WO2009098818A1 - 光スイッチ及びその製造方法 - Google Patents
光スイッチ及びその製造方法 Download PDFInfo
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- WO2009098818A1 WO2009098818A1 PCT/JP2008/072299 JP2008072299W WO2009098818A1 WO 2009098818 A1 WO2009098818 A1 WO 2009098818A1 JP 2008072299 W JP2008072299 W JP 2008072299W WO 2009098818 A1 WO2009098818 A1 WO 2009098818A1
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- waveguide
- optical switch
- waveguides
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- path
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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
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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
- G02B6/125—Bends, branchings or intersections
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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
- G02B2006/12133—Functions
- G02B2006/12142—Modulator
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/212—Mach-Zehnder type
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2202/00—Materials and properties
- G02F2202/32—Photonic crystals
Definitions
- the present invention relates to an optical switch and a manufacturing method thereof, and more particularly, to an optical switch using a waveguide and a manufacturing method thereof.
- optical circuits such as optical switches, wavelength filters, and 3 dB couplers (optical couplers) are connected via an optical waveguide such as an optical fiber to form an optical circuit.
- optical waveguide such as an optical fiber
- photonic crystal is a general term for structures in which the refractive index is periodically changed.
- photonic crystal and “photonic crystal” are used as synonyms.
- Photonic crystals have various special optical characteristics due to the periodic structure of the refractive index distribution.
- the most typical feature is a photonic band gap (PBG).
- PBG photonic band gap
- Light can pass through the photonic crystal, but if the periodic refractive index change in the photonic crystal is sufficiently large, light in a specific frequency band cannot propagate through the photonic crystal.
- the frequency band (or wavelength band) of light that can be transmitted through the photonic crystal is referred to as a photonic band.
- the band of light that cannot be transmitted is a gap existing between photonic bands, and is called a photonic band gap (PBG).
- a plurality of PBGs may exist in different frequency bands.
- the photonic bands divided by the PBG may be called a first band, a second band, a third band, etc. from the smaller frequency.
- Such a photonic crystal can be used as an optical waveguide.
- Such an optical waveguide formed in a photonic crystal is called a line defect waveguide.
- an optical functional element such as an optical modulator or an optical switch can be configured by one or a combination thereof. It is possible to form an optical circuit by forming main optical functional elements in the photonic crystal and connecting the optical functional elements. For these reasons, photonic crystals are expected as an optical integrated circuit platform.
- the refractive index distribution of the photonic crystal has a three-dimensional periodic structure.
- a photonic crystal whose refractive index distribution has a two-dimensional periodic structure (hereinafter sometimes referred to as “two-dimensional photonic crystal”) is often used.
- a two-dimensional photonic crystal having a finite thickness that has a periodicity in the refractive index distribution in the substrate plane but does not have a periodicity in the thickness direction is used. In that case, confinement of light in the thickness direction of the substrate is realized not by the effect of PBG but by total reflection due to the difference in refractive index.
- the characteristics of a two-dimensional photonic crystal having a finite thickness do not completely match the characteristics of a two-dimensional photonic crystal having an infinite thickness.
- the refractive index distribution in the thickness direction of a two-dimensional photonic crystal having a finite thickness is mirror-symmetric in a region where light propagates, the optical characteristics of the two-dimensional photonic crystal having an infinite thickness substantially coincide.
- the operation prediction of a device using a two-dimensional photonic crystal having an infinite thickness is much easier than the operation prediction considering a finite thickness. Therefore, if a two-dimensional photonic crystal with a refractive index distribution that is mirror-symmetric can be used, a device using the two-dimensional photonic crystal can be easily designed.
- a pillar-type square lattice photonic crystal has a feature that light propagation speed in a line defect waveguide is slow in a wide band. That is, a low group velocity.
- an optical circuit having the same function can be formed with a short waveguide length. Therefore, a line defect waveguide using a columnar square lattice photonic crystal is suitable for an optical integrated circuit.
- FIG. 8 is a schematic diagram showing the structure of a line defect waveguide of a columnar square lattice photonic crystal having a finite thickness.
- a cylinder 52a having a finite height made of a high dielectric constant material and a cylinder 52b having a smaller diameter than the cylinder 52a are square. Arranged in a grid.
- the appearance that these cylinders are arranged in a square lattice shape is similar to the state in which atoms are arranged in a lattice shape in a crystal such as silicon or quartz, and is a photonic crystal. It is called. Therefore, the low dielectric constant material 1 and the cylindrical material do not need to be crystals, and may be amorphous.
- the cylinder 52a is a complete photonic crystal cylinder, whereas the cylinder 52b is smaller in diameter than the cylinder 52a. Therefore, the cylinder 52b is regarded as a defect introduced into the complete crystal.
- the former is called a “non-linear defect column”, and the latter is called a “defect column”, a “defect column”, or a “line defect column”.
- the line defect column itself is not particularly defective.
- the line defect pillars 52b of the photonic crystal shown in FIG. 8 are arranged in a line on a certain straight line to form a line, and the line defect pillars 52b and the non-linear defect pillars 52a around the line defect pillars 52b are connected to each other.
- a waveguide is formed.
- the line defect column array corresponds to the core in a total reflection confinement waveguide such as an optical fiber, and the non-linear defect columns on both sides thereof.
- the grating and surrounding dielectric material correspond to the cladding.
- a line defect and a surrounding non-linear defect column or dielectric material are also present in the case of a line defect waveguide so that it works as a waveguide only when a core and a cladding exist. Operates as a waveguide for the first time.
- Optical devices and optical circuits using columnar square lattice photonic crystals are expected to be small and highly integrated, but it is effective to use photonic crystals for the 1 ⁇ 2 optical switch handled in the present invention. No structure has been utilized so far.
- FIG. 9 is a schematic diagram showing the configuration. The structure and operation of the optical switch of FIG. 9 are as follows.
- 3 dB branching waveguide 60 includes a 3 dB branching waveguide 60, a 3 dB directional coupler 61, and a waveguide 62 and a waveguide 63 between them.
- Light incident from the input port 70 propagates through the waveguide 71 and enters the 3 dB branch waveguide 60.
- the 3 dB branch waveguide 60 divides the incident light power in half.
- the divided lights propagate through the waveguide 62 and the waveguide 63, respectively, and are incident on the two waveguides 64 and 65 constituting the 3 dB directional coupler 61. Then, light is emitted from the emission ports 66 and 67 through the waveguides 68 and 69.
- the optical power emitted to the exit port 66 and the exit port 67 of the directional coupler depending on the phase relationship between the light incident on the waveguide 64 and the waveguide 65 (how much the phase is advanced or delayed). The ratio of changes.
- the light exit can be switched between the emission port 66 and the emission port 67 by adjusting the phase difference of the light while the light propagates through the waveguide 62 and the waveguide 63.
- the adjustment of the phase difference of light during the propagation of light through the waveguide 62 and the waveguide 63 is performed by changing the effective refractive index of only one waveguide, for example, the waveguide 63.
- the effective refractive index is changed by changing the refractive index of the waveguide material using heat or an electric field.
- both the waveguide 62 and the waveguide 63 are lengthened with the same length, or the effective refractive index is changed.
- the length of the waveguide 63 to be made may be increased.
- the case where the waveguide 62 and the waveguide 63 have the same length is called a symmetric Mach-Zehnder type 1 ⁇ 2 optical switch, and the case where the waveguide 62 and the waveguide 63 have different lengths is called a symmetric Mach-Zehnder type 1 ⁇ 2.
- Patent Document 1 discloses a structure of a 1 ⁇ 2 optical switch that is attempted to be miniaturized using a photonic crystal.
- the two-dimensional photonic crystal slab (31) includes a waveguide (20) that is a branched waveguide.
- the two-dimensional photonic crystal slab (31) includes an “interference channel” (35) and a “resonant member” (37).
- the operation speed of the optical switch may be decreased accordingly.
- the present invention has been made in view of the above circumstances, and an object thereof is to provide an optical switch that can be operated efficiently and a method for manufacturing the same.
- the optical switch according to the present invention is a Mach-Zehnder interferometer type optical switch composed of a photonic crystal line defect waveguide, and includes a branch, a directional coupler, and a two-path waveguide between them. Among the two paths, the first path waveguide and the second path waveguide have different group velocities of guided light.
- An optical switch is a Mach-Zehnder interferometer type optical switch composed of a line defect waveguide of a pillar type photonic crystal, and includes a branch, a directional coupler, and two paths between them.
- the defect pillar has a cross-sectional area that forms a line defect of at least one of the two paths, and a defect that forms a line defect of the waveguide that forms the branch and the directional coupler. It is characterized by being smaller than the cross-sectional area of the pillar.
- An optical switch is a Mach-Zehnder interferometer type optical switch composed of a line defect waveguide of a photonic crystal, and includes a branch, a directional coupler, and two paths between them.
- a resonator having a waveguide, and a part or all of the waveguide of at least one of the two paths resonates with light having a frequency other than the waveguide band of the waveguide constituting the directional coupler. It is characterized by operation.
- the manufacturing method of the optical switch according to the present invention is a manufacturing method of a Mach-Zehnder interferometer type optical switch composed of a photonic crystal line defect waveguide, and includes a branch, a directional coupler, and their Between the two paths, the first path waveguide and the second path waveguide have different group velocities of the guided light.
- FIG. 3 is a schematic cross-sectional view of the optical switch according to Embodiment 1.
- FIG. It is a figure which shows the transmission spectrum of the structure of the optical switch shown in FIG. It is a figure which shows the electromagnetic field distribution of the light in the case of radiate
- FIG. 6 is a schematic cross-sectional view showing a configuration of an optical switch according to Embodiment 2.
- FIG. 6 is a schematic cross-sectional view illustrating a configuration of an optical switch including a control light input unit according to a second embodiment. It is a three-dimensional view of a square lattice pillar type photonic crystal including a line defect. It is a schematic diagram of the 1 * 2 optical switch by a waveguide.
- Embodiment 1 An optical switch according to a first embodiment of the present invention will be described in detail with reference to the drawings.
- the optical switch according to the present embodiment is, for example, an mxn optical switch using a Mach-Zehnder interferometer having m input ports (input ends) and n output ports (output ends) ( m is an integer of 1 or more, and n is an integer of 2 or more).
- the Mach-Zehnder interferometer includes an asymmetric Mach-Zehnder interferometer and a symmetric Mach-Zehnder interferometer.
- FIG. 1 is a schematic diagram showing a configuration of a 1 ⁇ 2 optical switch 5 according to the present embodiment.
- the 1 ⁇ 2 optical switch 5 is often included as a part in an arbitrary pillar-shaped square lattice photonic crystal.
- the periodic lattice of the photonic crystal is a lattice of high-refractive-index dielectric columns arranged in a relatively low-refractive-index medium. That is, the 1 ⁇ 2 optical switch 5 is an asymmetric Mach-Zehnder interferometer type optical switch configured by a line defect waveguide of a photonic crystal.
- the 1 ⁇ 2 optical switch 5 includes a branch 7 and a directional coupler 15.
- the branch 7 is a T-branch in which a line defect waveguide is provided in a T-shape, and the optical power incident from one input end is divided in half and emitted from two output ends.
- the directional coupler 15 is provided with two waveguides close to each other. For example, optical power incident from two input ends is coupled and branched and emitted from two output ends.
- the 1 ⁇ 2 optical switch 5 includes a first path waveguide 8 and a second path waveguide 10 between them.
- the first path waveguide 8 and the second path waveguide 10 have different group velocities of the guided light.
- the group velocities of the guided light are made different by making the cross-sectional areas of the line defect pillars of the waveguides 8 and 10 of the respective paths different.
- the line defect pillar is a defect pillar that forms a line defect.
- the cross-sectional areas of the line defect pillars 12, 22, and 23 of the waveguide 10 of the second path are larger than the cross-sectional area of the line defect pillar 9 of the waveguide 8 of the first path.
- the waveguide length of the second path is longer than the waveguide length of the first path.
- tapered waveguides 13 and 14 are provided at both ends of the waveguide 10 of the second path.
- a connection waveguide 11 is provided between the two tapered waveguides 13 and 14. That is, the connection waveguide 11 is connected to the waveguide of the branch 7 via the tapered waveguide 13.
- the connection waveguide 11 is connected to the waveguide of the directional coupler 15 via the tapered waveguide 14.
- the cross-sectional areas of the line defect pillars 22 and 23 of the tapered waveguides 13 and 14 gradually increase or decrease from one end to the other end. Specifically, the cross-sectional areas of the line defect pillars 22 and 23 of the tapered waveguides 13 and 14 gradually decrease as the distance from the connection waveguide 11 increases.
- the cross-sectional areas of the line defect pillars 16 and 17 of the two waveguides constituting the directional coupler 15 are the same in both waveguides.
- the waveguide 10 of the second path has a large group velocity dispersion.
- a waveguide with large group velocity dispersion causes a large phase change even with a slight change in refractive index.
- the light output can be switched between the output end 19 and the output end 20 even with a refractive index change of the order of 0.1% of the waveguide 10 of the second path.
- the light exit can be switched with a refractive index change of about 1/10 compared to the related 1 ⁇ 2 optical switch.
- the operation of the 1 ⁇ 2 optical switch 5 can be facilitated without increasing the waveguide length of the 1 ⁇ 2 optical switch 5.
- the power of control signals such as electricity and light for changing the refractive index of the waveguide can be suppressed. That is, it can operate efficiently with respect to the power of the control signal. Therefore, it can be operated with low power and energy saving can be realized.
- the operation speed of the 1 ⁇ 2 optical switch 5 can be improved.
- the 1 ⁇ 2 optical switch 5 can be miniaturized. Further, since it can be incorporated into a photonic crystal optical integrated circuit, a highly integrated optical switch circuit can be realized. As described above, according to the present embodiment, it is possible to efficiently operate the optical switch by utilizing the novel feature of the photonic crystal waveguide.
- the group velocity dispersion is large only in the waveguide 10 of the second path, the light propagating through other waveguide portions is not significantly affected by the group velocity dispersion. Therefore, even when a high-speed optical signal passes through the optical switch of the present invention, the optical signal is hardly distorted. That is, the performance of the 1 ⁇ 2 optical switch 5 is unlikely to deteriorate.
- the photonic crystal body of this example can be manufactured using an SOI wafer (Silicon On Insulator Wafer) as a substrate.
- An SOI wafer having a buried oxide film thickness of 2.0 ⁇ m and a silicon active layer thickness of 1.0 ⁇ m is used.
- the silicon active layer is non-doped.
- the pattern shown in FIG. 1 is drawn using an electron beam exposure technique.
- the wavelength of guided light is set to 1.55 ⁇ m for optical communication
- the lattice constant is set to 0.4 ⁇ m
- the diameter of the non-linear defect pillar 6 is set to 0.24 ⁇ m.
- the diameter of the line defect pillar is 0.16 ⁇ m in the waveguide portion.
- the waveguide part here means a part other than the stub waveguide, that is, a part other than the waveguide 10 of the second path. That is, the diameter of the line defect pillars 9, 16, 17, 18, and 21 is 0.16 ⁇ m.
- the distance is gradually increased to 0.22 ⁇ m in a direction away from the connection point with the waveguide.
- the length of the waveguide stub is 15 ⁇ m.
- the silicon active layer is vertically processed according to the drawn resist pattern by anisotropic dry etching.
- an ultraviolet effect resin having a refractive index of 1.45 which is the same as that of the buried oxide film, is applied and cured with ultraviolet rays.
- the transmission spectrum in FIG. 2 is a calculation result when it is assumed that the silicon pillar is infinite in the thickness direction in the above structure for the sake of simplicity.
- a thick curve and a thin curve that vibrate greatly according to the wavelength represent the output intensity of light from the two output ends 19 and 20.
- Light is emitted alternately over a wide frequency range.
- the 1 ⁇ 2 optical switch 5 When heat or an electric field is applied to the 1 ⁇ 2 optical switch 5, these curves are simultaneously shifted to the long wavelength side or the short wavelength side due to a change in refractive index. Therefore, for light of a certain wavelength, the output ends 19 and 20 are interchanged due to a change in refractive index. Since there is oscillation of the output light intensity in the optical wavelength range, the 1 ⁇ 2 optical switch 5 can be used in a wide wavelength range. That is, the operating frequency of the 1 ⁇ 2 optical switch 5 is not limited.
- the broken line seen at the top in a wide wavelength range in FIG. 2 is the light intensity of the input light.
- 3 and 4 are calculation results of the electric field distribution of the optical switch when light is output to different output ports, respectively.
- this invention is not limited to the said embodiment.
- a cylinder other than the line defect pillar constituting the photonic crystal body can be displaced, or the cross-sectional area thereof can be increased or decreased.
- the non-line defect pillar 6 and the line defect pillars 9, 12, 16, 17, 18, 21, 22, and 23 are cylindrical, but the present invention is not limited thereto. These may have other shapes such as a quadrangular prism and an octagonal prism.
- FIG. 5 shows an optical switch equipped with a heater 80 as a temperature controller for causing a change in refractive index.
- a heater 80 as a temperature controller for causing a change in refractive index.
- the heater 80 is heated, the refractive index of the waveguide 10 in the second path is changed, and the transmission spectrum of the photonic crystal is shifted to the long wavelength side or the short wavelength side.
- the light transmittance changes and the 1 ⁇ 2 optical switch 5 operates.
- the tuner for changing the refractive index is an electric field strength controller or a current controller.
- Embodiment 2 an optical switch according to a second embodiment of the present invention will be described.
- the first embodiment provides a 1 ⁇ 2 optical switch that can efficiently switch the output end of light even if the waveguide of two paths between the branch and the directional coupler is short.
- This embodiment described below provides a particularly efficient structure when the refractive index of the path between the branch and the directional coupler is changed by the input of the control light.
- at least one of the waveguides of the two paths between the branch and the directional coupler includes a resonator, and the refractive index of the selected path is tuned with light resonated by the resonator. .
- FIG. 6 is a schematic diagram showing the configuration of the 1 ⁇ 2 optical switch 5 according to the present embodiment. Note that description of parts common to the first embodiment is omitted or simplified.
- the 1 ⁇ 2 optical switch 5 shown in FIG. 6 is included as a part in an arbitrary pillar-shaped square lattice photonic crystal.
- the 1 ⁇ 2 optical switch 5 includes a branch 7, a directional coupler 15, and two waveguides 90 and 91 between them.
- a Mach-Zehnder interferometer is formed.
- the branch 7 is arranged on the input side of the 1 ⁇ 2 optical switch 5, and the directional coupler 15 is arranged on the output side of the 1 ⁇ 2 optical switch 5.
- the branch 7 and the directional coupler 15 are connected by the waveguide 90 of the first path and the waveguide 91 of the second path.
- the cross-sectional area of the defect pillar forming the line defect of the waveguide of at least one path is smaller than the cross-sectional area of the defect pillar forming the line defect of the waveguide constituting the branch 7 and the directional coupler 15.
- the cross-sectional areas of the line defect pillars 101, 103, and 111 of the waveguide 90 of the first path are larger than the cross-sectional areas of the line defect pillars 16 and 21 of the waveguides that constitute the branch 7 and the directional coupler 15. small.
- the cross-sectional area of the line defect pillars 105, 107, 113 of the waveguide 91 of the second path is smaller than the cross-sectional area of the line defect pillars 17, 21 of the waveguide that forms the branch 7 and the directional coupler 15. .
- a waveguide line defect that is, a portion where line defect pillars are arranged may be simply referred to as a waveguide.
- the line defect of the waveguide indicated by reference numeral 100 in FIGS. 6 and 7 may be simply referred to as a waveguide in the specification.
- the waveguide having a path with a small cross-sectional area of the defect pillar has two tapered waveguides provided at both ends.
- a connection waveguide is provided between the two tapered waveguides and connected to the branch 7 and the directional coupler 15 via these tapered waveguides.
- the waveguide 90 of the first path includes two tapered waveguides 100 and 102 and a connection waveguide 110 provided between the two tapered waveguides 100 and 102.
- the waveguide 91 of the second path includes two tapered waveguides 104 and 106 and a connection waveguide 112 provided between the two tapered waveguides 104 and 106.
- the cross-sectional areas of the line defect pillars 101 and 103 of the photonic crystal waveguide forming the tapered waveguides 100 and 102 gradually increase as the distance from the connection waveguide 110 increases.
- the cross-sectional areas of the line defect pillars 105 and 107 of the photonic crystal waveguide forming the tapered waveguides 104 and 106 gradually increase as the distance from the connection waveguide 112 increases.
- the cross-sectional area of the line defect pillar of the tapered waveguide is smaller than the cross-sectional area of the line defect pillar of the branch 7 or the directional coupler 15 connected to one end, and the line defect pillar of the connection waveguide connected to the other end is disconnected. It is larger than the area.
- the 1 ⁇ 2 optical switch 5 is configured as described above.
- connection waveguides 110 and 112 can guide light having a frequency higher than the upper limit of the transmission band of the branch 7 and the directional coupler 15.
- the upper limit frequency of the transmission band of the branch 7 and the directional coupler 15 is f1
- the upper limit frequency of the transmission band of the connection waveguides 110 and 112 is f2.
- light having a frequency between f1 and f2 for example, a frequency of f3, causes resonance in the connection waveguides 110 and 112.
- connection waveguides 110 and 112 function as resonators.
- the 1 ⁇ 2 optical switch 5 according to the present embodiment can also be described as follows.
- a part or all of the waveguides of at least one of the two waveguides 90 and 91 between the branch 7 and the directional coupler 15 operate as a resonator. Further, this resonator resonates with respect to light having a frequency other than the waveguide band of the waveguide constituting the branch 7 and the directional coupler 15.
- the light causing this resonance has a frequency higher than the upper limit of the transmission band of the branch 7 and the directional coupler 15. For this reason, the light causing this resonance cannot pass through the waveguides that constitute the branch 7 and the directional coupler 15, and does not leak into the branch 7 and the directional coupler 15. A stable operation of the 1 ⁇ 2 optical switch 5 can be realized.
- connection waveguides 110 and 112 change to an extent that cannot be ignored.
- the connection waveguides 110 and 112 absorb even a small amount of light, a part of the energy of the high-intensity light accumulated in the connection waveguides 110 and 112 is absorbed and changed to heat.
- the refractive index changes due to the thermo-optic effect.
- the refractive indexes of the connection waveguides 110 and 112 can be modulated.
- connection waveguides 110 and 112 By combining the control light and the guided light, the refractive indexes of the connection waveguides 110 and 112 are selectively changed.
- the transmission characteristics of the connection waveguides 110 and 112 can be shifted to the short wavelength side or the long wavelength side.
- Light having a frequency f1 or less passes through the directional coupler 15 and can be switched by the 1 ⁇ 2 optical switch 5. That is, according to the present embodiment, an optical switch that can be controlled by light can be efficiently operated.
- the guided light of the connection waveguides 110 and 112 has a larger group velocity than the guided light of the branch 7 and the directional coupler 15. For this reason, as in the first embodiment, the effect of reducing the two-path waveguides 90 and 91 cannot be used. However, the refractive index of the connection waveguides 110 and 112 can be efficiently changed by the control light having the frequency f3. And the optical switch concerning this Embodiment can be operated as an optical switch in which optical control is possible.
- FIG. 7 is a schematic diagram showing the configuration of the 1 ⁇ 2 optical switch 5 including the control light input unit according to the present embodiment.
- the configuration other than the control light input unit is the same as the configuration of the 1 ⁇ 2 optical switch 5 shown in FIG. 6.
- the proximity waveguide 120 is provided in the vicinity of the connection waveguide 110.
- the proximity waveguide 122 is provided in the vicinity of the connection waveguide 112.
- the line defect pillars 121 and 123 of the adjacent waveguides 120 and 122 have a cross-sectional area equal to or less than the cross-sectional area of the line defect pillars 111 and 113 of the nearby connection waveguide 110 or the connection waveguide 112.
- the connection waveguide 110 and the proximity waveguide 120, and the connection waveguide 112 and the proximity waveguide 122 are optically coupled to each other.
- the adjacent waveguides 120 and 122 have, for example, an L-shape bent about 90 ° toward the connection waveguide 110 or the connection waveguide 112 in the vicinity. Thereby, the proximity waveguides 120 and 122 can be effectively brought close to the connection waveguide 110 or the connection waveguide 112.
- the proximity waveguides 120 and 122 serve as control light input portions and function as control waveguides.
- control waveguide is provided in the vicinity of the resonator.
- the control waveguide can guide light having a frequency within the band gap of the photonic crystal. Further, the control waveguide can guide light having the resonance frequency of each resonator of the two connection waveguides 110 and 112. Each resonator and the control waveguide are optically coupled.
- the Q (queue) value can be sufficiently increased by appropriately separating the control waveguides, that is, the adjacent waveguides 120 and 122 from the connection waveguides 110 and 112.
- the Q value is a value that is a measure of the strength with which the resonator confines light. That is, the intensity of the light accumulated in the connection waveguides 110 and 112 can be Q times that of the light having the frequency f3 guided through the adjacent waveguides 120 and 122. Since the Q value can be several thousand to several tens of thousands or more, if light having a low intensity frequency f3 is incident, high intensity optical energy is accumulated in the connection waveguides 110 and 112. As described above, the refractive index can be changed efficiently. Thereby, it can be operated as an optical switch capable of optical control.
- the intensity of light having a frequency f1 or less in the connection waveguides 110 and 112 is approximately the same as the intensity when passing through the branch 7 or the directional coupler 15.
- the intensity of leakage light having a frequency f1 or less from the connection waveguide 110 to the proximity waveguide 120 and from the connection waveguide 112 to the proximity waveguide 122 is the intensity of light transmitted through the connection waveguide 110 or the connection waveguide 112. It is only about 1 / Q of that and can be ignored.
- the cross-sectional area of the dielectric pillars that constitute the defect of the line defect may increase stepwise in a direction away from the connection waveguides 110 and 112. That is, in the tapered waveguides 100, 102, 104, 106, the cross-sectional areas of the line defect pillars 101, 103, 105, 107 may increase stepwise in a direction away from the connection waveguides 110, 112. Further, a part that gradually decreases and a part that increases stepwise may be included.
- the two paths 90 and 91 between the branch 7 and the directional coupler 15 may have the same length or different lengths. That is, the two-path waveguides 90 and 91 may be the same length to be a symmetric Mach-Zehnder interferometer, or the two-path waveguides 90 and 91 may be different to be an asymmetric Mach-Zehnder interferometer.
- the proximity waveguides 120 and 122 are placed close to both the connection waveguides 110 and 112. In this case, when the control light is input to only one of the two adjacent waveguides 120 and 122, the light output ends 19 and 20 are switched. Then, the operation of the logic circuit can be performed by the 1 ⁇ 2 optical switch 5 such that the light output terminals 19 and 20 are not switched when both the control lights are not input or are input together.
- the adjacent waveguides 120 and 122 are placed close to both the connecting waveguides 110 and 112 as described above. This makes it possible to cause the 1 ⁇ 2 optical switch 5 to operate the logic circuit different from the symmetric case. A combination of these is also possible.
- the photonic crystal is a square lattice pillar type photonic crystal, but may be a triangular lattice hole type photonic crystal.
- Two or more such 1 ⁇ 2 optical switches 5 are arranged, and the respective adjacent waveguides (control waveguides) 120 and 122 included in the individual 1 ⁇ 2 optical switches 5 are the same, Or they may be connected to each other.
- the present invention is applied to an optical switch and a manufacturing method thereof, and in particular, to an optical switch using a waveguide and a manufacturing method thereof.
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Abstract
Description
図9の光スイッチの構造と動作は次の通りである。
特許文献1の図2の番号に従うと、2次元フォトニック結晶スラブ(31)の中には、分岐導波路である導波路(20)がある。また、2次元フォトニック結晶スラブ(31)は、「干渉チャネル」(35)と「共振部材」(37)を含んでいる。
11 接続導波路、12 線欠陥ピラー、13 テーパー導波路、
14 テーパー導波路、15 方向性結合器16 線欠陥ピラー、17 線欠陥ピラー、
18 線欠陥ピラー、19 出力端、20 出力端、21 線欠陥ピラー、
22 線欠陥ピラー、23 線欠陥ピラー、80 ヒータ、
90 第1経路の導波路、91 第2経路の導波路、100 テーパー導波路、
101 線欠陥ピラー、102 テーパー導波路、103 線欠陥ピラー、
104 テーパー導波路、105 線欠陥ピラー、106 テーパー導波路、
107 線欠陥ピラー、110 接続導波路、111 線欠陥ピラー、
112 接続導波路、113 線欠陥ピラー、120 近接導波路、
121 線欠陥ピラー、122 近接導波路、123 線欠陥ピラー
本発明の実施の形態1にかかる光スイッチを、図面を用いて詳細に説明する。本実施の形態にかかる光スイッチは、例えば、m個の入力ポート(入力端)とn個の出力ポート(出力端)を有するマッハツェンダー型の干渉計を用いたm×n光スイッチである(mは1以上の整数、nは2以上の整数)。なお、マッハツェンダー型の干渉計とは、非対称マッハツェンダー型の干渉計及び対称マッハツェンダー型の干渉計を含むものとする。まず、図1を参照して、本実施の形態にかかる光スイッチの一例として非対称マッハツェンダー干渉計型の1×2光スイッチについて説明する。すなわち、1個の入力端と2個の出力端を有する1×2光スイッチについて説明する。図1は、本実施の形態にかかる1×2光スイッチ5の構成を示す模式図である。
本発明の1×2光スイッチ5の中で、第2経路の導波路10は群速度分散が大きい。群速度分散の大きな導波路は僅かな屈折率変化でも大きな位相変化を生じる。本実施の形態における導波路の場合、屈折率の変化率の数倍から10数倍以上の位相変化を生じる効果がある。その結果、第2経路の導波路10の0.1%のオーダーの屈折率変化でも、光の出力を出力端19と出力端20の間で切り替えることができる。
次に本発明の実施の形態2にかかる光スイッチについて説明する。
実施の形態1は、分岐と方向性結合器の間の2つの経路の導波路が短くても、効率的に光の出力端の切り替えができる1×2光スイッチを提供するものであった。これから説明する本実施の形態は、制御光の入力によって、分岐と方向性結合器の間の経路の屈折率を変化させる場合に、特に効率的な構造を提供する。本実施の形態では、分岐と方向性結合器の間の2つの経路の導波路の内の少なくとも1つが共振器を含み、選択した経路の屈折率のチューニングをその共振器で共振した光で行う。
Claims (15)
- フォトニック結晶の線欠陥導波路で構成されたマッハツェンダー干渉計型の光スイッチであって、
分岐と方向性結合器と、それらの間の2経路の導波路を有し、
上記2経路の内、第1経路の導波路と第2経路の導波路とでは、導波光の群速度が異なることを特徴とする光スイッチ。 - 前記第1経路の導波路と前記第2経路の導波路とでは、線欠陥を成す欠陥ピラーの断面積が前記第2経路の導波路のほうが大きいことを特徴とする請求項1に記載の光スイッチ。
- 前記第1経路の導波路長より、前記第2経路の導波路長のほうが長いことを特徴とする請求項2に記載の光スイッチ。
- 前記方向性結合器を構成する2つの導波路の線欠陥を成す欠陥ピラーの断面積は、両方の導波路で同じであることを特徴とする請求項2又は3に記載の光スイッチ。
- 前記第2経路の導波路は、
両端に1つずつ設けられた2つのテーパー導波路と、
2つの前記テーパー導波路の間に設けられ、前記テーパー導波路を介して前記分岐と前記方向性結合器とに接続された接続導波路とを有する請求項2乃至4のいずれか1項に記載の光スイッチ。 - 2つの前記テーパー導波路を成すフォトニック結晶導波路の欠陥ピラーの断面積は、前記接続導波路から離れるにつれて徐々に減少することを特徴とする請求項5に記載の光スイッチ。
- ピラー型フォトニック結晶の線欠陥導波路で構成されたマッハツェンダー干渉計型の光スイッチであって、
分岐と方向性結合器と、それらの間の2経路の導波路を有し、
上記2経路の内、少なくとも1経路の導波路の線欠陥を成す欠陥ピラーの断面積が、前記分岐及び前記方向性結合器を構成する導波路の線欠陥を成す欠陥ピラーの断面積よりも小さいことを特徴とする光スイッチ。 - 前記欠陥ピラーの断面積が小さい経路の導波路は、
両端に1つずつ設けられた2つのテーパー導波路と、
2つの前記テーパー導波路の間に設けられ、前記テーパー導波路を介して前記分岐と前記方向性結合器とに接続された接続導波路とを有する請求項7に記載の光スイッチ。 - 2つの前記テーパー導波路を成すフォトニック結晶導波路の欠陥ピラーの断面積は、前記接続導波路から離れるにつれて徐々に増加することを特徴とする請求項8に記載の光スイッチ。
- 前記接続導波路の線欠陥を成す欠陥ピラーの断面積以下の断面積をもつ欠陥ピラーを有する近接導波路を、前記接続導波路の近傍に備え、前記接続導波路と前記近接導波路は光学的に結合していることを特徴とする請求項8又は9に記載の光スイッチ。
- 請求項10に記載の光スイッチを2つ以上含み、それらの個々の光スイッチに含まれるそれぞれの前記近接導波路が同一であるか、または互いに接続されていることを特徴とする光スイッチ。
- フォトニック結晶の線欠陥導波路で構成されたマッハツェンダー干渉計型の光スイッチであって、
分岐と方向性結合器と、それらの間の2経路の導波路を有し、
上記2経路の少なくとも一方の経路の導波路の一部または全部が、前記方向性結合器を構成する導波路の導波帯域以外の周波数の光に対して共振する共振器として動作することを特徴とする光スイッチ。 - 前記フォトニック結晶のバンドギャップ内に周波数を有する光を導波可能であり、かつ前記共振器の共振周波数の光を導波可能な制御用導波路を、前記共振器の近傍に備え、前記共振器と前記制御用導波路は光学的に結合していることを特徴とする請求項12に記載の光スイッチ。
- 請求項13に記載の光スイッチを2つ以上含み、それらの個々の光スイッチに含まれるそれぞれの前記制御用導波路が同一であるか、または互いに接続されていることを特徴とする光スイッチ。
- フォトニック結晶の線欠陥導波路で構成されたマッハツェンダー干渉計型の光スイッチの製造方法であって、
分岐と方向性結合器と、それらの間の2経路の導波路を形成し、
上記2経路の内、第1経路の導波路と第2経路の導波路とでは、導波光の群速度が異なることを特徴とする光スイッチの製造方法。
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