JP5365521B2 - Photonic crystal - Google Patents

Description

  The present invention relates to a photonic crystal body in which a line defect waveguide is formed, and more particularly to a structure of an intersecting portion of the line defect waveguide.

  In recent years, a technique for realizing an optical integrated circuit in which optical components are integrated has been desired. An optical circuit in which optical components such as an optical switch, a wavelength filter, and a 3 dB coupler (optical coupler) are connected via an optical waveguide such as an optical fiber is known. However, if a plurality of optical components can be integrated in a small chip, the volume, power consumption, and manufacturing cost of the optical circuit can be drastically reduced.

  Many technologies have been developed to realize optical integrated circuits. One of the technologies aimed at realizing an optical integrated circuit is a photonic crystal technology. Photonic crystal or photonic crystal is a general term for structures whose refractive index changes periodically. In this specification, unless otherwise specified, “photonic crystal” and “photonic crystal” are used as synonyms.

  Photonic crystals exhibit various special optical characteristics due to the periodic structure of the refractive index distribution. The most typical feature is a photonic band gap (PBG). Light can be transmitted through the photonic crystal. However, if the periodic refractive index change in the photonic crystal is sufficiently large, light in a specific frequency band cannot propagate in the photonic crystal. The frequency band (or wavelength band) of light that can propagate through the photonic crystal is called a photonic band. On the other hand, the frequency band (or wavelength band) of light that cannot propagate through the photonic crystal is called a photonic band gap (PBG). The photonic band gap means a gap existing between photonic bands. There may be multiple PBGs in different frequency bands. The photonic bands divided by the PBG may be referred to as the first band, the second band, and the third band from the smaller frequency.

  If there is a minute defect in the photonic crystal that breaks the periodic structure of the refractive index distribution (periodicity of the refractive index distribution), the light in the PBG is confined in the minute defect. In that case, only light having a frequency corresponding to the size of the defect is confined, so that the photonic crystal functions as an optical resonator. Therefore, such a photonic crystal can be used as a frequency (wavelength) filter.

  In addition, when micro defects are continuously arranged in a row in the photonic crystal and a line defect is formed in the crystal, the light in the PBG is confined in the line defect and along the line defect. Propagate. Therefore, such a photonic crystal can be used as an optical waveguide. The above optical waveguide formed in the photonic crystal is called a line defect waveguide.

  If an optical filter or an optical waveguide is formed, an optical functional element such as an optical modulator or an optical switch can be configured by the optical filter or the optical waveguide. Furthermore, an optical circuit can be configured if main optical functional elements are formed in the photonic crystal and these optical functional elements are connected to each other. For these reasons, photonic crystals are expected as an optical integrated circuit platform.

  Here, in order to use the effect of PBG in three directions of x, y, and z perpendicular to each other, it is necessary that the refractive index distribution of the photonic crystal has a three-dimensional periodic structure. However, since the three-dimensional periodic structure is complicated, the manufacturing cost increases. Therefore, a photonic crystal whose refractive index distribution has a two-dimensional periodic structure (hereinafter sometimes referred to as “two-dimensional photonic crystal”) is often used. Specifically, a two-dimensional photonic crystal having a finite thickness is used in which the refractive index distribution in the in-plane direction of the substrate has periodicity, but the refractive index distribution in the thickness direction of the substrate does not have periodicity. In that case, confinement of light in the thickness direction of the substrate is realized not by the effect of PBG but by total reflection due to the difference in refractive index.

  However, the characteristics of the two-dimensional photonic crystal having a finite thickness do not completely match the characteristics of the two-dimensional photonic crystal having an infinite thickness. However, if the refractive index distribution in the thickness direction of the two-dimensional photonic crystal having a finite thickness is mirror symmetric in the light propagation region, the optical characteristics of the two-dimensional photonic crystal having a finite thickness are infinite thickness 2 The optical characteristics of the two-dimensional photonic crystal almost coincide. The operation prediction of a device based on a two-dimensional photonic crystal having an infinite thickness is much easier than the operation prediction of a device based on a two-dimensional photonic crystal having a finite thickness. Therefore, if a two-dimensional photonic crystal whose refractive index distribution has mirror symmetry can be used, device design becomes easy.

  There are several specific structures of the two-dimensional photonic crystal of finite thickness realized so far. Among them, a pillar-type square lattice photonic crystal has a feature that light propagation speed in a line defect waveguide is slow in a wide band. That is, a low group velocity. In general, when a waveguide having a low propagation speed is used, an optical circuit having the same function can be realized by a short waveguide. Therefore, a line defect waveguide using a columnar square lattice photonic crystal is suitable for an optical integrated circuit.

  FIG. 1 is a schematic diagram showing the structure of a line defect waveguide of a columnar square lattice photonic crystal having a finite thickness. In the pillar-shaped square lattice photonic crystal shown in the figure, in the low dielectric constant material 1, a cylinder 52a having a finite height made of a high dielectric constant material and a cylinder 52b having a smaller diameter than the cylinder 52a are formed. Arranged in a square lattice. However, the low dielectric constant material and the cylindrical material do not need to be crystalline, and may be amorphous.

  In the case of the photonic crystal shown in FIG. 1, the cylinder 52a is a complete photonic crystal cylinder, whereas the cylinder 52b has a smaller diameter than the cylinder 52a. Therefore, the cylinder 52b is regarded as a defect introduced into the complete crystal. In the following description, in order to distinguish between a perfect crystal cylinder and a cylinder corresponding to a defect, the former is called a “non-linear defect column”, and the latter is called a “defect column”, a “defect column”, or a “line defect column”. There is a case. However, the defective column itself is not particularly defective.

  In the line defect waveguide of the cylindrical square lattice photonic crystal shown in FIG. 1, the line of the line defect column corresponds to the core in the total reflection type waveguide such as an optical fiber. Further, the lattice of the non-linear defect columns on both sides and the surrounding dielectric material correspond to the clad in the row of the line defect columns. In the case of a total reflection waveguide, a core and a clad are essential for forming the waveguide. In the case of a line defect waveguide, in order to form a waveguide, a line defect and a non-linear defect column or dielectric material around the line defect are essential. In the following description, the line defect column may be referred to as a “line defect”.

  Here, in order to increase the density of the optical wiring in the optical integrated circuit, it may be necessary to cross the optical wiring (waveguide). The simplest cross structure in the line defect waveguide of the square lattice photonic crystal is a cross structure in which two line defects are crossed at right angles.

An example of a cross structure provided in a line defect waveguide of a cylindrical square lattice photonic crystal is shown in FIG. 2 includes a first straight portion 61 formed by a plurality of defect columns 52b arranged on a straight line Y, and a plurality of defect columns 52b arranged on a straight line X orthogonal to the straight line Y. And a second linear portion 62 formed by
1996 Physical Review Letter, 77, 3787-3790 (A. Mekis, JC Chen, I. Kurland, S. Fan, PR Villeneuve, and JD Joannopoulos, “High Transmission through Sharp Bends in Photonic Crystal Waveguides , ”Phys. Rev. Lett., Vol. 77, pp. 3787-3790, 1996.) 2005 Journal of Optical Society of America B, B22, 11, 11472 (M. Tokushima, J. Ushida, A. Gomyo, and H. Yamada, “Efficient Transmission Mechanisms for Waveguides with 90 ° Bends in Pillar Photonic Crystals ”, J. Opt. Soc. Am. B 22, 11, 2472 (2005).)

  However, the light incident on the intersection cannot be efficiently transmitted simply by providing a simple cross structure in the line defect waveguide of the photonic crystal. Specifically, optical power loss occurs due to reflection of light at the intersection.

  The present invention has been made in view of the above situation, and an object thereof is to realize a line defect waveguide having a crossing portion with high light transmittance.

  The photonic crystal body of the present invention is a photonic crystal body in which a line defect waveguide including an intersection where line defects intersect is formed. The line defect has a first straight portion, a second straight portion, a third straight portion, a fourth straight portion, and an intersecting portion.

  The first straight line portion is formed along a straight line Y1 parallel to the straight line Y. The second straight line portion is formed along a straight line X1 parallel to the straight line X orthogonal to the straight line Y. The third straight line portion is formed along the straight line Y2 in a mirror-symmetrical position with respect to the straight line Y1 with the straight line Y as the axis of symmetry, and is point-symmetric with the first straight line portion with respect to the intersection point P between the straight line Y and the straight line X. It is. The fourth straight line portion is formed along the straight line X2 that is mirror-symmetrical with the straight line X1 with the straight line X as the axis of symmetry, and is point-symmetric with respect to the second straight line portion with respect to the intersection point P.

  The center of gravity of the cross section in the xy plane including the straight line X and the straight line Y of the plurality of defect pillars constituting the first straight line portion is on the straight line Y1. The center of gravity of the cross section in the xy plane of the plurality of defect pillars constituting the second straight line portion is on the straight line X1. The center of gravity of the cross section in the xy plane of the plurality of defect pillars constituting the third straight line portion is on the straight line Y2. The center of gravity of the cross section in the xy plane of the plurality of defect pillars constituting the fourth straight line portion is on the straight line X2.

  The intersection is composed of n × n defect columns (n is an odd number) arranged in a lattice pattern. The center of gravity of the cross section in the xy plane of the central defect column located at the center of the plurality of defect columns constituting the intersection is located at the intersection P. The first apex defect column constituting one of the four corners of the intersecting portion is close to the end of the first straight portion on the intersection P side. The second apex defect column constituting the other one of the four corners of the intersecting portion is close to the end on the intersection P side of the third straight portion. The third apex defect column constituting the other one of the four corners of the intersecting portion is close to the end of the second straight portion on the intersection P side. The fourth apex defect column constituting the other one of the four corners of the intersecting portion is close to the end portion on the intersection P side of the fourth straight portion.

  According to the present invention, the above object can be achieved.

  The above and other objects, features, and advantages of the present invention will become apparent from the following description and reference to the accompanying drawings illustrating an example of the present invention.

It is a schematic diagram showing a typical structure of a columnar square lattice photonic crystal of finite thickness. It is typical sectional drawing which shows arrangement | positioning of the cylinder which comprises the line defect waveguide in the photonic crystal body shown in FIG. It is typical sectional drawing which shows arrangement | positioning of the cylinder which comprises the line defect waveguide in the photonic crystal body of this invention. It is a figure which shows the electromagnetic field distribution of the light which propagates the line defect waveguide in the photonic crystal body shown in FIG. It is a figure which shows the electromagnetic field distribution of the light which propagates the line defect waveguide in the photonic crystal body shown in FIG. It is typical sectional drawing which shows the modification of arrangement | positioning of a cylinder.

  The electromagnetic field structure of the guided light in the vicinity of the line defect formed in the photonic crystal body propagates in an oblique direction opposite to the traveling direction of the guided light while intersecting each other at the same angle and the same phase. It can be approximated by two plane wave electromagnetic fields. This is also described in Non-Patent Document 2 above.

  Therefore, when the line defect waveguide is cut at a plane of 90 ° with respect to the traveling direction of the guided light, the guided light is emitted obliquely at an angle of 45 ° to the left and right with respect to the direction of the waveguide. This is the reason why the guided light cannot efficiently pass through the intersection of a simple cross structure provided in the line defect waveguide.

  In the present invention, by cutting the line defect waveguide at an angle of 45 ° with respect to the light traveling direction, the light emitted at an angle of 45 ° from the waveguide is transmitted by the waveguide disposed in front of the propagation direction. Condensate. The light radiated from the waveguide and propagating at an angle of 45 ° is almost a plane wave, so that it does not spread in the direction of another waveguide that intersects the waveguide. Therefore, light does not leak into the intersecting waveguides, and the light can efficiently pass through the intersecting portion.

  Hereinafter, an example of an embodiment of the photonic crystal body of the present invention will be described in detail with reference to the drawings.

  FIG. 3 is a schematic cross-sectional view showing the arrangement of the columns constituting the photonic crystal body according to the present embodiment. Line defects 12 are formed in the illustrated photonic crystal. Specifically, the defective column 12b is arranged among many non-defective columns 12a arranged in a square lattice pattern. Here, the line-defect optical waveguide of the photonic crystal shown in FIG. 2 and the line-defect optical waveguide of the photonic crystal shown in FIG. 3 are common in that they have an intersection where the propagation directions of the guided light are orthogonal. ing. However, the detailed structure differs as follows.

  The line defect 52 constituting the line defect optical waveguide shown in FIG. 2 includes a first straight part 61 constituted by a plurality of defect pillars 52b arranged on the straight line Y and a straight line X orthogonal to the straight line Y. The second straight line portion 62 constituted by the plurality of defect pillars 52b arranged above is orthogonal at the intersection point P between the straight line X and the straight line Y. In other words, two line defects (the first straight line portion 61 and the second straight line portion 62) are orthogonal to each other, and the intersection is one defect arranged at the intersection point P between the straight line X and the straight line Y. It is comprised by the pillar 52b.

  In contrast, the line defect of the line defect optical waveguide shown in FIG. 3 has four straight portions (first straight portion 21, second straight portion 22, third straight portion 23, and fourth straight portion 24). And an intersection 30 formed at a position where these four straight portions are concentrated. Furthermore, the intersection 30 is constituted by a plurality of defect pillars.

  Specifically, the first straight portion 21 includes three defect pillars 12b arranged along a straight line Y1 parallel to the straight line Y.

  The second straight line portion 22 is composed of three defect pillars arranged along a straight line X1 parallel to the straight line X orthogonal to the straight line Y.

  The third straight line portion 23 is composed of three defect columns arranged along the straight line Y2 that is mirror-symmetrical with the straight line Y1 with the straight line Y as the axis of symmetry.

  The fourth straight line portion 24 is composed of three defect pillars arranged along the straight line X2 that is mirror-symmetrical with the straight line X1 with the straight line X as the symmetry axis.

  The intersection 30 is composed of 3 × 3 defect pillars 12b arranged in a lattice pattern.

  Here, in order to more clearly describe the positions of the defect pillars constituting the line defect 12 and the intersection 30, an X, Y coordinate system having an origin at an intersection P between the straight line X and the straight line Y is defined. In such a coordinate system, the right direction in FIG. 1 from the origin is the + X direction, and the left direction is the −X direction. Further, the upper direction in FIG. 1 from the origin is defined as + Y direction, and the lower direction is defined as −Y direction.

  The three defect pillars 12b constituting the first straight line portion 21 are arranged on a straight line Y1 parallel to the Y axis. More specifically, the centroids of the cross sections in the xy plane including the X axis and the Y axis of the three defect pillars 12b constituting the first straight part 21 are arranged on the straight line Y1. The three defect pillars 12b constituting the first straight portion 21 have a first lattice constant (y0) in a direction parallel to the Y axis.

  The three defect pillars 12b constituting the third straight line portion 23 are arranged on a straight line Y2 that is mirror-symmetrical with the straight line Y1 with the Y axis as a symmetry axis. More specifically, the centroids of the cross sections in the xy plane of the three defect pillars 12b constituting the third straight line portion 23 are arranged on the straight line Y2. The three defect pillars 12b constituting the third straight line portion 23 have the first lattice constant (y0) in the direction parallel to the Y axis. Further, the third straight line portion 23 is point-symmetric with the first straight line portion 21 with respect to the origin. Here, when the lengths of the first linear portion 21 and the third linear portion 23 are different, in a strict sense, they are not point-symmetric. However, the first straight line portion 21 and the third straight line portion 23 may be point-symmetric within a range where the distance from the origin is equal.

  The three defect pillars 12b constituting the second straight portion 22 are arranged on a straight line X1 parallel to the X axis. More specifically, the centroids of the cross sections in the xy plane of the three defect pillars 12b constituting the second straight line portion 22 are arranged on the straight line X1. Further, the three defect pillars 12b constituting the second linear portion 22 have a second lattice constant (x0) in a direction parallel to the X axis.

  The three defect pillars 12b constituting the fourth straight portion 24 are arranged on a straight line X2 that is mirror-symmetrical with the straight line X1 with the X axis as the symmetry axis. More specifically, the center of gravity of the cross section in the xy plane of the three defect pillars 12b constituting the fourth straight line portion 24 is arranged on the straight line X2. Further, the three defect pillars 12b constituting the fourth linear portion 24 have a first lattice constant (x0) in a direction parallel to the X axis. Furthermore, the fourth straight line portion 24 is point-symmetric with the second straight line portion 22 with respect to the origin. Again, when the lengths of the second straight line portion 22 and the fourth straight line portion 24 are different, they are not point-symmetric in the strict sense. However, the second straight line portion 22 and the fourth straight line portion 24 may be point-symmetric within a range where the distance from the origin is equal.

  The intersecting portion 30 is composed of nine (3 × 3) defect columns 12b arranged in a lattice pattern with the defect column 12b (central defect column 3a) located at the origin as the center.

  Of the plurality of defect pillars 12b constituting the intersecting portion 30, the defect pillar 12b (first vertex defect pillar 30b) constituting one of the four corners of the intersecting portion 30 is the first straight portion 21. Close to the end on the origin side.

  Of the plurality of defect pillars 12b constituting the intersecting portion 30, the defect pillar 12b (second vertex defect pillar 30c) constituting the other one of the four corners of the intersecting portion 30 is the second It is close to the end of the straight line portion 22 on the origin side.

  Further, among the plurality of defect pillars 12b constituting the intersecting portion 30, the defect pillar 12b (third vertex defect pillar 30d) constituting the other one of the four corners of the intersecting portion 30 is the third defect pillar 12b. It is close to the end of the straight line portion 23 on the origin side.

  Further, among the plurality of defect pillars 12b constituting the intersecting portion 30, the defect pillar 12b (fourth vertex defect pillar 30e) constituting the other one of the four corners of the intersecting portion 30 is the fourth defect pillar 12b. It is close to the end of the straight line portion 24 on the origin side.

  In addition, among the plurality of defect columns 12b constituting the intersecting portion 30, a pair of adjacent defect columns 30f and 30g located on both sides of the central defect column 30a are arranged on the Y axis. Further, among the plurality of defect columns 12b constituting the intersecting portion 30, the other pair of adjacent defect columns 30h and 30i located on both sides of the center defect column 30a are arranged on the X axis.

  The arrangement of the nine defect pillars constituting the intersection 30 will be described in more detail.

  The center of gravity of the cross section of the first apex defect column 30b in the xy plane is the same direction from the position moved from the end of the first straight line portion 21 by the distance of the first lattice constant (y0) in the -Y direction. Is moved by a distance (y1a) less than the first lattice constant (y0) and further moved in the + X direction by a distance (x1a) less than the second lattice constant (x0). That is, the first apex defect column 30b deviates from the square lattice arrangement and is close to the center defect column 30a. The absolute value of the shift amount of the first apex defect column 30b with respect to the square lattice arrangement corresponds to the combined distance of the distance (y1a) and the distance (x1a).

  The center of gravity of the cross section in the xy plane of the second apex defect column 30d is in the same direction from the position moved from the end of the third straight line portion 23 in the + Y direction by the distance of the first lattice constant (y0). The position is moved by a distance (y1a) less than the first lattice constant (y0), and further moved in the −X direction by a distance (x1a) less than the second lattice constant (x0). That is, the second apex defect column 30d deviates from the square lattice arrangement and is close to the center defect column 30a. The absolute value of the shift amount of the second apex defect column 30d with respect to the square lattice arrangement corresponds to the combined distance of the distance (y1a) and the distance (x1a).

  The center of gravity of the cross section of the third apex defect column 30c in the xy plane is the same in the same direction from the position moved from the end of the second straight line portion 22 by the distance of the second lattice constant (x0) in the + X direction. The position is moved by a distance (x1b) less than the second lattice constant (x0), and further moved in the + Y direction by a distance (y1b) less than the first lattice constant (y0). That is, the third vertex defect column 30c is out of the square lattice arrangement and is close to the center defect column 30a. The absolute value of the shift amount of the third apex defect column 30c with respect to the square lattice arrangement corresponds to the combined distance of the distance (y1b) and the distance (x1b).

  The center of gravity of the cross section of the fourth apex defect column 30e in the xy plane is the same direction from the position moved from the end of the fourth straight line portion 24 by the distance of the second lattice constant (x0) in the -X direction. Is moved by a distance (x1b) less than the second lattice constant (x0) and further moved in the −Y direction by a distance (y1b) less than the first lattice constant (y0). That is, the fourth apex defect column 30e deviates from the square lattice arrangement and is close to the center defect column 30a. The absolute value of the shift amount of the fourth apex defect column 30e with respect to the square lattice arrangement corresponds to the combined distance of the distance (y1b) and the distance (x1b).

  The center of gravity of the cross section in the xy plane of the adjacent defect column 30f on the Y axis is located at a position (y2) that is less than the first lattice constant (y0) in the + Y direction from the origin. The center of gravity of the cross section of the adjacent defect column 30g on the Y axis in the xy plane is located at a position (y2) that is less than the first lattice constant (y0) in the -Y direction from the origin.

  The center of gravity of the cross section in the xy plane of the adjacent defect column 30h on the X axis is located at a position (x2) that is less than the second lattice constant (x0) in the -X direction from the origin. Further, the center of gravity of the cross section in the xy plane of the adjacent defect pillar 30i on the X axis is located at a position (x2) that is less than the second lattice constant (x0) in the + X direction from the origin.

  Here, the distance (y1a) is preferably a distance corresponding to 5% to 15% of the first lattice constant (y0), and more preferably a distance corresponding to 10%. The distance (x1a) is preferably a distance corresponding to 5% to 15% of the second lattice constant (x0), and more preferably a distance corresponding to 10%.

  Further, the first lattice constant (y0) and the second lattice constant (x0) are equal, and the distance (y1a), the distance (y1b), the distance (x1a), and the distance (x1b) are equal within the above range. desirable.

  Furthermore, the distance (y2) is preferably a distance corresponding to 70% to 90% of the first lattice constant (y0), and more preferably a distance corresponding to 77.5%. The distance (x2) is preferably a distance corresponding to 70% to 90% of the second lattice constant (x0), and more preferably a distance corresponding to 77.5%.

  In the simulation conducted by the present inventors, the distance (y1a) and the distance (x1a) are 10% of the first lattice constant (x0) and the second lattice constant (x0), and the distance (y2) and the distance (x2) are The best results were obtained with 77.5% of the first lattice constant (y0) and the second lattice constant (x0). In the simulation, the first lattice constant (y0) and the second lattice constant (x0) were 0.4 μm, the diameter of the non-defective column was 0.24 μm, and the diameter of the defective column was 0.16 μm.

  FIG. 4 is a map showing the electromagnetic field distribution of the guided light propagating through the line defect optical waveguide that satisfies the above conditions. On the other hand, FIG. 5 is a map showing the electromagnetic field distribution of the guided light propagating through the line defect optical waveguide shown in FIG. In any map, light is incident from the lower side of the page. The map shown in the figure is an electromagnetic field distribution obtained by simulation.

  As shown in FIG. 5, the electromagnetic field of the guided light propagating through the line defect waveguide shown in FIG. 2 not only transmits through the intersection, but also leaks into the left and right waveguides.

  On the other hand, as shown in FIG. 4, the electromagnetic field of the guided light propagating through the line defect waveguide satisfying the above condition propagates in the direction of 45 ° to the left at the intersection, and then the efficiency is applied to the upper waveguide. It is well incident and propagating.

  As described above, according to the present invention, the light transmittance at the intersection of the line defect waveguide is improved as compared with the conventional case. Therefore, even if the line defect waveguide is designed by giving priority to characteristics other than the light transmittance at the intersecting portion, the light transmittance at the intersecting portion is maintained equal to or higher than the conventional one. Accordingly, it is possible to achieve both the light transmittance at the intersection and other characteristics, and to improve the characteristics of the entire optical integrated circuit using the photonic crystal. As a result, high integration and productivity improvement of the optical integrated circuit are realized.

  Next, the method for producing the photonic crystal of the present invention will be outlined. The photonic crystal of the present invention can be produced using an SOI wafer (Silicon On Insulator Wafer). For example, an SOI wafer in which a buried oxide film having a thickness of 2.0 μm and a silicon active layer having a thickness of 1.0 μm are formed can be used. The silicon active layer is non-doped.

  First, the pattern shown in FIG. 3 is drawn using an electron beam exposure technique. When the wavelength of the guided light is 1.55 μm, the lattice constant is 0.4 μm, the diameter of the cylinder is 0.24 μm, and the diameter of the line defect column is 0.16 μm.

  Next, the silicon active layer is vertically processed according to the drawn resist pattern by anisotropic dry etching.

  Thereafter, the remaining resist pattern is removed with acetone, and finally an ultraviolet curable resin having the same refractive index of 1.45 as that of the buried oxide film is applied and cured.

  As mentioned above, although the example of embodiment of the photonic crystal body of this invention was demonstrated, this invention is not limited to the said embodiment. For example, the numerical values described above as the number of line defect columns constituting the branch portion and the shift amount with respect to the periodic arrangement of the line defect columns are merely examples, and can be appropriately changed as necessary. For example, the defect column at the end of each straight line portion can be moved in the direction approaching the intersection. In the example shown in FIG. 6, of the defect pillars 12 b constituting the first straight line portion 21 and the third straight line portion 22, the two defect pillars 12 b closest to the intersection 30 are the first lattice. The intersection 30 is approached by 1/20 period of the constant (y0). Similarly, of the defect pillars 12b constituting the second straight part 22 and the fourth straight part 24, the two defect pillars 12b closest to the intersecting part 30 have the second lattice constant (x0). Is approaching the intersection 30 by 1/20 period.

  When optimizing the number of misaligned columns and the amount of misalignment, especially the number of misaligned columns constituting the intersection and the amount of misalignment, the number of misaligned columns and the amount of misalignment are determined by FDTD simulation (finite difference time domain simulation). It is desirable to optimize. Specifically, the change in the light transmittance at the intersection is confirmed while changing the number of defect columns and the amount of deviation.

  Further, it is possible to displace a cylinder other than the line defect column constituting the branching portion, and to increase or decrease the cross-sectional area thereof. Furthermore, the column does not necessarily have to be a cylinder, and may have another shape such as a quadrangular column or an octagonal column.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2007-257616 for which it applied on October 1, 2007, and takes in those the indications of all here.

Claims (9)

A photonic crystal in which a line defect waveguide including an intersection is formed,
The line defect of the line defect waveguide is
A first straight line portion formed along a straight line Y1 parallel to the straight line Y;
A second straight line portion formed along a straight line X1 parallel to the straight line X orthogonal to the straight line Y;
Formed along a straight line Y2 that is mirror-symmetrical with the straight line Y1 with the straight line Y as the axis of symmetry, and a first point that is point-symmetric with respect to the intersection point P between the straight line Y and the straight line X Three straight sections;
The straight line X is formed along the straight line X2 that is mirror-symmetrical with the straight line X1 with the symmetry axis as the symmetry axis, and the second straight line part and the fourth straight line part that is point-symmetric with respect to the intersection point P are provided. And
The first corner of the four corners of the intersection is close to the end on the intersection P side of the first straight portion,
The second corner of the four corners of the intersection is close to the end on the intersection P side of the third straight portion,
A third corner of the four corners of the intersecting portion is close to an end on the intersection P side of the second straight portion,
The fourth corner of the four corners of the intersection is close to the end on the intersection P side of the fourth straight portion,
Photonic crystal. The first straight line portion is composed of a plurality of defect columns in which the center of gravity of the cross section in the xy plane including the straight line X and the straight line Y is arranged on the straight line Y1,
The second straight line portion is composed of a plurality of defect pillars in which the center of gravity of the cross section in the xy plane is arranged on the straight line X1,
The third straight line portion is composed of a plurality of defect pillars in which the center of gravity of the cross section in the xy plane is arranged on the straight line Y2.
The fourth straight line portion is composed of a plurality of defect pillars whose cross-sectional centroids in the xy plane are arranged on the straight line X2.
The intersection is composed of n × n defect columns (n is an odd number) arranged in a lattice pattern,
The center defect column located at the center of the plurality of defect columns constituting the intersecting portion has a center of gravity of a cross section in the xy plane located at the intersection P,
Of the plurality of defect pillars constituting the intersection, the first vertex defect pillar constituting the first corner of the intersection is the intersection P side of the first straight part. Close to the end of the
Of the plurality of defect pillars constituting the intersection, the second vertex defect pillar constituting the second corner of the intersection is on the intersection P side of the third straight line. Close to the end of the
Of the plurality of defect pillars constituting the intersection, the third vertex defect pillar constituting the third corner of the intersection is on the intersection P side of the second straight line. Close to the end of the
Of the plurality of defect pillars constituting the intersection, the fourth vertex defect pillar constituting the fourth corner of the intersection is on the intersection P side of the fourth straight part. Close to the end of the
The photonic crystal body according to claim 1.   The photonic crystal body according to claim 2, wherein the intersecting portion is constituted by 3 × 3 defect pillars. The first straight line portion and the third straight line portion have a first lattice constant (y0) in the direction of the straight line Y;
The second straight line portion and the fourth straight line portion have a second lattice constant (x0) in the direction of the straight line X;
The center of gravity of the cross section in the xy plane of the first vertex defect column and the third vertex defect column is in the direction of the straight line Y from the end of the first straight portion or the third straight portion. Close to the central defect column by a distance (y1a) less than the first lattice constant (y0) in the direction of the straight line Y from a position close to the central defect column by the distance of the first lattice constant (y0) And, in the direction of the straight line X, is located close to the central defect column (7) by a distance (x1a) less than the second lattice constant (x0),
The center of gravity of the cross section in the xy plane of the second apex defect column and the fourth apex defect column is in the direction of the straight line X from the end of the second straight line part or the fourth straight line part. Close to the central defect column by a distance (x1b) less than the second lattice parameter (x0) in the direction of the straight line X from a position close to the central defect column by the distance of the second lattice parameter (x0) And, in the direction of the straight line Y, in the position close to the central defect column by a distance (y1b) less than the first lattice constant (y0),
A pair of adjacent defect columns located on both sides of the central defect column along the direction of the straight line Y has a center of gravity of a cross section in the xy plane from the intersection point P in the direction of the straight line Y. At a distance (y2) less than a constant (y0),
A pair of adjacent defect columns located on both sides of the central defect column along the direction of the straight line X has a center of gravity of a cross section in the xy plane, the second lattice extending from the intersection point P in the direction of the straight line X. At a distance (x2) less than a constant (x0),
The photonic crystal body according to claim 3.   The first lattice constant (y0) and the second lattice constant (x0) are equal, and the distance (y1a), the distance (y1b), the distance (x1a), and the distance (x1b) are equal. The photonic crystal body according to the fourth item in the range.   The distance (y1a) is a distance corresponding to 5% to 15% of the first lattice constant (y0), and the distance (x1a) is 5% to 15% of the second lattice constant (x0). The photonic crystal body according to claim 5, which has a corresponding distance.   The distance (y1a) is a distance corresponding to 10% of the first lattice constant (y0), and the distance (x1a) is a distance corresponding to 10% of the second lattice constant (x0). The photonic crystal body according to claim 6.   The distance (y2) is a distance corresponding to 70% to 90% of the first lattice constant (y0), and the distance (x2) is 70% to 90% of the second lattice constant (x0). 8. The photonic crystal body according to claim 5, wherein the photonic crystal body has a corresponding distance.   The distance (y2) is a distance corresponding to 77.5% of the first lattice constant (y0), and the distance (x2) is equivalent to 77.5% of the second lattice constant (x0). The photonic crystal body according to claim 8, which is a distance.

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