JP2005274844A - Light control element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturized/low-loss light control element capable of controlling the group speed delay and wavelength dispersion of light having short pulses. <P>SOLUTION: The light control element consists of a composite defective waveguide 6 obtained by arranging two defective waveguides 3, 5 in series which have respectively different refractive index ratios regulated by the refractive indexes of the defective waveguides 3, 5 to the background refractive indexes of photonic crystals 2, 4. When the background refractive indexes of respective photonic crystals 2, 4 corresponding to these defective waveguides 3, 5 are made different, constitution formed by combining the defective waveguide 3 having a secondary positive high-order dispersion waveguide mode e.g. and the defective waveguide 5 having secondary negative high-order dispersion waveguide mode e.g. can be obtained, frequency showing zero dispersion in a comparatively narrow frequency range which is used as incident light can be realized, and the wavelength dependency of a primary dispersion curve of the composite defective waveguide 6 can be sharply reduced, so that the light control element can be easily manufactured and has a large dispersion control effect and a large group speed delay effect. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical control element using a photonic crystal, and more specifically, a small and high-performance optical control element suitable for use in high-speed and high-capacity optical communication and high-speed optical signal processing in the field of optical transmission exceeding 10 Gbps. About.

  In recent years, photonic crystals have attracted attention, and dispersion compensation elements using photonic crystals have been proposed in, for example, Patent Documents 1 and 2. A dispersion compensator using a coupling defect waveguide has been proposed in, for example, Patent Document 3.

  Non-Patent Documents 1 and 2 and the like have been published regarding photonic crystals having a novel chirp structure.

JP 2000-121987, JP 2000-224109 A JP 2002-333536 A 64th JSAP Scientific Lecture Meeting; 1pZM14; October 1, 2003 50th Joint Conference on Applied Physics; 28pYN1; March 28, 2003

  When performing high-speed and high-capacity optical communication and high-speed optical signal processing, problems such as dispersion such as spread of optical signal pulses in a transmission path such as a fiber and skew in which the arrival time of each signal varies occur, which hinders speedup. Yes. In order to solve this problem, an element capable of controlling the dispersion and the group delay of the optical pulse that determines the arrival time is necessary. As a conventional technique, there is a method of using an optical fiber having unique dispersion characteristics. . This is realized by propagating light through an optical fiber having a specific dispersion by adjusting the length to a necessary length so that the group delay is appropriate. However, although the optical fiber is wound, it is necessary to use a long optical fiber, the element itself is very large, and the degree of freedom in the dispersion characteristic of the optical fiber is small, so that advanced signal processing and many It is impossible to realize downsizing and integration of devices necessary for enabling parallel processing of lines.

  Regarding dispersion compensation, there is also research that enables precise dispersion control and adjustment of the amount of dispersion compensation using a chirped fiber grating. However, in order to perform dispersion compensation, it is necessary to use an optical fiber having a long metric order, and it is impossible to realize downsizing and integration of the apparatus. Further, since the element using the chirped structure fiber grating always uses incident light reflected, a circulator is indispensable for obtaining high efficiency, and this also greatly hinders the miniaturization and integration of the apparatus.

  Recently, in order to solve these problems, attention has been paid to dispersion using a photonic crystal and a group velocity delay effect. In an optical waveguide called a defect waveguide into which a photonic crystal itself or a linear defect is introduced, a large specificity appears in the dispersion characteristic representing the relationship between frequency and wave number. Dispersion compensation elements using a photonic crystal are described in Patent Documents 1 and 2 and the like. However, since propagating light is not confined in the waveguide structure in the photonic crystal, the angle dependency is large and there is a problem in reliability. It is not practical because it is difficult to reduce the size of the device. On the other hand, it is theoretically predicted that the defect waveguide has a zero group velocity at the Brulian zone edge called the band edge, and is actually a low group of 1/90 of the speed of light in vacuum near the band edge. Speed has been observed. However, this defect waveguide generally has a very large chromatic dispersion value. When a short pulse having a broad spectrum width is incident, the group velocity can be slowed down. Arise. For this reason, it is difficult to realize an element that performs dispersion control or group velocity control using a simple defect waveguide.

  On the other hand, in a structure called a coupling defect waveguide in which point-like defects are continuously scattered, relatively large dispersion can be obtained in a relatively wide band, and these dispersion values are 6 digits of the value of an optical fiber. The fiber-type dispersion compensation element, which has been required to have a length of km order, may be reduced to the order of mm. A dispersion compensator using this coupling defect waveguide is described in Patent Document 3 and the like. A dispersion compensator using a coupling defect waveguide disclosed in Patent Document 3 is usually composed of a waveguide and a dispersion compensation waveguide having a coupling defect, and the dispersion compensation waveguide is 20 ps / nm depending on the configuration. / Mm. However, in an easily fabricated slab type photonic crystal that has been studied in the past, when such a coupling defect waveguide is fabricated, the period of light traveling direction becomes long, so the light leakage condition called a light line is limited. Inevitably, the loss is so great that it cannot be used in practice.

  On the other hand, recently, by using a one-dimensional periodic structure composed of a multilayer film and propagating light in a direction perpendicular to the multilayer film, it is possible to construct a dispersion control element based on the same principle as a coupling defect waveguide. Have been conceived. However, since this method itself propagates light not in a waveguide but in space, it is difficult to reduce the size and integrate the device.

  In contrast, the present inventors have devised a photonic crystal having a novel chirp structure, and a structure that gradually changes the diameter of a circular hole in a line defect waveguide is disclosed in Non-Patent Documents 1 and 2, etc. Has been. With such a new structure, it has been studied by theory and experiment that zero band velocity due to the band edge is achieved for a specific propagation frequency, and the possibility of performing distributed control and group velocity control has been announced. . However, when a short pulse is incident, localization of specific discrete wavelength components occurs, and the reflected pulse waveform may be spread or distorted.

  Further, the present applicant has proposed a refractive index distribution type photonic crystal that realizes dispersion control and group velocity control as Japanese Patent Application No. 2004-39817. This is characterized by having a refractive index distribution in which the background refractive index of the photonic crystal changes continuously. Compact optical control capable of performing group velocity delay of several ps and controlling chromatic dispersion in an ultrashort pulse of 1 ps or less without widening the pulse width by this refractive index distribution type photonic crystal An element can be realized. However, in such a refractive index distribution type photonic crystal, in order to continuously change the background refractive index of the photonic crystal, it is necessary to provide a material or structure that can easily change the refractive index. For this reason, since the material and structure of the photonic crystal are restricted, a problem arises when other light control elements and integration are provided on the same substrate.

  An object of the present invention is to provide a small-sized and low-loss optical control element capable of controlling the group velocity delay and controlling the chromatic dispersion of short-pulse light.

  More specifically, a first object of the present invention is to provide a small and low-loss light control element that is easy to manufacture and has a large dispersion control effect and a group velocity delay effect.

  A second object of the present invention is to provide a small and low-loss light control element having a large dispersion compensation effect.

  A third object of the present invention is to provide a light control element having a greater compensation effect for second-order dispersion.

  A fourth object of the present invention is to provide a light control element capable of obtaining a greater dispersion compensation effect in realizing the above object.

  A fifth object of the present invention is to provide a small and low-loss light control element that is easy to manufacture and has a large dispersion control effect and group velocity delay effect.

  A sixth object of the present invention is to provide a light control element having a large dispersion compensation effect.

  The seventh object of the present invention is to provide a light control element having a greater compensation effect for second-order dispersion.

  An eighth object of the present invention is to make it easier to manufacture a light control element in realizing the seventh object.

  A ninth object of the present invention is to reduce loss in realizing the above object.

  A tenth object of the present invention is to provide a light control element with further reduced loss.

  An eleventh object of the present invention is to provide an even smaller light control element.

  A twelfth object of the present invention is to provide a light control element capable of realizing greater dispersion control with respect to third-order or higher-order dispersion in realizing the above object.

  A thirteenth object of the present invention is to provide a light control element capable of dynamically varying the dispersion control amount and the group velocity delay amount.

  According to a first object of the present invention, in the light control element comprising a photonic crystal having a defect waveguide according to claim 1, a defect waveguide having a second or higher-order positive high-order dispersion waveguide mode, A light control element comprising a composite defect waveguide in which a defect waveguide having a waveguide mode of negative higher-order dispersion having the same order as that of positive higher-order dispersion is arranged in series.

  According to a second object of the present invention, the absolute value of the positive high-order dispersion and the absolute value of the negative high-order dispersion are substantially the same. Light control element "is realized.

  A third object of the present invention is the waveguide mode in which the wave number of one defect waveguide among the complex defect waveguides is increased with increasing frequency, and the other 3. The light control element according to claim 1, wherein the waveguide mode of the defective waveguide is a waveguide mode in which the wave number decreases with increasing frequency.

  A fourth object of the present invention is as set forth in claim 4, wherein the group velocities of the two defect waveguide portions constituting the composite defect waveguide are approximately the same. It is realized by the light control element according to one embodiment. "

  According to a fifth object of the present invention, in the light control element comprising a photonic crystal having a defect waveguide, the refractive index of the defect waveguide is defined with respect to the background refractive index of the photonic crystal. It consists of a composite defect waveguide in which two or more defect waveguides with different refractive index ratios are arranged in series, and the background refractive index of each photonic crystal corresponding to these two or more defect waveguides is different It is realized by the light control element.

  The sixth object of the present invention is that the background refractive index of the photonic crystal having a smaller refractive index ratio is smaller than the background refractive index of the photonic crystal having a larger refractive index ratio. The light control element according to claim 5 is realized.

  The sixth object of the present invention is that the background refractive index of the photonic crystal having the smaller refractive index ratio is larger than the background refractive index of the photonic crystal having the larger refractive index ratio. The light control element according to claim 5 is realized.

  A seventh object of the present invention is to provide a refractive index of the defective waveguide relative to a background refractive index of a photonic crystal comprising a defective waveguide having a waveguide mode whose wave number decreases with increasing frequency. The refractive index ratio specified is based on the refractive index ratio specified by the refractive index of the defect waveguide with respect to the background refractive index of the photonic crystal having a defect waveguide having a waveguide mode whose wave number increases with increasing frequency. The light control element according to claim 3, which is also smaller.

  An eighth object of the present invention is to provide a defect waveguide having a waveguide mode whose wave number increases with an increase in frequency, in a hole defect of a photonic crystal or a line defect structure of a pillar structure. 9. The light control element according to claim 3, wherein the light control element comprises a composite defect structure having a minute refractive index contrast structure different from the line defect structure.

  An eighth object of the present invention is the above-mentioned “the minute refractive index contrast structure is composed of a low refractive index hole structure or a pillar structure having a shape different from that of the background photonic crystal. Item 9. A light control element according to item 9.

  According to a ninth object of the present invention, the refractive index of two defect waveguide portions arranged in series constituting the composite defect waveguide is substantially the same. Or a light control element according to any one of 10).

  According to a tenth object of the present invention, there is provided an intermediate light propagation means between two defect waveguides arranged in series and constituting the composite defect waveguide. Or a light control element according to any one of 11).

  An eleventh object of the present invention is that the composite defect waveguide comprising two defect waveguides arranged in series is connected in series by a directional coupler. It implement | achieves by the light control element as described in any one of Claims 1 thru | or 11.

  The twelfth object of the present invention is that the group velocity of the defect waveguide portion of the composite defect waveguide composed of two defect waveguides arranged in series is substantially zero. It is implement | achieved by the light control element of claim | item 3. ".

  According to a thirteenth object of the present invention, the relationship between the background refractive index of a photonic crystal having a composite defect waveguide composed of two defect waveguides arranged in series and the refractive index of the defect waveguide portion is described in claim 15. 15. The light control element according to claim 1, wherein at least one of the refractive indexes is variable.

  According to the first aspect of the present invention, a defect waveguide having a waveguide mode of positive higher-order dispersion of the second order or higher and a negative higher-order dispersion waveguide mode of the same order as the positive higher-order dispersion is provided. Since it consists of a composite defect waveguide arranged in series with a defect waveguide, it is possible to realize a frequency or wavelength of zero dispersion in a relatively narrow frequency or wavelength range used as incident light, and the primary of the composite defect waveguide The wavelength dependency of the dispersion curve can be greatly reduced, and thus a small and low-loss light control element that is easy to manufacture and has a large dispersion control effect and group velocity delay effect can be provided.

  According to the invention described in claim 2, in the light control element described in claim 1, the dispersion compensation effect can be increased by making the absolute values of positive and negative high-order dispersions substantially the same.

  According to the third aspect of the invention, in the light control element according to the first or second aspect, the increase / decrease profile of the second order dispersion can be made almost symmetrical, and a greater dispersion compensation effect is exhibited with respect to the second order dispersion. Can be made.

  According to the invention described in claim 4, in the light control element according to any one of claims 1 to 3, since the group velocities of the two defect waveguide portions constituting the composite defect waveguide are substantially the same, An even greater dispersion compensation effect can be exhibited.

  According to the fifth aspect of the present invention, from the composite defect waveguide in which two or more defect waveguides having different refractive index ratios defined by the refractive index of the defect waveguide with respect to the background refractive index of the photonic crystal are arranged in series. Therefore, since the background refractive indexes of the photonic crystals corresponding to these two or more defect waveguides are different, the defect waveguide having a second or higher order positive high-order dispersion waveguide mode and the positive high It is possible to clarify a configuration example in which a defect waveguide having a waveguide mode of negative higher-order dispersion of the same order as the first-order dispersion is clarified. Therefore, a large dispersion control effect and a group velocity delay effect can be obtained easily. A small and low-loss light control element can be provided.

  According to the invention described in claim 6, in the light control element according to claim 5, the background refractive index of the photonic crystal having the smaller refractive index ratio is the background refractive index of the photonic crystal having the larger refractive index ratio. Therefore, a larger dispersion compensation effect can be exhibited.

  According to the invention described in claim 7, in the light control element according to claim 5, the background refractive index of the photonic crystal having the smaller refractive index ratio is the background refractive index of the photonic crystal having the larger refractive index ratio. Therefore, a larger dispersion compensation effect can be exhibited.

  According to an eighth aspect of the present invention, in the light control element according to the third aspect, the defect guide with respect to the background refractive index of a photonic crystal comprising a defect waveguide having a waveguide mode whose wave number decreases with increasing frequency. The refractive index ratio defined by the refractive index of the waveguide is defined by the refractive index of the defective waveguide with respect to the background refractive index of the photonic crystal having a defective waveguide having a waveguide mode whose wave number increases with increasing frequency. Therefore, the secondary dispersion increase / decrease profile can be made almost symmetrical, and a larger dispersion compensation effect can be exhibited with respect to the secondary dispersion.

  According to the ninth aspect of the present invention, a defect waveguide having a waveguide mode in which the wave number increases with an increase in frequency is included in the line defect structure of a hole or pillar structure of a photonic crystal. Since it is composed of a composite defect structure having another minute refractive index contrast structure, a waveguide mode in which the wave number increases with increasing frequency can be easily realized, and the fabrication of the light control element can be further facilitated. .

  According to the invention described in claim 10, in the light control element described in claim 9, since the minute refractive index contrast structure is composed of a low refractive index hole structure or a pillar structure different from the background photonic crystal, A waveguide mode in which the wave number increases with respect to the increase can be easily realized, and the fabrication of the light control element can be facilitated.

  According to the eleventh aspect of the present invention, in the light control element according to any one of the first to tenth aspects, the refractive indexes of the two defect waveguide portions arranged in series constituting the composite defect waveguide are substantially the same. Therefore, it is possible to provide a light control element having a composite defect waveguide in which the reflection at the connection portion between the two defect waveguides is further reduced to improve the transmittance.

  According to a twelfth aspect of the present invention, in the light control element according to any one of the first to eleventh aspects, the intermediate light propagation means is provided between two defect waveguides that are arranged in series and constitute a composite defect waveguide. Since the difference in refractive index between the defect waveguides can be reduced or the same, the interface reflection between different structures caused by the difference in refractive index can be reduced. Loss can be reduced and the transmittance of the composite defect waveguide can be improved.

  According to a thirteenth aspect of the present invention, in the light control element according to any one of the first to eleventh aspects, the composite defect waveguide comprising two defect waveguides connected in series is serially connected by the directional coupler. Therefore, the dispersion control effect and the group velocity delay effect can be exhibited while further reducing the size.

  The invention according to claim 14 is the light control element according to claim 3, wherein the group velocity of the defect waveguide portion of the composite defect waveguide composed of two defect waveguides arranged in series is substantially zero. In a frequency or wavelength range in which the group velocity used as light is approximately 0, a frequency or wavelength that is zero dispersion can be realized, and the wavelength dependence of the primary dispersion of the composite defect waveguide can be reduced. Greater dispersion control can be made possible with respect to the above higher-order dispersion.

  According to a fifteenth aspect of the present invention, in the light control element according to any one of the first to fourteenth aspects, the background refractive index of a photonic crystal having a composite defect waveguide composed of two defect waveguides arranged in series, and Since the refractive index of at least one of the refractive index of the defect waveguide portion is variable, the dispersion control amount and the group velocity delay amount can be dynamically varied by combining with the control means, and the wavelength variation etc. Can be dealt with appropriately.

  The best mode for carrying out the present invention will be described with reference to the drawings.

[First embodiment]
A light control element according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram schematically showing a light control element 1 made of a slab type two-dimensional photonic crystal according to the present embodiment. In FIG. 1, 2 is a photonic crystal including a defect waveguide 3 having a positive second-order dispersion waveguide mode, and 4 includes a defect waveguide 5 having a negative second-order dispersion waveguide mode. It is a photonic crystal, and a composite defect waveguide 6 is formed by arranging these two defect waveguides 3 and 5 in series connection. 7 is a high refractive index thin film made of silicon, 8 is an air hole having a two-dimensional periodic arrangement provided in the high refractive index thin film 7, and 9 is a defect waveguide having a negative second-order dispersion waveguide mode. 5 is an air hole having a one-dimensional periodic arrangement provided as a minute refractive index contrast structure different from the defect waveguide 5 structure.

FIG. 2 schematically shows a cross-sectional structure example of the light control element 1 made of the slab type two-dimensional photonic crystal of the present embodiment shown in FIG. 2, the high refractive index thin films 7, 8 are air holes, 10 denotes a substrate, 11 is an under-cladding layer made of SiO _2. The hole 8 is vertically formed in a cylindrical shape in the high refractive index thin film 7, and its upper part is opened. The under cladding layer 11 is made of a material having a refractive index lower than that of the high refractive index thin film 7 and is a waveguide layer in which the high refractive index thin film 7 serves as a core layer. A substrate 10 is provided under the under cladding layer 11. The cross-sectional structure of the photonic crystal as shown in FIG. 2 can form the shape of the slab type two-dimensional photonic crystal itself using a technique by conventional fine processing.

  The structures called photonic crystals 2 and 4 shown in FIG. 1 and FIG. 2 are generally “photonic band gaps” in a material having a structure in which the refractive index has a constant periodicity in the wavelength order of light. It is known that it has a region where no photon is called. FIG. 3 is a diagram for explaining a periodic arrangement of a general photonic crystal having no defect. FIG. 3A shows the period and hole diameter of holes 8 in real space characterizing the structure of the photonic crystal. FIG. 3 (b) is a diagram showing the relationship of the wave number space corresponding to the period in the real space shown in FIG. 3 (a). In FIG. 3A, the period of the hole 8 of the photonic crystal is a, and the hole diameter is indicated by a radius r. At this time, the array having periodicity in the real space of FIG. 3A is three-fold rotationally symmetric, and the Brillouin zone having a hexagonal structure of three-fold rotational symmetry also in the wave number space of FIG. 12 is formed. In the Brillouin zone 12, the direction in which the holes 8 are close to each other to form a straight line is denoted as the Γ-K direction, and the middle direction of the Γ-K direction is denoted as the Γ-M direction.

  FIG. 4 is a band diagram of a photonic crystal showing a band of light that can propagate in the photonic crystal without defects of FIG. In FIG. 4, the horizontal axis is a normalized wave vector k corresponding to the Γ-K direction and the Γ-M direction. In FIG. 4, a triangular arrangement as shown in FIG. 3A is used as a two-dimensional photonic crystal, the refractive index of the high refractive index thin film 7 is 3.0, the refractive index of the hole 8 is 1.0, r / a A value = 0.30 was calculated by a two-dimensional plane wave expansion method. The vertical axis represents the normalized frequency ωN obtained by normalizing the light frequency ω. The wave vector corresponds to the propagation characteristics of light in the periodic structure, and the normalized frequency is a normalized frequency of light to be propagated. This normalized frequency is represented by ωN = ωa / 2πc, and its unit is It is dimensionless. This is the same as a / λ and may be considered as the ratio of wavelength to period. At this time, as shown in FIG. 4, there is a region 13 where the normalized frequency ωN is in the vicinity of 0.25 to 0.3 and no band exists at any wave number, and this region is called a photonic band gap.

  Even if light having a frequency corresponding to the photonic band gap 13 is incident in a predetermined direction, it is only reflected, and cannot be used as a light control element other than a reflection application. However, by providing a defect structure in the periodicity of the photonic crystal having the photonic band gap 13, a band that becomes a propagation mode corresponding to the defect is generated in the photonic band gap 13 and corresponds to this band. By making light of a frequency appropriately incident on a predetermined defect, it can be used as a light control element. A case where the defect is a hole defect is called a point defect, and a case where the defect is a plurality of continuous one-dimensional defects is called a line defect. When a line defect is provided in the photonic crystal, a waveguide called a defect waveguide in which light of a specific frequency is guided in the line defect may be formed. This defect waveguide has a waveguide band in the original photonic band gap 13 and has light propagation characteristics peculiar to various photonic crystals which are very different from those of a waveguide based on normal total reflection.

FIG. 5 illustrates a waveguide band generated by a photonic crystal having a defect waveguide, and a part of the band diagram of the photonic crystal having a defect waveguide is enlarged for explanation. As the photonic crystal, a configuration similar to that of the photonic crystal 2 in FIG. 1 was used, and a band diagram of a defect waveguide due to a single line defect was calculated by a two-dimensional plane wave expansion method. However, the normalized wave number obtained by normalizing the wave vector is used as the horizontal axis, and its unit is [2π / a] (a is the minimum period of the photonic crystal, and r is the hole radius of the photonic crystal). Due to the Brillouin zone folding, the maximum value for a given wave vector direction is normalized to 0.5, half of 1. In FIG. 5, two bands appear in the photonic band gap 13 whose normalized frequency ωN is in the vicinity of 0.25 to 0.3. Both of these bands are bands that can guide light only in the photonic crystal along the defect waveguide. A normalized frequency ωN is obtained for light of a predetermined frequency, and a horizontal line is obtained from this ωN. A predetermined frequency can be guided in the defect waveguide when it has an intersection with the two bands when pulled. Further, as the propagation state of light in the SiO ₂ to be in the air and under cladding, it is shown as each of the air and SiO ₂ of the light line.

At this time, the light guided through the defect waveguide exhibits a waveguide behavior that is very different from that in a normal waveguide or vacuum. For example, the propagation velocity is indicated as the group velocity Vg of light, and this group velocity Vg substantially corresponds to the first-order differential value with respect to the normalized wave number of the band (hereinafter simply referred to as wave number). It can be seen that the group velocities differ greatly with respect to the frequency and the value is small. The band that propagates in the air is indicated by a band of 1 / n (where n is the refractive index of the defect waveguide portion) called the SiO ₂ light line in FIG. ₂ corresponds to the propagation speed of light in the air, that is, in a vacuum. On the other hand, in the lower band (M0) in FIG. 5, when the wave number is near 0.3, the absolute value of the slope, which is the first derivative, is 0.2 or less, and conversely than in the air. The propagation speed of light can be reduced by 5 times. Since the refractive index of the original constituent material is 3.0 and the light propagation speed of the original material in the bulk state is three times that in vacuum, the light propagation speed can be reduced by about 1.5 times. Therefore, it can be used as a light control element for group velocity delay. However, as can be seen from FIG. 5, the inclination of the waveguide band changes greatly in accordance with the frequency of light, so that dispersion with respect to the frequency of light, that is, wavelength dispersion is very large. Is difficult to use.

  FIG. 6 shows the background refractive index (solid line: left axis) of the photonic crystals 2 and 4 constituting the light control element 1 of the present embodiment shown in FIG. 1, and the refractive index of the defect waveguides 3 and 5 (broken line: (Left axis), the refractive index ratio defined by the ratio of the latter to the former (dotted line: right axis) is shown with respect to the light propagation direction. In FIG. 6, as a coordinate (au) of a light propagation direction, 0.0 is an incident position to the composite defect waveguide 6, 0.5 is a connection end surface of the two defect waveguides 3 and 5, 1.0 is the exit position of the composite defect waveguide 6. Here, “refractive index” means an effective refractive index that takes into account structural influences. Even in a thin film made of the same silicon material, the thickness of the thin film is reduced or an air structure is provided in the thin film. As a result, the refractive index which means this effective refractive index becomes small. In FIG. 1, since the material refractive indexes of the photonic crystals 2 and 4 are the same, the reflection of propagating light due to this material refractive index difference is relatively reduced, so that the transmittance can be secured. In addition, the “background refractive index” here is a photonic crystal having a two-dimensional periodic array structure of a hole structure (or pillar structure) made of a medium having a refractive index contrast, and the periodic row has no defect. Refractive index as a background that is determined by both the refractive index of the material of the constituent material, the hole structure (or pillar structure), and the film thickness structure, which is determined by both the structural refractive index. Means.

With the composite defect waveguide 6 structure shown in FIG. 1 and FIG. 6, it is easy to fabricate with respect to a short-pulse optical pulse, and it becomes a small and low-loss optical control element 1 having a large dispersion control effect and a group velocity delay effect. Will be described in detail with reference to band diagrams in the structure. FIG. 7 is a band diagram of the defect waveguide shown in FIG. First, FIG. 7A shows a band diagram of the defect waveguide 3 included in the photonic crystal 2, wherein 21 is a band, 22 is a SiO ₂ light line, and 23 is a photonic band gap. FIG. 7B shows a band diagram of the defect waveguide 5 included in the photonic crystal 4, where 24 and 25 are bands, 22 is a SiO ₂ light line, and 26 is a photonic band gap. FIG. 7C shows a band diagram of the composite defect waveguide 6 including the defect waveguides 3 and 5, 27 is a photonic band gap of the defect waveguide, and 28 is an optical frequency of incident light of the composite defect waveguide. . 27, since the photonic band gaps 23 and 26 of the two different defect waveguides 3 and 5 are not constant values, there may actually be a slight deviation from the position of the broken line. In FIG. 7, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it is possible to propagate through the two defect waveguides 3 and 5, as shown in FIG. Incident light having a certain frequency is subjected to a group velocity delay effect while receiving different types of dispersion in the two defect waveguides 3 and 5, respectively. The band of the composite defect waveguide 6 shown in FIG. 7 is an air hole 8 having a hole radius r of r / a = 0.25 to 0.30 with respect to a silicon thin film having a thickness of about 0.5 μm. It can produce by providing.

  In FIG. 8, since the first derivative in the band of FIG. 7 shows the group velocity Vg, the wavelength λ1 and the wavelength λ2 corresponding to the vicinity of the optical frequency used as the first-order dispersion of the band with respect to the wavelength of the composite defect waveguide 6 based on this. This is shown in the range of. FIG. 8A shows a first-order dispersion diagram of the band 21 of the defect waveguide 3, and 29 is the first-order dispersion curve. FIG. 8B shows a first-order dispersion diagram of the band 24 of the defect waveguide 5, and 30 is the first-order dispersion curve. FIG. 8C shows a first-order dispersion diagram of the composite defect waveguide 6 composed of the defect waveguides 3 and 5, 31 is a first-order dispersion curve of the composite defect waveguide 6, and 28 is in FIG. 7C. It is the optical frequency of the incident light to the composite defect waveguide 6 shown in FIG. In FIG. 8, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. 8C. The incident light having a different frequency is subjected to the group velocity delay effect while receiving different types of primary dispersion in the two defect waveguides 3 and 5, respectively. It becomes a curve. Since the value of the vertical axis in the first-order dispersion curve 31 is equal to the reciprocal 1 / Vg value with respect to the group velocity Vg at each wavelength, the 1 / Vg value of the composite defect waveguide 6 is equal to each defect waveguide 3, It can be seen that the wavelength dependence of the first-order dispersion curve 31 of the composite defect waveguide 6 is greatly reduced by dispersion compensation by combining 5 group velocity delays.

  FIG. 9 corresponds to the second order differentiation of the band of FIG. 7 and shows the second order dispersion characteristics with respect to the wavelength of the composite defect waveguide 6. FIG. 9A shows a second-order dispersion diagram of the band 21 of the defect waveguide 3, and 32 shows a second-order dispersion curve of the band 21. FIG. 9B shows a second-order dispersion diagram of the defect waveguide 5, and 33 is a second-order dispersion curve of the band 24. FIG. 9C shows a second-order dispersion diagram of the composite defect waveguide 6 composed of the defect waveguides 3 and 5, 34 shows a second-order dispersion curve of the composite defect waveguide 6, and 28 shows in FIG. 7C. The optical frequency of the incident light to the composite defect waveguide 6.

  In FIG. 9, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. 9C. The incident light having a different frequency is subjected to the group velocity delay effect while receiving the different types of second-order dispersion in the two defect waveguides 3 and 5, respectively, so that the second-order dispersion as indicated by 34 in FIG. It becomes a curve. The value of the vertical axis in the secondary dispersion curve 34 is equal to the chromatic dispersion GVDλ (Group Velocity Dispersion) of the group velocity Vg at each wavelength. The relationship of GVDλ = − (λ / ω) × GVDω is established between the chromatic dispersion GVDλ and the frequency dispersion GVDω. At this time, in FIG. 9, the signs of GVDλ, which are the second-order dispersion of the defect waveguides 3 and 5 constituting the composite defect waveguide 6, are different from each other as shown in FIGS. Since the other is negative, it is possible to realize a light frequency or light wavelength that is 0 dispersion in a relatively narrow light frequency or light wavelength range that is also used as incident light. It can be seen that the wavelength dependence of the secondary dispersion curve 31 can be greatly reduced. At this time, in the first Brillouin zone 12, when one is a waveguide mode in which the wave number increases with an increase in frequency and the other is a mode in which the wave number decreases with an increase in frequency, the increase / decrease in secondary dispersion Since the profile is substantially symmetrical, this dispersion compensation effect can be expressed more greatly, which is more preferable. The two different defect waveguides 3 and 5 exist below the light line in the photonic band gap, and the two different defect waveguides 3 and 5 have intersections in the band diagram other than the band ends. However, it is very effective for enhancing the dispersion control effect and the group velocity control effect.

  FIG. 10 corresponds to the third order differentiation of the band of FIG. 7 and shows the third order dispersion characteristic with respect to the wavelength of the composite defect waveguide 6. FIG. 10A shows a third-order dispersion diagram of the band 21 of the defect waveguide 3, and 35 is a third-order dispersion characteristic of the band 21. FIG. 10B shows a third-order dispersion diagram of the defect waveguide 5, and 36 is a third-order dispersion curve of the band 24. FIG. 10C shows a third-order dispersion diagram of the composite defect waveguide 6 composed of the defect waveguides 3 and 5, 37 is a third-order dispersion curve of the composite defect waveguide 6, and 28 is shown in FIG. 7C. The optical frequency of the incident light to the composite defect waveguide 6.

In FIG. 10, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. The incident light having a different frequency is subjected to the group velocity delay effect while receiving different kinds of third-order dispersion in the two defect waveguides 3 and 5, respectively, thereby obtaining the third-order dispersion as indicated by 37 in FIG. It becomes a curve. The value of the vertical axis in the third-order dispersion curve 37 is equal to the dispersion slope DSλ (Dispersion Slope) with respect to the wavelength that is the differential value of the chromatic dispersion GVDλ (Group Velocity Dispersion) at each wavelength. The relationship of GSλ = − (λ / ω) ² × DSω is established between the dispersion slope DSλ with respect to the wavelength and the dispersion slope DSω with respect to the frequency. At this time, in FIG. 10, the degree of increase / decrease in DS, which is the third-order dispersion of the defect waveguides 3 and 5 constituting the composite defect waveguide 6, is different from each other, and the line defect waveguides 3 of the photonic crystals 2 and 4 are mutually different. Therefore, it can be seen that a positive third-order dispersion curve having almost the same degree of increase / decrease and a substantially constant value can be obtained. The constant value of the third-order dispersion curve can be obtained by changing the profile of each band of the composite defect waveguide 6 and the relatively narrow optical frequency or optical wavelength used as incident light incident on the composite defect waveguide 6. It can be easily controlled, and as a result, the value of the secondary dispersion can be controlled.

  In implementing the light control element 1 of the present embodiment, the composite defect waveguide 6 composed of such two defect waveguides 3 and 5 has a two-dimensional periodic arrangement as shown in FIG. The group velocity of the defect waveguide is not limited to the slab type photonic crystal composed of, for example, a photonic crystal composed of a pseudo three-dimensional periodic array or a photonic crystal composed of a three-dimensional periodic array. It is very effective for performing control and distributed control.

  In the present embodiment, as shown in FIG. 6, the ratio of the refractive index of the defect waveguides 3 and 5 with respect to the background refractive index is different between the photonic crystals 2 and 4, so that the sign of the secondary dispersion is positive or negative. Thus, a composite defect waveguide 6 comprising a combination of different defect waveguides 3 and 5 is realized. This is because, by reducing the ratio of the refractive index of the defect waveguide to the background refractive index, the frequency of the waveguide mode due to slab propagation is increased, and the first Brillouin zone 12 is in the photonic band gap. Will be present as a band. For this reason, the inclination of the band becomes positive in the band diagram, and a waveguide mode in which the wave number decreases with increasing frequency can be easily realized. This band dispersion characteristic has symmetry of the profile of the band itself due to the Brillouin zone folding with respect to the waveguide mode in which the wave number increases with increasing frequency folded as the second Brillouin zone. Therefore, the dispersion compensation effect for the primary dispersion can be greatly increased.

  By the way, in order to reduce the refractive index ratio defined by the refractive index of the defect waveguide with respect to the background refractive index, the material refractive index itself of the defective waveguide portion itself may be decreased, or the structural refractive index of the defective waveguide portion. May be reduced. The “structural refractive index” here is the same as the “effective refractive index”. Here, in addition to the refractive index depending on the thin film structure used in the waveguide, the propagation varies depending on the minute refractive index contrast structure below the wavelength. The refractive index that effectively acts on light. In order to reduce the effective refractive index, it is effective to provide a minute hole structure 9 having a wavelength or less as shown in the defect waveguide 5 of FIG. As a structure for realizing the defect waveguide 5 of FIG. 1, in addition to providing the minute hole structure 9 shown in FIG. 1, for example, as shown in FIG. 12, the structure 42 in which the hole shape of the photonic crystal adjacent to the defect waveguide 5 is deformed as shown in FIG. 12, and the coupling in which holes 8 are provided in the defect waveguide 5 as shown in FIG. A minute refractive index contrast structure such as the defect waveguide structure 43 is effective. In the case of the coupling defect waveguide structure 43, it is necessary to optimize the period of the coupling defect and the optical confinement structure in the slab waveguide. As shown in FIG. 14, it is also effective to reduce the effective refractive index of the defect waveguide 5 ′ by using a narrow defect waveguide 5 ′ in which the width of the defect waveguide 5 is narrowed.

  Further, the present invention is not limited to the photonic crystals 2 and 4 having a hole structure, and is similarly effective in a photonic crystal having a pillar structure. For example, in FIG. 15, 44 is a pillar constituting the photonic crystal 45, and 46 is a defect waveguide structure having a one-dimensional array in which the diameter of the pillar 44 is small. In this case as well, the defect waveguide 5 shown in FIG. As in the case of, a mode in which the wave number decreases with increasing frequency can be easily realized. Further, as shown in FIG. 15, the invention is not limited to the combination of the hole structure and the pillar structure, and it is effective to combine the pillar structures. Further, the present invention is not limited to the two-dimensional photonic crystal, and is similarly effective in a three-dimensional photonic crystal.

  By the way, in the configuration of the present embodiment shown in FIG. 1, as shown in FIG. 7, the defect waveguide 3 having positive secondary dispersion and the defect degree having negative secondary dispersion constituting the composite defect waveguide 6. The frequency of light in the vicinity of the intersection of the bands of the waveguide 5 is used, and a defect waveguide having a profile in which the curve of the band is almost symmetrical with respect to the intersection is used. At this time, the absolute values of the secondary dispersion can be made substantially the same, and in this case, a very large dispersion compensation effect can be realized. Here, the absolute values are substantially the same, which means that the absolute value is within 10% in the wavelength range to be used, whereby the conventional wavelength dispersion can be reduced by 10 times or more. However, the present invention is not limited to the configuration in which the second-order dispersion value is substantially the same and the group velocity is substantially the same, and the absolute value of the second-order dispersion is different or the group velocity is different. Even so, it has a large dispersion control effect and group velocity control effect.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS. The same parts as those described above are denoted by the same reference numerals, and description thereof is omitted (the same applies to subsequent embodiments in order).

  FIG. 16 is a configuration diagram schematically showing a light control element 51 made of a slab type two-dimensional photonic crystal according to the present embodiment. In FIG. 16, reference numeral 2 denotes a photonic crystal including a defect waveguide 3 having a positive second-order dispersion waveguide mode. Reference numeral 4 denotes a photonic crystal including a defect waveguide 5 having a negative second-order dispersion waveguide mode. Reference numeral 52 denotes a photonic crystal including a defect waveguide 53 having positive secondary dispersion. A composite defect waveguide 54 is formed by connecting these three defect waveguides 3, 5, 53 in series. That is, in contrast to FIG. 1, the photonic crystal 52 having the same defect waveguide 53 as the defect waveguide 3 is further added to the light control element 1.

With respect to the structure of the composite defect waveguide 54 as shown in FIG. 16, it is easy to manufacture with respect to a short pulse of light, and it becomes a small and low loss light control element 51 having a large dispersion control effect and a group velocity delay effect. This will be described in detail with reference to a band diagram. FIG. 17 is a band diagram of the composite defect waveguide 54 having the structure shown in FIG. FIG. 17A shows a band diagram of the leftmost defect waveguide 3 in FIG. 16 and the rightmost defect waveguide 53 having the same structure as that shown in FIG. 16, wherein 21 is a band, 22 is a SiO ₂ light line, 23 Is the photonic band gap. FIG. 17B shows a band diagram of the defect waveguide 5 in the center of FIG. 16, wherein 24 and 25 are bands, 22 is a SiO ₂ light line, and 26 is a photonic band gap. FIG. 17C shows a band diagram of the composite defect waveguide 54 including the defect waveguides 3, 5, and 53 of FIG. 16, 27 is a photonic band gap of the composite defect waveguide 54, and 28 is the composite defect waveguide 54. Is the optical frequency of the incident light. 27, since the photonic band gaps 23 and 26 of the two different types of defect waveguides 3 and 5 (or 53 and 5) are not constant values, there may actually be a slight deviation from the position of the broken line.

  In FIG. 17, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, three defect waveguides 3, 5, and 53 are formed as shown in FIG. Incident light having a propagating frequency is subjected to a group velocity delay effect while receiving different types of dispersion in the two types of defect waveguides 3, 5, and 53. However, the defect waveguide 3 propagates twice as the defect waveguide 53, and the two can be combined to have a relatively large positive secondary dispersion. For this reason, the propagation state of light is different from that of the structure shown in FIG. 1 and the group velocity is substantially the same, but the absolute value of the second-order dispersion is greatly different as a result.

  FIG. 18 shows the wavelength λ1 corresponding to the vicinity of the optical frequency used as the first-order dispersion of the band with respect to the wavelength of the composite defect waveguide 54 based on the group velocity Vg because the first-order derivative in the band of FIG. 17 shows the group velocity Vg. This is shown in the range of the wavelength λ2. However, the defect waveguide 53 is the same as the defect waveguide 3, and substantially propagates twice through the defect waveguide 3. For the sake of explanation, effective dispersion is caused by the two propagations so that the effective dispersion is the original defect waveguide. It will be briefly described as being twice the above. FIG. 18A shows a combined first-order dispersion diagram of the band 21 of the defect waveguides 3 and 53, and 55 is a first-order dispersion curve. FIG. 18B shows a first-order dispersion diagram of the defect waveguide 5 at the center in FIG. 16, and 56 is a first-order dispersion curve of the band 24. 18C shows a first-order dispersion diagram of the composite defect waveguide 54 including the defect waveguides 3, 5, and 53, 57 is a first-order dispersion curve of the composite defect waveguide 54, and 28 is associated with FIG. It is the optical frequency of the incident light to the composite defect waveguide 54 shown. In FIG. 18, since the optical pulse is transmitted through the defect waveguide 3 and the optical pulse is transmitted through the defect waveguides 5 and 53, two types of defect waveguides 3 and 5 are formed as shown in FIG. , 53 receives the group velocity delay effect while receiving different types of first-order dispersion in the two types of defect waveguides 3, 5, 53, respectively, as shown in FIG. A first order dispersion curve as shown in FIG. As a result, the 1 / Vg value of the composite defect waveguide 54 is dispersion-compensated by combining the group velocity delays of the respective defect waveguides 3, 5, and 53, so that the composite defect waveguide is more than the original defect waveguide. It can be seen that the wavelength dependence of the first-order dispersion curve 57 of 54 is greatly reduced. As a result, the usable wavelength band can be increased.

  FIG. 19 corresponds to the second derivative of the band of FIG. 17 and shows the second-order dispersion characteristics with respect to the wavelength of the composite defect waveguide 54. However, the defect waveguide 53 is the same as the defect waveguide 3, and the defect waveguide 3 has substantially propagated twice. For the sake of explanation, the effective dispersion is caused by the two propagations to be the original defect waveguide. It will be briefly described as being twice that of 3. FIG. 19A shows a second-order dispersion diagram of the defect waveguides 3 and 53, and 61 is a second-order dispersion curve when the band 21 is combined. FIG. 19B shows a second-order dispersion diagram of the defect waveguide 5 at the center in FIG. 16, and 62 is a second-order dispersion curve of the band 24. FIG. 19C shows a second-order dispersion diagram of the composite defect waveguide 54 composed of the defect waveguides 3, 5, and 53, 53 is a second-order dispersion curve of the composite defect waveguide 54, and 28 is associated with FIG. It is the optical frequency of the incident light to the composite defect waveguide 54 shown. In FIG. 19, since the optical pulse is transmitted through the defect waveguide 3 and the optical pulse is transmitted through the defect waveguides 5 and 53, two types of defect waveguides 3 and 5 are provided as shown in FIG. , 53 is subjected to a group velocity delay effect while receiving different types of second-order dispersion in the three defect waveguides 3, 5, 53, respectively, thereby causing the reference numeral 63 in FIG. A quadratic dispersion curve as shown in FIG. At this time, in FIG. 19, the signs of GVDλ, which are the second-order dispersion of the defect waveguides 3, 5, and 53 constituting the composite defect waveguide 54, are different from each other, and one is positive and the other is negative. Although this absolute value is different when considered as a composite defect waveguide 54 having a negative dispersion and a negative dispersion, the dispersion can be reduced in a relatively narrow optical frequency or optical wavelength range used as incident light, It can be seen that the wavelength dependence of the primary dispersion of the composite defect waveguide 54 can be reduced as compared with the conventional photonic crystal.

  Note that the composite defect waveguide is not limited to two or three series combinations, and four or more defect waveguides may be arranged in series. In addition, the term “series” in the present invention means a serial state with respect to light propagation, and may be arranged in a serial state as a light propagation system even if they are not arranged directly and continuously. . Moreover, it is not necessary to be physically in series, and it is only necessary that the light propagation is arranged in a serial state even if it is arranged in a parallel state like a directional coupler.

[Third embodiment]
A third embodiment of the present invention will be described with reference to FIGS. FIG. 20 schematically shows a band diagram of a light control element made of a slab type two-dimensional photonic crystal according to the present embodiment. The configuration of this light control element is the same as that of the light control element 1 shown in FIG. 1, but a composite defect in which a defect waveguide whose secondary dispersion has positive and negative values with respect to the frequency of light used is combined. Although they are waveguides, their absolute values are different and their group velocities are different.

At this time, FIG. 20A shows a band diagram of the defect waveguide 3 shown on the left side in FIG. 1, wherein 21 is a band, 22 is a SiO ₂ light line, and 23 is a photonic band gap. FIG. 20B shows a band diagram of the defect waveguide 5 shown on the right side in FIG. 1, wherein 24 and 25 are bands, 22 is a SiO ₂ light line, and 26 is a photonic band gap. FIG. 20C shows a band diagram of the composite defect waveguide 6 composed of the defect waveguides 3 and 5 shown in FIG. 1, 27 is a photonic band gap of the defect waveguide, and 64 is the composite defect waveguide 6. It is the optical frequency of incident light. 27, since the photonic band gaps 23 and 26 of the two different defect waveguides 3 and 5 are not constant values, there may actually be a slight deviation from the position of the broken line. In FIG. 20, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. Incident light having a certain frequency is subjected to a group velocity delay effect while receiving different types of dispersion in the two defect waveguides 3 and 5, respectively. However, since the defect waveguides 3 and 5 have different group velocities and second-order dispersion values, the absolute values of the second-order dispersion in the composite defect waveguide 6 are greatly different as a result.

  FIG. 21 shows the wavelength corresponding to the vicinity of the optical frequency used as the first-order dispersion of the band with respect to the wavelength of the composite defect waveguide 6 based on the group velocity Vg because the first derivative in the band of FIG. 20 shows the group velocity Vg. This is shown in the range of λ1 and wavelength λ2. FIG. 21A shows a primary dispersion diagram of the defect waveguide 3, and 65 is a primary dispersion curve. FIG. 21B shows a first order dispersion diagram of the defect waveguide 5, and 66 is a first order dispersion curve of the band 24. FIG. 21C shows a first-order dispersion diagram of the composite defect waveguide 6 composed of the defect waveguides 3 and 5, 67 is a first-order dispersion curve of the composite defect waveguide 6, and 64 is shown corresponding to FIG. It is the optical frequency of the incident light to the composite defect waveguide 6. In FIG. 21, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. The incident light having a different frequency is subjected to the group velocity delay effect while receiving different kinds of first-order dispersion in the two defect waveguides 3 and 5, respectively. As a result, the first-order dispersion as indicated by 67 in FIG. It becomes a curve. The value of the vertical axis in the first-order dispersion curve 67 is equal to the 1 / Vg value with respect to the group velocity Vg at each wavelength, but the 1 / Vg value of the composite defect waveguide 6 is equal to each defect waveguide 3, 5. It can be seen that the wavelength dependence of the first-order dispersion curve 67 of the composite defect waveguide 6 is greatly reduced compared to the original defect waveguide by dispersion compensation by combining the group velocity delays. As a result, the usable wavelength band can be increased. As shown in FIG. 21, it can be seen that even if the group velocity and the absolute value of the secondary dispersion are different, a good dispersion control effect can be realized by combining the photonic crystals having different signs of the secondary dispersion.

[Fourth embodiment]
A fourth embodiment of the present invention will be described with reference to FIGS. FIG. 22 is a configuration diagram schematically showing a light control element 71 made of a slab type two-dimensional photonic crystal according to the present embodiment. In FIG. 22, 2 is a photonic crystal including a defect waveguide 3 having a positive second-order dispersion waveguide mode, and 4 is a photonic including a defect waveguide 5 having a negative second-order dispersion waveguide mode. It is a crystal. A composite defect waveguide 72 is configured by the serial arrangement of the two defect waveguides 3 and 5. Reference numeral 7 denotes a high refractive index thin film made of silicon and serving as a base of the photonic crystal 2, and reference numeral 73 denotes a low refractive index thin film made of GaAs and serving as a base of the photonic crystal 4. 8 is an air hole having a two-dimensional periodic arrangement provided in the high refractive index thin film 7 and the low refractive index thin film 73, and 9 is a minute air having a one-dimensional periodic arrangement provided in the defect waveguide 5. It is a hall.

  FIG. 23 shows the background refractive index (solid line: left axis) of the photonic crystals 2 and 4 shown in FIG. 22, the refractive index of the defect waveguides 3 and 5 (broken line: left axis), and the ratio of the latter to the former. The specified refractive index ratio (one-dot broken line: right axis) is shown with respect to the light propagation direction. 23, as coordinates (au) of the light propagation direction, 0.0 is an incident position on the composite defect waveguide 72, and 0.5 is a coupling end face between the two defect waveguides 3 and 5. Yes, 1.0 is the exit position of the composite defect waveguide 72. The refractive index here also means the effective refractive index considering the structural influence, and even in a thin film made of the same silicon material, by reducing the thickness of the thin film or providing an air structure in the thin film, The refractive index which means this effective refractive index becomes small. At this time, in FIG. 22, unlike the case shown in FIG. 1, the background refractive index of the defect waveguide 3 is larger than the background refractive index of the defect waveguide 5, and the refractive index ratio of the defect waveguide 3 is defect. It is larger than the refractive index ratio of the waveguide 5.

  The composite defect waveguide 72 structure as shown in FIGS. 22 and 23 makes it easy to fabricate a short pulse optical pulse, and has a small and low loss optical control element having a large dispersion control effect and a group velocity delay effect. 71 will be described using a band diagram.

FIG. 24 shows a band diagram of the composite defect waveguide 72 having the structure shown in FIG. FIG. 24A shows a band diagram of the defect waveguide 3 shown on the left side in FIG. 22, where 21 is a band, 22 is a SiO ₂ write line, and 23 is a photonic band gap. FIG. 24B shows a band diagram of the defect waveguide 5 shown on the right side in FIG. 22, wherein 74 and 75 are bands, 76 is a SiO ₂ write line, and 77 is a photonic band gap. FIG. 24C shows a band diagram of the composite defect waveguide 72 including the defect waveguides 3 and 5 shown in FIG. 22, 78 is a photonic band gap of the composite defect waveguide 72, and 79 is the composite defect waveguide 72. Is the optical frequency of the incident light. In FIG. 24, the photonic band gap 78 has a large difference between the photonic band gaps 23 and 77 of the two different defect waveguides 3 and 5, and the composite defect waveguide 72 has the photonic band gaps 23 and 77. As a result of this combination, a narrower photonic band gap is obtained. Further, the light line 80 is dominated by the light line having a smaller inclination as the composite defect waveguide 72, and becomes the light line 80 corresponding to the light line 76 in FIG.

  At this time, in FIG. 24, since the optical pulse is transmitted through the defect waveguide 3 and the optical pulse is transmitted through the defect waveguide 5 as in the case of the configuration shown in FIG. As shown, incident light having a frequency capable of propagating through the two defect waveguides 3 and 5 receives a group velocity delay effect while receiving different types of dispersion in the two defect waveguides 3 and 5.

  Here, when the band diagram of FIG. 24A and the band diagram of FIG. 24B are compared, the entire band gap 77 is shifted in the frequency increasing direction. This is because the background refractive index of the photonic crystal 4 is reduced. For this reason, shifting the waveguide band, whose wave number increases as the frequency increases, into the photonic band causes the small holes 9 to be defect-guided as compared to the defect waveguide in FIG. 1 where the background refractive index is the same. This can be realized by providing the waveguide 5. For this reason, the strength of the line defect waveguide 5 is improved, and a photonic crystal structure that is easier to manufacture can be obtained. In addition, since the shift amount from the waveguide band existing under the photonic band in the case where no hole is provided in the line defect waveguide is small, the distortion of the band is relatively small, and the band 21 in FIG. And the dispersion compensation effect and the group velocity delay effect can be further improved.

  25, as in the case of FIG. 8, the first-order derivative with respect to the band of FIG. 24, which is a band diagram, shows the group velocity Vg. This is shown in the range of wavelength λ1 and wavelength λ2 corresponding to the vicinity of the frequency. FIG. 25A shows a first-order dispersion diagram of the band 21 of the defect waveguide 3, and 29 is a first-order dispersion curve. FIG. 25B shows a first-order dispersion diagram of the defect waveguide 5 shown on the right side in FIG. 22, and 81 is a first-order dispersion curve of the band 74. FIG. 25C shows a first-order dispersion diagram of the composite defect waveguide 72 composed of the defect waveguides 3 and 5 in FIG. 22, 82 is a first-order dispersion curve of the composite defect waveguide 72, and 79 is in FIG. It is the optical frequency of the incident light to the composite defect waveguide 72 shown correspondingly.

  In FIG. 25, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. The incident light having a different frequency is subjected to the group velocity delay effect while receiving different kinds of primary dispersions in the two defect waveguides 3 and 5, respectively. As a result, the primary dispersion as indicated by 82 in FIG. It becomes a curve. Since the value of the vertical axis in the first-order dispersion curve 82 is equal to the 1 / Vg value for the group velocity Vg at each wavelength, the 1 / Vg value of the composite defect waveguide 72 is equal to each defect waveguide 3, 5. It can be seen that the wavelength dependence of the first-order dispersion curve 82 of the composite defect waveguide 72 is greatly reduced by dispersion compensation by combining the group velocity delays. These operations are substantially the same as those described with reference to FIG. 8 in the configuration of FIG.

  FIGS. 26 and 27 correspond to the second and third derivatives of the band of FIG. 24 and are shown as second-order dispersion and third-order dispersion with respect to the wavelength of the composite defect waveguide 72. 26A shows a second-order dispersion diagram of the band 21 of the defect waveguide 3 on the left side in FIG. 22, and 32 is a second-order dispersion curve of the band 21. FIG. FIG. 26B shows a second-order dispersion diagram of the defect waveguide 5 on the right side in FIG. 22, and 83 is a second-order dispersion curve of the band 74. 26C shows a second-order dispersion diagram of the composite defect waveguide 72 composed of the defect waveguides 3 and 5 shown in FIG. 22, 84 is a second-order dispersion curve of the composite defect waveguide 72, and 79 is FIG. It is the optical frequency of the incident light to the composite defect waveguide 72 shown corresponding to the inside.

  In FIG. 26, since the optical pulse is transmitted through the defect waveguide 3, and further, the optical pulse is transmitted through the defect waveguide 5, it is possible to propagate through the two defect waveguides 3, 5 as shown in FIG. The incident light having a different frequency is subjected to the group velocity delay effect while receiving the different types of second-order dispersion in the two defect waveguides 3 and 5, respectively, so that the second-order dispersion as indicated by 84 in FIG. It becomes a curve.

  At this time, in FIG. 26, the signs of GVDλ which are second-order dispersion of the defect waveguides 3 and 5 constituting the composite defect waveguide 72 are different from each other as shown in FIGS. Since the other is negative and has good symmetry, it is possible to realize a frequency of light or a wavelength of light that is 0 dispersion in a relatively narrow optical frequency or wavelength range used as incident light. It can be seen that the wavelength dependence of the second-order dispersion curve 84 of the defect waveguide 72 can be greatly reduced.

  FIG. 27A shows a third-order dispersion diagram of the band 21 of the defect waveguide 3 shown on the left side in FIG. 22, and 35 is a third-order dispersion curve of the band 21. FIG. 27B shows a third-order dispersion diagram of the defect waveguide 5 shown on the right side in FIG. 22, and 85 is a third-order dispersion curve of the band 24. FIG. 27C shows a third-order dispersion diagram of the composite defect waveguide 72 composed of the defect waveguides 3 and 5 shown in FIG. 22, 86 is the third-order dispersion curve of the composite defect waveguide 72, and 79 is FIG. It is the optical frequency of the incident light to the composite defect waveguide 72 shown corresponding to the inside.

  In FIG. 27, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. The incident light having a different frequency is subjected to the group velocity delay effect while receiving different kinds of third-order dispersion in the two defect waveguides 3 and 5, respectively, so that the third-order dispersion as indicated by 86 in FIG. It becomes a curve. At this time, in FIG. 27, the degree of increase / decrease in DS that is the third-order dispersion of the defect waveguides 3 and 5 constituting the composite defect waveguide 72 is different from each other as shown in FIGS. Since the photonic crystals 2 and 4 are line-defect waveguides, it can be seen that a positive third-order dispersion curve having almost the same degree of increase / decrease can be obtained. The constant value of the third-order dispersion curve 86 is compared by changing the profile of each band of the composite defect waveguide 72 and a relatively narrow optical frequency or wavelength used as incident light incident on the composite defect waveguide 72. It can be seen that the second order dispersion can be controlled as a result.

[Fifth embodiment]
A fifth embodiment of the present invention will be described with reference to FIGS. FIG. 28 is a configuration diagram schematically showing a light control element 91 made of a slab type two-dimensional photonic crystal according to the present embodiment. In FIG. 28, reference numeral 92 denotes a photonic crystal including a defect waveguide 93 having a negative second-order dispersion waveguide mode, and 94 denotes a photonic crystal including a defect waveguide 95 having a positive second-order dispersion waveguide mode. A composite defect waveguide 96 is formed by arranging two defect waveguides 93 and 95 in series. 7 is a high refractive index thin film made of silicon, 73 is a low refractive index thin film made of GaAs, and 6 is an air hole having a two-dimensional periodic array provided on the high refractive index thin film 7 or the low refractive index thin film 73. And 9 is a minute air hole having a one-dimensional periodic array that is provided inside the defect waveguide 93 and forms a minute refractive index contrast structure.

  FIG. 29 is defined as the background refractive index (solid line: left axis) of the photonic crystals 92 and 94 shown in FIG. 28, the refractive index of the defect waveguides 93 and 95 (broken line: left axis), and the ratio of the latter to the former. The refractive index ratio (one-dot broken line: right axis) is shown with respect to the light propagation direction. In FIG. 29, 0.0 is an incident position to the composite defect waveguide 96 and 0.5 is a connection end face between the two defect waveguides 93 and 95 as coordinates (au) in the light propagation direction. Yes, 1.0 is the exit position of the composite defect waveguide 96. The refractive index here also means the effective refractive index in consideration of the structural influence as in the case described above. Even in a thin film made of the same silicon material, the thickness of the thin film is reduced, or the air structure is added to the thin film. By providing it, the refractive index which means this effective refractive index becomes small. In FIG. 29, unlike the structure shown in FIG. 22 (the reverse is true), the background refractive index of the defect waveguide 93 is larger than the background refractive index of the defect waveguide 95, and the refractive index ratio of the defect waveguide 93 is increased. Is configured to be smaller than the refractive index ratio of the defect waveguide 95.

  At this time, in order to shift the waveguide band whose wave number increases as the frequency increases into the photonic band and to have the intersection with the defect waveguide 95 of the low refractive index thin film 73, It is necessary to lower the refractive index of the defect waveguide 93 by increasing the diameter of the air holes 9 provided in a one-dimensional periodic arrangement so that the band is positioned at the higher frequency. For this reason, the volume of the silicon portion of the defect waveguide 93 is reduced, and the strength is slightly reduced. However, as can be seen from FIG. 29, since the refractive index of the line defect waveguide is almost the same in the two defect waveguides 93 and 95 combined, the reflection at the two connecting portions is further reduced and the transmittance is increased. An improved composite defect waveguide 96 can be realized.

[Sixth embodiment]
A sixth embodiment of the present invention will be described with reference to FIG. FIG. 30 is a configuration diagram schematically showing a light control element 101 made of a slab type two-dimensional photonic crystal according to the present embodiment. The light control element 101 according to the present embodiment has a refractive index as an intermediate light propagation means between the photonic crystals 2 and 4 with respect to the light control element 1 including the photonic crystals 2 and 4 shown in FIG. A distributed photonic crystal 102 is provided. The gradient index photonic crystal 102 is formed on a gradient index thin film 103 made of a material whose refractive index decreases linearly from the photonic crystal 2 side to the photonic crystal 4 side, and the gradient index thin film 103. An air hole 104 having a two-dimensional periodic arrangement and an intermediate defect waveguide 105 made of an arrangement defect of the air hole 104 are formed. Therefore, in the present embodiment, the composite defect waveguide 106 is formed by the three defect waveguides 3, 105, and 5.

  At this time, the intermediate defect waveguide 105 made of a refractive index distribution type material has a refractive index distribution that allows the refractive index distribution of the defect waveguide 105 to be the same even though the hole arrangement structure is the same on the left and right. The structure can be different on the left and right. As a result, the difference in refractive index between the defect waveguide 3 and the defect waveguide 5 shown in FIG. 6 can be reduced or made the same. For this reason, interface reflection between different structures due to the difference in refractive index can be reduced, and the transmittance of the composite defect waveguide 106 can be improved.

  The intermediate defect waveguide 105 provided between the defect waveguides 3 and 5 arranged in series reduces the difference in propagation constant in addition to reducing the difference in refractive index between the left and right defect waveguides 3 and 5. It is also very effective to perform other light control such as controlling the transmittance for performing deflection rotation.

  The intermediate light propagation means provided between the defect waveguides 3 and 5 arranged in series is not limited to the defect waveguide 105 as shown in FIG. 30, but a simple optical fiber, waveguide, or chirp. It is also very effective to use a conventionally known light propagation means such as an optical fiber grating, AWG, external modulator or mode converter in combination with its light control function.

  In the case of the light control element 91 having the configuration as shown in FIG. 28, an intermediate having a refractive index distribution between the photonic crystals 92 and 94 that is opposite to that of the photonic crystal 102 is provided. What is necessary is just to interpose a light propagation means.

[Seventh embodiment]
A seventh embodiment of the present invention will be described with reference to FIG. FIG. 31 is a configuration diagram schematically showing a light control element 111 made of a slab type two-dimensional photonic crystal according to the present embodiment.

  In FIG. 31, 112a and 112b are defect waveguides having positive second-order dispersion waveguide modes formed in the photonic crystals 113a and 113b, respectively, and 114a and 114b are formed in the photonic crystals 113a and 113b, respectively. Further, it is a defect waveguide having a negative second-order dispersion waveguide mode. Directional couplers 115a and 115b are also provided for each of these two defect waveguides 112 and 114, and are connected in series as light propagation by the directional couplers 115a and 115b to form composite defect waveguides 116a and 116b. Is configured.

  At this time, for example, in the configuration of FIG. 31A, incident light 117 incident on the defect waveguide 112a of the photonic crystal 113a is incident on the other defect waveguide 114a by the directional coupler 115a in the photonic crystal 113a. And then exits from the defect waveguide 114a. At this time, the incident light 117 is subjected to the group velocity delay effect while receiving different types of second-order dispersion in the two defect waveguides 112a and 114a. The light control element having an effect can be reduced in size. The same applies to the case of FIG. 31B, but the incident light 117 is folded and emitted to the incident side.

  FIGS. 32 and 33 show another example in which a plurality of directional couplers 118 and 119 are provided, and the composite line defect waveguide 120 is formed by the directional couplers 118 and 119. By having a plurality of directional couplers 118 and 119, for example, as shown in FIG. 32, the light is emitted from the third defect waveguide 121, or as shown in FIG. 112 can be emitted, and the size can be further reduced.

[Eighth embodiment]
An eighth embodiment of the present invention will be described with reference to FIGS. FIG. 34 shows a band diagram relating to the light control element of the present embodiment. The band of the composite defect waveguide 6 is changed by changing the hole structure in the same configuration as in FIG.

34A shows a band diagram corresponding to the defect waveguide 3 shown on the left side in FIG. 1, wherein 131 is a band, 22 is a SiO ₂ light line, and 132 is a photonic band gap. FIG. 34B shows a band diagram corresponding to the defect waveguide 5 shown on the right side in FIG. 1, wherein 24 and 25 are bands, 22 is a SiO ₂ light line, and 26 is a photonic band gap. FIG. 34 (c) shows a band diagram corresponding to the composite defect waveguide 6 comprising the defect waveguides 3 and 5 shown in FIG. 1, 133 is a photonic band gap of the composite defect waveguide, and 134 is a composite defect guide. This is the optical frequency of the incident light in the waveguide 6. Since the photonic band gaps 132 and 26 of the two different defect waveguides 3 and 5 are not constant values, the photonic band gap 133 may actually deviate slightly from the position of the broken line. In FIG. 34, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 6, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. Incident light having a certain frequency is subjected to a group velocity delay effect while receiving different types of dispersion in the two defect waveguides 3 and 5, respectively.

  FIG. 35 shows the range of the wavelength λ1 and the wavelength λ2 corresponding to the vicinity of the optical frequency used as the primary dispersion of the band with respect to the wavelength of the composite defect waveguide based on the first order derivative in the band of FIG. This is shown in FIG. FIG. 35A shows a first-order dispersion diagram of a band 131 corresponding to the defect waveguide 3 on the left side in FIG. 1, and 135 is a first-order dispersion curve. FIG. 35B shows a first-order dispersion diagram of the band 24 corresponding to the defect waveguide 5 on the right side in FIG. 1, and 30 is a first-order dispersion curve of the band 24. FIG. 35 (c) shows a first-order dispersion diagram corresponding to the composite defect waveguide 6 composed of the defect waveguides 3 and 5 shown in FIG. 1, 136 is a first-order dispersion curve of the composite defect waveguide 6, and 134 is It is the optical frequency of the incident light to the composite defect waveguide 6 shown corresponding to FIG. In FIG. 35, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. The incident light having a different frequency is subjected to the group velocity delay effect while receiving different types of primary dispersion in the two defect waveguides 3 and 5, respectively, thereby obtaining the primary dispersion as indicated by 136 in FIG. It becomes a curve. Since the value of the vertical axis in the first-order dispersion curve 136 is equal to the 1 / Vg value for the group velocity Vg at each wavelength, the 1 / Vg value of the composite defect waveguide 6 is equal to the defect waveguides 3 and 5. It is understood that the dispersion compensation is performed by combining the group velocity delays of the first and second components, and the wavelength dependence of the first-order dispersion curve 136 of the composite defect waveguide 6 is reduced in the vicinity where the group velocities coincide with each other.

  FIG. 36 shows the second-order dispersion with respect to the wavelength of the composite defect waveguide 6 corresponding to the second derivative of the band of FIG. 36A shows a second-order dispersion diagram of the band 131 corresponding to the defect waveguide 3 shown on the left side in FIG. 1, and 137 is a second-order dispersion curve of the band 131. FIG. FIG. 36B shows a second-order dispersion diagram of the band 24 corresponding to the defect waveguide 5 shown on the right side in FIG. 1, and 33 is a second-order dispersion curve of the band 24. FIG. 36C shows a second-order dispersion diagram corresponding to the composite defect waveguide 6 composed of the defect waveguides 3 and 5 shown in FIG. 1, 138 is the secondary dispersion curve of the composite defect waveguide 6, and 134 is the figure. 34 is the optical frequency of the incident light to the composite defect waveguide 6 shown corresponding to.

  In FIG. 36, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, it can propagate through the two defect waveguides 3 and 5, as shown in FIG. The incident light having a different frequency is subjected to the group velocity delay effect while receiving the different types of second-order dispersion in the two defect waveguides 3 and 5, respectively, so that the second-order dispersion as indicated by 138 in FIG. It becomes a curve. At this time, in FIG. 36, the signs of the secondary dispersion of the defect waveguides 3 and 5 constituting the composite defect waveguide 6 are different from each other as shown in FIGS. Since it is negative, in the range of the optical frequency or optical wavelength where the group velocity used also as incident light is substantially zero, it is possible to realize the frequency of light or the wavelength of light that becomes zero dispersion, and the composite defect waveguide 6 It can be seen that the wavelength dependence of the first-order dispersion curve 136 can be reduced. At this time, it is preferable that the sign of the band inclination in the band diagram is in the opposite direction as in the case of FIG.

  37 and 38 correspond to the third and fourth derivatives of the band shown in FIG. 34, respectively, and are shown as third-order dispersion and fourth-order dispersion with respect to the wavelength of the composite defect waveguide 6. 37 (a) and 38 (a) show the third-order dispersion and fourth-order dispersion diagrams of the band 131 corresponding to the defect waveguide 3, and 139 and 140 are the third-order dispersion curve and the fourth-order dispersion curve of the band 131, respectively. is there. FIGS. 37B and 38B show a third-order dispersion diagram and a fourth-order dispersion diagram of the band 24 corresponding to the defect waveguide 5, and 141 and 142 denote the third-order dispersion curve and the fourth-order dispersion curve of the band 24, respectively. It is. 37 (c) and 38 (c) show a third-order dispersion diagram and a fourth-order dispersion diagram corresponding to the composite defect waveguide 6 composed of the defect waveguides 3 and 5 shown in FIG. The third-order dispersion curve and the fourth-order dispersion curve 134 of the composite defect waveguide 6 are optical frequencies of light incident on the composite defect waveguide 6 shown in correspondence with FIG. In FIG. 37 and FIG. 38, since the optical pulse is transmitted through the defect waveguide 3 and further the optical pulse is transmitted through the defect waveguide 5, as shown in FIG. 37 (c) and FIG. Incident light having a frequency capable of propagating through the defect waveguides 3 and 5 is subjected to group velocity delay while receiving higher-order dispersions such as different types of third-order dispersion and fourth-order dispersion in the two defect waveguides 3 and 5. By receiving the effect, the third-order dispersion curve and the fourth-order dispersion curve as shown by 143 in FIG. 37C and 145 in FIG. 38C are obtained.

  At this time, in FIG. 37, the degree of increase / decrease of the third-order dispersion and the fourth-order dispersion of the defect waveguides 3 and 5 constituting the composite defect waveguide 6 is different from each other. This can be realized by the background refractive index of the photonic crystals 2 and 4 forming the respective defect waveguides 3 and 5, the hole structure or pillar structure, the defect waveguide width, and the minute refractive index contrast structure provided in the defect waveguide. . These values are composed of photonic crystals when the group velocity Vg is approximately 0, and the slopes of the bands in the band diagrams are different, so that the higher-order dispersion is symmetric with the same or different signs. Can be realized, and the amount of dispersion can be increased. Therefore, by optimizing these, by constructing a photonic crystal having the desired dispersion effect of the third-order dispersion and fourth-order dispersion and the group velocity delay effect, in addition to the second-order dispersion, an ultra-small third-order dispersion It is effective as a high-order dispersion compensation element such as quaternary dispersion. These are also very effective in combination with a conventional dispersion compensation element having a secondary dispersion effect.

  Here, the group velocity Vg is “substantially 0” is a state in which the group velocity Vg is at least 1/5 times, more preferably at most 1/10 times the light velocity in vacuum, If the group velocity Vg is larger than this, the dispersion itself of the single defect waveguide is small, so that the effect of combining is reduced.

[Ninth embodiment]
A ninth embodiment of the present invention will be described with reference to FIG. FIG. 39 is a configuration diagram schematically showing a light control element 141 made of a slab type two-dimensional photonic crystal according to the present embodiment.

  The light control element 141 of the present embodiment has the same configuration as that of the light control element 1 shown in FIG. 1 as an example. However, the high refractive index thin film constituting the defect waveguide 3 portion in the photonic crystal 2 is used. 7 is made of a material whose refractive index can be changed by a temperature change, for example, and the photonic crystal 2 is configured as a correction element portion.

  A dispersion compensation correction amount varying means 145 including a wavelength band measuring means 142, a dispersion correction amount determining means 143, and a temperature control means 144 is provided for the photonic crystal 2 serving as the correction element portion of the light control element 141. ing. Reference numeral 146 denotes incident light to the light control element 141, and a part 146 a of the incident light 146 is branched and transmitted to the wavelength band measuring unit 142 of the dispersion compensation correction amount varying unit 145. Reference numeral 147 denotes light emitted from the light control element 141.

  In FIG. 39, the dispersion compensation correction amount varying means 145 detects the wavelength incident on the light control element 141 by the wavelength band measuring means 142 based on the light of the part 146a, and the dispersion compensation correction amount determining means 1143 according to this data. Determines the dispersion compensation correction amount, and the temperature control means 144 controls the temperature of the defect waveguide 3 in the photonic crystal 2 in accordance with this data. As a result, good dispersion control and delay time control can always be performed even if the wavelength varies. It is also effective to provide a dispersion measurement unit for incident light in addition to the wavelength band measurement unit 142 to perform appropriate dispersion control.

  The method for controlling the refractive index of the defect waveguide 3 is not limited to the temperature control method, and various other refractive indexes and electromagnetic field strengths in the waveguide, such as an electro-optic effect, a magneto-optic effect, and a nonlinear optical effect. It is possible to use a method of changing Thereby, dispersion control and group velocity control can be performed with higher accuracy.

  In addition, the refractive index is controlled by combining with the defect waveguide 5 instead of the defect waveguide 3 alone, or by combining with a light control element different from the composite defect waveguide 6. It is very effective to optimally control the optical path and the like.

It is the block diagram which showed typically the light control element which consists of a slab type | mold two-dimensional photonic crystal which is 1st embodiment of this invention. It is the block diagram which showed the example of the cross-section structure typically. It is a figure for demonstrating the arrangement | sequence with the periodicity of the general photonic crystal without a defect, (a) is explanatory drawing which showed typically the period and hole diameter in real space, (b) is a wave number. It is explanatory drawing of space. It is a general band figure of a photonic crystal without a defect. It is explanatory drawing of the waveguide band produced by the photonic crystal which has a defect waveguide. It is a characteristic view regarding a refractive index and a refractive index ratio. It is a band figure of the defect waveguide in the light control element of this embodiment. It is a characteristic view which shows the primary dispersion curve. It is a characteristic view which shows the secondary dispersion curve. It is a characteristic view which shows the cubic dispersion curve. It is the block diagram which showed typically the modification regarding a defect waveguide. It is the block diagram which showed typically the other modification regarding a defect waveguide. It is the block diagram which showed typically the further another modification regarding a defect waveguide. It is the block diagram which showed typically the another modification regarding a defect waveguide. It is the block diagram which showed typically the structural example of the light control element of a pillar structure. It is the block diagram which showed typically the light control element which consists of a slab type | mold two-dimensional photonic crystal which is 2nd embodiment of this invention. It is a band figure of the defect waveguide in the light control element of this embodiment. It is a characteristic view which shows the primary dispersion curve. It is a characteristic view which shows the secondary dispersion curve. It is a band figure of the defect waveguide in the light control element of a third embodiment of the present invention. It is a characteristic view which shows the primary dispersion curve. It is the block diagram which showed typically the light control element which consists of a slab type | mold two-dimensional photonic crystal which is the 4th embodiment of this invention. It is a characteristic view regarding a refractive index and a refractive index ratio. It is a band figure of the defect waveguide in the light control element of this embodiment. It is a characteristic view which shows the primary dispersion curve. It is a characteristic view which shows the secondary dispersion curve. It is a characteristic view which shows the cubic dispersion curve. It is the block diagram which showed typically the light control element which consists of a slab type | mold two-dimensional photonic crystal which is the 5th Embodiment of this invention. It is a characteristic view regarding a refractive index and a refractive index ratio. It is the block diagram which showed typically the light control element which consists of a slab type | mold two-dimensional photonic crystal which is the 6th Embodiment of this invention. It is the block diagram which showed typically the light control element which consists of a slab type | mold two-dimensional photonic crystal which is the 7th Embodiment of this invention. It is a block diagram which shows the modification. It is a block diagram which shows another modification. It is a band figure of the defect waveguide in the light control element of the 8th embodiment of the present invention. It is a characteristic view which shows the primary dispersion curve. It is a characteristic view which shows the secondary dispersion curve. It is a characteristic view which shows the cubic dispersion curve. It is a characteristic view which shows the quartic dispersion curve. It is the block diagram which showed typically the light control element which consists of a slab type | mold two-dimensional photonic crystal which is the 9th embodiment of this invention, and its control system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light control element 2 Photonic crystal 3 Defect waveguide 4 Photonic crystal 5 Defect waveguide 6 Compound defect waveguide 45 Photonic crystal 51 Light control element 52 Photonic crystal 53 Defect waveguide 54 Compound defect waveguide 71 Light control element 72 composite defect waveguide 91 light control element 92 photonic crystal 93 defect waveguide 94 photonic crystal 95 defect waveguide 96 composite defect waveguide 101 light control element 102 photonic crystal 105 intermediate light propagation means 106 composite defect waveguide 111 light Control element 112 Defect waveguide 113 Photonic crystal 115 Directional coupler 116 Composite defect waveguide 118 Directional coupler 119 Directional coupler 120 Compound defect waveguide 121 Defect waveguide 141 Light control element

Claims (15)

In a light control element made of a photonic crystal having a defect waveguide,
A composite in which a defect waveguide having a waveguide mode of positive higher-order dispersion of the second order or higher and a defect waveguide having a negative higher-order dispersion waveguide mode of the same order as the positive higher-order dispersion are arranged in series An optical control element comprising a defect waveguide.   2. The light control element according to claim 1, wherein the absolute value of the positive high-order dispersion and the absolute value of the negative high-order dispersion are substantially the same.   The waveguide mode of one of the composite defect waveguides is a waveguide mode in which the wave number increases with increasing frequency, and the wave mode of the other defect waveguide has a wave number with increasing frequency. 3. The light control element according to claim 1, wherein the light control element is a decreasing waveguide mode.   The light control element according to any one of claims 1 to 3, wherein the group velocities of the two defect waveguide portions constituting the composite defect waveguide are substantially the same. In a light control element made of a photonic crystal having a defect waveguide,
It comprises a composite defect waveguide in which two or more defect waveguides having different refractive index ratios defined by the refractive index of the defect waveguide with respect to the background refractive index of the photonic crystal are arranged in series, and these two or more A light control element, wherein each photonic crystal corresponding to a defect waveguide has a different background refractive index.   6. The light control element according to claim 5, wherein a background refractive index of a photonic crystal having a smaller refractive index ratio is smaller than a background refractive index of a photonic crystal having a larger refractive index ratio.   6. The light control element according to claim 5, wherein a background refractive index of a photonic crystal having a smaller refractive index ratio is larger than a background refractive index of a photonic crystal having a larger refractive index ratio.   The refractive index ratio defined by the refractive index of the defective waveguide with respect to the background refractive index of a photonic crystal having a defect waveguide having a waveguide mode whose wave number decreases with increasing frequency is such that the wave number with respect to increasing frequency. 4. The light control element according to claim 3, wherein the light control element is smaller than a refractive index ratio defined by a refractive index of the defect waveguide with respect to a background refractive index of a photonic crystal having a defect waveguide having an increasing waveguide mode. .   A defect waveguide having a waveguide mode whose wave number increases with an increase in frequency is a composite having a minute refractive index contrast structure different from this line defect structure in a hole defect or pillar structure of a photonic crystal. 9. The light control element according to claim 3, comprising a defect structure.   10. The light control element according to claim 9, wherein the minute refractive index contrast structure is formed of a low refractive index hole structure or a pillar structure having a shape different from that of the background photonic crystal.   The light control element according to any one of claims 1 to 10, wherein the refractive indexes of two defect waveguide portions arranged in series constituting the composite defect waveguide are substantially the same.   12. The light control element according to claim 1, further comprising intermediate light propagation means between two defect waveguides arranged in series and constituting the composite defect waveguide.   12. The light control element according to claim 1, wherein a composite defect waveguide composed of two defect waveguides connected in series is connected in series by a directional coupler.   4. The light control element according to claim 3, wherein the group velocity of the defect waveguide portion of the composite defect waveguide composed of two defect waveguides arranged in series is substantially zero. A refractive index of at least one of a background refractive index of a photonic crystal having a composite defect waveguide composed of two defect waveguides arranged in series and a refractive index of a defect waveguide portion is variable. The light control element according to claim 1.

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