JP2006267207A - Optical resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical circuit with which refractive index of the medium can greatly be changed. <P>SOLUTION: Optical resonation or optical wave guidance can be conducted in the optical circuit. The optical circuit is divided into a plurality of parts and a displacing means is provided to spatially displace a portion of the divided parts with respect to the remaining parts. The optical circuit is the optical resonator or an optical waveguide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical circuit, and relates to an optical circuit of an optical resonator or an optical waveguide.

Conventionally, in an optical resonator or optical waveguide optical circuit using a photonic crystal, in order to dynamically tune characteristics such as the resonance wavelength of the optical resonator and the dispersion characteristics of the optical waveguide, A technique for changing the refractive index is used (for example, see Non-Patent Document 1). In this case, the property that the resonance wavelength of the optical resonator and the transmission characteristic or dispersion characteristic of the optical waveguide greatly change depending on the refractive index value of the medium constituting the photonic crystal is used.
Examples of the method of changing the refractive index include an electro-optic effect in which the refractive index is changed by voltage such as Pockels effect, an effect in which the refractive index is changed by current injection such as carrier plasma effect, an effect in which the refractive index is changed by light irradiation such as Kerr effect, Various phenomena are used, such as a thermo-optic effect in which the refractive index changes depending on the temperature. A similar technique is used in the same way in ultra-compact optical circuits such as ring optical resonators that do not use photonic crystals.
T. T. et al. Baba et al. “Carrier plasma shift in GaInAsP photonic crystal point defect cavities” ELECTRON LETTERS 16th October 2003 Vol. 39 no. 21

  However, regardless of which phenomenon is used, there is a problem that the amount of change in refractive index is very small, and usually only a change in refractive index of about 1/1000 to 1/1000 can be realized. This limit limits the size of dynamic tuning of photonic crystal optical resonators and optical waveguides, and a tuning method that can further increase the amount of change has been desired. In addition, the optical circuit such as a ring optical resonator that does not use a photonic crystal has the same problem.

  The present invention has been made in view of the above points, and an object thereof is to provide an optical circuit capable of greatly changing the refractive index of a medium.

The invention according to claim 1 is an optical circuit that performs optical resonance or optical waveguide,
Dividing the optical circuit into a plurality of parts;
By having a displacement means for spatially displacing the divided part with respect to the remaining part, the refractive index of the medium can be greatly changed, and the resonance wavelength of the optical resonator and the transmission characteristics or dispersion characteristics of the optical waveguide can be changed. The characteristics can be greatly tuned dynamically.

  According to a second aspect of the present invention, since the optical circuit is an optical resonator, the resonance wavelength of the optical resonator can be tuned dynamically.

  According to a third aspect of the present invention, since the optical circuit is an optical waveguide, the characteristics of the optical waveguide can be tuned greatly and dynamically.

  According to a fourth aspect of the present invention, the optical circuit is configured as a two-dimensional photonic crystal.

The invention according to claim 5 divides the slab of the two-dimensional photonic crystal into a plurality of parts on a plane parallel to the slab surface,
The displacing means displaces the divided part in a direction perpendicular to the divided plane with respect to the remaining part.

The invention according to claim 6 divides the slab of the two-dimensional photonic crystal by a plane perpendicular to the slab surface and passing through the optical resonator,
The displacing means displaces the divided part in a direction perpendicular to the divided plane with respect to the remaining part.

The invention according to claim 7 divides the slab of the two-dimensional photonic crystal by a plane perpendicular to the slab surface and passing through the optical waveguide,
The displacing means displaces the divided part in a direction perpendicular to the divided plane with respect to the remaining part.

  According to an eighth aspect of the present invention, the optical circuit is a whispering gallery mode optical resonator.

  According to the present invention, the refractive index of the medium can be greatly changed without using the change in the refractive index of the substance, and the resonance wavelength of the optical resonator and the characteristics of the optical waveguide can be tuned dynamically.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In the present invention, an optical circuit such as a micro optical resonator represented by a photonic crystal optical resonator or a micro optical waveguide represented by a photonic crystal optical waveguide is divided into a plurality of parts so as not to impair the characteristics. Then, by dynamically displacing some of the divided parts, dynamic tuning of the characteristics of the optical circuit such as the resonance wavelength of the optical resonator and the effective refractive index of the optical waveguide is realized.

<First Embodiment>
FIG. 1 shows a plan view and a side view of a first embodiment of an optical circuit of the present invention. In the plan view of FIG. 1A, a triangular lattice air hole two-dimensional photonic crystal 10 includes air holes 14 (low refractive index) arranged in a triangular lattice shape on a silicon slab 12 that is a high refractive index material having an air bridge structure. Material). The photonic crystal 10 indicates a structure in which the refractive index is periodically modulated. By using this, an optical resonator having a very small size and strong confinement, that is, a high Q (Quality Factor) can be realized.

  The optical resonator 16 widens the air holes adjacent to both ends in the X-axis direction of the three-point defect (deletion of three air holes) extending in the X-axis direction so as to be separated from the three-point defect. In addition, the diameter is reduced.

  When the input light matching the resonance wavelength of the optical resonator 16 is applied to the optical resonator 16 portion shown in FIG. 1A from the direction perpendicular to the slab 12 (Z-axis direction), the input light is irradiated with the optical resonator 16. Accumulated within.

  As shown in the side views of FIGS. 1C and 1D, the photonic crystal 10 is cut along a plane (XY plane) orthogonal to the Z axis at the center position of the slab 12 on the Z axis, 10a and the second portion 10b are divided into two. The first portion 10a is fixed to the minute displacement device 20, and the second portion 10b is fixed to a base portion (not shown).

  The side view of FIG. 1B shows a state where the first portion 10a is in contact with the second portion 10b (distance L = 0). From this state, the minute displacement device 20 slightly displaces the first portion 10a upward in the Z-axis direction, and the first portion 10a is separated from the second portion 10b by a distance L = as shown in the side view of FIG. Further, the first portion 10a is separated from the second portion 10b by a distance L = 100 nm as shown in the side view of FIG. 1D. Further, the minute displacement device 20 is driven so as to slightly displace the first portion 10a in the reverse direction and bring it into contact with the second portion 10b.

  In the present embodiment, the lattice constant of the photonic crystal 10 is 400 nm, the diameter of the air hole 14 is 210 nm, and the slab thickness of each of the first portion 10a and the second portion 10b is 100 nm. Although the refractive index of the silicon slab is 3.46, the effective refractive index of the pair of the first portion 10a and the second portion 10b when L = 0 (total slab thickness is 200 nm) is approximately 2.8.

  Here, the effective refractive index will be described. In the slab optical waveguide, light propagation is limited only within the slab surface, and the refractive index that determines dispersion in the slab surface, that is, the degree of freedom in the propagation direction, is the effective refractive index. Specifically, when the wave number k in the propagation direction, the speed of light c in vacuum, and the angular frequency ω of light, ck / ω is the effective refractive index.

  The effective refractive index is the refractive index physically felt when the guided mode propagates in the slab plane, so if the slab thickness is reduced and the guided mode oozes into the low refractive index cladding, Therefore, the effective refractive index is reduced accordingly.

  Further, the resonance wavelength of the optical resonator formed in the slab surface can be obtained by pure two-dimensional calculation that does not include the degree of freedom in the direction perpendicular to the slab surface if an effective refractive index is given. That is, if only the slab thickness is changed in the optical resonator having the same structure, the resonance wavelength is changed by the change in the effective refractive index.

  Therefore, in FIG. 1, when the distance L is increased, the waveguide mode oozes out into the air between the first portion 10a and the second portion 10b, and the effective refractive index of the pair of the first portion 10a and the second portion 10b is Decrease from 2.8, so that the resonant wavelength of the optical resonator 16 changes.

  In FIG. 2, a change in the resonance wavelength of the optical resonator 16 when the distance L is changed is indicated by a solid line I. At the distance L = 210 nm, the resonance wavelength change of about 14% is realized with respect to the distance L = 0 nm. Such a large resonance wavelength change cannot be realized by the refractive index modulation of a substance due to optical nonlinearity that has been conventionally used.

  On the other hand, as the distance L is increased, the optical confinement characteristic of the optical resonator 16 may deteriorate and the Q value of the optical resonator 16 may decrease. As shown, even if the distance L is changed, the Q value of the optical resonator 16 is almost constant.

  Therefore, it can be seen that the resonance wavelength can be changed greatly without impairing the characteristics of the optical resonator 16. As the minute displacement device 20 that changes the distance L, a micromachine that is driven by applying a voltage is used. In addition, a specific medium is interposed between the first portion 10a and the second portion 10b, and a method of changing the distance L of the volume of the specific medium by temperature, pressure, voltage, or the like, or the first portion 10a and the second portion 10b There is a method in which the distance L is changed by applying pressure to one side by an air flow or the like.

  In FIG. 1, the first portion 10 a and the second portion 10 b are mirror-image symmetric with respect to the cut surface. However, the mirror-image symmetry is not a requirement, and the first portion 10 a and the second portion 10 b are asymmetric. However, the same effect can be obtained.

<Second Embodiment>
FIG. 3 shows a plan view and a side view of a second embodiment of the optical circuit of the present invention. In the figure, the same parts as those in FIG.

  3A, a triangular lattice air hole two-dimensional photonic crystal 10 includes air holes 14 (low refractive index) arranged in a triangular lattice shape on a silicon slab 12 that is a high refractive index material having an air bridge structure. Material). The photonic crystal 10 refers to a structure in which the refractive index is periodically modulated. By using this structure, an optical resonator having a very small size and strong confinement, that is, a high Q can be realized.

  The optical resonator 16 widens the air holes adjacent to both ends in the X-axis direction of the three-point defect (deletion of three air holes) extending in the X-axis direction so as to be separated from the three-point defect. In addition, the diameter is reduced.

  When the input light that matches the resonance wavelength of the optical resonator 16 is applied to the optical resonator 16 portion shown in FIG. 3A from the direction perpendicular to the slab 12 (Z-axis direction), the input light is the optical resonator 16. Accumulated within.

  As shown in the side view of FIG. 3B, the photonic crystal 10 is cut along a plane (YZ plane) orthogonal to the X axis at the position of the optical resonator 16 on the X axis, It is divided into four parts 10d. The third portion 10c is fixed to the minute displacement device 22, and the fourth portion 10d is fixed to a base portion (not shown). Note that the cut surface for cutting the third portion 10c and the fourth portion 10d may be a plane (XZ plane) orthogonal to the Y axis at the position of the optical resonator 16.

  The side view of FIG. 3B shows a state where the third portion 10c is in contact with the fourth portion 10d (distance L = 0). From this state, the minute displacement device 22 slightly displaces the third portion 10c to the right in the X-axis direction to separate the third portion 10c from the fourth portion 10d. Further, the minute displacement device 22 is driven so as to slightly displace the third portion 10c in the reverse direction and contact the fourth portion 10d.

  In this case, even if the distance L changes, the effective refractive index of the slab 12 does not change. However, when the distance L increases, the resonance mode of the optical resonator 16 is in the air portion between the third portion 10c and the fourth portion 10d. Since the amount to be emitted increases, the resonance wavelength shifts to the short wavelength side as in the first embodiment.

  In the first and second embodiments, the input light matching the resonance wavelength is irradiated from the direction perpendicular to the slab. However, an optical waveguide coupled to the resonator 16 is provided to resonate the input light from the optical waveguide. The configuration may be such that it is input to the device 16. Also, the description has been given using the slab 12 of the two-dimensional photonic crystal 10, but also for the optical resonator formed in the three-dimensional photonic crystal, this optical resonator is divided into two parts and one part is displaced. Allows resonance wavelength tuning. In the first and second embodiments, the optical resonator 16 is divided into two parts. However, it is obvious that the same effect can be obtained even if the optical resonator 16 is divided into three or more parts.

  In the first and second embodiments, the case where the slab of the silicon photonic crystal is used has been described. However, the same applies to the case where another material such as GaAs or another structure such as a three-dimensional photonic crystal is used. The effect is obtained.

<Third Embodiment>
FIG. 4 shows a plan view and a side view of a third embodiment of the optical circuit of the present invention. 4A, a triangular lattice air hole two-dimensional photonic crystal 30 includes air holes 34 (low refractive index) arranged in a triangular lattice pattern in a silicon slab 32 that is a high refractive index material having an air bridge structure. Material). The optical waveguide 36 is configured by removing the air holes 34 of the photonic crystal in the X-axis direction overlapping one side of the triangular lattice. Light having an arbitrary wavelength is input from the end to the optical waveguide 36 and guided.

  As shown in the side view of FIG. 4B, the photonic crystal 30 is cut along a plane (XY plane) orthogonal to the Z axis at the center position of the slab 32 on the Z axis, and the first portion 30a and the second portion 30 Divided into two parts 30b. The first portion 30a is fixed to the minute displacement device 40, and the second portion 30b is fixed to a base portion (not shown).

  The minute displacement device 40 slightly displaces the first portion 30a upward in the Z-axis direction to separate the first portion 30a from the second portion 30b. Further, the first portion 30a is slightly displaced in the reverse direction and driven so as to contact the second portion 30b.

  In the present embodiment, the lattice constant of the photonic crystal 30 is 400 nm, the diameter of the air hole 34 is 210 nm, and the slab thickness of each of the first portion 10a and the second portion 10b is 100 nm. To do. Although the refractive index of the silicon slab is 3.46, the effective refractive index of the pair of the first portion 10a and the second portion 10b when L = 0 (total slab thickness is 200 nm) is approximately 2.8.

  In FIG. 4, when the distance L is increased, the effective refractive index is decreased, and the guided mode oozes out into the air between the first portion 30a and the second portion 30b, so that the pair of the first portion 30a and the second portion 30b. The effective index of refraction decreases from 2.8. In general, the characteristics of a waveguide are expressed using propagation constants. If the propagation constant is determined, the characteristics of the waveguide are almost determined. This propagation constant is determined by the effective refractive index. Can be changed. Due to the change in the propagation constant, various characteristics such as the propagation speed of the optical signal, the pulse waveform, and the mode spread change.

<Fourth embodiment>
FIG. 5 shows a plan view and a side view of a fourth embodiment of the optical circuit of the present invention. In the figure, the same parts as those in FIG.

  5A, a triangular lattice air hole two-dimensional photonic crystal 30 includes air holes 34 (low refractive index) arranged in a triangular lattice shape in a silicon slab 32 that is a high refractive index material having an air bridge structure. Material). The optical waveguide 36 is configured by removing a single row of photonic crystal air holes 34 in the X-axis direction overlapping one side of the triangular lattice. Light having an arbitrary wavelength is input from the end to the optical waveguide 36 and guided.

  As shown in the side view of FIG. 5B, the photonic crystal 30 is cut along a plane (XZ plane) orthogonal to the Y axis at the position of the optical waveguide 36 on the Y axis, and the third portion 30c and the fourth portion It is divided into two parts 30d. The third portion 30c is fixed to the minute displacement device 42, and the fourth portion 30d is fixed to a base portion (not shown). Note that the cut surface for cutting the third portion 30c and the fourth portion 30d may be a plane (YZ plane) orthogonal to the X axis at the position of the optical waveguide 36.

  The minute displacement device 42 slightly displaces the third portion 30c upward in the Y-axis direction to separate the third portion 30c from the fourth portion 30d. Further, the third portion 30c is driven so as to be slightly displaced in the reverse direction and brought into contact with the fourth portion 30d.

  In the present embodiment, the lattice constant of the photonic crystal 30 is 400 nm, the diameter of the air hole 34 is 210 nm, and the slab thickness of each of the third portion 30c and the fourth portion 30d is 100 nm. Although the refractive index of the silicon slab is 3.46, the effective refractive index of the pair of the third portion 30c and the fourth portion 30d when L = 0 (total slab thickness is 200 nm) is approximately 2.8.

  In this case, even if the distance L changes, the effective refractive index of the slab 32 does not change, but when the distance L increases, the waveguide mode of the optical waveguide 36 blots into the air portion between the third portion 30c and the fourth portion 30d. Since the amount to be output increases, as in the second embodiment, the effective refractive index of the pair of the third portion 30c and the fourth portion 30d changes, and the change in the propagation constant of the optical waveguide 36 changes the propagation speed of the optical signal, for example. Various characteristics such as pulse waveform and mode spread change.

  In the first to fourth embodiments, the optical resonator and the optical waveguide using the photonic crystal have been described. However, the same effect can be expected for other optical resonators and optical waveguides. Similarly, for a whispering gallery mode optical resonator and a silicon fine wire optical waveguide that is an optical waveguide having a high refractive index difference, the element is similarly divided into a plurality of portions, and a part thereof is spatially displaced. As a result, the resonance wavelength of the optical resonator and the dispersion characteristics of the optical waveguide can be changed. The silicon fine wire optical waveguide is a waveguide constituted by, for example, silicon having a refractive index of 3.46 and silica having a refractive index of 1.44 (or air having a refractive index of 1).

  6A and 6B are a perspective view and a plan view of a disk-type whispering gallery mode optical resonator, respectively. In the figure, a disk-type optical resonator 50 is made of a high refractive index material, and is placed in the air of a low refractive material or placed in a clad of a low refractive material.

  7A and 7B are a perspective view and a plan view of a ring-type whispering gallery mode optical resonator, respectively. In the figure, the ring-type optical resonator 52 is made of a high refractive index material, and is placed in the air of a low refractive material or disposed in a clad of a low refractive material.

  In FIGS. 6 and 7, the optical resonators 50 and 52 are divided into two on a plane passing through the central axis of the optical resonators 50 and 52, or a plane orthogonal to the central axis, and the distance between the two divided parts is changed. Thus, the resonance wavelength of the optical resonators 50 and 52 is changed.

  The minute displacement devices 20, 22, 40, and 42 correspond to the displacement means described in the claims.

It is the top view and side view of 1st Embodiment of the optical circuit of this invention. It is a figure which shows the change of the resonant wavelength and Q of an optical resonator when the distance L is changed. It is the top view and side view of 2nd Embodiment of the optical circuit of this invention. It is the top view and side view of 3rd Embodiment of the optical circuit of this invention. It is the top view and side view of 4th Embodiment of the optical circuit of this invention. It is the perspective view and top view of a disk-type whispering gallery mode optical resonator. It is the perspective view and top view of a ring-type whispering gallery mode optical resonator.

Explanation of symbols

10, 30 Photonic crystal 12, 32 Slab 14, 34 Air hole 16, 50, 52 Optical resonator 36 Optical waveguide 20, 22, 40, 42 Micro displacement device

Claims (8)

An optical circuit that performs optical resonance or optical waveguide,
Dividing the optical circuit into a plurality of parts;
An optical circuit comprising displacement means for spatially displacing a divided part with respect to the remaining part.   The optical circuit according to claim 1, wherein the optical circuit is an optical resonator.   The optical circuit according to claim 1, wherein the optical circuit is an optical waveguide.   4. The optical circuit according to claim 2, wherein the optical circuit is formed of a two-dimensional photonic crystal. Dividing the slab of the two-dimensional photonic crystal into a plurality of parts by a plane parallel to the slab surface;
5. The optical circuit according to claim 4, wherein the displacing means displaces a divided part in a direction perpendicular to the divided plane with respect to the remaining part. Dividing the slab of the two-dimensional photonic crystal by a plane perpendicular to the slab surface and passing through the optical resonator;
5. The optical circuit according to claim 4, wherein the displacing means displaces a divided part in a direction perpendicular to the divided plane with respect to the remaining part. Dividing the slab of the two-dimensional photonic crystal by a plane perpendicular to the slab surface and passing through the optical waveguide;
5. The optical circuit according to claim 4, wherein the displacing means displaces a divided part in a direction perpendicular to the divided plane with respect to the remaining part.   2. The optical circuit according to claim 1, wherein the optical circuit is a whispering gallery mode optical resonator.

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