An electro-optic modulated waveguide, polarization controller, and phase shifter

Abstract

The application discloses an electro-optical modulation waveguide. The electro-optical modulation waveguide comprises a substrate, a waveguide structure, a cladding structure, a first electrode, a second electrode and a third electrode. The substrate comprises a first groove and a second groove, the first electrode is arranged at the bottom of the first groove, and the second electrode is arranged at the bottom of the second groove. The thickness of the first electrode is less than the depth of the first groove in a first direction, and the thickness of the second electrode is less than the depth of the second groove in the first direction. The waveguide structure is arranged on a first region of the substrate, and the first region is located between the first groove and the second groove. The cladding structure is used for wrapping the waveguide structure, the first electrode and the second electrode. The third electrode is separated from the waveguide structure by the cladding structure. The first electrode, the second electrode and the third electrode are used for loading voltage. The waveguide structure, the first electrode, the second electrode and the third electrode extend in a second direction, and incident light is transmitted in the waveguide structure along the second direction. The first direction is perpendicular to the second direction.

Description

Technical Field

[0001] This application relates to the field of optical communication, and more particularly to an electro-optic modulation waveguide, a polarization controller, and a phase shifter. Background Technology

[0002] Electro-optic modulators, as core components in optical communication and optical interconnect links, are responsible for loading high-speed electrical signals onto optical carrier signals, realizing the conversion of electrical signals to optical signals and the modulation of optical signals by electrical signals. Further improving the modulation efficiency and bandwidth of electro-optic modulators is of paramount importance for enhancing the performance of the entire optical communication system.

[0003] Currently, electro-optic modulation devices typically include a waveguide for transmitting light and electrodes located on both sides of the waveguide. The electrodes apply a transverse electric field to the waveguide to modulate the phase and intensity of the light within it. It should be understood that by shortening the distance between the electrodes and the waveguide, a higher electric field intensity can be generated within the waveguide under the same voltage conditions, thereby improving modulation efficiency. However, if the electrodes are too close to the waveguide, there will be significant spatial overlap with the optical mode field, leading to a substantial increase in optical signal loss and insertion loss. Therefore, improving the modulation efficiency of electro-optic modulation devices without increasing losses is a pressing problem to be solved. Summary of the Invention

[0004] This application provides an electro-optic modulation waveguide, a polarization controller, and a phase shifter, which can effectively improve electro-optic modulation efficiency.

[0005] In a first aspect, this application provides an electro-optic modulation waveguide. The electro-optic modulation waveguide includes: a substrate, a waveguide structure, a cladding structure, a first electrode, and a second electrode. The substrate includes a first groove and a second groove, the first electrode is disposed at the bottom of the first groove, and the second electrode is disposed at the bottom of the second groove. The thickness of the first electrode is less than the depth of the first groove in a first direction, and the thickness of the second electrode is less than the depth of the second groove in the first direction. The waveguide structure is disposed on a first region of the substrate, the first region being located between the first groove and the second groove. The cladding structure is used to enclose the waveguide structure, the first electrode, and the second electrode. The first electrode and the second electrode are used to apply a voltage. The waveguide structure, the first electrode, and the second electrode extend in a second direction, and incident light propagates in the waveguide structure along the second direction. The first direction is perpendicular to the second direction.

[0006] In this embodiment, in the third direction, the first and second electrodes are located adjacent to the sidewalls of the grooves below the waveguide structure on both sides, thus reducing the lateral distance between the electrodes and the waveguide structure. Under the same voltage conditions, reducing the lateral distance between the electrodes and the waveguide structure enhances the lateral electric field strength in the waveguide structure and improves the electro-optic modulation efficiency. Furthermore, since the first and second electrodes are located in the grooves on both sides of the waveguide structure, they are at a certain distance from the waveguide structure in the first direction, which increases the longitudinal distance between the electrodes and the waveguide structure, reducing the transmission loss of the optical signal in the waveguide structure. This design satisfies the requirements for both optical signal loss and modulation efficiency.

[0007] In some possible implementations, the first electrode and the second electrode form an electric field in a third direction, which is perpendicular to the first and second directions, respectively. The electric field formed in the third direction can modulate the incident light, enhancing the practicality of this solution.

[0008] In some possible implementations, an electric field formed in the third direction is used to adjust the phase of the incident light, further enhancing the practicality of this solution.

[0009] In some possible implementations, the incident light includes a first polarized light and a second polarized light, which are orthogonal to each other. The electric field formed in the third direction is used to adjust the polarization state of the incident light, which can effectively solve polarization-related damage in the system such as polarization mode dispersion, polarization-related loss, and polarization-related modulation, thereby improving the performance of the optical fiber communication system.

[0010] In some possible implementations, the electro-optic modulation waveguide further includes a third electrode, which is separated from the waveguide structure by a cladding structure. The third electrode is used to apply a voltage, and it forms an electric field with the first and second electrodes in a first direction. In this implementation, an approximately perpendicular longitudinal electric field distribution can be formed between the first and second electrodes and the third electrode. The superposition of the longitudinal and transverse electric fields can increase the intensity of the longitudinal electric field within the waveguide structure, thereby improving the electro-optic modulation efficiency.

[0011] In some possible implementations, the electric field formed in the first direction is used to adjust the phase of the incident light, enhancing the flexibility of the scheme.

[0012] In some possible implementations, the incident light includes a first polarized light and a second polarized light, which are orthogonal to each other. The electric field formed in the first direction is used to adjust the polarization state of the incident light, which can effectively solve polarization-related damage in the system such as polarization mode dispersion, polarization-related loss, and polarization-related modulation, thereby improving the performance of the optical fiber communication system.

[0013] In some possible implementations, the displacement deviation between the center position of the third electrode and the center position of the waveguide structure in the third direction is less than a first threshold, and the width difference between the third electrode and the waveguide structure in the third direction is less than a second threshold. This design can increase the intensity of the longitudinal electric field within the waveguide structure 20, thereby improving the electro-optic modulation efficiency.

[0014] In some possible implementations, the electro-optic modulation waveguide further includes a fourth electrode and a fifth electrode. The fourth electrode is disposed on a second region of the substrate, and the fifth electrode is disposed on a third region of the substrate. A first groove is located between the first and second regions, and a second groove is located between the first and third regions. A cladding structure is also used to enclose the fourth and fifth electrodes. The fourth and fifth electrodes are used to apply a voltage to form an electric field in a third direction. In this implementation, a transverse electric field can also be formed between the fourth and fifth electrodes. This transverse electric field can be superimposed on the transverse electric field formed between the first and second electrodes to enhance the strength of the transverse electric field within the waveguide structure, thereby improving the electro-optic modulation efficiency under the same voltage conditions.

[0015] In some possible implementations, the first electrode is electrically connected to the fourth electrode, and the second electrode is electrically connected to the fifth electrode. This simplifies implementation, as only one electrode (either the first or fourth) needs to be applied with voltage, and similarly, only one electrode (either the second or fifth) needs to be applied with voltage.

[0016] In some possible implementations, the electro-optic modulation waveguide further includes a protective layer structure for enclosing the cladding structure. The protective layer structure effectively protects the cladding structure.

[0017] In some possible implementations, the waveguide structure is a fully etched structure. That is, there is no waveguide plate made of the same material as the waveguide structure underneath, which enhances the waveguide structure's ability to confine the optical field and reduces losses.

[0018] In some possible implementations, the refractive index of the cladding material is lower than that of the waveguide material, in order to enhance the waveguide structure's ability to confine the optical field.

[0019] In some possible implementations, the first and second electrodes are made of transparent conductive oxide (TCO) materials to increase the electric field strength and improve modulation efficiency.

[0020] Secondly, embodiments of this application provide a polarization controller. The polarization controller includes a controller, a voltage source, and an electro-optic modulation waveguide as described in any of the embodiments of the first aspect above. The controller controls the voltage source to output a voltage to the electrodes of the electro-optic modulation waveguide, thereby causing the electro-optic modulation waveguide to modulate the polarization state of the incident light.

[0021] Thirdly, embodiments of this application provide a phase shifter. The phase shifter includes a controller, a voltage source, and an electro-optic modulation waveguide as described in any of the embodiments of the first aspect above. The controller controls the voltage source to output a voltage to the electrodes of the electro-optic modulation waveguide, thereby causing the electro-optic modulation waveguide to adjust the phase of the incident light. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of an optical fiber communication system;

[0023] Figure 2 This is a schematic diagram of the first structure of the electro-optic modulation waveguide in the embodiments of this application;

[0024] Figure 3 This is a schematic diagram of a second structure of the electro-optic modulation waveguide in the embodiments of this application;

[0025] Figure 4 This is a schematic diagram of the third structure of the electro-optic modulation waveguide in the embodiments of this application;

[0026] Figure 5 This is a schematic diagram of the fourth structure of the electro-optic modulation waveguide in the embodiments of this application;

[0027] Figure 6 This is a schematic diagram of the fifth structure of the electro-optic modulation waveguide in the embodiments of this application;

[0028] Figure 7 This is a schematic diagram of the first simulation result of the electric field strength in the embodiments of this application;

[0029] Figure 8 This is a schematic diagram of the second simulation result of the electric field strength in the embodiments of this application;

[0030] Figure 9(a) is a schematic diagram of the first structure of the polarization controller in the embodiment of this application;

[0031] Figure 9(b) is a schematic diagram of the second structure of the polarization controller in an embodiment of this application;

[0032] Figure 9(c) is a schematic diagram of the third structure of the polarization controller in the embodiments of this application;

[0033] Figure 10(a) is a schematic diagram of the first structure of the electro-optic modulator in the embodiment of this application;

[0034] Figure 10(b) is a schematic diagram of the second structure of the electro-optic modulator in the embodiment of this application;

[0035] Figure 10(c) is a schematic diagram of the third structure of the electro-optic modulator in the embodiments of this application;

[0036] Figure 11 This is a schematic diagram of a fabrication process for an electro-optic modulated waveguide in an embodiment of this application. Detailed Implementation

[0037] This application provides an electro-optic modulation waveguide, polarization controller, and phase shifter, which can effectively improve electro-optic modulation efficiency. The terms "first," "second," etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0038] Figure 1 This is a schematic diagram of an optical fiber communication system. For example... Figure 1 As shown, the transmitter includes an electrical chip, a laser, a modulator, and a wavelength division multiplexer (WDM), etc., and is used to convert electrical signals into optical signals. The electrical chip drives the laser to emit laser light, the modulator modulates the emitted laser light with an electrical signal to obtain an optical signal, and the WDM combines optical signals of different wavelengths and couples the combined optical signal into an optical fiber for transmission. The receiver includes a WDM, a detector, and an electrical chip, etc., and is used to convert optical signals into electrical signals. The WDM separates optical signals of different wavelengths and outputs them to different detectors, and the electrical chip drives the detectors to convert the optical signals into electrical signals. It should be understood that modulators are mainly used in transmitters of optical fiber communication systems and can be divided into electro-optic modulators, electro-absorption modulators, etc. External modulation loads an electrical signal onto an optical carrier to change the characteristics of the optical signal, such as phase or intensity, thereby realizing the conversion of electrical signals into optical signals. The electro-optic modulation waveguide provided in this application is an important component of the modulator.

[0039] The electro-optic modulation waveguide provided in this application will be described in detail below.

[0040] Figure 2This is a schematic diagram of the first structure of the electro-optic modulation waveguide in this application embodiment. Figure 2 As shown, the electro-optic modulation waveguide includes a substrate 10, a waveguide structure 20, a cladding structure 30, a first electrode 401, and a second electrode 402. The substrate 10 includes a first groove 101 and a second groove 102. The first electrode 401 is disposed at the bottom of the first groove 101, and the second electrode 402 is disposed at the bottom of the second groove 102. The thickness of the first electrode 401 is less than the depth of the first groove 101 in a first direction, and the thickness of the second electrode 402 is less than the depth of the second groove 102 in the first direction. The waveguide structure 20 is disposed on a first region 103 of the substrate 10, located between the first groove 101 and the second groove 102. The cladding structure 30 is used to enclose the waveguide structure 20, the first electrode 401, and the second electrode 402. The waveguide structure 20, the first electrode 401, and the second electrode 402 extend in a second direction, and incident light is transmitted in the waveguide structure 20 along the second direction. A voltage is applied to the first electrode 401 and the second electrode 402. In one possible implementation, the first electrode 401 and the second electrode 402 form an electric field in a third direction, namely a transverse electric field, which can modulate the light transmitted in the waveguide structure 20. It should be understood that the first direction, the second direction, and the third direction are mutually perpendicular.

[0041] In some possible implementations, the electro-optic modulation waveguide further includes a protective layer structure 50, which encloses the cladding structure 30 and effectively protects it. The protective layer structure 50 is typically an insulator, and its materials include, but are not limited to, silicon dioxide, silicon nitride, air, and vacuum.

[0042] In some possible implementations, the waveguide structure 20 can employ a fully etched structure, meaning that there is no waveguide plate made of the same material as the waveguide structure 20 beneath it. This enhances the waveguide structure 20's ability to confine the optical field and reduces losses. The cross-sectional shape of the waveguide structure 20 in the first direction includes, but is not limited to, trapezoidal and rectangular shapes. The material of the waveguide structure 20 includes electro-optic materials with linear electro-optic effects, such as thin-film lithium niobate, lithium tantalate, potassium tantalate-niobate, barium titanate, etc. When an electric field is applied to the waveguide structure 20 externally, the refractive index of the waveguide structure 20 can change due to the linear electro-optic effect of the electro-optic material. This change can alter the propagation characteristics of the optical signal in the waveguide, such as the phase, amplitude, or polarization of the optical signal.

[0043] In some possible implementations, the refractive index of the cladding structure 30 is lower than that of the waveguide structure 20, which enhances the waveguide structure 20's ability to confine the optical field. The cladding structure 30 is preferably an insulating material that is transparent in the communication band, has a low refractive index, and a high dielectric constant. Under the same applied voltage conditions, this increases the electric field division of the waveguide structure 20, i.e., increases the electric field strength within the waveguide core, thereby improving modulation efficiency. For example, the cladding structure 30 can preferably be, but is not limited to, perovskite oxides such as calcium titanate (CaTiO3) and calcium carbonate (CaCO3), metal oxides such as alumina (Al2O3) and magnesium oxide (MgO), and fluorides such as lithium fluoride (LiF) and lanthanum fluoride (LaF3). Furthermore, the cladding material can also be commonly used cladding materials such as silicon dioxide and silicon oxynitride.

[0044] Specifically, in this embodiment, the first electrode 401 and the second electrode 402 are located adjacent to the sidewalls of the grooves below both sides of the waveguide structure 20 in the third direction, thus reducing the lateral distance between the electrodes and the waveguide structure 20. Under the same voltage conditions, reducing the lateral distance between the electrodes and the waveguide structure 20 can enhance the lateral electric field strength in the waveguide structure 20 and improve the electro-optic modulation efficiency. Furthermore, since the first electrode 401 and the second electrode 402 are located in the grooves on both sides of the waveguide structure 20, and are a certain distance from the waveguide structure 20 in the first direction, the longitudinal distance between the electrodes and the waveguide structure 20 is increased, reducing the transmission loss of the optical signal in the waveguide structure 20. This design satisfies the requirements for optical signal loss and modulation efficiency.

[0045] Figure 3 This is a schematic diagram of a second structure of the electro-optic modulation waveguide in an embodiment of this application. For example... Figure 3 As shown above, in the above Figure 2 Based on the electro-optic modulation waveguide shown, the electro-optic modulation waveguide may further include a third electrode 403, which is separated from the waveguide structure 20 by the cladding structure 30. The third electrode 403 forms an electric field, i.e., a longitudinal electric field, with the first electrode 401 and the second electrode 402 in a first direction. This longitudinal electric field can also modulate the light transmitted in the waveguide structure 20. In some possible embodiments, the displacement deviation of the center position of the third electrode 403 from the center position of the waveguide structure 20 in a third direction is less than a first threshold, and the width difference between the third electrode 403 and the waveguide structure 20 in a third direction is less than a second threshold. This can increase the intensity of the longitudinal electric field within the waveguide structure 20 and improve the electro-optic modulation efficiency. It should be noted that the third electrode 403 can be as follows: Figure 3 The structure shown is enclosed by a protective layer structure 50, or it can be enclosed by a cladding structure 30; the specific type is not limited here.

[0046] Figure 4This is a schematic diagram of the third structure of the electro-optic modulation waveguide in the embodiments of this application. For example... Figure 4 As shown above, in the above Figure 2 Based on the electro-optic modulation waveguide shown, the electro-optic modulation waveguide may further include a fourth electrode 404 and a fifth electrode 405. The fourth electrode 404 is disposed on a second region 104 of the substrate 10, and the fifth electrode 405 is disposed on a third region 105 of the substrate 10. A first groove 101 is located between the first region 103 and the second region 104, and a second groove 102 is located between the first region 103 and the third region 105. The cladding structure 30 is also used to enclose the fourth electrode 404 and the fifth electrode 405. The fourth electrode 404 and the fifth electrode 405 are used to apply a voltage to form an electric field in a third direction, i.e., a transverse electric field. In some possible embodiments, the first electrode 401 may be electrically connected to the fourth electrode 404, and the second electrode 402 may be electrically connected to the fifth electrode 405, thereby forming a... Figure 4 The diagram shows two stepped electrode structures. This allows for the application of voltage to either the first electrode 401 or the fourth electrode 404, and similarly, to either the second electrode 402 or the fifth electrode 405, making the implementation simpler.

[0047] Figure 5 This is a schematic diagram of the fourth structure of the electro-optic modulation waveguide in the embodiments of this application. For example... Figure 5 As shown, it differs from the above. Figure 4 In the electro-optic modulation waveguide shown, the first electrode 401 may not be electrically connected to the fourth electrode 404, and the second electrode 402 may not be electrically connected to the fifth electrode 405. In this structure, voltages need to be applied to the first electrode 401 and the fourth electrode 404, and also to the second electrode 402 and the fifth electrode 405.

[0048] Figure 4 and Figure 5 The embodiments shown are relative to those described above. Figure 2 The embodiment shown, the Figure 4 and Figure 5 In the embodiment shown, a transverse electric field can also be formed between the fourth electrode 404 and the fifth electrode 405. This transverse electric field can be superimposed with the transverse electric field formed between the first electrode 401 and the second electrode 402 to enhance the intensity of the transverse electric field within the waveguide structure 20, thereby improving the electro-optic modulation efficiency under the same voltage conditions.

[0049] Figure 6 This is a schematic diagram of the fifth structure of the electro-optic modulation waveguide in the embodiments of this application. Figure 6 As shown above, refer to the above Figure 4 The electro-optic modulation waveguide shown above Figure 3Based on the electro-optic modulation waveguide shown, the electro-optic modulation waveguide may further include a fourth electrode 404 and a fifth electrode 405. The distribution of the fourth electrode 404 and the fifth electrode 405 can be referred to the above. Figure 4 The relevant descriptions of the illustrated embodiments will not be repeated here. The third electrode 403 can also form an electric field, i.e., a longitudinal electric field, with the fourth electrode 404 and the fifth electrode 405 in the first direction. It should be understood that an approximately perpendicular longitudinal electric field distribution can be formed between the first electrode 401 and the second electrode 402 and the third electrode 403. In addition, the fourth electrode 404 and the fifth electrode 405 can also form a longitudinal electric field distribution with the third electrode 403. The superposition of the longitudinal electric fields can increase the intensity of the longitudinal electric field within the waveguide structure 20 and improve the electro-optic modulation efficiency.

[0050] In some possible implementations, the above Figures 2-6 The electrodes in the electro-optic modulation waveguide shown are preferably made of transparent conductive oxide (TCO) material with low loss and high conductivity. The use of this TCO material allows for a closer distance between the electrodes and the waveguide, increasing the electric field strength and improving modulation efficiency. It should be understood that electrodes can also be made of metals such as gold, copper, and aluminum. Since metals absorb light, spatial overlap between the electrode and the optical field causes propagation loss of the optical signal; the closer the electrode is to the waveguide structure, the greater the propagation loss. Therefore, the distance between the electrode and the waveguide structure cannot be too close. However, if the distance between the electrode and the waveguide structure is too far, the electric field distribution in the waveguide structure will be weaker under the same voltage conditions, affecting the electro-optic modulation efficiency. Therefore, during the design process, it is necessary to select an appropriate distance between the electrode and the waveguide core based on the requirements for optical signal loss and modulation efficiency.

[0051] It should be understood that, in practical applications, the electrode distribution in electro-optic modulated waveguides is not limited to the above. Figures 2-6 The structure is shown. For example, in some possible implementations, electrodes may also be introduced below the waveguide structure to enhance the electric field strength within the waveguide structure.

[0052] It should also be understood that, based on the electro-optic modulation waveguides described in the above embodiments, the voltage applied to each electrode can be flexibly adjusted according to actual needs, thereby achieving scenarios where only a transverse electric field is applied, only a longitudinal electric field is applied, or both transverse and longitudinal electric fields are applied simultaneously. As an example, please refer to the above... Figure 2 The electro-optic modulation waveguide shown has a voltage V1 applied to the first electrode 401 and a voltage V2 applied to the second electrode 402, thereby generating a transverse electric field. As another example, please refer to the above. Figure 3The electro-optic modulation waveguide shown above allows the third electrode 403 to be grounded. A voltage V1 is applied to the first electrode 401, and a voltage V2 is applied to the second electrode 402, thereby forming a transverse electric field and a longitudinal electric field. As another example, please refer to the above... Figure 3 The electro-optic modulated waveguide shown has the first electrode 401 and the second electrode 402 loaded with the same voltage V1 or both grounded, and the third electrode 403 loaded with voltage V2, thereby forming a longitudinal electric field.

[0053] The following comparison between this application and the traditional scheme is based on the simulation results of the electric field intensity inside the waveguide structure. The traditional scheme refers to the arrangement of electrodes on both sides parallel to the waveguide structure.

[0054] It should be noted that the first simulation result below was obtained by simultaneously applying transverse and longitudinal electric fields to the electro-optic modulated waveguide, with the waveguide structure material being an x-cut thin-film lithium niobate. Here, x-cut specifically refers to the direction perpendicular to the wafer surface being the x-axis of the lithium niobate crystal, i.e., the first direction mentioned above. That is, the first direction corresponds to the x-axis direction of the lithium niobate crystal, the third direction corresponds to the y-axis direction, and the second direction corresponds to the z-axis direction. Lithium niobate is a negative uniaxial crystal, with the same refractive index along both the x and y axes, no = 2.211@1550nm, unlike the z-axis refractive index ne = 2.137@1550nm. The propagation of the optical signal along the z-axis within the waveguide structure can overcome the influence of the birefringence effect of lithium niobate on the phase velocity matching of the optical mode. In the simulation, the electrode material was gold, the substrate was silicon dioxide, and the cladding material was calcium titanate (CaTiO3).

[0055] Figure 7 This is a schematic diagram of the first simulation result of the electric field strength in an embodiment of this application. For example... Figure 7 As shown, (a) represents the simulation results of the electric field strength of the conventional scheme, and (b) represents the simulation results of the electric field strength of this application. According to the simulation results in (a), the VπL value under the transverse electric field is 3.25 V*cm, and the VπL value under the longitudinal electric field is 4.6 V*cm. According to the simulation results in (b), the VπL value under the transverse electric field is 2.13 V*cm, and the VπL value under the longitudinal electric field is 3.09 V*cm. Comparing the simulation results, it can be seen that the modulation efficiency of this application is improved by 34.5% under the longitudinal electric field and by 32.8% under the transverse electric field. Under the same optical transmission loss and the same applied voltage, the electric field strength within the waveguide structure of this application is significantly stronger, and the corresponding VπL value is smaller, indicating that the electro-optic modulation waveguide provided by this application has higher modulation efficiency.

[0056] It should be noted that the VπL value represents the product of the voltage Vπ required across the electrodes and the modulation region length L to produce a phase change of magnitude π for the optical signal. Therefore, a smaller value indicates higher electro-optic modulation efficiency. Figure 7 In the simulation results shown, Vπ specifically refers to the voltage required to generate a π-phase difference between the transverse electric (TE) and transverse magnetic (TM) modes. Furthermore, under the influence of a longitudinal electric field, the principal axes of the lithium niobate crystal rotate by 45°, an angle independent of the strength of the applied longitudinal electric field. However, variations in the strength of this longitudinal electric field can modulate the mode transition between the two orthogonal modes, TE and TM. By applying a longitudinal electric field along the x-axis of the lithium niobate crystal and controlling the phase difference between the TE and TM modes in the new refractive index principal axis system, mode transitions from TE to TM (or from TM to TE) can be achieved. The transverse electric field applied along the y-axis of the lithium niobate crystal causes a very small, negligible rotation angle in the crystal's principal axes; it only alters the phase difference between the two orthogonal modes, TE and TM, and does not affect the mode transition between TE and TM.

[0057] It should be noted that the second simulation result below was obtained by applying only a longitudinal electric field to the electro-optic modulated waveguide, with the waveguide structure material being a z-cut thin-film lithium niobate. Here, z-cut specifically refers to the direction perpendicular to the wafer surface being the z-axis of the lithium niobate crystal, i.e., the first direction mentioned above. The longitudinal electric field is along the z-axis of the thin-film lithium niobate, utilizing the maximum electro-optic coefficient of lithium niobate. The light propagation direction in the waveguide structure is along either the x-axis or y-axis of the lithium niobate crystal.

[0058] Figure 8 This is a schematic diagram of a second simulation result of the electric field strength in an embodiment of this application. For example... Figure 8 As shown, (a) represents the simulation results of the electric field strength of the conventional scheme, and (b) represents the simulation results of the electric field strength of this application. According to the simulation results in (a), the VπL value corresponding to the longitudinal electric field is 1.04 V*cm. According to the simulation results in (b), the VπL value corresponding to the longitudinal electric field is 0.70 V*cm. By comparing the simulation results, it can be seen that the modulation efficiency of this application is improved by 33.6% compared to the conventional scheme. Furthermore, the electric field strength within the waveguide structure of this application is stronger. It should be noted that... Figure 8 In the simulation results shown, Vπ specifically refers to the voltage required to achieve a phase difference of π between the optical signals on the two arms of the electro-optic modulator, and... Figure 7 The simulation results shown describe Vπ differently, but the essence is the same: the value of VπL reflects the modulation efficiency of the device.

[0059] In some possible implementations, any polarized light beam can be composed of the superposition of two orthogonal polarized beams; that is, any polarized light can be decomposed into two orthogonal polarized beams carrying corresponding amplitude and phase information. The electro-optic modulation waveguide provided in this application allows the incident light to be decomposed into a first orthogonal polarized beam and a second polarized beam based on polarization state characteristics. For ease of explanation, the first and second polarized beams will be referred to as TE light and TM light, respectively. Specifically, in the above embodiments, the electric field formed in the third direction (transverse electric field) can adjust the phase difference between the TE light and the TM light, thereby achieving adjustment of the polarization state of the incident light. The electric field formed in the first direction (longitudinal electric field) can adjust the energy ratio between the TE light and the TM light, which can also be understood as adjusting the mode conversion between the TE light and the TM light, thereby achieving adjustment of the polarization state of the incident light.

[0060] In some possible implementations, by optimizing the waveguide structure parameters (such as the width, height, tilt angle, and cladding material), the effective refractive indices of TE and TM light can be made the same or nearly the same, and the phase velocities of TE and TM light propagating within the waveguide structure can be the same. Alternatively, the same phase velocities of TE and TM light propagating within the waveguide structure can also be achieved through other methods, such as thermal tuning. Furthermore, the transmission losses of TE and TM light within the waveguide structure should be the same or nearly the same.

[0061] In some possible implementations, the transverse and longitudinal electric fields described in the above embodiments can also be used to adjust the phase of the incident light. Specifically, the electric field distribution generated within the waveguide structure of the electro-optic modulated waveguide can change the refractive index of the waveguide structure, thereby achieving phase adjustment of the light transmitted within the waveguide structure.

[0062] Considering that the electro-optic modulation waveguide described above can adjust the polarization state of the incident light, it can be applied to a polarization controller. Furthermore, considering that the electro-optic modulation waveguide described above can adjust the phase of the incident light, it can be applied to a phase shifter. The polarization controller and phase shifter provided in the embodiments of this application will be described below.

[0063] It should be understood that in optical communication systems, manufacturing processes can lead to asymmetry in the optical fiber structure and the presence of internal stress, causing the fiber itself to exhibit birefringence. Furthermore, environmental factors such as temperature variations and external stresses in the fiber link can also introduce birefringence, resulting in polarization mode dispersion. This means that the polarization state of the optical signal changes in real time during transmission through the fiber. This change in the polarization state of the optical signal can limit the capacity and transmission distance of high-speed optical communication systems to some extent. Therefore, a polarization controller is needed to control the polarization state of the optical signal in real time. As a device for controlling the polarization state of an optical signal, a polarization controller can convert an input optical signal with an arbitrary polarization state into an output optical signal with another arbitrary polarization state. Polarization controllers are mainly used for real-time control of the polarization state of optical signals in optical communication systems to effectively address polarization-related impairments such as polarization mode dispersion, polarization-dependent loss, and polarization-dependent modulation, thereby improving the performance of optical fiber communication systems.

[0064] Figure 9(a) is a schematic diagram of the first structure of the polarization controller in this application embodiment. As shown in Figure 9(a), the polarization controller can be composed of multiple cascaded electro-optic modulation waveguides to convert light of arbitrary input polarization state into light output of arbitrary polarization state. The electro-optic modulation waveguides can refer to the above-described... Figures 2 to 6 The relevant descriptions of the illustrated embodiments will not be repeated here. It should be understood that in some application scenarios, the polarization controller may also include only one electro-optic modulation waveguide, and this is not limited here. For ease of explanation, this embodiment uses... Figure 6 The following example illustrates a polarization controller formed by cascading electro-optic modulated waveguides. Specifically, the polarization controller also includes a voltage source and a controller (not shown in the figure). The controller controls the voltage source to output voltage to the electrodes of each electro-optic modulated waveguide, thereby allowing the electro-optic modulated waveguide to adjust the polarization state of the incident light. As an example, the polarization controller consists of three cascaded electro-optic modulated waveguides and includes nine electrodes: three ground electrodes and six signal electrodes. Each stage of the electro-optic modulated waveguide can adjust the polarization state of the optical signal within the waveguide structure using transverse and longitudinal electric fields.

[0065] Each electro-optic modulation waveguide in the polarization controller can be understood as a waveplate with adjustable azimuth and variable thickness, achieving high-speed modulation through the electro-optic effect of the material. Under the control of an applied voltage, each stage of the tunable waveplate can change its azimuth for mode conversion modulation, or change its thickness for phase delay (phase difference) modulation, thereby controlling the polarization state of the output optical signal. The specific implementation of the electro-optic modulation waveguide in adjusting the polarization state of the incident light can be found in the description of the above embodiments, and will not be repeated here.

[0066] Polarization controllers can be classified into three types according to their technology: (1) multi-stage waveplate cascade, fixed phase delay, variable azimuth angle; (2) multi-stage waveplate cascade, fixed azimuth angle, variable phase delay; (3) simultaneous variation of phase delay and azimuth angle. Typically, a waveplate cascade type dynamic polarization controller consists of three or more cascaded waveplates, each capable of independent operation. The most common waveplate type dynamic polarization controller scheme is composed of a quarter-wave plate + a half-wave plate + a quarter-wave plate. Utilizing the electro-optic effect of the material, the phase delay of each waveplate can be controlled to be π / 2, π, π / 2 respectively under an applied electrical signal. Simultaneously, the azimuth angle of each waveplate can be endlessly rotated by the applied electrical signal, thereby achieving dynamic polarization control.

[0067] Figure 9(b) is a schematic diagram of the second structure of the polarization controller in an embodiment of this application. As shown in Figure 9(b), unlike the polarization controller shown in Figure 9(a), this polarization controller includes 7 electrodes, including 1 ground electrode and 6 signal electrodes, that is, each electro-optic modulation waveguide shares a ground electrode. Figure 9(c) is a schematic diagram of the third structure of the polarization controller in an embodiment of this application. As shown in Figure 9(c), unlike the polarization controller shown in Figure 9(a), the 3 cascaded electro-optic modulation waveguides are arranged in a curved manner, which can reduce the overall size of the polarization controller.

[0068] In one possible implementation, the phase shifter provided in this application includes a controller, a voltage source, and an electro-optic modulation waveguide. The controller controls the voltage source to output a voltage to the electrodes of the electro-optic modulation waveguide, so that the electro-optic modulation waveguide adjusts the phase of the incident light. Specifically, this phase shifter can be applied in an electro-optic modulator, which will be further described below.

[0069] Figure 10(a) is a schematic diagram of the first structure of the electro-optic modulator in an embodiment of this application. As shown in Figure 10(a), the electro-optic modulator includes a 1×2 beam splitter, a 2×1 beam combiner, and two phase shifters on the two arms. Specifically, the optical signal is split into two parts by the 1x2 beam splitter at the optical input end and transmitted to the phase shifters on the two arms respectively. At least one phase shifter on the arm is used to adjust the phase of the optical signal, thereby changing the intensity or phase of the optical signal at the optical output end. The optical signals of the two arms are combined by the 2x1 beam combiner, and the two optical signals interfere with each other, causing the characteristics of the combined output optical signal to change compared to the input optical signal. The change in the characteristics of the optical signal can be reflected in the intensity or phase of the light. The modulated optical signal is output from the optical output end. It should be understood that the phase shifters of the two arms of this electro-optic modulator may share at least one electrode or may not share one. Figure 10(b) is a schematic diagram of the second structure of the electro-optic modulator in an embodiment of this application. As shown in Figure 10(b), the phase shifters of the two arms share one electrode. Figure 10(c) is a schematic diagram of the third structure of the electro-optic modulator in the embodiments of this application. As shown in Figure 10(c), the phase shifters of the two arms do not share a single electrode. It should be understood that in practical applications, the structure of the electro-optic modulator is not limited to the electro-optic modulator shown in Figure 10(a) above. The electro-optic modulator can also adopt structures such as micro-ring resonators or Fabry-Perot (FP) resonators.

[0070] It should be noted that the electro-optic modulation waveguide provided in this application can be used not only in the polarization controllers and phase shifters described above, but also in other electro-optic devices involving electro-optic modulation such as electro-optic switches, sensors, and frequency shifters. Specific applications are not limited here.

[0071] The fabrication method of the electro-optic modulation waveguide provided in this application is described below, with a specific example below. Figure 6 The electro-optic modulated waveguide shown is used as an example for introduction.

[0072] Figure 11 This is a schematic diagram illustrating one fabrication process of the electro-optic modulated waveguide in an embodiment of this application. Figure 11 As shown, the fabrication process of the electro-optic modulated waveguide can be roughly divided into 6 steps (a)-(f).

[0073] (a) Step: This preparation method begins with a bilayer structure consisting of an electro-optic material and a substrate. The electro-optic material is preferably lithium niobate, but other electro-optic materials such as lithium tantalate, potassium tantalate niobate, and barium titanate can also be used. The substrate material is an insulator, such as silicon dioxide. Furthermore, a carrier can be located beneath the substrate; the carrier material can be silicon, quartz, lithium niobate, etc.

[0074] (b) Step: A fully etched waveguide structure is formed on a lithium niobate thin film electro-optic material layer. Substrate grooves of a certain width and depth are formed on the substrate on both lateral sides of the waveguide structure. This process can be based on photolithography and etching techniques. The tilt angle of the sidewalls of the waveguide structure can be 30 degrees to 90 degrees. The sidewalls of the substrate grooves can be vertical or have a certain tilt angle.

[0075] (c) Step: Form electrodes on both sides of the waveguide structure. This process can be achieved through techniques such as electron beam evaporation, magnetron sputtering, atomic layer deposition, or electroplating. The electrode material is preferably a TCO material, but it can also include materials such as gold, copper, and aluminum.

[0076] (d) Step: Form a cladding structure around the waveguide structure and in the substrate groove. This process can be achieved using techniques such as magnetron sputtering, thermal evaporation, and atomic layer deposition. The cladding structure is preferably an insulating material that is communication-transparent, has a low refractive index, and a high dielectric constant, such as calcium titanate or alumina, but it can also be made of materials such as silicon dioxide or silicon oxynitride.

[0077] (e) Step: Form an upper electrode on the upper surface of the cladding structure above the waveguide structure. The implementation technique and electrode material for this process are the same as in step (c) above.

[0078] (f) Step: Forming a protective layer structure on the cladding structure. This process can be achieved using techniques such as plasma-enhanced chemical vapor deposition (PECVD) or chemical vapor deposition (CVD). The protective layer structure material can be silicon dioxide, silicon nitride, or air or a vacuum.

[0079] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An electro-optic modulation waveguide, characterized in that, include: The device comprises a substrate, a waveguide structure, a cladding structure, a first electrode, and a second electrode. The waveguide structure and the substrate form a double-layer structure. The substrate includes a first groove and a second groove. The first electrode is disposed at the bottom of the first groove, and the second electrode is disposed at the bottom of the second groove. The thickness of the first electrode is less than the depth of the first groove in a first direction, and the thickness of the second electrode is less than the depth of the second groove in the first direction. The waveguide structure is disposed on a first region of the substrate, which is located between the first groove and the second groove. The cladding structure is used to enclose the waveguide structure, the first electrode, and the second electrode. The first electrode and the second electrode are used to apply a voltage. The waveguide structure, the first electrode, and the second electrode extend in a second direction, and incident light is transmitted in the waveguide structure along the second direction, where the first direction is perpendicular to the second direction.

2. The electro-optic modulation waveguide according to claim 1, characterized in that, The first electrode and the second electrode form an electric field in a third direction, which is perpendicular to the first direction and the second direction, respectively.

3. The electro-optic modulation waveguide according to claim 2, characterized in that, The electric field formed upwards by the third party is used to adjust the phase of the incident light.

4. The electro-optic modulation waveguide according to claim 2 or 3, characterized in that, The incident light includes a first polarized light and a second polarized light, the first polarized light and the second polarized light being orthogonal to each other, and the electric field formed in the third direction is used to adjust the polarization state of the incident light.

5. The electro-optic modulation waveguide according to claim 2 or 3, characterized in that, The electro-optic modulation waveguide further includes a third electrode, which is separated from the waveguide structure by the cladding structure. The third electrode is used to apply a voltage, and the third electrode forms an electric field with the first electrode and the second electrode in the first direction.

6. The electro-optic modulation waveguide according to claim 5, characterized in that, The electric field formed in the first direction is used to adjust the phase of the incident light.

7. The electro-optic modulation waveguide according to claim 5, characterized in that, The incident light includes a first polarized light and a second polarized light, the first polarized light and the second polarized light being orthogonal to each other, and the electric field formed in the first direction is used to adjust the polarization state of the incident light.

8. The electro-optic modulation waveguide according to claim 5, characterized in that, The displacement deviation between the center position of the third electrode and the center position of the waveguide structure in the third direction is less than a first threshold, and the width difference between the third electrode and the waveguide structure in the third direction is less than a second threshold.

9. The electro-optic modulation waveguide according to claim 2 or 3, characterized in that, The electro-optic modulation waveguide further includes a fourth electrode and a fifth electrode. The fourth electrode is disposed on a second region of the substrate, and the fifth electrode is disposed on a third region of the substrate. The first groove is located between the first region and the second region, and the second groove is located between the first region and the third region. The cladding structure is also used to enclose the fourth electrode and the fifth electrode. The fourth electrode and the fifth electrode are used to apply a voltage, and the fourth electrode and the fifth electrode form an electric field in the third direction.

10. The electro-optic modulation waveguide according to claim 9, characterized in that, The first electrode is electrically connected to the fourth electrode, and the second electrode is electrically connected to the fifth electrode.

11. The electro-optic modulation waveguide according to any one of claims 1 to 3, characterized in that, The electro-optic modulation waveguide further includes a protective layer structure for wrapping the cladding structure.

12. The electro-optic modulation waveguide according to any one of claims 1 to 3, characterized in that, The waveguide structure is a fully etched structure.

13. The electro-optic modulation waveguide according to any one of claims 1 to 3, characterized in that, The refractive index of the cladding structure is less than that of the waveguide structure.

14. The electro-optic modulation waveguide according to any one of claims 1 to 3, characterized in that, The first electrode and the second electrode are made of transparent conductive oxide (TCO) materials.

15. A polarization controller, characterized in that, include: The controller, voltage source, and electro-optic modulated waveguide as described in any one of claims 1 to 14, wherein the controller is configured to control the voltage source to output a voltage to the electrodes of the electro-optic modulated waveguide, so that the electro-optic modulated waveguide modulates the polarization state of the incident light.

16. A phase shifter, characterized in that, include: The controller, voltage source, and electro-optic modulated waveguide as described in any one of claims 1 to 14, wherein the controller is configured to control the voltage source to output a voltage to the electrodes of the electro-optic modulated waveguide, such that the electro-optic modulated waveguide modulates the phase of the incident light.

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