of the member and the size ratio between the constituent members are not limited to the design example, but the incident beam diameter of the light pulse and the refractive index of the material used for each constituent member (more specifically, each constituent It can be set to an optimum size according to the ratio of the refractive index of the material used for the member.

  The high refractive index optical transmission unit 6 functions as an optical transmission unit in the present invention together with the low refractive index optical transmission unit 5 and is made of, for example, silicon nitride whose refractive index is adjusted to about 2.0. In the beam converging part A, the cross-sectional area of the plane perpendicular to the light traveling direction (xz plane in FIG. 1) continuously and gradually increases in the light traveling direction (y direction in FIG. 1). It is formed (etched) in a tapered shape and functions as an example of the first waveguide section in the present invention. When the optical transmission line of the present invention is applied to the output side of the optical element, the cross-sectional area is formed (etched) in a forward tapered shape that gradually and gradually decreases in the light traveling direction.

  The high-refractive-index light transmission unit 6 is formed so that the cross-sectional area of the surface perpendicular to the light traveling direction is constant in the light traveling direction in the beam converging unit B continuous with the beam converging unit A. And functions as an example of the second waveguide in the present invention. Further, a part of the high refractive index light transmission unit 6 is partially laminated on the photonic crystal layer 7. More specifically, as illustrated in FIG. 5A, the high-refractive-index optical transmission unit 6 is stacked at the central portion of the photonic crystal layer 7 in the single mode waveguide unit.

  With such a configuration, as the light propagates (advances), the cross-sectional area of the high-refractive-index optical transmission unit 6 increases, and light is confined in the high-refractive-index optical transmission unit 6 and more refracted. The mode field expands so as to be drawn to the silicon layer 4b formed (etched) in the inversely tapered shape of the photonic crystal layer 7 having a high rate.

  Then, the cross-sectional area of the silicon layer 4b formed in the inversely tapered shape of the photonic crystal layer 7 increases, and the center of the light beam moves to the silicon layer 4b formed in the inversely tapered shape of the photonic crystal layer 7. Go. In other words, light is freely guided by the difference in refractive index of each material forming each component of the low refractive index light transmission unit 5, the high refractive index light transmission unit 6, and the silicon layer 4b of the photonic crystal layer 7. It becomes possible to do.

  Therefore, before inputting to the optical element 1, that is, in the optical fiber, by the portion formed in the reverse taper shape of the high refractive index optical transmission unit 6 and the silicon layer 4b formed in the reverse taper shape of the photonic crystal layer 7. It can be configured such that the light beam having a Gaussian shape is gradually guided to the mode shape in the single mode waveguide portion 7.

  As described above, the beam converging portion A of the coupling portion as the optical transmission path is composed of the high refractive index light transmission portion 6 and the low refractive index light transmission having a lower refractive index than the high refractive index light transmission portion 6. 1, and a low refractive index light transmission section 5 is arranged around the high refractive index light transmission section 6, and two directions perpendicular to the high refractive index light transmission section 6 (z direction in FIG. 1). Since the ridge portion 5a and the trench portion 5c projecting to the low refractive index optical transmission portion 5 are provided in the low refractive index optical transmission portion 6, light can be confined in the vertical direction with respect to the high refractive index optical transmission portion 6. Further, since the ridge portion 5a and the trench portion 5c are formed with a predetermined width, both the diffusion (loss) of light in the horizontal direction (x direction in FIG. 1) with respect to the high refractive index optical transmission portion 6 can be prevented. In addition, it is possible to realize light confinement around the high refractive index optical transmission unit 6 as an axis. Furthermore, since the high refractive index optical transmission unit 6 is formed in a reverse taper shape, light can be gradually guided into the optical element.

  Further, in the beam converging part B that is continuous with the beam converging part A of the coupling part as an optical transmission path, the cross section of the surface of the high refractive index optical transmission part 6 perpendicular to the light traveling direction is constant. Thus, the light can be stably focused and the light can be propagated with high stability.

  FIG. 6 is another example of a cross-sectional view of the zy plane in FIG. 1 at the center of the high refractive index optical transmission unit 6. Thus, the ridge portion 5a of the low refractive index optical transmission portion 5 may not be provided in the single mode waveguide portion.

<2. Profile comparison>
FIG. 7 shows a comparative experiment example of mode profiles of light output from the optical element according to the prior art and the optical element according to the present embodiment.

  In this experiment, a light pulse output from a single mode fiber having a core diameter of 9 μm, a clad diameter of 125 μm, and a relative refractive index difference of 0.34% is input to and output from the optical element according to the prior art and the optical element according to the present embodiment. 1 is a mode profile in the x-axis direction in FIG.

  In FIG. 7, the solid line is the mode profile of the light propagated through the optical element in the present embodiment, the broken line is the mode profile of the light propagated through the optical element using the rectangular optical transmission line according to the prior art, and the dotted line Is the mode profile of the light output from the single mode fiber.

  As shown in the figure, by using the optical element of the present embodiment, it is possible to detect light having an ideal mode profile that approximates a Gaussian profile that is an ideal profile of light intensity distribution.

  As described above, the optical transmission line used in the optical element according to the present embodiment includes the high refractive index optical transmission unit 6 and the low refractive index optical transmission unit having a lower refractive index than the high refractive index optical transmission unit 6. 5 and a ridge portion 5a and a trench portion 5c projecting in a direction perpendicular to the high refractive index light transmission portion 6 are provided in the low refractive index light transmission portion 5, and the ridge portion 5a and the trench portion 5c are further provided. Since it is formed with a predetermined width, it is possible to confine light by gradually changing the effective refractive index along the light propagation direction without arranging a cladding portion for enclosing these light transmission portions in the light transmission path. Can be performed.

  The high-refractive-index light transmission unit 6 is formed so that the cross-sectional area of the surface perpendicular to the light traveling direction is constant in the light traveling direction in the beam converging unit B continuous with the beam converging unit A. Therefore, it is possible to stably focus the light and propagate the light with high stability.

  When such an optical transmission path is used for an optical element such as the optical element 1, the beam converging unit B has a higher refractive index than the high refractive index optical transmission unit 6 included in the optical element on the silicon layer 4b. In addition, since the high refractive index optical transmission unit 6 is laminated, the light from the coupling unit can be guided to the photonic crystal layer 7 of the single mode waveguide unit with low loss and high efficiency. Therefore, light can be taken into the optical element more efficiently.

  At this time, since the silicon layer 4b has a reverse taper shape (the output end is a forward taper shape), the change in the effective refractive index is moderated, and the light from the coupling portion is singled with a further low loss and high efficiency. It can be incorporated into the photonic crystal layer 7 of the mode waveguide portion.

  The optical element described above can also be applied as an optical element on the output side by simply changing the tapered shape forward / reversely by simply changing the shape of the high refractive index light transmission unit 6 or the silicon layer 4b.

  Therefore, according to the present embodiment, light can be input and output into the element with low loss and high efficiency at the input and output ends thereof, so that the light is simple and does not require difficult alignment. The best optical element that can be connected to a fiber or the like can be provided.

<3. Other variants>
3-1. Other Modifications of the Coupling Unit Next, other modifications of the high refractive index optical transmission unit 6 and the silicon layer 4b in the coupling unit will be described.

Variant 1
In the embodiment described above, the high-refractive-index light transmission unit 6 is formed in an inversely tapered shape in the beam converging unit A, and the cross-sectional area of the surface perpendicular to the light traveling direction in the beam converging unit B is the light traveling direction. However, the present invention is not limited to this, and the high-refractive-index optical transmission unit 6 can be formed in a forward tapered shape in the beam converging unit B so as to function as the third waveguide unit in the present invention. It is.

  More specifically, as shown in FIG. 8, the cross-sectional area of the surface of the high-refractive-index optical transmission unit 6 perpendicular to the light traveling direction in the beam converging unit B continuously decreases in the light traveling direction. To form.

  According to this, the change in the mode profile, that is, the change in the effective refractive index at the boundary between the beam focusing part A and the beam focusing part B can be reduced, and the light from the coupling part can be further reduced in loss and high. Since light can be efficiently guided to the photonic crystal layer 7 of the single mode waveguide portion, light can be taken into the optical element more efficiently. Further, if the above configuration is used at the output end of the optical element, light can be emitted more efficiently to the outside of the optical element.

Variant 2
Further, in the above-described embodiment, the silicon layer 4b formed in the reverse tapered shape of the photonic crystal layer 7 is formed only by silicon which is the base material of the photonic crystal layer 7, but not limited to this, the silicon layer 4b is formed of silicon. It is also possible to form holes filled with a silicon oxide film (SiO ₂ ) or the like in the formed silicon layer 4b in a planar shape with a predetermined size and a predetermined arrangement interval.

More specifically, as shown in FIG. 9, a hole filled with a silicon oxide film (SiO ₂ ) or the like of the photonic crystal layer 7 is formed also in the silicon layer 4b.

  According to this, the change in the effective refractive index can be reduced at the boundary between the beam converging part B and the single mode waveguide part, and the light from the coupling part can be united with even lower loss and higher efficiency. Since light can be guided (propagated) to the photonic crystal layer 7 in the mode waveguide portion, light can be taken into the optical element more efficiently. Further, if the above configuration is used at the output end, it is possible to emit light to the outside of the optical element more efficiently.

3-2. Next, other modifications of the single mode waveguide section will be described.

Variant 3
In the embodiment described above, the photonic crystal layer 7 is simply arranged in the single mode waveguide portion so as to be continuous with the beam converging portion B of the coupling portion. 7 may be configured such that silicon, which is a base material of the photonic crystal layer 7, and a silicon oxide film (SiO ₂ ) are alternately arranged at the boundary surface between the coupling portion 7 and the beam focusing portion B. .

  More specifically, as shown in FIG. 10, the line connecting the centers of the holes formed in the photonic crystal layer 7 is the boundary surface with the beam converging part B of the coupling part of the photonic crystal layer 7. Is more preferable.

Since the hole formed in the photonic crystal layer 7 is filled with a silicon oxide film (SiO ₂ ) having a refractive index lower than that of the high-refractive index optical transmission unit 6, light is transmitted at the end face of the photonic crystal layer 7. The phase can be shifted by λ / 4.

  This prevents light that is about to enter the photonic crystal layer 7 from the beam converging portion B of the coupling portion from being reflected from the end face of the photonic crystal layer 7, and further reduces the loss and increases the efficiency. Since light can be guided (propagated) to the photonic crystal layer 7 in the mode waveguide portion, light can be taken into the optical element more efficiently.

Variant 4
In the above-described embodiment, only the silicon layer 4b of the photonic crystal layer 7 is formed in an inversely tapered shape in the beam converging part B. However, the cladding part 3 (FIG. 5) as the second cladding part in which the silicon layer 4b is laminated. (B), a part of the clad part 3B and a part of the substrate 2 and a part of the clad part 3 on which the silicon layer 4b is laminated, The cross-sectional area of the surface perpendicular to the traveling direction may be formed in an inversely tapered shape, in other words, so as to continuously increase in the traveling direction of light.

  This will be described more specifically with reference to FIG. 11A is a cross-sectional view on the input side connected to the optical fiber of the optical element 1 according to the modified embodiment 4, and FIG. 11B is a cross-sectional view at the boundary surface between the beam focusing part A and the beam focusing part B of the optical element 1. FIG. 11C is a cross-sectional view of the optical element 1 in the beam converging part B, and FIG. 11D is a cross-sectional view of the single-mode waveguide part of the optical element 1.

  As shown in FIGS. 11A to 11D, in the beam converging portion B, the clad portion 3 and the substrate 2 also have a portion where the silicon layer 4b of the photonic crystal layer 7 is laminated in the same manner as the silicon layer 4b. It is formed (etched) to have a reverse taper shape.

  According to this, the change in the mode profile, that is, the change in the effective refractive index at the boundary between the beam focusing part A and the beam focusing part B can be reduced, and the light from the coupling part can be further reduced in loss and high. Since light can be efficiently guided (propagated) to the photonic crystal layer 7 of the single mode waveguide portion, light can be taken into the optical element more efficiently. Further, if the above configuration is used at the output end of the optical element, light can be emitted more efficiently to the outside of the optical element.

It is explanatory drawing of the optical element concerning this embodiment. 2 is a cross-sectional view on the input side connected to the optical fiber of the optical element 1. FIG. 2 is a cross-sectional view of a boundary surface between a beam focusing portion A and a beam focusing portion B of the optical element 1. FIG. 2 is a cross-sectional view of a single mode waveguide portion of the optical element 1. FIG. (A) It is sectional drawing of the xy plane of the optical element 1 in FIG. (B) is sectional drawing of the zy surface of the optical element 1 in FIG. It is sectional drawing of the zy plane of the optical element 1 in FIG. 1 in another example. It is the mode profile of the light output from the optical element by a prior art, and the optical element by this embodiment. It is explanatory drawing of the deformation | transformation form 1. FIG. It is explanatory drawing of the deformation | transformation form 2. FIG. It is explanatory drawing of the deformation | transformation form 3. FIG. It is explanatory drawing of the modification 4. (A) It is sectional drawing in the input end surface connected with the optical fiber of the optical element 1 in the modification 4. (B) It is sectional drawing in the interface of the beam focusing part A and the beam focusing part B of the optical element 1 in the modification 4. (C) It is sectional drawing in the beam condensing part B of the optical element 1 in the modification 4. FIG. (D) It is sectional drawing in the single mode waveguide part in the modification 4.

Explanation of symbols

1 Optical elements
2 Substrate
3 (3A, 3B) Clad part 4a, 4b Silicon layer
Reference Signs List 5 Low refractive index light transmission section 5a Ridge section 5b Slab section 5c Trench section 6 High refractive index light transmission section 7 Photonic crystal layer A, B Beam focusing section

Claims (9)

A first optical transmission medium and a material having a lower refractive index than that of the first optical transmission medium, disposed around the first optical transmission medium, and with respect to the first optical transmission medium In an optical transmission line having an optical transmission unit for guiding light composed of a second optical transmission medium protruding in a horizontal direction and a vertical direction,
Portions projecting in two perpendicular directions of the second optical transmission medium each have a predetermined width to form a light confinement portion;
The first optical transmission medium includes a first waveguide section formed so that a cross-sectional area of a plane perpendicular to the traveling direction of the light continuously increases or decreases in the traveling direction of the light. An optical transmission line characterized by that. The optical transmission line according to claim 1,
The first transmission medium has a second waveguide that is continuous with the first waveguide,
The second waveguide section is formed so that a cross-sectional area of a plane perpendicular to the light traveling direction is constant. The optical transmission line according to claim 1,
The first transmission medium has a third waveguide section that is continuous with the first waveguide section,
When the first waveguide section is formed so that a cross-sectional area of a plane perpendicular to the light traveling direction continuously increases in the light traveling direction, the third waveguide is formed. The portion is formed such that a cross-sectional area of a plane perpendicular to the traveling direction of the light continuously decreases in the traveling direction of the light,
When the first waveguide section is formed so that a cross-sectional area of a plane perpendicular to the light traveling direction continuously decreases in the light traveling direction, the third waveguide is formed. The section is formed so that a cross-sectional area of a plane perpendicular to the traveling direction of the light continuously increases in the traveling direction of the light. In the optical element having the optical transmission line according to any one of claims 1 to 3,
A fourth waveguide portion made of a material having a higher refractive index than the first optical transmission medium;
The fourth waveguide part is formed such that a cross-sectional area of a plane perpendicular to the light traveling direction continuously increases or decreases in the light traveling direction,
The optical element, wherein the second or third waveguide part of the first optical transmission medium is formed on the fourth waveguide part. The optical element according to claim 4,
It has a photonic crystal layer that imparts chromatic dispersion variation having predetermined dispersion characteristics to incident light,
A portion of the first optical transmission medium is partially stacked on the photonic crystal layer; and
The photonic crystal layer is composed of a first material and a second material having different refractive indexes, and the first material is arranged in a planar shape in the second material at a predetermined size and a predetermined arrangement interval. Formed, and
The optical element, wherein the fourth waveguide section is formed of the second substance. The optical element according to claim 5, wherein
The optical element, wherein the fourth waveguide section is formed by arranging the first substance in a planar shape in the second substance with a predetermined size and a predetermined arrangement interval. The optical element according to claim 5 or 6,
The first material and the second material of the photonic crystal layer are alternately arranged at the interface between the photonic crystal layer and the optical transmission path; and
The optical element, wherein the first substance is made of a material having a refractive index lower than that of the first optical transmission medium. The optical element according to any one of claims 4 to 7,
A first clad part and a second clad part made of a material having a refractive index lower than that of the second optical transmission medium;
One of the light confinement portions of the second optical transmission medium is stacked on the first cladding portion,
The photonic crystal layer is stacked on the second cladding part,
The optical element, wherein the first clad part and the second clad part are stacked on a substrate. The optical element according to claim 8, wherein
The fourth waveguide section is stacked on the second cladding section;
A part of the second clad part on which the fourth waveguide part is laminated and a part of the substrate on which the second clad part on which the fourth waveguide is laminated are laminated on the light. An optical element, wherein a cross-sectional area of a surface perpendicular to the traveling direction of the light beam is continuously increased or decreased in the traveling direction of the light.

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