JP5658894B2 - Optical element - Google Patents

Description

  The present invention relates to an optical element having an optical waveguide using a semiconductor as a core.

  The amount of information transmitted by optical communication is steadily increasing. To cope with this, measures are being taken such as (I) increasing the transmission speed of signals and (II) increasing the number of channels of wavelength division multiplexing communication.

  In optical communication, optical signals are transmitted using optical pulses. Therefore, regarding (I), since the interval between the optical pulses is narrowed, it is important to control the time waveform of the optical pulse. In an optical fiber that is a transmission path, the time width of an optical pulse is increased as it propagates through the optical fiber due to chromatic dispersion in which the propagation speed varies depending on the wavelength of light. For this reason, a chromatic dispersion compensation technique is required in which an optical element having a wavelength dispersion opposite in sign to that of an optical fiber is provided in the optical fiber transmission line, and the chromatic dispersion of the optical pulse after propagating through the transmission line is removed. Become.

  On the other hand, if the countermeasure of (II) is advanced, the number of optical components increases and the transmission path becomes complicated, resulting in a problem that the optical communication equipment is increased in size, complexity, and cost.

In order to avoid the increase in size and complexity of optical communication equipment, it is necessary to reduce the size of components such as equipment parts and circuits that make up the equipment, and also to reduce the number of components by integrating the miniaturized components. is necessary. In order to reduce the size of the optical component, it is essential to reduce the size of the optical element that is a basic element constituting the optical component. Optical elements for optical communication are often configured using optical waveguides. For this reason, downsizing the optical waveguide is important in promoting downsizing of optical components. In order to reduce the size of the optical waveguide, it is essential to use a material having a high refractive index such as silicon (Si). This is because the wavelength of light in the medium is inversely proportional to the refractive index of the medium, and the higher the refractive index, the smaller the dimensions such as the core width of the optical waveguide. The refractive index of Si is about 3.5, which is 2.3 times or more that of silica (SiO ₂ ) (about 1.5). Since a high refractive index material such as Si is formed on a flat substrate, it is easy to couple a plurality of optical waveguides and is suitable for the purpose of integrating a plurality of optical components.

  In order to avoid an increase in the cost of optical components, it is important to reduce the manufacturing cost of the optical element. If the optical waveguide is downsized, the raw material cost per optical element is reduced, and the unit price can be reduced. Since a high refractive index material such as Si is formed on a flat substrate, a large area substrate can be used to manufacture a large number of optical elements on a single substrate, thereby further reducing manufacturing costs. become.

  Under such circumstances, an optical element using a silicon optical waveguide as shown in Patent Document 1 has been proposed. Non-Patent Document 1 discloses that a voltage is applied to a silicon optical waveguide to electrically control optical characteristics.

Republished WO2007-91465

Richard A. Soref et. Al. “Electrooptical Effects in Silicon”, IEEE Journal of Quantum Electronics, vol. QE-23, No. 1, January 1987

  In a single mode optical waveguide composed of a core of a single material, a part of the optical waveguide has a variable mechanism such as disclosed in Patent Document 1 to change the refractive index by applying a voltage to the optical waveguide. Devices with variable optical properties have been realized. In this case, a semiconductor core region whose refractive index is variable by applying a voltage, and a core region whose refractive index is not variable other than that (transmission path to other functional units on the same integrated circuit, optical elements outside the element, etc. In addition, a leakage current is generated via a core region where the refractive index is not variable.

  The present invention has been made in view of such circumstances, and a refractive index is variable at a connection portion between a semiconductor core region whose refractive index is variable by applying a voltage and a core region whose refractive index is not variable. An object of the present invention is to provide an optical element capable of reducing a leakage current passing through a core region that is not.

In order to solve the above-described problems, the present invention provides an optical element having a semiconductor core for guiding light, and an insulating gap extending along the light guiding direction at the center in the width direction of the core. The core includes, as a partial region, a separation region that is electrically separated by the gap portion in a direction orthogonal to the light guiding direction, and the separation region includes a first conductivity type first portion. A semiconductor core region; a second semiconductor core region of a second conductivity type disposed opposite to the first semiconductor core region across the gap portion; and a first adjacent to the first semiconductor core region in a light guiding direction . a third semiconductor core region of the second conductivity type, adjacent in the guiding direction of the second semiconductor core region and a light, first of the first conductivity type disposed facing each other across the gap portion and the third semiconductor core region 4 semiconductor core region is a partial region Included, the second conductivity type, wherein the first conductivity type is the opposite polarity, the optical element wherein the first semiconductor core region and the second electrode for voltage application to the semiconductor core region is connected provide.

The present invention is an optical element having a semiconductor core that guides light, and has an insulating gap portion extending along a light guiding direction at a central portion in the width direction of the core. , Including a separation region electrically separated in a direction orthogonal to the light guide direction by the gap portion, the separation region including a first semiconductor core region of a first conductivity type, and the first A second-conductivity-type second semiconductor core region disposed opposite to the semiconductor core region with the gap therebetween, and a non-polar third semiconductor core region adjacent to the first semiconductor core region in the light guiding direction; The non-polar fourth semiconductor core region adjacent to the second semiconductor core region in the light guiding direction and disposed opposite to the third semiconductor core region with the gap portion interposed therebetween is included as a partial region. and the second conductivity type, said first The conductivity type are opposite polarity, to provide an optical element wherein the first electrode of the voltage applied to the semiconductor core region and said second semiconductor core region are connected.

  In the optical element according to the aspect of the invention, it is preferable that the core has a non-separation region that does not include the gap portion in a cross section orthogonal to the light guide direction at a position adjacent to the separation region in the light guide direction. .

  In the optical element of the present invention, the core includes a polarity inversion region including a plurality of semiconductor core regions arranged so that the first conductivity type and the second conductivity type are alternately switched along the outer periphery of the gap portion. It is desirable to include it as a partial area.

  In the optical element according to the aspect of the invention, the polarity inversion region may be a second side that bypasses the tip of the gap part from the first side parallel to the light guiding direction of the gap part and faces the first side. It is desirable that it is provided in the end region of the gap portion leading to

  In the optical element of the present invention, the polarity inversion region is provided in the entire outer peripheral region of the gap portion from the first semiconductor core region to the second semiconductor core region through the end region of the gap portion. It is desirable.

  In the optical element according to the aspect of the invention, it is preferable that the core includes the polarity reversal region and the nonpolar semiconductor core region adjacent to the polarity reversal region and the outer periphery of the gap portion as partial regions.

  In the optical element of the present invention, the core extends from a first side parallel to the light guiding direction of the gap part to a second side that bypasses the tip part of the gap part and faces the first side. It is desirable that the end region of the gap portion includes a nonpolar semiconductor core region as a partial region.

  In the optical element of the present invention, it is desirable that the non-separation region includes a pair of semiconductor core regions having opposite polarities adjacent to each other in a direction orthogonal to the light guiding direction as partial regions.

  In the optical element of the present invention, it is desirable that the non-isolation region has a nonpolar semiconductor core region.

  In the optical element of the present invention, in the separation region, a conductive block composed of a pair of semiconductor core regions having opposite polarities arranged opposite to each other with the gap portion interposed therebetween has a polarity of the semiconductor core region of the conductive block. It is desirable that a plurality of light sources are provided along the light guiding direction so that the light sources are alternately switched along the light guiding direction.

  In the optical element of the present invention, the portion of the gap that separates the first semiconductor core region and the second semiconductor core region is refracted more than both the first semiconductor core region and the second semiconductor core region. A portion that is made of a material having a low rate and separates the third semiconductor core region and the fourth semiconductor core region of the gap portion is refracted more than any of the third semiconductor core region and the fourth semiconductor core region. It is desirable that the material is made of a material having a low rate.

  In the optical element of the present invention, each of the first semiconductor core region and the second semiconductor core region has a rib shape in which a thickness of a portion in contact with the gap portion is formed to be thicker than other portions, It is desirable that the electrode is connected to the thin portions of the first semiconductor core region and the second semiconductor core region.

In the optical element according to the aspect of the invention, it is preferable that the gap portion is formed of an insulator or a nonpolar semiconductor.
The present invention is an optical element having a semiconductor core that guides light, and has an insulating gap portion extending along a light guiding direction at a central portion in the width direction of the core. The separation region includes a separation region electrically separated in a direction perpendicular to the light guiding direction by the gap portion, and the separation region includes the first to fourth semiconductor regions that guide light as the partial region. The first semiconductor region is of a first conductivity type, the second semiconductor region is of a second conductivity type having a polarity opposite to that of the first conductivity type, and the first semiconductor region and the gap portion are interposed therebetween. Opposed, the third semiconductor region is of a second conductivity type , adjacent to the first semiconductor region in the light guiding direction, the fourth semiconductor region is of a first conductivity type , and the second semiconductor region Adjacent to each other in the light guiding direction and the third semiconductor region Across the gap portion and is opposed to provide an optical element which is a voltage can be applied between the first semiconductor region and the second semiconductor region.
The present invention is an optical element having a semiconductor core that guides light, and has an insulating gap portion extending along a light guiding direction at a central portion in the width direction of the core. The separation region includes a separation region electrically separated in a direction perpendicular to the light guiding direction by the gap portion, and the separation region includes the first to fourth semiconductor regions that guide light as the partial region. The first semiconductor region is of a first conductivity type, the second semiconductor region is of a second conductivity type having a polarity opposite to that of the first conductivity type, and the first semiconductor region and the gap portion are interposed therebetween. Opposed, the third semiconductor region is nonpolar , adjacent to the first semiconductor region in the light guiding direction, the fourth semiconductor region is nonpolar , and the second semiconductor region is light-guided. Adjacent in the wave direction and the third semiconductor region and the It is opposed across the cap portion, to provide an optical element which is a voltage can be applied between the first semiconductor region and the second semiconductor region.

  According to the optical element of the present invention, an insulating gap is provided between the first semiconductor core region and the second semiconductor core region. The gap portion is formed longer than a portion where the first semiconductor core region and the second semiconductor core region whose refractive index is variable are opposed to each other, and a part of the gap portion includes the third semiconductor core region and the fourth semiconductor layer whose refractive index is not variable. Projecting to the semiconductor core region side. Therefore, when a voltage is applied between the first semiconductor core region and the second semiconductor core region, the first semiconductor bypasses the gap, that is, passes through the third semiconductor core region and the fourth semiconductor core region. Leakage current generated between the core region and the second semiconductor core region can be reduced.

It is explanatory drawing of the optical element of 1st Embodiment. It is sectional drawing which cut | disconnected the composite core optical waveguide by the plane perpendicular | vertical to the waveguide direction of light. It is a simulation result which shows distribution of the light intensity in a 3rd core. It is sectional drawing which cut the intermediate | middle optical waveguide by the surface parallel to a board | substrate. It is sectional drawing which cut the single core optical waveguide by the plane perpendicular | vertical to the waveguide direction of light. It is a figure which shows the leak characteristic of the Example and comparative example of this invention. It is a figure which shows the example which applied the optical element to the Mach-Zehnder interferometer. It is explanatory drawing of the optical element of 2nd Embodiment. It is explanatory drawing of the optical element of 3rd Embodiment. It is explanatory drawing of the optical element of 4th Embodiment. It is explanatory drawing of the optical element of 5th Embodiment. It is sectional drawing which cut the optical element which employ | adopted the grating structure by the plane perpendicular | vertical to the light waveguide direction. It is sectional drawing which cut the intermediate | middle optical waveguide by the surface parallel to a board | substrate. It is a figure which shows the core which employ | adopted the grating structure, (a) is a top view, (b) is sectional drawing, (c) is a fragmentary perspective view.

  Embodiments of the present invention will be described below with reference to the drawings. In the embodiment described below, the optical element of the present application is applied to an optical waveguide having silicon (Si) as a core material.

  In the following drawings, an XYZ orthogonal coordinate system may be set, and the positional relationship of each member may be described with reference to the XYZ orthogonal coordinate system. In this case, the light guiding direction is referred to as the Y direction, the width direction of the optical waveguide orthogonal to the waveguide direction is referred to as the X direction, and the height direction orthogonal to the X direction and the Y direction is referred to as the Z direction. Since the optical waveguide is formed on the substrate, the X direction and the Y direction are directions parallel to the substrate, and the Z direction is a direction perpendicular to the substrate. In the following embodiments, the optical waveguide is a straight optical waveguide whose core extends in the Y direction, but it may be a curved optical waveguide having a curved core.

[First Embodiment]
FIG. 1 is an explanatory diagram of an optical element WG1 according to the first embodiment of the present invention. The optical element WG1 is optically connected between the single-core optical waveguide 10 which is a single-mode optical waveguide having a core made of a single material, the composite core optical waveguide 30 having a gap structure, and the optical element WG1. And an intermediate optical waveguide 20.

  The cores 11, 41, and 42 of the optical waveguides 10, 20, and 30 constitute three partial regions that are continuous in the Y direction of the core 1 that is formed on the lower cladding 6. The core 1 is configured as a band-shaped semiconductor layer having a longitudinal direction in the Y direction, and one end surface in the longitudinal direction is a first light incident / exit end surface, and the other end surface is a second light incident / exit end surface. . On one end side in the longitudinal direction of the core 1 (light guiding direction; Y direction), the longitudinal direction of the core 1 is in the center of the width direction of the core 1 (direction orthogonal to the light guiding direction; X direction). An insulating gap portion 40 extending along the core 1 is provided, and the gap portion 40 divides the region on one end side of the core 1 into two in a direction perpendicular to the longitudinal direction. The core 1 includes a separation region that is divided into two in the direction orthogonal to the light guiding direction by the gap 40 as described above, and one end surface in the longitudinal direction of the core 1 in the separation region. A part of the region including the (first light incident / exit end face) is the core 42, and a region including the remaining region divided into two is the core 41. The other end side of the core 1 is a non-separation region where the gap portion 40 is not provided, and a part of the non-separation region including the other end surface in the longitudinal direction of the core 1 (second light incident / exit end surface). The region is the core 11.

  The “light incident / exit end face” means a light incident end face or a light exit end face. When light is guided from the single core optical waveguide 10 side to the composite core optical waveguide 30 side, the light incident / exit end face on the single core optical waveguide 10 side is the light incident end face, and the composite core optical waveguide 30 side The light incident / exit end face is a light exit end face. When light is guided from the composite core optical waveguide 30 side to the single core optical waveguide 10 side, the light incident / exit end surface on the single core optical waveguide 10 side is the light output end surface, and the composite core optical waveguide 30 side The light incident / exit end face is a light incident end face. In the present embodiment, light is guided from the single core optical waveguide 10 side to the composite core optical waveguide 30 side, but this direction may be reversed.

  In the present embodiment, the intermediate optical waveguide 20 is provided as an interface between the single core optical waveguide 10 and the composite core optical waveguide 30, and the first composite core conductive portion 32 and the second composite core conductivity of the composite core optical waveguide 30 are provided. When a voltage is applied between the first and second composite core conductive portions 32 and 33, the first composite core from the surface facing the first composite core conductive portion 32 and the second composite core conductive portion 33 in a direction perpendicular to the light guiding direction. The first leakage current flowing between the conductive portion 32 and the second composite core conductive portion 33 and the intermediate optical waveguide adjacent to the first composite core conductive portion 32 and the second composite core conductive portion 33 An optical waveguide in which the second leakage current flowing between the first composite core conductive portion 32 and the second composite core conductive portion 33 via the 20 cores 41 is reduced is provided.

  Here, as the first intermediate core conductive portion 22 and the second intermediate core conductive portion 23 of the intermediate optical waveguide 20, the first composite core conductive portion 32 and the second composite core conductive portion 33 of the composite core optical waveguide 30 are used. This is an example of a semiconductor material having a polarity opposite to that of the semiconductor material.This is an example, and the present invention uses an intrinsic semiconductor as a high-resistance material as shown in another embodiment later, It is also possible to use an area composed of three or more areas.

  Next, an outline of each area will be described.

  The single core optical waveguide 10 is an optical waveguide composed of a core made of a single material. The single core optical waveguide 10 plays a role of guiding light from a portion having other functions to the composite core optical waveguide 30 having the gap structure of the present invention. The other function is a function using light, such as a light receiving and emitting device, an interferometer, and the like, and is a function that is essential to input or output light outside the functional element in use. This also includes functions required for connection with optical components outside the optical element, such as a mode field converter (MFC) (spot size converter). Examples of the structure include generally known silicon fine wire optical waveguides and rib optical waveguides.

  Here, “single” indicates a structure constituted by a core made of a material having a high refractive index and a clad made of a material having a low refractive index. It is used to distinguish it from “composite” in “composite core optical waveguide” and has a structure in which the core is not separated by a low refractive index material. For example, in a structure using silicon as a core material, a structure in which rectangular silicon is embedded in silica, or a structure in which silicon is a rib structure, a lower part is silica and an upper part is air or silica is known. Also, a structure having a second core having a lower refractive index than the first core around the first core is also included in the term “single core” in that the core is not separated. And

  A single core is an optical waveguide having a general structure and is used in various places. The intermediate optical waveguide of the present invention has a role of connecting the single core optical waveguide and the composite core optical waveguide having a gap structure, and both ends have the shape of the optical waveguide to be connected. As a result, it is possible to realize a device in which a composite core optical waveguide structure having a gap structure and a single core optical waveguide structure having no gap structure are fused.

  In the composite core optical waveguide 30, the first composite core conductive portion 32 and the second composite core conductive portion 33 are separated by the composite core gap portion 31 located in the center thereof, and light is spread across these regions. An optical waveguide having a composite core structure that propagates. The core 42 includes a first composite core conductive portion (first semiconductor core region) (first semiconductor region) 32 and a second composite core conductive portion (second semiconductor core region) that are separated with the composite core gap 31 interposed therebetween. ) (Second semiconductor region) 33 as a partial region. The composite core optical waveguide 30 is a single mode optical waveguide in which a single mode is propagated across the two partial regions.

  The composite core gap portion 31 is made of an insulating material having a lower electrical conductivity than the first composite core conductive portion 32 and the second composite core conductive portion 33, such as an insulator or an undoped nonpolar semiconductor. It is configured. The first composite core conductive portion 32 and the second composite core conductive portion 33 are electrically separated by a high resistance composite core gap portion 31, and the first composite core conductive portion 32 and the second composite core Since the first leak current flowing between the conductive portion 33 and the composite core gap portion 31 is reduced, a high voltage is generated between the first composite core conductive portion 32 and the second composite core conductive portion 33. It is possible to apply.

  For example, in the present embodiment, P-type and N-type silicon are used as the first composite core conductive portion 32 and the second composite core conductive portion 33, and a voltage is applied between the two, whereby the refractive index due to the carrier plasma effect is obtained. A device that variably controls optical characteristics by utilizing the change is realized. At this time, since the first composite core conductive portion 32 and the second composite core conductive portion 33 are separated by the composite core gap portion 31 having low electrical conductivity, the first leakage current is reduced, The effect of reducing the influence due to the increase in heat generation and reducing the power consumption itself can be obtained. Note that the change in refractive index due to the change in carrier density is described in Non-Patent Document 1.

  When the composite core gap portion 31 is made of a material having a refractive index lower than that of the first composite core conductive portion 32 and the second composite core conductive portion 33, a single unit without the composite core gap portion 31 is provided. Compared with a core optical waveguide made of a material, the manufacturing tolerance can be increased.

  The intermediate optical waveguide 20 is located between the single core optical waveguide 10 and the composite core optical waveguide 30 and connects the single core optical waveguide 10 and the composite core optical waveguide 30 with low loss. When a voltage is applied between the 30 first composite core conductive portion 32 and the second composite core conductive portion 33, the second leakage current generated in the single core optical waveguide 10 or the intermediate optical waveguide 20 is reduced. It is formed for the purpose of reducing.

  FIG. 2 is a cross-sectional view of the composite core optical waveguide 30 taken along the XZ plane. In this embodiment, an optical waveguide manufactured by processing based on an SOI substrate is shown. The substrate 5 is a substrate from which the optical element WG1 is manufactured. In the present embodiment, it is made of silicon (Si).

The lower clad 6 positioned on the upper portion of the substrate 5 is a material having a refractive index lower than that of the first composite core conductive portion 32 and the second composite core conductive portion 33. For example, in this embodiment, the lower clad 6 is an SOI substrate. The thermal oxide film (SiO ₂ ) is used as it is. The upper clad 7 has the same conditions as the lower clad 6. In the present embodiment, SiO ₂ is also used for the upper clad 7. As a material of the lower clad 6 and the upper clad 7, silicon oxynitride (SiO _x N _y ) or silicon nitride (Si _x N _y ) can be applied. For example, in silicon oxynitride SiO _x N _y By controlling the composition ratio x: y, it is possible to control the refractive index in the manufacturing stage.

  The first composite core conductive portion 32 and the second composite core conductive portion 33 are each provided with P-type or N-type conductivity by appropriately adding impurities to a semiconductor material such as Si. Can do. For example, the first composite core conductive portion 32 may be a P-type region, the second composite core conductive portion 33 may be an N-type region, and the first composite core conductive portion 32 may be an N-type region. The conductive portion 33 may be a P-type region. When any one of the P-type and the N-type is the first conductivity type and the other is the second conductivity type, the first composite core conductive portion 32 is the first conductivity type, and the second composite core The conductive portion 33 may be the second conductivity type.

  An impurity (dopant) that imparts conductivity to the first composite core conductive portion 32 and the second composite core conductive portion 33 made of a semiconductor can be appropriately selected and used according to the base medium. For example, when the base medium is a group IV semiconductor such as silicon, a group III element such as boron (B) is used as an additive that imparts P-type polarity, and phosphorus (P) is used as an additive that imparts N-type polarity. And V group elements such as arsenic (As).

  The core 42 of the composite core optical waveguide 30 has a rib shape having a thick portion at the center and thin portions on both sides. In the example of FIG. 2, the core 42 has two ribs, which are a first composite core conductive portion 32 that is a first rib and a second composite core conductive portion 33 that is a second rib, as partial regions. Including. The first composite core conductive portion 32 and the second composite core conductive portion 33 are made of a material having a higher refractive index than the composite core gap portion 31.

  The first composite core conductive portion 32 and the second composite core conductive portion 33 have the same shape and shapes reversed in the horizontal direction. Specifically, the first composite core conductive portion 32 is located on a thin flat plate portion (thin plate portion) 32b and an edge of the flat plate portion 32b on the side of the composite core gap 31 and extends from the flat plate portion 32b to the upper clad. It is comprised from the thick convex part (thick board part) 32a which protrudes in 7 side. The second composite core conductive portion 33 is located on the thin flat plate portion (thin plate portion) 33b and the edge of the flat plate portion 33b on the composite core gap 31 side, and protrudes from the flat plate portion 33b to the upper clad 7 side. It is comprised from the thick convex-shaped part (thick board part) 33a. The convex portion 32 a and the convex portion 33 a are arranged to face each other with the both sides of the composite core gap portion 31 therebetween, and are in contact with the side surface of the composite core gap portion 31. The material constituting the convex portions 32a and 33a and the material constituting the flat plate portions 32b and 33b are the same.

The rib-type optical waveguide has a structure that does not affect the light propagation characteristics in a region sufficiently away from the thick convex portions 32a and 33a at the center, and the shape can be appropriately processed. For example, in this embodiment, an electrode pad (electrode) (not shown) is provided via the thin flat plate portions 32b and 33b, and a voltage is applied.
In the above embodiment, the configuration is shown in which the electrodes are connected to the flat plate portions 32b and 33b, respectively, but a voltage is applied between the first composite core conductive portion 32 and the second composite core conductive portion 33. The configuration for this is not limited to this. For example, a configuration in which a voltage is applied between the composite core conductive portions 32 and 33 by wirings electrically connected to the flat plate portions 32b and 33b is also possible.
Specifically, when the optical element WG1 is integrated, the composite core conductive portions 32 and 33 are connected by other devices electrically connected to the flat plate portions 32b and 33b of the composite core conductive portions 32 and 33. A voltage may be applied between them.

The composite core gap portion 31 is made of a high resistance material having a lower electrical conductivity than the first composite core conductive portion 32 and the second composite core conductive portion 33. In the present embodiment, SiO ₂ that is an insulator is used. By doing so, the first composite core conductive portion 32 and the second composite core conductive portion 33 are electrically connected to the separated electrode pads via the thin flat plate portions 32b and 33b, and a voltage is applied to the electrode pads. As a result, electric charges are stored in both side regions of the first composite core conductive portion 32 and the second composite core conductive portion 33 across the composite core gap portion 31, and a change in refractive index is induced by a change in carrier density, so that the optical element WG1. It becomes possible to change the optical characteristics of the. As the material of the composite core gap portion 31, the above-described silicon oxynitride (SiO _x N _y ), silicon nitride (Si _x N _y ), or nonpolar Si can also be applied.

FIG. 3 shows a simulation result calculated by the mode solver in the case where the composite core optical waveguide 30 configured as described above continues uniformly in the light guiding direction (Y direction). 3 shows that the upper clad 7, the lower clad 6, and the composite core gap portion 31 are made of SiO ₂ having a refractive index of 1.45, and the first composite core conductive portion 32 and the second composite core conductive portion 33 are made of refractive index 3. 2 is a contour diagram showing the light intensity distribution of the simulation result of the basic propagation mode when the dimensions of each part in FIG. 2 are t ₁ = 250 nm, t ₂ = 50 nm, W ₁ = 280 nm, and W ₂ = 160 nm. It is a thing. In addition, the interface of each material was described simultaneously for reference. At this time, the effective refractive index of the fundamental propagation mode was 2.1640.

  As shown in FIG. 3, the light propagating through the composite core optical waveguide is mainly confined in the convex portion of the composite core conductive portion. A part of the light oozes out to the flat plate part and the composite core gap part, but most of it is confined in the thick convex part, and sufficient confinement is performed in the width direction (X direction) of the core. I understand. For this reason, the convex portion whose carrier density changes when a voltage is applied becomes a portion where the light intensity is strong in the propagation mode, and the effective refractive index change in the propagation mode with respect to the refractive index fluctuation of the convex portion is increased. In addition, the structure of the pair of composite core conductive parts facing each other with the composite core gap part interposed therebetween has a capacitor-like structure in which a dielectric is sandwiched between conductive flat plates, thereby increasing the carrier density due to voltage application. It is done.

As shown in FIG. 3, in each composite core conductive portion (semiconductor core region), the range in which light is guided may not be the entire composite core conductive portion. That is, the range in which light is guided may be the entire composite core conductive portion or a part thereof.
Since the composite core conductive portion (semiconductor core region) may include a portion where light is not guided, the word “core” generally recognized as “a region where light propagates over the entire region”. Should not be construed as limited to this general concept.
That is, since the “core region” is a “region including a portion that guides light”, the “semiconductor core region” can also be referred to as a “semiconductor region” including a portion that guides light.

  FIG. 4 is an explanatory diagram illustrating the configuration of the intermediate optical waveguide 20. 4A is a cross-sectional view of the intermediate optical waveguide 20 taken along the XY plane, and FIG. 4B is a cross-section obtained by cutting the region 20a on the composite core optical waveguide 30 side of the intermediate optical waveguide 20 along the XZ plane. FIG. 4C is a cross section of the intermediate optical waveguide 20 in which the region 20b on the single core optical waveguide 10 side is cut along the XZ plane.

  As shown in FIG. 4A, the intermediate optical waveguide 20 is provided with an intermediate core gap portion 21 that is continuous with the composite core gap portion 31. The intermediate core gap portion 21, together with the composite core gap portion 31, separates part or all of the first core 42 and the second core 41 of the optical element WG1 in a direction (X direction) orthogonal to the light guiding direction. The unit 40 is configured.

  The intermediate core gap portion 21 of the present embodiment exists only in the region 20a of the core 41 on the composite core optical waveguide 30 side. When a pair of end faces facing each other in the light guiding direction of the intermediate core gap portion 21 are a first end face 21a and a second end face 21b, the second end face 21b on the composite core optical waveguide 30 side is the intermediate optical waveguide 20 and the composite core. The first end face 21 a on the single core optical waveguide 10 side is disposed on the side of the composite core optical waveguide 30 with respect to the connection interface between the intermediate optical waveguide 20 and the single core optical waveguide 10. Has been.

  As shown in FIG. 4B, in the region 20 a on the side of the composite core optical waveguide 30 of the intermediate optical waveguide 20, the intermediate optical waveguide 20 is composed of the core 41 by the intermediate core gap portion 21, similarly to the composite core optical waveguide 30. It has a gap structure separated into two. The intermediate optical waveguide 20 has a structure composed of three regions of an intermediate core gap portion 21, a first intermediate core conductive portion 22 located on both sides thereof, and a second intermediate core conductive portion 23. The core 41 includes a first intermediate core conductive portion (third semiconductor core region) (third semiconductor region) 22 and a second intermediate core conductive portion (fourth semiconductor core region) separated with the intermediate core gap portion 21 therebetween. ) (Fourth semiconductor region) 23 as a partial region. The intermediate optical waveguide 20 is a single mode optical waveguide in which a single mode is propagated across the two partial regions.

  The core 41 of the intermediate optical waveguide 20 has a rib shape having a thick portion at the center and thin portions on both sides thereof. In the example of FIG. 4B, the core partially includes two ribs, a first intermediate core conductive portion 22 that is a first rib and a second intermediate core conductive portion 23 that is a second rib. Include as an area. The first intermediate core conductive portion 22 and the second intermediate core conductive portion 23 are made of a material having a higher refractive index than the intermediate core gap portion 21.

  The first intermediate core conductive portion 22 and the second intermediate core conductive portion 23 have the same shape and shapes reversed in the horizontal direction. Specifically, the first intermediate core conductive portion 22 is positioned on the thin flat plate portion (thin plate portion) 22b and the edge on the intermediate core gap 21 side of the flat plate portion 22b, and is formed from the flat plate portion 22b to the upper clad. 7 is formed of a thick convex portion (thick plate portion) 22a protruding to the 7th side. The second intermediate core conductive portion 23 is located on a thin flat plate portion (thin plate portion) 23b and an edge of the flat plate portion 23b on the intermediate core gap 21 side, and protrudes from the flat plate portion 23b to the upper clad 7 side. It is composed of a thick convex portion (thick plate portion) 23a. The convex portion 22 a and the convex portion 23 a are disposed to face each other with both sides of the intermediate core gap portion 21 therebetween, and are in contact with the side surface of the intermediate core gap portion 21. The material constituting the convex portions 22a and 23a and the material constituting the flat plate portions 22b and 23b are the same.

  The intermediate core gap portion 21 is made of a high resistance material having a low electrical conductivity, such as an insulator or an undoped nonpolar semiconductor. In the case of the present embodiment, the composite core gap portion 31 of the composite core optical waveguide 30 is made of the same material, but may be made of a material different from the composite core gap portion 31. The first intermediate core conductive part 22 and the second intermediate core conductive part 23 are made of the same material as the core material constituting the first composite core conductive part 32 and the second composite core conductive part 33 (in the present embodiment). In this case, it is made of Si). In the first intermediate core conductive portion 22, an impurity having a polarity opposite to that of the first composite core conductive portion 32 adjacent in the light guiding direction is doped. In the second intermediate core conductive portion 23, An impurity having a polarity opposite to that of the second composite core conductive portion 33 adjacent in the light guiding direction is doped. That is, when the first composite core conductive portion 32 is P-type and the second composite core conductive portion 33 is N-type, the first intermediate core conductive portion 22 is N-type and the second intermediate core conductive portion 23 is. Is P-type, when the first composite core conductive portion 32 is N-type and the second composite core conductive portion 33 is P-type, the first intermediate core conductive portion 22 is P-type and second intermediate core The conductive portion 23 is N-type.

  As shown in FIG. 4C, in the region 20b of the intermediate optical waveguide 20 on the single core optical waveguide 10 side, the intermediate core gap is not provided, and the single core in which the core 41 is not separated by the gap structure. It has a structure (non-separation region). The core 41 in the region 20b is made of the same material as that of the first intermediate core conductive portion 22, and is formed integrally with the first intermediate core conductive portion 22. The third intermediate core conductive portion (fifth semiconductor core region) (the fifth semiconductor core region) (5 semiconductor region) 24 and the fourth intermediate core conductive portion (sixth semiconductor core region) (the sixth semiconductor core region) made of the same material as the second intermediate core conductive portion 23 and formed integrally with the second intermediate core conductive portion 23 6 semiconductor regions) 25 as partial regions, which have a connection interface parallel to the YZ plane and are in contact with each other.

  The core 41 in the region 20b has a rib shape having a thick portion at the center and thin portions on both sides. In the example of FIG. 4C, the core partially includes two ribs, a third intermediate core conductive portion 24 that is a first rib and a fourth intermediate core conductive portion 25 that is a second rib. Include as an area.

  The third intermediate core conductive portion 24 and the fourth intermediate core conductive portion 25 have the same shape and shapes reversed in the horizontal direction. Specifically, the third intermediate core conductive portion 24 is located on a thin flat plate portion (thin plate portion) 24b and an edge on the core central side of the flat plate portion 24b, and is on the upper clad 7 side from the flat plate portion 24b. It is comprised from the thick convex-shaped part (thick board part) 24a which protrudes in this. The fourth intermediate core conductive portion 25 is positioned on the thin flat plate portion (thin plate portion) 25b and the edge of the flat plate portion 25b on the core center side, and has a thickness protruding from the flat plate portion 25b to the upper clad 7 side. It is comprised from the thick convex part (thick board part) 25a. The material constituting the convex portions 24a and 25a and the material constituting the flat plate portions 24b and 25b are the same.

  The third intermediate core conductive portion 24 and the fourth intermediate core conductive portion 25 are made of the same material as the core material constituting the first intermediate core conductive portion 22 and the second intermediate core conductive portion 23 (in the present embodiment). In this case, it is made of Si). The third intermediate core conductive portion 24 is doped with an impurity having the same polarity as that of the first intermediate core conductive portion 22 adjacent in the light guiding direction, and the fourth intermediate core conductive portion 25 An impurity having the same polarity as that of the second intermediate core conductive portion 23 adjacent in the waveguide direction is doped. That is, when the first intermediate core conductive portion 22 is P-type and the second intermediate core conductive portion 23 is N-type, the third intermediate core conductive portion 24 is P-type and the fourth intermediate core conductive portion 25. Is N-type, where the first intermediate core conductive portion 22 is N-type and the second intermediate core conductive portion 23 is P-type, the third intermediate core conductive portion 24 is N-type and fourth intermediate core The conductive portion 25 is P-type.

  In the intermediate optical waveguide 20 and the composite core optical waveguide 30 configured as described above, the first occurrence occurs when a voltage is applied between the first composite core conductive portion 32 and the second composite core conductive portion 33. Of the two leakage current paths, the path through the intermediate optical waveguide 20 is the first composite core conductive part 32 -the first intermediate core conductive part 22 -the third intermediate core conductive part 24 -the fourth intermediate core. Conductive portion 25-second intermediate core conductive portion 23-second composite core conductive portion 33, or vice versa. That is, it is a path that connects the first composite core conductive part 32 and the second composite core conductive part 33 counterclockwise or clockwise along the outer periphery of the intermediate core gap part 21.

  Here, when the first intermediate core conductive portion 22 and the first composite core conductive portion 32 and the second intermediate core conductive portion 23 and the second composite core conductive portion 33 have the same polarity, respectively. In the intermediate optical waveguide 20, the region where the third intermediate core conductive portion 24 and the fourth intermediate core conductive portion 25 are in contact is a PN junction, and the second leakage current flows in the forward direction. However, as in this embodiment, the first intermediate core conductive portion 22 and the first composite core conductive portion 32, and the second intermediate core conductive portion 23 and the second composite core conductive portion 33 are opposite to each other. In this case, the polarity of the semiconductor in the above path is PNPN or NPNP. In either case, the polarity from the N type to the P type along the path through which the second leakage current flows. Including changing joints. In the P-type and N-type junctions, when a voltage is applied in the forward direction, that is, a voltage higher than the N-type side is applied to the P-type side, a leakage current flows from the P-type side to the N-type side. However, when a voltage is applied in the opposite direction, that is, when a voltage higher than the P-type side is applied to the N-type side, the leakage current from the N-type side to the P-type side is suppressed. For this reason, there is a change from N-type to P-type along the path through which the second leakage current flows, that is, a high potential is applied to the N-type side with respect to the P-type side in the P-type and N-type junction. In this state, the second leakage current flowing from the N type to the P type is reduced.

  In this case, the same effect can be obtained in principle even when the intermediate core gap 21 is not present. That is, even when the intermediate core gap portion 21 does not exist, the first composite core conductive portion 32 and the second intermediate core conductive portion 23, and the second composite core conductive portion 33 and the first intermediate core conductive portion 22. Are separated by the composite core gap portion 31, the path of the second leakage current is the first composite core conductive portion 32-first intermediate core conductive portion 22-third intermediate core conductive portion 24- Fourth intermediate core conductive portion 25 -second intermediate core conductive portion 23 -second composite core conductive portion 33, or vice versa. Therefore, the polarity of the semiconductor in the above path is PNPN or NPNP, and in either case, includes a junction whose polarity changes from N-type to P-type along the path through which the second leakage current flows.

  However, when the width of the composite core gap portion 31 in the composite core optical waveguide 30 is small, the first intermediate core conductive portion 22, the second composite core conductive portion 33, and the second intermediate core conductive portion 23 Since the first composite core conductive portions 32 are close to each other, the second leakage current is increased as compared with the case where there is a sufficient space charge layer.

  On the other hand, when the intermediate core gap 21 is disposed between the first intermediate core conductive portion 22 and the second intermediate core conductive portion 23 as in the present embodiment, the boundaries can be sufficiently separated. Therefore, even when the width of the composite core gap portion 31 is small, the second leakage current can be reliably reduced.

  In this embodiment, the intermediate core gap portion 21 is provided in a part of the longitudinal direction (Y direction) of the core 41. However, this configuration is not essential, and the intermediate core gap portion 21 is provided over the entire intermediate optical waveguide 20. A structure, that is, a structure without the third intermediate core conductive portion 24 and the fourth intermediate core conductive portion 25 is also possible.

  For example, when the core 11 of the single core optical waveguide 10 in contact with the intermediate optical waveguide 20 is a nonpolar semiconductor that is not doped with impurities, the first composite core conductive portion 32 and the second composite core conductive portion 33 Of the second leakage current paths that occur when a voltage is applied between them, the path that passes through the intermediate optical waveguide is the first composite core conductive portion 32 -the first intermediate core conductive portion 22 -the core 11-. Second intermediate core conductive portion 23-second composite core conductive portion 33, or vice versa. In this path, the polarity of the semiconductor core region changes twice. Therefore, the second leakage current can be further reduced.

  FIG. 5 is a cross-sectional view of the single core optical waveguide 10 taken along the XZ plane. The core 11 of the single-core optical waveguide 10 has a rib shape having a thick portion at the center and thin portions on both sides. The core 11 includes a thin flat plate portion 11b and a convex portion 11a that is located at the center of the flat plate portion 11b and protrudes from the flat plate portion 11b to the upper clad 7 side. The material constituting the convex portion 11a and the material constituting the flat plate portion 11b are the same. In the core 11, the convex portion 11a is not separated by a gap portion having a low refractive index, but is a single core (non-separation region) made of a single material.

In the present embodiment, the core 11 is made of silicon, and the core 42 (first composite core conductive portion 32, second composite core conductive portion 32) of the composite core optical waveguide 30 and the core 41 ( The same width (W ₃ = 2W ₁ + W ₂ ) and high as the first intermediate core conductive part 22, the second intermediate core conductive part 23, the third intermediate core conductive part 24, the fourth intermediate core conductive part 25) (T ₁ , t ₂ ) and formed at a time. The single core optical waveguide 10 of FIG. 5 is the same as the region 20b on the single core optical waveguide side of the intermediate optical waveguide 20 shown in FIG. 4 except that the core 11 does not require doping of impurities. This is the same as the portion constituted by the third intermediate core conductive portion 24 and the fourth intermediate core conductive portion 25.

  In the case of this embodiment, the core 11 is formed using the silicon layer of the surface layer part of the SOI substrate. The cores of the intermediate optical waveguide and the composite core optical waveguide are doped with P-type or N-type impurities. However, in the case of the core 11, such impurities are not doped and are nonpolar semiconductors. .

  Here, “non-polar” means that the silicon layer is not doped with impurities from the outside, and not only when the silicon layer is made of an intrinsic semiconductor but also with a small amount of conductivity contained in the SOI substrate. This includes the case where a trace amount of conductive impurities is contained in the silicon layer due to the conductive impurities. For example, a silicon substrate manufactured by a manufacturing method such as the Czochralski method generally contains a small amount of P-type or N-type conductive impurities. When an SOI substrate is manufactured using such a silicon substrate, a small amount of conductive impurities are also contained in the obtained core 11 due to the conductive impurities present in the SOI substrate.

  The material and shape of the core 11 are not limited to this, and can be appropriately selected under the condition that the upper cladding 7 and the lower cladding 6 form an optical waveguide. Moreover, regarding the polarity when a semiconductor is used as a material, it is not necessarily a nonpolar semiconductor, and it is possible to use a semiconductor material having N-type and P-type polarities used in the intermediate core conductive portion. is there.

[Example]
FIG. 6 is an explanatory diagram for explaining the effect of the present invention. In FIG. 6, the “example” refers to the structure of FIG. 1, that is, a structure in which the composite core optical waveguide is a gap structure and an intermediate optical waveguide is provided between the composite core optical waveguide and the single core optical waveguide. The “comparative example” is a structure in which the composite core optical waveguide has a single core structure, and no intermediate optical waveguide is provided between the composite core optical waveguide and the single core optical waveguide. Further, the horizontal axis of FIG. 6 is a voltage applied between the first composite core conductive part 32 and the second composite core conductive part 33, and the vertical axis is the first composite core conductive part 32 and the second composite core. The total leakage current of the first leakage current and the second leakage current flowing between the core conductive portion 33 is shown.

  As shown in FIG. 6, the optical element of this example has a smaller total leakage current than the optical element of the comparative example. In the optical element of the comparative example, as the applied voltage is increased, the total leakage current generated between the composite core conductive portions is also increased. When the applied voltage is 10 V, a large total leakage current of 36.2 mA is generated. On the other hand, in the optical element of this example, the magnitude of the total leakage current hardly changes even when the applied voltage is increased. Even when an applied voltage of 10 V is applied, only a very small total leakage current of 11.9 μA is generated.

[Examples of using optical elements]
A case where the optical element of the present invention is used as a part of a Mach-Zehnder Interferometer (MZI) will be described with reference to FIG. FIG. 7 is a schematic view showing a cross section of the Mach-Zehnder interferometer taken along a plane (XY plane) horizontal to the substrate.

The MZI optical waveguide 101 has the same cross-sectional structure as the single core optical waveguide in the present embodiment, and is formed as a silicon rib optical waveguide on the SOI substrate.
The phase adjustment unit 102 is installed on one side of the two arms of the Mach-Zehnder interferometer, and has the same cross-sectional structure as the composite core optical waveguide in the present embodiment.
The first connection unit 103 and the second connection unit 104 on both sides of the phase adjustment unit 102 are configured by the optical element of this embodiment.
In the first connection unit 103 and the second connection unit 104, the composite core optical waveguide of the optical element is connected to the phase adjustment unit 102, and the single core optical waveguide of the optical element is connected to the MZI optical waveguide 101. Thereby, the MZI optical waveguide 101 and the phase adjustment unit 102 are connected.

As a specific example, a case where the optical element WG1 illustrated in FIG. 1 is used for the first connection unit 103 and the second connection unit 104 will be described.
In the first connection portion 103, the end portions of the composite core conductive portions 32 and 33 are connected to one end portion of the phase adjustment portion 102, and the end portion of the single core optical waveguide 10 is connected to the MZI optical waveguide 101. The In the second connection portion 104, the end portions of the composite core conductive portions 32 and 33 are connected to the other end portion of the phase adjustment portion 102, and the end portion of the single core optical waveguide 10 is connected to the MZI optical waveguide 101. The
Accordingly, one end of the phase adjusting unit 102 is connected to the MZI optical waveguide 101 through the first connection unit 103, and the other end is connected to the MZI optical waveguide 101 through the second connection unit 104. .

  The phase adjustment unit 102 induces a refractive index change in the composite core conductive part by applying a voltage from the outside to the composite core conductive part through the electrode, thereby changing the propagation speed of light. Then, the light intensity at the output end is controlled by generating a phase difference with respect to the light passing through the arm on the opposite side where the phase adjusting unit 102 is not provided.

[Second Embodiment]
FIG. 8 is an explanatory diagram of an optical element WG2 according to the second embodiment of the present invention. In the optical element WG2 of FIG. 8, the same reference numerals are given to the same components as those of the optical element WG1 of the first embodiment shown in FIG. 1, and detailed description thereof is omitted.

  In the optical element WG1 of the first embodiment shown in FIG. 1, the core of the intermediate optical waveguide 20 is divided into two semiconductor core regions (intermediate core conductive portions 22, 24 and intermediate core conductive portions 23, 25). However, the structure of the intermediate optical waveguide 20 is not limited to this example. For example, the P-type and N-type semiconductor core regions may be arranged so as to alternately switch twice or more according to the light guiding direction. As a specific example, FIG. 8 shows a case where the P-type and N-type semiconductor core regions are repeated twice.

  In the optical element WG2 of FIG. 8, the intermediate core gap portion 201 is provided in the entire longitudinal direction of the core 45 of the intermediate optical waveguide 20 so that both ends thereof reach from the single core optical waveguide 30 to the composite core optical waveguide 30. ing. That is, when the pair of end faces facing each other in the light guiding direction of the intermediate core gap portion 21 are the first end face 201a and the second end face 201b, the second end face 201b on the composite core optical waveguide 30 side is the same as the intermediate optical waveguide 20. The first end surface 201 a on the single core optical waveguide 10 side is disposed at the connection interface between the intermediate optical waveguide 20 and the single core optical waveguide 10.

  The core 45 of the intermediate optical waveguide 20 includes a first separation region 45a and a second separation region 45b separated with the intermediate core gap 201 interposed therebetween as partial regions. The first isolation region 45a includes a first intermediate core conductive portion 202 and a third intermediate disposed so that the P-type and the N-type are alternately switched along the light guiding direction along the light guiding direction. A first polarity inversion region 206 composed of the core conductive portion 204 is included as a partial region. The second isolation region 45b includes a second intermediate core conductive portion 203 and a fourth intermediate disposed so that the P-type and the N-type are alternately switched along the light guiding direction along the light guiding direction. A second polarity inversion region 207 including the core conductive portion 205 is included as a partial region. The second intermediate core conductive portion 203 and the third intermediate core conductive portion 204 are made of a semiconductor material having the same polarity as the first composite core conductive portion 32, and the first intermediate core conductive portion 202 and the first intermediate core conductive portion 202 The 4 middle core conductive part 205 is made of a semiconductor material having the same polarity as the second composite core conductive part 33. The core 11 is made of a nonpolar semiconductor.

  The first intermediate core conductive portion 202, the second intermediate core conductive portion 203, the third intermediate core conductive portion 204, and the fourth intermediate core conductive portion 205 have a higher refractive index than the intermediate core gap portion 201. Made of material. In addition, the intermediate core gap portion 201 includes a first intermediate core conductive portion 202, a second intermediate core conductive portion 203, a third intermediate core conductive portion 204, such as an insulator or an undoped nonpolar semiconductor. And it consists of a high resistance material whose electric conductivity is smaller than the 4th intermediate | middle core electroconductive part 205. FIG.

  In the optical element WG2, the second leak current path generated when a voltage is applied between the first composite core conductive portion 32 and the second composite core conductive portion 33 passes through the intermediate optical waveguide. The route is: first composite core conductive portion 32 -first intermediate core conductive portion 202 -third intermediate core conductive portion 204 -core 11 -fourth intermediate core conductive portion 205 -second intermediate core conductive portion 203. The second composite core conductive portion 33, or vice versa. In this path, the polarity of the semiconductor core region changes four times. If the core 11 is not taken into account, at this time, the change in polarity that changes from the N-type to the P-type appears along the path through which the second leakage current flows, and when a constant voltage is applied, As compared with the case where the change from the N-type to the P-type is performed only once, the voltage applied per location is lower. Although there is a difference depending on the material of the core 11, the second leakage current flowing in this junction can be further reduced.

  In the example of FIG. 8, conductive blocks 208 and 209 made up of a pair of reverse-polarity intermediate core conductive portions disposed opposite to each other with the intermediate core gap 201 sandwiched between the cores 45 of the intermediate optical waveguide 20 are light beams. Two sets are provided along the waveguide direction. This number is not limited to two, and may be three or more. That is, the connection interface between the P-type semiconductor core region and the N-type semiconductor core region appears twice in the second leakage current path along the outer periphery of the intermediate core gap portion 201, but the number of times is not limited to twice. It is also possible to make it four or more times. By doing so, the second leakage current can be further reduced.

[Third Embodiment]
FIG. 9 is an explanatory diagram of an optical element WG3 according to the third embodiment of the present invention. In the optical element WG3 of FIG. 9, the same reference numerals are given to the same components as those of the optical element WG2 of the second embodiment shown in FIG. 8, and detailed description thereof is omitted.

  The optical element WG2 of the second embodiment shown in FIG. 8 has a structure in which the intermediate core gap 201 extends over the entire longitudinal direction of the core 45 of the intermediate optical waveguide. However, the structure of the intermediate optical waveguide 20 is not limited to this example. For example, the single core optical waveguide 10 side end surface 201 a of the intermediate core gap portion 201 is configured to be disposed closer to the composite core optical waveguide 30 than the connection interface between the intermediate optical waveguide 20 and the single core optical waveguide 10. Is also possible. A specific example is shown in FIG.

  In the optical element WG3 of FIG. 9, the intermediate core gap 211 exists only on the composite core optical waveguide 30 side. When a pair of end faces facing each other in the light guiding direction of the intermediate core gap portion 211 are a first end face 211a and a second end face 211b, the second end face 211b on the composite core optical waveguide 30 side is the intermediate optical waveguide 20 and the composite core. The first end surface 211a on the single core optical waveguide 10 side is disposed on the side of the composite core optical waveguide 30 with respect to the connection interface between the intermediate optical waveguide 20 and the single core optical waveguide 10. Has been.

On the composite core optical waveguide 30 side of the intermediate optical waveguide 20, the core 46 has a gap structure separated by the intermediate core gap portion 211. The core 46 includes, as partial regions, a first separation region 46a and a second separation region 46b separated with the intermediate core gap 211 therebetween. The first separation region 46a includes a first intermediate core conductive portion 212 and a third intermediate portion arranged so that the P-type and the N-type are alternately switched along the light guiding direction along the light guiding direction. A first polarity inversion region 228 including the core conductive portion 214 is included as a partial region. The second isolation region 46b includes a second intermediate core conductive portion 213 and a fourth intermediate disposed so that the P-type and the N-type are alternately switched along the light guiding direction along the light guiding direction. A second polarity inversion region 229 formed of the core conductive portion 215 is included as a partial region. The second intermediate core conductive portion 213 and the third intermediate core conductive portion 214 are made of a semiconductor material having the same polarity as the first composite core conductive portion 32, and the first intermediate core conductive portion 212 and the first intermediate core conductive portion 212 The 4 middle core conductive portion 215 is made of a semiconductor material having the same polarity as the second composite core conductive portion 33. The core 11 is made of a nonpolar semiconductor.

  On the single core optical waveguide 10 side of the intermediate optical waveguide 20, the core 46 has a single core structure (non-isolation region) that is not separated by the intermediate core gap portion 211. The core 46 includes a fifth intermediate core conductive portion (fifth semiconductor core region) 216 made of the same material as the third intermediate core conductive portion 214 and formed integrally with the third intermediate core conductive portion 214, and a fourth core 46. A sixth intermediate core conductive portion (sixth semiconductor core region) 217 made of the same material as the intermediate core conductive portion 215 and formed integrally with the fourth intermediate core conductive portion 215 is included as a partial region. It has a connection interface parallel to the plane and in contact with each other.

  First intermediate core conductive portion 212, second intermediate core conductive portion 213, third intermediate core conductive portion 214, fourth intermediate core conductive portion 215, fifth intermediate core conductive portion 216, and sixth intermediate The core conductive portion 217 is made of a material having a higher refractive index than that of the intermediate core gap portion 211. The intermediate core gap 211 includes a first intermediate core conductive portion 212, a second intermediate core conductive portion 213, a third intermediate core conductive portion 214, such as an insulator or an undoped nonpolar semiconductor. The fourth intermediate core conductive portion 215, the fifth intermediate core conductive portion 216, and the sixth intermediate core conductive portion 217 are made of a high resistance material having a smaller electric conductivity.

  In the optical element WG3, the second leak current path that occurs when a voltage is applied between the first composite core conductive portion 32 and the second composite core conductive portion 33 passes through the intermediate optical waveguide. The route is the first composite core conductive portion 32 -the first intermediate core conductive portion 212 -the third intermediate core conductive portion 214 -the fifth intermediate core conductive portion 216 -the sixth intermediate core conductive portion 217 -the fourth. Intermediate core conductive portion 215-second intermediate core conductive portion 213-second composite core conductive portion 33, or vice versa. In this path, the polarity of the semiconductor core region changes three times. Therefore, the second leakage current can be further reduced. In addition, since the intermediate core gap 211 does not reach the core 11, the intrusion of the second leak current into the core 11 can be reduced.

  In the example of FIG. 9, the core 46 of the intermediate optical waveguide 20 has conductive blocks 218 and 219 formed of a pair of opposite-polarity intermediate core conductive portions opposed to each other with the intermediate core gap portion 211 interposed therebetween. Two sets are provided along the wave direction. This number is not limited to two, and may be three or more. In the case of three or more sets, the end surface 211 a on the single core optical waveguide 10 side of the intermediate core gap portion 211 only needs to be disposed on the composite core optical waveguide 30 side with respect to the connection interface between the core 11 and the core 46. . That is, the connection interface between the P-type semiconductor core region and the N-type semiconductor core region appears three times in the second leakage current path along the outer periphery of the intermediate core gap 211, but the number of times is not limited to three. It is also possible to make it 5 times or more. By doing so, the second leakage current can be further reduced.

[Fourth Embodiment]
FIG. 10 is an explanatory diagram of an optical element WG4 according to the fourth embodiment of the present invention. In the optical element WG4 of FIG. 10, the same reference numerals are given to the same components as those of the optical element WG1 of the first embodiment shown in FIG. 1, and detailed description thereof is omitted.

  In the optical element WG1 of the first embodiment shown in FIG. 1, in the intermediate optical waveguide 20, the first intermediate core conductive portion 22 and the second intermediate core conductive portion 23 have structures having opposite polarities, respectively. However, it is also possible to use a nonpolar semiconductor for this part. A specific example is shown in FIG.

  In the optical element WG4 of FIG. 10, the intermediate core gap portion 221 exists only on the composite core optical waveguide 30 side. That is, when the pair of end faces facing each other in the light guiding direction of the intermediate core gap portion 221 are the first end face 221a and the second end face 221b, the second end face 221b on the composite core optical waveguide 30 side is the same as the intermediate optical waveguide 20. The first end surface 221a on the single core optical waveguide 10 side is disposed at the connection interface with the composite core optical waveguide 30 and the composite core optical waveguide 30 side is closer to the connection interface between the intermediate optical waveguide 20 and the single core optical waveguide 10 Is arranged.

  In the region of the intermediate optical waveguide 20 on the composite core optical waveguide 30 side, the intermediate optical waveguide 20 has a gap structure in which the core 47 is separated by the intermediate core gap portion 221. The core 47 is a partial region of the first intermediate core nonpolar part (third semiconductor core region) 222 and the second intermediate core nonpolar part (fourth semiconductor core region) 223 separated with the intermediate core gap part 221 interposed therebetween. Include as. The intermediate optical waveguide 20 is an optical waveguide having a composite core structure in which light propagates across two partial regions separated by the intermediate core gap portion 221.

  In the region of the intermediate optical waveguide 20 on the single core optical waveguide 10 side, the intermediate optical waveguide 20 has a single core structure (non-isolated region) in which the core 47 is not separated by the intermediate core gap portion. The core 47 is made of the same material as the first intermediate core nonpolar part 222 and the second intermediate core nonpolar part 223, and is formed integrally with the first intermediate core nonpolar part 222 and the second intermediate core nonpolar part 223. A third intermediate core nonpolar part (non-separation region) 224 made of a nonpolar semiconductor is included as a partial region.

  The first intermediate core nonpolar part 222 and the second intermediate core nonpolar part 223 are made of a material having a higher refractive index than that of the intermediate core gap part 221. The intermediate core gap portion 221 is a high-resistance material having a lower electrical conductivity than the first intermediate core nonpolar portion 222 and the second intermediate core nonpolar portion 223, such as an insulator or an undoped nonpolar semiconductor. Consists of.

  In this configuration, the intermediate core nonpolarity is present at the boundary between the first composite core conductive portion 32 and the intermediate core nonpolar portion 222 and at the boundary between the second composite core conductive portion 33 and the intermediate core nonpolar portion 223. Carrier diffusion to the parts 222 and 223 occurs. Therefore, when the intermediate core gap part 221 is not provided, the first composite core conductive part 32 -the first intermediate core nonpolar part 222 -the third intermediate core nonpolar part 224 -the second intermediate core nonpolar part 223 -It is conceivable that the path connecting the second composite core conductive portion 33 in the shortest is not a sufficiently low leakage current because the nonpolar semiconductor region is short. However, the intermediate core nonpolar portions 222, 223, and 224 are made of a material with less carrier diffusion from the composite core conductive portions 32 and 33, and the length of the intermediate core gap portion 221 (the length in the Y direction) is the same as that described above. When the length is sufficiently longer than the diffusion region on the path, the path includes a nonpolar semiconductor region having a high electrical resistance. As a result, the first composite core conductive portion 32 and the second composite core are included. It is possible to reduce the second leakage current that flows through the intermediate optical waveguide when a voltage is applied to the conductive portion 33.

[Fifth Embodiment]
FIG. 11 is an explanatory diagram of an optical element WG5 according to the fifth embodiment of the present invention. In the optical element WG5 of FIG. 11, the same reference numerals are given to the same components as those of the optical element WG4 of the fourth embodiment shown in FIG. 10, and detailed description thereof is omitted.

  In the optical element WG4 of the fourth embodiment shown in FIG. 10, the first composite core conductive portion 32 and the intermediate core nonpolar portion 222, and the second composite core conductive portion 33 and the intermediate core nonpolar portion 223 are included. The structure is in direct contact. However, the structure of the intermediate optical waveguide 20 is not limited to this example. For example, between the first composite core conductive part 32 and the intermediate core nonpolar part 222 and between the second composite core conductive part 33 and the intermediate core nonpolar part 223, respectively, P type and N type Alternatively, the semiconductor core regions may be alternately arranged so as to be switched at least twice. As a specific example, FIG. 11 shows a case where the P-type and N-type semiconductor core regions are repeated twice.

  In the optical element WG5 of FIG. 11, the intermediate core gap portion 231 exists only on the composite core optical waveguide 30 side. That is, when the pair of end faces facing each other in the light guiding direction of the intermediate core gap portion 231 are a first end face 231a and a second end face 231b, the second end face 231b on the composite core optical waveguide 30 side is The first end surface 231a on the single core optical waveguide 10 side is disposed on the connection interface with the composite core optical waveguide 30 and the composite core optical waveguide 30 side is closer to the connection interface between the intermediate optical waveguide 20 and the single core optical waveguide 10 Is arranged.

In the region of the intermediate optical waveguide 20 on the composite core optical waveguide 30 side, the core 48 has a gap structure separated by the intermediate core gap portion 231. The core 48 includes a first separation region 48a and a second separation region 48b separated with the intermediate core gap portion 231 interposed therebetween as partial regions. The first separation region 48a includes a first intermediate core conductive portion 232 and a third intermediate portion arranged so that the P-type and the N-type are alternately switched along the light guiding direction along the light guiding direction. A first polarity reversal region 251 comprising a core conductive portion 234, and a first intermediate core comprising a nonpolar semiconductor connected to the light incident end face of the third intermediate core conductive portion 234 on the single core optical waveguide 10 side And a nonpolar portion 236 as a partial region. The second isolation region 48b includes a second intermediate core conductive portion 233 and a fourth intermediate disposed so that the P-type and the N-type are alternately switched along the light guiding direction along the light guiding direction. A second polarity reversal region 252 composed of the core conductive portion 235, and a second intermediate core composed of a nonpolar semiconductor connected to the light incident end face of the fourth intermediate core conductive portion 235 on the single core optical waveguide 10 side. And a nonpolar portion 237 as a partial region. The second intermediate core conductive portion 233 and the third intermediate core conductive portion 234 are made of a semiconductor material having the same polarity as the first composite core conductive portion 32, and the first intermediate core conductive portion 232 and the second intermediate core conductive portion 234 The 4 middle core conductive part 235 is made of a semiconductor material having the same polarity as the second composite core conductive part 33. The core 11 is made of a nonpolar semiconductor.

  In the region of the intermediate optical waveguide 20 on the single core optical waveguide 10 side, the core 48 has a single core structure (non-isolated region) that is not separated by the intermediate core gap portion. The core 48 is made of the same material as the first intermediate core nonpolar part 236 and the second intermediate core nonpolar part 237, and is formed integrally with the first intermediate core nonpolar part 236 and the second intermediate core nonpolar part 237. 3 middle core nonpolar part 238 is included as a partial region.

  The first intermediate core conductive portion 232, the second intermediate core conductive portion 233, the third intermediate core conductive portion 234, the fourth intermediate core conductive portion 235, the first intermediate core nonpolar portion 236, and the second intermediate The core nonpolar part 237 is made of a material having a higher refractive index than that of the intermediate core gap part 231. In addition, the intermediate core gap part 231 includes a first intermediate core conductive part 232, a second intermediate core conductive part 233, a third intermediate core conductive part 234, such as an insulator or an undoped nonpolar semiconductor. The fourth intermediate core conductive portion 235, the first intermediate core nonpolar portion 236, and the second intermediate core nonpolar portion 237 are made of a high resistance material having a smaller electric conductivity.

  In the optical element WG5, the second leak current path generated when a voltage is applied between the first composite core conductive portion 32 and the second composite core conductive portion 33 passes through the intermediate optical waveguide. The path is the first composite core conductive part 32-the first intermediate core conductive part 232-the third intermediate core conductive part 234-the first intermediate core nonpolar part 236-the third intermediate core nonpolar part 238-second. Intermediate core nonpolar part 237-fourth intermediate core conductive part 235-second intermediate core conductive part 233-second composite core conductive part 33, or vice versa. In this path, the polarity of the semiconductor core region changes five times. Therefore, the second leakage current can be further reduced.

  In the example of FIG. 11, the conductive block 241 and 242 composed of a pair of reverse-polarity intermediate core conductive portions opposed to each other with the intermediate core gap portion 231 sandwiched between the cores 48 of the intermediate optical waveguide 20 are guided light. Two sets are provided along the wave direction. This number is not limited to two, and may be three or more. In the case of three or more sets, the end surface 231a on the single core optical waveguide 10 side of the intermediate core gap portion 231 may be disposed on the composite core optical waveguide 30 side with respect to the connection interface between the core 11 and the core 48. . That is, the connection interface between the P-type semiconductor core region and the N-type semiconductor core region appears twice in the second leakage current path along the outer periphery of the intermediate core gap portion 231, but the number of times is not limited to two. It is also possible to make it four or more times. By doing so, the second leakage current can be further reduced.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

  For example, in the above embodiment, Si is used as the core material, but the core material is not limited to this, and other semiconductor materials such as Ge and SiGe may be used.

  In the first, second, third, and fifth embodiments, the core of the intermediate optical waveguide 20 that is connected to the light incident / exit end surface of the core of the composite core optical waveguide 30 has a polarity opposite to each other. In the fourth embodiment, this portion is a nonpolar semiconductor core region. However, the configuration of the intermediate optical waveguide 20 is not limited to this. For example, the first intermediate core conductive portion may be a nonpolar semiconductor core region, and the second intermediate core conductive portion may be a semiconductor core region having a polarity opposite to that of the second composite core conductive portion 33. Conversely, the second intermediate core conductive portion may be a nonpolar semiconductor core region, and the first intermediate core conductive portion may be a semiconductor core region having a polarity opposite to that of the first composite core conductive portion 32.

  In the first, second, third, and fifth embodiments, the same number of P-type semiconductor core regions are provided in the pair of separation regions separated in the direction orthogonal to the light guiding direction by the intermediate core gap portion. And an N-type semiconductor core region. However, the configuration of the intermediate optical waveguide 20 is not limited to this. For example, i P-type semiconductor core regions and N-type semiconductor core regions are provided in one isolation region, and j (≠ i) P-type semiconductor core regions and N-type semiconductor core regions are provided in the other isolation region. Also good. Further, either one of the isolation regions may be configured only with a nonpolar semiconductor core region without providing the P-type semiconductor core region or the N-type semiconductor core region. Further, when a region where the P-type semiconductor core region and the N-type semiconductor core region are alternately arranged along the light guiding direction is used as one polarity inversion region, the plurality of polarity inversion regions are guided by the light. While arranging along a direction, you may provide a nonpolar semiconductor core area | region between polarity inversion area | regions.

  That is, in the above-described embodiment, at least one of the pair of separation regions includes a plurality of semiconductor core regions arranged so that the P-type and the N-type are alternately switched along the light guiding direction. Or at least one of the pair of isolation regions is a polarity inversion region composed of a plurality of semiconductor core regions arranged so that P-type and N-type are alternately switched along the light guiding direction And a non-polar semiconductor core region connected to the light incident / exit end face of the polarity reversal region.

[Sixth Embodiment]
12-14 is explanatory drawing of the optical element WG6 concerning 5th Embodiment of this invention, and employs a grating structure.
FIG. 14 shows the core 50, and only the core 50 is illustrated here, but it is assumed that the cladding surrounds the core 50. A substrate (not shown) exists under the cladding, and the bottom surface 54 of the core 50 is parallel to the substrate surface. The horizontal direction means a direction parallel to the substrate surface, and the vertical direction means a direction perpendicular to the substrate surface.

FIG. 14A is a plan view of a part of the core 50. The symbol C represents a single central axis in the horizontal plane of the core 50, and light propagates along the central axis C in the optical waveguide. This optical waveguide has a Bragg grating pattern (described later in detail), and at least one reflection band appears in the spectrum of the optical waveguide.
The center wavelength λ ₀ of the reflection band is given by λ ₀ = p _G / n _eff where the period of the Bragg grating is p _G and the effective refractive index of the optical waveguide is n _eff . Here, the effective refractive index n _eff is a value when the width of the core 50 of the optical waveguide is the average width w ₀ .

The average width w ₀ of the core 50 is equal to the average value in one cycle of the horizontal width w _out of the core 50.
The side wall 52 of the core 50, recesses 52a and protrusions 52b are alternately formed in the waveguide direction of the light, the first Bragg grating pattern width w _out is increased or decreased for each one period p _G is formed.

  An optical waveguide having a rectangular cross section has its own waveguide mode when the linearly polarized electric field of light is mainly along the horizontal direction (hereinafter referred to as TE-type polarization) and mainly along the vertical direction (hereinafter referred to as TM-type polarization). Exists. Then, there is a polarization dependency that an effective refractive index inherent to each waveguide mode exists.

The effective refractive index n _eff ^TE of the eigen mode in the TE-type polarized light changes more sensitively to changes in the width of the optical waveguide than the effective refractive index n _eff ^TM of the eigen mode in the TM-type polarized light.
The effective refractive index n _eff ^TM of the eigenmode in the TM-type polarization changes more sensitively to changes in the height (ie, thickness) of the optical waveguide than the effective refractive index n _eff ^TE of the eigenmode in the TE-type polarization. To do.
Therefore, in order to reduce the polarization dependence of the Bragg grating, it is preferable not only to periodically change the width of the optical waveguide but also to periodically change the height of the optical waveguide.

Considering application to a rectangular optical waveguide (optical waveguide having a substantially rectangular cross section), the first Bragg grating pattern is provided on one or both side walls of the core, and the second Bragg grating pattern is provided on the top and bottom surfaces of the core. It is preferable to provide one or both of them.
By combining the first Bragg grating pattern and the second Bragg grating pattern, it is possible to equalize the action on the TE-type polarization and the action on the TM-type polarization, thereby reducing the polarization dependence.
In the illustrated example, the first Bragg grating pattern is provided on both side walls of the core, and the second Bragg grating pattern is provided on the upper surface of the core.
The shape of the core 50 is symmetrical in the horizontal direction with respect to the vertical plane including the central axis C (symmetric in the vertical direction with respect to the central axis C in FIG. 14A).

As shown in FIG. 14 (b), the core 50, the width w _in the groove provided in the core upper (trench) 53 is periodically changed in the light propagation direction. The height of the core is _{t out,} the depth of the groove 53 is _{t in.} As shown in FIG. 14 (a), the groove 53 extends in a direction along the central axis C, the horizontal coordinate of the midpoint of the width w _in the groove 53, located on the central axis C.
With this structure, the effective refractive index can be changed equivalently to changing the height of the core 50 periodically.
Recess 53a and the convex portion 53b on the side walls of the groove 53 are formed alternately, the groove width w _in the form a second Bragg grating pattern is increased or decreased for each one period p _G.
The groove 53 can be formed, for example, by drawing (lithography) using an optical mask and etching.

As shown in FIG. 14 (a), the core 50, in the light propagation direction, narrow groove width _{w in} the wide portion of the core width _{w out} of the side wall 52 (projecting portions 52 b) and the groove 53 inner wall section ( protrusion 53b) and correspond, and is the core width _{w out,} narrow portion of the side wall 52 (the recess 52a) and the groove 53 groove width _{w in} a wide portion of the inner wall (recess 53a) correspond. Thus, unevenness of the first Bragg grating pattern and the unevenness of the second Bragg grating pattern is synchronized, each local period p _G match. This facilitates the design of the optical waveguide dimensions.

12 and 13 are cross-sectional views of an optical element employing the grating structure.
In the following description, the same components as those described above may be denoted by the same reference numerals and description thereof may be omitted.
The optical element of this embodiment has a composite core composed of an inner core 60 and an outer core 64.
The inner core 60 includes gap portions 21 and 31, core conductive portions 22 and 32, and core conductive portions 23 and 33.
The outer core 64 is made of a material having a lower refractive index than the core conductive portions 22, 32, 23, and 33. The refractive index of the outer core 64 is higher than the refractive index of the upper cladding 7. The thickness of the outer core 64 at _{t out,} the depth of the groove 64c is _{t in.}

  By forming the gap portions 21 and 31, the cross-sectional area of the region where light is confined in the inner core 60 can be increased while maintaining the condition that only a single mode exists in a single polarization state. In addition, since it is possible to reduce the accuracy deterioration of the effective refractive index due to a processing error of a Bragg grating (described later) formed in the outer core 64, it is also effective to reduce the polarization dependence of the effective refractive index.

For example, the core conductive portions 22, 32, 23, and 33 are silicon (Si), the gap portions 21 and 31 are silica (SiO ₂ ), silicon oxynitride (SiO _x N _y ), or nitridation. Silicon (Si _x N _y ), outer core 64 is silicon oxynitride (SiO _x N _y ) or silicon nitride (Si _x N _y ), substrate 5 is silicon (Si), lower cladding 6 and upper cladding 7 are silica (SiO 2). ₂ ).

The core conductive portions 22, 32, 23, 33 have a conductivity type when one of the P type and the N type is the first conductivity type and the other is the second conductivity type. , 33 can be the first conductivity type, and the core conductive portions 23 and 32 can be the second conductivity type.
A first electrode (not shown) is connected to the flat plate portion 22b of the core conductive portion 22, a second electrode (not shown) is connected to the flat plate portion 23b of the core conductive portion 23, and the first and second electrodes are connected to each other. By applying a voltage between the two, the refractive indexes of the core conductive portions 22 and 23 can be variably controlled.
The first electrode (not shown) is connected to the flat plate portion 32b of the core conductive portion 32, the second electrode (not shown) is connected to the flat plate portion 33b of the core conductive portion 33, the first electrode and the second electrode, The refractive index of the core conductive portions 32 and 33 can be variably controlled by applying a voltage between them.

The outer core 64 is provided on the core conductive portions 22, 32, 23, 33.
First and second Bragg grating patterns similar to the core 50 of FIG. 14 are formed on the upper surface 64a and the side wall 64b of the outer core 64, respectively.
Specifically, a first Bragg grating pattern, the width w _in the groove (trench) 64c formed on the upper surface 64a of the outer core 64 periodically with a width w _out of the outer core 64 is periodically changed A changed second Bragg grating pattern is provided.
According to the optical element having this configuration, the gap 40 can reduce the current generated between the core conductive portions 22 and 32 and the core conductive portions 23 and 33 in the direction orthogonal to the waveguide direction. Is possible. In addition, by adopting the Bragg grating, the effective refractive index of the optical waveguide can be changed.

DESCRIPTION OF SYMBOLS 1 ... Core, 11 ... Single core (non-separation area | region), 22 ... 1st intermediate | middle core electroconductive part (3rd semiconductor core area | region), 23 ... 2nd intermediate | middle core electroconductive part (4th semiconductor core area | region), 24 ... 3rd intermediate core conductive part (non-isolation region), 25 ... 4th intermediate core conductive part (non-isolation region), 32 ... 1st composite core conductive part (1st semiconductor core region), 32a, 32b ... Flat part (thin part with thin core), 33 ... second composite core conductive part (second semiconductor core region), 40 ... gap part, 45a, 45b, 46a, 46b, 48a, 48b ... separation region, 202 ~ 205, 212 to 217, 222 to 224, 232 to 238 ... semiconductor core region, 208, 209, 218, 219, 241, 242 ... conductive block, 206, 207, 228, 229, 251, 252 ... polarity inversion region, WG1, WG , WG3, WG4, WG5 ... optical element

Claims (15)

An optical element having a semiconductor core (1) for guiding light,
An insulating gap portion (40) extending along the light guiding direction at the center in the width direction of the core;
The core includes, as a partial region, a separation region that is electrically separated by the gap portion in a direction orthogonal to a light guide direction,
The isolation region includes a first conductivity type first semiconductor core region (32), and a second conductivity type second semiconductor core region (33) disposed opposite to the first semiconductor core region with the gap therebetween. ), The third semiconductor core region (22) of the second conductivity type adjacent to the first semiconductor core region in the light guiding direction, and adjacent to the second semiconductor core region in the light guiding direction, A third semiconductor core region and a fourth semiconductor core region (23) of the first conductivity type disposed opposite to each other across the gap portion are included as partial regions;
The second conductivity type is opposite in polarity to the first conductivity type,
An electrode for applying a voltage is connected to the first semiconductor core region and the second semiconductor core region. An optical element having a semiconductor core (1) for guiding light,
An insulating gap portion (40) extending along the light guiding direction at the center in the width direction of the core;
The core includes, as a partial region, a separation region that is electrically separated by the gap portion in a direction orthogonal to a light guide direction,
The isolation region includes a first conductivity type first semiconductor core region (32), and a second conductivity type second semiconductor core region (33) disposed opposite to the first semiconductor core region with the gap therebetween. ), A nonpolar third semiconductor core region (22) adjacent to the first semiconductor core region in the light guiding direction, and adjacent to the second semiconductor core region in the light guiding direction, A non-polar fourth semiconductor core region (23) disposed opposite to the semiconductor core region with the gap portion interposed therebetween, is included as a partial region;
The second conductivity type is opposite in polarity to the first conductivity type,
An electrode for applying a voltage is connected to the first semiconductor core region and the second semiconductor core region.   The said core has the non-separation area | region (11) which does not contain the said gap part in the cross section orthogonal to the optical waveguide direction in the position adjacent to the said isolation | separation area | region in an optical waveguide direction. Or the optical element of 2.   The core includes, as a partial region, a polarity inversion region (206) including a plurality of semiconductor core regions arranged so that the first conductivity type and the second conductivity type are alternately switched along the outer periphery of the gap portion. The optical element according to claim 3.   The polarity inversion region is an end portion of the gap portion that extends from a first side parallel to the light guide direction of the gap portion to a second side that bypasses the tip portion of the gap portion and faces the first side. The optical element according to claim 4, wherein the optical element is provided in a region.   6. The optical element according to claim 4, wherein the core includes the polarity reversal region, and a nonpolar semiconductor core region adjacent to the polarity reversal region along the outer periphery of the gap portion as a partial region. .   The core is provided in an end region of the gap portion that extends from a first side parallel to the light guide direction of the gap portion to a second side that bypasses the tip portion of the gap portion and faces the first side. The optical element according to claim 3, comprising a nonpolar semiconductor core region as a partial region.   5. The optical element according to claim 4, wherein the non-separating region includes a pair of semiconductor core regions having opposite polarities adjacent to each other in a direction orthogonal to the light guiding direction as partial regions.   The optical element according to claim 3, wherein the non-isolation region has a nonpolar semiconductor core region.   In the separation region, a conductive block composed of a pair of semiconductor core regions having opposite polarities arranged opposite to each other with the gap portion interposed therebetween, and the polarity of the semiconductor core region of the conductive block is along the light guiding direction. The optical element according to claim 4, wherein a plurality of the optical elements are provided along a light guiding direction so as to be switched alternately. A portion that separates the first semiconductor core region and the second semiconductor core region of the gap portion is made of a material having a refractive index smaller than any of the first semiconductor core region and the second semiconductor core region, The portion of the gap that separates the third semiconductor core region and the fourth semiconductor core region is made of a material having a refractive index smaller than that of any of the third semiconductor core region and the fourth semiconductor core region. the optical element according to any one of claims 1 to 10, characterized in that there. Each of the first semiconductor core region and the second semiconductor core region has a rib shape in which a thickness of a portion in contact with the gap portion is thicker than other portions, and the first semiconductor core region and the second semiconductor core region The optical element according to any one of claims 1 to 11 , wherein the electrode is connected to the thin portion of the second semiconductor core region. The gap portion, the optical element according to any one of claims 1 to 12, characterized in that it is constituted by an insulator or non-polar semiconductor. An optical element having a semiconductor core (1) for guiding light,
An insulating gap portion (40) extending along the light guiding direction at the center in the width direction of the core;
The core includes, as a partial region, a separation region that is electrically separated by the gap portion in a direction orthogonal to a light guide direction,
The isolation region includes first to fourth semiconductor regions (32, 33, 22, 23) for guiding light as partial regions,
The first semiconductor region (32) is of a first conductivity type;
The second semiconductor region (33) is a second conductivity type having a polarity opposite to that of the first conductivity type, and is disposed opposite to the first semiconductor region with the gap portion interposed therebetween.
The third semiconductor region (22) is of a second conductivity type, and is adjacent to the first semiconductor region in a light guiding direction;
The fourth semiconductor region (23) is of the first conductivity type, is adjacent to the second semiconductor region in the light guiding direction, and is disposed opposite to the third semiconductor region with the gap portion in between.
An optical element, wherein a voltage can be applied between the first semiconductor region and the second semiconductor region. An optical element having a semiconductor core (1) for guiding light,
An insulating gap portion (40) extending along the light guiding direction at the center in the width direction of the core;
The core includes, as a partial region, a separation region that is electrically separated by the gap portion in a direction orthogonal to a light guide direction,
The isolation region includes first to fourth semiconductor regions (32, 33, 22, 23) for guiding light as partial regions,
The first semiconductor region (32) is of a first conductivity type;
The second semiconductor region (33) is a second conductivity type having a polarity opposite to that of the first conductivity type, and is disposed opposite to the first semiconductor region with the gap portion interposed therebetween.
The third semiconductor region (22) is nonpolar, and is adjacent to the first semiconductor region in a light guiding direction;
The fourth semiconductor region (23) is non-polar, adjacent to the second semiconductor region in the light guiding direction, and opposed to the third semiconductor region across the gap;
An optical element, wherein a voltage can be applied between the first semiconductor region and the second semiconductor region.

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