JP2018031896A - Optical buffer element structure, method for producing the same, and analyzing method therefor - Google Patents

Abstract

The present invention provides an optical buffer device structure having good matching with an existing silicon-based integrated device, a manufacturing method thereof, and an analysis method thereof. An optical element includes an optical waveguide having a silicon core that is surrounded by a clad and propagates light. The optical waveguide 80 of the optical element 50 has a convex portion 74 on the upper surface portion 72 of the silicon core 70. And the metamaterial 100 which shows a negative Goose-Henschen shift is provided adjacent to the convex part 74. FIG. [Selection] Figure 7

Description

  The present invention relates to an optical buffer element structure, a manufacturing method thereof, and an analysis method thereof.

  2. Description of the Related Art Conventionally, an optical element that performs optical delay by an optical trap effect due to a negative Goos-Hanchen shift is known (see, for example, Patent Document 1).

JP 2011-164777 A

  However, in such a conventional optical buffer element structure, line-shaped irregularities are periodically formed at the interface between the optical waveguide layer and the reflective layer. A large number of concave and convex groove directions must be formed orthogonal to the light direction. For this reason, it is not easy to produce, and since it is not produced through the same manufacturing process as other existing silicon-based integrated elements, the consistency with the manufacturing process of silicon-based integrated elements is not good.

  Accordingly, an object of the present invention is to provide an optical buffer element structure having good matching with existing silicon-based integrated elements, a manufacturing method thereof, and an analysis method thereof.

  An optical buffer element structure according to the present invention includes an optical waveguide having a silicon core that is surrounded by a clad and propagates light. The optical waveguide has a convex portion on an upper surface portion of the silicon core and is adjacent to the convex portion. It features a metamaterial that exhibits a negative Goose Henschen shift.

  According to such a configuration, the light propagating inside the optical waveguide is delayed by the negative Goose Henschen shift of the metamaterial.

  According to the present invention, there is provided an optical buffer element structure having good matching when used in combination with a silicon-based integrated element having an existing silicon core, a manufacturing method thereof, and an analysis method thereof.

It is a schematic diagram which shows a mode that the optical network and the electrical data network are mixed in the communication network. It is a conceptual diagram which shows a mode that an optical router merges several data strings, without making it interfere. It is the table | surface which compared the characteristic of the optical buffer using a metamaterial with another optical buffer. It is a schematic diagram of the optical buffer element structure explaining the propagation of light in an optical waveguide. It is a schematic diagram of the optical buffer element structure explaining a negative Goose Henschen shift. It is a perspective view explaining the structure of the optical waveguide of a comparative example. It is a typical perspective view explaining the structure of the principal part by the optical buffer element structure of embodiment. FIG. 8 is a cross-sectional view of a main part at a position along the line VIII-VIII in FIG. 7 in the optical buffer element structure of the embodiment. It is a typical perspective view explaining the structure of the principal part using the set dimensional relationship in the optical buffer element structure of the embodiment. FIG. 10 is a schematic diagram showing a magnetic field around a main part in the optical buffer element structure of the embodiment, viewed from the direction of arrow X in FIG. 9. FIG. 10 is a schematic diagram at a position along the line XI-XI in FIG. 9, showing an electric field around a main part in the optical buffer element structure of the embodiment. It is a figure explaining the dimension of the metamaterial depending on a frequency with the optical buffer element structure of embodiment. It is a figure of the dispersion | distribution curve which shows a mode that the light was trapped with the optical buffer element structure of embodiment. It is a figure which expands and shows a mode that the light was trapped with the optical buffer element structure of embodiment. It is a figure which shows the loss when the light is trapped with the optical buffer element structure of embodiment. The manufacturing method of the optical buffer element structure of embodiment is shown, (a) is typical sectional drawing which shows the mode of the laminated | stacked silicon dioxide layer and a silicon layer. (B) is typical sectional drawing which shows a mode that dry etching was carried out. (C) is typical sectional drawing which shows a mode that the aluminum oxide film layer was formed. (D) is typical sectional drawing which shows a mode that the metamaterial was vapor-deposited. (E) is typical sectional drawing which shows a mode that the silicon layer was etched. (F) is typical sectional drawing which shows a mode that the silicon dioxide layer was coat | covered by the circumference | surroundings. It is typical sectional drawing which shows the optical buffer element structure analyzed with the analysis method of the optical buffer element structure of embodiment. It is typical sectional drawing explaining the simplification process with the analysis method of the optical buffer element structure of embodiment. It is a flowchart explaining the analysis process including the simplification process in the analysis method of the optical buffer element structure of the embodiment.

  An embodiment of the present invention will be described in detail with reference to FIGS. In the description, the same elements are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is a schematic diagram showing a state in which an optical communication network 2 and an electrical data network 3 are mixed in the communication network 1.
In optical communication or the like, in order to ensure smooth communication of optical packet signals, a router inserted between each network is provided with a data buffering function and a routing (path control) function.

Specifically, a router equipped with an optical / electrical conversion function (light → photodetector → electricity → memory → semiconductor laser → light) generally buffers data in the state of electricity converted from light, The signal processing for returning to light is performed again.
However, high-speed optical communication requires a switching speed of about 1 Tbps, and the conventional method reduces the communication speed.
There is also a problem that power consumption is large when performing optical / electrical conversion.

  For this reason, development of an optical router 10 that can reduce power consumption with little decrease in speed by processing an optical signal as light has been progressing in recent years.

2 shows that the optical router 10 has a plurality of lines Ch. 1, Ch. 2 (see FIG. 1), the data streams A and B are joined together without interference, and the line Ch. 3 is a conceptual diagram showing a state in which a data string C is sent to FIG.
In such a case, the line Ch. 1 to the data string A are also transmitted via the optical fiber 12 to the line Ch. 2, the data string B enters the optical router 10.
At timing t1 before incidence, Ch. 1 in the data string A where no data exists. The data of the second data string B is synthesized. As a result, the Ch. 3 can be combined into one data string C having no interference (see timing t4).

However, if the data of the data string A and the data of the data string B are combined as they are at the timings t2 and t3, interference occurs. For this reason, the optical router 10 needs to be buffered (delayed) by an optical buffer or the like so that data in the data string B comes to a portion where there is no data in the data string A.
In the optical router 10, when the data string B is combined after being delayed by buffering, the data in the data string A and the data in the data string B do not interfere with each other (see timings t5 and t6).

Generally, fiber delay buffers, PhC (photonic crystal) buffers, and metamaterial buffers are known as optical buffers.
FIG. 3 is a table comparing the characteristics of optical buffers using metamaterials with other optical buffers.
The fiber delay buffer delays light through a long optical fiber cable (several kilometers to several tens of kilometers).
However, such a fiber delay buffer has a problem that the buffer device itself becomes large.

Further, for example, the PhC buffer can be downsized to some extent due to the effect of slow light using a photonic crystal.
However, the delay time of light cannot be continuously controlled, and the time during which buffering is possible is also fixed, so that all interference cannot be removed.
Therefore, an optical buffer element structure called a metamaterial buffer, which has a metamaterial that delays light propagating through the silicon core by exhibiting an optical trap effect by a negative Goose Henschen shift, has been proposed.

First, the principle of the optical trap due to the negative Goose-Henschen shift of the metamaterial will be briefly described.
FIG. 4 is a schematic diagram of an optical buffer element structure for explaining the propagation of light through an optical waveguide.
Here, a silicon dioxide layer 21 is provided on one surface side of the silicon core 20 constituting the optical waveguide. The silicon dioxide layer 21 is formed by oxidizing one side of the silicon core 20 with heat. The silicon dioxide layer 21 has a refractive index 1.5 lower than the refractive index 3.5 of the silicon core 20, and can reflect light at the interface and confine it in the silicon core 20.

A metamaterial layer 30 composed of a metamaterial 31 is provided on the other surface side of the silicon core 20. The metamaterial 31 of this embodiment is made of gold (Au), and both the dielectric constant (ε) and the magnetic permeability (μ) of the metamaterial layer 30 are positive (ε> 0, μ> 0). ).
In this state, the light introduced from the input side is emitted from the output side while being reflected at each interface between the silicon dioxide layer 21 and the metamaterial layer 30 when propagating through the optical waveguide constituted by the silicon core 20. Is done.

FIG. 5 is a schematic diagram of an optical buffer element structure for explaining how light is trapped by a negative Goose Henschen shift.
The metamaterial 31 can have a negative refractive index by changing the relative permeability by the resonance of the electromagnetic field due to the applied light or voltage due to the metal microstructure.
Here, when the dielectric constant (ε) and the magnetic permeability (μ) of the metamaterial layer 30 are negative (ε <0, μ <0), the silicon core 20 at the interface between the silicon core 20 and the metamaterial layer 30. The light propagating inside is trapped and delayed by the negative Goose Henschen shift.
In this way, the light emitted from the output side is delayed while maintaining the data sequence of the optical signal when introduced from the input side. The amount of delay can be controlled by adjusting the applied light or voltage. For this reason, if an optical trap based on the negative Goose-Henschen shift of the metamaterial 31 is used, a delay buffer that can be controlled by varying the delay amount can be obtained.

FIG. 6 is a perspective view illustrating the configuration of an optical waveguide used in the optical router 10 of the comparative example.
The metamaterial 15 of the comparative example is an example in which a metal microstructure is embodied.
That is, in the optical router 10 of the comparative example, a plurality of metamaterials 15 are arranged and arranged on the upper surface portion 14a of the silicon core 14 that confines and guides light. The metamaterial 15 plays a role as an optical buffer that exhibits an optical trap effect by negative Goose Henschen shift.
Each metamaterial 15 is a substantially C-shaped ring in plan view with substantially the same thickness, and is arranged so that the directions of the rings are aligned in a state where the metamaterial 15 is tilted along the flat surface on the upper surface portion 14a. Due to this, the negative Goose Hengshen shift effect is exhibited.

  The metamaterial 15 of the comparative example configured in this way excites carriers in the silicon material of the adjacent silicon core 14. When the capacitor characteristics of the metamaterial 15 are changed by adjusting the light or voltage to be applied, carriers are generated and disappeared alternately by the carrier plasma effect. In this way, the speed of light propagating in the optical waveguide can be dynamically controlled by inducing a change in the characteristics of the metamaterial 15.

That is, in a state where photoexcitation or voltage application is stopped, carriers disappear and light propagating in the optical waveguide is optically trapped and delayed.
The light generated by the optical excitation or voltage application and propagating in the optical waveguide is not trapped and is not delayed.
For this reason, the delay buffer can be controlled variably by adjusting the ratio of the carrier generation and extinction time by modulating the metamaterial characteristics by switching the applied light or voltage. The delay time can be controlled as follows.

  However, as shown in FIG. 6, the substantially C-shaped metamaterial 15 in plan view is disposed in a state of being tilted along the upper surface portion 14 a. Further, the diameter of the ring of the metamaterial 15 is as fine as about 100 nm. The metamaterial 15 having such dimensions is difficult to form in a desired shape. Further, during the lift-off process after the metal vapor deposition step, a force in the direction of peeling in the out-of-plane direction C of the metamaterial 15 is easily applied.

For this reason, partial lifting occurs in the metamaterial 15 or the shape of the metamaterial 15 is deformed. Furthermore, there is a possibility that the position at which the lens is disposed is shifted from the predetermined position.
Therefore, it is difficult to align the plurality of metamaterials 15 at desired positions while maintaining the same shape in the same manufacturing process as the silicon-based integrated device.
In particular, in order for the metamaterial 15 to exhibit the light trap effect due to the negative Goose Henschen shift, it is required to form a substantially C-shaped shape in plan view with high dimensional accuracy.

  Therefore, this embodiment provides an optical buffer element that has good matching when used in combination with a silicon-based integrated element having an existing silicon core and can exhibit an optical trap effect due to a negative Goose Henschen shift. Provide structure.

FIG. 7 is a schematic perspective view illustrating the structure of the main part of the optical buffer element structure according to the embodiment of the present invention.
The optical element 50 of this embodiment includes an optical waveguide 80 as a silicon waveguide having a silicon core 70 that is surrounded by a clad 60 and propagates light.
The optical waveguide 80 integrally has a convex portion 74 on the upper surface portion 72 of the silicon core 70. The convex portion 74 of this embodiment has a width dimension w and a height dimension h that are smaller than the wavelength λ of the propagating light (see FIG. 9). The convex portions 74 are formed so as to be integrated with the silicon core 70 in a straight line with substantially the same cross section along the extending direction of the optical waveguide 80.

  In addition, a plurality of metamaterials 100 exhibiting a negative Goose Henschen shift are provided adjacent to the convex portion 74. The metamaterial 100 includes gold (Au) and titanium (Ti), and improves the adhesion of the gold layer by vapor deposition by providing a titanium layer on the convex portion 74 side. This metamaterial 100 delays light propagating in the optical waveguide 80 by exhibiting an optical trap effect due to negative Goose Henschen shift.

Furthermore, the metamaterial 100 of this embodiment has an upper surface portion 110 and side surface portions 120 and 130 as three planes parallel to the traveling direction of light.
The upper surface portion 110 and the side surface portions 120, 120 are bent at a substantially right angle by depositing the metamaterial 100 so as to be in close contact with the outer surface of the convex portion 74 from above the convex portion 74. And each surface is formed flat.
For this reason, the three flat surfaces constituted by the upper surface portion 110 and the side surface portions 120 and 120 are in close contact with the convex portion 74 with the surface extending direction parallel to the light traveling direction, In a cross-section perpendicular to the portion 74, the upper surface portion 110 and the side surface portions 120, 120 are integrated so that the substantially U-shape is raised and the open end of the substantially U shape faces the silicon core 70. The protrusion 74 is fitted.

In the optical element 50, a plurality of metamaterials 100 having a plane perpendicular to the traveling direction of light are arranged with a constant interval L1 (for example, 100 nm) along the extending direction of the convex portions 74. Has been. In the embodiment, an optical element 50 including four units in which one metamaterial 100 is regarded as one unit and four metamaterials 100 are arranged in series is shown.
And the length L of this optical element 50 is comprised so that it may become about 0.6-1 micrometer or less.
However, the present invention is not limited to this, and the total length of one unit composed of one metamaterial 100 may be about 15 to 20 nm. And the number of the metamaterial 100 is not specifically limited, Single or any plural may be sufficient.

FIG. 8 is a cross-sectional view of the main part at the position along the line VIII-VIII in FIG. 7 in the optical buffer element structure of the embodiment.
A coating 76 of aluminum oxide (Al 2 O 3) as an oxide film is provided around the silicon core 70 that forms the optical waveguide 80 of this embodiment. A clad 60 made of silicon oxide (SiO ₂ ) is provided around the coating portion 76.
A control device (not shown) provided outside the optical waveguide 80 receives an external signal 90 by electricity or light. The aluminum oxide coating 76 generates carriers when a voltage is applied as a gate oxide film. Thereby, the property of the metamaterial can be modulated and the delay time can be controlled.

FIG. 9 is a schematic perspective view illustrating the structure of the main part using the set dimensional relationship in the optical buffer element structure of the embodiment.
The protrusion 74 of the silicon core 70 has a width dimension w and a height dimension h in a direction orthogonal to the extending direction L of the optical waveguide 80, and the It is formed so as to have a substantially square cross-sectional shape orthogonal to the traveling direction.

Further, the thickness dimension of the metamaterial 100 that covers the convex portion 74 is set to a fixed dimension a (for example, a = about 15 to 20 nm), and the depth dimension along the extending direction L of the optical waveguide 80 is set to a fixed dimension d. (Eg, d = about 50 nm), width dimension w (eg, w = about 50 nm) and height dimension h (eg, h = about 50 nm).
Therefore, when the wavelength of light is λ = 1550 nm, the convex portion 74 has a sufficiently small width dimension w and height dimension h as compared with the wavelength λ of propagating light. Therefore, the metamaterial 100 can delay the light propagating in the optical waveguide 80 by the negative Goose Henschen shift.

FIG. 10 is a schematic diagram showing the magnetic field around the main part in the optical buffer element structure of the embodiment, viewed from the X direction in FIG.
FIG. 11 is a schematic diagram showing the electric field around the main part in the optical buffer element structure of the embodiment, at a position along the line XI-XI in FIG.
The magnetic field and electric field in the silicon core 70 cause a carrier plasma effect due to fluctuations in the capacitor characteristics of the metamaterial 100, thereby affecting the generation and annihilation of carriers that perform optical trapping.

In particular, high dimensional accuracy is required for the width dimension w and the height dimension h of the metamaterial 100 in order to exhibit the optical trap effect due to the negative Goose Henschen shift.
FIG. 12 is a diagram illustrating the frequency-dependent metamaterial dimensions in the optical buffer element structure of the embodiment.
In FIG. 12, the vertical dimension represents the height dimension h of the metamaterial, and the horizontal axis represents the width dimension w of the metamaterial. Contour lines indicated by broken lines indicate at which frequency the metamaterial operates to exhibit the light trapping effect.
Metamaterials have different dimensions depending on the frequency of light in which the optical trap effect due to the negative Goose Henschen shift occurs.
In the embodiment, the metamaterial 100 having a height dimension h = 50 nm and a width dimension w = 50 nm, which are close to the dotted line B, is employed so as to operate at a frequency of 193 THz used for optical communication indicated by the dotted line B.

FIG. 13 is a dispersion curve showing how light is trapped in the optical buffer element structure of the embodiment.
Here, the horizontal axis indicates the β propagation multiplier (real = real part). The vertical axis indicates the wavelength ω / c (μm ⁻¹ ) of light. The slope of the dispersion curve indicates the delay, that is, the reflectance. The closer the tilt angle is to 0, the more light is trapped.

For comparison, a light line C (Light line) indicating light in a vacuum is shown.
A device curve D (Device curve: λ to 1550 nm) having a gentler slope than the light line C indicates light propagating in the optical waveguide 80 of the optical element 50 of the embodiment.

FIG. 14 is an enlarged view of a part A in FIG. 13 showing a state in which light is trapped in the optical buffer element structure of the embodiment.
When light in the optical waveguide 80 is trapped by the metamaterial 100 in which the dimensions of the convex portions 74 of the optical element 50 are the height dimension h = 50 nm and the width dimension w = 50 nm, ω / c (μm ⁻¹ ) = In the vicinity of about 4, it was confirmed that a sufficient delay that can be used as an optical buffer occurred.

FIG. 15 is a diagram illustrating a loss when light is trapped in the optical buffer element structure of the embodiment.
The horizontal axis represents the β propagation multiplier (imag = imaginary part). It can be seen that the loss increases in the vicinity of ω / c (μm ⁻¹ ) = about 4 where the light in the optical waveguide 80 is trapped by the metamaterial 100 (see FIG. 3). Thus, there is a correlation between loss and delay, and it can be seen that the metamaterial 100 has a strong interaction and delays light in the vicinity of ω / c (μm ⁻¹ ) = about 4.

[Method of manufacturing optical buffer element structure]
FIG. 16 illustrates a method for manufacturing the optical buffer element structure of the embodiment.
Here, the manufacturing method of the optical buffer element structure which has a metamaterial is demonstrated along a manufacturing process, referring FIG.
FIG. 16A is a schematic cross-sectional view showing a state of the laminated silicon layer 170 and silicon dioxide layer 160.

  As the structural material 150 including the silicon layer 170 and the silicon dioxide layer 160, the structural material 150 having the same configuration as that of other elements forming the optical waveguide is used. In addition, the manufacturing process of the optical element 50 serving as the optical buffer according to the present embodiment described below is performed in the same process as that of an element having another optical waveguide.

  First, the upper surface portion 170a of the structural material 150 on the silicon layer 170 side is dry-etched. For dry etching, fluorine-based gas or the like may be used.

FIG. 16B is a schematic cross-sectional view showing a state in which the structural material 150 is dry etched.
By dry etching, a convex portion 74 is formed at the center in the width direction of the upper surface portion 72 that has been scraped off.
Dry etching can be finely processed. For this reason, a thing with high dimensional accuracy of the convex part 74 is obtained.

FIG. 16C is a schematic cross-sectional view showing a state in which the aluminum oxide film layer 172 has been formed.
The upper surface portion 170a on the silicon layer 170 side is covered with the aluminum oxide film layer 172 by vapor deposition of aluminum oxide. By the aluminum oxide film layer 172, carriers are generated and disappeared smoothly.

FIG. 16D is a schematic cross-sectional view illustrating a state in which the metamaterial 100 is deposited on the convex portion 74.
Titanium and gold are vapor-deposited on the convex portion 74. When vapor deposition is performed, a window is formed in the convex portion 74 by etching at a desired position at a predetermined interval. Then, titanium and gold are vapor-deposited in a thin plate shape from this window so as to straddle the upper surface side of the convex portion 74 and both the left and right side surfaces.
The convex portion 74 is configured to have a similar cross-sectional shape perpendicular to the extending direction.
As a result, the metamaterial 100 deposited on the upper surface side and the left and right side surfaces of these convex portions 74 is self-aligned along the window and has the same shape with a predetermined interval in the extending direction. Formed (see FIG. 7).

Further, in the metamaterial 100 of this embodiment, the upper surface portion 110 and the side surface portions 120 and 130 have parallel planes extending in the light traveling direction, respectively. The upper surface portion 110 and the side surface portions 120 and 130 are covered and fitted so as to cover the convex portion 74 from above, left, and right directions by crimping the inner surface to the three outer surfaces of the convex portion 74. ing.
For this reason, even if a lift-off process is performed after a metal vapor deposition process, the metamaterial 100 does not peel from the convex part 74, or move upward or laterally. Therefore, the shape stability of the metamaterial 100 is good, and an optical trap effect can be exhibited.

  FIG. 16E is a schematic cross-sectional view illustrating a state in which the left and right side surfaces 170b and 170b of the silicon layer 170 are etched. On the left and right side surfaces 170b and 170b of the silicon layer 170, removal portions 173 and 173 to be removed by etching are indicated by virtual lines.

FIG. 16 (f) is a schematic cross-sectional view showing a state in which the clad 60 of silicon dioxide is covered around the convex portion 74. The silicon core 70 and the convex portion 74 are covered with silicon dioxide constituting the clad 60 (see FIG. 9) to form the optical waveguide 80.
Processes such as dry etching, vapor deposition, and etching for the silicon layer 170 are the same as the processes for manufacturing other elements having optical waveguides.
Thus, in the same process as the element having the conventional optical waveguide, the optical waveguide 80 in which the metamaterial 100 is deposited on the convex portion 74 is surrounded by the clad 60, and the optical element 50 serving as an optical buffer can be manufactured. it can. Therefore, almost no change in manufacturing equipment is required.

In FIG. 16B, in the pre-process for depositing the metamaterial 100, the protrusion 74 is finely processed by dry etching so as to have the same or similar cross-sectional shape in the longitudinal direction.
For this reason, the dimension inside the some metamaterial 100 covered along the convex part 74 is decided accurately.

Further, in FIG. 16D, the thin plate-like upper surface portion 110 and side surface portions 120 and 120 of the metamaterial 100 formed on the convex portion 74 are in close contact with the outer surface of the convex portion 74. A plane extending parallel to the traveling direction of light is provided. The metamaterial 100 adheres to the inner plane with a relatively wide area.
Further, the upper surface 110 is in close contact with the outer surface of the convex portion 74 in a direction perpendicular to the mold removal direction with the plane located inside the side surface portions 120, 120 having the out-of-plane direction different by about 90 degrees. .
For this reason, it does not move from a desired position even during the lift-off process. Therefore, accurate dimensions and position accuracy by self-alignment are maintained, and the shape is stable.
Therefore, the movement and deformation of the metamaterial 100 do not occur as compared with the case where the ring is laid like a ring having a substantially C shape in plan view shown in the comparative example (see FIG. 6). For this reason, the metamaterial 100 of this embodiment can reliably exhibit the optical trap effect that requires accurate dimensional accuracy.

[Analysis method of optical buffer element structure]
FIG. 17 is a schematic cross-sectional view showing an element structure analyzed by the optical buffer element structure analysis method of the embodiment, and FIG. 18 is a schematic cross-sectional view for explaining a simplification process.
FIG. 19 is a flowchart for explaining an analysis process including a simplification process in the optical buffer element structure analysis method of the embodiment.
As shown in FIG. 17, in the optical element 50 of this embodiment, a convex portion 74 is integrally projected from a part of the center of the upper surface portion 72 of the silicon core 70 having a substantially square cross section. Only, it has a complicated structure in which the metamaterial 100 is provided.
For this reason, a method for deriving the characteristics of the optical element 50 by inputting to the analysis device such as a waveguide analysis method (FDTD (Finite-difference time-domain method)) generally used for the entire structure is calculated. Time will be enormous. In addition, since the target portion to be analyzed includes metal, it is not easy to analyze the waveguide.

  Therefore, in this embodiment, homogenization mode analysis is performed as a technique for performing mode analysis of a waveguide including metal while performing electromagnetic field calculation of a metamaterial. Then, this homogenization mode analysis facilitates the analysis of the waveguide. Hereinafter, a method for analyzing the homogenization mode of the optical buffer element structure will be described.

The homogenization mode analysis will be described along the flowchart shown in FIG. 19 with reference to FIGS. When the homogenization mode analysis is started, in step S100, only the periphery M of the metamaterial 100 is regarded as a homogeneous space having a certain dielectric constant (ε) and magnetic permeability (μ), and the scattering parameter S is expressed as an electromagnetic field distribution. Calculate
At this time, the material in the periphery M of the metamaterial 100 is regarded as uniform, and the periphery M is separated from the silicon core 70 as a homogeneous space having a certain dielectric constant (ε) and magnetic permeability (μ).
Thereby, the scattering parameter of the periphery M of the convex part 74 is derived | led-out.

In step S101, the frequency dependence of the dielectric constant ε and permeability μ of the metamaterial 100 is calculated from the derived scattering parameter S.
In step S102, the optical waveguide 80 is simplified using the calculated frequency dependence.
At this time, the optical waveguide 80 is simplified to have a rectangular cross section that does not have the protrusion 74 (see FIG. 18). For example, here, when the optical waveguide 80 is simplified, the upper surface portion 72 is ε = (1.7) ² , the silicon core 70 is ε = (3.45) ² , and the cladding 60 is ε = (1.5). ² , represented as

In step S103, the chromatic dispersion characteristics of the entire optical element 50 are analyzed.
The step of performing the homogenization mode analysis in this embodiment includes analyzing the chromatic dispersion of the entire optical element 50 including the simplified optical waveguide 80 by regarding the substance in the periphery M of the metamaterial 100 as uniform. It is known that wavelength dispersion characteristics can be analyzed easily and quickly if the dielectric constant (ε) and magnetic permeability (μ) of the substance are homogeneous.
For this reason, the homogenization mode analysis of the optical buffer element structure of this embodiment is performed by applying the scattering parameter S of only the periphery M of the metamaterial 100 calculated in advance to the simplified optical waveguide 80, thereby calculating the cross section. The rectangular shape is analyzed as a homogeneous material having a dielectric constant ε and a magnetic permeability μ.
Therefore, the waveguide analysis of the optical element 50 having the metamaterial 100 can be performed quickly and accurately, and the wavelength dispersion characteristic of the optical waveguide 80 can be obtained.

As described above, the optical buffer element structure, the manufacturing method thereof, and the analysis method thereof according to the embodiment have the following operational effects.
That is, the light propagating through the silicon core 70 is delayed by the negative Goose Henschen shift of the metamaterial 100.

According to this embodiment, by forming the convex portion 74 with good accuracy, the stability of the shape of the fine metamaterial 100 provided adjacently is improved.
Further, it can be manufactured from the same silicon core structural material 150 (see FIG. 16) by the same production process as a silicon integrated device having an existing silicon core, and is matched when used in combination with other silicon integrated devices. Good properties.

  Further, the metamaterial 100 is formed by fitting a flat surface parallel to the light traveling direction to the convex portion 74. For this reason, it fixes to the flat upper surface part 74a and side part 74b, 74b (refer FIG. 7) of the convex part 74 with favorable adhesive force. For this reason, the attachment stability to the convex part 74 of the metamaterial 100 can be improved.

  Further, the three planes constituting the metamaterial 100 are fitted so as to be parallel to the traveling direction of the light, and stand up in a substantially U shape in a shape perpendicular to the extending direction of the convex portion 74. . For this reason, the light in the TE mode optical waveguide 80 is also excited between the side surface portions 120 and 120 serving as a pair of capacitors in the incident electric field by the control signal from above the upper surface portion 110, and the optical trap effect is effectively achieved. Can be generated.

The convex portion 74 has a width dimension w and a height dimension h smaller than the wavelength λ of the propagating light. The size of the convex portion 74 that defines the inner dimension of the metamaterial 100 is the dimension at which the optical trap effect due to negative Goose Henschen shift occurs (here, the height dimension h = 50 nm, the width dimension w = 50 nm, see FIG. 12). ).
In the metamaterial 100, the upper surface portion 74a and the side surface portions 74b, 74b are arranged with high dimensional accuracy so as to be parallel to the light traveling direction with respect to the outer surface of the upper surface portion 74a and the side surface portions 74b, 74b of the convex portion 74. Have arranged. Further, the metamaterial 100 supports the upper surface portion 74a and the side surface portions 74b and 74b of the convex portion 74 in close contact with the outer surface of the upper surface portion 74a and the side surface portions 74b and 74b of the convex portion 74 from the inner surface.
For this reason, the shape stability of the metamaterial 100 is good, and light propagating in the optical waveguide 80 can be reliably trapped and delayed by the negative Goose Henschen shift.

Further, as shown in FIG. 8, carriers in the optical waveguide 80 are excited by an electrical or optical external signal given from outside the optical waveguide 80 to control the resonance of the metamaterial 100 and freely trap light. Can be delayed.
For this reason, the control unit can delay the optical signal in the optical waveguide 80 as light by controlling the electrical or optical external signal applied to the optical element 50.
The light delayed by being buffered by the optical element 50 can be merged without interfering with data strings flowing through a plurality of lines (see FIG. 2), and signal processing used as a router becomes possible. Therefore, it is possible to provide the optical router 10 with reduced speed and less power consumption than a router that needs to convert to an electrical signal. Further, the standby power until an external signal is given can be made zero.

  Further, the width dimension w of the silicon core 70 is the same as the width dimension w (w = about 500 nm) of the optical waveguide 80 disposed on the integrated body (see FIG. 7). For this reason, as shown in FIG. 16 (e), the removal portions 173 and 173 are removed, and the silicon-based integrated element used for the optical element 50 can be shared with other silicon-based integrated elements.

Further, the size of the convex portion 74 formed integrally with the silicon layer 170 is formed by cutting the upper surface portion 72 to an arbitrary size in accordance with the size at which the optical trap effect due to the negative Goose Henschen shift occurs. be able to. For this reason, the width w of the silicon core 70 can be the same as the silicon core used in other silicon-based integrated elements.
For this reason, the optical element 50 can be manufactured using the same production equipment as other silicon-based integrated elements. Therefore, a special production line is not required, and an increase in production cost is suppressed.

Control involving generation and disappearance of carriers is smoothly performed by a coating 76 (see FIG. 8) of aluminum oxide (Al 2 O 3) as an oxide film provided around the silicon core 70.
For this reason, the operativity of the delay time using the optical element 50 can be improved.

  As described above, the optical buffer element structure, the manufacturing method, and the analysis method thereof according to this embodiment have been described in detail. However, the present invention is not limited to these embodiments, and does not depart from the spirit of the present invention. Needless to say, it can be changed as appropriate.

  For example, in the present embodiment, description has been made by showing the case where one convex portion 74 is provided in the central portion of the upper surface portion 72 of the silicon core 70, but the present invention is not limited to this, and a plurality of convex portions 74 are provided on the upper surface portion 72. It may be.

  In addition, the shape of the convex portion 74 is not limited to this, and may be any convex portion provided on the upper surface portion 72 such as a semicircular cross section, a polygonal cross section, or a substantially triangular cross section. May be buried in the silicon core 70.

  Further, in the embodiment, the projection 74 has been described as being continuously formed in a straight line along the extending direction of the optical waveguide 80, but is not limited thereto. That is, as long as the metamaterial 100 is disposed adjacent to each other, the convex portions may be formed by being partially interrupted, and the number of the convex portions is not limited to a single number but may be plural. .

  In the embodiment, gold and titanium are exemplified as the constituent metals of the metamaterial 100, but only one of gold and titanium may be used. In addition to or instead of gold or titanium, any other metal such as platinum, silver, aluminum, tungsten, chromium, etc. may be used as a metamaterial, and some or all of these metals may be used. Any material can be used.

DESCRIPTION OF SYMBOLS 1 Communication network 2 Optical communication network 3 Electrical data network 10 Optical router 11 Optical fiber 50 Optical element 60 Cladding 70 Silicon core 72 Upper surface part 74 Convex part 74a Upper surface part 74b Side surface part 76 Coating part 80 Optical waveguide 90 External signal 100 Metamaterial 110 Top surface (one of the planes)
120 Side (one of the planes)

Claims (10)

An optical waveguide having a silicon core surrounded by a clad and propagating light,
The optical waveguide has a convex portion on the upper surface of the silicon core,
An optical buffer element structure comprising a metamaterial exhibiting a negative Goose Henschen shift adjacent to the convex portion.   2. The optical buffer device structure according to claim 1, wherein the metamaterial is formed in a plane perpendicular to a light traveling direction, and one or more metamaterials are arranged in the light traveling direction.   3. The light according to claim 1, wherein the metamaterial delays light propagating in the optical waveguide by having the convex portion having a width and height smaller than a wavelength of propagating light. Buffer element structure.   The delay of the propagating light is controlled by exciting the carriers in the optical waveguide by an electric or optical external signal given from outside the optical waveguide and controlling the resonance of the metamaterial. The optical buffer element structure according to claim 3, wherein   5. The optical buffer element structure according to claim 1, wherein a width dimension of the silicon core is the same as a width dimension of a silicon waveguide disposed on the integrated body. 6.   The optical buffer element structure according to claim 1, wherein an oxide film is formed on the upper surface portion. Forming the protrusion on the upper surface of the silicon core;
Depositing a metamaterial on the convex part;
The method for manufacturing an optical buffer element structure according to claim 1, further comprising a step of surrounding the optical waveguide with a clad.   8. The step of forming the convex portion includes cutting the upper surface portion of the silicon core disposed on the integrated body into a convex shape to form a waveguide on the upper portion of the silicon core. Manufacturing method of optical buffer element structure. Deriving the scattering parameter of the convex portion in which the metamaterial is disposed out of the silicon core;
Calculating the frequency dependence of the permittivity and permeability of the metamaterial from the scattering parameters;
Homogenizing the optical waveguide using the frequency dependence of the permittivity and permeability; and
A method for analyzing an optical buffer element structure according to any one of claims 1 to 6, further comprising a step of performing a homogenization mode analysis for analyzing the wavelength dispersion of the homogenized optical waveguide. The step of homogenizing has a simplification in which the optical waveguide has a rectangular cross section without the convex portion,
10. The method for analyzing an optical buffer element structure according to claim 9, wherein the step of performing the homogenization mode analysis includes analyzing the chromatic dispersion of the entire element including the simplified optical waveguide.

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