CN117492236B

CN117492236B - Thermo-optic phase shifter

Info

Publication number: CN117492236B
Application number: CN202311558181.5A
Authority: CN
Inventors: 李明; 李昂; 谢毓俊; 孙雨舟; 杨先超; 任之良; 赵志勇; 李伟; 祝宁华
Original assignee: Institute of Semiconductors of CAS
Current assignee: Institute of Semiconductors of CAS
Priority date: 2023-11-21
Filing date: 2023-11-21
Publication date: 2024-07-16
Anticipated expiration: 2043-11-21
Also published as: CN117492236A

Abstract

The invention relates to the technical field of optical communication electronic devices, and provides a thermo-optical phase shifter, which comprises: a substrate, a cladding layer, a multilayer core waveguide network, and a heat source; wherein the cladding layer is positioned on the upper surface of the substrate; each core layer waveguide network is positioned in the cladding layer and is arranged in a layered manner in the vertical direction relative to the upper surface of the substrate, and the projections of the waveguide paths of two adjacent core layer waveguide networks on the substrate are at least partially overlapped or partially overlapped; the heat source is arranged in the cladding layer, is positioned above the multilayer core layer waveguide network, and has an intersection area with the projection of at least part of the multilayer core layer waveguide network on the substrate. The thermal-optical phase shifter fully utilizes space, reduces phase shift power consumption, effectively improves phase shift efficiency of the thermal-optical phase shifter, reduces the volume of the thermal-optical phase shifter, enables the design of the thermal-optical phase shifter to be flexible and compatible with the existing silicon-based process, and reduces implementation cost.

Description

Thermo-optic phase shifter

Technical Field

The invention relates to the technical field of optical communication electronic devices, in particular to a thermo-optical phase shifter.

Background

With the development of semiconductor technology and the advent of the big data age, the size and performance of integrated electric chips have been approaching the limit, but the rapid expansion of information makes it difficult for the bandwidth of electric chips to increase at a speed that meets the increasing demand of data volume, so new ways are needed to solve the limit problem of electric chips in terms of transmission and bandwidth. A silicon-based optoelectronic chip aimed at realizing optical interconnection has been developed, and a method for modulating in the silicon-based optoelectronic chip includes modulating intensity, phase, frequency, amplitude, polarization, etc. of an optical signal by thermo-optical, electro-optical, acousto-optic, magneto-optical, etc. The thermo-optical phase shifter which utilizes the thermo-optical effect of silicon materials to realize the phase modulation of optical signals is a functional device in silicon-based photoelectrons.

The thermo-optic phase shifters are currently typically implemented by high resistivity metal or doped waveguides and heating the waveguides from above or from both sides. The realization method of the thermo-optic phase shifter using high-resistivity metal is that a heat source is connected above a target optical waveguide, voltage is applied to enable the heat source to generate ohmic heat, heat is provided for the inside and the outside of the optical waveguide, and the effective refractive index of an optical signal is changed through a thermo-optic effect to realize the phase modulation of the optical signal. However, the heat is consumed by the silicon dioxide around the optical waveguide due to the larger heat conductivity coefficient of the silicon dioxide, so that the heating power which actually reaches pi phase shift of the optical signal in the optical waveguide is larger, the modulation efficiency is low, and the performance, the power consumption and the stability of the modulator are seriously affected. Therefore, how to reduce pi-phase shift power of the thermo-optic phase shifter is a need for solving the problem.

Disclosure of Invention

First, the technical problem to be solved

In view of the above, the present invention provides a thermo-optic phase shifter to at least partially solve the problems of high power consumption, low efficiency, poor stability and the like of the existing thermo-optic phase shifter.

(II) technical scheme

The invention provides a thermo-optic phase shifter comprising: a substrate, a cladding layer, a multilayer core waveguide network, and a heat source; wherein the cladding layer is positioned on the upper surface of the substrate; each core layer waveguide network is positioned in the cladding layer and layered in the vertical direction relative to the upper surface of the substrate, and the projections of the waveguide paths of two adjacent core layer waveguide networks on the substrate are at least partially overlapped or partially overlapped; the heat source is arranged in the cladding layer, is positioned above the multilayer core layer waveguide network, and has an intersection area with the projection of at least part of the multilayer core layer waveguide network on the substrate.

According to an embodiment of the invention, the ports of the two adjacent layers of the core waveguide network are parallel to each other and overlap in a vertical direction with respect to the upper surface of the substrate, and the overlapping area forms a directional coupling region.

According to an embodiment of the present invention, the substrate sequentially includes, from bottom to top: a back substrate and an oxygen-buried layer; the back substrate is made of a silicon material, and the oxygen-buried layer is made of a silicon dioxide material.

According to an embodiment of the invention, the cladding is a silica material.

According to an embodiment of the present invention, the material of the core waveguide network is a silicon-based semiconductor material, and the materials of the core waveguide networks are different.

According to an embodiment of the present invention, the material of the heat source is a metal or an alloy having a preset resistance value.

According to the embodiment of the invention, the directional coupling region is formed by an inverted cone structure and an extended rectangular structure, and the length of the directional coupling region is 5um-50um.

According to an embodiment of the invention, the core waveguide network has a width of 0.1-1um and a thickness of 0.1-0.5um.

According to an embodiment of the invention, the heat source is located 0.5um-2.5um above the multilayer core waveguide network.

According to the embodiment of the invention, the number of layers of the core layer waveguide network is 1-5.

(III) beneficial effects

1. According to the thermo-optical phase shifter provided by the invention, by utilizing the optical wave coupling among different core layer waveguide networks, the transmission length of the optical wave is increased, the use power consumption is reduced, the pi phase shift power is reduced, and the heat utilization rate and the modulation efficiency are improved.

2. According to the thermo-optical phase shifter provided by the invention, different waveguide paths are designed according to different process and performance requirements, and the coupling mode does not influence the working performance of other devices, so that the thermo-optical phase shifter has great design flexibility; the waveguide length is designed according to the power consumption requirement and the sensitivity of the device to temperature, so that the temperature requirement is greatly reduced, the optical waveguide is ensured to be suitable for high-density integration, the area of the phase shifter is effectively reduced, and the process tolerance is improved; meanwhile, the length of the waveguide is accurately controlled, the accuracy of phase modulation is improved, and the design difficulty of the modulator is reduced.

Drawings

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 schematically illustrates a cross-sectional view of a thermo-optic phase shifter according to an embodiment of the present invention;

FIG. 2 schematically illustrates a plan view of a thermo-optic phase shifter according to an embodiment of the present invention;

FIG. 3 schematically illustrates a plan view of a thermo-optic phase shifter including two directional coupling regions and two heat sources provided by an embodiment of the present invention;

FIG. 4 schematically illustrates a plan view of a thermo-optic phase shifter including four directional coupling regions, a heat source and a three-layer core waveguide network, in accordance with an embodiment of the present invention;

FIG. 5 schematically illustrates a cross-sectional view of a thermo-optic phase shifter including four directional coupling regions, a heat source and a three-layer core waveguide network, in accordance with an embodiment of the present invention;

FIG. 6 schematically illustrates a plan view of another thermo-optic phase shifter provided by an embodiment of the present invention;

FIG. 7 schematically illustrates a cross-sectional view of another thermo-optic phase shifter provided by an embodiment of the present invention;

Fig. 8 schematically illustrates a plan view of another thermo-optic phase shifter comprising two directional coupling regions and two heat sources provided by an embodiment of the present invention.

Reference numerals illustrate:

1-a substrate;

2-cladding;

3-core waveguide network

4-Heat Source

5-Directional coupling region.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be understood that the description is only illustrative and is not intended to limit the scope of the invention. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It may be evident, however, that one or more embodiments may be practiced without these specific details. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms "comprises," "comprising," and/or the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein should be construed to have meanings consistent with the context of the present specification and should not be construed in an idealized or overly formal manner.

The thermo-optic phase shifter provided by the embodiment of the invention comprises: a substrate 1, a cladding layer 2, a multilayer core waveguide network 3, and a heat source 4.

Further, the cladding layer 2 is located on the upper surface of the substrate 1; each core waveguide network 3 is positioned in the cladding 2 and layered in the vertical direction relative to the upper surface of the substrate 1, and the projections of the waveguide paths of two adjacent core waveguide networks 3 on the substrate 1 are at least partially overlapped or partially overlapped; the heat source 4 is arranged inside the cladding layer, above the multilayer core waveguide network 3, and has an intersection area with the projection of at least part of the multilayer core waveguide network 3 onto the substrate 1.

The thermo-optical phase shifter provided by the embodiment of the invention increases the optical wave transmission length by utilizing the optical wave coupling between different core layer waveguide networks 3, reduces the use power consumption, reduces pi phase shift power, improves the heat utilization rate and the modulation efficiency of the modulator, can precisely control the waveguide length of the core layer waveguide network 3, increases the accuracy of phase modulation, reduces the design difficulty of the modulator, reduces the required area, and ensures that the optical waveguide is suitable for high-density integration. Therefore, the thermo-optical phase shifter has the characteristics of compatibility with the existing integration process, good optical characteristics, mechanical strength and stability, low cost, high design flexibility and the like, and can be used for photoelectric integrated links.

In the embodiment of the invention, the substrate 1 sequentially comprises a back substrate and an oxygen burying layer from bottom to top, wherein the back substrate is made of a silicon material, and the oxygen burying layer is made of a silicon dioxide material.

Silicon-based integration includes bulk silicon, SOI (silicon on insulator), and the like. Bulk silicon has no buried oxide layer and only a silicon substrate. Under the action of the buried oxide layer, the SOI can reduce light leakage of the MOS tube and the light wave to the substrate, reduce the substrate capacitance and improve the device performance.

In the embodiment of the present invention, the cladding 2 is a silicon dioxide material. The cladding layer 2 is mainly used to create a refractive index difference confining light in the core waveguide network 3.

In the embodiment of the invention, the number of layers of the core layer waveguide network 3 is 1-5, the materials are silicon-based semiconductor materials, the materials of the core layer waveguide networks 3 are different, the width of the core layer waveguide network 3 is 0.1-1um, and the thickness of the core layer waveguide network 3 is 0.1-0.5um.

Specifically, the materials of the multilayer core waveguide network 3 include, but are not limited to, silicon, etched silicon, silicon nitride, doped silicon, polysilicon, and the like, as well as materials having different spatial layers and refractive indices within the cladding layer 2. Each layer of the core waveguide network 3 contains an input optical waveguide and an output optical waveguide as input and output ports, and a transmission optical waveguide located between the input optical waveguide and the output optical waveguide. The core waveguide network 3 serves as an optical mode transmission waveguide, the core waveguide forming an intermediate optical waveguide. The transmission waveguides of different adjacent core waveguide networks 3 may be crisscrossed or curved crossed to reduce waveguide mode crosstalk.

In the embodiment of the present invention, the material of the heat source 4 is a metal or alloy with a preset resistance value, and the heat source 4 is located 0.5um-2.5um above the multilayer core waveguide network 3.

The heat source 4 is made of a material with high resistivity, which can generate ohmic heat, including but not limited to titanium nitride, nichrome, tungsten, copper, and other metals or alloys with certain resistance. The heat source 4 corresponds to the heat inside and outside the intermediate optical waveguide formed by the partial core waveguide network 3, is used for regulating and controlling the temperature thereof, and realizes the thermo-optical phase shift modulation for providing the optical mode field in the multilayer core waveguide network 3, and changes the phase of the optical signal propagated in the intermediate optical waveguide.

In the embodiment of the present invention, the ports of the two adjacent core waveguide networks 3 are parallel to each other and overlap in a vertical direction with respect to the upper surface of the substrate 1, and the overlapping area forms the directional coupling region 5. The directional coupling region 5 is formed by an inverted cone structure and an extended rectangular structure, and the length of the directional coupling region 5 is 5um-50um.

By designing the inverted cone structure, light is vertically coupled between two adjacent upper and lower core layer waveguide networks 3 due to evanescent wave coupling, one waveguide enters the other waveguide, two-way coupling of an optical mode field between different core layer waveguide networks 3 is realized, and a directional coupling region 5 and the multi-core layer waveguide networks 3 jointly provide an optical transmission medium.

Example 1

Fig. 1 schematically illustrates a cross-sectional view of a thermo-optic phase shifter according to an embodiment of the present invention, and fig. 2 schematically illustrates a plan view of a thermo-optic phase shifter according to an embodiment of the present invention. Wherein fig. 1 is a cross-sectional view of the thermo-optic phase shifter along line A1-A1' shown in fig. 2.

As shown in fig. 1, the high efficiency thermo-optic phase shifter may include: a substrate 1, a cladding layer 2, a multilayer core waveguide network 3, a heat source 4 and a directional coupling region 5.

As shown in fig. 2, the device at least comprises two directional coupling regions 5, at least two core waveguide networks 3 and a heat source 4, wherein the two core waveguide networks 3 are composed of three sections of core waveguides.

In this embodiment, the number of directional coupling regions 5 is not limited, so long as it is not less than two, and the number of heat sources 4 is not limited, so long as it is not less than one, and the number of segments of the core waveguide network 3 is not limited, so long as it is not less than three, for example, fig. 3 shows a plan view of a thermo-optical phase shifter having two directional coupling regions 5 and two heat sources 4. Fig. 4 schematically shows a plan view of a thermo-optic phase shifter comprising a three-layer core waveguide network 3 with four directional coupling regions 5, a five-segment core waveguide network 3, and a heat source 4, according to an embodiment of the present invention. The number of the heat sources 4 may be other, and is not limited herein, and may be set according to circumstances. In the present embodiment, the number of segments of the multilayer core waveguide network 3 is one more than the number of directional coupling regions 5, and the number is not limited and may be set according to the specific circumstances.

As shown in fig. 4, in the transmission process of the thermo-optic phase shifter, the light wave enters the thermo-optic phase shifter from the first layer, first-time transmission is performed on the first layer, the light wave reaches the directional coupling region to be coupled into the second layer, second-time transmission is performed on the second layer, third-time transmission is performed on the third layer, the light wave reaches the directional coupling region, third-time transmission is performed on the third layer, second-time transmission is performed on the third layer, first-time transmission is performed on the first layer, and the thermo-optic phase shifter is transmitted from the first layer. In the embodiment, a three-layer core layer waveguide network is adopted, the crosstalk of an intersection area between two adjacent layers is smaller than-49 dB, and the loss of an independent coupling area is smaller than 0.9dB.

Fig. 5 schematically shows a cross-sectional view of a thermo-optic phase shifter comprising four directional coupling regions 5, a heat source 4 and a three-layer core waveguide network 3 according to an embodiment of the present invention. Wherein fig. 5 is a cross-sectional view of the thermo-optic phase shifter along line A3-A3' shown in fig. 4. The thermo-optic phase shifter comprises a substrate 1, a cladding layer 2, a heat source 4, a core layer waveguide network 3 in the middle cladding layer and a directional coupling region 5.

According to the invention, ohmic heat generated by the heat source 4 is diffused into surrounding medium by applying voltage to the heat source 4, and is transmitted into and out of the core layer waveguide network 3, and the material of the heat source 4 can be titanium nitride, nichrome and other metals. The increase in the internal and external temperatures of the core waveguide network 3 causes a change in the refractive index of the temperature-increased portion of the core waveguide network 3 such that the phase of the light as it leaves the waveguide changes relative to when it is unheated. In the transmission process of the thermo-optical phase shifter, the light wave firstly enters the thermo-optical phase shifter from the silicon layer, is coupled into the silicon nitride layer when the silicon layer carries out primary transmission and reaches the directional coupling region 5, is coupled into the silicon layer when the silicon nitride layer carries out secondary transmission and reaches the directional coupling region again, and is transmitted out of the thermo-optical phase shifter from the silicon layer. In the embodiment, a double-layer core layer waveguide network 3 is adopted, the thickness of the titanium nitride heat source is 0.18um, and the width is 3.5um; the thickness of the first layer core layer waveguide network 3 is 0.215um, and the width is 0.45um; the thickness of the second-layer core layer waveguide network 3 is 0.4um, and the width is 1um; the distance between the heat source 4 and the transmission optical waveguide is 1.635um; the cross-zone crosstalk is less than-45 dB and the coupling zone loss is less than 1dB. The pi phase shift achieved by the traditional thermo-optic phase shifter is different from 2mw to 30mw, and the pi phase shift achieved by the thermo-optic phase shifter is only below 0.5 mw. In addition, the thermo-optic phase shifter of the embodiment does not influence the performance of other devices, meanwhile, the area is greatly reduced, and the process tolerance of the devices is effectively improved.

As an example, the material of the heat source 4 of the high-integration-level high-efficiency thermo-optical phase shifter of the present embodiment may be any suitable material according to the specific situation, for example, a metal having a certain resistance value such as titanium nitride, nichrome, tungsten, copper, etc. may be selected, and titanium nitride is selected for use in the first embodiment.

By way of example, the multilayer core waveguide network 3 includes, but is not limited to, single mode waveguides, multimode waveguides, etc. structures commonly used in photonic integration, the width and height of the waveguides being arbitrarily designed as desired. Preferably, the multilayer core waveguide network 3 includes a strip waveguide, a ridge waveguide, a slab waveguide, and the like. More preferably, the multilayer core waveguide network 3 comprises step-type and graded-type waveguide structures.

By way of example, the length, width, etc. of the directional coupling region 5 are chosen to be any suitable parameter depending on the particular situation.

As an example, the positional relationship between the silicon layers and the silicon nitride layers in the multilayer core waveguide network 3 may be selected from any suitable arrangement, such as, but not limited to, vertical distribution or interval arrangement.

As an example, the thermo-optic phase shifter may adjust any phase between 0-2 pi.

Example two

Fig. 6 is a schematic plan view of a high efficiency thermo-optic phase shifter according to a second embodiment of the present invention. Fig. 7 is a cross-sectional view of the thermo-optic phase shifter along line A5-A5' shown in fig. 6.

As shown in fig. 7, the semiconductor device includes a substrate 1, a cladding layer 2, a multilayer core waveguide network 3, a heat source 4, and a directional coupling region 5 according to the first embodiment.

As shown in fig. 6, the device at least comprises two directional coupling region structures 5, at least three sections of core waveguide networks 3 and a heat source 4, wherein the heat source 4 is used for adjusting the phase of the light waves guided by the corresponding core waveguide networks 3. The input/output port of the core waveguide network 3 is connected to the intermediate transmission optical waveguide, which is coupled in the directional coupling region 5.

The number of the directional coupling region structures 5 is not limited in the present embodiment, and is not less than two; the number of the heat sources 4 is not limited, and is not less than one; the number of segments of the core waveguide network 3 is not limited, and is not less than three. For example, fig. 6 shows two directional coupling regions 5 and one heat source 4, fig. 8 shows two directional coupling regions 5 and two heat sources 4, but other numbers are possible, and are not limited thereto, and are set according to the specific situation. In the present embodiment, the number of segments of the core waveguide network 3 is not limited as long as it is one more than the number of directional couplers 5, and is set according to the specific situation.

In the transmission process of the thermo-optic phase shifter, the light wave firstly enters the thermo-optic phase shifter from the silicon nitride layer, is transmitted once by the silicon nitride layer, is coupled into the silicon layer when reaching the directional coupling region 5, is transmitted twice by the silicon layer, is coupled into the silicon nitride layer when reaching the directional coupling region 5 again, and is transmitted out of the thermo-optic phase shifter from the silicon nitride layer. In the embodiment, a double-layer core layer waveguide network is adopted, the thickness of the source titanium nitride is 0.18um, and the width is 3.5um; the thickness of the first layer core layer waveguide network 3 is 0.215um, and the width is 0.45um; the thickness of the second-layer core layer waveguide network 3 is 0.4um, and the width is 1um; the spacing between the heat source and the core layer waveguide network is 1.635um; the cross-zone crosstalk is less than-48 dB and the coupling zone loss is less than 0.8dB. The pi phase shift achieved by using the thermo-optic phase shifter of the present invention is only below 0.5 mw. The embodiment can realize the input and output of light waves of the silicon nitride layer, can realize the input and output between the silicon layer and the silicon nitride layer, is not limited to silicon base, is suitable for coupling by material layers according to the principle of specific conditions, can apply the thermo-optic phase shifter of the invention, and has very important significance for improving the photo-electric integrated link based on the thermo-optic phase shifter.

In summary, according to the high-integration-level high-efficiency thermo-optic phase shifter, the core layer waveguide network is respectively arranged on at least two material layers, at least one directional coupling region is arranged, and at least one heat source provides heat, so that the transmission length of light waves can be increased on the premise of not increasing the area of a device, and the power consumption of the thermo-optic phase shifter is effectively reduced. In addition, the design difficulty based on the thermo-optic phase shifter is greatly reduced, and meanwhile, the process tolerance is improved. In addition, the performance of other devices is not changed along with the change of temperature in the working process of the thermo-optic phase shifter, the precision and the accuracy of phase modulation are improved, and the design difficulty of a control circuit is reduced. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

Further, implementations not shown or described in the drawings or in the text of the specification are all forms known to those of ordinary skill in the art and have not been described in detail. The directional terms mentioned in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., are merely directions with reference to the drawings, and are not intended to limit the scope of the present invention. Examples of parameters that include particular values may be provided herein, but these parameters need not be exactly equal to the corresponding values, but may approximate the corresponding values within acceptable error margins or design constraints.

While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.

Claims

1. A thermo-optic phase shifter, comprising:

The device comprises a substrate, a cladding layer, a multilayer core layer waveguide network, a directional coupling region and a heat source; wherein,

The cladding layer is positioned on the upper surface of the substrate;

each core waveguide network is positioned in the cladding layer, is arranged in a layered manner in the vertical direction relative to the upper surface of the substrate, and the projections of the waveguide paths of two adjacent core waveguide networks on the substrate are at least partially overlapped or partially overlapped so as to perform optical wave coupling between different core waveguide networks, and the waveguide paths of each core waveguide network are different and adjustable in length and width, and each core waveguide network comprises an input optical waveguide, an output optical waveguide and a transmission optical waveguide, wherein the transmission optical waveguides of the adjacent core waveguide networks are crisscrossed or bent and crossed;

The ports of the two adjacent core layer waveguide networks are parallel to each other and overlap in the vertical direction relative to the upper surface of the substrate, the overlapped area forms the directional coupling area, the directional coupling area is formed by an inverted cone structure and an extended rectangular structure together, and the length of the directional coupling area is 5um-50um;

the heat source is arranged in the cladding layer, is positioned above the multilayer core layer waveguide network, and has an intersection area with the projection of at least part of the multilayer core layer waveguide network on the substrate.

2. The thermo-optic phase shifter according to claim 1, wherein the substrate comprises, in order from bottom to top:

a back substrate and an oxygen-buried layer; wherein,

The backing bottom is made of silicon material, and the oxygen burying layer is made of silicon dioxide material.

3. The thermo-optic phase shifter according to claim 1, wherein the cladding is a silica material.

4. The thermo-optic phase shifter according to claim 1, wherein the material of the core waveguide network is a silicon-based semiconductor material and the material of each of the core waveguide networks is different.

5. The thermo-optic phase shifter according to claim 1, wherein the material of the heat source is a metal or alloy having a predetermined resistance value.

6. The thermo-optic phase shifter according to claim 1, wherein the core waveguide network has a width of 0.1-1um and a thickness of 0.1-0.5um.

7. The thermo-optic phase shifter according to claim 1, wherein the heat source is located 0.5um-2.5um above the multilayer core waveguide network.

8. The thermo-optic phase shifter according to claim 1, wherein the number of layers of the core waveguide network is 1-5.