KR100905658B1 - Nonlinear optical silicon waveguides with refractive index control of polymer cladding and Method for manufacturing the same - Google Patents

Abstract

Disclosed are a nonlinear silicon optical waveguide device by controlling the refractive index of a polymer clad and a method of manufacturing the same. The present invention is a non-conducting silica substrate; A silicon core formed on the silica substrate and receiving pump light; And a polymer clad formed around the silicon core and having a refractive index or thickness that matches the traveling phase of the pump light with nonlinear optical signals generated by a nonlinear optical effect in the silicon core. According to the present invention, by forming a polymer clad around the core of the silicon optical waveguide formed on the silica substrate, it is easy to fabricate the device, relatively easy to select the size of the core through the appropriate refractive index control of the polymer clad, the polymer clad It is easy to control chromatic dispersion by adjusting the refractive index and thickness of the material, and the effective refractive index in the core can be constant by selecting the appropriate refractive index of the clad material, thereby increasing the temperature stability, as well as the pump light and the nonlinear photon generating light. By matching the phases, the efficiency of nonlinear optical signal generation can be increased.

Description

Nonlinear optical silicon waveguides with refractive index control of polymer cladding and method for manufacturing the same

The present invention relates to a nonlinear silicon optical waveguide device by controlling the refractive index of a polymer clad. In particular, in the silicon-based third-order nonlinear optical device, the phase matching between the pump light and the nonlinear optical signals increases the efficiency of generating the nonlinear optical signal. The present invention relates to a silicon optical device.

Recently, the interest in the structure of integrated optical devices using silicon optical waveguides is increasing, and researches on light source devices and optical functional devices using nonlinear optical effects in silicon optical waveguides have been actively conducted. In particular, research results on silicon light sources and photon pair generation techniques using Raman scattering effects in silicon optical waveguides have been reported, and interest in them is increasing.

In particular, in the nonlinear photon generation structure by Raman scattering and / or multiphoton mixing, a structure for satisfying a phase matching condition for maximizing nonlinear optical effects has been considered, and research results have been reported.

1 shows a silicon optical waveguide device structure formed in a conventional non-conducting silica. As shown in FIG. 1, in a conventional silicon nonlinear optical device composed of an optical waveguide 110 having a core using silicon-on-insulator (SOI) formed on an insulator, the surroundings are formed of silicon oxide, that is, silica (SiO ₂ ). The structure of the cradle 120 is configured.

In this structure, a method of optimizing the size of the core 110 for phase matching is as follows. That is, in this scheme, the phase matching is adjusted by adjusting only the size of the core 110, that is, the width w and the height h, due to the fixed core refractive index and the clad refractive index. However, this approach has the disadvantage that the size of the core 110, in particular the range of the height h, is limited. In addition, the work of forming the silica insulator 120 outside the silicon core 110 is a rather difficult process, and the difference in refractive index between the core 110 and the clad 120 is large, so that the loss in connection with the conventional transmission optical fiber is reduced. It has a big disadvantage. In addition to the efficiency due to the difference in dispersion value according to the wavelength, the silica of SOI has a limiting property that the effective refractive index value that the pump pump undergoes may change due to the change of the refractive index according to the temperature change.

In addition, Jay E. Sharping, Kim Fook Lee, et al ., “Generation of correlated photons in nanoscale silicon waveguides,” OPTICS EXPRESS, Vol. 14, No. 25, 12388 (11 December 2006), introduces a technique for generating quantum-linked photon pairs by nonlinear optical effects with optimized core size in a clad structure composed of a silicon core and SiO _2. Rong, H. et al . , "A continuous-wave Raman silicon laser," Nature 433, 725-728 (Feb. 2005), introduces a laser oscillation technique induced by nonlinear optical effects by Raman scattering in an optical waveguide of a silicon core structure. These documents introduce techniques based on silicon-based nonlinear optical effects, but Jay E. Sharping et al . In the paper, it is not easy to integrate other optical devices in the future because it uses a clad structure composed of SiO ₂ , and Rong, H. et. al . The paper only introduces a technique using a semiconductor PIN structure to maximize the Raman scattering effect in a silicon optical waveguide.

Therefore, conventionally reported silicon device-based nonlinear optical device method is difficult to implement technically, there is a constraint that the size of the core is small due to the large difference in refractive index between the core and the clad, and newly generated by the pump light and the nonlinear optical effect The core size is limited to match phase synchronization with the signals, and there is a problem that loss is large in coupling with conventional optical transmission lines due to the small core.

The first technical problem to be achieved by the present invention is easy to fabricate the device, relatively easy to select the size of the core, easy to adjust the chromatic dispersion, constant refractive index in the core can be improved temperature stability, The present invention provides a nonlinear silicon optical waveguide device by controlling the refractive index of a polymer clad that can increase the efficiency of nonlinear optical signal generation.

The second technical problem to be achieved by the present invention is to provide a method for manufacturing a non-linear silicon optical waveguide device by controlling the refractive index of the polymer clad.

In order to achieve the first technical problem, the present invention is a non-conductive silica substrate; A silicon core formed on the silica substrate and receiving pump light; And a polymer clad formed around the silicon core and having a refractive index or thickness that matches the traveling phase of the pump light with nonlinear optical signals generated by a nonlinear optical effect in the silicon core. Provided is a nonlinear silicon optical waveguide device by adjusting the refractive index of a clad.

In order to achieve the above second technical problem, the present invention comprises the steps of forming a silicon core receiving the pump light on the non-conductive silica substrate; And forming a polymer clad around the silicon core having a refractive index or thickness that matches the traveling phase of the pump light with the nonlinear optical signals generated by the nonlinear optical effect in the silicon core. Provided is a method of manufacturing a nonlinear silicon optical waveguide device by controlling the refractive index of a polymer clad.

According to the present invention, by forming a polymer clad around the core of the silicon optical waveguide formed on the silica substrate, it is easy to fabricate the device, relatively easy to select the size of the core through the appropriate refractive index control of the polymer clad, the polymer clad It is easy to control chromatic dispersion by adjusting the refractive index and thickness of the material, and the effective refractive index in the core can be constant by selecting the appropriate refractive index of the clad material, thereby increasing the temperature stability, as well as the pump light and the nonlinear photon generating light. By matching the phases, the nonlinear optical signal generation efficiency can be increased.

The present invention provides a silicon optical device for increasing the efficiency of nonlinear optical signal generation by performing phase matching between pump light and nonlinear optical signals in a silicon-based tertiary nonlinear optical device, and forming a polymer clad on a silicon core optical waveguide. Provided are methods for obtaining phase matching through proper refractive index control of the polymer.

Hereinafter, with reference to the drawings will be described a preferred embodiment of the present invention. However, embodiments of the present invention illustrated below may be modified in many different forms, and the scope of the present invention is not limited to the embodiments described below.

Figure 2 illustrates the structure of a non-linear silicon optical waveguide device by controlling the refractive index of the polymer cladding according to an embodiment of the present invention.

It is assumed here that an optical signal is generated with nonlinear optical characteristics with respect to the input pump light.

Below, refractive index n ₁ , n ₂ , n ₃ Are different refractive index values, and mean those values that can be easily selected by one of ordinary skill in the art to which the present invention pertains (hereinafter referred to as a person skilled in the art) by repeated experiments or the like.

The silicon core 210 is formed on the nonconductive substrate having the refractive index n ₂ , that is, the silica substrate 220. The silicon core 210 has a width w and a height h of a condition having a single mode in a silicon-on-insulator (SOI) composed of silicon having a refractive index n ₁ .

Polymer clad 230 has a refractive index n ₃ and is formed around silicon core 210. Here, the refractive index of the polymer clad 230 is adjusted to satisfy the conditions where the phase shifting and nonlinear optical effects of the wavelength shifting optical signals due to the nonlinear optical effects in the silicon core 210 may be maximized with respect to the pump light. You can.

That is, by adjusting both the refractive index and the thickness of the polymer clad 230, or by adjusting either the refractive index or the thickness, the light generated by the pump light and the nonlinear effect proceeding in the core in relation to the size of the silicon core optical waveguide Adjust the wavelength dispersion value relative to the signals.

According to the structure as shown in Figure 2, through the appropriate selection of the polymer material formed on the upper clad layer, that is, the polymer clad 230, it is possible to obtain the control of the size of the silicon core 210 and to stabilize the dispersion and thermal properties There is an advantage. Selection of the refractive index and thermo-optic properties of the polymer can be made through various synthesis of materials. In other words, the polymeric materials used are those that can be readily selected by those skilled in the art.

In particular, in the silicon core 110 and the silica clad 120 structure of the conventional SOI structure, there is a disadvantage that a constant value of the silicon core 110 must be adjusted in order to obtain a phase match between the pump light and the nonlinear optical signals. . On the other hand, in the structure of the silicon core 210 formed on the silica substrate 220 and the polymer clad 230 formed thereon according to the present invention, a method of properly selecting the refractive index and the thickness of the polymer may be used to select the size of the core. Is large, and it is easy to secure a phase matching condition. In this case, the relationship between the size of the silicon core 210 and the refractive index and the thickness of the polymer clad 230 may be determined based on the following theoretical basis.

The chromatic dispersion σ for the light propagating in the core of the optical waveguide is related to the change amount (dβ / dλ, d ² β / dλ ² ) according to the wavelength of the wave vector β of the traveling light. It is related to the changes with the wavelength of the effective refractive index n _eff .

Where c is a constant and represents the speed of light. The effective refractive index of the light traveling through the optical waveguide can be calculated or experimentally measured by conventional optical waveguide theory, and Equations 2 and 3 below show effective refractive indices for vertical polarization and horizontal polarization, respectively. How the lower substrate, that is, the refractive index n _sub of the silica substrate 220 and the refractive index n _clad of the _clad 230, the thickness t _{clad of the clad} 230, and the refractive index n _core and thickness t _{core of the core} 210 An analytical two-dimensional equation showing the degree involved in. The effective refractive index n _eff for the actual optical waveguide structure can be accurately calculated by conventional three-dimensional optical waveguide numerical analysis or can be obtained through experimental measurements.

Equations 2 and 3 illustrate a case of calculating the effective refractive index n _eff for the two-dimensional case with respect to the basic refractive index n _core of the silicon core 210 used as the core optical waveguide. In the structure provided by the present invention, n _sub indicates a refractive index of the silica substrate 220 which is a lower substrate, and n _clad indicates a refractive index of the polymer _clad 230. However, in the case of Equations 2 and 3, since the two-dimensional equation is expressed, the effective effective refractive index can be accurately calculated by the numerical analysis of the three-dimensional method, and in this case as well, The effective refractive index for the wavelength is related to the refractive index of the core 210 and the clad 230, the silica substrate 220 and the core 210 size and the clad 230 thickness.

In the conventional invention, the phase synchronization condition between the pump light and the nonlinear generated optical signals is obtained by obtaining abnormal chromatic dispersion with only the core size for the fixed refractive index of the silicon core 110 and the silica clad 120. Determining the thickness of the silicon core 210 to maximize the non-linear effect, and adjusts one of the refractive index or the thickness of the polymer clad 230, or by adjusting both the refractive index and the thickness of the polymer clad 230 to prevent abnormal color dispersion With this structure, phase synchronization condition can be obtained.

In particular, the conventional method may cause a change in the characteristics of the non-linear optical device due to the change in the effective refractive index in the core according to the temperature change, but in the device structure according to the present invention constant effective refractive index in the core by selecting the appropriate refractive index of the clad material In addition to increasing the temperature stability, it also has a dispersive effect control function to match the phase of the pump light with the nonlinear photon-generated light.

FIG. 3 illustrates a phenomenon in which phase matching between the pump light and optical signals generated by the nonlinear optical effect in the silicon core waveguide occurs in FIG. 2.

FIG. 3 schematically illustrates a phenomenon in which phase matching between a pump light and a signal generated by a nonlinear optical effect occurs in a silicon core waveguide in a nonlinear optical waveguide. In the case of the silicon core optical waveguide 300, the effective refractive index of the silicon core 210 has an abnormal chromatic dispersion with respect to the pump light and a normal chromatic dispersion with respect to the nonlinear generated optical signals Signal. In the case of normal chromatic dispersion, mutual phase matching is achieved.

Meanwhile, the nonlinear silicon optical waveguide device according to the present invention may further include an optical wavelength separation means 340 connected to one side of the silicon core 210 to separate the nonlinear optical signals from the pump light. . Here, the optical wavelength separation means 340 may be composed of optical fiber type optical elements. The optical wavelength separation means 340 may use, for example, a diffraction grating, a wavelength splitting coupler, an arrayed waveguide grating (AWG), an optical fiber bragg grating (FBG), or the like.

4 illustrates a structure of a nonlinear silicon optical waveguide device by controlling a refractive index of a polymer clad according to another embodiment of the present invention.

4 shows a planted strip optical waveguide in which a core 410 composed of silicon having a refractive index n ₁ is formed in silica 420 which is a non-conductor of refractive index n ₂ , and composed of a polymer clad 430 having only a refractive index n ₃ . The structure of a silicon optical waveguide device for generating a nonlinear optical signal in the form of an embedded strip waveguide is shown.

Using the structure of FIG. 4, the phase matching between the pump light and the nonlinear optical signals may be performed by adjusting the refractive index of the polymer clad 430 as in FIG. 2.

5 illustrates the structure of a nonlinear silicon optical waveguide device by controlling the refractive index of a polymer clad according to another embodiment of the present invention.

A layer composed of silicon having a refractive index n ₁ is formed entirely on the silica substrate 520 having a refractive index n ₂ , and has a structure in which only the core portion 510 protrudes. 5 shows a structure of a silicon optical waveguide device for generating a nonlinear optical signal in the form of a rib waveguide formed of a polymer clad 530 having a refractive index n ₃ on the top and side surfaces of the silicon core 510.

FIG. 6 illustrates a structure of a nonlinear silicon optical waveguide device by controlling a refractive index of a polymer clad according to another embodiment of the present invention.

6 is a structural core 610 consisting of a silicone having a refractive index n ₁ is planted in the non-conductor 620, the refractive index n _2, the polymer is part of the upper surface of body and side of the silicon core 610 having a refractive index n ₃ greater It is a structure composed of rads.

That is, a silicon optical waveguide for generating a nonlinear optical signal in the form of a strip waveguide in which a top surface and a part of a side are formed of a polymer clad 630 in a structure in which a silicon core 610 is planted on the inside of the silica substrate 620. Device structure.

5 and 6, phase matching between the pump light and the nonlinear optical signals may be performed by controlling the refractive index of the polymer in which the effective refractive index of the core contacts the upper and side surfaces.

2, 4, and 6, in the case of FIG. 2, the silicon core 210 has the largest area in contact with the polymer clad 230, and in the case of FIG. 4, the silicon core 410. ) Is the smallest area in contact with the polymer clad 430, the case of Figure 6 is in the middle of Figures 2 and 4. The larger the area where the silicon core is in contact with the polymer clad, the more sensitive it is to the change in refractive index of the polymer clad. That is, in FIG. 2, even if the change in the refractive index of the polymer clad 230 is small, the phase change of the nonlinear optical signals is large. In FIG. 4, even if the change in the refractive index of the polymer clad 430 is large, the nonlinear light is large. The phase change of the signals is small.

7 is a flowchart illustrating a method for manufacturing a nonlinear silicon optical waveguide device by controlling the refractive index of the polymer clad according to the present invention.

First, silicon cores 210, 410, 510, and 610 receiving pump light are formed on silica substrates 220, 420, 520, and 620 which are insulators (step 710). In this case, a non-conductor silica substrate uses a conventional planar substrate in the case of FIGS. 1 and 5, and a substrate having a groove having a size equal to the width w of the silicon core in FIGS. 4 and 6.

Next, an appropriate polymer clad 230, 430, 530, 630 to be formed around the silicon cores 210, 410, 510, 610 is determined (step 720). In this case, the appropriate polymer cladding 230, 430, 530, and 630 is a refractive index for matching the propagation phase of the pump light with nonlinear optical signals generated by nonlinear optical effects in the silicon cores 210, 410, 510, and 610. Or it means having a thickness.

Preferably, this process 720 may include selecting a polymer material having a refractive index that matches the traveling phase of the nonlinear optical signals and the pump light. In this case, the refractive index may be calculated according to Equations 2 and 3 below.

The polymer clads 230, 430, 530, and 630 are actually formed around the silicon cores 210, 410, 510, and 610 according to the thickness or the refractive index determined in the above process (720).

Preferably, this process (730) is a process of determining the rotational speed in the spin coding process for forming the polymer clad (230, 430, 530, 630) or the concentration of the polymer solution applied to the spin coding It may include.

Finally, in order to control the refractive index of the polymer clads 230, 430, 530, and 630 formed in the above process (730), the polymer clads 230, 430, 530, and 630 are irradiated with ultraviolet rays or heat. Process 740. Through this process (740), the refractive indices of the polymer clads 230, 430, 530, and 630 which exactly match the traveling phase of the nonlinear optical signals and the pump light can be obtained.

On the other hand, the method for manufacturing a nonlinear silicon optical waveguide device by controlling the refractive index of the polymer clad according to the present invention, in order to separate the generated nonlinear optical signal from the pump light, the wavelength separation optical system, that is, optical wavelength separation on one side of the nonlinear silicon optical waveguide device The process of connecting the means 340 may be added.

The nonlinear optical signals generated in the above-described structures may be utilized in quantum optical communication as optical signal pairs in which physical characteristics such as phase and polarization are interconnected. In particular, the present invention enables an efficient and economical light source that can be used in quantum optical communication and quantum computing in the future.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and will be understood by those of ordinary skill in the art that various modifications and variations can be made therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 illustrates a structure of a silicon optical waveguide device for generating a nonlinear optical signal in the form of a silicon core optical waveguide formed in a conventional non-conductive silica.

Figure 2 illustrates the structure of a nonlinear silicon optical waveguide device by controlling the refractive index of the polymer cladding according to an embodiment of the present invention.

FIG. 3 illustrates a phenomenon in which phase matching between the pump light and optical signals generated by the nonlinear optical effect in the silicon core waveguide occurs in FIG. 2.

Figure 4 shows the structure of a nonlinear silicon optical waveguide device by controlling the refractive index of the polymer clad according to another embodiment of the present invention.

FIG. 5 illustrates a structure of a nonlinear silicon optical waveguide device by controlling a refractive index of a polymer clad according to another embodiment of the present invention.

FIG. 6 illustrates a structure of a nonlinear silicon optical waveguide device by controlling a refractive index of a polymer clad according to another embodiment of the present invention.

7 is a flowchart illustrating a method for manufacturing a nonlinear silicon optical waveguide device by controlling the refractive index of the polymer clad according to the present invention.

Claims (10)

A silica substrate which is an insulator; A silicon core formed on the silica substrate and receiving pump light; And A polymer clad formed around the silicon core and having a refractive index or thickness that matches the traveling phase of the pump light with nonlinear optical signals generated by a nonlinear optical effect in the silicon core, The effective refractive index in the silicon core is determined according to the refractive index of the silica substrate, the refractive index and size of the silicon core, and the refractive index and thickness of the polymer clad, The refractive index or thickness of the polymer clad is non-linear silicon optical waveguide device by controlling the refractive index of the polymer clad, characterized in that the effective refractive index is determined to have an abnormal chromatic dispersion at the pump light wavelength. The method of claim 1, Nonlinear silicon optical waveguide device connected to one side of the silicon core, the optical wavelength separation means for separating the non-linear optical signals from the pump light by the refractive index of the polymer clad. The method of claim 2, The optical wavelength separation means, Nonlinear silicon optical waveguide device by controlling the refractive index of the polymer clad, characterized in that consisting of optical fiber type optical elements. The method of claim 1, The silicon core, A nonlinear silicon optical waveguide device formed by adjusting a refractive index of a polymer clad, wherein the entire surface is embedded in a silica substrate, and the surface not covered with the silica substrate is in the form of a planted strip optical waveguide covered with the polymer clad. . The method of claim 1, The silicon core, The silicon layer is formed to cover the silica substrate, and only the core portion protrudes, and the upper surface and the side of the core portion is a rib optical waveguide in which the polymer clad is characterized in that the refractive index control of the polymer clad. Nonlinear silicon optical waveguide device. The method of claim 1, The silicon core, A portion of the core made of silicon is embedded in a silica substrate, and the nonlinear silicon light by controlling the refractive index of the polymer clad, characterized in that a strip optical waveguide is formed in which all of the top and side surfaces of the core are covered with the polymer clad. Waveguide device. Forming a silicon core receiving pump light on a non-conductive silica substrate; And Forming a polymer cladding around the silicon core having a refractive index or thickness that matches the traveling phase of the pump light with the nonlinear optical signals generated by a nonlinear optical effect in the silicon core, The effective refractive index in the silicon core is determined according to the refractive index of the silica substrate, the refractive index and size of the silicon core, and the refractive index and thickness of the polymer clad, The refractive index or thickness of the polymer clad, the effective refractive index is determined so as to have an abnormal chromatic dispersion at the pump light wavelength, the method of manufacturing a non-linear silicon optical waveguide device by controlling the refractive index of the polymer clad. The method of claim 7, wherein Forming the polymer clad around the silicon core, A method of manufacturing a non-linear silicon optical waveguide device by controlling the refractive index of a polymer clad, the method comprising adjusting the thickness of the polymer clad according to the rotational speed in the spin coding process or the concentration of the polymer solution applied. The method of claim 7, wherein Forming the polymer clad around the silicon core, And selecting a polymer material having a refractive index that matches the non-linear optical signals and the propagating phase of the pump light. The method of claim 7, wherein Forming the polymer clad around the silicon core, And irradiating ultraviolet light or applying heat to the polymer cladding to adjust the refractive index of the polymer cladding.

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