An on-chip polarization beam splitter based on a double-slot waveguide

Abstract

The disclosure provides an on-chip polarization beam splitter based on a double-slot waveguide, comprising a substrate, two core waveguides and three restriction waveguides. The three restriction waveguides are arranged alternately with the two core waveguides, and there are hollow slots between two adjacent waveguides; the first core waveguide, the first restriction waveguide, the second restriction waveguide and the two hollow slots between adjacent waveguides together constitute a first double-slot waveguide; the second core waveguide, the second restriction waveguide, the third restriction waveguide and the two hollow slots between adjacent waveguides together constitute a second double-slot waveguide. The double-slot waveguide structure has a strong polarization-dependent mode field distribution regulation characteristic, which can directly separate the fundamental transverse electric mode and the fundamental transverse magnetic mode to different waveguides without the help of high-order mode conversion, avoiding mode conversion loss; the polarization beam splitter provided by the disclosure has the advantages of small coupling loss, short coupling distance, high polarization extinction ratio and simple preparation process while realizing effective polarization beam splitting, which is beneficial to compact and large-scale photonic integration applications.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of integrated microwave photonics, in particular to a polarization beam splitter on chip based on double slot waveguide. BACKGROUND

[0002] 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 use the polarization degree of freedom to encode information, so passive devices that can effectively perform polarization splitting are needed.

[0003] Lithium niobate (LN) is known as an excellent optical material in the field of communication science and technology due to its high performance in electro-optic, acousto-optic and nonlinear optics. Thanks to the latest development of crystal ion slicing technology for thin film LN manufacturing, lithium niobate on insulator (LNOI) has become a promising photonic integrated circuit (PIC) with subwavelength optical confinement. LNOI has polarization-related problems due to the birefringence caused by the asymmetric waveguide structure and the intrinsic anisotropic properties of LN. Polarization multiplexing system is a general solution to solve the polarization-related problems in PICs. Polarization beam splitter is one of the most basic devices in polarization multiplexing technology.

[0004] As a kind of polarization beam splitter, directional coupler (DC) has a wide application in the field of on-chip integration. However, the traditional DC polarization beam splitter usually has the process of converting a kind of fundamental mode into a high-order mode and then re-converting it into a fundamental mode, which will introduce a large mode conversion loss and the device occupies a large size.

[0005] DISCLOSURE

[0006] The main purpose of the present disclosure is to provide a polarization beam splitter on chip based on double slot waveguide, which aims to solve at least one of the above technical problems.

[0007] To achieve the above purpose, the present disclosure provides a polarization beam splitter on chip based on double slot waveguide, comprising:

[0008] a substrate;

[0009] a restriction waveguide, comprising a first restriction waveguide, a second restriction waveguide and a third restriction waveguide, the first restriction waveguide, the second restriction waveguide and the third restriction waveguide are arranged on the substrate with a certain interval;

[0010] a first core waveguide, arranged on the substrate and located between the first restriction waveguide and the second restriction waveguide, the first core waveguide comprises an input waveguide, a first coupling waveguide, an S-shaped waveguide and a first output waveguide;

[0011] a second core waveguide disposed on the substrate and located between the second confinement waveguide and the third confinement waveguide, the second core waveguide comprising a tapered waveguide, a second coupling waveguide, and a second output waveguide;

[0012] wherein 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.

[0013] Optionally, the overlapping part of the first double-slot waveguide and the second double-slot waveguide forms a coupling region, and the coupling region has the same length as the first confinement waveguide, the second confinement waveguide, the third confinement waveguide, the first double-slot waveguide, and the second double-slot waveguide.

[0014] Optionally, the first double-slot waveguide and the second double-slot waveguide share the second confinement waveguide located therebetween, and the second confinement waveguide is used to form a hollow slot and to provide a mode coupling interval.

[0015] Optionally, the on-chip polarization beam splitter based on double-slot waveguides further comprises a cladding layer disposed on the substrate and wrapping the confinement waveguide, the first core waveguide, and the second core waveguide to play a protective role.

[0016] Optionally, the tapered waveguide gradually increases in width along the mode transmission direction until the width is the same as that of the second coupling waveguide.

[0017] 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.

[0018] Optionally, one end of the second coupling waveguide is connected to the tapered waveguide, and the other end is connected to the second output waveguide.

[0019] Optionally, the S-shaped waveguide extends away from the second output waveguide to physically separate the first output waveguide and the second output waveguide.

[0020] Optionally, the confinement waveguide, the first core waveguide, and the second core waveguide are all strip waveguides, and the side walls are all inclined.

[0021] Optionally, the height, width, and height of the confinement waveguide, the first core waveguide, and the second core waveguide along the mode transmission direction are all maintained unchanged, and the heights are all the same.

[0022] The first core waveguide and the second core waveguide have equal widths, and the first limiting waveguide, the second limiting waveguide and the third limiting waveguide have equal widths.

[0023] The on-chip polarization beam splitter based on the double-slot waveguide provided by the present disclosure comprises a substrate, a limiting waveguide, a first core waveguide and a second core waveguide. The limiting waveguide comprises a first limiting waveguide, a second limiting waveguide and a third limiting waveguide, which are spaced apart on the substrate. The first core waveguide is arranged on the substrate and located 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 located between the second limiting waveguide and the third limiting waveguide, and comprises a tapered 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 slots between adjacent waveguides jointly constitute a first double-slot waveguide, and the second core waveguide, the second limiting waveguide, the third limiting waveguide and two hollow slots between adjacent waveguides jointly constitute a second double-slot waveguide. The double-slot waveguide structure of the present disclosure has strong polarization-dependent mode field distribution control characteristics, and can directly separate the fundamental transverse electric mode (TE0) and the fundamental transverse magnetic mode (TM0) to different waveguides without the aid of high-order mode conversion, thereby avoiding mode conversion loss. The mode field distribution of TM0 is obviously controlled, especially the effective mode field area of the transverse expansion TM0, and the TE0 mode field distribution is not greatly affected. By selecting appropriate limiting waveguide width, waveguide spacing and coupling region length, the TE0 mode can be retained to a large extent in the first double-slot waveguide, and the TM0 is almost fully coupled into the second double-slot waveguide. The coupling process does not require the aid of high-order mode evolution, thereby reducing the mode conversion loss and facilitating the realization of a compact on-chip polarization beam splitter.

[0024] In addition, the effective refractive index of TE0 and TM0 in the double-slot waveguide is similar to the effective refractive index thereof in the core waveguide, and the introduction of the tapered waveguide structure further realizes the gradual change of the mode refractive index, reduces the mode reflection loss caused by the structural mutation at the starting position of the limiting waveguide, realizes the adiabatic transmission of the mode, and is beneficial to reducing the insertion loss of the device. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings shown.

[0026] Figure 1 Structure diagram of an embodiment of a dual-slot waveguide based on-chip polarization beam splitter provided by the present disclosure;

[0027] Figure 2 For Figure 1 Schematic diagram of the cross section of the coupling region.

[0028] Brief Description of the Drawings:

[0029] Reference Name Reference Name 1 First confinement waveguide 41 Tapered 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-slotted waveguide 24 First output waveguide 7 Second double-slotted waveguide 3 Second confinement waveguide 8 Coupling region 4 Second core waveguide 9 Substrate 10 Cladding

[0030] The implementation, functional features and advantages of the present disclosure will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present disclosure.

[0032] It should be noted that if the directionality indication is involved in the embodiments of the present disclosure, the directionality indication is only used to explain the relative position relationship, movement condition and the like between components in a certain posture, and if the certain posture changes, the directionality indication also changes accordingly.

[0033] In addition, if the description of "first", "second" and the like is involved in the embodiments of the present disclosure, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes. Taking "A and / or B" as an example, it includes A scheme, or B scheme, or A and B simultaneously meet the scheme. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of the person skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the scope of protection claimed by the present disclosure.

[0034] Referring to Figure 1 and Figure 2The embodiment of the present application discloses a kind of on-chip polarization beam splitter based on double-slot waveguide, including substrate 9, two core waveguides, three limit waveguides.Limit waveguide includes first limit waveguide 1, second limit waveguide 3, third limit waveguide 5, the first limit waveguide 1, the second limit waveguide 3 and the third limit waveguide 5 are spaced on the substrate 9.First core waveguide 2 is located between the first limit waveguide 1 and the second limit waveguide 3 and is arranged on the substrate 9, and the first core waveguide 2 includes input waveguide 21, first coupling waveguide 22, S-shaped waveguide 23 and first output waveguide 24.Second core waveguide 4 is located between the second limit waveguide 3 and the third limit waveguide 5 and is arranged on the substrate 9, and the hollow slot formed between the two waveguides is equal in interval.

[0035] The second core waveguide 4 includes tapered waveguide 41, second coupling waveguide 42 and second output waveguide 43.

[0036] It should be noted that the material of the substrate 9 is silicon dioxide (SiO2), and the thickness is 2um.

[0037] Further, in the embodiment, the overlapping part of the first double-slot waveguide 6 and the second double-slot waveguide 7 forms a coupling region 8, as shown by the dashed box. Figure 1 The coupling region 8 has the same length as the first limit waveguide 1, the second limit waveguide 3, the third limit waveguide 5, the first double-slot waveguide 6 and the second double-slot waveguide 7.

[0038] Further, in the embodiment, the first double-slot waveguide 6 and the second double-slot waveguide 7 share the second limit waveguide 3 located therebetween, which is used to form a hollow slot and provide a mode coupling interval.

[0039] Further, in the embodiment, the on-chip polarization beam splitter based on double-slot waveguide further includes a cladding layer 10, which is arranged on the substrate 9 and wraps the limit waveguide, the first core waveguide 2 and the second core waveguide 4 to play a protective role.

[0040] Further, in the embodiment, the tapered waveguide 41 gradually increases in width along the mode transmission direction until it has the same width as the second coupling waveguide 42.

[0041] Further, in the embodiment, one end of the first coupling waveguide 22 is connected with the input waveguide 21, one end of the S-shaped waveguide 23 is connected with the first coupling waveguide 22, and the other end is connected with the first output waveguide 24.

[0042] Further, in the embodiment, the S-shaped waveguide 23 extends 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 the extinction ratio of each output port of the polarization beam splitter.

[0043] Further, in the embodiment, the first limiting waveguide 1, the first core waveguide 2, the second limiting waveguide 3, the second core waveguide 4, and the third limiting waveguide 5 have equal heights. The first limiting waveguide 1, the second limiting waveguide 3, and the third limiting waveguide 5 have equal widths. The first core waveguide 2 and the second core waveguide 4 have equal widths. All the above waveguides are etched from X-cut thin film lithium niobate, and the sidewalls of each waveguide are inclined due to the process preparation conditions. The input mode light sources are TE0 and TM0 with a wavelength of 1550 nm. The length of the coupling region 8 is closely related to the width of the limiting waveguide and the distance between the limiting waveguide and the core waveguide. Preferably, the length of the coupling region 8 has an optimal value, which makes the separation of TE0 and TM0 optimal. Specifically, under the optimal length of the 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, which realizes effective on-chip splitting.

[0044] In summary, the thin film lithium niobate on-chip polarization beam splitter based on the double-slot waveguide provided by the embodiment can directly realize the coupling separation of TE0 mode and TM0 mode without the aid of high-order mode assistance, realize compact on-chip splitting, and has important significance for small volume and high density on-chip integration.

[0045] The above-described specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the present disclosure. It should be understood that the above-described specific embodiments are merely specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure. Finally, it should be noted that the above embodiments are merely used to describe the technical solutions of the present disclosure but not to limit the present disclosure. Although the present disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still make modifications to the technical solutions recorded in the foregoing embodiments or make equivalent replacements to some technical features, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. An on-chip polarization beam splitter based on a dual-slot waveguide, characterized in that, include: Substrate; A confining waveguide, including a first confining waveguide, a second confining waveguide, and a third confining waveguide, wherein the first confining waveguide, the second confining waveguide, and the third confining waveguide are disposed on the substrate at intervals; A first core waveguide is disposed on the substrate and located between the first confining waveguide and the second confining waveguide. The first core waveguide includes an input waveguide, a first coupling waveguide, an S-shaped waveguide, and a first output waveguide. The second core waveguide is disposed on the substrate and located between the second confining waveguide and the third confining waveguide. The second core waveguide includes a tapered waveguide, a second coupling waveguide, and a second output waveguide. The first core waveguide, the first confining waveguide, the second confining waveguide, and the two hollow slots between adjacent waveguides together constitute a first double-slot waveguide. The second core waveguide, the second confining waveguide, the third confining waveguide, and the two hollow slots between adjacent waveguides together constitute a second double-slot waveguide. The height and width of the confining waveguide, the first core waveguide, and the second core waveguide along the mode transmission direction remain unchanged, and their heights are all the same. The widths of the first core waveguide and the second core waveguide are equal, and the widths of the first confining waveguide, the second confining waveguide, and the third confining waveguide are equal.

2. The dual-slot waveguide based on-chip polarization beamsplitter of claim 1, wherein, The overlapping portion of the first double-slot waveguide and the second double-slot waveguide forms a coupling region, and the length of the coupling region is equal to that of the first confining waveguide, the second confining waveguide, the third confining waveguide, the first double-slot waveguide, and the second double-slot waveguide.

3. The dual-slot waveguide based on-chip polarization beamsplitter of claim 1, wherein, The first dual-slot waveguide and the second dual-slot waveguide share the second confining waveguide located between them. The second confining waveguide is used to form a hollow slot and to provide mode coupling spacing.

4. The dual-slot waveguide based on-chip polarization beamsplitter of claim 1, wherein, The on-chip polarization beam splitter based on the dual-slot waveguide further includes a cladding layer disposed on the substrate, which encloses the confinement waveguide, the first core waveguide, and the second core waveguide for protection.

5. The dual-slot waveguide based on-chip polarization beamsplitter of claim 1, wherein, The tapered waveguide gradually increases in width along the mode transmission direction until it becomes the same as the width of the second coupled waveguide.

6. The dual-slot waveguide based on-chip polarization beamsplitter of claim 1, wherein, 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.

7. The dual-slot waveguide based on-chip polarization beamsplitter of claim 1, wherein, One end of the second coupling waveguide is connected to the tapered waveguide, and the other end is connected to the second output waveguide.

8. The dual-slot waveguide based on-chip polarization beamsplitter of claim 1, wherein, The S-shaped waveguide extends away from the second output waveguide to physically separate the first output waveguide and the second output waveguide.

9. The dual-slot waveguide based on-chip polarization beamsplitter of claim 1, wherein, The confinement waveguide, the first core waveguide, and the second core waveguide are all strip waveguides, and their sidewalls are all inclined.

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