Thermo-optical phase shifter

Abstract

The present invention provides a thermo-optical phase shifter including a cladding layer and an optical waveguide core, the cladding layer surrounding the optical waveguide core, the optical waveguide core including a first step and a second step, the first step and the second step having different radial dimensions, the thermo-optical phase shifter can improve the efficiency of the phase shifter and reduce optical crosstalk.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to a Chinese patent application with application number 2021112202324, filed on October 20, 2021. The contents of the above application are incorporated herein by reference.

[0002] The present invention relates to the field of integrated optics, and in particular to thermo-optic phase shifters. [Background technology]

[0003] Thermo-optic phase shifters are an important component of photonic integrated circuits. Conventional thermo-optic phase shifters typically include a conductive heater adjacent to or integrated with an optical waveguide. When an electric current flows through the heater, thermal energy is generated in the heater, which can change the refractive index of the waveguide through the thermo-optic effect. Thus, a phase shift occurs in the light wave propagated by the optical waveguide.

[0004] Currently, a common approach to improving the efficiency of thermo-optic phase shifters is to loop the waveguides so that heat generated by one heater can be shared by multiple waveguides. However, in such structures, the waveguides are usually very long, and some portions of the waveguide, such as looped waveguides, cannot be heated. These portions still occupy a large amount of space and do not promote phase shifting. Furthermore, the geometry of the looped waveguide must be carefully optimized, otherwise it will cause excessive optical loss. However, in ring-shaped waveguides, while a too small waveguide spacing can improve the efficiency of the thermo-optic phase shifter, it will cause optical crosstalk between the waveguides. A too large waveguide spacing will make the device too compact and reduce heating efficiency.

[0005] Therefore, there is an urgent need to provide a thermo-optic phase shifter that can balance the heating efficiency and optical crosstalk of the thermo-optic phase shifter. Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a thermo-optic phase shifter that improves the efficiency of the phase shifter and reduces optical crosstalk. [Means for solving the problem]

[0007] According to a first aspect, the present invention provides a thermo-optic phase shifter including a cladding layer and an optical waveguide core, the cladding layer surrounding the optical waveguide core, the optical waveguide core including a first step and a second step, the first step and the second step having different radial dimensions.

[0008] The beneficial effect of the thermo-optic phase shifter according to the present invention is that, based on coupled mode theory, the evanescent coupling between steps with different radial dimensions in the optical waveguide core cannot realize phase matching, so the optical crosstalk at a certain interval between steps with different radial dimensions can be ignored, and compared with the thermo-optic phase shifter with an optical waveguide core using the same radial dimension, the thermo-optic phase shifter according to the present invention has a more compact structure, thereby greatly improving the phase shifting efficiency. It can be seen that the thermo-optic phase shifter according to the present invention can improve the efficiency of the phase shifter and reduce the optical crosstalk.

[0009] In one possible embodiment, the thermo-optic phase shifter further includes a resistive heater surrounded by the cladding layer, located on one side of the optical waveguide core, and separated from the optical waveguide core by the cladding layer, and a certain distance is maintained between the resistive heater and the optical waveguide core to ensure that the optical waveguide core is sufficiently heated and improve the efficiency of the phase shifter, but the distance between the resistive heater and the optical waveguide core cannot be too far, otherwise it will affect the heating efficiency. In this way, when a current flows through the heater, thermal energy is generated, and the waveguides with different radial dimensions at the heater will experience changes in refractive index due to the thermo-optic effect, which will ultimately cause a phase shift in the light wave propagated by the optical waveguide core.

[0010] In one possible embodiment, some optical waveguide cores made of semiconductor materials can be provided with resistance properties by ion doping, in this way, the optical waveguide core itself after doping also has a heating function, when a current flows through the optical waveguide core, thermal energy is generated, and waveguides with different radial dimensions will experience changes in refractive index due to the thermo-optic effect, which ultimately causes a phase shift in the light wave after being propagated by the optical waveguide core.

[0011] In one possible embodiment, the optical waveguide core is spiral or ring-shaped in space, which helps to save space on the optical integrated circuit component and allows for a higher degree of integration of the optical integrated circuit component.

[0012] In one possible embodiment, the optical waveguide core further includes a bridge structure, one end of which is connected to the first step and the other end of which is connected to the second step, and the bridge structure serves to realize the connection of different steps. Optionally, the bent shape of the bridge structure includes at least one of an arc shape, an Euler bend shape, and a sine curve shape.

[0013] In one possible embodiment, the bent portion of the step of the optical waveguide core also includes at least one of an arc shape, an Euler bend shape, and a sine curve shape so as to realize a spatial spiral or ring-shaped distribution.

[0014] In one possible embodiment, the radial dimension of the bridge structure gradually increases or decreases from one end to the other.

[0015] In one possible embodiment, the bridge structure includes a first bridge structure portion having a uniform radial dimension in a spiral waveguide and a second bridge structure portion having a linear waveguide whose radial dimension gradually changes from one end to the other end.

[0016] In one possible embodiment, an air wall or an air groove for thermal insulation is provided in the cladding layer, and the air wall or the air groove is located around the optical waveguide core. By deep dry etching and wet etching process, an air wall or an air groove, for example, an air-filled sealed cavity or an air opening, can be formed around the thermo-optic phase shifter. Such an air wall or an air groove can reduce the heat transfer route, thereby locally collecting heat energy and improving heating efficiency.

[0017] In one possible embodiment, the material of the resistive heater includes, but is not limited to, at least one of titanium nitride, doped silicon, tungsten, gold, or other types.

[0018] In one possible embodiment, the resistive material includes, but is not limited to, at least one of titanium nitride, doped silicon, tungsten, and gold.

[0019] In one possible embodiment, the material of the optical waveguide core includes, but is not limited to, at least one of silicon, silicon nitride, silica, alumina, lithium niobate, polymer, germanium or III-V material or other types.

[0020] In one possible embodiment, the waveguide type of the optical waveguide core includes, but is not limited to, at least one of a channel waveguide, a ridge waveguide, a slot waveguide, a diffused waveguide, or other types.

[0021] In one possible embodiment, the wavelength of the optical waveguide core includes, but is not limited to, at least one of the visible range, O-band, C-band, mid-infrared, or other ranges.

[0022] Other features are described in specific embodiments. [Brief explanation of the drawings]

[0023] [Figure 1] 1A and 1B are plan and cross-sectional views of a thermo-optic phase shifter in accordance with the present invention, without showing an external resistive heater; [Figure 2] 1 shows two different bridge structures according to the present invention. [Figure 3A] FIG. 10 is a plan view of another thermo-optic phase shifter in accordance with the present invention without displaying an external resistive heater. [Figure 3B] 3B is a cross-sectional view taken along line L in FIG. 3A according to the present invention. [Figure 4] 10A and 10B are plan and cross-sectional views of another thermo-optic phase shifter according to the present invention, in which the external resistive heater is not shown. [Figure 5] 5 is a plan view of the thermo-optic phase shifter with air walls and air bottom grooves according to FIG. 4 in accordance with the present invention; [Figure 5A] 1 is a three-dimensional view of another thermo-optic phase shifter with a resistive heater according to the present invention; [Figure 5B] 5B is a plan view of the thermo-optic phase shifter of FIG. 5A in accordance with the present invention. [Figure 5C] FIG. 5C is a cross-sectional view taken along line L in FIG. 5B according to the present invention. [Figure 5D] 5B is a schematic diagram of the thermo-optic phase shifter with air-wall or air-bottom grooves of FIG. 5A according to the present invention; [Figure 6] Simulation results of the operating efficiency of three thermo-optic phase shifters on a silicon photonics platform. DETAILED DESCRIPTION OF THE INVENTION

[0024] In order to clarify the objectives, technical solutions, and advantages of the present invention, the following clearly and completely describes the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. It is clear that the described embodiments are only a part of the embodiments of the present invention, and do not include all the embodiments. All other embodiments obtained based on the embodiments of the present invention without the need for creative efforts by those skilled in the art are within the scope of protection of the present invention. Unless otherwise defined, technical or scientific terms used herein have the ordinary meanings understood by those skilled in the art. As used in this specification, similar words such as "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects.

[0025] To address the problems existing in the prior art, a first embodiment of the present invention provides a thermo-optic phase shifter 10, as shown in FIG. 1, including a cladding layer 101 and an optical waveguide core 102 that has resistive properties provided in advance by ion doping.

[0026] Here, the optical waveguide core 102 includes a first step 1021 and a second step 1022, and the first step 1021 and the second step 1022 have different radial dimensions. In Fig. 1, the radial dimension of the first step 1021 is larger than the radial dimension of the second step 1022. Note that the radial dimension of the first step 1021 may be smaller than the radial dimension of the second step 1022; Fig. 1 is provided for a schematic explanation and is not specifically limited.

[0027] In another possible embodiment, the optical waveguide core 102 itself has conductive properties due to ion doping. In this way, after doping, the optical waveguide core 102 itself also has a heating function. When a current flows through the optical waveguide core, thermal energy is generated, and waveguides with different radial dimensions will experience a change in refractive index due to the thermo-optic effect, ultimately resulting in a phase shift in the light wave propagated by the optical waveguide core. For example, FIG. 1 shows that the optical waveguide core may be composed of a lightly doped silicon ridge waveguide.

[0028] 1 also shows a cross-sectional view corresponding to line L, which shows that adjacent optical waveguide cores on the cross section have different radial dimensions. Based on coupled mode theory, evanescent coupling between different waveguides cannot achieve phase matching, so optical waveguide cores can ignore optical crosstalk at a certain interval between steps with different radial dimensions. Compared with optical waveguide cores with the same radial dimensions, the thermo-optic phase shifter has a more compact structure, which can greatly improve phase shifting efficiency and reduce optical crosstalk.

[0029] In Figure 1, some areas of the signal (S) pad and ground (G) pad are heavily doped to form ohmic contact. A voltage can be passed through the signal (S) and ground (G) areas, generating a current through the waveguide. The solid arrow between the signal (S) pad and ground (G) pad in Figure 1 indicates the direction of current flow, and the dashed arrow 01 in Figure 1 indicates the direction of light input, and the dashed arrow 02 indicates the direction of light output.

[0030] In one possible embodiment, in addition to the optical waveguide cores spatially distributed in a spiral shape as shown in Figure 1, the optical waveguide cores can also be spatially distributed in a ring shape. In the following description, the optical waveguide cores distributed in a spiral shape will be described as an example, and the following structural design will also be applied to a thermo-optic phase shifter in which the optical waveguide cores are distributed in a ring shape.

[0031] In another possible embodiment, the thermo-optic phase shifter 10 further includes a bent bridge structure 1023 to realize a transitional connection between the first step 1021 and the second end 1022 of the optical waveguide core. One end of the bridge structure 1023 is connected to the first step 1021, and the other end of the bridge structure 1023 is connected to the second step 1022. Because the radial dimension of the first step 1021 is different from that of the first step 1022, the radial dimension of the bridge structure 1023 gradually increases from one end to the other, as shown in FIG. 2(a). Optionally, the bent shape of the bridge structure 1023 may include at least one of a circular arc shape, a linear bend shape, an Euler bend shape, a sine curve shape, or other types of shapes. Alternatively, the bridge structure 1023 may include a first bridge structure portion having a uniform radial dimension in a circular waveguide and a second bridge structure portion having a linear waveguide whose radial dimension gradually increases or decreases from one end to the other. For example, as shown in FIG. 2(b), the bent bridge structure 1023 may include one regular bent (having a constant radial dimension) shape and one linear cone shape.

[0032] Although FIG. 1 illustrates an optical waveguide core having two different radial dimensions, the optical waveguide core is not limited to an optical waveguide core having only two different radial dimensions. In one possible embodiment, the optical waveguide core 102 may include steps with two or more different radial dimensions. That is, the thermo-optical phase shifter may further include N third steps and M bridge structures, even if the radial dimensions are entirely or partially different, such that the radial dimensions of two spatially adjacent steps are different. For example, the optical waveguide core 102 in the thermo-optical phase shifter shown in FIG. 3A includes a first step 3021, a second step 3022, a third step 3023, and a bridge structure 3024. The thermo-optical phase shifter in FIG. 3A further includes a signal (S) pad and a ground (G) pad (not shown). Here, the first step 3021, the second step 3022, and the third step 3023 have different radial dimensions. For example, in FIG. 3A, the radial dimension of the first step 3021 is larger than that of the second step 3022, and the radial dimension of the third step 3023 is larger than that of the first step 3021. Note that the bridge structures 3024 each have a different bending shape to achieve bending. A schematic cross-sectional view corresponding to the dashed line L in FIG. 3A is shown in FIG. 3B. As can be seen from FIG. 3B, the radial dimensions of adjacent optical waveguide cores on the cross section are different. Based on the coupled mode theory, the optical waveguide core cannot achieve phase matching for evanescent coupling between steps with different radial dimensions, so the optical crosstalk at a certain interval between optical waveguide cores with different radial dimensions can be ignored. Compared with the optical waveguide cores with the same radial dimensions, the thermo-optic phase shifter has a more compact structure, which can greatly improve the phase shifting efficiency and reduce the optical crosstalk.

[0033] In another possible embodiment, an air barrier for thermal insulation is installed within the cladding layer 101, and the air barrier is positioned around the optical waveguide core to further improve phase shifting efficiency. As shown in FIG. 4, a thermo-optic phase shifter 10 with an air barrier or air-bottom groove, and a corresponding cross-sectional view of the thermo-optic phase shifter 10 along line L, can be shown. Vertical trenches can be fabricated near the different waveguides, the bases of the different waveguides can be cut, and air openings can be formed around the thermo-optic phase shifter using deep dry etching and wet etching processes. This separation can reduce heat transfer routes, locally collect heat energy, and improve heating efficiency.

[0034] To address the problems existing in the prior art, an embodiment of the present invention further provides a thermo-optic phase shifter 10 including a cladding layer 101, an optical waveguide core 102, and a resistive heater 103, as shown in Figures 5A to 5C.

[0035] That is, the optical waveguide core 102 does not need to be ion-doped in advance, and the thermo-optical phase shifter 10 is a typical thermo-optical phase shifter without electrical properties. However, the thermo-optical phase shifter 10 includes a resistive heater 103 surrounded by a cladding layer 101, located on one side of the optical waveguide core 102, and maintained at a certain distance from the optical waveguide core 102 by the cladding layer 101, thereby achieving sufficient heating of the optical waveguide core 102. Optionally, the resistive heater 103 may be located above, beside, or below the optical waveguide core 102, and the material of the resistive heater may include, but is not limited to, at least one of titanium nitride, doped silicon, tungsten, gold, or other types.

[0036] Illustratively, FIG. 5A shows the three-dimensional structure of a thermo-optical phase shifter 10 including a resistive heater 103 and an optical waveguide core 102, FIG. 5B shows a plan view of FIG. 4A, and FIG. 5C is a cross-sectional view taken along line L in FIG. 5B, which shows that adjacent optical waveguide cores on the cross section have different radial dimensions.

[0037] From the structure shown in Figures 5A and 5B, it can be seen that a single resistive heater 103 is positioned on top of the spiral-shaped optical waveguide core. When a voltage is applied across the resistive heater 103, for example, via the signal (S) pad and the ground (G) pad, a current is generated. The solid arrow between the signal (S) pad and the ground (G) pad in Figure 5B indicates the direction of current flow, while the dashed arrow O1 in Figure 5B indicates the direction of light input and the dashed arrow O2 indicates the direction of light output. As the current passing through the resistive heater 103 generates heat, different steps of the optical waveguide core at the resistive heater 103 cause changes in refractive index due to the thermo-optic effect, ultimately resulting in a phase shift in the propagating light wave. Because the radial dimensions between different steps are different, based on coupled mode theory, the evanescent coupling between different waveguides cannot realize phase matching, so the optical waveguide core may neglect optical crosstalk at a certain interval between steps with different radial dimensions, and compared with the optical waveguide core with the same radial dimension, the optical crosstalk may be neglected at a small interval, and compared with the waveguide with the same width, its structure is more compact, thereby greatly improving the phase shift efficiency.

[0038] In another possible embodiment, a thermo-optic phase shifter with a resistive heater may have an air wall or air-bottom groove installed in the cladding layer 101 for thermal insulation. For example, as shown in FIG. 5D, a thermo-optic phase shifter 10 with an air wall or air-bottom groove is shown. Vertical trenches can be fabricated near different waveguides, the bases of the different waveguides can be cut, and air openings can be formed around the thermo-optic phase shifter by deep dry etching and wet etching processes. Such separation can reduce the heat transfer route, thereby locally collecting heat energy and improving heating efficiency.

[0039] The number of turns in the spatial spiral of the optical waveguide core can be adjusted as needed. The number of turns shown in the figure is merely an example; more or fewer turns can result in a longer or shorter overall waveguide length. In this embodiment, the curvature radii of the steps and bridge structures should be selected according to actual needs to minimize optical loss due to bending. The shape of the bends may also be appropriately selected, including but not limited to, at least one of a circular arc, a spline curve, an Euler bend, a sine curve, or other types. To further reduce loss, a multimode waveguide may be used with different steps of the waveguide. The material of the optical waveguide core may include, but is not limited to, at least one of silicon, silicon nitride, silica, alumina, lithium niobate, polymer, germanium, III-V, or other types. The waveguide type of the optical waveguide core may include, but is not limited to, at least one of a channel waveguide, a ridge waveguide, a slot waveguide, a diffusion waveguide, or other types. The wavelength of the optical waveguide core may include, but is not limited to, at least one of the visible range, the O-band, the C-band, the mid-infrared range, or other ranges.

[0040] It should be noted that the application fields of the thermo-optical phase shifter include, but are not limited to, optical sensing, optical computing, optical communication, optical storage, optical radar and other scenes, and the present invention is not limited thereto.

[0041] To verify negligible crosstalk in different optical waveguide cores, we performed a simulation on a set of five silicon waveguides with different radial dimensions. For example, in this simulation, five optical waveguide cores with different radial dimensions were arranged horizontally in parallel, with adjacent steps having different radial dimensions (e.g., 0.5 μm and 0.8 μm, respectively), and the center-to-center spacing between adjacent waveguides was less than 2 μm. Light was launched into one end of the optical waveguide core, and the light passed through the waveguide completely to the right without passing through other waveguides. Therefore, optical crosstalk between adjacent waveguides can be ignored. Although this simulation was performed on straight, different waveguides here, the same concept can also be applied to the thermo-optic phase shifter shown in this example. Comparing the test results, if the five waveguides were the same width, light would pass through the other waveguides and there would be a significant crosstalk problem, but the thermo-optic phase shifter shown in this example had almost no optical crosstalk.

[0042] To verify the improved efficiency of the phase shifter, Figure 6 shows the simulation results of the operating efficiency of three thermo-optic phase shifters on a silicon photonics platform. The three curves represent three phase shifter structures: a conventional straight waveguide phase shifter, a spiral waveguide phase shifter with equal dimensions, and the phase shifter according to this embodiment (the present invention). It can be seen that the spiral waveguide phase shifter with unequal dimensions consumes the least power to achieve a constant phase shift.

[0043] Although the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as defined by the appended claims. Furthermore, the present invention described herein may have other embodiments and may be practiced or realized in multiple ways. [Explanation of symbols]

[0044] 10 Thermo-optic phase shifter 101 Cladding layer 102 Optical waveguide core 103 Resistance heater

Claims

1. A thermo-optic phase shifter including a cladding layer and an optical waveguide core, the cladding layer surrounds the optical waveguide core; the optical waveguide core includes a first step portion and a second step portion, and the first step portion and the second step portion have different radial dimensions; In a plan view of the thermo-optic phase shifter, the optical waveguide core is formed in a spiral shape, a signal pad is provided so as to surround the optical waveguide core, and a ground pad is provided in a central space of the optical waveguide core, and the signal pad and the ground pad generate a current passing through a waveguide of the optical waveguide core, and thermal energy generated by the current flowing through the optical waveguide core is used to heat the optical waveguide core, an air wall or an air bottom groove for heat insulation is provided in the cladding layer, and the air wall or the air bottom groove is located around the optical waveguide core; A thermo-optic phase shifter characterized by:

2. the thermo-optical phase shifter further includes a resistive heater surrounded by the cladding layer, located on one side of the optical waveguide core, and separated from the optical waveguide core by the cladding layer; 2. The thermo-optic phase shifter according to claim 1.

3. The optical waveguide core is provided with resistance properties by ion doping.

2. The thermo-optic phase shifter according to claim 1.

4. the optical waveguide core is a connection portion between the first step portion and the second step portion, and includes a bridge structure having one end connected to the first step portion and the other end connected to the second step portion; 2. The thermo-optic phase shifter according to claim 1.

5. the bent portion of the optical waveguide core and the bridge structure have at least one shape selected from the group consisting of a circular arc shape, a linear bend shape, an Euler bend shape, and a sine curve shape; 5. The thermo-optic phase shifter according to claim 4.

6. The radial dimension of the bridge structure gradually increases from one end to the other end.

5. The thermo-optic phase shifter according to claim 4.

7. the bridge structure includes a first bridge structure portion having a uniform radial dimension in a spiral waveguide, and a second bridge structure portion having a linear waveguide whose radial dimension gradually changes from one end to the other end; 5. The thermo-optic phase shifter according to claim 4.

8. The thermo-optical phase shifter further includes N third step portions having different radial dimensions and M bridge structures, and two adjacent step portions of the thermo-optical phase shifter have different radial dimensions.

4. The thermo-optic phase shifter according to claim 1, wherein the phase shifter is a thermo-optic phase shifter.

9. the material of the optical waveguide core comprises at least one of silicon, silicon nitride, silica, alumina, lithium niobate, polymer, germanium, or III-V material; 4. The thermo-optic phase shifter according to claim 1, wherein the phase shifter is a thermo-optic phase shifter.

10. The waveguide type of the optical waveguide core includes at least one of a channel waveguide, a ridge waveguide, a slot waveguide, or a diffusion waveguide.

4. The thermo-optic phase shifter according to claim 1, wherein the phase shifter is a thermo-optic phase shifter.

11. The wavelength of the optical waveguide core includes, but is not limited to, at least one of the visible light range, the O-band, the C-band, and the mid-infrared range; 4. The thermo-optic phase shifter according to claim 1, wherein the phase shifter is a thermo-optic phase shifter.

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