CN113900280A - Polarization independent optical switch - Google Patents
Polarization independent optical switch Download PDFInfo
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- CN113900280A CN113900280A CN202010575864.1A CN202010575864A CN113900280A CN 113900280 A CN113900280 A CN 113900280A CN 202010575864 A CN202010575864 A CN 202010575864A CN 113900280 A CN113900280 A CN 113900280A
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims abstract description 60
- 229910052581 Si3N4 Inorganic materials 0.000 claims abstract description 42
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims abstract description 42
- 239000000463 material Substances 0.000 claims abstract description 40
- 229910052751 metal Inorganic materials 0.000 claims abstract description 22
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
- G02F1/0316—Electrodes
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/061—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on electro-optical organic material
- G02F1/065—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on electro-optical organic material in an optical waveguide structure
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure
- G02F1/2257—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure the optical waveguides being made of semiconducting material
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Abstract
The invention discloses a polarization-independent optical switch, which relates to the field of semiconductors, and is of a bilateral symmetry structure, comprising: the lower cladding, the lithium niobate waveguide layer, the upper cladding and the silicon nitride layer, wherein the lithium niobate waveguide layer is integrated above the lower cladding, the silicon nitride layer is above the lithium niobate waveguide layer, and the upper cladding is filled between the lithium niobate waveguide layer and the silicon nitride layer; etching the upper half parts of the uniform light-splitting multimode interference coupler and the upper and lower interlayer coupling structures on the silicon nitride layer in sequence along the light propagation direction; etching the lower half part of the upper and lower interlayer coupling structures and the polarization-independent modulation waveguide on the lithium niobate waveguide layer; and manufacturing metal electrodes on two sides of the polarization-independent modulation waveguide of the lithium niobate waveguide layer, and adjusting the positions of the metal electrodes according to the modulation characteristics of the lithium niobate waveguide layer. The optical switch utilizes the silicon nitride material, realizes the polarization independence of a basic passive device, and simultaneously utilizes the electro-optic characteristic of the lithium niobate material to realize the modulation characteristic with low loss and high speed.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to a polarization-independent optical switch.
Background
The advent of the information age, cloud, and data-intensive computing has led to ever increasing data traffic and ever increasing bandwidth requirements. In a data switching network, the development of the current electrical switch gradually meets the bottleneck, and the current performance requirements of large bandwidth, low power consumption, low time delay and the like cannot be met gradually. The optical communication technology has the advantages of large bandwidth, low time delay, low power consumption and the like, and provides a feasible technical scheme for the current communication network.
The optical switch is used as a key device in an optical communication network, is mainly applied to a large-scale data switching center and a supercomputer, and generally requires that the optical switch has the characteristics of large bandwidth, low loss, independence on polarization and the like. In addition, in the packet switching type, the switching speed of the optical switch needs to reach nanosecond level to avoid data packet loss, so that the realization of large bandwidth, low loss, high switching speed and independence of polarization is an urgent problem to be solved in the current optical switch.
Optical switches can be classified into wavelength routing switching and path switching according to their operating principles. The wavelength routing realizes the switching of the optical path by changing the wavelength of the carrier wave, although the communication bandwidth is narrow and the channel data carrying capacity is limited, the wavelength routing still takes the wavelength routing as the main application at present because the principle is simple and easy to realize and the data communication capacity can be improved by increasing the channel. The array of path switching can be divided into a space type and a waveguide type, and the space type is mainly based on MEMS, and is currently popular commercially due to its low cost. The waveguide type can be divided into different material types such as silicon dioxide, silicon, three-five material and the like, and the performance of the waveguide type is more superior compared with the former two, but the waveguide type is still in the research stage at present.
Silicon-based photonics, an emerging discipline based on silicon and silicon-based substrate materials for optical device development and integration using the current advanced Complementary Metal Oxide (CMOS) process, has been extensively studied. Therefore, when the lower waveguide type optical switch is mainly made of silicon materials, a few new materials such as lithium niobate and novel phase change materials are adopted. The former utilizes silicon-based plasma dispersion effect, and process ion implantation forms a PIN structure in a ridge waveguide form, so that nanosecond switching speed is realized. The latter makes use of some electro-optical effects of the material and can also achieve nanosecond or even faster switching speeds.
However, it is difficult to simultaneously realize the performance of polarization independence and low loss and high switching speed no matter the silicon-based optical switch based on the conventional silicon-based plasma dispersion effect PIN structure or the optical switch using a new material. In practical applications, the optical switch, as a switching node of data in a communication network, is generally required to have characteristics of large bandwidth, polarization independence, low loss, high switching speed, and the like.
The existing optical switches have the following disadvantages:
(1) the carrier injection introduces extra light absorption loss of the silicon-based high-speed optical switch realized by utilizing the silicon-based plasma dispersion effect, and the loss is larger during actual use.
(2) The silicon-based high-speed optical switch realized by utilizing the silicon-based plasma dispersion effect is difficult to realize due to the harsh condition of the thin-film silicon material polarization-independent waveguide.
(3) The high-speed optical switch realized by using new materials such as lithium niobate, phase-change materials and the like has high difficulty in the etching process of the lithium niobate and high loss of the phase-change materials.
In summary, how to provide a low-loss high-speed polarization-independent optical switch structure becomes one of the technical problems to be solved at present.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.
Therefore, the invention aims to provide a polarization-independent optical switch, which solves the technical problem of polarization-independent characteristics difficult to realize by silicon waveguides or other materials and solves the technical problem of large extra loss introduced during electro-optical modulation.
In order to achieve the above object, an embodiment of the present invention provides a polarization independent optical switch, which has a left-right symmetric structure, and includes:
the silicon nitride waveguide layer is arranged above the lithium niobate waveguide layer, and the upper cladding layer is filled between the lithium niobate waveguide layer and the silicon nitride layer;
etching the upper half parts of the uniform light-splitting multimode interference coupler and the upper and lower interlayer coupling structures on the silicon nitride layer in sequence along the light propagation direction, wherein the upper half parts are connected with the output of the uniform light-splitting multimode interference coupler;
etching the lower half part of the upper and lower interlayer coupling structure and the polarization-independent modulation waveguide on the lithium niobate waveguide layer, wherein the lower half part is connected with the polarization-independent modulation waveguide; and
and manufacturing metal electrodes on two sides of the polarization-independent modulation waveguide of the lithium niobate waveguide layer, and adjusting the positions of the metal electrodes according to the modulation characteristics of the lithium niobate waveguide layer.
The polarization-independent optical switch provided by the embodiment of the invention is a novel optical switch with a hetero-integration of a silicon nitride material and a lithium niobate material, wherein a lithium niobate wafer on an insulator is utilized to etch and form a modulation waveguide of an optical switch modulation arm, a silicon nitride film is grown on lithium niobate, and a multimode interference coupler and other basic passive devices are etched and formed. The optical switch structure utilizes silicon nitride materials to realize the polarization independence of basic passive devices, and simultaneously utilizes the electro-optic characteristic of lithium niobate materials to realize the modulation characteristic with low loss and high speed.
In addition, the polarization independent optical switch according to the above embodiment of the present invention may further have the following additional technical features:
further, in one embodiment of the present invention, the metal electrode is opened above and exposed to air.
Further, in an embodiment of the present invention, light is input from one port of the uniform splitting multimode interference coupler, coupled to the polarization-independent modulation waveguide through the upper and lower interlayer coupling structures, an external voltage is applied to the metal electrode to change an optical phase, so that an optical path is changed, and then output from one port of the uniform splitting multimode interference coupler through the upper and lower interlayer coupling structures.
Further, in one embodiment of the present invention, the upper cladding and the lower cladding are silica materials.
Further, in one embodiment of the present invention, the silicon nitride layer is a structure with a gradually narrowing width.
Further, in one embodiment of the present invention, the length of the tapered structure of the silicon nitride layer and the interlayer spacing of the lithium niobate waveguide layer and the silicon nitride layer are changed to couple the transverse electric mode and the transverse magnetic mode with low loss.
Further, in one embodiment of the present invention, the uniform splitting multimode interference coupler is a polarization independent 2 × 2 uniform splitting multimode interference coupler, and includes 4 input-output curved waveguides and an intermediate multimode waveguide.
Further, in an embodiment of the present invention, in the process of adjusting the position of the metal electrode according to the modulation characteristics of the lithium niobate waveguide layer, the distribution of the electric field lines in the waveguide is changed so that the modulation efficiency of the two modes of the transverse electric mode and the transverse magnetic mode is the same.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram of a polarization independent optical switch, according to one embodiment of the present invention;
FIG. 2 is a graph illustrating simulation results of single-mode conditions for a silicon nitride material in accordance with one embodiment of the present invention;
FIG. 3 is a top view of a silicon nitride layer in an optical switch according to one embodiment of the present invention;
fig. 4 is a schematic cross-sectional view of a lithium niobate waveguide layer in an optical switch, according to one embodiment of the present invention.
Reference numerals: a lower cladding-1; a lithium niobate waveguide layer-2; a silicon nitride layer-3; uniform light-splitting multimode interference couplers-4 and 9; upper and lower interlayer coupling structures-5, 8; a polarization-independent modulation waveguide-6; a metal electrode-7.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
At present, a common high-speed optical switch is usually realized by adopting a silicon-based plasma dispersion effect. Ion doping is introduced into the silicon waveguide, and the effective refractive index of the waveguide mode is changed by applying an electric signal to achieve the phase shift purpose. The injection of carriers brings extra loss while causing extra phase shift, and meanwhile, the polarization-independent condition of the thin-film silicon material is harsh, and the difficulty in realizing polarization independence of the high-speed optical switch realized by utilizing the silicon-based plasma dispersion effect is a technical problem existing in the conventional silicon-based high-speed optical switch.
Besides the silicon-based plasma dispersion effect, the high-speed optical switch is realized by utilizing the phase-change material, and the problems of high loss, polarization correlation and difficult heterogeneous integration also exist. The embodiment of the invention provides a polarization-independent optical switch structure with low loss and high switching speed, which solves the technical problem of polarization-independent characteristic difficult to realize by silicon waveguide or other materials through heterogeneous integration of a silicon nitride material and a lithium niobate material, and also solves the technical problem of large extra loss introduced during electro-optic modulation.
The proposed polarization independent insensitive optical switch according to embodiments of the present invention is described below with reference to the accompanying drawings.
Fig. 1 is a schematic diagram of a polarization independent optical switch according to an embodiment of the present invention.
As shown in fig. 1, the polarization independent optical switch has a left-right symmetric structure.
Referring to fig. 1, the polarization independent optical switch includes a lower cladding layer 1, a lithium niobate waveguide layer 2, an upper cladding layer (not shown), and a silicon nitride layer 3.
The lower cladding layer 1 is arranged at the bottommost layer, the lithium niobate waveguide layer 2 is integrated above the lower cladding layer 1, the silicon nitride layer 3 is integrated above the lithium niobate waveguide layer 2, and the upper cladding layer is filled between the lithium niobate waveguide layer and the silicon nitride layer.
In one embodiment of the invention, both the upper and lower cladding layers are silica material.
A uniform spectroscopic Multimode Interference coupler 4(MMI, Multimode Interference), an upper and lower interlayer coupling structure 5, a polarization-independent modulation waveguide 6, a metal electrode 7, a uniform spectroscopic Multimode Interference coupler 9, and an upper and lower interlayer coupling structure 8 are etched in this order along the light propagation direction (direction from left to right in fig. 1).
Specifically, the MMI is etched on a silicon nitride layer, and is a polarization-independent 2 × 2 uniform-splitting multimode interference coupler which comprises 4 input-output curved waveguides and an intermediate multimode waveguide.
The upper half part of the upper and lower interlayer coupling structure 5 is etched on the silicon nitride layer, the lower half part is etched on the lithium niobate waveguide layer, the upper half part is connected with the output of the uniform light-splitting multimode interference coupler 4(2 multiplied by 2MMI), and the lower half part is connected with the polarization-independent modulation waveguide 6. Thereby, coupling of light between different layers is achieved.
The polarization-independent modulation waveguide 6 and the metal electrode 7 are manufactured on the lithium niobate waveguide layer, the metal electrode 7 is manufactured on two sides of the polarization-independent modulation waveguide 6, a hole is formed above the metal electrode 7, the metal electrode is exposed to air, and the optical phase is changed by externally applying voltage on the metal electrode.
Further, the position of the metal electrode can be adjusted according to the modulation characteristics of the lithium niobate waveguide layer. Therefore, the distribution of electric field lines in the waveguide is changed, the modulation efficiency of the transverse electric mode and the transverse magnetic mode is the same, and the polarization independence is realized.
The optical switch has a bilaterally symmetrical structure, so that the structure of the right uniform splitting multimode interference coupler 9 and the upper and lower interlayer coupling structures 8 is the same as the structure of the left uniform splitting multimode interference coupler 4 and the upper and lower interlayer coupling structures 5.
It can be understood that, in the embodiment of the present invention, the polarization independent passive device is designed and manufactured by the silicon nitride material, the process difficulty of the device is reduced, the function of low loss and high switching speed is realized by utilizing the anisotropic characteristic and the excellent electro-optic characteristic of the lithium niobate material, and the polarization independence is realized. Thus, the switch structure of embodiments of the present invention may be varied widely, such as micro-ring, MZI (Mach-Zehnder interferometer).
In one embodiment of the present invention, light is input from one of the ports of the uniform splitting multimode interference coupler 4, coupled to the polarization-independent modulation waveguide 6 through the upper and lower interlayer coupling structures 5, and the optical path is changed by applying a voltage to the metal electrode 7 to change the optical phase, and finally the light is output from one of the ports of the second uniform splitting multimode interference coupler 9.
As shown in fig. 2, a single-mode condition simulation result of the silicon nitride material is shown, and it can be seen from the simulation result that the silicon nitride material can realize the polarization-independent characteristic when the height is 900nm and the width is about 700nm, as shown in the figure, the effective refractive index curves of the TE mode (transverse electric mode, electric field is only polarized along the transverse direction) and the TM mode (transverse magnetic mode, magnetic field is only polarized along the transverse direction) intersect. The size structure is large, and the size structure is easy to realize through process manufacturing, so that the process etching difficulty is reduced. Based on the result, the present invention can realize the basic passive device of the MMI which is independent of the polarization through the design.
As shown in fig. 3, Si3N4taper is a silicon nitride taper structure, LN Waveguide is a lithium niobate Waveguide, and silicon nitride designed in the embodiment of the present invention is a taper width taper structure, an optical field gradually diverges and couples with the lithium niobate Waveguide when propagating in the silicon nitride Waveguide, and light is gradually coupled from the silicon nitride Waveguide to the lithium niobate Waveguide, and is reversible according to an optical path and has the same backward propagation characteristic. According to the embodiment of the invention, the low-loss coupling of a transverse electric mode (TE) and a transverse magnetic mode (TM) can be realized by designing the reasonable length of the silicon nitride layer taper and the interlayer spacing between the lithium niobate waveguide layer and the silicon nitride layer. Because the process difficulty of the lithium niobate material is high, the embodiment of the invention only makes large width change on the silicon nitride waveguide and reduces the width change of the lithium niobate waveguide as much as possible.
As shown in fig. 4, according to the anisotropic characteristic of the lithium niobate material, the refractive index thereof can be written in a tensor form:
wherein n isoIs the refractive index of the lithium niobate material in the x and y directions, neIs a lithium niobate materialThe z-direction refractive index. Taking the example of applying the electric field in the z direction, when the direction of the electric field lines and the light polarization direction are the same, the modulation efficiency is the largest, the modulation efficiency gradually changes along with the angle change between the direction of the electric field lines and the light polarization direction, and when the electric field lines are perpendicular to the polarization direction, the modulation efficiency is the lowest, which is about one eighth of the former. According to the modulation characteristics of the lithium niobate material, the embodiment of the invention reasonably controls the position of the metal electrode through design, changes the distribution of electric field lines in the waveguide, enables the modulation efficiency of two modes of TE and TM to be the same, and realizes polarization independence.
Due to the modulation characteristic of the lithium niobate material, an electric field directly acts on the lithium niobate, so that extra light absorption loss is not introduced when the refractive index of the lithium niobate material is changed, and the lithium niobate material has extremely high response speed. According to reported documents, the bandwidth of the lithium niobate material is at least more than 70GHz, and the index level of the lithium niobate material is far higher than the nanosecond switching speed in the current data packet communication mode.
The polarization-independent optical switch provided by the embodiment of the invention provides a novel optical switch with a silicon nitride material and a lithium niobate material which are heterogeneously integrated, a lithium niobate wafer on an insulator is utilized to etch and form a modulation waveguide of an optical switch modulation arm, a silicon nitride film is grown on the lithium niobate, and a multimode interference coupler and other basic passive devices are etched and formed. The optical switch structure utilizes silicon nitride materials to realize the polarization independence of basic passive devices, and simultaneously utilizes the electro-optic characteristic of lithium niobate materials to realize the modulation characteristic with low loss and high speed.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (8)
1. A polarization independent optical switch, wherein the optical switch is a left-right symmetric structure, comprising:
the silicon nitride waveguide layer is arranged above the lithium niobate waveguide layer, and the upper cladding layer is filled between the lithium niobate waveguide layer and the silicon nitride layer;
etching the upper half parts of the uniform light-splitting multimode interference coupler and the upper and lower interlayer coupling structures on the silicon nitride layer in sequence along the light propagation direction, wherein the upper half parts are connected with the output of the uniform light-splitting multimode interference coupler;
etching the lower half part of the upper and lower interlayer coupling structure and the polarization-independent modulation waveguide on the lithium niobate waveguide layer, wherein the lower half part is connected with the polarization-independent modulation waveguide; and
and manufacturing metal electrodes on two sides of the polarization-independent modulation waveguide of the lithium niobate waveguide layer, and adjusting the positions of the metal electrodes according to the modulation characteristics of the lithium niobate waveguide layer.
2. The polarization independent optical switch of claim 1,
and an opening is formed above the metal electrode and is exposed to the air.
3. The polarization independent optical switch of claim 2,
light is input from one port of the uniform light-splitting multimode interference coupler, coupled to the polarization-independent modulation waveguide through the upper and lower interlayer coupling structures, applied with an external voltage on the metal electrode to change the optical phase so as to change the optical path, and output from one port of the uniform light-splitting multimode interference coupler through the upper and lower interlayer coupling structures.
4. The polarization independent optical switch of claim 1,
the upper cladding and the lower cladding are silica materials.
5. The polarization independent optical switch of claim 1,
the silicon nitride layer is a structure with gradually narrowed width.
6. The polarization independent optical switch of claim 5,
and changing the length of the gradually narrowing structure of the silicon nitride layer and the interlayer spacing between the lithium niobate waveguide layer and the silicon nitride layer so as to couple the transverse electric mode and the transverse magnetic mode with low loss.
7. The polarization independent optical switch of claim 1,
the uniform light-splitting multimode interference coupler is a polarization-independent 2 x 2 uniform light-splitting multimode interference coupler and comprises 4 input and output curved waveguides and an intermediate multimode waveguide.
8. The polarization independent optical switch of claim 1, wherein during the adjustment of the position of said metal electrode according to the modulation characteristics of said lithium niobate waveguide layer, the distribution of electric field lines in the waveguide is changed so that the modulation efficiency of both transverse electric mode and transverse magnetic mode is the same.
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