A testing method for optical waveguides

Abstract

This invention provides a testing method for optical waveguides, relating to the field of optical waveguide testing. The required instruments for this testing method include a laser source, a microscope objective, a measuring instrument, a spectrometer, a coupling device, and a prism. The testing employs a prism coupling method, using a high-refractive-index prism to achieve phase matching between the incident light wave and the waveguide mode, thus realizing waveguide optical excitation. This invention improves the sensitivity and accuracy of optical waveguide testing, enabling the measurement of minute changes in optical parameters and providing accurate measurement results. It allows for rapid measurement, significantly reducing testing time and enabling testing to be completed in a short period. Furthermore, it allows for real-time monitoring and analysis of the testing process, thereby providing crucial data support for the design, manufacturing, and performance evaluation of optical waveguide devices.

Description

Technical Field

[0001] This invention relates to the field of optical waveguide testing, specifically to a testing method for optical waveguides. Background Technology

[0002] The effective refractive index of an optical waveguide is a crucial parameter characterizing it. Knowing the effective refractive index allows for the calculation of the waveguide's propagation constant, and subsequently, based on the waveguide's dispersion equation, the thickness, dielectric constant, and other parameters of the waveguide medium. Therefore, calculating the waveguide film thickness and refractive index by measuring the effective refractive index of an optical waveguide is of great significance for the design of waveguide devices. Traditional optical waveguide testing generally employs the m-line method, which involves observing the m-line with the naked eye, recording the angle, and calculating the effective refractive index. However, due to significant human visual error and considering the special cases where the m-line is difficult to observe, the m-line error can sometimes be substantial, leading to inaccurate refractive index results for optical waveguides. Therefore, this invention proposes a testing method for optical waveguides, effectively solving the aforementioned problems and difficulties. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, this invention provides a testing method for optical waveguides. By closely contacting or bringing a prism close to the optical waveguide, the prism enables efficient coupling of light from the light source to the optical waveguide and from the optical waveguide to the detection device. This improves the sensitivity and accuracy of optical waveguide testing, allowing for the measurement of minute changes in optical parameters and providing accurate measurement results. It also enables rapid measurement, significantly reducing testing time and allowing for completion of tests in a short period. Furthermore, the detection process can be monitored in real time, allowing for real-time observation and analysis of the measurement process. This provides crucial data support for the design, manufacturing, and performance evaluation of optical waveguide devices.

[0005] (II) Technical Solution

[0006] To achieve the above objectives, the present invention provides the following technical solution: a testing method for optical waveguides, wherein the instruments required for this testing method include a laser light source, a microscope objective, a measuring instrument, a spectrometer, a coupling device, and a prism; the steps of this optical waveguide testing method are as follows:

[0007] S1: Adjust the laser source's emitting head to a horizontal position so that the laser emitted by the laser and the optical waveguide of the microscope objective are in the same straight line;

[0008] S2: After adjustment, turn on the laser source to emit laser light. The laser light shines on the coupling device and is refracted onto the glass. The light is coupled into the glass through the three-dimensional adjustment frame and the optical waveguide stage. Then, slowly adjust the three-dimensional adjustment frame and the optical waveguide stage to couple the light into the optical waveguide.

[0009] S3: Adjust the optical wave stage to observe the number of light rays forming optical waveguides in the glass matrix;

[0010] S4: Fix the coupling device and the prism together so that there is an air gap between the waveguide layer, i.e. the thin film surface of the coupling device and the prism, and observe the refraction angle of the light waveguide refracted from the prism into the coupling device.

[0011] S5: When the prism is fixed together with the coupling device as the output coupling, each mode of the output light corresponds to a different incident angle. By receiving the output light through the spectrum analyzer, the pattern line corresponding to the mode can be observed. When the pattern appears in the corresponding direction, the light waveguide image appears with the bright spot as the center in the direction perpendicular to the output surface. As the distance from the waveguide increases, the degree of curvature becomes gentler and the brightness becomes darker.

[0012] S6: In the prism coupling test method for optical waveguides, when the incident angle θ is greater than the critical angle for total internal reflection... When light beam particles penetrate the waveguide layer, i.e., the thin film of the coupling device, they excite the waveguide guided mode to form the input beam. Coupling occurs when the incident angle θ equals the propagation constant β of the light wave in the waveguide. The formulas for calculating the refractive index and thickness of the waveguide are:

[0013] (2π / λ0)(cosθ)hn3+ψ 10 +ψ 12 =mπ:

[0014] in:

[0015] Where ψ 10 express:

[0016] Phase shift between the air gap and the thin-film waveguide layer of the coupling device;

[0017] ψ 12 express:

[0018] Phase shift between the thin-film waveguide layer of the coupling device and the surface of the substrate layer of the coupling device;

[0019] mπ is the phase matching condition for stable propagation of the guided wave mode, where the total phase change of the guided wave mode in the vertical direction of the thin film guided wave layer of the coupling device is an integer multiple of π. λ0 is the wavelength of the incident laser in vacuum.

[0020] Preferably, the test method for the optical waveguide is to use the prism coupling method. The prism coupling uses a high refractive index prism to achieve phase matching between the incident light wave and the waveguide mode to realize waveguide optical excitation.

[0021] Preferably, in the prism coupling test method for this optical waveguide, the refractive index of the air gap is n0, the refractive index of the thin film layer (i.e., the waveguide layer) of the coupling device is n1, the refractive index of the substrate layer is n2, and the refractive index of the prism is n... p， If the incident angle of the sawtooth ray of the waveguide mode at the upper and lower interfaces of the thin film is θ, the thickness of the thin film is h, and the height of the air gap is d, then the propagation constant β of this beam in the waveguide is:

[0022] β=k z = k1 sinθ.

[0023] Where k1 is the total wavenumber of the light wave in the waveguide layer, i.e. the thin film of the coupling device. Specifically, it describes the total phase change of the light wave per unit length in the waveguide layer and is the core parameter reflecting the waveguide layer's ability to modulate the phase of the light wave. k2 is the wavenumber component of the light wave in the z-direction perpendicular to the waveguide propagation direction, i.e., perpendicular to the plane of the waveguide layer.

[0024] Preferably, in the prism coupling test method of the optical waveguide, the intensity of the incident beam should not be too weak or too strong. If the beam is too weak, the transmission line brightness will be too low; if the beam is too strong, it may cause the spectrum analyzer to saturate and affect the fitting accuracy.

[0025] Preferably, in the prism coupling test method of the optical waveguide, the laser source probe should not be too close to the waveguide, and the laser source, except for the lens, should be wrapped with a black cloth to reduce reflected light interference.

[0026] Preferably, in the prism coupling test method of the optical waveguide, near the coupling point between the prism and the waveguide, the scattered light is particularly strong, so this part needs to be covered with a strip of black paper.

[0027] Working principle: In this prism coupling detection method for optical waveguides, the prism base angle θ0 is first measured. Then, after the beam reaches a specified angle on the prism's incident surface, the reflected light on the prism's incident surface is made to strictly coincide with the pinhole, determining the initial incident angle of the beam. The synchronization angle of three adjacent guided modes is then measured on the spectrum of a spectrometer, thereby determining the angular position θ. n 0， n 1， n 2， The thickness and refractive index of the thin film can be solved by using the propagation constants of the four adjacent guided modes n3 and the refractive index and thickness calculation formula of the waveguide.

[0028] (III) Beneficial Effects

[0029] This invention provides a testing method for optical waveguides. It has the following beneficial effects:

[0030] This invention provides a testing method for optical waveguides. The waveguide testing employs a prism coupling test method. Compared to the traditional m-line observation test method, the prism coupling test method achieves efficient coupling of light from the light source to the waveguide and from the waveguide to the detection device by closely contacting or bringing the prism close to the waveguide. This improves the sensitivity and accuracy of the optical waveguide test, allowing for the measurement of minute changes in optical parameters and providing accurate measurement results. It also enables rapid measurement, significantly reducing test time and allowing for completion of the test in a short period. Furthermore, it allows for real-time monitoring and analysis of the measurement process, providing crucial data support for the design, manufacturing, and performance evaluation of optical waveguide devices. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the refraction principle of the prism coupling test method for the optical waveguide testing method of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In the description of this application, it should be noted that the terminology used herein is only for describing specific implementations and is not intended to limit the exemplary implementations according to this application. For ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings indicate similar items, and therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0033] Example 1:

[0034] like Figure 1 As shown, this embodiment of the invention provides a testing method for optical waveguides. The instruments required for this testing method include a laser light source, a microscope objective, a measuring instrument, a spectrometer, a coupling device, and a prism. The steps of this optical waveguide testing method are as follows:

[0035] S1: Adjust the laser source's emitting head to a horizontal position so that the laser emitted by the laser and the optical waveguide of the microscope objective are in the same straight line;

[0036] S2: After adjustment, turn on the laser source to emit laser light. The laser light shines on the coupling device and is refracted onto the glass. The light is coupled into the glass through the three-dimensional adjustment frame and the optical waveguide stage. Then, slowly adjust the three-dimensional adjustment frame and the optical waveguide stage to couple the light into the optical waveguide.

[0037] S3: Adjust the optical wave stage to observe the number of light rays forming optical waveguides in the glass matrix;

[0038] S4: Fix the coupling device and the prism together so that there is an air gap between the waveguide layer, i.e. the thin film surface of the coupling device and the prism, and observe the refraction angle of the light waveguide refracted from the prism into the coupling device.

[0039] S5: When the prism is fixed together with the coupling device as the output coupling, each mode of the output light corresponds to a different incident angle. By receiving the output light through the spectrum analyzer, the pattern line corresponding to the mode can be observed. When the pattern appears in the corresponding direction, the light waveguide image appears with the bright spot as the center in the direction perpendicular to the output surface. As the distance from the waveguide increases, the degree of curvature becomes gentler and the brightness becomes darker.

[0040] S6: In the prism coupling test method for optical waveguides, when the incident angle θ is greater than the critical angle for total internal reflection... When light beam particles penetrate the waveguide layer, i.e., the thin film of the coupling device, they excite the waveguide guided mode to form the input beam. Coupling occurs when the incident angle θ equals the propagation constant β of the light wave in the waveguide. The formulas for calculating the refractive index and thickness of the waveguide are:

[0041] (2π / λ0)(cosθ)hn3+ψ 10 +ψ 12 =mπ:

[0042] Where ψ 10 express:

[0043] Phase shift between the air gap and the thin-film waveguide layer of the coupling device;

[0044] ψ 12 express:

[0045] Phase shift between the thin-film waveguide layer of the coupling device and the surface of the substrate layer of the coupling device;

[0046] mπ is the phase matching condition for stable propagation of the guided wave mode, where the total phase change of the guided wave mode in the vertical direction of the thin film guided wave layer of the coupling device is an integer multiple of π. λ0 is the wavelength of the incident laser in vacuum.

[0047] The optical waveguide was tested using a prism coupling method. A high-refractive-index prism was employed for prism coupling to achieve phase matching between the incident light wave and the waveguide mode, thus exciting the waveguide. The refractive index of the air gap was n0, the refractive index of the thin film layer (waveguide layer) of the coupling device was n1, the refractive index of the substrate layer was n2, and the refractive index of the prism was n... p， If the incident angle of the sawtooth ray of the waveguide mode at the upper and lower interfaces of the thin film is θ, the thickness of the thin film is h, and the height of the air gap is d, then the propagation constant β of this beam in the waveguide is:

[0048] β=k z = k1sinθ.

[0049] Where k1 is the total wavenumber of the light wave in the waveguide layer, i.e. the thin film of the coupling device. Specifically, it describes the total phase change of the light wave per unit length in the waveguide layer and is the core parameter reflecting the waveguide layer's ability to modulate the phase of the light wave. k2 is the wavenumber component of the light wave in the z-direction perpendicular to the waveguide propagation direction, i.e. perpendicular to the plane of the waveguide layer.

[0050] When the incident angle θ is greater than the critical angle for total internal reflection When light beam particles penetrate the thin film, they excite the waveguide guided mode to form the input beam. When the incident angle θ equals the propagation constant β of the light wave in the waveguide, coupling occurs. The formulas for calculating the refractive index and thickness of the waveguide are:

[0051] (2π / λ0)(cosθ)hn3+ψ 10 +ψ 12 =mπ

[0052] (ψ 10 and ψ 12 (This refers to the phase shift between the air-film and film-substrate surfaces).

[0053] In this prism coupling test method for optical waveguides, the intensity of the incident beam should not be too weak or too strong. If the beam is too weak, the transmission line brightness will be too low; if the beam is too strong, it may cause the spectrum analyzer response to saturate, affecting the fitting accuracy. The laser source probe should not be too close to the waveguide. The laser source, except for the lens, should be wrapped with black cloth to reduce reflected light interference. Near the coupling point between the prism and the waveguide, due to the particularly strong scattered light, this part needs to be covered with black paper strips. In this prism coupling detection method for optical waveguides, firstly, the prism base angle θ0 needs to be measured. Secondly, after the beam reaches a specified angle on the prism incident surface, the reflected light on the prism incident surface should be strictly aligned with the pinhole to determine the initial incident angle of the incident beam. The synchronization angle of three adjacent guided modes is measured on the spectrum of the spectrum analyzer to determine the angular position θ. 0， n 1， n 2， The thickness and refractive index of the thin film can be solved by using the propagation constants of the four adjacent guided modes n3 and the refractive index and thickness calculation formula of the waveguide.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A testing method for optical waveguides, characterized in that: The instruments required for this optical waveguide testing method include a laser light source, a microscope objective, a measuring instrument, a spectrometer, a coupling device, and a prism. The steps of this optical waveguide testing method are as follows: S1: Adjust the laser source's emitting head to a horizontal position so that the laser emitted by the laser and the optical waveguide of the microscope objective are in the same straight line; S2: After adjustment, turn on the laser source to emit laser light. The laser light shines on the coupling device and is refracted onto the glass. The light is coupled into the glass through the three-dimensional adjustment frame and the optical waveguide stage. Then, slowly adjust the three-dimensional adjustment frame and the optical waveguide stage to couple the light into the optical waveguide. S3: Adjust the optical wave stage to observe the number of light rays forming optical waveguides in the glass matrix; S4: Fix the coupling device and the prism together so that there is an air gap between the waveguide layer, i.e. the thin film surface of the coupling device and the prism, and observe the refraction angle of the light waveguide refracted from the prism into the coupling device. S5: When the prism is fixed together with the coupling device as the output coupling, each mode of the output light corresponds to a different incident angle. By receiving the output light through the spectrum analyzer, the pattern line corresponding to the mode can be observed. When the pattern appears in the corresponding direction, the light waveguide image appears with the bright spot as the center in the direction perpendicular to the output surface. As the distance from the waveguide increases, the degree of curvature becomes gentler and the brightness becomes darker. S6: In the prism coupling test method for optical waveguides, when the incident angle θ is greater than the critical angle for total internal reflection... When light beam particles penetrate the waveguide layer, i.e., the thin film of the coupling device, they excite the waveguide guided mode to form the input beam. Coupling occurs when the incident angle θ equals the propagation constant β of the light wave in the waveguide. The formulas for calculating the refractive index and thickness of the waveguide are: (2π / λ0)(cosθ)hn3+ψ 10 +ψ 12 =mπ: Where ψ 10 express: Phase shift between the air gap and the thin-film waveguide layer of the coupling device; ψ 12 express: Phase shift between the thin-film waveguide layer of the coupling device and the surface of the substrate layer of the coupling device; mπ is the phase matching condition for stable propagation of the guided wave mode, where the total phase change of the guided wave mode in the vertical direction of the thin-film guided wave layer of the coupling device is an integer multiple of π. λ0 is the wavelength of the incident laser in vacuum.

2. The testing method for an optical waveguide according to claim 1, characterized in that: The test method for this optical waveguide is to use the prism coupling method. The prism coupling uses a high refractive index prism to achieve phase matching between the incident light wave and the waveguide mode to realize waveguide optical excitation.

3. The testing method for an optical waveguide according to claim 1, characterized in that: In this prism coupling test method for optical waveguides, the refractive index of the air gap is n0, the refractive index of the thin film layer (waveguide layer) of the coupling device is n1, the refractive index of the substrate layer is n2, and the refractive index of the prism is n... p， If the incident angle of the sawtooth ray of the waveguide mode at the upper and lower interfaces of the thin film is θ, the thickness of the thin film is h, and the height of the air gap is d, then the propagation constant β of this beam in the waveguide is: β=k z =k1 sinθ. Where k1 is the total wavenumber of the light wave in the waveguide layer, i.e. the thin film of the coupling device. Specifically, it describes the total phase change of the light wave per unit length in the waveguide layer and is the core parameter reflecting the waveguide layer's ability to modulate the phase of the light wave. k2 is the wavenumber component of the light wave in the z-direction perpendicular to the waveguide propagation direction, i.e., perpendicular to the plane of the waveguide layer.

4. The testing method for an optical waveguide according to claim 1, characterized in that: In the prism coupling test method for this optical waveguide, the intensity of the incident beam should not be too weak or too strong. If the beam is too weak, the transmission line brightness will be too low; if the beam is too strong, it may cause the spectrum analyzer to saturate and affect the fitting accuracy.

5. The testing method for an optical waveguide according to claim 1, characterized in that: In the prism coupling test method for this optical waveguide, the laser source probe should not be too close to the waveguide, and the laser source, except for the lens, should be wrapped with a black cloth to reduce reflected light interference.

6. The testing method for an optical waveguide according to claim 1, characterized in that: In the prism coupling test method for this optical waveguide, near the coupling point between the prism and the waveguide, the scattered light is particularly strong, so this part needs to be covered with a strip of black paper.

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