CN117192690A - On-chip polarization beam splitter based on double-slot waveguide - Google Patents

Abstract

The present disclosure provides an on-chip polarizing beam splitter based on a dual-slot waveguide, comprising a substrate, two core waveguides, and three confining waveguides. Three limiting waveguides and two core waveguides are alternately arranged, and a hollow groove is formed between two adjacent waveguides; the first core waveguide, the first limiting waveguide, the second limiting waveguide and two hollow grooves between adjacent waveguides jointly form a first double-groove waveguide; the second core waveguide, the second confinement waveguide, the third confinement waveguide and the two hollow slots between adjacent waveguides together form a second double-slot waveguide. The double-slot waveguide structure has strong polarization related mode field distribution regulation and control characteristics, and can directly separate the fundamental transverse electric mode and the fundamental transverse magnetic mode into different waveguides without the help of high-order mode conversion, so that mode conversion loss is avoided; the polarization beam splitter provided by the disclosure realizes effective polarization beam splitting, and has the advantages of small coupling loss, short coupling distance, high polarization extinction ratio, simple preparation process and contribution to compact large-scale photon integration application.

Description

On-chip polarization beam splitter based on double-slot waveguide

Technical Field

The disclosure relates to the technical field of integrated microwave photons, in particular to an on-chip polarization beam splitter based on a double-slot waveguide.

Background

The field of integrated microwave photonics is one of the fastest growing and most promising fields in the world today. In the field of on-chip integration, there are many devices that encode information using polarization degrees of freedom, and thus passive devices capable of efficiently performing polarization beam splitting are required.

Lithium Niobate (LN) is known as an excellent optical material in the fields of communication science and technology because of its high performance in electro-optical, acousto-optical, and nonlinear optics. Thanks to the recent development of crystal ion slicing technology for thin film LN fabrication, lithium Niobate On Insulator (LNOI) has become a promising type of Photonic Integrated Circuit (PIC) with sub-wavelength optical confinement. LNOI presents polarization-related problems due to the birefringence caused by the asymmetric waveguide structure and the inherent anisotropic nature of LN. Polarization multiplexing systems are a general solution to solve polarization-related problems in PICs. Polarizing beam splitters are one of the most basic devices in polarization multiplexing technology.

As one of the polarization beam splitters, a Directional Coupler (DC) has been widely used in the field of on-chip integration, however, a conventional DC polarization beam splitter generally has a process of converting a fundamental mode into a higher order mode and then reconverting the same into the fundamental mode, which introduces a large mode conversion loss and occupies a large size of the device.

BRIEF SUMMARY OF THE PRESENT DISCLOSURE

It is a primary object of the present disclosure to provide an on-chip polarizing beam splitter based on a dual slot waveguide, which aims to solve at least one of the above technical problems.

To achieve the above object, the present disclosure provides an on-chip polarizing beam splitter based on a dual-slot waveguide, comprising:

a substrate;

a confining waveguide comprising a first confining waveguide, a second confining waveguide, and a third confining waveguide, the first confining waveguide, the second confining waveguide, and the third confining waveguide being spaced apart on the substrate;

the first core waveguide is arranged on the substrate and positioned between the first limiting waveguide and the second limiting waveguide, and comprises an input waveguide, a first coupling waveguide, an S-shaped waveguide and a first output waveguide;

the second core waveguide is arranged on the substrate and positioned between the second limiting waveguide and the third limiting waveguide, and comprises a conical graded waveguide, a second coupling waveguide and a second output waveguide;

the first core waveguide, the first limiting waveguide, the second limiting waveguide and two hollow grooves between adjacent waveguides jointly form a first double-groove waveguide, and the second core waveguide, the second limiting waveguide, the third limiting waveguide and two hollow grooves between adjacent waveguides jointly form a second double-groove waveguide.

Optionally, the overlapping portion of the first dual-slot waveguide and the second dual-slot waveguide forms a coupling region, and the coupling region is equal to the first confinement waveguide, the second confinement waveguide, the third confinement waveguide, the first dual-slot waveguide, and the second dual-slot waveguide in length.

Optionally, the first dual slot waveguide and the second dual slot waveguide share the second confining waveguide therebetween, the second confining waveguide being for forming a hollow slot and for providing a mode coupling spacing.

Optionally, the on-chip polarization beam splitter based on the dual-slot waveguide further includes a cladding layer, where the cladding layer is disposed on the substrate and encapsulates the confining waveguide, the first core waveguide, and the second core waveguide, so as to play a role in protection.

Optionally, the tapered graded waveguide gradually increases in width along the mode transmission direction until the tapered graded waveguide is the same as the second coupling waveguide.

Optionally, one end of the first coupling waveguide is connected to the input waveguide, one end of the S-shaped waveguide is connected to the first coupling waveguide, and the other end is connected to the first output waveguide.

Optionally, one end of the second coupling waveguide is connected with the tapered graded waveguide, and the other end is connected with the second output waveguide.

Optionally, the S-shaped waveguide extends in a direction away from the second output waveguide to physically separate the first and second output waveguides.

Optionally, the confining waveguide, the first core waveguide, and the second core waveguide are all bar waveguides, and sidewalls are all inclined.

Optionally, the heights and widths of the confining waveguide, the first core waveguide and the second core waveguide along the mode transmission direction are kept unchanged, and the heights are the same;

the widths of the first core waveguide and the second core waveguide are equal, and the widths of the first limiting waveguide, the second limiting waveguide and the third limiting waveguide are equal.

The on-chip polarization beam splitter based on the double-slot waveguide comprises a substrate, a limiting waveguide, a first core waveguide and a second core waveguide; the confining waveguide comprises a first confining waveguide, a second confining waveguide and a third confining waveguide, and the first confining waveguide, the second confining waveguide and the third confining waveguide are arranged on the substrate at intervals; the first core waveguide is arranged on the substrate and positioned between the first limiting waveguide and the second limiting waveguide, and comprises an input waveguide, a first coupling waveguide, an S-shaped waveguide and a first output waveguide; the second core waveguide is arranged on the substrate and positioned between the second limiting waveguide and the third limiting waveguide, and comprises a tapered graded waveguide, a second coupling waveguide and a second output waveguide; the first core waveguide, the first confinement waveguide, the second confinement waveguide and two hollow slots between adjacent waveguides together form a first double-slot waveguide, and the second core waveguide, the second confinement waveguide, the third confinement waveguide and two hollow slots between adjacent waveguides together form a second double-slot waveguide. The double-slot waveguide structure disclosed by the invention has the mode field distribution regulation and control characteristics related to strong polarization, and can directly separate the fundamental transverse electric mode (TE 0) and the fundamental transverse magnetic mode (TM 0) into different waveguides without resorting to high-order mode conversion, so that mode conversion loss is avoided. Has obvious regulation and control effect on the mode field distribution of TM0, especially the effective mode field area of TM0 is transversely expanded, and has no great influence on the mode field distribution of TE 0. By choosing the proper confinement waveguide width, waveguide spacing, and coupling region length, it is possible to retain the TE0 mode in the first dual-slot waveguide to a greater extent, while TM0 is almost fully coupled into the second dual-slot waveguide. The coupling process does not need to use high-order mode evolution, reduces mode conversion loss, and is convenient for realizing compact on-chip polarization beam splitting.

In addition, the effective refractive indexes of TE0 and TM0 in the double-slot waveguide are similar to the effective refractive indexes of TE0 and TM0 in the core waveguide, and the tapered graded waveguide structure is introduced, so that the gradual change of the mode refractive index is further realized, the mode reflection loss caused by the structural mutation at the initial position of the limiting waveguide is reduced, the adiabatic transmission of the mode is realized, and the insertion loss of a device is reduced.

Drawings

In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present disclosure, and other drawings may be obtained from the structures shown in these drawings without inventive effort to those of ordinary skill in the art.

FIG. 1 is a schematic diagram of one embodiment of a dual slot waveguide-based on-chip polarizing beam splitter provided by the present disclosure;

fig. 2 is a schematic diagram of a cross-section of the coupling region of fig. 1.

Reference numerals illustrate:

reference numerals	Name of the name	Reference numerals	Name of the name
				1	First confinement waveguide	41	Tapered graded waveguide
2	First core waveguide	42	Second coupling waveguide
				21	Input waveguide	43	Second output waveguide
22	First coupling waveguide	5	Third confinement waveguide
				23	S-shaped waveguide	6	First double-slot waveguide
24	First output waveguide	7	Second double-slot waveguide
				3	Second confinement waveguide	8	Coupling region
4	Second core waveguide	9	Substrate and method for manufacturing the same
						10	Cladding layer

The achievement of the objects, functional features and advantages of the present disclosure will be further described with reference to the accompanying drawings, in conjunction with the embodiments.

Detailed Description

The technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure, and it is apparent that the described embodiments are only some embodiments of the present disclosure, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without inventive effort, based on the embodiments in this disclosure are intended to be within the scope of this disclosure.

It should be noted that, if a directional indication is referred to in the embodiments of the present disclosure, the directional indication is merely used to explain a relative positional relationship between the components, a movement condition, and the like in a certain specific posture, and if the specific posture is changed, the directional indication is correspondingly changed.

In addition, if there is a description of "first," "second," etc. in the embodiments of the present disclosure, the description of "first," "second," etc. is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, the meaning of "and/or" as it appears throughout includes three parallel schemes, for example "A and/or B", including the A scheme, or the B scheme, or the scheme where A and B are satisfied simultaneously. Also, the technical solutions of the embodiments may be combined with each other, but it is necessary to be based on the fact that those skilled in the art can implement the technical solutions, and when the technical solutions are contradictory or cannot be implemented, it should be considered that the combination of the technical solutions does not exist and is not within the scope of protection claimed in the present disclosure.

Referring to fig. 1 and 2, an embodiment of the present invention discloses an on-chip polarizing beam splitter based on a dual-slot waveguide, comprising a substrate 9, two core waveguides, three confining waveguides. The confining waveguides include a first confining waveguide 1, a second confining waveguide 3, and a third confining waveguide 5, and the first confining waveguide 1, the second confining waveguide 3, and the third confining waveguide 5 are disposed on the substrate 9 at intervals. A first core waveguide 2 is arranged on the substrate 9 and between the first confining waveguide 1 and the second confining waveguide 3, the first core waveguide 2 comprising an input waveguide 21, a first coupling waveguide 22, an S-shaped waveguide 23 and a first output waveguide 24. The second core waveguide 4 is disposed on the substrate 9 and located between the second confining waveguide 3 and the third confining waveguide 5, and hollow grooves formed between the waveguides are equally spaced.

The second core waveguide 4 includes a tapered waveguide 41, a second coupling waveguide 42, and a second output waveguide 43. Wherein the first core waveguide 2, the first confining waveguide 1, the second confining waveguide 3, and two hollow slots between adjacent waveguides together form a first double-slot waveguide 6, and the second core waveguide 4, the second confining waveguide 3, the third confining waveguide 5, and two hollow slots between adjacent waveguides together form a second double-slot waveguide 7.

The substrate 9 was made of silicon dioxide (SiO 2) and had a thickness of 2um.

Further, in this embodiment, the overlapping portion of the first dual-slot waveguide 6 and the second dual-slot waveguide 7 forms a coupling region 8, as shown in a dashed box in fig. 1. The coupling region 8 is of equal length as the first confining waveguide 1, the second confining waveguide 3, the third confining waveguide 5, the first double-slot waveguide 6 and the second double-slot waveguide 7.

Further, in the present embodiment, the first double-slot waveguide 6 and the second double-slot waveguide 7 share the second confining waveguide 3 therebetween, and the second confining waveguide 3 is used to form a hollow slot and to provide a mode coupling interval.

Further, in this embodiment, the on-chip polarization beam splitter based on the dual-slot waveguide further includes a cladding layer 10, where the cladding layer 10 is disposed on the substrate 9 and wraps the confining waveguide, the first core waveguide 2, and the second core waveguide 4, so as to play a role in protection. The cladding layer 10 is made of silicon dioxide (SiO 2) and has a thickness of 2um.

Further, in the present embodiment, the tapered graded waveguide 41 gradually increases in width in the mode transmission direction until the same width as the second coupling waveguide 42.

Further, in the present embodiment, one end of the first coupling waveguide 22 is connected to the input waveguide 21, and one end of the S-shaped waveguide 23 is connected to the first coupling waveguide 22, and the other end is connected to the first output waveguide 24.

Further, in the present embodiment, the S-shaped waveguide 23 extends in a direction away from the second output waveguide 43 to physically separate the first output waveguide 24 and the second output waveguide 43. The S-shaped waveguide 23 is used to physically separate the first output waveguide 24 and the second output waveguide 43, prevent mode coupling at the output end, reduce crosstalk, and improve extinction ratio of each output port of the polarization beam splitter.

Further, in the present embodiment, the first confining waveguide 1, the first core waveguide 2, the second confining waveguide 3, the second core waveguide 4, and the third confining waveguide 5 are equal in height. The first confining waveguide 1, the second confining waveguide 3 and the third confining waveguide 5 have equal widths. The first core waveguide 2 and the second core waveguide 4 have the same width. All the waveguides are etched by adopting X-cut film lithium niobate, and are limited to process preparation conditions, and the side walls of all the waveguides are inclined. The input mode light sources are TE0 and TM0, respectively, at a wavelength of 1550 nm. The length of the coupling region 8 is closely related to the width of the confining waveguide and the spacing between the hollow slots formed by the confining waveguide and the core waveguide, and preferably the length of the coupling region 8 has an optimum value to optimize the separation of TE0 from TM0. Specifically, at the length of the optimal coupling region 8, when the input waveguide 21 inputs the mode TE0, the TE0 power output by the first output waveguide 24 is 99.8% of the total input power; when the input waveguide 21 inputs the mode TM0, the TM0 power output by the second output waveguide 43 is 98.5% of the total input power, and efficient on-chip beam splitting is achieved.

In summary, through the on-chip polarization beam splitter based on the dual-slot waveguide thin film lithium niobate provided by the embodiment, on the premise of not assisting by a high-order mode, coupling and separation of a TE0 mode and a TM0 mode can be directly realized, compact on-chip beam splitting is realized, and the on-chip polarization beam splitter has important significance for on-chip integration with small volume and high density.

While the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be understood that the foregoing embodiments are merely illustrative of the invention and are not intended to limit the invention, and that any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the present disclosure are intended to be included within the scope of the present disclosure. Finally, it should be noted that: the above embodiments are merely for illustrating the technical solution of the present disclosure, and are not limiting thereof; although the present disclosure has been described in detail with reference to the foregoing embodiments, it should 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 corresponding technical solutions of the embodiments of the present disclosure.

Claims (10)

1. An on-chip polarizing beam splitter based on a dual slot waveguide, comprising:

a substrate;

a confining waveguide comprising a first confining waveguide, a second confining waveguide, and a third confining waveguide, the first confining waveguide, the second confining waveguide, and the third confining waveguide being spaced apart on the substrate;

the first core waveguide is arranged on the substrate and positioned between the first limiting waveguide and the second limiting waveguide, and comprises an input waveguide, a first coupling waveguide, an S-shaped waveguide and a first output waveguide;

the second core waveguide is arranged on the substrate and positioned between the second limiting waveguide and the third limiting waveguide, and comprises a conical graded waveguide, a second coupling waveguide and a second output waveguide;

the first core waveguide, the first limiting waveguide, the second limiting waveguide and two hollow grooves between adjacent waveguides jointly form a first double-groove waveguide, and the second core waveguide, the second limiting waveguide, the third limiting waveguide and two hollow grooves between adjacent waveguides jointly form a second double-groove waveguide.

2. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, wherein overlapping portions of the first dual slot waveguide and the second dual slot waveguide form a coupling region that is equal in length to the first confining waveguide, the second confining waveguide, the third confining waveguide, the first dual slot waveguide, and the second dual slot waveguide.

3. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, wherein the first dual slot waveguide and the second dual slot waveguide share the second confining waveguide therebetween for forming hollow slots and for providing mode coupling spacing.

4. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, further comprising a cladding layer disposed on the substrate and surrounding the confining waveguide, the first core waveguide, and the second core waveguide for protection.

5. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, wherein the tapered graded waveguide increases in width in the mode transmission direction until the same width as the second coupling waveguide.

6. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, wherein the first coupling waveguide has one end connected to the input waveguide and the S-shaped waveguide has one end connected to the first coupling waveguide and the other end connected to the first output waveguide.

7. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, wherein the second coupling waveguide is connected at one end to the tapered waveguide and at the other end to the second output waveguide.

8. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, wherein the S-shaped waveguide extends in a direction away from the second output waveguide to physically separate the first output waveguide from the second output waveguide.

9. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, wherein the confining waveguide, the first core waveguide, and the second core waveguide are each bar waveguides and the sidewalls are all sloped.

10. The dual slot waveguide based on-chip polarizing beam splitter of claim 1, wherein the height and width of the confining waveguide, the first core waveguide, and the second core waveguide in the mode transmission direction are all maintained and the heights are the same;

the widths of the first core waveguide and the second core waveguide are equal, and the widths of the first limiting waveguide, the second limiting waveguide and the third limiting waveguide are equal.