Broadband integrated polarization rotation beam splitter based on complex linear gradient structure

Abstract

The invention discloses a broadband integrated polarization rotation beam splitter based on a complex linear gradient structure, which belongs to the technical field of integrated optical devices and comprises a substrate layer and a dielectric waveguide layer. A buried oxide layer is arranged between the substrate layer and the dielectric waveguide layer, upper cladding layers are arranged on the upper surface and two sides of the dielectric waveguide layer, and an input spot size converter, a mode evolver, a directional coupler and two output spot size converters are etched in the dielectric waveguide layer along the light wave transmission direction; and a bent waveguide is etched between the directional coupler and the first output spot size converter. The mode evolution effect and the mode hybridization phenomenon are utilized, the linear structure of the mode evolver is designed, the mode evolution efficiency is improved, separation of a TM0 component and a TE0 component in input light is achieved, the TM0 component is rotated, and pure TE0 light is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of integrated optical devices, and in particular relates to a broadband integrated polarization rotation beam splitter based on a complex linear gradient structure. Background Art

[0002] In the field of optoelectronics, precise control of light polarization is particularly important. For example, by finely controlling the polarization state of an optical carrier, polarization multiplexing can be implemented, thereby significantly improving the data transmission capacity of a communication system. Since most integrated photonic devices are very sensitive to the polarization state, precise control of light polarization is necessary to ensure that these devices can perform at their best. In this context, polarization rotation beam splitters, as a key passive device, play a vital role in the field of integrated photonics.

[0003] The working principle of the polarization rotation beam splitter is based on the mode evolution theory. The core is to realize the conversion of the light mode from the TM0 mode to the TE1 mode by carefully designing the structure of the mode evolver. Subsequently, the TE1 mode is further converted into the TE0 mode using a specific device, thereby realizing the conversion from the TM0 mode to the TE0 mode. However, existing polarization rotation beam splitters face some challenges. The mode evolvers in these devices usually adopt a simple linear structure, which leads to relatively low mode conversion efficiency. In order to achieve complete mode conversion, a longer device size is often required, which brings about the problems of excessive device size and low conversion efficiency. These problems not only increase the manufacturing cost, but also limit the performance of the polarization rotation beam splitter in practical applications. Therefore, the development of a new type of polarization rotation beam splitter to improve the mode conversion efficiency and shorten the device size has become an important topic of current research. Summary of the invention

[0004] In view of the problem of large size in the prior art, the present invention provides a broadband integrated polarization rotation beam splitter based on a complex linear gradient structure, which utilizes the mode evolution effect and mode hybridization phenomenon, and improves the mode evolution efficiency by designing the linear structure of the mode evolver, thereby realizing the separation of the TM0 component and the TE0 component in the input light, and rotating the TM0 component to obtain pure TE0 light.

[0005] The technical solution adopted by the present invention is:

[0006] A broadband integrated polarization rotation beam splitter based on a complex linear gradient structure comprises a substrate layer and a dielectric waveguide layer; a buried oxide layer is arranged between the substrate layer and the dielectric waveguide layer, and an upper cladding layer is arranged on the upper surface and both sides of the dielectric waveguide layer; along the light wave transmission direction, an input mode spot converter, a mode evolver, a directional coupler and two output mode spot converters are etched in the dielectric waveguide layer; and a curved waveguide is etched between the directional coupler and the first output mode spot converter.

[0007] Preferably, a ridge waveguide structure is adopted.

[0008] Preferably, the directional coupler comprises a first straight waveguide and a second straight waveguide, the first straight waveguide is connected to the second output spot converter, and the second straight waveguide is connected to the first output spot converter via a bent waveguide.

[0009] Preferably, the dielectric waveguide layer is a light field limiting layer, and its material is one of silicon, silicon nitride, indium phosphide, and thin-film lithium niobate.

[0010] Preferably, the input mode spot converter, the first output mode spot converter and the second output mode spot converter adopt a tapered gradually changing waveguide structure, and the waveguide widths of the tapered gradually changing waveguides increase sequentially.

[0011] Preferably, the mode evolver adopts a complex linear gradient waveguide structure, the waveguide width of the complex linear gradient waveguide structure gradually increases from small to large according to a specific complex function, so as to realize the mutual conversion between the TM0 mode at the minimum waveguide width end and the TE1 mode at the maximum waveguide width end, while the TE0 mode remains unchanged; the minimum waveguide width w0 of the mode spot converter is smaller than the hybridization width of the TM0 mode and the TE1 mode, and supports the transmission of TE0 and TM0 modes, and the maximum waveguide width w3 of the mode evolver is larger than the hybridization width of the TM0 mode and the TE1 mode.

[0012] Preferably, the specific complex function includes one of a parabola type, a hyperbola type, a high-order linear type, and an exponential type.

[0013] Preferably, the width of the first straight waveguide is equal to the maximum waveguide width of the mode evolver, and the width of the second straight waveguide satisfies the following conditions: the effective refractive index Neff of the TE0 mode of the second straight waveguide is TE0 The effective refractive index Neff of the TE1 mode of the first straight waveguide TE1 equal.

[0014] Preferably, the width of the first straight waveguide of the directional coupler is equal to the length of the second straight waveguide, and the lengths satisfy the condition that the TE1 mode energy in the first straight waveguide can be completely transferred to the second straight waveguide after being transmitted through this length.

[0015] Preferably, the width of the second straight waveguide of the directional coupler is equal to the width of the curved waveguide.

[0016] Compared with the prior art, the advantages and positive effects of this application are:

[0017] The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure disclosed in the present invention includes a substrate layer, a buried oxide layer, a dielectric waveguide layer and an upper cladding layer from bottom to top. The main function of the substrate layer is to provide necessary support for the entire device to ensure the stability and reliability of its structure. The buried oxide layer and the upper cladding layer are located below and above the dielectric waveguide layer, respectively. Their main function is to protect the dielectric waveguide layer from the influence of the external environment, and at the same time provide a certain restriction effect on the light field to ensure the effective transmission of the optical signal in the dielectric waveguide layer. The dielectric waveguide layer is the core part of the present invention, which contains multiple key components, including an input spot converter, a mode evolver, a directional coupler, a bending waveguide, and a first output spot converter and a second output spot converter. These components are connected in sequence in a certain order to form a complete optical transmission path.

[0018] The function of the input spot mode converter is to convert the spot mode of the input optical signal into a mode suitable for transmission in the dielectric waveguide layer. The mode evolver is responsible for appropriately evolving and adjusting the mode of the optical signal during transmission. The directional coupler is used to realize the splitting or combining of optical signals. According to the specific application requirements, the optical signal can be divided into different paths or the optical signals from different paths can be combined. The curved waveguide is used to change the transmission direction of the optical signal to adapt to the spatial layout inside the device. The first output spot mode converter and the second output spot mode converter are respectively used to convert the optical signal in the dielectric waveguide layer into a spot mode suitable for reception by external devices.

[0019] The present invention realizes a broadband integrated polarization rotation beam splitting function on an integrated optical substrate, and this function is of great significance for realizing polarization division multiplexing technology. Polarization division multiplexing technology can simultaneously transmit two or more optical signals with different polarization states in the same transmission medium, thereby improving the transmission capacity of the communication system. The present invention has the advantages of small size, large optical bandwidth, large extinction ratio and easy integration, so that it has broad application prospects in the fields of optical communication, optical sensing and optical computing. Through the implementation of the present invention, the size of the device can be effectively reduced, the integration of the system can be improved, and high-performance optical transmission and processing capabilities can be guaranteed at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A cross-sectional view of a preferred embodiment of the present application;

[0022] Figure 2 This is a structural diagram of a preferred embodiment of the present application;

[0023] Figure 3 A graph showing changes in effective refractive index of different modes as waveguide width changes in a preferred embodiment of the present application;

[0024] Figure 4 This is a simulation diagram of the mode field transmission of the light field in the beam splitter in the preferred embodiment of the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0026] See also Figures 1 to 4 A broadband integrated polarization rotation beam splitter based on a complex linear gradient structure comprises a substrate layer 1 and a dielectric waveguide layer 3; a buried oxide layer 2 is arranged between the substrate layer 1 and the dielectric waveguide layer 3, and an upper cladding layer 4 is arranged on the upper surface and both sides of the dielectric waveguide layer 3: along the light wave transmission direction, an input mode spot converter 5, a mode evolver 6, a directional coupler 7 and two output mode spot converters are etched in the dielectric waveguide layer 3; a curved waveguide 8 is etched between the directional coupler 7 and the first output mode spot converter 9.

[0027] In order to more deeply understand the technical solution of the present invention, the following non-limiting examples are given:

[0028] See also Figure 1 , using a ridge waveguide structure, it can be seen from the cross section that it includes, from bottom to top: substrate layer, buried oxide layer, dielectric waveguide layer and upper cladding layer;

[0029] See also Figure 2 The dielectric waveguide layer 3 is etched to form an input spot mode converter 5, a mode evolver 6, a directional coupler 7, a curved waveguide 8, a first output spot mode converter 9, and a second output spot mode converter 10.

[0030] The dielectric waveguide layer 3 is a light field limiting layer, which may be but is not limited to dielectric films such as silicon, silicon nitride, indium phosphide, and thin-film lithium niobate.

[0031] The input mode spot converter 5, the first output mode spot converter 9, and the second output mode spot converter 10 adopt a tapered gradient waveguide structure, and the waveguide width of the tapered gradient waveguide increases successively, which is used to expand the mode field in the waveguide structure, reduce the mode field mismatch between it and the tapered lens optical fiber, and improve the optical fiber coupling efficiency.

[0032] The mode evolver 6 adopts a complex linear gradient waveguide structure, wherein the waveguide width of the structure gradually increases according to a specific complex function, and the specific form of the function includes but is not limited to a parabola, a hyperbola, a high-order linear type, and an exponential type. The design aims to achieve mutual conversion between the TM0 mode at the minimum waveguide width end and the TE1 mode at the maximum waveguide width end, while ensuring that the TE0 mode remains unchanged. This mode evolver has higher conversion efficiency and more compact length. In addition, the minimum waveguide width w0 of the mode spot converter 6 is set to be smaller than the width when the TM0 mode and the TE1 mode are hybridized, and can support the transmission of the TE0 and TM0 modes. The maximum waveguide width w3 of the mode evolver is set to be larger than the width when the TM0 mode and the TE1 mode are hybridized.

[0033] The directional coupler 7 is composed of two straight waveguides arranged side by side. The width of the first straight waveguide 11 is equal to the maximum waveguide width of the mode evolver 6. The width of the second straight waveguide 12 must meet the following conditions: the effective refractive index Neff of the TE0 mode of the second straight waveguide is TE0 The effective refractive index Neff of the TE1 mode of the first straight waveguide TE1 equal.

[0034] The width of the first straight waveguide 11 of the directional coupler 7 is equal to the length of the second straight waveguide 12, and the lengths thereof satisfy the condition that the TE1 mode energy in the first straight waveguide can be completely transferred to the second straight waveguide after being transmitted through this length.

[0035] The width of the second straight waveguide 12 of the directional coupler is equal to the width of the curved waveguide 8 .

[0036] The substrate layer 1 may be, but is not limited to, silicon, quartz, sapphire, indium phosphide, etc.

[0037] In a specific example, the substrate layer 1 is made of silicon material with a thickness of 450 microns; the buried oxide layer 2 is made of silicon dioxide with a thickness of 4.7 microns. The dielectric waveguide layer 3 is made of X-cut with a thickness of 600 nanometers and an etching depth of 300 nanometers. The upper cladding layer 4 is made of silicon oxynitride with a thickness of 3.8 microns.

[0038] The width variation of the mode evolver 6 is not a simple linear increase or decrease, but presents a complex linear shape. Specifically, its width variation is a parabola, and the mathematical expression can be described as W=ax^2+b. Here, the minimum waveguide width of the mode evolver 6 is 1.4 microns, the maximum waveguide width is extended to 2 microns, and its overall length is set to 500 microns.

[0039] The width of the first straight waveguide 11 of the directional coupler 7 is consistent with the width of the mode evolver 6, both of which are 2 microns. Figure 3 The variation of the effective refractive index of different modes as the waveguide width changes is shown in detail. Figure 3 According to the data, the width of the second straight waveguide 12 of the directional coupler 7 is set to 0.74 microns to ensure that the effective refractive index NeffTE0 of the TE0 mode of the second straight waveguide 12 is equal to the effective refractive index NeffTE1 of the TE1 mode of the first straight waveguide 11.

[0040] The distance between the first straight waveguide 11 and the second straight waveguide 12 of the directional coupler 7 is 0.5 micrometers, and the lengths of both are 38.5 micrometers, and the efficiency is as high as 0.95. The radius of the curved waveguide 8 is set to 100 micrometers.

[0041] Figure 4 The mode field transmission of TE0 and TM0 modes in a compact broadband polarization rotation beam splitter based on thin-film lithium niobate is demonstrated, from which it can be clearly seen that this structure can achieve efficient polarization rotation beam splitting.

[0042] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention. The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A broadband integrated polarization rotation beam splitter based on a complex linear gradient structure, comprising a substrate layer (1) and a dielectric waveguide layer (3); characterized in that: A buried oxide layer (2) is provided between the substrate layer (1) and the dielectric waveguide layer (3); an upper cladding layer (4) is provided on the upper surface and both sides of the dielectric waveguide layer (3); along the light wave transmission direction, an input mode spot converter (5), a mode evolver (6), a directional coupler (7) and two output mode spot converters are etched in the dielectric waveguide layer (3); and a curved waveguide (8) is etched between the directional coupler (7) and the first output mode spot converter (9).

2. The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure according to claim 1, characterized in that: The directional coupler (7) comprises a first straight waveguide (11) and a second straight waveguide (12), wherein the first straight waveguide (11) is connected to a second output spot mode converter (10), and the second straight waveguide (12) is connected to the first output spot mode converter (9) via a curved waveguide (8).

3. The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure according to claim 1 or 2, characterized in that: The dielectric waveguide layer (3) is a light field limiting layer, and its material is one of silicon, silicon nitride, indium phosphide, and thin-film lithium niobate.

4. The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure according to claim 2, characterized in that: The input mode spot converter (5), the first output mode spot converter (9) and the second output mode spot converter (10) adopt a tapered gradually changing waveguide structure, and the waveguide widths of the tapered gradually changing waveguides increase sequentially.

5. The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure according to claim 2, characterized in that: The mode evolver (6) adopts a complex linear gradient waveguide structure, the waveguide width of the complex linear gradient waveguide structure gradually increases from small to large according to a specific complex function, and is used to realize the mutual conversion between the TM0 mode at the minimum waveguide width end and the TE1 mode at the maximum waveguide width end, while the TE0 mode remains unchanged; the minimum waveguide width w0 of the mode spot converter (6) is smaller than the hybrid width of the TM0 mode and the TE1 mode, and supports the transmission of the TE0 and TM0 modes, and the maximum waveguide width w3 of the mode evolver is larger than the hybrid width of the TM0 mode and the TE1 mode.

6. The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure according to claim 5, characterized in that: The specific complex function includes one of a parabola type, a hyperbola type, a high-order linear type, and an exponential type.

7. The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure according to claim 2, characterized in that: The width of the first straight waveguide (11) is equal to the maximum waveguide width of the mode evolver (6), and the width of the second straight waveguide (12) satisfies the following conditions: the effective refractive index Neff of the TE0 mode of the second straight waveguide is TE0 The effective refractive index Neff of the TE1 mode of the first straight waveguide TE1 equal.

8. The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure according to claim 2, characterized in that: The width of the first straight waveguide (11) is equal to the length of the second straight waveguide (12), and the length satisfies the condition that the TE1 mode energy in the first straight waveguide can be completely transferred to the second straight waveguide after being transmitted over this length.

9. The broadband integrated polarization rotation beam splitter based on a complex linear gradient structure according to claim 2, characterized in that: The width of the second straight waveguide (12) is equal to the width of the curved waveguide (8).

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