WO2022027851A1 - Thermo-optic phase shifter - Google Patents

Abstract

A thermo-optic phase shifter, comprising: a transmitting waveguide used for light transmission; a heating unit thermally coupled to the transmitting waveguide and used for heating at least part of the transmitting waveguide to change the phase of light passing through the transmitting waveguide; at least one grating structure formed in the inner sidewall or outer surface of the transmitting waveguide and used for reflecting at least once the light in the transmitting waveguide to enable the light to pass though the heated transmitting waveguide twice or more times. The present invention allows light to be repeatedly heated without affecting the volume of the shifter, thus using mode resonance to increase the number of times that light is heated, and effectively improves phase shifting efficiency without increasing the volume of the shifter.

Description

A thermo-optic phase shifter

This application claims the priority of the Chinese patent application with the application number 202010780195.1 and the invention titled "A Thermo-Optic Phase Shifter" filed with the China Patent Office on August 5, 2020, the entire contents of which are incorporated into this application by reference .

technical field

The invention relates to the field of optoelectronic technology, in particular to a thermo-optic phase shifter.

Background technique

With the development of semiconductor technology, the size of the chip has been shrunk to the limit. In order to further develop chips with higher performance and break through Moore's Law, silicon-based optoelectronic chips that can improve performance without reducing the size of the device came into being. Silicon-based optoelectronic chips generally modulate the intensity, amplitude, frequency, phase, polarization, and propagation direction of light through electro-optic, thermo-optic, and acousto-optic methods. Among them, a thermo-optic phase shifter, which uses thermo-optics to realize the phase change of light, is a commonly used functional device in silicon-based chips.

However, the thermo-optic phase shifter in the prior art has low phase shifting efficiency.

SUMMARY OF THE INVENTION

The technical problem solved by the present invention is to provide a thermo-optic phase shifter, which can make the light heated repeatedly without affecting the volume of the phase shifter, so as to use the mode resonance to increase the number of times the light is heated, without increasing the shift. The phase shift efficiency is effectively improved in the case of the volume of the phase device.

In order to solve the above technical problem, an embodiment of the present invention provides a thermo-optical phase shifter, including: a transmission waveguide for transmitting light; a heating unit, thermally coupled to the transmission wave, for at least a part of the transmission waveguide heating to change the phase of light passing through the transmission waveguide; at least one grating structure formed on the inner sidewall or outer surface of the transmission waveguide for at least one reflection of the light in the transmission waveguide to make the transmission waveguide The light passes through the heated transmission waveguide two or more times.

Optionally, for each reflection of the grating structure, the incident TE _i mode is converted into a TE _i+1 mode after the current reflection, where i is a non-negative integer.

Optionally, the transmission waveguide is a multi-mode waveguide; the thermo-optic phase shifter further includes: a first single-mode waveguide optically coupled to the multi-mode waveguide, and incident light is transmitted to the multi-mode waveguide via the first single-mode waveguide. the multi-mode waveguide; a second single-mode waveguide, the second single-mode waveguide is directionally coupled with the multi-mode waveguide, and is used for extracting the light after at least one reflection in the transmission waveguide to form outgoing light, the The outgoing light is TE ₀ mode.

Optionally, the cross-sectional diameter of the first single-mode waveguide is equal to the cross-sectional diameter of the second single-mode waveguide; wherein, the direction of the cross-sectional diameter is perpendicular to the light transmission direction in the multi-mode waveguide .

Optionally, the ratio between the cross-sectional diameter of the multi-mode waveguide and the cross-sectional diameter of the first single-mode waveguide is M˜2M; where M is the number of reflections of the light in the transmission waveguide , the direction of the cross-sectional diameter is perpendicular to the direction of light transmission in the multimode waveguide.

Optionally, the grating structure includes one or more repeated grating units, and different grating structures have different repetition times; wherein, each grating unit includes two adjacent rows of gratings, and the two rows of gratings are adjacent to each other. The arrangement period is the same or different; the extension direction of each row of gratings is the same as the light transmission direction in the transmission waveguide; the grating structure with the repetition times of the grating unit is used to reflect the incident TE _k-1 mode to form TE _k modulo, k is a positive integer.

Optionally, the grating structure for reflecting the incident TE _m mode to form the TE _m+1 mode is located on one side of the heating unit, and the grating structure for reflecting the incident TE _n mode to form the TE _n+1 mode is located on the side of the heating unit. the other side of the heating unit; wherein m is singular, n is even and zero.

Optionally, the average period of the two rows of gratings in each repeated grating unit is determined by the following formula: λ=(n1+n2)Λ; where λ is used to represent the wavelength of the light, and n1 is used to represent the current grating. The modal effective refractive index of the light before the structure reflects, n2 is used to represent the modal effective refractive index of the light reflected by the current grating structure, and Λ is used to represent the average period of the two rows of gratings.

Optionally, the period ratio of the two rows of gratings in each grating unit is 80% to 125%.

Optionally, between different grating structures, the period ratio of the two rows of gratings in the grating unit is the same or different.

Optionally, the heating unit surrounds the outer surface of the transmission waveguide, and the heating unit includes one or more of the following: a metal wire and a doped waveguide.

Optionally, the transmission waveguide is selected from a strip waveguide, a ridge waveguide and a slab waveguide.

Optionally, the grating structure is formed by etching from the inner sidewall or outer surface of the transmission waveguide.

Compared with the prior art, the technical solutions of the embodiments of the present invention have the following beneficial effects:

In the embodiment of the present invention, the grating structure is formed on the inner sidewall or outer surface of the transmission waveguide, and the light passes through the heated transmission waveguide two or more times, so that the volume of the phase shifter is not affected. In this case, the light is repeatedly heated, thereby effectively improving the phase shifting efficiency.

Further, for each reflection of the grating structure, the incident TE _i mode is converted into a TE _i+1 mode after the current reflection, so that the mode of light can be improved during the reflection process, and the optical path can be further controlled to avoid the reflected light. It returns from the single-mode waveguide along the return path, and realizes the coupling and output of the light of the high-order mode.

Further, in the case where the thermo-optic phase shifter further includes a first single-mode waveguide, a second single-mode waveguide is arranged to be directionally coupled with the multi-mode waveguide, so as to convert the transmission waveguide after at least one reflection. The outgoing light is TE ₀ mode, which can effectively form a directional coupler between the multi-mode waveguide and the second single-mode waveguide to realize optical path control and avoid reflected light from the single-mode waveguide. Return along the way, and realize the coupling and output of the light of the high-order mode.

Further, by setting the ratio between the cross-sectional diameter of the multi-mode waveguide and the cross-sectional diameter of the first single-mode waveguide to be M˜2M, where M is the number of reflections of the light in the transmission waveguide , for the light with more reflection times, the thicker multi-mode waveguide is used for resonant transmission, which can effectively reduce the loss of the phase shifter and improve the efficiency of the phase shifter.

Further, the grating structure includes one or more repeated grating units, and different grating structures have different repetition times, wherein each grating unit includes two adjacent rows of gratings, and the distance between the two rows of gratings is If the arrangement period is the same or different, after the light in the TE _k-1 mode is reflected by the grating structure, the mode of the light can be converted from TE _k-1 to TE _k , so that in the process of light reflection by the grating , improve the light mode, further realize the optical path control, avoid the reflected light returning from the single-mode waveguide along the return path, and realize the coupling and output of the high-order mode light.

Further, by arranging that the grating structure for reflecting the incident TE _m mode to form the TE _m+1 mode is located on one side of the heating unit, the grating structure for reflecting the incident TE _n mode to form the TE _n+1 mode is located on the side of the heating unit. The other side of the heating unit, where m is an odd number, n is an even number and zero, can realize the resonant transmission and mode enhancement of light in the heating unit, effectively utilize all the grating structures, and improve the space utilization.

Further, the Bragg formula is used to determine the average period of the two rows of gratings in each grating unit, and different grating structures can be used to reflect the corresponding light, thereby realizing that the light is heated multiple times.

Description of drawings

Fig. 1 is a top-view structural schematic diagram of a thermo-optic phase shifter in an embodiment of the present invention;

2 is a top view of a grating structure for reflecting light in TE ₀ mode to form TE ₁ mode according to an embodiment of the present invention;

3 is a top view of a grating structure for reflecting light in TE ₁ mode to form TE ₂ mode according to an embodiment of the present invention;

4 is a top view of a grating structure for reflecting light in TE ₂ mode to form TE ₃ mode in an embodiment of the present invention;

5 is a top view of a grating structure for reflecting light in TE ₃ mode to form TE ₄ mode according to an embodiment of the present invention;

FIG. 6 is a schematic top-view structure diagram of another thermo-optic phase shifter in an embodiment of the present invention.

detailed description

As mentioned above, in the prior art, a thermo-optic phase shifter can be used to modulate the phase of light. However, the thermo-optic phase shifter in the prior art has low phase shifting efficiency.

In an existing technical solution, the heating efficiency of the heating unit can be improved by adding heat insulating grooves on both sides of the waveguide or making a cantilever beam structure, thereby improving the phase shifting efficiency of the thermo-optic phase shifter.

However, the inventors of the present invention have found through research that the above solution reduces the modulation speed of the thermo-optic phase shifter, increases the technological difficulty and the overall size of the device, and causes the problem of increasing the volume of the phase shifter, which is not conducive to the phase shifter. Use in LiDAR, photonic artificial intelligence and other networks on silicon substrates

In another existing technical solution, the phase shifting efficiency of the thermo-optic phase shifter can be improved by bending the waveguide to increase the heating length of the waveguide.

However, the inventors of the present invention have found through research that the increase in the heating length will also bring about the problem of increasing the volume of the phase shifter, resulting in a limited application range of the phase shifter.

In an embodiment of the present invention, a thermo-optical phase shifter includes: a transmission waveguide for transmitting light; a heating unit thermally coupled to the transmission wave for heating at least a portion of the transmission waveguide to change the passage of light through the transmission waveguide the phase of the light in the transmission waveguide; at least one grating structure formed on the inner sidewall or outer surface of the transmission waveguide for at least one reflection of the light in the transmission waveguide so that the light passes through the heated transmission Waveguide twice or more. Using the above scheme, the light can be repeatedly heated without affecting the volume of the phase shifter, so that the mode resonance is used to increase the number of times the light is heated, and the phase shift efficiency can be effectively improved without increasing the volume of the phase shifter.

In order to make the above objects, features and beneficial effects of the present invention more clearly understood, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Referring to FIG. 1 , FIG. 1 is a schematic top-view structure diagram of a thermo-optic phase shifter in an embodiment of the present invention. The thermo-optic phase shifter may include a transmission waveguide 11 , a heating unit 12 and a grating structure 13 .

The transmission waveguide 11 is used to transmit light, and the heating unit 12 is thermally coupled to the transmission waveguide 11 for heating at least a part of the transmission waveguide 11 to change the phase of light in the transmission waveguide ; The grating structure 13 is formed on the inner sidewall or outer surface of the transmission waveguide 11, and is used to reflect the light in the transmission waveguide 11 at least once, so that the light passes through the heated transmission waveguide 11 twice or more than twice.

Further, the heating unit 12 may surround the outer surface of the transmission waveguide 11, and the heating unit 12 may include one or more of the following: a metal wire and a doped waveguide.

Specifically, a metal wire may be wound on the outer surface of the transmission waveguide 11, and the heating function of the heating unit 12 may be realized by heating the metal wire, for example, a connected electrode may be used for heating.

Doped waveguides may also be formed around the transmission waveguides.

Specifically, in the prior art, the transmission waveguide can be formed on a semiconductor substrate, and then a protective layer (eg, a dielectric layer) is covered on the surface and side surfaces of the transmission waveguide for protection.

In the embodiment of the present invention, before forming the protective layer, a doped waveguide may be formed on the surface or side of the transmission waveguide, so as to emit heat when the current passes through, so as to realize the heating function of the heating unit 12 .

It should be pointed out that conventional heating structures in photonic integrated devices such as PN junction (PN junction) and photonic integration circuit (PIC) can also be used, and the specific structure of the heating unit 12 is not limited in the embodiment of the present invention.

Further, structures such as heat insulating grooves and cantilever beams can be made on both sides of the heating unit 12, which helps to further achieve heat insulation and effectively improve heating efficiency.

Further, the transmission waveguide 11 may be selected from one or more of the following: a strip waveguide, a ridge waveguide and a slab waveguide.

Further, the transmission waveguide 11 may be selected from one or more of the following: a stepped waveguide and a graded waveguide.

Further, the grating structure 13 may be formed by etching from the outer surface of the transmission waveguide 11 .

Specifically, a semiconductor substrate may be provided, the transmission waveguide 11 may be formed on the surface of the semiconductor substrate, and then the surface of the transmission waveguide 11 may be etched to form the grating structure 13 . At this time, the grating structure 13 may be located at The inner sidewall of the transmission waveguide 11 . It can be understood that, when forming the transmission waveguide 11 , a silicon material with a predetermined thickness may be reserved to form the grating structure 13 therein, and the grating structure 13 may be located on the outer surface of the transmission waveguide 11 . Furthermore, after the grating structure 13 is formed, a protective layer may also be formed on the surface of the transmission waveguide 11 .

In the embodiment of the present invention, the grating structure 13 is formed on the inner sidewall or outer surface of the transmission waveguide 11, so that the light can pass through the heated transmission waveguide 11 twice or more than twice without affecting the phase shifter. In the case of volume, the light is repeatedly heated, thereby effectively improving the phase shifting efficiency.

Further, in the thermo-optic phase shifter shown in FIG. 1 , the transmission waveguide 11 may be a multi-mode waveguide 16 , and the thermo-optic phase shifter may further include: a first single-mode waveguide 14 , which is connected to the multi-mode waveguide 14 . The mode waveguide 16 is optically coupled, and the incident light is transmitted to the multi-mode waveguide 16 via the first single-mode waveguide 14 ; the second single-mode waveguide 15 is directionally coupled with the multi-mode waveguide 16 , which is used to extract the light after at least one reflection in the transmission waveguide 11 (16) to form outgoing light, and the outgoing light is TE ₀ mode.

It should be pointed out that a directional coupler can be formed between the multimode waveguide 16 and the second single mode waveguide 15 to realize optical path control. It can be understood that the multimode waveguide 16 is opposite to a part of the second single mode waveguide 15 parallel with a gap (GAP) between them.

In the embodiment of the present invention, when the thermo-optic phase shifter further includes the first single-mode waveguide 14, the second single-mode waveguide 15 is directionally coupled with the multi-mode waveguide 16, so as to connect the The light after at least one reflection in the transmission waveguide is extracted to form outgoing light, and the outgoing light is TE ₀ mode, which can effectively form a directional coupler between the multi-mode waveguide 16 and the second single-mode waveguide 15 to realize optical path control. , to prevent the reflected light from returning from the first single-mode waveguide 14 along the return path, and realize the coupling and output of the light of the high-order mode.

Further, the cross-sectional diameter of the first single-mode waveguide 14 is equal to the cross-sectional diameter of the second single-mode waveguide 15 ; wherein the direction of the cross-sectional diameter is perpendicular to the light in the multi-mode waveguide 16 transfer direction.

In the embodiment of the present invention, by reasonably setting the length of the relatively parallel and the gap (GAP) size between the multimode waveguide 16 and the second single mode waveguide 15, the optical coupling of the TE ₁ mode in the multimode waveguide can be formed in the first TE ₀ mode in the two single-mode waveguides 15, so as to realize the light output in the phase shifter. Further, since the cross-sectional diameter of the first single-mode waveguide 14 and the cross-sectional diameter of the second single-mode waveguide 15 are set It is beneficial to improve the consistency and standardization of process preparation and improve the quality of the device.

Further, the ratio between the cross-sectional diameter of the multi-mode waveguide 16 and the cross-sectional diameter of the first single-mode waveguide 14 may be M˜2M, where M is the light in the transmission waveguide. The number of reflections, it can be understood that if the mode of the incident light is TE ₀ , the output light from the multi-mode waveguide 16 can be _TEM , and the direction of the cross-sectional diameter is perpendicular to the light in the multi-mode waveguide 16 transfer direction.

In the embodiment of the present invention, the ratio between the cross-sectional diameter of the multi-mode waveguide 16 and the cross-sectional diameter of the first single-mode waveguide 14 is set to be M˜2M, where M is where the light is located. The number of reflections in the transmission waveguide 11 (16), for light with more reflections, the thicker multimode waveguide 16 is used for resonant transmission, which can effectively reduce the loss of the phase shifter and improve the efficiency of the phase shifter.

Further, between the first single-mode waveguide 14 and the multi-mode waveguide 16 , an adiabatic mode-spot converter may also be provided to realize the transmission of light from the first single-mode waveguide 14 to the multi-mode waveguide 16 . It should be noted that the adiabatic mode spot converter does not convert the mode of light, that is, when the light TE ₀ transmitted by the first single-mode waveguide 14 enters the multi-mode waveguide 16 after passing through the adiabatic mode spot converter Still can be TE ₀ .

Further, the grating structure includes one or more repeated grating units, and different grating structures have different repetition times; wherein, each grating unit includes two adjacent rows of gratings, and between the two rows of gratings The arrangement period is the same or different; the extension direction of each row of gratings is the same as the light transmission direction in the transmission waveguide; the grating structure with a repetition number of k of grating units is used to reflect the incident TE _k-1 mode to form a TE _k mode , k is a positive integer.

In the embodiment of the present invention, for each reflection of the grating structure, the incident TE _i mode is converted into a TE _i+1 mode after the current reflection, and i is a non-negative integer.

By adopting the solution of the embodiment of the present invention, the mode of light can be improved in the process of two or more reflections, the optical path control can be further realized, the reflected light can be prevented from returning from the single-mode waveguide along the return path, and the high-order Mode light is coupled out.

Referring to FIG. 2 , FIG. 2 is a top view of a grating structure for reflecting light in TE ₀ mode to form TE ₁ in an embodiment of the present invention.

Wherein, the grating structure shown in FIG. 2 is used to reflect light in TE ₀ mode, that is, N=1, then 2N=2 rows of gratings can be included, and the mode of the light is converted from TE ₀ to TE ₁ after reflection .

Further, the periods of the two rows of gratings are Λ ₁₀ and Λ ₀₁ respectively, and the average period of the two rows of gratings can be determined by the following formula:

λ=(n1+n2)Λ;

Among them, λ is used to represent the wavelength of the light, n1 is used to represent the mode effective refractive index of the light before being reflected by the current grating structure, n2 is used to represent the mode effective refractive index of the light after being reflected by the current grating structure, and Λ is used for is the average period of the two rows of gratings. It should be noted that the refractive index of light may change in different modes, and the mode effective refractive index of light is used to represent the refractive index of light in the current mode.

In the embodiment of the present invention, by using the above formula to determine the average period of the two gratings in each grating unit, it can be realized that the light with an appropriate mode order (for example, the light of the TE ₀ mode shown in FIG. 2 is formed by reflection of the gratings) TE ₁ mode) to reflect and achieve a mode change so that the light is heated multiple times.

Further, the periods of the two rows of gratings in each grating unit may be the same or different. On the basis of determining Λ, Λ ₁₀ and Λ ₀₁ may be further determined.

Specifically, if the periods of the two rows of gratings are the same, they are both equal to Λ; if the periods of the two rows of gratings are different, they can be set according to specific conditions and their average value is Λ.

Further, the ratio of the periods of the two grating rows in each grating unit should not be too large, otherwise it is easy to cause poor consistency of the grating structure.

As a non-limiting example, the period ratio of the two rows of gratings in each grating unit may be 80%˜125%. In this embodiment of the present invention, the period ratio of the two rows of gratings may be set to be 90%.

Referring to FIG. 3 , FIG. 3 is a top view of a grating structure for reflecting light in TE ₁ mode according to an embodiment of the present invention.

Wherein, the grating structure shown in FIG. 3 is used to reflect the light of the TE ₁ mode, that is, N=2, then 2N=4 rows of gratings can be included, and the mode of the light is converted from TE ₁ to TE ₂ after reflection .

Further, the periods of the two rows of gratings are Λ ₁₂ and Λ ₂₁ respectively, and the average period of the two rows of gratings can be determined by the following formula:

λ=(n1+n2)Λ;

Among them, λ is used to represent the wavelength of the light, n1 is used to represent the mode effective refractive index of the light before being reflected by the current grating structure, n2 is used to represent the mode effective refractive index of the light after being reflected by the current grating structure, and Λ is used for is the average period of the two rows of gratings.

It can be understood that, since the effective refractive index of light of different mode orders in the same transmission waveguide is usually different, the average period Λ calculated by the two rows of gratings shown in Fig. 3 and the two rows of gratings shown in Fig. The average period Λ varies.

Further, on the basis of determining Λ, Λ ₁₂ and Λ ₂₁ can be further determined.

For more details about the grating structure shown in FIG. 3 , please refer to the grating structure shown in FIG. 2 , which will not be repeated here.

Referring to FIG. 4 , FIG. 4 is a top view of a grating structure for reflecting light in TE ₂ mode according to an embodiment of the present invention.

Wherein, the grating structure shown in FIG. 4 is used to reflect the light of TE ₂ mode, that is, N=3, then 2N=6 rows of gratings can be included, and the mode of the light is converted from TE ₂ to TE ₃ after reflection .

Further, the periods of the two rows of gratings are Λ ₂₃ and Λ ₃₂ respectively, and the average period of the two rows of gratings can be determined by the following formula:

λ=(n1+n2)Λ;

Among them, λ is used to represent the wavelength of the light, n1 is used to represent the mode effective refractive index of the light before being reflected by the current grating structure, n2 is used to represent the mode effective refractive index of the light after being reflected by the current grating structure, and Λ is used for is the average period of the two rows of gratings.

It can be understood that since the refractive indices of light with different mode orders are usually different in the same transmission waveguide, the average period Λ calculated by the two rows of gratings shown in FIG. 4 is the same as the two rows of gratings shown in FIG. The calculated average period Λ varies.

Further, on the basis of determining Λ, Λ ₂₃ and Λ ₃₂ can be further determined.

For more details about the grating structure shown in FIG. 4 , please refer to the grating structures shown in FIG. 2 to FIG. 3 , which will not be repeated here.

Referring to FIG. 5 , FIG. 5 is a top view of a grating structure for reflecting light in TE ₃ mode according to an embodiment of the present invention.

Wherein, the grating structure shown in FIG. 5 is used to reflect the light of TE ₃ mode, that is, N=4, then 2N=8 rows of gratings can be included, and the mode of the light is converted from TE ₃ to TE ₄ after reflection .

Further, the periods of the two rows of gratings are Λ ₃₄ and Λ ₄₃ respectively, and the average period of the two rows of gratings can be determined by the following formula:

λ=(n1+n2)Λ;

Among them, λ is used to represent the wavelength of the light, n1 is used to represent the mode effective refractive index of the light before being reflected by the current grating structure, n2 is used to represent the mode effective refractive index of the light after being reflected by the current grating structure, and Λ is used for is the average period of the two rows of gratings.

It can be understood that, since the refractive indices of light with different mode orders are usually different in the same transmission waveguide, the average period Λ calculated by the two rows of gratings shown in FIG. 5 may be different from those of the two rows shown in FIG. The calculated mean period Λ of the grating varies.

Further, on the basis of determining Λ, Λ ₃₄ and Λ ₄₃ can be further determined.

For more details about the grating structure shown in FIG. 5 , please refer to the grating structures shown in FIG. 2 to FIG. 4 , which will not be repeated here.

It should be pointed out that between different grating structures, the period ratio of the two rows of gratings in the grating unit is the same or different, that is, the ratio between Λ ₁₀ and Λ ₀₁ shown in FIG. 2 may be different from that shown in FIG. 3 . The ratio between Λ ₁₂ and Λ ₂₁ .

In an embodiment of the present invention, the grating structure includes one or more repeated grating units, and different grating structures have different repetition times, wherein each grating unit includes two adjacent rows of gratings, and the two The arrangement period between the gratings is the same or different. After the light in the TE _k-1 mode is reflected by the grating structure, the mode of the light can be converted from TE _k-1 to TE _k , so that the light in the TE k-1 mode can be converted twice. In the process of two or more reflections, the mode of light is improved, and the optical path is further controlled, so as to prevent the reflected light from returning from the single-mode waveguide along the return path, and realize the coupling and output of the light in the high-order mode through the directional coupler.

Referring to FIG. 6 , FIG. 6 is a schematic top-view structural diagram of another thermo-optic phase shifter according to an embodiment of the present invention.

The thermo-optic phase shifter may include the transmission waveguide 11 and the heating unit 12 shown in FIG. 1 , and may also include grating structures 231, 232, 233 and 234.

Wherein, the transmission waveguide 11 can be used to transmit light, and the heating unit 12 is thermally coupled to the transmission waveguide 11 for heating the light in the transmission waveguide 11 to change the phase of the light.

The grating structures 231 , 232 , 233 and 234 may be formed on the inner sidewall or the outer surface of the transmission waveguide 11 for at least one reflection of the light in the transmission waveguide 11 so that the light passes through the heated The waveguide 11 is transmitted twice or more.

Further, the grating structure for reflecting the incident TE _m mode to form the TE _m+1 mode is located at one side of the heating unit, and the grating structure for reflecting the incident TE _n mode to form the TE _n+1 mode is located at the same side. The other side of the heating unit; wherein, m is a singular number, n is an even number and zero.

Specifically, the grating structure 232 is used to reflect the light of the mode TE ₁ , and the grating structure 234 is used to reflect the light of the mode TE ₃ , that is, the grating structure used to reflect the light of the TE _m mode can be arranged in all side of the heating unit.

The grating structure 231 is used to reflect the light of the mode TE ₀ , and the grating structure 233 is used to reflect the light of the mode TE ₂ , that is, the grating structure used to reflect the light of the TE _n mode can be arranged on the heating unit on the other side.

In the embodiment of the present invention, the grating structure for reflecting the incident TE _m mode to form the TE _m+1 mode is located on one side of the heating unit, so as to reflect the incident TE _n mode to form the TE _n+1 The mode grating structure is located on the other side of the heating unit, where m is an odd number, n is an even number and zero, which can realize the resonant transmission and mode enhancement of light in the heating unit, effectively utilize all the grating structures, and improve the space utilization.

It should be pointed out that, since the grating structure only reflects the light that satisfies the foregoing formula, the light that does not satisfy the foregoing formula can directly pass through. That is to say, in the thermo-optic phase shifter shown in FIG. 6 , the mode of the incident light can be set as TE ₀ , so that it will not be reflected in the process of passing through the grating structure 232 , the grating structure 234 , and the grating structure 233 , After being reflected by the grating structure 231, its mode is converted to TE ₁ . After passing through the grating structure 233 , a portion of the transmission waveguide 11 heated by the heating unit 12 for the second time passes through the grating structure 234 and is reflected by the grating structure 232 , and its mode is converted to TE ₂ . Further, a part of the transmission waveguide 11 heated by the heating unit 12 for the third time is reflected by the grating structure 233 , and its mode is converted to TE ₃ . Further, a part of the transmission waveguide 11 heated by the heating unit 12 for the fourth time is reflected by the grating structure 234 , and its mode is converted to TE ₄ .

It can be understood that a second single-mode waveguide as shown in FIG. 1 can also be provided, and the light in the output mode TE ₄ will form a TE ₀ mode in the second single-mode waveguide through a directional coupler, so as to be coupled out.

It should be pointed out that the number of times the light is heated as shown in Figure 6 is increased to 5 times, and the power consumption of the thermo-optic phase shifter to achieve π phase shift can be reduced to around Pπ/5 without causing the thermo-optic phase shifter's power consumption. Increase in rising and falling edge times.

For more details about the thermo-optic phase shifter shown in FIG. 6 , please refer to the thermo-optic phase shifter shown in FIG. 1 , which will not be repeated here.

Further, in the embodiment of the present invention, the single-mode waveguide and the multi-mode waveguide may include a small bending radius waveguide structure capable of realizing 180° transformation of the light propagation direction, including but not limited to Euler curves, circular arcs, elliptical arcs and Quadratic function curve and other structures.

The grating structure can also be implemented according to Moiré gratings and other grating structures that can realize mode resonance.

The semiconductor substrate of the thermo-optic phase shifter shown in FIG. 1 and FIG. 6 can be selected according to the actual situation, including but not limited to silicon dioxide, silicon, silicon nitride, SOI and III-V compounds and other semiconductors and polymers and other materials.

In the embodiment of the present invention, the grating structure is formed on the inner sidewall or the outer surface of the transmission waveguide 11, and the light passes through the heated transmission waveguide 11 twice or more than twice, so that the phase shifter can be maintained without being affected. In the case of volume, the light is heated repeatedly, so that the mode resonance is used to increase the number of times the light is heated, and the phase shift efficiency is effectively improved without increasing the volume of the phase shifter.

Although the present invention is disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, so the protection scope of the present invention should be based on the scope defined by the claims.

Claims (13)

1. A thermo-optic phase shifter, comprising:

   Transmission waveguides for transmitting light;

   a heating unit, thermally coupled to the transmission waveguide, for heating at least a portion of the transmission waveguide to change the phase of light passing through the transmission waveguide;

   At least one grating structure, formed on the inner sidewall or outer surface of the transmission waveguide, is used for at least one reflection of the light in the transmission waveguide, so that the light passes through the heated transmission waveguide twice or more.
2. The thermo-optic phase shifter according to claim 1, wherein, for each reflection of the grating structure, the incident TE _i mode is converted into a TE _i+1 mode after the current reflection, and i is a non-negative integer.
3. The thermo-optic phase shifter according to claim 2, wherein the transmission waveguide is a multi-mode waveguide;

   The thermo-optic phase shifter also includes:

   a first single-mode waveguide, optically coupled to the multi-mode waveguide, and incident light is transmitted to the multi-mode waveguide via the first single-mode waveguide;

   A second single-mode waveguide, the second single-mode waveguide is directionally coupled with the multi-mode waveguide, and is used for extracting the light after at least one reflection in the transmission waveguide to form outgoing light, and the outgoing light is TE ₀ mode .
4. The thermo-optic phase shifter according to claim 3, wherein the cross-sectional diameter of the first single-mode waveguide is equal to the cross-sectional diameter of the second single-mode waveguide;

   Wherein, the direction of the cross-sectional diameter is perpendicular to the light transmission direction in the multimode waveguide.
5. The thermo-optic phase shifter according to claim 3, wherein the ratio between the cross-sectional diameter of the multi-mode waveguide and the cross-sectional diameter of the first single-mode waveguide is M˜2M;

   Wherein, M is the number of reflections of the light in the transmission waveguide, and the direction of the cross-sectional diameter is perpendicular to the light transmission direction in the multimode waveguide.
6. The thermo-optic phase shifter according to any one of claims 1 to 3, wherein the grating structure comprises one or more repeated grating units, and different grating structures have different repetition times;

   Wherein, each grating unit includes two adjacent rows of gratings, and the arrangement period between the two rows of gratings is the same or different;

   The extension direction of each row of gratings is the same as the light transmission direction in the transmission waveguide;

   The grating structure with a repetition number of k of the grating unit is used to reflect the incident TE _k-1 mode to form the TE _k mode, where k is a positive integer.
7. The thermo-optic phase shifter according to claim 6, wherein,

   The grating structure for reflecting the incident TE _m mode to form the TE _m+1 mode is located on one side of the heating unit, and the grating structure for reflecting the incident TE _n mode to form the TE _n+1 mode is located on the heating unit on the other side;

   where m is singular, n is even and zero.
8. The thermo-optic phase shifter according to claim 6, wherein the average period of the two rows of gratings in each repeated grating unit is determined by the following formula:

   λ=(n1+n2)Λ;

   Among them, λ is used to represent the wavelength of the light, n1 is used to represent the mode effective refractive index of the light before being reflected by the current grating structure, n2 is used to represent the mode effective refractive index of the light after being reflected by the current grating structure, and Λ is used for is the average period of the two rows of gratings.
9. The thermo-optic phase shifter according to claim 6, wherein,

   The period ratio of the two rows of gratings in each grating unit is 80% to 125%.
10. The thermo-optic phase shifter according to claim 6, wherein,

    Between different grating structures, the period ratios of the two rows of gratings in the grating unit are the same or different.
11. The thermo-optic phase shifter of claim 1, wherein the heating unit surrounds the outer surface of the transmission waveguide, and the heating unit comprises one or more of the following:

    Metal wires and doped waveguides.
12. The thermo-optic phase shifter according to claim 1, wherein the transmission waveguide is selected from the group consisting of: a strip waveguide, a ridge waveguide and a slab waveguide.
13. The thermo-optic phase shifter according to claim 1, wherein the grating structure is formed by etching from the inner sidewall or the outer surface of the transmission waveguide.

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