CN116047660A

CN116047660A - Spot-size converter

Info

Publication number: CN116047660A
Application number: CN202211462410.9A
Authority: CN
Inventors: 周治平; 朱科建; 孙鹏斐
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2022-11-21
Filing date: 2022-11-21
Publication date: 2023-05-02

Abstract

The invention relates to the technical field of integrated optics, and provides a spot-size converter, which comprises: a substrate layer; the input waveguide is arranged on the substrate layer, and the refractive index of the input waveguide is larger than that of the substrate layer; the output waveguide is arranged on the substrate layer, and the refractive index of the output waveguide is larger than that of the substrate layer; the surface plasmon waveguide is arranged between the input waveguide and the output waveguide, is communicated with the input waveguide and the output waveguide, and is used for generating a surface plasmon effect on electromagnetic waves transmitted by the input waveguide. The invention effectively solves the problems of large size and lower extinction ratio of the spot-size converter in the prior art, further achieves the purposes of short size and high extinction ratio, and saves raw materials and process cost.

Description

Spot-size converter

Technical Field

The invention relates to the technical field of integrated optics, in particular to a spot-size converter.

Background

The on-chip polarization multiplexing system has high requirements on the purity of the polarization state, namely, unnecessary polarization states are effectively filtered out, and only the required polarization states are reserved. The mode spot conversion device for greatly improving the polarization state purity of the system has important application in various fields such as quantum communication, biosensing and the like. Although the conventional spot-size converter made of optical medium material is easy to process, the birefringence effect is weak, and the device needs a long length to accumulate the polarization effect, so that the size is large. Although the device size can be reduced with sub-wavelength grating structures, the desired extinction effect is not achieved for highly integrated optical interconnect systems. How to obtain a spot-size converter with small device size and high extinction ratio is a problem to be solved by the person skilled in the art.

Disclosure of Invention

The invention provides a spot-size converter, which is used for solving the problems of large size and low extinction ratio of the spot-size converter in the prior art, achieving the purposes of short size and high extinction ratio and saving raw materials and process cost.

The invention provides a spot-size converter comprising: a substrate layer; the input waveguide is arranged on the substrate layer, and the refractive index of the input waveguide is larger than that of the substrate layer; the output waveguide is arranged on the substrate layer, and the refractive index of the output waveguide is larger than that of the substrate layer; the surface plasmon waveguide is arranged between the input waveguide and the output waveguide, is communicated with the input waveguide and the output waveguide, and is used for generating a surface plasmon effect on electromagnetic waves transmitted by the input waveguide.

According to the mode spot-size converter provided by the invention, the surface plasmon waveguide comprises: and the effect plate is used for exciting the surface plasmon effect of the electromagnetic wave, is arranged on two sides of the central axes of the input waveguide and the output waveguide, is provided with a gap, and has a negative dielectric constant.

According to the mode spot converter provided by the invention, the transmission waveguide is arranged between the effect plates, two ends of the transmission waveguide are respectively and smoothly connected with the input waveguide and the output waveguide, and a gap is reserved between the effect plates and the transmission waveguide.

According to the invention, the input waveguide comprises: an input unit; the first conversion part is smoothly connected with the wave outlet end of the input part; the first conversion part and the input part are made of optical medium materials, the wave inlet end and the wave outlet end of the input part are equal in width, and the wave inlet end of the first conversion part is wider than the wave outlet end of the first conversion part.

According to the invention, the output waveguide comprises: a second conversion section; the output part is smoothly connected with the wave outlet end of the second conversion part; the second conversion part and the output part are both made of optical medium materials; the wave inlet end and the wave outlet end of the output part are equal in width, and the wave inlet end width of the second conversion part is smaller than the wave outlet end width of the second conversion part.

According to the spot-size converter provided by the invention, the input part and the output part are of rectangular structures with equal width and equal height, the first conversion part and the second conversion part are of the same structure and are of a straight quadrangular prism structure with isosceles trapezoid bottom surfaces, wherein the height of the quadrangular prism is equal to that of the rectangular parallelepiped, and the opposite surfaces of the smallest side surfaces of the straight quadrangular prism are connected with the cross section of the rectangular parallelepiped in a congruent manner; the height of the transmission waveguide is smaller than that of the first conversion part and the second conversion part, and the height of the transmission waveguide is equal to that of the effect plate.

According to the mode spot-size converter provided by the invention, the transmission waveguide, the input waveguide and the output waveguide are all made of the same optical medium material.

According to the invention, the optical medium material comprises: silicon on insulator or silicon nitride.

According to the spot-size converter provided by the invention, the outer side edge of the effect plate is provided with a plurality of extinction teeth which are arranged along the axial direction of the transmission waveguide, and the extinction teeth and the effect plate are made of the same material.

According to the spot-size converter provided by the invention, the extinction teeth are cuboid, the thickness of the extinction teeth is equal to that of the effect plate, and the intervals among the extinction teeth are equal.

According to the spot-size converter provided by the invention, the number of the extinction teeth on one side of the effect plate is greater than or equal to 18.

According to the spot-size converter provided by the invention, the substrate layer is made of silicon dioxide.

According to the mode spot converter provided by the invention, the surface plasmon waveguide is arranged between the input waveguide and the output waveguide, so that the surface plasmon effect of the surface plasmon waveguide can be utilized, the effect breaks through the diffraction limit of the traditional optical medium material, and the optical field is limited in a very small range of the metal surface of the surface plasmon waveguide and is enhanced, so that the problem that the accumulation of the polarization effect can be realized only by a long length of the traditional optical medium device is solved; meanwhile, TM waves (transverse magnetic waves) in electromagnetic waves transmitted by an input waveguide can be mostly filtered through the surface plasmon effect, and most TE waves (transverse electric waves) are reserved, so that the aim of high extinction ratio can be achieved, and the problem that an ideal extinction effect cannot be achieved for a high-integration optical interconnection system in the prior art is solved.

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

In order to more clearly illustrate the invention or the technical solutions of the prior art, the following description will briefly explain the embodiments or the drawings needed in the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the invention and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a three-dimensional structure of a spot-size converter according to the present invention;

FIG. 2 is a schematic view of an effect plate setup position provided by the present invention;

fig. 3 is a schematic diagram of a connection structure between a transmission waveguide and an input waveguide and between a transmission waveguide and an output waveguide provided by the invention;

FIG. 4 is an enlarged view of FIG. 3A;

FIG. 5 is a schematic diagram of a cross-sectional configuration of a spot-size converter according to the present invention;

FIG. 6 is a schematic diagram of a three-dimensional structure of an input waveguide and an output waveguide provided by the invention;

FIG. 7 is a schematic view of the matting tooth setup position provided by the present invention;

FIG. 8 is a schematic perspective view of the extinction teeth and effect plate provided by the invention;

fig. 9 is a graph showing the intensity distribution of the light field obtained in the experiment of the spot-size converter according to the present invention.

Reference numerals:

1-substrate layer, 2-input waveguide, 201-input section, 202-first conversion section, 3-surface plasmon waveguide, 301-effect plate, 302-extinction tooth, 4-output waveguide, 401-output section, 402-second conversion section, 5-transmission waveguide, 6-effect gap.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the described embodiments are some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In the description of the embodiments of the present invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely for convenience in describing the embodiments of the present invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the embodiments of the present invention. Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In describing embodiments of the present invention, it should be noted that, unless explicitly stated and limited otherwise, the terms "coupled," "coupled," and "connected" should be construed broadly, and may be either a fixed connection, a removable connection, or an integral connection, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium. The specific meaning of the above terms in embodiments of the present invention will be understood in detail by those of ordinary skill in the art.

In embodiments of the invention, unless expressly specified and limited otherwise, a first feature "up" or "down" on a second feature may be that the first and second features are in direct contact, or that the first and second features are in indirect contact via an intervening medium. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is level higher than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.

In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means 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 embodiments of the present invention. In this specification, schematic representations of the above terms are not necessarily directed 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, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

First, some optical concepts are explained:

surface plasmon effect: when light waves (electromagnetic waves) are incident on the interface between the metal and the medium, free electrons on the metal surface are subjected to collective oscillation, near-field electromagnetic waves which are formed by coupling the free electrons on the electromagnetic waves and the metal surface and propagate along the metal surface generate resonance if the oscillation frequency of the electrons is consistent with the frequency of the incident light waves, and the energy of the electromagnetic fields is effectively converted into collective vibration energy of the free electrons on the metal surface in the resonance state, so that a special electromagnetic mode is formed: the electromagnetic field is confined to a very small area of the metal surface and enhanced, a phenomenon known as surface plasmon phenomenon.

Birefringence of the optical waveguide: it is well known in physical optics that there is a birefringence phenomenon in uniaxial or biaxial crystals, i.e. o-light and e-light have different propagation speeds in the crystal (reflecting that the crystal has different refractive indices for o-light and e-light). A similar phenomenon also exists in waveguides, where the transmission speed of light waves differs (and thus the different polarization modes have different effective refractive indices) when the light transmitted in the optical waveguide (or optical fiber) has different polarization directions, which is also a birefringence phenomenon, and an optical device has polarization sensitivity if its performance is related to the polarization of the light transmitted therein. Since the polarization state of the signal light changes randomly after being transmitted through the common optical fiber, it is very important for the optical devices on the optical fiber line that the polarization is insensitive. The cause of birefringence is mainly due to the waveguide structure and the material itself.

The technical solution of the present invention is described below with reference to the embodiment shown in fig. 1:

an embodiment of the present invention provides a spot-size converter, including: the optical waveguide comprises a substrate layer 1, an input waveguide 2, an output waveguide 4 and a surface plasmon waveguide 3, wherein the input waveguide 2 is arranged on the substrate layer 1, and the refractive index of the input waveguide is larger than that of the substrate layer; the output waveguide 4 is arranged on the substrate 1 layer, and the refractive index of the output waveguide is larger than that of the substrate layer; the plasmon waveguide 3 is disposed between the input waveguide 2 and the output waveguide 4, and is in communication with the input waveguide 2 and the output waveguide 4, and is configured to generate a surface plasmon effect on electromagnetic waves transmitted from the input waveguide.

In a specific application, the substrate layer 1 is an insulating silica plate having a thickness of 2 μm and a refractive index of 1.444; the input waveguide 2 and the output waveguide 4 are both made of silicon materials, the refractive index of the input waveguide 2 and the output waveguide 4 is 3.478, the input waveguide 2 and the output waveguide 4 are manufactured into a strip shape by using a photoetching technology so that light waves are conducted in the strip shape, meanwhile, a surface plasmon waveguide 3 is arranged between the input waveguide 2 and the output waveguide 4, and the input waveguide 2, the surface plasmon waveguide 3 and the output waveguide 4 are all arranged on the same straight line and are sequentially communicated, so that the light waves can smoothly reach the inside of the surface plasmon waveguide 3, and then the surface plasmon effect is generated. In this embodiment, the surface plasmon waveguide is composed of two silver metal plates, and the two silver metal plates are respectively located at two sides of the middle area of the input waveguide 2 and the output waveguide 4 and are fixed on the silicon dioxide plate of the substrate layer 1, a gap is left between the two silver metal plates, when the light wave is conducted into the gap, a surface plasmon effect is generated, under the surface plasmon effect, a main electric field component exists in a form perpendicular to the metal surface, and an electric field component parallel to the metal surface can hardly exist, so that TM waves (transverse magnetic waves) in the input waveguide are blocked, and most TE waves (transverse electric waves) are reserved, thereby achieving the purpose of high extinction ratio.

According to the mode spot converter provided by the embodiment of the invention, the surface plasmon waveguide is arranged between the input waveguide and the output waveguide, so that the surface plasmon effect of the surface plasmon waveguide can be utilized, the effect breaks through the diffraction limit of the traditional optical medium material, the optical field is limited in a small range of the metal surface of the surface plasmon waveguide and is enhanced, and the problem that the traditional optical medium device needs a long length to realize polarization effect accumulation is solved; meanwhile, TM waves (transverse magnetic waves) in electromagnetic waves transmitted by an input waveguide can be mostly filtered through the surface plasmon effect, and most TE waves (transverse electric waves) are reserved, so that the aim of high extinction ratio can be achieved, and the problem that an ideal extinction effect cannot be achieved for a high-integration optical interconnection system in the prior art is solved.

According to the mode spot-size converter provided by the embodiment of the present invention, as shown in fig. 2, on the basis of the above scheme, the surface plasmon waveguide 3 includes: the effect plate 301 is used for exciting the surface plasmon effect of the electromagnetic wave, the effect plate 301 is arranged on two sides of the central axes of the input waveguide and the output waveguide, a gap is formed between the effect plates, and the dielectric constant of the effect plates is negative.

In a specific application, the surface plasmon waveguide 3 consists of two effect plates 301, which may preferably be gold plates, with a refractive index of 0.238+11.263i and a thickness of 40nm; of course, it may also be: copper, aluminum, conductive glass, alkali metal, alloy, intermetallic compound, or graphene layer, etc. As long as the dielectric constant thereof is negative, since the surface plasmon is a surface wave existing at the interface between the positive dielectric constant and the negative dielectric constant material, the property of the surface plasmon requires that the dielectric constant of one of the materials is negative, otherwise the surface plasmon phenomenon cannot exist. The effect plates 301 are disposed on both sides of the central axes of the input and output waveguides with a gap therebetween, in which a surface plasmon effect can be generated, i.e., a main electric field component of the surface plasmon exists in a form perpendicular to the metal surface, and an electric field component parallel to the metal surface hardly exists, which makes a TM wave in the input waveguide blocked. The opposite ends of the input waveguide and the output waveguide are also provided with a mode spot conversion structure, namely, the size of the light wave mode spot in the input waveguide is converted into the mode spot size capable of being transmitted in the metal gap, after the surface plasmon waveguide 3 filters the components of the input light wave, the filtered pure light wave is converted into the mode spot size of the output waveguide from the slit mode spot size.

According to the spot-size converter provided by the embodiment of the invention, the surface plasmon waveguide 3 is arranged to comprise two gold thin plates with the thickness of 40nm, and the metal slits are reserved between the two plates, so that the inner side surface of the gold effect plate can be well utilized for exciting the surface plasmon; by setting the mode spot conversion structure, the filter effect can be realized and the filter can be adapted to the mode spot sizes of the input waveguide and the output waveguide.

According to the mode spot-size converter provided by the embodiment of the invention, as shown in fig. 3-5, on the basis of the technical scheme, the transmission waveguides 5 are arranged between the effect plates, two ends of the transmission waveguides 5 are respectively and smoothly connected with the input waveguides 2 and the output waveguides 4, and a gap is reserved between the effect plates 301 and the transmission waveguides 5.

In a specific application, the transmission waveguide 5 is also formed by photoetching a silicon material into a strip shape, and two ends of the transmission waveguide are smoothly connected with the mode spot conversion structures of the input waveguide 2 and the output waveguide 4, wherein the smooth connection is provided for preventing the size of the optical wave mode spot of the input waveguide from being suddenly changed, so that the optical wave can be smoothly transmitted from the input waveguide to the transmission waveguide, and finally transmitted from the transmission waveguide to the output waveguide; the transmission waveguide, the input waveguide and the output waveguide can be manufactured into an integral molding during photoetching molding; the transmission waveguide 5 is disposed in the metal slit of the above-mentioned effect plate 301, and the length and the height of the transmission waveguide are equal to those of the metal slit, and the transmission waveguide 5 is of a cuboid structure, wherein the axis is in the same vertical plane as the central axis of the metal slit (see fig. 5), i.e. the effect gaps 6 on both sides of the transmission waveguide are equal in width, and after the transmission waveguide 5 is disposed in the metal slit, mixed-state surface plasmons can be realized, so that TM (transverse magnetic wave) of light waves on the silicon waveguide is mostly blocked, and most TE waves (transverse electric waves) are reserved to pass, thereby achieving the effect of filtering TM waves (transverse magnetic waves). And it has better practical applicability, and its transmission distance is longer with smaller loss.

According to the mode spot converter provided by the embodiment of the invention, the silicon transmission waveguide which is made of the same material as the input waveguide and the output waveguide is arranged in the metal slit of the effect plate 301, so that most of TM waves in the silicon waveguide can be filtered, and compared with the mode spot converter without the transmission waveguide, the mode spot converter has better practical applicability, smaller loss and longer transmission distance.

As shown in fig. 6, the input waveguide 2 provided in the embodiment of the present invention includes: an input unit 201 and a first conversion unit 202, wherein the first conversion unit 202 is smoothly connected to the output end of the input unit 201; the first conversion portion 202 and the input portion 201 are made of optical medium materials, the wave inlet end and the wave outlet end of the input portion are equal in width, and the wave inlet end width of the first conversion portion 202 is larger than the wave outlet end width of the first conversion portion.

The output waveguide 4 includes: a second conversion unit 402 and an output unit 401, the output unit 401 being smoothly connected to the output end of the second conversion unit 402; the second conversion part 402 and the output part 401 are both made of optical medium materials; the wave-in end of the output part 401 has the same width as the wave-out end, and the wave-in end of the second conversion part 402 has a smaller width than the wave-out end.

In practical applications, the input portion 201 may be fabricated into a strip shape by photolithography, which is made of silicon material, and the size of the transversal width determines the size of the optical wave pattern, so that the input end and the output end of the input portion 201 need to be kept at the same width in the input stage, so as to ensure that the size of the input optical wave pattern is constant, and meanwhile, the first conversion portion 202 is smoothly connected with the output end of the input portion 201, so as to ensure that the size of the optical wave pattern will not be suddenly changed when the optical wave is turned from the input portion 201 to the first conversion portion 202; meanwhile, the width of the wave-in end of the first conversion part 202 is larger than that of the wave-out end of the first conversion part, and the arrangement is to convert the larger size of the optical wave pattern in the input part into the size of the optical wave pattern which can be locally transmitted in the metal slit or the transmission waveguide 5, and meanwhile, the optical wave can generate the surface plasmon effect.

Similarly, the output portion 401 may be fabricated into a strip shape by photolithography, and is made of silicon material, after the optical wave of the surface plasmon waveguide 3 is filtered, relatively pure TE wave (transverse electric wave) needs to be output, at this time, TE wave (transverse electric wave) with smaller spot size in the surface plasmon waveguide 3 needs to be converted into normal output spot size or output spot size, so that the wave-in end and the wave-out end of the output portion 401 are equal in width, and the wave-in end width of the second conversion portion 402 is smaller than the wave-out end width thereof. Of course, the widths of the input portion 201 and the output portion 401 may be equal or unequal, and the widths may be flexibly selected according to actual requirements.

According to the mode spot converter provided by the embodiment of the invention, the input waveguide 2 is arranged as the input part 201 and the first conversion part 202, so that stable transmission of the input light wave can be better realized, the large mode spot size is converted into the small mode spot size required by the surface plasmon effect, and finally, the TE wave (transverse electric wave) reserved after filtering is converted and output according to the required mode spot size.

According to the spot-size converter provided by the embodiment of the invention, as shown in fig. 3-6, on the basis of the above technical scheme, the input part 201 and the output part 401 are rectangular structures with equal width and equal height, the first conversion part 202 and the second conversion part 402 are identical in structure and are all straight quadrangular prism structures with isosceles trapezoid bottom surfaces, wherein the height of the quadrangular prism is equal to that of the rectangular prism, and the opposite surfaces of the smallest side surfaces of the straight quadrangular prism are connected with the cross section of the rectangular prism in a congruent manner; the height of the transmission waveguide is smaller than the heights of the first conversion part and the second conversion part, and the height of the transmission waveguide 5 is equal to the height of the effect plate.

In practical applications, the input portion 201 and the output portion 401 are made of silicon materials, and are manufactured by photolithography, the height is preferably 220nm, the width is preferably 400nm, so that the heights and widths of the contact surfaces between the first conversion portion 202 and the second conversion portion 402 and the input portion 201 and the output portion 401 are also 220nm and 400nm, the first conversion portion 202 and the second conversion portion 402 are identical in structure and are both in a rectangular prism structure with isosceles trapezoid bottom surfaces, so that the included angles of the two equal sides of the first conversion portion 202 and the second conversion portion 402 relative to the central axis are equal, the distances are also equal, at this time, the stepless reduction of the size of the input optical wave pattern can be achieved until the required size of the surface plasmon waveguide 3 is achieved, meanwhile, the transmission waveguide 5 is also in a cuboid structure, the width is identical to the smallest surface of the first conversion portion 202 and the second conversion portion 402, the height is identical to the height of the effect plate, in this embodiment, the thickness of the gold effect plate is preferably 40nm, the height of the transmission waveguide 5 is 40nm, and the same size of the TE mode is ensured after filtering is finished, and the input optical wave pattern is converted to be identical to the input optical wave pattern with the same size (the same size as the input optical wave pattern and the input optical wave pattern is large as the size.

According to the mode spot-size converter provided by the embodiment of the present invention, the transmission waveguide 5, the input waveguide 2 and the output waveguide 4 are all made of the same optical medium material, and the optical medium material includes: silicon on insulator, silicon nitride, and other semiconductor materials.

Among them, silicon-on-insulator (SOI) refers to a substrate technology that replaces conventional bulk substrate silicon with an "engineered" substrate, which is composed of three layers: a monocrystalline silicon top layer on which an etching circuit is formed; a fairly thin insulating silicon dioxide interlayer (i.e. substrate layer 1 as referred to in the present invention); a very thick substrate underlayer, which primarily serves to provide mechanical support for the upper two layers. The silicon on insulator is utilized, the manufacturing process is mature, the dielectric isolation of components in the integrated circuit can be realized, and the parasitic latch-up effect in the bulk silicon CMOS circuit is thoroughly eliminated; meanwhile, silicon nitride and other semiconductor materials can also be used as waveguide materials as long as the refractive index of the silicon nitride is larger than that of the substrate layer, wherein the refractive index of the silicon nitride can be up to about 2.0, so that the silicon nitride is also one of good waveguide manufacturing materials.

According to the spot-size converter provided by the embodiment of the invention, as shown in fig. 7-8, a plurality of extinction teeth 302 are arranged at the outer edge of the effect plate 301 along the axial direction of the transmission waveguide, and the extinction teeth 302 and the effect plate 301 are made of the same material. The extinction teeth are cuboid, the thickness of the extinction teeth is equal to that of the effect plate, and the distance between the extinction teeth is also equal. The number of the extinction teeth on one side of the effect plate is more than or equal to 18.

In practical application, the outer edge of the above-mentioned effect plate 301 may be cut by using photolithography technology, and the extinction teeth 302 with cuboid structure are formed, so that the thickness of the extinction teeth is equal to that of the effect plate, and the intervals between the extinction teeth are equal, in this embodiment, the number of extinction teeth is preferably formed into 18 on one side and 36 on two sides, so that the purpose of this arrangement is to perform multistage transformation on the TM wave (transverse magnetic wave) remained in the transmission waveguide 5, thereby better eliminating the eigenmode (TM mode) with low similarity to the TE mode, and making the extinction ratio of the whole device very high. The number of the single-sided extinction teeth of the effect plate is set to 18, because the extinction performance is balanced optimally and the length of the device is balanced optimally, and the number of the single-sided extinction teeth of the effect plate can be larger than 18, so that the extinction effect is better, but the overall length of the device is increased. Of course, the number of the extinction teeth can be set to be smaller than 18, but the extinction effect is weakened along with the reduction of the extinction teeth number.

According to the spot-size converter provided by the embodiment of the invention, through the arrangement of the multi-stage extinction teeth, the residual TM wave (transverse magnetic wave) can be further filtered under the action of the effect plate 301 without the extinction teeth, so that compared with the embodiment, the spot-size converter has a better filtering effect, and the polarization state purity of the output light wave is higher.

According to the spot-size converter provided by the invention, the extinction teeth and the effect plate are made of gold, silver, copper, aluminum, conductive glass, alkali metal, alloy, intermetallic compound or graphene layers. As long as the dielectric constant thereof is negative, since the surface plasmon is a surface wave existing at the interface between the positive dielectric constant and the negative dielectric constant material, the property of the surface plasmon requires that the dielectric constant of one of the materials is negative, otherwise the surface plasmon phenomenon cannot exist.

The spot-size converter according to the embodiment of the invention is shown in fig. 9, which is a light field intensity distribution diagram of a spot-size converter with multi-stage extinction. The light field energy flow distribution situation in the spot-size converter is obtained through a numerical simulation technology of a three-dimensional full-wave vector finite element method (3D full vector finite element method,FEM). FIG. 9 (a) is a graph showing the intensity distribution of the light field of the spot-size converter according to the present invention when TE polarized light waves are input in a top view; FIG. 9 (b) is a cross-sectional light field intensity profile of FIG. 9 (a); FIG. 9 (c) is a graph showing the intensity distribution of the light field of the spot-size converter according to the present invention when a TM polarized light wave is input; FIG. 9 (d) is a cross-sectional light field intensity profile of FIG. 9 (c); wherein the hardware parameters of the device are as follows:

the substrate material is silicon, and the refractive index is 3.478;

the buried oxide material layer is silicon dioxide, the thickness is 2 mu m, and the refractive index is 1.444;

the cladding material is silicon dioxide, and the refractive index is 1.444;

the input waveguide, the transmission waveguide and the output waveguide are all made of silicon, the refractive index is 3.478, the height is 220nm, and the width is 400nm;

the negative dielectric constant material of the multi-stage extinction teeth and the effect plate is gold, the refractive index is 0.238+11.263i, and the thickness is 40nm;

the number of the comb-shaped saw teeth on the outer side of the effect plate is 18 on one side;

the wavelength of the input light wave is 1550nm;

as can be seen from fig. 9, most of the light is retained after the input light with TE polarization passes through the spot-size converter in this embodiment, and the extinction ratio of the input light with TM polarization can reach 16.8dB due to the effect of surface plasmon and the effect of multi-stage extinction teeth.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A spot-size converter, comprising:

a substrate layer;

the input waveguide is arranged on the substrate layer, and the refractive index of the input waveguide is larger than that of the substrate layer;

the output waveguide is arranged on the substrate layer, and the refractive index of the output waveguide is larger than that of the substrate layer;

the surface plasmon waveguide is arranged between the input waveguide and the output waveguide, is communicated with the input waveguide and the output waveguide, and is used for generating a surface plasmon effect on electromagnetic waves transmitted by the input waveguide.

2. The spot-size converter according to claim 1, wherein the surface plasmon waveguide comprises:

and the effect plate is used for exciting the surface plasmon effect of the electromagnetic wave, is arranged on two sides of the central axes of the input waveguide and the output waveguide, is provided with a gap, and has a negative dielectric constant.

3. The spot-size converter according to claim 2, wherein a transmission waveguide is arranged between the effect plates, two ends of the transmission waveguide are respectively and smoothly connected with the input waveguide and the output waveguide, and a gap is left between the effect plates and the transmission waveguide.

4. A spot-size converter according to claim 3, wherein the input waveguide comprises:

an input unit;

the first conversion part is smoothly connected with the wave outlet end of the input part;

the first conversion part and the input part are made of optical medium materials, the wave inlet end and the wave outlet end of the input part are equal in width, and the wave inlet end of the first conversion part is wider than the wave outlet end of the first conversion part.

5. The spot-size converter according to claim 4, wherein the output waveguide comprises:

a second conversion section;

the output part is smoothly connected with the wave outlet end of the second conversion part;

the second conversion part and the output part are both made of optical medium materials; the wave inlet end and the wave outlet end of the output part are equal in width, and the wave inlet end width of the second conversion part is smaller than the wave outlet end width of the second conversion part.

6. The spot-size converter according to claim 5, wherein the input portion and the output portion have a rectangular parallelepiped structure having equal width and equal height, and the first conversion portion and the second conversion portion have the same rectangular prism structure having isosceles trapezoid bottom surfaces, wherein the height of the rectangular prism is equal to the height of the rectangular parallelepiped, and the opposite surfaces of the smallest sides of the rectangular prism are congruent and connected to the cross section of the rectangular parallelepiped;

the height of the transmission waveguide is smaller than that of the first conversion part and the second conversion part, and the height of the transmission waveguide is equal to that of the effect plate.

7. The spot-size converter according to claim 6 wherein the transmission waveguide, the input waveguide and the output waveguide are all of the same optical medium material.

8. The spot-size converter according to claim 7, wherein the optical medium material comprises: silicon on insulator or silicon nitride.

9. A spot-size converter according to claim 3 wherein a plurality of matting teeth are provided on the outer edge of the effect plate in the direction of the axis of the transmission waveguide, the matting teeth being of the same material as the effect plate.

10. The spot-size converter according to claim 9, wherein the matting teeth have a rectangular parallelepiped shape, and the thickness of the matting teeth is equal to the thickness of the effect plate, and the pitch between the matting teeth is equal.

11. The spot-size converter according to claim 10, wherein the number of matt teeth on one side of the effect plate is greater than or equal to 18.

12. The spot-size converter according to any one of claims 1-11, wherein the substrate layer is made of silica.