JP4890021B2 - OPTICAL ELEMENT AND OPTICAL MODULATOR HAVING OPTICAL ELEMENT - Google Patents

Description

  The present invention relates to a technical field of an optical element using a photonic crystal, and particularly relates to an optical element that imparts phase modulation to propagating light, an optical modulator having the optical element, and the like.

  In recent years, the increase in information processing speed accompanying the increase in the amount of content transmitted in optical communication has further increased the need for faster optical information processing technology. Accordingly, optical modulators and optical attenuators that respond quickly Various optical elements such as these are required.

  For example, Non-Patent Document 1 discloses a technique related to an optical modulator using a silicon Mach-Zehnder (MZ) type optical waveguide.

“High-Speed sillicon Mach-Zehnder modulator” L. Liao et al, Optics Express vol.13, No.8, pp.3129-3135 (2005)

  However, conventional devices made of silicon are large in size. For example, an optical modulator using the silicon Mach-Zehnder (MZ) type optical waveguide has an arm waveguide length of 3.450 mm or more. When it is very long and includes the vicinity of the branch of Mach-Zehnder, the waveguide length actually reaches 13.000 mm, which is unsuitable for miniaturization.

  In particular, with the advancement of technology of optical switches having a plurality of channels corresponding to wavelength multiplexing transmission, optical switches that switch optical signals as they are without being converted into electrical signals have been put into practical use. In such an optical switch, since the power obtained by amplification is different for each channel having different wavelengths, an optical attenuator for adjusting the light intensity so that the light intensity is equalized in all channels having different wavelengths However, since the size of the wafer must be observed for manufacturing reasons, the optical element array cannot be applied to an optical element array that can handle multiple channels.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a highly efficient and compact optical element, an optical modulator having the optical element, and the like.

In order to solve the above problem, the invention according to claim 1 is a transmission path that guides light incident from an incident end to an output end, and a photonic crystal portion that applies predetermined phase modulation to the light. An energy applying unit that applies energy to the photonic crystal unit so as to control the phase modulation by changing a refractive index of the photonic crystal unit, and the photonic crystal unit is disposed on the transmission path. Alternatively, the photonic crystal part is formed only in one of the transmission lines, and the photonic crystal part is sandwiched between the transmission line and a cladding layer made of SiO ₂ or SiON.

  According to this, it is possible to give phase modulation to the light propagating through the transmission line by changing the refractive index of the photonic crystal part only by giving a little energy such as current or voltage to the photonic crystal part. A possible highly efficient and small optical element can be provided.

  In order to solve the above-mentioned problem, the invention according to claim 2 is the optical element according to claim 1, wherein the transmission path is re-coupled with a branching part that branches the light in two directions, to the output end. And the photonic crystal part is formed on at least one of the transmission paths after branching or below the transmission path.

  According to this, since it was set as the structure which can respectively give independent phase modulation with respect to the light guide | induced by the one path after the branch of a transmission path by the photonic crystal part, or both paths, more efficient A highly compact optical element can be provided.

  In order to solve the above-mentioned problem, the invention according to claim 3 is the optical element according to claim 1 or 2, wherein the incident end of the transmission path has a cross-sectional area perpendicular to the light traveling direction. The cross-sectional area of the plane perpendicular to the light traveling direction continuously decreases in the light traveling direction. It is formed as follows.

  According to this, the change in the effective refractive index can be moderated, and light can be taken into the optical element more efficiently or can be emitted out of the optical element.

  In order to solve the above-mentioned problem, according to a fourth aspect of the present invention, in the optical element according to any one of the first to third aspects, at least a part of the photonic crystal portion is in a traveling direction of the light. The cross-sectional area of a plane perpendicular to the surface is formed so as to continuously increase or decrease in the light traveling direction.

  According to this, the change in the effective refractive index is reduced, and the light propagating through the transmission line is prevented from being reflected by the end face of the photonic crystal portion, and phase modulation is performed with respect to the light with low loss and high efficiency. Can be granted.

  In order to solve the above-mentioned problem, the invention according to claim 5 is the optical element according to any one of claims 1 to 4, wherein light is provided on both sides along the light traveling direction of the photonic crystal portion. It has a barrier region that suppresses the propagation of.

  According to this, it is possible to prevent light from diffusing in the direction perpendicular to the traveling direction of light and to propagate light efficiently and reliably.

  In order to solve the above-mentioned problem, according to a sixth aspect of the present invention, in the optical element according to any one of the first to fifth aspects, the photonic crystal portion includes a first material and a second material having different refractive indexes. The first substance is arranged in a plane in the second substance with a predetermined size and a predetermined arrangement interval, and the first substance is formed from the transmission line. It is characterized by comprising a material having a low refractive index.

  According to this, the photonic crystal part can be formed by arranging the first materials having different dielectric constants in the second material in a predetermined size and a predetermined arrangement interval in a plane shape, so that it is particularly complicated. An optical element can be realized at a relatively low cost without a structure.

  In order to solve the above-mentioned problem, according to a seventh aspect of the present invention, there is provided the optical element according to the sixth aspect, wherein an end portion of the photonic crystal portion has a higher refractive index than the transmission path. The end portion is formed such that a cross-sectional area of a plane perpendicular to the light traveling direction continuously increases or decreases in the light traveling direction.

  According to this, light entering the photonic crystal part is prevented from being reflected by the end face of the photonic crystal part, and light can be taken into the photonic crystal part with even lower loss and higher efficiency. it can.

  In order to solve the above-mentioned problem, the invention according to claim 8 is the optical element according to claim 6 or claim 7, wherein the second substance is made of a semiconductor having a predetermined carrier density in a steady state. The energy applying unit includes a voltage applying unit that applies a voltage to the photonic crystal unit in order to change a carrier density of the semiconductor.

  According to this, in order to change the refractive index of the waveguide, it is possible to freely control the phase modulation applied to the light by providing an energy applying unit for applying energy such as electricity, heat and pressure independently from the outside. can do.

  In order to solve the above-mentioned problem, the invention according to claim 9 is the optical element according to claim 8, wherein the photonic crystal portions are formed on both of the transmission lines after branching or below the transmission lines, respectively. The energy applying unit includes the voltage applying unit that applies a voltage independently for each photonic crystal unit.

  According to this, since energy can be individually applied to each photonic crystal part, the phase of light propagating through each branched transmission line corresponding to each photonic crystal part is made independent. Can be controlled.

  In order to solve the above-described problem, the invention according to claim 10 is the optical element according to any one of claims 2 to 9, wherein the transmission path, the energy applying unit, and the photonic crystal unit are And formed on an SOI (Silicon-On-Insulator) substrate, and the photonic crystal portion is formed at least under one of the transmission lines after branching.

  According to this, a highly efficient and small size capable of giving a large phase modulation to light propagating through a transmission line by slightly changing energy such as current or voltage applied to the photonic crystal part. An optical element can be provided.

  In order to solve the above-described problem, the invention according to claim 11 is the optical element according to any one of claims 2 to 9, wherein the transmission path, the energy applying unit, and the photonic crystal unit are The photonic crystal portion is formed on at least one of the transmission paths after branching, formed on a silicon substrate.

  According to this, a highly efficient and small size capable of giving a large phase modulation to light propagating through a transmission line by slightly changing energy such as current or voltage applied to the photonic crystal part. The optical element can be provided at a lower cost.

  In order to solve the above-described problem, an invention according to claim 12 is the optical modulator having the optical element according to any one of claims 2 to 11, wherein the photonic crystal is formed at the energy applying unit. Energy is applied to the unit, and predetermined light phase modulation is applied to the light guided by the transmission path to make the light modulated light according to the energy.

  According to this, a highly efficient and small-sized optical modulator can be manufactured relatively easily.

  In order to solve the above-mentioned problem, the invention according to claim 13 is the optical modulator according to claim 12, wherein the photonic crystal part is formed on both of the transmission lines after branching or on the transmission line. The voltage application unit that applies a voltage independently to each photonic crystal part applies voltages having inverted signs to each photonic crystal part.

  According to this, it is possible to suppress the spread of the spectrum and the phase shift associated with the phase modulation whose code is inverted, that is, the chirp phenomenon can be suppressed, and an optical modulator with higher modulation efficiency can be manufactured.

  In order to solve the above-mentioned problem, an invention according to claim 14 is an optical attenuator having the optical element according to any one of claims 2 to 11, wherein the light emitted from the optical element is changed. It has a detection part to detect, and a control part which controls energy which the energy grant part should give to the photonic crystal part based on the intensity of the detected light, It is characterized by the above-mentioned.

  According to this, a highly efficient and small optical attenuator can be manufactured relatively easily.

  In order to solve the above-mentioned problem, the invention described in claim 15 is a wireless-to-optical converter having the optical element according to any one of claims 2 to 11, wherein the energy applying unit includes an antenna. Based on the radio wave received through the device, energy is applied to the photonic crystal unit, and a predetermined phase modulation is applied to the light guided by the transmission path, and the light is modulated according to the energy. It is characterized by.

  According to this, a highly efficient and small-sized wireless-optical converter can be manufactured at low cost.

  In order to solve the above-mentioned problem, according to a sixteenth aspect of the present invention, in the radio-optical converter according to the fifteenth aspect, the photonic crystal portion is on both the transmission lines after branching or under the transmission lines. Each of the photonic crystal portions, each of which is formed, applies a voltage independently for each photonic crystal portion, and the voltage application unit applies voltages whose signs are inverted to each other based on radio waves received via the antenna. It applies to a part.

  According to this, a radio-optical converter with higher modulation efficiency can be produced.

  According to the present invention, it is possible to apply phase modulation to light propagating through a transmission line by changing a refractive index of a photonic crystal portion with a slight amount of energy such as current or voltage. In addition, a small optical element or the like can be provided.

  Hereinafter, the best embodiment of the present application will be described with reference to the drawings.

<1. Configuration and function of optical element>
The configuration and function of the optical element according to this embodiment will be described.

  FIG. 1 is a diagram schematically showing an optical element 1 according to the present embodiment. The optical element 1 according to the present embodiment is manufactured by forming a phase modulation section including a transmission path 11 and photonic crystal sections 12a and 12b on an SOI (Silicon-On-Insulator) substrate. Light that is incident from an optical fiber or the like (for example, having a frequency in the 1.55 μm band that is a communication wavelength band) is guided to a phase modulation unit that applies predetermined phase modulation to apply phase modulation. In the figure, the configuration other than the transmission line 11, the photonic crystal parts 12a and 12b, the electrodes 13a, 13b and 13c, and the barrier region 14, for example, a SiON (silicon oxynitride) layer covering the transmission line 11 is omitted. Illustrated. Hereinafter, the schematic configuration of the optical element according to the present embodiment will be described with reference to FIG. In the following description, the photonic crystal portions 12a and 12b are also collectively referred to as the photonic crystal portion 12.

  The transmission line 11 is a so-called Mach-Zehnder (MZ) type optical waveguide, and is made of, for example, silicon nitride (SiN) whose refractive index is adjusted to about 2.0. Further, at least a part of the transmission line 11 is laminated on the photonic crystal part 12 of the phase modulation part, confines the light incident on the optical element 1, passes through the photonic crystal part 12, and then goes to the emission end. Lead. Moreover, the Y branch part 11a and the coupling part 11b are provided, the incident light is branched in two directions by the Y branch part 11a, and the light propagating through each path is received by the photonic crystal parts 12a and 12b. Independent phase modulation is performed, and light from each path is combined and emitted again by the coupling unit 11b.

  In the embodiment of the present invention, the transmission path 11 constituted by one waveguide and the Y branching section 11a are branched into two paths, and independent phase modulation is applied to the light propagating through each path. However, the present invention is not limited to such a configuration. For example, incident light demultiplexed by a directional coupler or the like is separated by about 1 μm in the direction perpendicular to the light traveling direction. Propagating using two transmission lines that are adjacent to each other in parallel, performing independent phase modulation on the light propagating through each transmission line, and then coupling by a directional coupler etc. Also good.

  The size of the cross section perpendicular to the light propagation direction of the transmission line 11 is not particularly limited. For example, when the electric field of incident light is parallel to the upper surface of the substrate (TE polarized light), the width is about The thickness is preferably about 1000 nm and the thickness is about 400 nm. When the magnetic field of the incident light is parallel to the upper surface of the substrate (TM and TE polarized light) and the polarization dependence is weakened, the cross-sectional dimension can be changed as appropriate. preferable.

  Note that the branching angle θ1 of the Y branching unit 11a, the coupling angle θ2 of the coupling unit 11b, the length L of the phase modulation unit of the transmission path 11, and the interval W between the transmission paths after branching are not particularly limited. However, for example, the branching angle θ1 of the Y branching portion 11a and the coupling angle θ2 of the coupling portion 11b are about 4.8 degrees to 5.2 degrees, and preferably about 5 degrees. Moreover, the interval W between the transmission lines after branching is set to about 25 μm to 35 μm, and preferably about 30 μm.

  In particular, if the angle of the branching angle θ1 of the Y branching portion 11a is too large, the light propagating through the transmission path 11 will still go straight through the Y branching section 11a and later and escape the transmission path 11. In addition, if the branch angle θ1 of the Y branch portion 11a is too small, a considerable length is required for the path after branching in order to completely branch the light in two directions, thereby preventing miniaturization of the optical element itself. It becomes.

  The length L of the phase modulation section of the transmission line 11 is preferably as short as possible in order to make the optical element 1 itself as compact as possible. On the other hand, a desired length for the light propagating through the transmission line 11 is desired. The length is required so that the phase modulation can be reliably applied. The relationship between the length L of the phase modulation unit of the transmission line 11 and the phase modulation will be described in detail later.

The phase modulation unit includes the photonic crystal unit 12 and applies phase modulation to light propagating through each path after branching of the transmission path 11. The photonic crystal portion 12 has a plurality of holes formed in a planar shape in a base material formed of silicon (Si) or the like as a second material, and a refraction different from the refractive index (dielectric constant) of the base material. A dielectric cylinder is formed by filling silicon oxide (SiO ₂ ) or the like as a first substance having a refractive index (dielectric constant) lower than that of the transmission line 11 to form a dielectric cylinder. It is formed in a planar shape in the base material with a size and a predetermined arrangement interval. The planar shape means a planar shape or the like arranged in a two-dimensional direction in the photonic crystal portion, and the photonic crystal portion 12 is a curved surface or a shape in which a plane and a curved surface are combined in the manufacturing process. In such a case, an arrangement along the shape is also included. For example, as shown in the present embodiment, when the optical element 1 is manufactured using an SOI substrate, the optical element 1 can be configured with a simple manufacturing process if the SOI layer is used as a base material of the photonic crystal portion 12. can do.

  Further, the photonic crystal portion 12 is formed in a reverse taper shape in which the cross-sectional area of the surface perpendicular to the light traveling direction continuously and gradually increases in the light traveling direction on the light incident end side. The exit end side is formed to have a forward tapered shape in which the cross-sectional area gradually and gradually decreases in the light traveling direction. For example, the dielectric cylinders are arranged in a triangular lattice pattern on the base material, and at this time, the incident end side is one, two, three,... In a direction orthogonal to the propagation of light on the transmission path 11. Arranged so as to gradually increase one by one until the number, the emission end side gradually decreases from the predetermined number of 3, 2, 1, ... in the direction orthogonal to the propagation of light on the transmission line 11 Arrange to do. This is because the light propagating through the transmission line 11 is prevented from being reflected by the end face of the photonic crystal portion 12 and phase modulation can be applied with low loss and high efficiency.

  Further, the first dielectric cylinder on the incident end side and the emission end side of the photonic crystal portion 12 is formed so as to overlap the center line of the transmission path 11 in the phase modulation portion, and the base of the equilateral triangle constituting the triangular lattice Is preferably orthogonal to the light propagation direction. This is because phase modulation is more uniformly applied to the light propagating through the transmission path 11. The predetermined number is not particularly limited, but is preferably about 12, for example.

  A current or voltage is applied to the photonic crystal part 12a by the electrodes 13a and 13c (energy application) as the energy application part, whereby the base material (for example, silicon (Si)) constituting the photonic crystal part 12a is applied. By changing the refractive index, phase modulation is applied to the light propagating through the transmission line 11 in one of the phase modulation units after branching. Similarly, the base material (for example, silicon (Si)) which comprises the photonic crystal part 12b by applying an electric current or a voltage to the photonic crystal part 12b by the electrodes 13b and 13c (energy application) as an energy application part. And the phase modulation is applied to the light propagating through the transmission path 11 in the other phase modulation section after the branching. The electrode 13c may be connected to the ground, and a current or a voltage may be applied (energized) only to the electrode 13a and the electrode 13b.

Further, the optical element 1 is provided with a barrier region 14 by removing the SOI layer in a region other than the vicinity of the transmission path 11 by etching or the like. The barrier region 14 is configured by filling with a material having a refractive index smaller than that of the base material constituting the photonic crystal portion 12. Thereby, it is possible to prevent (suppress) the light propagating through the transmission path 11 from diffusing in the direction perpendicular to the light traveling direction via the SOI layer. As a material having a refractive index smaller than that of the base material constituting the photonic crystal part 12, for example, when the base material constituting the photonic crystal part 12 is silicon (Si), silicon oxide (SiO ₂ ). Alternatively, silicon oxynitride (SiON) may be used.

<2. Operation principle of phase modulation>
Here, an operation principle of phase modulation of the optical element of the present invention will be described.

FIG. 2 is a cross-sectional view of the optical element 1a according to the present embodiment. The optical element 1a includes a transmission line 11, a photonic crystal part 12, electrodes 13s and 13t, a Si (silicon) substrate 15, a SiO ₂ (silicon oxide) layer 16, an SOI layer 17, and a SiON (silicon oxynitride) layer 18. Configured. Here, in order to explain the operation principle of the phase modulation of light in an easy-to-understand manner, a description of supplementary members in the case where the optical element of the present invention is used as a phase modulation element, for example, the barrier layer 8 is omitted. The functions of the transmission line 11 and the photonic crystal unit 12 are the same as those described with reference to FIG. 1, and the electrodes 13s and 13t are also similar to the electrodes 13a and 13c (or 13b and 13c). A current or a voltage is applied (energy is applied) to the light propagating through the light.

The optical element 1a is manufactured using an SOI substrate. This SOI substrate has a structure in which a SiO ₂ layer 16 is laminated on a Si substrate 15 to which impurities are added in order to provide conductivity, and an SOI layer 17 which is a Si layer is further laminated thereon. A known SOI substrate can be used.

More specifically, the Si substrate 15 has a thickness of, for example, about 750 μm, and the SiO ₂ layer 16 also functions as a lower cladding layer for light propagating through the transmission line 11, so that the thickness is, for example, 1000 nm. It is preferable to have.

By processing such an SOI substrate, the SOI layer 17 is partially removed, and the above-described photonic crystal part 12 using silicon as a base material is formed on the SiO ₂ layer 16, and photonics are formed at both ends thereof. Electrodes 13 s and 13 t for applying energy to the crystal part 12 are provided.

  Then, when current or voltage is applied to the photonic crystal part 12 by the electrodes 13s and 13t, the refractive index of the base material of the photonic crystal part 12 changes, and the phase of the light propagating through the transmission line 11 is changed. Modulation is applied.

  FIG. 3 is a graph showing light propagation characteristics as a dispersion curve of frequency f (Hz) and wave number k.

  Normally, in the case of a uniform substance, the frequency f (Hz) of light propagating in the substance and the wave number k are in a proportional relationship (dotted line in the figure). On the other hand, in the case of a photonic crystal, the gradient between the frequency f of light propagating in the photonic crystal and the wave number k gradually decreases as it approaches the photonic gap by the photonic crystal portion 12, and the solid line in FIG. So that it deviates greatly from the straight line.

  Further, when a current or voltage is applied to the photonic crystal part 12 by the electrodes 13s and 13t to apply a bias Vbias and the refractive index of the base material of the photonic crystal part 12 is changed, the dispersion curve is shown by a solid line in the figure. It can be shifted to a dashed line curve. In the example shown in the figure, the bias Vbias is applied to increase the refractive index of the base material of the photonic crystal portion 12, and as a result, the light frequency f (Hz) is shifted to the low frequency side. However, in this way, the wave number k can be freely shifted according to the energy such as current or voltage applied to the photonic crystal portion 12.

  Even if the dispersion curve is changed slightly, the shift amount Δk of the wave number k becomes large. In particular, when the frequency f (Hz) of incident light is in a frequency region where the slope of the dispersion curve is small, the shift amount Δk of the wave number k is larger than in the frequency region where the slope of the dispersion curve is large. The phase shift (phase modulation amount) Δφ of light can be expressed by the following equation (1) using the wave number shift amount Δk and the length L of the phase modulation unit.

  Accordingly, when the frequency f (Hz) of the incident light is in a frequency region where the gradient of the dispersion curve is small, the light phase shift (phase modulation amount) Δφ becomes larger.

  As described above, according to the optical element 1 a according to the present embodiment, a large phase with respect to the light propagating through the transmission line 11 can be obtained by slightly changing the energy such as current or voltage applied to the photonic crystal unit 12. Modulation can be given.

  The same effect can be obtained when the optical element of the present invention is configured as an optical element 1 including a Mach-Zehnder (MZ) type optical waveguide as shown in FIG. That is, by applying a current or voltage to each photonic crystal part 12a and 12b by the electrodes 13a, 13b and 13c, respectively, and applying a bias, independent phase modulation is applied to the light propagating through each path. can do.

  In addition, the optical element 1 of the present invention can be used not only as a highly efficient optical phase modulator, but also by converting a phase change of light into an intensity change so that an optical modulator (light intensity modulator), variable light It can also be used as an attenuator or a radio-optical converter.

  Next, the principle of light intensity change due to light phase change will be described.

As shown in FIG. 1, the light incident on the optical element 1 propagates through the transmission path 11 and is branched into two paths by the Y branching section 11a. And in a phase modulation part, phase modulation is provided by each photonic crystal part 12a and 12b. When the phase shift amounts are Δφ ₁ and Δφ ₂ , the modulated light, that is, the light E _out emitted from the optical element 1 is expressed by Expression (2).

In Equation (2), | E _arm | is the electric field intensity of light propagating through each path, and the branching ratio and coupling ratio at the Y branching portion 11a and the coupling portion 11b are 50:50.

From the above equation (2), the power P _out of the light emitted from the optical element 1 is expressed by equation (3), where P _arm is the power of the light propagating through each path.

When continuous light is incident on the optical element 1, the intensity of light emitted from the optical element 1 changes (modulates) in accordance with the difference in the phase shift amount Δφ generated in the photonic crystal portions 12a and 12b. The intensity of light emitted from the optical element 1 is minimum (zero) when the phase shift difference Δφ ₁ −Δφ ₂ is an odd multiple of π, and is maximum when the difference is an even multiple of π (including zero). Become.

  Therefore, when the optical element 1 is used as an optical modulator, the optical element can be changed by changing the difference in the phase shift amount Δφ generated in the photonic crystal portions 12a and 12b from an even multiple of π to an odd multiple of π. The power of light emitted from 1 can be changed from on to off, and light can be emitted as a modulation signal.

  Further, when the optical element 1 is used as a variable optical attenuator, the difference in the phase shift amount Δφ generated in each of the photonic crystal portions 12a and 12b is controlled according to the power fluctuation of the propagating light, and a constant power Feedback control or the like is performed so as to maintain the above. At this time, the current or voltage applied to each of the photonic crystal parts 12a and 12b is changed so that the difference of the phase shift amount Δφ changes minutely in the vicinity of an appropriate value between an even multiple of π and an odd multiple of π. Control energy.

  When the optical element 1 is used as a wireless-to-optical converter, radio waves received by the antenna are input to the electrodes 13a and 13b, and voltage fluctuations due to the radio waves cause the photonic crystal portions 12a and 12b to The difference in the amount of phase shift Δφ that occurs is varied, and the light intensity is modulated in accordance with the electric field vibration of the radio wave. At this time, if the modulation voltages whose phases are reversed are applied to the electrodes 13a and 13b, the voltage difference can be doubled and the modulation efficiency can be increased.

  A specific configuration when the optical element 1 is used as an optical modulator, a variable optical attenuator, or a radio-optical converter will be described in detail later with reference to the drawings.

<3. Refractive index change mechanism>
Here, a change in the refractive index of the base material of the photonic crystal portion 12 due to voltage application will be described with reference to FIG. Note that the detailed mechanism of the change in refractive index due to voltage application has not yet been determined. Therefore, here, several actions that occur in the photonic crystal portion 12 due to the voltage application that are now clear will be described.

A source power source (source voltage Vs) is connected to the electrode 13c. Since this can be replaced by direct connection to the ground terminal, hereinafter, the source voltage Vs is set to 0V. A drain power supply (drain voltage Vd) is connected to the electrode 13b. Further, a back gate electrode (gate voltage V _BG ) is ohmically connected to the back side of the substrate (not shown).

  Further, impurities are added to the SOI layer and carriers are distributed. Examples of such impurities include p-type elements B (boron), Al (aluminum), Ga (gallium), In (indium), Tl (thallium), and n-type elements N (nitrogen), which are also used in semiconductors. ), P (phosphorus), As (arsenic), Sb (antimony), Bi (bismuth), and the like. Of these, p-type elements can be easily doped, so B (boron) is particularly suitable. Therefore, here, boron (B), which is a p-type impurity, is added and holes ( Hole) is distributed.

  In addition, when an n-type impurity such as phosphorus (P) is added, electrons are distributed as carriers. Even when electrons are distributed, the action generated by voltage application described below is a change in refractive index due to free carrier absorption. Except for qualitatively.

  Further, the impurities may be added uniformly in the plane, or p-type impurities and n-type impurities may be added so as to provide a pn junction at the bottom of the transmission line.

Action 1 caused by voltage application
(1) By increasing the drain voltage Vd of the electrode 13b, when the carrier velocity of the SOI layer exceeds the saturation velocity, a dipole layer (dipole layer) in which the density of space charge is locally increased or decreased near the region where the electric field is concentrated. A bipolar region called layer) occurs. FIG. 4 shows the distribution of the dipole layer in the photonic band structure. The drain voltage Vd is 35V. This figure is a distribution diagram when the photonic crystal portion 12 is observed from the upper surface, and a dielectric cylinder made of silicon oxide (SiO ₂ ) is triangular in silicon (Si) which is a base material of the photonic crystal portion 12. This is an example in which 10 lattices are arranged between electrodes (interval 50 mm) with a lattice-like distribution and a triangular lattice as a unit lattice.

  As for the distribution of space charge, the red region has a higher density, and the blue region has a reversed sign. That is, in the red region, the carrier density is excessive as compared with the concentration of impurity ions present in the background, and in the blue region, the carrier density is deficient. The green region indicates that the space charge density is almost zero, that is, the density of carriers and impurity ions is almost balanced.

  In such a dipole layer, the electric field is locally strengthened, and as a result, the energy band gap of the electron system has a spatial gradient. As a result, due to the Franz-Keldysh effect, the band gap is shifted by low energy, and the refractive index increases due to the Kramers-Kronig relationship. This is qualitatively consistent with the experimental results of increasing the refractive index with voltage application.

  (2) If a dipole layer is present, the carrier density locally increases or decreases. As the carrier density increases, the band gap shifts to a lower energy due to the many-body correlation effect based on electrostatic interactions. In this case as well, the refractive index increases due to the Kramers-Kronig relationship. The effect of low energy shift is stronger when the carrier density is higher and weaker when the carrier density is low. Therefore, the refractive index of the entire photonic crystal portion 12 is increased.

  (3) Furthermore, as the carrier density increases, free carrier absorption increases and, as a result, the refractive index decreases. When holes are carriers, the refractive index change due to the density increase / decrease is not linear (depends on the 0.8th power of the density), so the average refractive index change is not zero even if averaged over the entire phase modulation section. Since the influence of the low density region is relatively strong, the refractive index increases due to the presence of the dipole layer. However, on average overall, the change is not likely to be significant.

Action 2 caused by voltage application
When a voltage is applied between the electrodes, a current flows and heat is generated. When the temperature of silicon that is the base material of the photonic crystal part 12 rises due to heat generation, the energy band gap of the electronic system shifts to a low energy, and the refractive index increases due to the Kramers-Kronig relationship. According to the simulation, it is known that the refractive index changes on the order of a thousandth with a temperature increase of several tens of degrees. In particular, in the case of a device with a low operating speed, a change in the refractive index due to a temperature rise of silicon cannot be ignored.

  As described above, voltage application to the photonic crystal portion 12 acts on the photonic crystal portion 12 as described above, and as a result, the refractive index of the base material of the photonic crystal portion 12 changes. This change in refractive index appears as a wave number k shift in the photonic crystal portion.

<4. Length of phase modulation section of transmission line 11>
Next, the length L of the transmission line 11 in the phase modulation unit will be described. Here, the length L determined when the optical element 1 is used as an optical modulator will be described. In addition, the length L of each path | route in a phase modulation part shall be the same.

  When the optical element 1 is used as an optical modulator, the length at which the difference between the phase shift amounts Δφ of the paths becomes π is obtained as the length L of the phase modulation unit of the transmission path 11.

  When the applied voltage to the photonic crystal parts 12a and 12b is 0V, the effective refractive index is 3.480, which is equal to silicon (Si) that is the base material of the photonic crystal part 12, and in each path. There is no phase difference, and the power of light emitted from the optical element 1 is maximized.

An arbitrary voltage is applied to the photonic crystal parts 12a and 12b, and the power of the light emitted from the optical element 1 is monitored to determine the length L at which the power of the 1st-mode light is zero. For example, when the applied voltage is increased and the refractive index of the base material of the photonic crystal portion 12 is changed, the length L at which the power of the 1st-mode light becomes 0 is estimated as follows.
(1) When the refractive index of the base material of the photonic crystal portion 12 is 3.481, L is 1.200 μm,
(2) When the refractive index of the base material of the photonic crystal portion 12 is 3.485, L is 220 μm,
(3) When the refractive index of the base material of the photonic crystal portion 12 is 3.490, L is 120 μm.

  By varying the applied voltage to obtain the length L at which the power of the 1st-mode light becomes 0, the length L of the phase modulation section of the transmission line 11 corresponding to the various applied voltages, in other words, various The length L of the phase modulation part of the transmission line 11 corresponding to the refractive index of the base material of the photonic crystal part 12 can be obtained.

  In the case of the structure of the optical element according to the present invention, since the photonic crystal is used, the refractive index change with respect to the applied voltage is large, and the refractive index can be increased to about 3.490 or more with an applied voltage of about 5V. It is.

  Thereby, a compact optical element having a low voltage, that is, low power consumption can be produced. If the distance between the electrode 13a and the electrode 13c and the distance between the electrode 13b and the electrode 13c are reduced or the contact resistance is reduced for each electrode, higher efficiency can be realized.

  According to the embodiment described above, the optical element 1 is split in two directions from the light incident from the incident end, and then coupled again and led to the output end, and the transmission path 11 is connected to the photonic crystal unit. 12 is configured such that a predetermined phase modulation is independently applied to the light that is stacked on the light 12 and guided by the path after the branch of the transmission path 11 by the photonic crystal unit 12. The optical element can be provided.

  The transmission line 11 has a Y branch portion 11a and a coupling portion 11b, and is formed so that propagating light is branched in two directions and then coupled again and guided to the emission end. Further, the photonic crystal portion 12 is formed. Are formed under the path after each branch, phase control can be performed independently for the light propagating through each path, and an optical element with higher control operability can be provided. In addition, it is possible to remove the influence of power supply noise on phase modulation by using a phase drift due to temperature fluctuation or a common power supply. Furthermore, when optical modulation or radio-optical conversion is performed using the optical element, the voltage difference can be doubled by applying modulation voltages whose phases are inverted to each other to the electrodes 13a and 13b. The efficiency can be increased and the chirp phenomenon accompanying phase modulation can be suppressed.

  In the above-described embodiment, the photonic crystal portions 12 are formed under both paths after the branching of the transmission path 11. However, the present invention is not limited to this form, and is under one path. Only the photonic crystal part 12 may be formed, and the phase control may be performed only on the light propagating through one path.

  Further, below the transmission path 11, in other words, the top surface of the SOI substrate is processed and the photonic crystal portion 12 is arranged. However, the present invention is not limited to this configuration, and the photonic crystal portion 12 is transmitted. It is sufficient if phase modulation can be applied to the light propagating through the transmission path 11 by being arranged in the vicinity of the path 11. For example, the photonic crystal part 12 may be laminated on the transmission path 11. Several modified embodiments will be described in detail later with reference to the drawings.

  In the above description, the size of the transmission line 11, the branching angle θ1 of the Y branching unit 11a, the coupling angle θ2 of the coupling unit 11b, the interval W between the paths after the branching of the transmission line 11, the phase modulation unit of the transmission line 11 Although the design example such as the length L, the number of dielectric cylinders of the photonic crystal portion 12 is shown, the optical element in the present invention is not limited to the design example in terms of the size of each of these constituent members, The optimum size can be set according to the beam diameter of incident light and the refractive index of the material used for each constituent member (more specifically, the ratio of the refractive index of the material used for each constituent member). it can.

  Further, the optical element 1 of the present invention may be provided with other layers in addition to the above-described layers.

<5. Variation of Optical Element>
Subsequently, another modification of the optical element 1 will be described.

5-1-1. Other Forms of Optical Element Using SOI Substrate FIG. 5 is an explanatory diagram of the optical element 1b. In the embodiment described above with reference to FIG. 1 and the like, the electrode 13c for applying a current or voltage to each photonic crystal portion 12 is common to each photonic crystal portion 12, but the optical element in this embodiment In 1b, instead of the electrode 13c in FIG. 1, the photonic crystal parts 12a and 12b are provided with independent electrodes 13d and 13e, respectively. Other configurations are the same as those in FIG.

  The refractive index of the base material of the photonic crystal portion 12a is changed by the current or voltage applied between the electrode 13a and the electrode 13d, and the photonic crystal is changed by the current or voltage applied between the electrode 13b and the electrode 13e. The refractive index of the base material of the part 12b can be changed. Note that the electrode 13d and the electrode 13e may be grounded, and a current or voltage may be applied to the electrode 13a and the electrode 13b.

  According to this, since the voltage applied to each photonic crystal part 12 can be made completely independent, the operation can be further stabilized.

5-1-2. Other Forms of Optical Element Using SOI Substrate FIG. 6A is an explanatory diagram of the optical element 1c. FIG. 6B is an enlarged view of a main part on the emission end side of the photonic crystal part 12a in FIG.

  7 is a side view of the optical element 1c from the light incident end side, FIG. 8 is a cross-sectional view of the EE plane in FIG. 6A, and FIG. 9 is a cross-sectional view of the FF plane in FIG. showed that. The optical element 1c in the present embodiment is formed such that the incident end side and the emission end side of the transmission line 11 have a reverse taper shape and a forward taper shape, respectively, and the incident end and the emission end of the photonic crystal portion 12 are formed of a base material. A tapered shape of only certain silicon (Si) was further formed.

  As shown in FIG. 6A and FIG. 7, in the transmission line 11, the cross-sectional area of the surface perpendicular to the light traveling direction on the light incident end side is continuously moderate in the light traveling direction. It has a SiN taper portion 11c formed in a reverse taper shape that gradually increases, and on the emission end side, it is formed in a forward taper shape in which the cross-sectional area gradually and gradually decreases in the light traveling direction. The SiN taper portion 11d is provided.

  The SiN taper portions 11 c and 11 d are stacked on the SiON layer 18. By the SiN taper portions 11c and 11d, the change in the effective refractive index with respect to incident light can be moderated, and light can be taken in and emitted from the optical element 1c with much lower loss and higher efficiency.

  Then, as shown in FIGS. 6B and 8, a tapered shape (Si taper) is formed only at the base material portion at the ends (incident end and outgoing end) of the photonic crystal portion 12. FIG. 6B shows an enlarged view of the main part of the exit end of the photonic crystal part 12a as an example, but the entrance end of the photonic crystal part 12a and the entrance end and exit end of the photonic crystal part 12b are also the same. A taper shape (Si taper) is formed only by the base material portion. Therefore, it is possible to moderate the change in the effective refractive index, guide light to the photonic crystal part 12 with higher loss and higher efficiency, and derive the light from the photonic crystal part 12.

Further, as shown in FIGS. 6A and 9, barrier regions 14a are provided on both sides of the photonic crystal portion 12 to confine light. The barrier region 14a is formed with a plurality of holes in a silicon (Si) base material, like the photonic crystal portion 12, and silicon oxide (SiO ₂ ) having a refractive index different from the refractive index of the base material is formed in the holes. It is made by filling to form a dielectric cylinder.

  Here, the barrier region 14a of the optical element 1c in the present embodiment will be specifically described.

  First, the case where the photonic crystal part 12 corresponds to a photonic band region that becomes a leg branch in the light propagation region will be described.

Assuming that the radius of the hole in the photonic crystal portion 12 is r _R1 , the radius of the hole in the barrier region 14 a is r _R2 , and the center interval between adjacent holes at the boundary between the barrier region 14 a and the photonic crystal portion 12 is dx. In order to make the region 14 a a photonic band gap region, the relationship between the radius r _R1 of the hole in the photonic crystal portion 12 and the radius r _R2 of the hole in the barrier region 14 a is set to r _R1 <r _R2. .

  At this time, the center distance dx between adjacent holes at the boundary between the barrier region 14a and the photonic crystal portion 12 is configured so as to satisfy the condition represented by Expression (4). The lower limit of the hole center interval dx is set so that adjacent holes do not overlap at the boundary between the barrier region 14a and the photonic crystal part 12, and the upper limit is set at the boundary. This is to prevent light from being trapped. Holes in each region are formed so as to satisfy the conditions.

Further, even if the gaps between the photonic crystal part 12 and the barrier region 14a are equal (a _R1 and a _R2 respectively) (that is, a _R1 = a _R2 ), the radius of the hole in the photonic crystal part 12 is r _R1 , When the radius of the hole in the barrier region 14a is r _R2 , the barrier region 14a can be a photonic gap by configuring the relationship so that r _R1 > r _R2 . In this case, since the interval (pitch) of the holes does not change (is uniform) in each region, the distance between the centers of adjacent holes at the boundary between the barrier region 14a and the photonic crystal portion 12 (hereinafter referred to as the center interval). ) It is not necessary to set dx conditions.

On the other hand, the case where the photonic crystal part 12 corresponds to a photonic band region that becomes an upper limb branch in the light propagation region will be described. In order to make the barrier region 14a a photonic band gap region, the correlation between the hole intervals (pitch) in each region is a _R1 > a _R2 or the correlation between the hole radii in each region is Each r _R1 <r _R2 is configured. At this time, the center distance dx between the holes adjacent to each other at the boundary between the barrier region 14a and the photonic crystal portion 12 is configured to satisfy the condition expressed by the equation (4) as in the case described above.

Further, even if the distance between the holes in the photonic crystal portion 12 and the barrier region 14a is equal (that is, a _R1 = a _R2 ), the radius of the hole in the photonic crystal portion 12 is r _R1 and the radius of the hole in the barrier region 14a is. By configuring so that the correlation of r _R2 is r _R1 <r _R2 , the barrier region 14a can be a photonic gap.

  In FIG. 6B, the number of holes (dielectric cylinders) formed in the photonic crystal part 12 and the barrier region 14a is omitted, but for example, the photonic crystal part is formed on the incident end side. 12 is formed in the barrier region 14a when the predetermined number of holes is gradually increased by one to a predetermined number in the direction orthogonal to the propagation of light in the transmission path 11, one by one. The number of holes to be formed is preferably about 5 to 6, for example.

Further, the barrier region 14 a may be formed of a material having a refractive index smaller than the refractive index of the base material of the photonic crystal portion 12, similarly to the barrier region 14. For example, when the base material of the photonic crystal portion 12 is silicon, it may be formed using SiO ₂ or SiON having a refractive index smaller than that of the silicon.

5-1-3. Other Forms of Optical Element Using SOI Substrate FIG. 10 is an explanatory diagram of the optical element 1d.

  The optical element in the embodiment described with reference to FIG. 1 and FIG. 6 performs independent phase modulation on the light propagating through each path after branching of the transmission path 11 by the photonic crystal portions 12a and 12b. Although the optical element 1d in the present embodiment is configured to be provided, the photonic crystal portion 12b is disposed only for the light propagating through one of the paths after the branching of the transmission path 11 as shown in FIG. A current or voltage is applied by the electrodes 13b and 13c at both ends, and phase modulation is applied only to light propagating through the one path.

  Thus, by controlling the phase of only the light propagating through one path after the branching of the transmission path 11, the difference from the phase of the light propagating through the other path can be changed. Similarly, an optical element with high efficiency can be provided.

5-2. Other Forms of Optical Element Using Si Substrate FIG. 11 is an explanatory diagram of an optical element 1e using a Si substrate.

  In the above-described embodiment, the SOI layer is processed using the SOI substrate, and the photonic crystal portion 12 is disposed on the SOI substrate to produce the optical element 1. Here, the optical element 1 is made of silicon. A case of manufacturing using a (Si) substrate will be described.

The optical element 1e includes a transmission line 11, a photonic crystal part 12, electrodes 13a, 13b and 13c, a Si (silicon) substrate 15, a SiO ₂ (silicon oxide) layer 16, and a SiON (silicon oxynitride) layer 19. Is done. In the figure, a silicon oxynitride (SiON) layer covering the transmission line 11 and the photonic crystal portion 12 is omitted. The photonic crystal part 12 is different from the above-described embodiment in that it is stacked on the transmission line 11. Note that the function and operation of each member are the same as in the above-described embodiment.

A SiO ₂ layer 16 is vapor-deposited on the Si substrate 15, and a SiON layer 19 is further laminated. Then, the transmission line 11 is formed of SiN (silicon nitride). Then, the photonic crystal portion 12 is laminated on the transmission line 11. Note that the Si layer that is the base material of the photonic crystal portion 12 may be formed by a substrate pasting technique or a chemical vapor deposition method. May be.

  Further, as in the optical element 1f shown in FIG. 12, the photonic crystal portion 12b is arranged only for light propagating through one of the paths after branching of the transmission path 11, and the electrodes 13b and 13c at both ends are used. A configuration may be adopted in which phase modulation is applied only to light propagating through the one path by applying a current or voltage.

As described above, the optical element 1e can be manufactured by laminating the SiO ₂ layer 16 and the SiON layer 19 on the conventionally known Si substrate 15 without using the SOI substrate.

<6. Application example of optical element to each device>
6-1. Application Example to Optical Modulator Next, an example in which an optical element is used as an optical modulator will be described.

  FIG. 13 is a schematic explanatory diagram when the optical element of the present invention is used as an optical modulator. FIG. 13A shows an example in which the photonic crystal portion 12 is provided only on one of the paths after branching the transmission path 11, and FIG. 13B shows the photonic crystal section 12 in the transmission path 11. It is an example in the case of being provided on both paths after branching.

  Continuous light from a semiconductor laser or the like is incident on an optical modulator, and based on the phase shift amount Δφ of light propagating through each path after branching of the transmission path 11, the emitted light (modulated light) is a bit string of an electrical signal for modulation. The bit string waveform is the same as the waveform. That is, if the difference in the phase shift amount Δφ generated in each of the photonic crystal portions 12a and 12b is changed from an even multiple of π to an odd multiple of π, the power of the light emitted from the optical element 1 is switched from on to off. Thus, light can be emitted as a modulation signal.

  As shown in FIG. 13A, when the photonic crystal portion 12 is provided only on one of the paths after the branching of the transmission path 11, the base voltage for phase modulation is set on the electrode 13b. A DC power supply and a high-frequency modulation electrical signal are connected via a bias tee, and the electrode 13c is grounded.

  As shown in FIG. 13B, when the photonic crystal part 12 is provided on both paths after the branching of the transmission line 11, a direct current for setting a phase modulation base voltage to the electrode 13a and the electrode 13b. A power source and a high-frequency modulation electrical signal are connected via a bias tee, and the electrode 13c is grounded.

  If the voltages V2 and V1 of the DC power supply connected to the electrode 13a and the electrode 13b are shared, and a single power supply is connected to the electrode 13a and the electrode 13b, noise due to fluctuations in the power supply voltage is canceled, so Low light modulation is possible.

  On the other hand, if the modulation electrical signals input to the electrodes 13a and 13b are phase-inverted (sign-inverted) with each other using a common modulation electrical signal and input to the electrodes 13a and 13b, the modulation voltage Since the amplitude is doubled, the chirp phenomenon can be suppressed at the same time as the modulation efficiency is further increased.

  When the power of the modulation electrical signal is relatively small, it may be input only to either the electrode 13a or the electrode 13b.

  Further, when the electrode 13a and the electrode 13b are connected to a high-frequency transmission circuit, no bias tee is required.

  In the optical modulator described above, since the size of one optical element itself is small, a plurality of optical modulators can be easily integrated on the same substrate. For example, when the size of the wafer is 8 inches, it is possible to realize a small-sized optical modulator that can be integrated on 32 optical modulators on the same substrate and can handle 32 ch of incident light.

  Furthermore, it is also possible to integrate an electric amplification circuit for a modulation signal and the like on the same substrate as the optical modulator. The optical element used in the optical modulator described above may be an SOI substrate or an Si substrate. Further, the photonic crystal part 12 may be formed either above or below the transmission path 11.

6-2. Application example to optical attenuator Next, an example in which an optical element is used as an optical attenuator will be described.

  FIG. 14 is a schematic explanatory diagram when the optical element of the present invention is used as an optical attenuator.

  The optical attenuator uses a directional coupler (not shown) to demultiplex light from a control unit that controls the voltage to be applied to the electrodes 13a and 13b and an optical element constituting the optical attenuator. An external light detection unit as a detection unit that detects a part (for example, about 1 to 10%) as monitor light is provided. The electrode 13c is grounded.

  The voltage signal (intensity) of the monitor light detected by the external light detection unit is received by the control unit, and the control unit receives the electrode 13a so that the light voltage signal transmitted from the external light detection unit is stabilized. In addition, feedback control is performed on the DC voltage to be applied to the electrode 13b. At this time, the voltage fed back to the electrode 13a and the electrode 13b reverses the phase with respect to the electrode 13a and the electrode 13b. Since the fluctuation of the voltage signal of the monitor light detected by the external light detector is considered to be about several percent, the phase shift amount Δφ is minute, and as a result, the feedback voltage is also considered minute.

  Since the optical attenuator described above is also small in the size of one optical element itself, a plurality of optical modulators can be integrated on the same substrate to realize a compact optical attenuator that can handle a plurality of channels. . Further, when the control circuit is constituted by a silicon electronic circuit, the control circuit can also be integrated on the same substrate as the optical modulator.

  Note that the optical element used in the optical attenuator described above may be one using an SOI substrate or one using a Si substrate. Further, the photonic crystal part 12 may be arranged only on one path after branching of the transmission line 11, and the photonic crystal part 12 may be formed above or below the transmission line 11. Good.

6-3. Application Example to Wireless-Optical Converter Next, an example in which an optical element is used as a wireless-optical converter will be described.

  FIG. 15A is a schematic explanatory view when the optical element of the present invention is used as a wireless-to-optical converter, and FIG.

  In the radio-optical converter, a loop antenna is formed on the same substrate. At this time, in order to increase the radio wave reception efficiency of the antenna, in order to prevent the radio wave from penetrating into the silicon (Si) substrate having a relatively high refractive index, the silicon under the antenna (shown by a dotted line in FIG. The Si) substrate is removed by etching.

  A DC power supply for setting a phase modulation base voltage is connected to the electrodes 13a and 13b, and an electric field vibration (modulation electric signal) received as a radio wave via a loop antenna is also composed of a metal thin film. It is connected through a high-frequency transmission line. The electrode 13c is grounded.

  Then, continuous light from a semiconductor laser or the like is incident on the wireless-to-optical converter, and is received as a radio wave via a loop antenna based on the phase shift amount Δφ of light propagating through each path after branching of the transmission path 11. By changing the difference of the phase shift amount Δφ generated in each photonic crystal portion 12a and 12b by the modulation electrical signal, the emitted light (modulated light) whose light intensity is modulated in accordance with the modulation electrical signal is obtained. . At this time, if the modulation voltages whose phases are reversed are applied to the electrodes 13a and 13b, the voltage difference can be doubled, the modulation efficiency can be increased, and at the same time, the chirp phenomenon can be suppressed.

  Note that the optical element used in the above-described wireless-to-optical converter may be an SOI substrate or an Si substrate. Furthermore, the photonic crystal unit 12 may be arranged only on one path after the transmission path 11 is branched.

  The wireless-to-optical converter described above can execute information processing in a short time, and thus can be particularly useful for a device that converts radio waves such as radio waves and microwaves into optical signals. For example, when a signal received by an ITS system, a device of a photonic network for telematics (for a vehicle), or ETC (registered trademark) is converted into light and transmitted, it is reflected from a surrounding vehicle in an on-board collision prevention system. For example, when a radar signal is received, converted into light, and transmitted, light conversion in a region exceeding 10 GHz can be handled. It can also be used for communication networks involving conversion from radio signals to optical signals.

  Since transmission using an optical network has a characteristic that it is not affected by electrical noise, it is possible to improve the stability of various systems.

  Furthermore, by using an optical fiber instead of the metal wiring used for transmitting an electric signal, the device can be reduced in weight and cost can be reduced. Furthermore, since silicon that can be easily recycled is used as the material of the wireless-to-optical converter, it is preferable from the environmental viewpoint.

  The optical element used in the above-described wireless-to-optical converter may be an SOI substrate or a Si substrate, and the photonic crystal unit 12 is only on one path after the transmission path 11 is branched. The photonic crystal part 12 may be formed either above or below the transmission line 11.

It is the figure which represented typically the optical element concerning this embodiment. It is sectional drawing of the optical element 1a concerning this embodiment. It is the graph which expressed the propagation characteristic of light with the dispersion curve of frequency f (Hz) and wave number k. It is distribution of the dipole layer in a photonic band structure. It is explanatory drawing of the optical element 1b concerning a deformation | transformation form. (A) It is explanatory drawing of the optical element 1c concerning a deformation | transformation form. (B) It is a principal part enlarged view of the photonic crystal part 12a of FIG. 6 (A). It is a side view from the incident end side of the light of the optical element 1c in FIG. It is sectional drawing of the EE surface of the optical element 1c in FIG. 6 (A). It is sectional drawing of the FF surface of the optical element 1c in FIG. 6 (A). It is explanatory drawing of the optical element 1d concerning a modification. It is explanatory drawing of the optical element 1e using the Si substrate concerning a deformation | transformation form. It is explanatory drawing of the optical element 1f using the Si substrate concerning a deformation | transformation form. It is a schematic explanatory drawing in the case of using the optical element of the present invention as an optical modulator. It is a schematic explanatory drawing at the time of using the optical element of this invention as an optical attenuator. (A) It is a schematic explanatory drawing in the case of using the optical element of this invention as a radio-optical converter. (B) It is sectional drawing of the EE surface of FIG. 15 (A).

Explanation of symbols

1 (1a, 1b, 1c, 1d, 1e, 1f) Optical element 11 Transmission path 11a Y branch part 11b Coupling part 11c, 11d SiN taper part 12 (12a, 12b) Photonic crystal part 13 (13a, 13b, 13c, Electrode 13d, electrodes 13e, 13s, 13t)
14, 14a Barrier region 15 Si (silicon) substrate 16 SiO ₂ (silicon oxide) layer 17 SOI (Silicon-On-Insulator) layer 18, 19 SiON (silicon oxynitride) layer

Claims (16)

A transmission path that guides light incident from the incident end to the output end;
A photonic crystal part for applying a predetermined phase modulation to the light;
An energy application unit that applies energy to the photonic crystal unit in order to control the phase modulation by changing a refractive index of the photonic crystal unit,
The photonic crystal part is formed only on either the transmission line or the transmission line,
An optical element, wherein the photonic crystal portion is sandwiched between the transmission line and a cladding layer made of SiO ₂ or SiON. The optical element according to claim 1,
The transmission path includes a branching portion that branches the light in two directions, and a coupling portion that is coupled again and led to the emission end,
The photonic crystal part is formed on at least one of the transmission paths after branching or below the transmission path. The optical element according to claim 1 or 2,
The incident end of the transmission path is formed such that a cross-sectional area of a plane perpendicular to the traveling direction of light continuously increases in the traveling direction of the light,
The optical element is characterized in that the emission end of the transmission path is formed such that a cross-sectional area of a plane perpendicular to the light traveling direction continuously decreases in the light traveling direction. The optical element according to any one of claims 1 to 3,
At least a part of the photonic crystal part is formed so that a cross-sectional area of a plane perpendicular to the light traveling direction continuously increases or decreases in the light traveling direction. . The optical element according to any one of claims 1 to 4,
An optical element comprising barrier regions for suppressing light propagation on both sides of the photonic crystal portion along a light traveling direction. The optical element according to any one of claims 1 to 5,
The photonic crystal portion is composed of a first material and a second material having different refractive indexes, and the first material is arranged in a planar shape in the second material at a predetermined size and a predetermined arrangement interval. Formed, and
The optical element, wherein the first substance is made of a material having a refractive index lower than that of the transmission path. The optical element according to claim 6,
An end portion of the photonic crystal portion is made of the second material having a higher refractive index than the transmission path, and the end portion has a cross-sectional area of a plane perpendicular to the traveling direction of the light. An optical element formed so as to continuously increase or decrease in a traveling direction. The optical element according to claim 6 or 7,
The second substance is made of a semiconductor having a predetermined refractive index in a steady state,
The optical element, wherein the energy applying unit includes a voltage applying unit that applies a voltage to the photonic crystal unit in order to change a refractive index of the semiconductor. The optical element according to claim 8, wherein
When the photonic crystal part is formed on both of the transmission paths after branching or under the transmission path, the energy applying part applies a voltage independently for each of the photonic crystal parts. An optical element comprising the voltage application unit. The optical element according to any one of claims 2 to 9,
The transmission path, the energy applying unit, and the photonic crystal unit are formed on an SOI (Silicon-On-Insulator) substrate,
The optical element, wherein the photonic crystal portion is formed at least under one of the transmission paths after branching. The optical element according to any one of claims 2 to 9,
The transmission path, the energy applying unit, and the photonic crystal unit are formed on a silicon substrate,
The optical element, wherein the photonic crystal part is formed on at least one of the branched transmission lines. An optical modulator comprising the optical element according to any one of claims 2 to 11.
Energy is applied to the photonic crystal unit by the energy application unit, and a predetermined phase modulation is applied to the light guided by the transmission path to make the light modulated light according to the energy. An optical modulator characterized by. The optical modulator according to claim 12, wherein
The photonic crystal portions are formed on both of the transmission paths after branching or under the transmission paths, respectively, and the voltage application sections that apply voltages independently for each of the photonic crystal sections have the same sign. An optical modulator, wherein an inverted voltage is applied to each of the photonic crystal portions. The optical attenuator having the optical element according to any one of claims 2 to 11,
A detection unit for detecting the light emitted from the optical element;
An optical attenuator comprising: a control unit that controls energy to be applied to the photonic crystal unit by the energy applying unit based on the detected intensity of the light. A wireless-to-optical converter comprising the optical element according to any one of claims 2 to 11.
The energy applying unit applies energy to the photonic crystal unit based on a radio wave received via an antenna, and applies predetermined phase modulation to the light guided by the transmission path to thereby output the light. Is a modulated light according to the energy. The radio-to-optical converter according to claim 15,
The photonic crystal part is formed on both of the transmission paths after branching or under the transmission path, respectively, and the voltage application unit that applies a voltage independently for each photonic crystal part includes the antenna. A radio-to-optical converter characterized in that, based on the radio wave received via the voltage, voltages having opposite signs are applied to the photonic crystal portions.

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