WO2004081625A1 - フォトニック結晶を用いた導波路素子 - Google Patents
フォトニック結晶を用いた導波路素子 Download PDFInfo
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- WO2004081625A1 WO2004081625A1 PCT/JP2004/002719 JP2004002719W WO2004081625A1 WO 2004081625 A1 WO2004081625 A1 WO 2004081625A1 JP 2004002719 W JP2004002719 W JP 2004002719W WO 2004081625 A1 WO2004081625 A1 WO 2004081625A1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/1225—Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
Definitions
- the present invention relates to a waveguide element for controlling propagation of an electromagnetic wave, and more particularly to a waveguide element using a one-dimensional photonic crystal.
- Photonic crystals have a structure in which dielectrics with different refractive indices are arranged with a period about the wavelength of light.
- the present inventors have studied electromagnetic wave propagation inside a one-dimensional or two-dimensional photonic crystal having no periodicity in the propagation direction.
- the content is disclosed in Japanese Patent Application Laid-Open No. 2002-236620.
- a plane wave is incident as incident light from the end face of a photonic crystal having no periodicity in the propagation direction of the incident light
- propagating light is generated by a plurality of photonic bands depending on the frequency of the incident light.
- light propagating in non-lowest-order bands hereinafter referred to as higher-order band propagating light
- has characteristics such as "extremely large chromatic dispersion" and "group velocity anomaly” as described above. Can be used.
- the light propagates as the light propagating in this band (hereinafter referred to as first band propagating light).
- the first band propagating light has the “very large chromatic dispersion” described above.
- the first band propagation light is merely a loss.
- the first band propagating light not only greatly reduces the efficiency of using the incident light energy of the device, but also causes the device to lower the SZN ratio as stray light.
- phase modulation of the incident light can be realized by a simple method, for example, by passing a plane wave through a phase grating.
- the electric field of higher-order band propagating light in a photonic crystal without periodicity in the propagation direction is divided into two regions by two nodes within one period of the refractive index periodicity of the photonic crystal. . Also, the phase of the propagating light is shifted by a half period in each region of the photonic crystal. In order to obtain such propagating light, the phase grating for modulating the phase of the incident light has the same period in the same direction as the period of the photonic crystal. However, since the period of the refractive index of a photonic crystal is usually shorter than the wavelength of light, the period of the phase grating is also shorter than the wavelength of light, making fabrication difficult.
- a method can be considered in which a groove is formed in a photonic crystal to partially separate the photonic crystal and divide the photonic crystal into a waveguide portion and a phase grating portion.
- a groove having a narrow width and a large aspect ratio can be considered. It is technically difficult to form accurately.
- by reducing the proportion of the first band propagating light In order to increase the combination, it is necessary to adjust the distribution ratio and phase of the 0th-order diffracted light intensity and ⁇ 1st-order diffracted light intensity by the phase grating, and an optimization design for that is required. Disclosure of the invention
- the present invention has been made in view of such problems in the related art, and provides a waveguide element using a photonic crystal that can make use of a function unique to the photonic crystal and that can be easily manufactured.
- the purpose is to:
- the present invention relates to a waveguide element using a photonic crystal having a periodicity of refractive index in one direction, comprising an input unit for generating a propagation light by a band on a Brillouin zone boundary in the photonic crystal.
- FIG. 1 is a cross-sectional view showing electromagnetic wave propagation of a photonic crystal having a periodic refractive index in one direction.
- FIG. 2 is a band diagram of the photonic crystal shown in FIG.
- FIG. 3A is a band diagram including light incident on the photonic crystal shown in FIG.
- FIG. 3B is a band diagram showing the band diagram of FIG. 3A limited to the Z-axis direction.
- FIG. 4A is a cross-sectional view schematically showing the intensity of the electric field of the first band propagation light in the Z-axis direction in the photonic crystal shown in FIG.
- FIG. 4B is a cross-sectional view schematically showing the electric field strength of higher-order band propagation light in the Z-axis direction in the photonic crystal shown in FIG.
- FIG. 5 shows a waveguide device having a phase grating and a photonic crystal
- FIG. 3 is a cross-sectional view schematically showing the intensity of an electric field of a propagating light in a Z-axis direction
- FIG. 6 is a band diagram in the case where incident light is obliquely incident on the photonic crystal shown in FIG. 1 at an incident angle of zero.
- FIG. 7A is a band diagram when incident light is incident on the photonic crystal shown in FIG. 1 at a predetermined incident angle ⁇ .
- FIG. 7B is a band diagram showing the band diagram on the Brillouin zone boundary in FIG. 7A limited to the Z-axis direction.
- FIG. 8A is a cross-sectional view schematically showing a propagation form of the photonic crystal shown in FIG. 1 by the first band.
- FIG. 8B is a cross-sectional view schematically showing the propagation form of the photonic crystal shown in FIG. 1 by the second band.
- FIG. 8C is a cross-sectional view schematically showing a propagation shape obtained by superimposing the propagation shapes of the photonic crystal shown in FIGS. 8A and 8B by the first band and the second band.
- FIG. 9 is a band diagram in the second method.
- FIG. 10 is a cross-sectional view of the photonic crystal shown in FIG. 1 for explaining the third method.
- FIG. 11 is a cross-sectional view of the photonic crystal shown in FIG. 1 for explaining the fourth method.
- FIG. 12A is a cross-sectional view showing an electric field pattern of propagating light in a photonic crystal in which electromagnetic waves propagate on the Brillouin zone boundary between the first band and the second band.
- FIG. 12B is a diagram showing a simulation result of the propagation shape of the emitted light when each portion shown in FIG. 12A is set as an emission end.
- FIG. 13A is a perspective view showing a configuration of an optical waveguide device using the photonic device according to the present embodiment.
- FIG. 13B is a perspective view showing a configuration of a waveguide element using another photonic crystal of the present embodiment.
- FIG. 13C is a perspective view showing a configuration of a waveguide element using another photonic crystal of the present embodiment.
- FIG. 13D is a perspective view showing a configuration of a waveguide element using another photonic crystal of the present embodiment.
- FIG. 14A is a cross-sectional view showing a structure of a photonic crystal provided with a reflective layer.
- FIG. 14B is a cross-sectional view showing the structure of a photonic crystal provided with a photonic crystal cladding.
- FIG. 15 is a band diagram of a one-dimensional photonic crystal adjacent to each other and a one-dimensional photonic crystal clad for a specific wavelength.
- FIG. 16A is a band diagram of the photonic crystal for TE polarized light.
- FIG. 16B is a diagram showing an electric field intensity distribution as a simulation result in Calculation Example 1.
- FIG. 17A is a band diagram in Calculation Example 2.
- FIG. 17B is a diagram showing an electric field intensity distribution as a simulation result in Calculation Example 2.
- FIG. 18 is a diagram illustrating an electric field intensity distribution as a simulation result in Calculation Example 3.
- FIG. 19 is a diagram illustrating an electric field intensity distribution as a simulation result in Calculation Example 4.
- FIG. 2OA is a diagram showing the intensity distribution of the electric field as a simulation result in Calculation Example 5.
- FIG. 20B is a cross-sectional view showing the configuration of the phase grating.
- Figure 21 shows the electric field obtained by simulation of light obliquely incident on the phase grating. It is a figure which shows the intensity
- FIG. 22 is a diagram showing an electric field intensity distribution as a simulation result in Calculation Example 6.
- FIG. 23 is a diagram illustrating an electric field intensity distribution as a simulation result in Calculation Example 7.
- FIG. 24A is an XZ plane sectional view showing the configuration of the waveguide element used in Calculation Example 8.
- FIG. 24B is a YZ plane sectional view showing the configuration of the waveguide element used in Calculation Example 8.
- FIG. 24C is a partially enlarged view of FIG. 24B.
- FIG. 25A is a diagram showing an intensity distribution of an electric field in a central cross section of the waveguide portion.
- FIG. 25B is a diagram showing the intensity distribution of the electric field at the center of the high refractive index layer.
- FIG. 25C is a diagram showing the intensity distribution of the electric field at the center of the low refractive layer.
- the waveguide element using the photonic crystal according to the present embodiment can utilize the propagation by the band on the prillian zone boundary in the photonic band structure.
- the lowest order band has the same characteristics as the electromagnetic wave propagation by the higher order band, so it can be used as an electromagnetic wave control element. Therefore, it can be widely applied as an element utilizing dispersion compensation due to anomalous group velocity of higher-order band propagation light, enhancement effect of optical nonlinearity, and the like.
- the input unit causes at least one substantially plane-wave electromagnetic wave to be incident at an incident angle of 0 from the end face of the photonic crystal, which is substantially parallel to the direction of the refractive index period, to the end face.
- N is the refractive index of the medium in contact with the end face of the photonic crystal, and ⁇ . Is true of the electromagnetic wave
- the incident angle ⁇ is
- the input unit is installed close to or in contact with an end face of the photonic crystal, which is substantially parallel to the direction of the refractive index periodicity, and modulates the phase of an approximately plane wave electromagnetic wave
- An incident-side phase modulating unit that makes the light incident from the end face of the nick crystal and an incident unit that makes the electromagnetic wave incident on the incident-side phase modulating unit are provided.
- propagation by a band on the Brillouin zone boundary can be realized in the photonic crystal. Therefore, it can be widely applied as an element utilizing dispersion compensation caused by group velocity anomalies of higher-order band propagation light, enhancement of optical nonlinearity, and the like.
- the incident-side phase modulation unit has a refractive index period that is the same as the direction of the refractive index period of the photonic crystal, and is a refraction that is an integral multiple of the refractive index period of the photonic crystal. It is a phase grating with a rate period.
- propagation by a band on the Brillouin zone boundary can be realized in the photonic crystal. Therefore, it can be widely applied as a device utilizing dispersion compensation caused by group velocity anomalies of higher-order band propagating light, enhancement effect of optical nonlinearity, and the like.
- the incident-side phase modulation section has a refractive index period that is the same as the direction of the refractive index period of the photonic crystal, and is twice the refractive index period of the photonic crystal.
- the incident light is made substantially perpendicular to the direction of the fold ratio. Therefore, it can be widely applied as an element utilizing the dispersion compensation caused by anomalous group velocity of higher-order band propagating light, the enhancement effect of optical nonlinearity, and the like. As a result, it is possible to realize a waveguide device using higher-order band propagation light in a photonic crystal.
- the incident-side phase modulation section has a refractive index cycle that is the same as the direction of the refractive index cycle of the photonic crystal, and has a refractive index twice as large as the refractive index cycle of the photonic crystal.
- a phase grating having a refractive index period, the phase grating being included on a plane including a direction of the refractive index period of the phase grating and a direction perpendicular to the direction of the refractive index period, and perpendicular to the direction of the refractive index period.
- the incident portion makes the electromagnetic wave incident on the phase grating so that the angle becomes 6> with respect to the direction, n is a refractive index of a medium in contact with an incident end face of the phase grating, and ⁇ . Is the wavelength of the electromagnetic wave in a vacuum, and a is the period of the photonic crystal.
- the period of the phase grating is twice as long as the period of the photonic crystal, which facilitates fabrication. Furthermore, since the phase grating only needs to increase the intensity of the ⁇ 1st-order diffracted waves as much as possible, the optimization design is simplified.
- the incident-side phase modulation section has a refractive index cycle that is the same as the direction of the refractive index cycle of the photonic crystal, and has the same refractive index as the refractive index cycle of the photonic crystal.
- the incident part makes the electromagnetic wave incident on the phase grating so that the angle becomes 0 with respect to, where n is the refractive index of a medium in contact with the incident end face of the phase grating, and ⁇ . Is the wavelength of the electromagnetic wave in vacuum, and a is the photonic coupling In the case of a crystal period, the angle ⁇ is
- the incident-side phase modulation unit is formed integrally with the photonic crystal.
- the electromagnetic wave propagates in the photonic crystal in a direction perpendicular to the direction of the refractive index period of the photonic crystal
- the electromagnetic wave propagates in the direction of the refractive index period of the photonic crystal.
- a confinement unit for confining the electromagnetic waves propagating in the photonic crystal so as not to leak is further provided. As a result, a waveguide element with low loss can be realized without leakage of guided light.
- the confinement portion may be a reflection layer provided on at least one of the side surfaces of the photonic crystal perpendicular to the direction of the refractive index period of the photonic crystal.
- the confinement portion is provided on at least one of the side surfaces of the photonic crystal perpendicular to the direction of the refractive index period of the photonic crystal, and has a refractive index in the same direction as the refractive index period of the photonic crystal.
- a photonic crystal having periodicity may be used.
- an output-side phase modulation unit which is close to or in contact with an end surface opposite to the end surface of the photonic crystal on which the incident-side phase modulation unit is provided is further provided. Thereby, a plane wave can be emitted.
- the output-side phase modulation section may be a phase grating having a refractive index periodicity in the same direction as the refractive index period of the photonic crystal.
- the emission-side phase modulation section has a refractive index period that is the same as the direction of the refractive index period of the photonic crystal, and has the same refractive index as the refractive index period of the photonic crystal.
- the emission-side phase modulation section may have the same refractive index periodic structure as the incidence-side phase modulation section.
- the emission-side phase modulation section may be installed so that the directions of the incident end and the emission end are opposite to those of the incidence-side phase modulation section.
- the electromagnetic wave propagating inside the photonic crystal is a wave belonging to one or both of the photonic band from the lowest order and the second order from the lower order.
- the electromagnetic wave propagating inside the photonic crystal is a wave belonging to one or both of the photonic band from the lowest order and the second order from the lower order.
- FIG. 1 is a cross-sectional view showing the propagation of electromagnetic waves in a photonic crystal 1 having a refractive index periodicity in one direction.
- the propagation direction of the electromagnetic wave is the Z-axis direction
- the direction perpendicular to the propagation direction of the electromagnetic wave is the Y-axis direction.
- Photonic crystal 1 is a one-dimensional photonic crystal having a refractive index periodicity only in the Y-axis direction.
- the substance 5a and the substance 5b are alternately stacked in the Y-axis direction to form a multilayer structure 5.
- the thickness of the material 5 a is t A, refractive Oriritsu is a n A. Further, the thickness of the material 5 b is t B, the refractive index and n B.
- the photonic crystal 1 has a multilayer structure 5 with a period a in which the substances 5a and the substances 5b are alternately stacked. The period a is a (t A + t B).
- the photonic crystal 1 is a core, and the air (not shown) around the photonic crystal 1 is a clad, and forms an optical waveguide. You.
- the wavelength in vacuum is ⁇ from the end face 1a, which is the incident end of the photonic crystal 1.
- this plane wave When this plane wave is made incident as incident light 2, it propagates in the photonic crystal 1 as propagating light 4.
- the propagating light 4 is emitted as the outgoing light 3 from the end face 1b which is the outgoing end opposite to the incident end.
- How this propagating light 4 propagates in the multilayer film of the substance 5a and the substance 5b in the photonic crystal 1 can be known by calculating and showing a photonic band.
- the band calculation method is described in detail in, for example, "Photonic Crystals", Princeton University Press (1995) or Physical Review B 44, 16, p.8565, 1991.
- the photonic crystal 1 shown in Fig. 1 has a periodic structure that continues infinitely in the Y direction (layer direction), and extends infinitely in the X and Z directions (layer direction).
- FIG. 2 FIG. 3A and FIG. 3B will be described. Since these relate to the photonic crystal 1 of FIG. 1, they will be described with reference to FIG.
- FIG. 2 shows the results of band calculation in the Y-axis and Z-axis directions of the photonic crystal 1, which is a multilayer structure having a period a in which the substance 1a and the substance 1b are alternately stacked.
- FIG. 1 shows the results of band calculation in the Y-axis and Z-axis directions of the photonic crystal 1, which is a multilayer structure having a period a in which the substance 1a and the substance 1b are alternately stacked.
- Fig. 2 shows the first, second, and third bands of the polarized light within the range of the first Prillian zone.
- Fig. 2 is a contour line connecting the points where the normalized frequency ⁇ a ⁇ 27T c has the same value. This contour line is hereinafter referred to as a contour line. The suffix of each line indicates the value of the standardized frequency ⁇ a / 27Tc.
- the normalized frequency ⁇ a Z 2 ⁇ c is expressed using the angular frequency ⁇ of the incident light 2, the period a of the structure, and the speed of light c in a vacuum.
- the normalized frequency is the wavelength ⁇ of the incident light 2 in vacuum. Using a / ⁇ . Can also be expressed as In the following, simply standardized frequency a / ⁇ . It is described.
- the width of the Brillouin zone in the ⁇ -axis direction is 2 Tc Za, but since there is no periodicity in the Z-axis direction, there is no Brillouin zone boundary in the lateral direction, and the Brillouin zone extends far.
- TE polarized light indicates polarized light whose electric field is in the X-axis direction.
- the band diagram of the TM polarized light whose magnetic field is polarized in the X-axis direction is similar to the band diagram of the TE polarized light, but has a slightly different shape.
- FIG. 3A is a band diagram including light incident on the photonic crystal 1 shown in FIG.
- FIG. 4 is a band diagram when a plane wave (TE polarized light) of FIG.
- the end face 1a is perpendicular to the Z axis.
- n be the refractive index of the medium in contact with this end face l a.
- this medium is air, for example, and is a homogeneous medium having a uniform refractive index.
- the right side is a band diagram in the photonic crystal 1
- the left side is a band diagram of a homogeneous medium (air) outside the photonic crystal 1.
- the upper part shows the coupling between the incident light and the first band
- the lower part shows the coupling between the incident light and the second band.
- the band diagram of the incident light 2 is a band diagram in the air.
- the band diagram of the homogeneous medium is a sphere whose radius r is expressed by the following equation (YZ Circle on a plane).
- the binding band on the photonic crystal 1 side can be obtained by drawing.
- FIG. 3A normalized frequencies a ⁇ ⁇ on the first and second bands. Since there is a corresponding point 3 05 and a corresponding point 3 06 in which the light coincides with the incident light, a wave corresponding to each band propagates in the photonic crystal 1.
- the direction and period of the wavefront of the incident light are represented by the reciprocal of the direction and magnitude of the arrow 300, which is a wavenumber vector, and the wavefront direction and the period of the propagating light are similarly wavenumber-based.
- the vectors are represented by arrows 303 (first band) and arrow 304 (second band).
- the traveling direction of the wave energy of the propagating light is the normal direction of each equi-frequency line, and is represented by arrows 301 and 302.
- the light propagated by any band travels in the Z-axis direction.
- Fig. 3B shows the band diagram of Fig. 3A limited to the Z-axis direction.
- Fig. 3B shows the wavelength of the incident light 2 in vacuum.
- the wave number vector k 2 corresponding to each band exists in the photonic crystal 1.
- wavelength ⁇ of light in vacuum Is divided by the wavelength (for example, ⁇ 2, etc.) when propagating in the photonic crystal 1 and is defined as “effective refractive index”.
- the normalized frequency of the first band a. (Vertical axis) and wave number vector kz (horizontal axis) are almost proportional,
- the folding rate is also ⁇ .
- the effective refractive index is ⁇ in the higher-order propagation band (the second and third bands in Fig. 3 ⁇ ). It changes greatly, and from Fig. 3 ⁇ , even if kz approaches 0, a Z is included. Is almost constant. That is, the effective refractive index may be less than 1.
- the value obtained by differentiating the band curve shown in Fig. 3B with kz is the group velocity of the propagating light.
- the group velocity anomaly in a photonic crystal is extremely large and opposite to the usual dispersion of a homogeneous substance (the group velocity decreases as the wavelength of incident light increases). Therefore, an optical waveguide that can use higher-order propagation band light can be used for an optical control element such as an optical delay element or a dispersion compensation element in optical communication.
- FIG. 4A and 4B are cross-sectional views schematically showing the electric field strength of the propagating light in the photonic crystal 1 shown in FIG. Figure 4A shows in Figure 1
- FIG. 3 is a cross-sectional view schematically showing the intensity of the electric field of the first band propagating light in the Z-axis direction in the photonic crystal 1.
- FIG. 4B shows the intensity of the electric field of the higher-order band propagating light (for example, the propagating light of the second band shown in FIG. 3A) in the Z-axis direction in the photonic crystal 1 shown in FIG.
- FIG. 3 is a schematic cross-sectional view. 4A and 4B also refer to FIG.
- Photonic crystal 1 is a periodic multilayer body composed of substance 5a and substance 5b.
- the photonic crystal 1 is a so-called one-dimensional photonic crystal in which the substance 5 a and the substance 5 b are alternately stacked, and the sum of the thickness of the substance 5 a and the thickness of the substance 5 b has a multilayer structure.
- a period of 5 is a.
- the refractive index period direction is the Y-axis direction, and the refractive index is uniform in the Z-axis direction, which is the propagation direction of the propagating light.
- the electric field of light is represented by waves.
- the electric field peak 4a is represented by a solid line
- the electric field valley 4b is represented by a broken line.
- the magnitude of the amplitude is represented by the thickness of each line, and the thicker the line, the greater the amplitude.
- the wavelength of the propagating light is ⁇ .
- the first-band propagating light has different electric field amplitudes in substance 5a and substance 5b, but the electric field peaks 4a and valleys 4b are planes perpendicular to the Z axis, respectively. Therefore, the propagation is close to a plane wave.
- node 4c in which the electric field amplitude becomes 0 occurs near the boundary between the substance 5a and the substance 5b. Therefore, one cycle of the layered structure formed by the adjacent substances 5a and 5b is divided into two regions of peaks and valleys. In the adjacent regions (Material 5a and Material 5b), the phases of the waves are shifted by half a wavelength, so the peaks and valleys appear interchanged. Thus, two nodes 4 c per cycle occur in the second or third band. In the case of light guided by higher-order bands, the number of nodes in one cycle further increases, and a half-wave shift in one cycle occurs. Will happen many times.
- the propagating light 4 with respect to the incident light 2 having a wavelength in which both the first band and the higher-order band are involved overlap each other and exhibit a complicated electric field pattern.
- FIG. 5 is a cross-sectional view schematically showing the intensity of an electric field in the Z-axis direction of propagating light in a waveguide element including a phase grating and a photonic crystal.
- the waveguide element 10 of FIG. 5 has a phase grating 6 as phase modulation means provided on the end face 1a side of the photonic crystal 1 shown in FIG.
- the phase grating 6 is a phase modulation means that generates a substantially half-wavelength difference with a period a in the Y direction.
- the optical path is folded in the opposite direction, it can be seen that the higher-order band propagation light can be returned to a plane wave by installing appropriate phase modulation means after being emitted from the end face 1b of the photonic crystal 1. .
- the phase grating 6 for obtaining the phase modulation corresponding to the higher-order band propagation light has the same refractive index period in the same direction as the photonic crystal 1.
- the period a must be equal to the light wavelength ⁇ . It is desirable to make it smaller.
- the refractive index period of the phase grating 6 also becomes smaller than the wavelength, which makes the fabrication difficult.
- Groove that makes space 1 8 in photonic crystal 1 A method is considered in which a groove is formed and a part of the groove is separated and used as a phase grating.
- FIG. 6 is a band diagram in a case where incident light is incident on the photonic crystal 1 shown in FIG. 1 at an oblique incident angle of ⁇ .
- the incident angle S is a direction perpendicular to the incident surface, that is, the angle between the Z axis and the incident light.
- the inclination of the incident light is limited to the YZ plane. Note that the incident end face la of the photonic crystal 1 is perpendicular to the Z axis.
- the traveling direction of the wave propagating in the photonic crystal 1 is the normal direction of the equal frequency line, there are two types, and it can be seen that the wave does not become perpendicular to the Z axis.
- the normalized frequency a ⁇ ⁇ on the first and second bands.
- the wave number vector of the incident light is indicated by an arrow 600
- the wave number vector of the propagating light is indicated by an arrow 603 (first band) and an arrow 600 (second band).
- the energy traveling direction of the band is indicated by an arrow 601, and the energy traveling direction of the second band of the propagating light can be represented by an arrow 602.
- FIG. 7D is a band diagram when incident light is incident on the photonic crystal 1 shown in FIG. 1 at a predetermined incident angle 0.
- n is the refractive index of the medium in contact with the end face 1a of the photonic crystal 1, and ⁇ . Is the wavelength of the incident light 2 in a vacuum, and a is the period of the photonic crystal 1.
- the first and second propagation bands exist on the Brillouin zone boundary 608.
- the wavenumber vector of the incident light 2 is represented by an arrow 607
- the energy traveling directions of the propagating light 4 in the photonic crystal 1 are indicated by arrows 609 (first band) and 610 ( (2nd band).
- 6 13 and 6 14 are the corresponding points where the normalized frequency a ⁇ ⁇ 0 on the first and second bands coincides with the incident light, respectively, and the wave number vector of the propagating light is indicated by an arrow 6 1 1 (first band) and arrow 6 1 2 (second band).
- the traveling direction of the wave energy coincides with the ⁇ axis, so that the propagating light 4 travels in the ⁇ axis direction.
- the condition that the incident angle 0 satisfies for example, considering the periodicity in the ⁇ direction of the prilling zone,
- Fig. 7B shows the band diagram on the Brillouin zone boundary in Fig. 7 ⁇ limited to the ⁇ axis direction.
- all bands including the first band, exhibit a change on the Brillouin zone boundary similar to the higher band shown in Figure 3B.
- “significant changes in effective refractive index due to wavelength” and “group velocity anomaly” occur in all bands. It can be applied to control elements.
- the research by the present inventors has revealed that “propagation at the Brillouin zone boundary” shown in FIG. 7A can be realized by several methods, and these will be described below.
- the first method for achieving propagation at the Brillouin zone boundary multi-band propagation by oblique incidence
- FIG. 8A is a cross-sectional view schematically showing a propagation shape of the photonic crystal 1 shown in FIG. 1 by the first band.
- FIG. 8B is a cross-sectional view schematically showing the propagation shape of the photonic crystal 1 shown in FIG. 1 by the second band.
- FIG. 8C is a cross-sectional view schematically showing a propagation shape in which the propagation shapes of the first band and the second band of the photonic crystal shown in FIGS. 8A and 8B are superimposed.
- a peak 800 1 (a position where the electric field amplitude has a maximum on the plus side)
- a valley 800 2 a position where the electric field amplitude has a maximum on the minus side
- the photonic crystal 1 is the same as that used in FIG.
- the light propagated by the first band has a high refractive index layer (eg, substance 5a) as an antinode and a low refractive index layer (eg, substance 5b) as a node (FIG. 8A).
- a high refractive index layer eg, substance 5a
- a low refractive index layer eg, substance 5b
- the phase is shifted by a half cycle between the high refractive index layers (substance 5a).
- the light propagated by the second band has the antinodes in the low refractive index layer (material 5b) and the nodes in the high refractive index layer (material 5a), and has a longer period than the light propagated by the first band (Fig. 8B ).
- the phase is shifted by a half cycle between the adjacent low refractive index layers (substance 5b).
- FIG. 8C shows the propagation shape when light in the frequency range where both the first band and the second band exist is incident on the photonic crystal 1 at an incident angle 0 that satisfies the condition of equation (1). It is.
- FIG. 8C overlaps FIG. 8A and FIG. 8B and shows the peak of the electric field as a line.
- the portion connected by the solid line 8 11 1 is a peak of the propagating light
- the portion connected by the broken line 8 12 is a valley of the propagating light.
- the light in the photonic crystal 1 has a pattern in which the valley lines are arranged in a zigzag pattern.
- the “wavelength of the effective refractive index” is obtained. Phenomena such as “significant change due to” and “abnormal group velocity”.
- This method is the simplest because it only tilts the incident light (plane wave). Also, since the “frequency range in which both the first band and the second band exist” is wide, the incident angle ⁇ and the refractive index n can be selected in a range that is easy to implement.
- the reflectance at the end face 1a of the photonic crystal 1 is also small, and most of the incident light is propagating light in the photonic crystal. Furthermore, a / ⁇ . If the value of is increased, the light propagated by the third or higher order band can be added.
- this method results in the mixing of propagating light from two or more bands. Since the light propagating in different bands has different wavelengths and group velocities in the photonic crystal, it is necessary that these characteristics be single. This is a major obstacle for the device. Therefore, this method (method by multi-band propagation by oblique incidence) is particularly suitable for applications such as "the nonlinear action only needs to increase as the group velocity of the propagating light decreases".
- the wavelength range in which the characteristics as an optical element can be maintained may be limited.
- FIG. 9 is a band diagram in the second method.
- Figure 9 shows the normalized frequency a Z A only on the first band. Since there is a corresponding point 903 corresponding to the incident light, a band diagram in a frequency range where only the propagating light of the first band exists and no other band exists is shown.
- arrow 900 indicates the wave number vector of the incident light
- arrow 902 indicates the wave number vector of the propagating light
- arrow 901 indicates the energy traveling direction.
- the propagating light propagating in the photonic crystal has a propagating shape as shown in FIG. 8A.
- the high-refractive-index layer (substance 5a) is an antinode
- the low-refractive-index layer (substance 5b) is a node
- the phase between adjacent high-refractive-index layers (substance 5a) is shifted by half a period.
- it has the characteristics of higher-order propagation despite being the propagation of the first band (see Calculation Example 2 described later and Fig. 17B).
- the angle of incidence of the incident light (plane wave) is only tilted. Wear.
- the "frequency range where only the first band exists" is. Since the value of is small, it is necessary to increase both the incident angle 0 and the refractive index n, which causes a problem that the reflectivity at the photonic crystal end face becomes considerably large and the loss increases. Also, if the wavelength of the incident light is changed while the incident angle 0 remains the same, the equation (1) does not hold completely, so that the direction of energy propagation is shifted from the Z-axis as in the first method.
- FIG. 10 is a cross-sectional view of the photonic crystal 1 shown in FIG. 1 for explaining the third method.
- the photonic crystal 1 is the same as that used in FIG.
- plane waves 21 and 22 having the same wavelength intersect each other as an angle of incidence ⁇ and are incident on the photonic crystal 1.
- the solid lines show the peaks 21 a and 22 a of the electric field
- the broken lines show the troughs 2 lb and This is the part of 2 2 b.
- the incident end 1a of the photonic crystal 1 is caused by the interference of the two plane waves 21 and 22.
- An electric field pattern with nodes and antinodes in the Y direction is formed. Therefore, the photonic crystal 1 is arranged such that a high refractive index layer (substance 5a) is formed on the antinode.
- a peak 111 and a valley 112 of the propagating light are illustrated. As a result, only light propagated by the first band is generated (see Calculation Example 3 and FIG. 18 described later).
- the photonic crystal 1 is arranged so that the low refractive index layer is located at the antinode, only light propagated by the second band is generated (see Calculation Example 4 and FIG. 19 described later).
- the value of the incident angle 0 is calculated by the equation (1) as in the first and second methods. Must be satisfied.
- FIG. 11 is a cross-sectional view of the photonic crystal 1 shown in FIG. 1 for explaining the fourth method.
- a phase having a refractive index period (2 a) twice as long as the refractive index period a of the photonic crystal 1 is brought into contact with or close to the input end 1 a and the output end 1 b of the photonic crystal 1.
- Grids 6a and 6b are installed. At this time, the entrance and exit ends of the phase gratings 6a and 6b are perpendicular to the propagation direction (Z-axis direction).
- the phase grating 6a has a shape optimized so that the first-order diffraction light of the soil is as strong as possible.
- phase grating optimized for a specific wavelength remains at a high level even if the wavelength slightly changes, without the efficiency of the first-order diffracted light dropping sharply. Therefore, the wavelength range that can be used in the fourth method (phase modulation of incident light by a phase grating having a period of 2a) can be made wider than in other methods. Further, by arranging a phase grating 6b having the same period as the phase grating 6a on the emission end 1b side of the photonic crystal 1, the light 8b emitted from the photonic crystal 1 is converted into a plane wave 7 Can be converted to 1.
- FIG. 12A is a cross-sectional view showing an electric field pattern of propagating light in a photonic crystal in which an electromagnetic wave propagates on a Brillouin zone boundary between a first band and a second band generated by the first method.
- Fig. 12A is a figure obtained by simulating Fig.
- FIG. 12B is a diagram showing a simulation result of the propagation shape of the emitted light when each point (S1, S2, P) shown in FIG. 12A is set as the emission end.
- FIG. 12A when the point on the slope of the zigzag pattern is the emission end as in the position S1 or S2, the one-sided diffracted light becomes strong as shown in FIG. 12B.
- the intensity of the double-sided diffracted light becomes almost equal as shown in FIG. 12B.
- the interference pattern due to the emitted light in which the intensity of the diffracted light on both sides is almost equal
- a multilayer film or the like having the same structure can be used for the phase grating and the photonic crystal.
- the sixth method for realizing propagation at the Brillouin zone boundary (using a phase grating with a period of 2a and interference waves caused by oblique incidence) will be described.
- a / ⁇ When the value is less than 0.5, for example, it becomes difficult to increase the intensity of the first-order diffracted light with the phase gratings 6a and 6b made of a low refractive index material such as quartz or air. If the phase gratings 6a and 6b are formed using a high refractive index material such as silicon, the ⁇ 1st-order diffracted light can be strengthened, but the amount of reflected light increases or the phase gratings 6a and 6b There is a problem that it becomes difficult to fabricate.
- n is the refractive index of the medium adjacent to the input end of the phase grating.
- the phase grating used was a phase grating having the same or twice the refractive index period a of the photonic crystal 1, but the refractive index period a
- a phase grating having a refractive index period that is an integral multiple of the above may be used.
- FIG. 13A is a perspective view showing a configuration of an optical waveguide device 100 using the photonic device according to the present embodiment.
- a one-dimensional photonic crystal 1 shown in FIG. 1 and having a refractive index period in one direction is formed on an appropriate substrate 20.
- phase gratings 16a and 16b which are phase modulation sections by the fourth method, are provided.
- an incident means such as a rod lens 12a for inputting the incident light 2 to the phase grating 16a is provided.
- the incident light 23 is focused on the end face of the phase grating 16a by the rod lens 12a. By doing this, Light can be perpendicularly incident on the phase grating 16a.
- the waveguide element 100 can be used as an optical control element such as an optical delay element or a dispersion compensation element in optical communication.
- FIG. 13B is a perspective view showing a configuration of a waveguide element 110 using another photonic crystal of the present embodiment.
- the aperture lens 13a not only allows light to be perpendicularly incident on the phase grating 16a (light travels in the Z-axis direction), but also has an incident angle ⁇ , for example. As described above, light may be incident obliquely.
- the incident light 23 is coupled to the photonic crystal 1 from the end face 1a via the phase grating 16a.
- the photonic crystal 1 is an optical waveguide, and the coupled light propagates through the photonic crystal 1.
- the light After propagating in the photonic crystal 1, the light is emitted from the emission end face 1b, for example, enters the emission rod lens 12b via the phase grating 16b according to the fourth method, and is emitted.
- the emitted light 33 is emitted.
- the arrangement of the phase grating 16a and the photonic crystal 1, and the respective refractive index periods may be set as described in the fifth and sixth methods described above. That is, the light 23 emitted from the rod lens 12a is incident on the phase grating 16a at an incident angle 0 satisfying the expression (1). Thereby, in the photonic crystal 1, propagation at the Brillouin zone boundary can be realized. As a result, "extremely large chromatic dispersion” and "group velocity anomaly” can be caused. Therefore, the waveguide element 110 can be used as an optical control element such as an optical delay element or a dispersion compensation element in optical communication.
- a phase grating 16b by the fourth, fifth, or sixth method may be provided on the emission end face lb.
- FIG. 13A and FIG. 13B are both cases according to the fourth method.
- the light emitted from the end face 1b is phase-modulated, so that the emitted light can be prevented from being remarkably diffracted.
- the phase modulation is applied through the phase grating 16b, the light can be made into a plane wave-like outgoing light.
- the phase grating 16 b may be installed with the directions of the incident end and the outgoing end opposite to those of the phase grating 16 a on the incident side. That is, the end face of the phase grating 16a on the photonic crystal 1 side may be the end face of the phase grating 16b on the photonic crystal 1 side.
- phase grating is symmetrically arranged on both the incident side and the outgoing side of the photonic crystal 1, the same effect is obtained for propagating light in either direction.
- An optical fiber or the like can be directly coupled to each of the phase gratings 16a and 16b. That is, either of the two ends of the photonic crystal 1 may be the incident side. (See Calculation Example 5 and Fig. 20A described later).
- the phase gratings 16 a and 16 b are near the end faces 1 a and 1 b of the photonic crystal 1. Or, it may be installed in contact with the end faces 1a and 1b. If the structures of the photonic crystal 1 and the phase gratings 16a and 16b are the same, they may be integrally formed.
- FIG. 13C is a perspective view showing a configuration of a waveguide device 200 using another photonic crystal of the present embodiment.
- the phase grating 16a of Fig. 13A is not installed, and instead of the rod lens 12a, the end face 1a is (1)
- a rod lens 13a (input section) that allows light to enter at an incident angle ⁇ ⁇ ⁇ ⁇ that satisfies the condition of the formula is installed.
- FIG. 13D is a perspective view showing a configuration of a waveguide element 210 using another photonic crystal of the present embodiment.
- the waveguide element 210 shown in FIG. 13D is the same as the waveguide element 200 shown in FIG. 13C, and furthermore, a rod lens 13 b (input) that allows light to be incident from the end face 1 a at an incident angle ( ⁇ S). Part).
- a waveguide device using the photonic crystal according to the present embodiment using the third method can be realized.
- the vertical direction is the direction of the refractive index period of the photonic crystal 1.
- the effective refractive index of the higher-order propagation band light in the Z direction is larger than the refractive index of the surrounding medium in contact with the photonic crystal 1 part, confinement is performed as it is by the difference in refractive index.
- the effective refractive index is smaller than the refractive index of the surrounding medium, the propagating light leaks to the medium side due to refraction. That is, light does not propagate through the photonic crystal 1.
- the surrounding medium is air or the substrate 20.
- the effective refractive index of the higher-order propagation band light is less than the refractive index of the substrate 20, it is impossible to prevent the propagation light from leaking even when the surrounding medium is air.
- FIG. 14A is a cross-sectional view showing the structure of the photonic crystal 1 provided with the reflective layer 32.
- Figure 14B shows a photonic crystal cladding 11
- FIG. 2 is a cross-sectional view illustrating a structure of a photonic crystal 1 according to the first embodiment.
- a reflective layer 32 such as a metal film may be provided above and below the photonic crystal 1 as shown in FIG. 14A.
- problems such as a decrease in the strength of the multilayer film due to the reflective layer 32 and attenuation of propagating light due to an insufficient reflectivity of the reflective layer may occur. In this case, for example, as shown in FIG.
- a photonic crystal clad 11 having a different refractive index period or a different structure from the photonic crystal 1 may be provided above and below the photonic crystal 1.
- the structure of the photonic crystal 11 may be appropriately designed according to the structure of the photonic crystal 1.
- the reflection layer 32 and the photonic crystal clad 11 may be provided on either one of the photonic crystals 1 instead of being provided on both sides thereof.
- FIG. 15 shows a specific wavelength ⁇ between the one-dimensional photonic crystal 1 having the period a and the one-dimensional photonic crystal cladding 11 having the period b adjacent to each other.
- This is a schematic diagram of a band diagram (assuming b> a) for (see Fig. 14B).
- the material and structure of the confinement photonic crystal cladding 11 It may be different from Otonic crystal 1. Considering the efficiency of manufacturing a multilayer film that is a one-dimensional photonic crystal, it is desirable to use the same material and reduce the period.
- the band calculation confirmed that the band corresponding to the wavenumber vector of the propagating light in the wavelength region and the propagation band used on the photonic crystal 1 side did not exist on the photonic crystal cladding 11 side. (See Calculation Example 7 and Figure 23 below).
- the determination of light confinement based on the band diagram shown in FIG. 15 is based on the premise that the photonic crystal cladding 11 has an infinite periodic structure. If the period is about three cycles, the confinement is insufficient and the propagating light may leak to the outside. Unnecessarily increasing the number of cycles is not preferable in terms of cost, durability and accuracy of the multilayer film. Therefore, it is desirable that the minimum number of cycles actually required be determined by experiment or electromagnetic wave simulation.
- Photonic crystal 1 has a uniform refractive index in the horizontal direction (X direction).
- the lateral (X-axis) side surface of the photonic crystal 1 of the waveguide elements 100, 110, 200, and 210 shown in FIGS. 13A to 13D is a photonic crystal.
- the core part of the crystal is exposed to the air layer.
- “alternate electric field patterns” are exposed on the side surfaces of the photonic crystal 1 and that the amplitudes at the electric field peaks are all equal. Therefore, the diffracted waves from the side surface of the photonic crystal 1 cancel each other out and do not propagate to the air side, so they are confined as they are (see Calculation Example 8 and Fig. 25 described later). .
- the group velocity of high-order band propagation light greatly changes depending on the wavelength of the incident light as described above. Therefore, the dispersion compensation of signal light for optical communication and the optical delay element Can be used for applications. Also, as described above, the propagating light with a low group velocity has the effect of enhancing the nonlinear optical effect.
- a thin-film layer containing a material exhibiting nonlinear optical action is installed at each period of the photonic crystal (waveguide) part.
- FIG. 13A to FIG. 13D As a material of the photonic crystal 1 of the waveguide elements 100, 110, 200, and 210 using the photonic crystal according to the present embodiment, There is no particular limitation as long as transparency in the wavelength range can be ensured.
- silica, silicon, titanium oxide, tantalum oxide, niobium oxide, magnesium fluoride, silicon nitride, and the like which are generally used as materials for multilayer films and have excellent durability and film formation cost, are suitable. These materials can be easily formed into a multilayer film by a well-known method such as sputtering, vacuum deposition, ion assist deposition, and plasma CVD.
- the wavelength dispersion tends to increase.Therefore, there is a large difference between the refractive indices for applications that require such characteristics. It is desirable to combine a high refractive index material and a low refractive index material. That is, the photonic crystal 1 in Fig. 1
- the substance 5a may be a high refractive index material
- the substance 5b may be a low refractive index material. That is, the refractive index ratio between the substance 5a and the substance 5b may be increased.
- the refractive index ratio of the material (substance 5a and substance 5b) constituting the photonic crystal 1 decreases, the difference in characteristics depending on the polarization direction tends to decrease. Therefore, in the waveguide element using the photonic crystal according to the present embodiment, it is useful to reduce the refractive index ratio of substance 5a and substance 5b in order to realize polarization independence. It is.
- the photonic crystal 1 is provided on the substrate 20.
- a so-called air bridge structure may be used without using the substrate 20.
- the action of the waveguide element using the photonic crystal according to the present embodiment can be performed in the wavelength range of about 200 nm to 20 / xm, which is usually used, that is, when light is used. , Is especially effective.
- the waveguide device using the photonic crystal according to the present embodiment can be applied to radio waves having longer wavelengths, X-rays and gamma rays having shorter wavelengths. It can also be applied.
- the waveguide device using the photonic crystal according to the present embodiment has been described as an optical device, it is not limited to light, and can be used for electromagnetic waves of any wavelength depending on the design. That is, the waveguide element using the photonic crystal according to the present embodiment can be used as an electromagnetic wave control element.
- the waveguide element using the photonic crystal of the present embodiment is limited to the case where the photonic crystal has only one refractive index period in one direction. Not necessarily.
- a new function can be added by making a part of the photonic crystal have a refractive index periodicity in another direction. For example, by forming a groove having a period in the Z direction in a part of the photonic crystal 1 shown in FIGS. 13A to 13D, light propagated in a specific frequency range is reflected by Bragg reflection.
- a waveguide element can be manufactured.
- electromagnetic wave simulation was performed under the following conditions when a plane wave was incident on the end face of the periodic multilayer structure.
- the electromagnetic wave simulation uses the finite element method (FiniteEleme n tMe thod, hereinafter referred to as FEM method).
- FEM method FiniteEleme n tMe thod
- the calculation example 1 will be described with reference to FIG.
- Photonic crystal 1 is a material in which substance 5a and substance 5b are periodically and alternately stacked (see FIG. 1).
- FIG. 16A The band diagram of this photonic crystal 1 for TE polarized light is shown in FIG. 16A.
- the arrow 5110 indicates the wave number vector of the incident light 2
- the arrow 5111 indicates the energy traveling direction of the propagating light 4 in the first band
- the arrow 512 indicates the second The energy traveling direction of the propagating light 4 in the band is shown.
- the corresponding points 5 15 and 5 16 are the normalized frequencies a Z ⁇ on the first and second bands. Where matches the incident light Arrows 5 13 and 5 14 are the wavenumber vectors of the propagating light 4.
- n'sini'a / A. ) 0.5
- the condition of the expression (1) is satisfied.
- the calculation was performed in a finite area, and the width of the incident portion on the end face 1a of the photonic crystal 1 was set to about 12 periods.
- FIG. 16B shows the intensity distribution of the electric field as a simulation result in Calculation Example 1.
- the black spots indicate where the electric field is strong (peaks and valleys with amplitude).
- a unique zigzag electric field pattern appears under the conditions of Calculation Example 1 because the first band and the second band propagate at the Brillouin zone boundary. . That is, “very large chromatic dispersion” and “group velocity anomaly” can occur.
- the calculation example 2 will be described with reference to FIG.
- Photonic crystal 1 is a material in which substances 5a and 5b are periodically and alternately stacked (see Fig. 1).
- FIG. 17A is a band diagram in Calculation Example 2.
- an arrow 52 0 indicates the wave number vector of the incident light 2
- an arrow 52 1 indicates the energy traveling direction of the propagating light 4 in the first band
- a corresponding point 52 3 Normalized frequency a / ⁇ on the first band. Is the part that coincides with the incident light, and the arrows 5 2 2 are the wavenumber vectors of the propagating light 4.
- the bands in Figure 17 ⁇ and Figure 16A are the same, but a / ⁇ . , The corresponding point 5 2 3 exists only in the first band.
- FIG. 17B shows the intensity distribution of the electric field, which is the simulation result in Calculation Example 2.
- black spots indicate places where the electric field is strong (peaks and valleys of amplitude).
- the band diagram (Fig. 9)
- the high refractive index layer is the antinode
- the low refractive index layer is the node
- a higher-order band propagation pattern appears in which the phase of the electric field is shifted by half a period.
- Photonic crystal 1 is a material in which substances 5a and 5b are periodically and alternately stacked (see Fig. 1).
- the incident lights 21 and 22 are incident from two directions and cross each other.
- the antinode of the interference wave was matched with the high refractive index layer.
- the calculation was performed in a finite area, and the width of the incident portion of the end face 1a of the photonic crystal 1 was set to about 13 periods.
- FIG. 18 shows the intensity distribution of the electric field, which is the simulation result of Calculation Example 3.
- black spots indicate areas where the electric field is strong (peaks and valleys with amplitude).
- the electric field is localized in the high refractive index layer. Therefore, it can be seen that only the propagation light by the first band is generated.
- Calculation Example 4 has the same conditions as Calculation Example 3, except that the antinode of the interference wave matches the low refractive index layer.
- FIG. 19 shows the intensity distribution of the electric field as a simulation result in Calculation Example 4.
- the black spots indicate where the electric field is strong (peaks and valleys with amplitude).
- the electric field is localized in the low refractive index layer. Also, it can be seen that only the propagation light by the second band is generated. In the case of Calculation Example 4, the electric field is localized in the low refractive index layer
- the calculation example 5 will be described with reference to FIG.
- photonic crystal 1 Installed on an end face of the photonic crystal 1 the phase grating 6 a and 6 b, is t (1) photonic crystal 1 a calculation example of a case where is the plane wave 7 normal incidence is the incident light is a flat surface waves Structural conditions
- Photonic crystal 1 is a material in which substance 5a and substance 5b are periodically and alternately stacked (see FIG. 1).
- FIG. 20B is a cross-sectional view illustrating a configuration of the phase grating 6a.
- Phase grating 6a Is a structure in which the substance 6c and the substance 6d are arranged in a rectangular shape.
- the phase gratings 6a and 6b in FIG. 11 have a configuration in which either the material 6c or the material 6d is air, and a material and air are alternately stacked.
- FIG. 20B is a cross-sectional view showing the configuration of the phase grating 6a. As shown in FIG. 20B, the phase grating 6a (phase grating 6b) has a configuration in which the materials 6c and 6d are alternately stacked.
- Material 6 c is a Y-axis direction of the thickness Saga t c, a refractive index of n c.
- material 6 d is a Y-axis direction of the thickness t D, a refractive index of n D.
- the configuration of the phase grating 6b is the same as that of the phase grating 6a.
- the thickness of the layer 6 e in the Z-axis direction is t E.
- phase grating and the air layer t E (width of layer 6 e) 0.9434 a or more, and the shapes of the phase gratings 6 a and 6 b were optimized so that ⁇ 1st-order diffracted light was strong.
- phase gratings 6a and 6b The layers are arranged such that the centers of the substances 6c and 6d, which are each layer of the phase grating 6a on the incident side, coincide with the center of the high refractive index layer of the photonic crystal 1.
- the same phase grating 6 b as that on the incident side was arranged on the exit side of the photonic crystal 1, and the emitted light from the photonic crystal 1 was converted into a plane wave.
- the position of the phase grating 6 b on the emission side in the Y-axis direction is shifted from the incidence side by a half period a. This is to make the optical path length difference in the Z-axis direction constant.
- the calculation was performed in a finite area, and the width of the incident portion on the end face 1a of the photonic crystal 1 was set to about 9 periods.
- Calculation Example 5 is a case of the fourth method (phase modulation of incident light by installing a phase grating), and FIG. 2OA shows an electric field intensity distribution as a simulation result in Calculation Example 5.
- Fig. 20A black spots indicate places where the electric field is strong (peaks and valleys with amplitude). Since the photonic crystal 1 is placed so that the high refractive index layer is located at the antinode of the propagating light, only the propagating light of the first band is generated as shown in FIG. 2OA. In addition, restoration of the plane wave by the output-side phase grating 6 b has been achieved.
- the calculation example 6 will be described with reference to FIG. 13B.
- phase modulation is performed by oblique incidence of a phase grating having a period of 2a, and the phase modulation is coupled to the photonic crystal 1.
- Photonic crystal 1 is a material in which substances 5a and 5b are periodically and alternately stacked (see Fig. 1).
- the phase grating 6a has a structure in which the substance 6c and the substance 6d are arranged in a rectangular shape.
- the shape of the phase grating 6a has been optimized so that specific diffracted light is strong.
- FIG. 21 shows the electric field strength obtained by simulation of light obliquely incident on the phase grating 6a.
- black spots indicate places where the electric field is strong (peaks and valleys with amplitude).
- the refractive index in each region will be described.
- the incident light 23 proceeds from the region where the refractive index is 1.0 to the region where the refractive index is 2.0, and enters the phase grating 6a.
- the light is emitted from the phase grating 6a to a region where the refractive index is 2.0.
- the light incident on the phase grating 6a at an incident angle 6> has interference waves that spread on both sides. Since the interference wave that is strong and that travels perpendicular to the phase grating 6a is weak, it can be seen that the interference pattern is alternate.
- FIG. 22 shows the intensity distribution of the electric field as a simulation result in Calculation Example 6.
- black spots indicate areas where the electric field is strong (peaks and valleys with amplitude).
- the distance u between the phase grating 6a and the photonic crystal 1 is 0.90909a, the refractive index at that point is 2.0, and the photonic crystal 1
- the position in the Y-axis direction was adjusted so that the antinode of the interference wave came to the center of the high refractive index layer.
- the width of the incident portion on the end face 1a of the photonic crystal 1 was about 24 periods.
- Calculation example 6 is the case of the sixth method (using a phase grating with a period of 2a and interference waves due to oblique incidence).
- a / ⁇ Since the value of is small, it can be seen that the wavelength of the electromagnetic wave propagating in the photonic crystal 1 is very long, and that the spread in the Y direction is remarkable.
- Calculation example 7 is a calculation example in which photonic crystals 11 with different periods are provided above and below the photonic crystal 1 in calculation example 6, and confinement is performed. The calculation example 7 will be described with reference to FIG. 14B.
- Photonic crystal cladding 1 1 are those substances and the thickness t e the refractive index of the refractive index n F in the thickness t F is superimposed alternating material n s, the photonic crystal 1 Assume a different structure.
- the band diagram of the photonic crystal 11 is the same as that shown in FIG.
- the photonic crystal 11 has five periods each for the upper and lower sides.
- FIG. 23 shows the intensity distribution of the electric field as a simulation result in Calculation Example 7.
- the black spots indicate where the electric field is strong (peaks and valleys with amplitude).
- the electromagnetic wave energy is confined in the Y direction and propagates in the Z direction.
- Calculation example 8 is a calculation example of lateral (X-axis) confinement. A calculation example will be described with reference to FIGS. 24A, 24B, and 24C.
- FIG. 24A is an XZ plane sectional view showing a configuration of a waveguide element 240 used in Calculation Example 8.
- photonic crystal 1 has a uniform refractive index in the X and Z axis directions.
- FIG. 24A shows only a half surface of the waveguide element 240.
- the air layer 24 1 is around the photonic crystal 1.
- the waveguide element 240 includes the phase grating 6a on the incident end side.
- FIG. 24B is a sectional view taken along the YZ plane showing the configuration of the waveguide element 240 used in Calculation Example 8.
- Figure 2 4B shows only a part of the waveguide element 240.
- FIG. 24C is a partial C enlarged view of FIG. 24B.
- Photonic crystal 1 is a material in which substances 5a and 5b are periodically and alternately stacked (see Fig. 1).
- the phase grating 6a has a structure in which the substance 6c and the substance 6d are arranged in a rectangular shape.
- phase grating and the air layer t E (width of layer 6 e) 0.47 17 a or more, and the shapes of the phase gratings 6 a and 6 b were optimized so that ⁇ 1st-order diffracted light was strong.
- the width (length in the X-axis direction) of the photonic crystal 1 was 9.434a, and both sides of the photonic crystal 1 were air layers having a refractive index of 1.0.
- the photonic crystal 1 was divided at the center in the X-axis direction and used as a reflective surface, displaying half of the area. I have.
- Figures 25A, 25B and 25C show the calculation results of the electric field intensity distribution by the FEM method when the incident light 242 is incident.
- Fig. 25A shows the intensity distribution of the electric field in the center section of the waveguide, Fig.
- Fig. 25B shows the intensity distribution of the electric field in the center of the high refractive index layer
- Fig. 25C shows the low refractive index.
- the intensity distribution of the electric field at the center of the layer is shown.
- the black spots indicate where the electric field is strong (peaks and valleys of amplitude).
- the electric field intensity is almost 0, indicating that the propagating light is confined in the photonic crystal 1.
- the waveguide element using the photonic crystal of the present invention can be used as an electromagnetic wave control element corresponding to a wide wavelength range.
Abstract
Description
Claims
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US10/547,828 US7421176B2 (en) | 2003-03-04 | 2004-03-04 | Waveguide element using photonic crystal |
JP2005503492A JPWO2004081625A1 (ja) | 2003-03-04 | 2004-03-04 | フォトニック結晶を用いた導波路素子 |
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US7688512B2 (en) | 2006-09-21 | 2010-03-30 | Nippon Sheet Glass Company, Limited | Transmissive diffraction grating, and spectral separation element and spectroscope using the same |
JP2012226081A (ja) * | 2011-04-19 | 2012-11-15 | Canon Inc | X線導波路 |
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WO2006077765A1 (ja) * | 2005-01-18 | 2006-07-27 | Nippon Sheet Glass Company, Limited | 導波路素子、導波路素子の製造方法及び光学センサ |
JP5864945B2 (ja) * | 2010-09-02 | 2016-02-17 | キヤノン株式会社 | X線導波路 |
JP2013064713A (ja) * | 2011-08-30 | 2013-04-11 | Canon Inc | X線導波路及びx線導波システム |
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Also Published As
Publication number | Publication date |
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EP1605286A1 (en) | 2005-12-14 |
CN1761897A (zh) | 2006-04-19 |
US20070058915A1 (en) | 2007-03-15 |
EP1605286A4 (en) | 2006-04-26 |
US7421176B2 (en) | 2008-09-02 |
JPWO2004081625A1 (ja) | 2006-06-15 |
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