KR20240055638A - Integrated optical device - Google Patents

Abstract

The present invention discloses an integrated optical device. Its element includes an input waveguide that receives an input optical pulse, an output waveguide connected to the input waveguide and outputting an output optical pulse of the input optical pulse, branched from the input waveguide and connected to the output waveguide, and an output waveguide connected to the input optical pulse. Branch waveguides that provide a portion of a pulse to the output waveguide to generate the output optical pulse, and an optical grating structure that is selectively provided to one of the branch waveguides to decelerate or refract a portion of the input optical pulse. do.

Description

Integrated optical device

The present invention relates to optical devices, and more particularly to integrated optical devices.

Time-bin decoding is one of the methods of creating a qubit using photons. One way to implement time bin decoding is to use an asymmetric Mach Zehnder interferometer (AMZI). A typical asymmetric Mach-Zehnder interferometer could have a spiral optical waveguide.

The problem to be solved by the present invention is to provide an integrated optical device that can increase the degree of integration and production yield.

The present invention discloses an integrated optical device. Its device includes an input waveguide that receives an input optical pulse; an output waveguide connected to the input waveguide and outputting an output optical pulse of the input optical pulse; branch waveguides branched from the input waveguide and connected to the output waveguide, and providing a portion of the input optical pulse to the output waveguide to generate the output optical pulse; and an optical grating structure selectively provided to one of the branch waveguides to decelerate or refract a portion of the input optical pulse.

As described above, the integrated optical device according to an embodiment of the present invention can increase the degree of integration and production yield by reducing the length of the branch waveguide using an optical lattice structure.

Figure 1 is a plan view showing an example of a general optical element.
Figures 2 and 3 are plan views showing an example of a general optical element.
Figure 4 is a plan view showing an example of an integrated optical device according to the concept of the present invention.
Figure 5 is a plan view showing an example of an integrated optical device according to the concept of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The advantages and features of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in different forms. Rather, the embodiments introduced herein are provided so that the disclosed content will be thorough and complete and so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art, and the present invention is defined only by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

The terminology used herein is for describing embodiments and is not intended to limit the invention. As used herein, singular forms also include plural forms, unless specifically stated otherwise in the context. As used in the specification, 'comprises' and/or 'comprising' means that a referenced component, operation and/or element excludes the presence or addition of one or more other components, operations and/or elements. I never do that. Additionally, since this is according to a preferred embodiment, reference signs presented according to the order of description are not necessarily limited to that order.

Additionally, embodiments described in this specification will be described with reference to cross-sectional views and/or plan views, which are ideal illustrations of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for effective explanation of technical content. Accordingly, the form of the illustration may be modified depending on manufacturing technology and/or tolerance. Accordingly, embodiments of the present invention are not limited to the specific form shown, but also include changes in form produced according to the manufacturing process.

Figure 1 shows an example of a general optical element 100.

Referring to FIG. 1, a general optical device 100 may include an asymmetric Mach-Zehnder interferometer. According to one example, a general optical device 100 may include an input waveguide 10, an output waveguide 20, and branch waveguides 30.

The input waveguide 10 may receive the input optical pulse 12 and provide it to the branch waveguides 30 and the output waveguide 20. Input light pulse 12 may include laser light.

Output waveguide 20 may be connected to input waveguide 10 and branch waveguides 30. The output waveguide 20 may extend in the same direction as the input waveguide 10. The output waveguide 20 may output an output optical pulse 14 generated by interference of the input optical pulse 12.

The branch waveguides 30 may branch from the input waveguide 10 and be connected to the output waveguide 20 . According to one example, the branch waveguides 30 may include a first branch waveguide 32 and a second branch waveguide 34. The first branch waveguide 32 and the second branch waveguide 34 may have a first length (L1) and a second length (L2), respectively. The first branch waveguide 32 and the second branch waveguide 34 may have different refractive indices. For example, the first branch waveguide 32 may have a first refractive index (n ₁ ), and the second branch waveguide 34 may have a second refractive index (n ₂ ). The first optical length of the first branch waveguide 32 may be calculated as the product of the first refractive index (n ₁ ) and the first length (L ₁ ). The second optical length of the second branch waveguide 34 may be calculated as the product of the second refractive index (n ₂ ) and the second length (L ₂ ). If the second light length is greater than the first light length, the time difference (T) of the input light pulse 12 may be calculated as the difference between the first light length and the second light length divided by the speed of light.

If the difference in optical length between both paths is greater than the optical pulse width, an output optical pulse 14 divided into two can be obtained at the output end.

To create time bins using asymmetric Mach-Zehnder interferometry, single photons are used instead of light pulses. When a single photon instead of an optical pulse is incident on an asymmetric Mach-Zehnder interferometer as shown in FIG. 1, the photon coming out of the output stage is a superposition of the light that passed through the first branch waveguide 32 and the light that passed through the second branch waveguide 34. It becomes. In other words, it is not determined which path a single photon has taken until it is detected at the output stage, and which path it has taken is determined after the single photon is detected.

When forming a time bin, the difference between the optical length of the first branch waveguide 32 and the optical length of the second branch waveguide 34 must be longer than the coherence length so that the two lights can be distinguished. To use the asymmetric Mach-Zehnder interferometer output stage 106 in a typical time bin production system, the time difference (T) between two optical pulses in the output waveguide 20 must have a value of about 1 ns, which is This means that the length difference is 30 cm. Using free space optics or optical fiber components, an asymmetric Mach-Zehnder interferometer with an optical length difference of 30 cm between both paths can be easily implemented.

Asymmetric Mach-Zehnder interferometers manufactured using free space optical systems or optical fiber components have the problem of increasing the overall size of the components. Recently developed silicon photonics (Si photonics) technology for producing optical waveguides on silicon on insulator (SOI) substrates, planar lightwave circuits, and titanium (on lithium niobate (LiNbO3) substrates) Integrated optical technology, such as producing optical waveguides by doping Ti), etc., is making great progress. Using this technology, a Mach-Zehnder interferometer can be manufactured on a single substrate and the component size can also be reduced. An optical modulator using a high-speed Mach-Zehnder interferometer required for optical communication is manufactured and used using this technology.

The biggest differences between the asymmetric Mach-Zehnder interferometer for forming time bins and the Mach-Zehnder interferometer used in optical communication modulators are the purpose of using the Mach-Zehnder interferometer, the difference in the optical lengths of both optical paths of the Mach-Zehnder interferometer, and the difference in the light source. . The Mach-Zehnder modulator used in optical communication modulators uses continuous wave light and changes the difference in optical length between both optical paths from 0 to wavelength/2 so that constructive or destructive interference can occur at the output end. In an asymmetric Mach-Zehnder modulator for optical communication, the physical length of both optical paths is manufactured to be the same and the optical length of one optical path is changed using voltage.

The asymmetric Mach-Zehnder interferometer for time bin formation does not operate as a modulator, but uses one of the two optical paths as an optical delay line. A single photon is used as a light source, and the difference in the optical lengths of both optical paths must be sufficiently large so that the photonics that have passed through both paths can be distinguished at the output end. If the time difference (T) at the output stage is 1 ns, the difference in optical length between both optical paths should be 30 cm. To realize such a large difference in optical paths, it cannot be changed using voltage, and the physical lengths of both optical paths must be manufactured to be significantly different.

Since the refractive index of silicon is ~3.4, to obtain a T of 1 nS, the difference in optical length between both optical paths on the silicon substrate must be 8.8 cm or more. In addition, the effective refractive index of a silicon channel optical waveguide surrounded by SiO2 with a width of 1.1 m and a height of 0.26 m is 2.88. In this case, for the optical length difference to be 30 cm, the physical length difference between the silicon optical waveguides on both optical paths must be 10.4 cm. do.

It is difficult to make a straight silicon optical waveguide with a length of 10 cm or more, and due to size limitations of silicon-on-insulator substrates or lithium niobate substrates, there is a problem that many optical waveguides with a length of 10 cm or more cannot be manufactured on the substrate. In order to solve this problem and create an optical waveguide with a length of 10 cm or more on a silicon-on-insulator substrate or a lithium niobate substrate, the second branch waveguide 34 may have the spiral structure of FIGS. 2 and 3.

2 and 3 show an example of a general optical element 100.

Referring to FIGS. 2 and 3 , the second branch waveguide 34 of the general optical device 100 may include spiral waveguides.

Referring to FIG. 2, the second branch waveguide 34 may include a circular spiral waveguide.

Referring to FIG. 3, the second branch waveguide 34 may include a square spiral waveguide.

Using the above structure, an optical waveguide of more than 10 cm in length can be made on a silicon-on-insulator or lithium niobate substrate of limited size. However, as optical waveguides manufactured on a silicon-on-insulator substrate or lithium niobate substrate become longer, the following The same problem occurs.

First, as the optical waveguide becomes longer, the yield of optical waveguide manufacturing decreases.

Next, among the losses occurring in silicon optical waveguides, the loss due to surface roughness of the optical waveguide accounts for a large amount. Even if it is possible to manufacture an optical waveguide with a straight line length of 10 cm, it is inevitable that loss due to surface roughness of the optical waveguide increases as the length increases. In a straight silicon optical waveguide, the loss is 1 to 3 dB/cm, which means that when the length becomes 10 cm, the loss becomes 10 to 30 dB.

In the folded structure and the spiral structure, the optical waveguide is not a straight line but a curve, so radiation loss occurs in the curved part of the optical waveguide, where light is emitted to the outside of the optical waveguide. The loss of a silicone tube with a radius of curvature of 50 um surrounded by SiO2 with a height of 0.22 um and a width of 0.5 um is 110 dB/cm. In this case, if the length of the tube is 10 cm, this means that no optical output comes out of the output terminal.

As shown above, when an asymmetric Mach-Zehnder interferometer for forming a time bin is manufactured using a straight optical waveguide with a length of 10 cm or more, or a folded structure or a spiral structure optical waveguide, a problem occurs in which loss rapidly increases in one path. In the case of Mach-Zehnder interferometer for optical communication, if the loss of one optical path is large, the problem can be solved by adjusting the optical distribution ratio of the input optical coupler. In the case of an asymmetric Mach-Zehnder interferometer for forming time bins, if the loss of one optical path is large, a problem occurs in which time bin formation is not performed well at the output stage.

Figure 4 shows an example of an integrated optical device 200 according to the concept of the present invention.

Referring to FIG. 4, the integrated optical device 200 of the present invention may further include an optical grid structure 50 and a modulation electrode 60.

An optical grating structure 50 may be provided in the second branch waveguide 34 . The optical grid structure 50 may be a slow light structure. For example, the optical grating structure 50 may include a photonic crystal waveguide, an all-pass cavity array, a coupled-resonator optical waveguide, and a high-Q microsphere. It may contain microspheres. The optical grating structure 50 may include a plurality of photonic crystals 52 therein. Each of the photonic crystals 52 may include a quantum dot. A second branch waveguide 34 may be provided between the photonic crystals 52 . The optical grating structure 50 can adjust the optical path of a portion of the input optical pulse 12. The optical grating structure 50 may have an effective refractive index of 10 of the refractive index of silicon. If the effective refractive index of the optical grating structure 50 is 10 times the optical refractive index of silicon, the optical length of the second branch waveguide 34 may be about 0.88 cm, corresponding to 30 cm of the optical length of the first branch waveguide 32. . The optical grating structure 50 can increase the effective refractive index of the second branch waveguide 34 and arrange the second branch waveguide 34 in a straight line.

Accordingly, the integrated optical device 200 of the present invention can increase or improve integration and production yield by reducing the extension length of the second branch waveguide 34 using the optical grid structure 50.

The modulation electrode 60 may be provided on the first branch waveguide 32. The modulation electrode 60 can adjust the effective refractive index of the first branch waveguide 32. The modulation electrode 60 can adjust the effective refractive index by heating the first branch waveguide 32. In contrast, the modulation electrode 60 can adjust the effective refractive index by providing an electric field to the first branch waveguide 32.

A first optical coupler 42 may be provided between the input waveguide 10 and the branch waveguides 30. The first optical coupler 42 may include a Wi branch or a multi-mode interferometer. The first optical coupler 42 may be a 1X2 optical coupler. The first optical coupler 42 may be an input optical coupler. The first optical coupler 42 may split the input optical pulse 12 and provide the split signals to the first branch waveguide 32 and the second branch waveguide 34.

A second optical coupler 44 may be provided between the output waveguide 20 and the branch waveguides 30. The second optical coupler 44 may include a Wi branch or a multi-mode interferometer. The second optical coupler 44 may be a 1X2 optical coupler. The second optical coupler 44 may be an output optical coupler. The input optical pulse 12 that has traveled through the second branch waveguide 34 and the first branch waveguide 32 or a single photon of the input optical pulse 12 is combined in the second optical coupler 44 and output waveguide 20 ) can be provided.

Figure 5 shows an example of an integrated optical device 200 according to the concept of the present invention.

Referring to FIG. 5, the integrated optical device 200 of the present invention may include a curved second branch waveguide 34 within the optical grating structure 50.

The input waveguide 10, the output waveguide 20, the first branch waveguide 32, the first optical coupler 42, and the second optical coupler 44 may be configured in the same manner as in FIG. 3.

The second branch waveguide 34 may be bent at 90° or n-shaped within the optical grid structure 50. The input optical pulse 12 in the second branch waveguide 34 may be slowed by the optical grating structure 50. The optical grating structure 50 may reduce or minimize radiation loss of the input optical pulse 12 in the second branch waveguide 34.

The optical grid structure 50 exhibits its characteristics only in a limited wavelength range, and the wavelength bandwidth that can be used is determined depending on its structure. Additionally, depending on the optical grid structure 50, the loss may be greater than the loss when using a general optical waveguide structure without using a slow light structure.

In the case of an optical grid structure, the usable wavelength width can be expressed as normalized delay bandwidth-product (NDBP). The normalized delay-bandwidth (NDBP) is the refractive index (n _g ) of the optical grating structure 50 and the wavelength difference of the input optical pulses 12 in the first branch waveguide 32 and the second branch waveguide 34 ( ) and may be inversely proportional to the wavelength of the input light pulse 12. As research progresses, it has been experimentally proven that in the case of a silicon photonic crystal optical waveguide formed on a silicon-on-insulator substrate, a 23-inch structure can be created when light with a wavelength of 1.5 m is used. Additionally, it has been experimentally proven that loss can be reduced up to 2 dB/cm in the case of silicon photonic crystals formed on a silicon-on-insulator substrate.

Above, embodiments of the present invention have been described with reference to the attached drawings, but those skilled in the art will understand that the present invention can be implemented in other specific forms without changing its technical idea or essential features. You will understand that it exists. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims (1)

an input waveguide that receives an input optical pulse;
an output waveguide connected to the input waveguide and outputting an output optical pulse of the input optical pulse;
branch waveguides branched from the input waveguide and connected to the output waveguide, and providing a portion of the input optical pulse to the output waveguide to generate the output optical pulse; and
An integrated optical device comprising an optical grating structure selectively provided to one of the branch waveguides to slow down or refract a portion of the input optical pulse.