KR20230160546A - An optical interferometer - Google Patents

Abstract

Optical interferometry is disclosed. An optical interferometer formed on one side of a substrate according to various embodiments includes an optical splitter that splits an input optical signal into a plurality of optical signals and outputs a plurality of waveguides, one end of which is connected to the output of the optical splitter, and the other end of the waveguide. An optical reflector that is connected and reflects a plurality of divided optical signals propagating through the waveguide, and is located between the waveguide and the optical reflector and is formed to vertically cross the waveguide, and has an optical axis at an angle of 45 degrees or 135 degrees with respect to the one surface. degree direction and may include a quarter-wave plate that changes the polarization state of the plurality of divided optical signals.

Description

AN OPTICAL INTERFEROMETER}

The disclosure below relates to optical interferometry.

An optical interferometer is a device or system that utilizes the phenomenon that the distribution of light intensity varies depending on the relative phase when light from two paths are combined. Since it is difficult to measure the phase of light directly, it is measured using the interference phenomenon and can be used in optical communication using phase modulation.

Optical interferometers have the advantage of being able to be used as sensors because they respond sensitively to changes in the optical path difference of less than one fraction of the wavelength. However, if the optical path difference changes due to some unintended factor, the output may vary. You can. An optical interferometer responds more sensitively to changes in the optical path difference as the optical path length of the interferometer becomes longer, and when birefringence occurs in the optical path, it may have polarization dependence with different characteristics depending on polarization.

Since planar waveguide devices manufactured through semiconductor processes also generally generate birefringence, waveguide-based optical interferometers may also have polarization dependence.

By implementing a light reflector on the top surface of the substrate, various embodiments can simplify the packaging process and increase reliability compared to other examples of optical interferometers that attach bulky Faraday mirrors to the sides of the waveguide chip.

Various embodiments can provide an integrated polarization-insensitive optical interferometer with a stable and simple structure that is advantageous for miniaturization of the optical interferometer by implementing a light reflector on the upper surface of the substrate.

However, technical challenges are not limited to the above-mentioned technical challenges, and other technical challenges may exist.

An optical interferometer formed on one side of a substrate according to an embodiment includes an optical splitter that splits an input optical signal into a plurality of optical signals and outputs them, a plurality of waveguides, one end of which is connected to the output of the optical splitter, and the other end of the waveguide. An optical reflector that is connected and reflects a plurality of divided optical signals propagating through the waveguide, and is located between the waveguide and the optical reflector and is formed to vertically cross the waveguide, and has an optical axis at 45 degrees or 135 degrees with respect to the one surface. direction, and may include a quarter-wave plate that changes the polarization state of the plurality of divided optical signals.

The optical splitter may include a directional coupler (DC) or a multimode interference device (MMI).

The DC or the MMI may have an optical distribution ratio of 1:1.

The waveguide may include a first waveguide of a first length and a second waveguide of a second length.

The first length and the second length may be different from each other.

The first waveguide may be semicircular and the second waveguide may be straight.

The waveguide may include a flat waveguide with a rectangular cross-section.

The light reflector may include a light splitter different from the light splitter and a waveguide different from the waveguide.

The first port of the other optical splitter is connected to the other end, the two ports included in the second port of the other optical splitter are connected to one end and the other end of the other waveguide, respectively, and the other waveguide may be in the form of a loop. there is.

The other waveguide may include a flat waveguide with a rectangular cross-section.

1 is a diagram to explain the principle and polarization dependence of an optical interferometer.
Figure 2 is a diagram to explain the structure of a Michaelson interferometer using a Faraday mirror that can suppress polarization dependence.
Figure 3 is a diagram for explaining another example of an optical interferometer capable of suppressing polarization dependence.
FIG. 4 is a diagram illustrating an optical interferometer capable of suppressing polarization dependence according to various embodiments.
FIG. 5 is a diagram for explaining an example of the light reflector shown in FIG. 4.

Specific structural or functional descriptions of the embodiments are disclosed for illustrative purposes only and may be changed and implemented in various forms. Accordingly, the actual implementation form is not limited to the specific disclosed embodiments, and the scope of the present specification includes changes, equivalents, or substitutes included in the technical idea described in the embodiments.

Terms such as first or second may be used to describe various components, but these terms should be interpreted only for the purpose of distinguishing one component from another component. For example, a first component may be named a second component, and similarly, the second component may also be named a first component.

When a component is referred to as being “connected” to another component, it should be understood that it may be directly connected or connected to the other component, but that other components may exist in between.

Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "have" are intended to designate the presence of the described features, numbers, steps, operations, components, parts, or combinations thereof, but are not intended to indicate the presence of one or more other features or numbers, It should be understood that this does not exclude in advance the possibility of the presence or addition of steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art. Terms as defined in commonly used dictionaries should be interpreted as having meanings consistent with the meanings they have in the context of the related technology, and unless clearly defined in this specification, should not be interpreted in an idealized or overly formal sense. No.

Hereinafter, embodiments will be described in detail with reference to the attached drawings. In the description with reference to the accompanying drawings, identical components will be assigned the same reference numerals regardless of the reference numerals, and overlapping descriptions thereof will be omitted.

1 is a diagram to explain the principle and polarization dependence of an optical interferometer.

An optical interferometer may be a device that measures the interference phenomenon of two lights propagating through different optical paths. Referring to Figure 1, since light is a wave, when light propagating along different paths (P1 and P2, or P3 and P4) meets a point (b or c), interference (e.g., interference) occurs depending on the light path difference or polarization direction. : The type of interference (constructive interference or destructive interference) may vary.

Figure 1(a) shows an example of constructive interference. Referring to (a) of FIG. 1, when the optical path difference (D2 - D1) of different optical paths (P1 and P2) is an integer multiple (e.g., 2 times) of one wavelength of light, constructive interference occurs at point (b). This can happen.

Figure 1(b) shows an example of destructive interference. Referring to (b) of FIG. 2, when the optical path difference (D4 - D3) of different optical paths (P3 and P4) is an odd multiple (e.g., 5 times) of the half wavelength of light, they cancel out at point (c). Interference may occur.

The output of an optical interferometer can become larger when constructive interference occurs and smaller when destructive interference occurs. Optical interferometers can be used as sensors because the results of interference (e.g., constructive interference or destructive interference) vary depending on the optical path difference. However, if the optical path difference changes due to other unintended factors, the output may change and cause errors, so it may be necessary to properly control other factors.

Light incident on an optical interferometer may be split into two lights with different polarizations if birefringence occurs in the optical path inside the interferometer. Depending on the difference in the optical paths of two lights with different polarizations, optical interferometry can have polarization dependence. Optical fibers have a circular cross-section of the core, so in theory they do not have polarization dependence, but in reality, optical fibers are difficult to manufacture perfectly symmetrically, and can be installed in a curved shape, which can cause birefringence. Since planar waveguide devices manufactured through semiconductor processes also generate birefringence, waveguide-based optical interferometers may also generally have polarization dependence.

To improve the reliability of optical interferometry, it may be necessary to suppress polarization dependence. In order to suppress polarization dependence, the components of the optical interferometer can be made insensitive to polarization, or the input polarization can be split into two polarizations perpendicular to each other and then made to pass through an optical interferometer manufactured exactly the same. However, this method may have problems in that it is difficult to integrate in a small size, the number of components of the optical interferometer increases, and it is realistically difficult to manufacture an entirely identical optical interferometer.

Figure 2 is a diagram to explain the structure of a Michaelson interferometer using a Faraday mirror that can suppress polarization dependence.

Referring to FIG. 2, the interferometer 200 may be a Michelson interferometer using a Faraday structure (eg, a Faraday mirror). Interferometer 200 may include a light splitter 203 and one or more Faraday mirrors 205 and 207.

Light emitted from the light source 201 may be split by the light splitter 203 into light propagating through different optical paths (P1 and P2). The split light may have its reflection and polarization direction rotated by 90 degrees through the Faraday mirrors 205 and 207 to return to the same optical path. When light travels back and forth through the optical paths (P1 and P2), the phase of the light changes the same regardless of the input polarization, so polarization dependence can be suppressed. Although the interferometer 200 is relatively simple, it may have the disadvantage of requiring packaging work to attach two Faraday mirrors 205 and 207 to the chip and making it difficult to miniaturize.

Figure 3 is a diagram for explaining another example of an optical interferometer capable of suppressing polarization dependence.

Referring to FIG. 3, the interferometer 300 may be a polarization insensitive optical interferometer. The interferometer 300 may include a light splitter 301, waveguides 303 and 305, a quarter wave plate 307, and a mirror 309 (e.g., a mirror whose cross-section is coated with metal). there is. The light splitter 301, waveguides 303 and 305, and quarter wave plate 307 may be formed on the upper surface of the substrate (e.g., the substrate of a waveguide chip) 311, and the mirror 309 may be formed on the substrate 311. It can be formed on the side. For example, the optical splitter 301 may be a directional coupler (DC) or a multimode interference device (MMI), but is not necessarily limited thereto.

Half of the light passing through the light splitter 301 may propagate along the upper waveguide 303 and the other half may propagate along the lower waveguide 305. Light propagating through the waveguides 303 and 305 passes through the quarter-wave plate (e.g., a quarter-wave plate whose optical axis is oriented at 45 or 135 degrees to the surface of the substrate 311) 307 and then is transmitted by the mirror 309. It can be reflected. Since the reflected light passes through the quarter-wave plate 307 again, the light may pass through the quarter-wave plate 307 a total of two times. As the light passes through the quarter wave plate 307 twice, the polarization of the light may be rotated by 90 degrees (e.g., vertical polarization to horizontal polarization or horizontal polarization to vertical polarization). The fact that the polarization of light is rotated by 90 degrees can be known through calculation of the Jones matrix. Since the polarization of all light can be expressed as the sum of vertical and horizontal polarization, the light incident on the interferometer can also be separated into vertical and horizontal polarization. While the light incident on the interferometer 300 passes through the light splitter 301, is reflected by the mirror 311, and reaches the light splitter 301 again, any one of the two waveguides 303 and 305 (e.g., waveguide ( Light passing through 303)) may be propagated as horizontally polarized light, and light passing through the other (e.g., waveguide 305) may be propagated as vertically polarized light. That is, since there is no optical path difference depending on the incident polarization, the output of the interferometer 300 due to interference (eg, constructive interference or destructive interference) may not be affected by the incident polarization. However, Faraday mirrors (e.g., Faraday mirrors 205 and 207 in FIG. 2) rotate both polarizations in the same direction and by the same angle, but the interferometer 300 rotates the horizontal polarization into vertical polarization and the vertical polarization into horizontal polarization. By rotating it, a relative phase difference of 180 degrees can occur. In terms of the function of rotating polarization, the Faraday mirror (e.g., Faraday mirrors 205 and 207 in FIG. 2) and the interferometer 300 may not perform completely the same operation.

Since the optical interferometer 300 shown in FIG. 3 cannot be applied when the side of the substrate 311 cannot be coated with metal, an optical interferometer according to an embodiment that can implement a light reflector on the upper surface of the substrate 311 will be explained through Figures 4 and 5.

FIG. 4 is a diagram for explaining an optical interferometer capable of suppressing polarization dependence according to various embodiments, and FIG. 5 is a diagram for explaining an example of the light reflector shown in FIG. 4.

Referring to FIGS. 4 and 5 , according to various embodiments, the optical interferometer 400 may be a waveguide-based plain tube insensitive interferometer. The optical interferometer 400 may include a light splitter 401, waveguides 403 and 405, a quarter wave plate 407, and a light reflector 409. The light splitter 401, waveguides 403 and 405, quarter wave plate 407, and light reflector 409 may be formed on one side of the substrate 411 (e.g., the substrate of a waveguide chip). For example, the optical splitter 401 may be a directional coupler (DC) or a multimode interference device (MMI), but is not necessarily limited thereto.

Half of the light that has passed through the light splitter 401 may propagate along the upper waveguide 403 and the other half may propagate along the lower waveguide 405. The light splitter 401 may have a light distribution ratio of 1:1. The length of each waveguide 403 and 405 may be different, and one of the waveguides 403 and 405 (e.g., waveguide 403) may be semicircular and the other (e.g., waveguide 405) may be straight. there is. Each of the waveguides 403 and 405 may be a flat waveguide with a rectangular cross-section.

Light propagating through each waveguide (403 and 405) passes through the quarter-wave plate (e.g., a quarter-wave plate whose optical axis is oriented at 45 or 135 degrees to the surface of the substrate 411) 407 and then into the light reflector 409. It can be reflected and pass through the quarter wave plate 407 again. As light (e.g., horizontally polarized light or vertically polarized light) incident on the optical interferometer 400 passes through the quarter wave plate 407 twice, the polarization of the light may be rotated by 90 degrees. The fact that the polarization of light is rotated by 90 degrees can be known through the calculation of the Jones matrix. Since the optical interferometer 400 has no optical path difference depending on the incident polarization, the output of the optical interferometer 400 due to interference may not be affected by the incident polarization.

The light reflector 409 formed on the upper surface of the waveguide chip 411 may include a light splitter 501 and a waveguide 503. The first port 511 of the optical splitter 501 is connected to the other end of each waveguide 403 and 405, and the two ports 521 and 523 included in the second port 513 of the optical splitter 501 are It may be connected to one end and the other end of the waveguide 503, respectively. The waveguide 503 may have a loop shape or a flat waveguide with a rectangular cross-section.

The hardware devices described above may be configured to operate as one or multiple software modules to perform the operations of the embodiments, and vice versa.

As described above, although the embodiments have been described with limited drawings, those skilled in the art can apply various technical modifications and variations based on this. For example, the described techniques are performed in a different order than the described method, and/or components of the described system, structure, device, circuit, etc. are combined or combined in a different form than the described method, or other components are used. Alternatively, appropriate results may be achieved even if substituted or substituted by an equivalent.

Therefore, other implementations, other embodiments, and equivalents of the claims also fall within the scope of the claims described below.

Claims (10)

In the optical interferometer formed on one side of the substrate,
An optical splitter that splits an input optical signal into a plurality of optical signals and outputs them;
a plurality of waveguides, one end of which is connected to the output of the optical splitter;
an optical reflector connected to the other end of the waveguide to reflect a plurality of divided optical signals propagating through the waveguide; and
A quarter-wave plate ( quarter-wave plate)
Including, optical interferometer.
According to paragraph 1,
The optical splitter,
Directional coupler (DC) or multimode interference device (MMI)
Optical interferometry, including
According to paragraph 2,
The DC or the MMI,
Optical interferometer with a light distribution ratio of 1:1.
According to paragraph 1,
The waveguide is,
a first waveguide of a first length; and
second waveguide of second length
Including, optical interferometer.
According to paragraph 4,
The first length and the second length are different from each other.
According to clause 5,
The first waveguide is,
It is semicircular,
The second waveguide is,
A linear, optical interferometer.
According to paragraph 1,
The waveguide is,
Flat waveguide with a rectangular cross-section
Including, optical interferometer.
According to paragraph 1,
The light reflector,
An optical splitter different from the above optical splitter; and
An optical interferometer comprising a waveguide different from the waveguide.
According to clause 8,
A first port of the other optical splitter is connected to the other end, and two ports included in the second port of the other optical splitter are connected to one end and the other end of the other waveguide, respectively,
An optical interferometer, wherein the other waveguide is in the form of a loop.
According to clause 9,
As for the other waveguides,
Flat waveguide with a rectangular cross-section
Including, optical interferometer.