Polarization-independent prism coupling method and waveguide structure

Abstract

The invention relates to the technical field of optical waveguides, and particularly provides a polarization-independent prism coupling method and a waveguide structure, an optical anisotropic material is introduced into a substrate layer, a core layer and / or a cladding in a prism coupling waveguide, and a transverse electric mode and a transverse magnetic mode in the waveguide have the same effective refractive index by adjusting the refractive index distribution of the optical anisotropic material, so that the polarization-independent prism coupling method is realized. Different polarization states in the same light beam can be coupled into an optical waveguide at the same time, prism coupling is not limited by polarization sensitivity any more, the problem that a traditional prism coupling mode is limited by phase matching constraint is solved, and light of different polarization states in the same light beam has the optimal coupling angle.

Description

Technical Field

[0001] The invention belongs to the technical field of optical waveguides, and in particular relates to a polarization-independent prism coupling method and a waveguide structure. Background Art

[0002] Optoelectronic devices need to develop rapidly in the direction of miniaturization and integration. Under the guidance of this plan, integrated optics has received extensive attention, among which optical waveguides are the foundation and core of integrated optics. An important issue in integrated optics is how to couple light from free space into waveguides. The existing solutions mainly include fiber end face coupling, grating coupling, prism coupling, etc. Among them, prism coupling has unique advantages such as simple structure and optional waveguide mode excitation.

[0003] However, in traditional prism coupling, due to the constraints of phase matching conditions, light in different polarization states has different optimal coupling angles. Therefore, different polarization states in the same light beam cannot be efficiently coupled at the same time, which seriously limits the application scope of prism coupling. Summary of the invention

[0004] In view of this, the present invention aims to provide a polarization-independent prism coupling method, which solves the polarization sensitivity problem existing in traditional prism coupling, realizes simultaneous coupling of different polarization states in the same light beam, and overcomes the limitation of polarization sensitivity in prism coupling on integrated optical devices.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows: The invention provides a polarization-independent prism coupling method, in which an optically anisotropic material is used in a waveguide provided with a prism coupling structure, and the refractive index distribution of the optically anisotropic material is adjusted so that the transverse electric mode and the transverse magnetic mode in the waveguide have the same effective refractive index.

[0006] Preferably, one or more of the substrate layer, the core layer and the cladding layer in the waveguide is an optically anisotropic material.

[0007] Preferably, the optically anisotropic material is liquid crystal or lithium niobate.

[0008] Another aspect of the invention provides a waveguide structure, comprising: a coupling prism, a substrate layer, a core layer and a cladding layer; wherein one or more layers of the substrate layer, the core layer and the cladding layer are made of optically anisotropic materials, and the refractive index distribution of the optically anisotropic materials is adjusted so that the transverse electric mode and the transverse magnetic mode in the waveguide have the same effective refractive index.

[0009] Preferably, the coupling prism is arranged below the substrate layer, the core layer is arranged on the upper surface of the substrate layer, and the upper surface of the core layer is provided with a cladding layer with orientation layers on both the upper and lower sides.

[0010] Preferably, it also includes an electrode layer and a glass cover plate arranged on the outer surface.

[0011] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention realizes polarization-independent optical coupling by introducing optical anisotropic materials into the prism-coupled waveguide structure and designing its refractive index distribution, so that light of different polarization states can be efficiently coupled into the waveguide at the same time, solving the polarization sensitivity problem of traditional prism coupling. Since polarization-independent coupling is realized, the present invention can effectively improve the coupling efficiency of light from free space to the waveguide structure, which is of great significance for improving the performance of optical communication systems and reducing optical losses. In addition, the realization of polarization-independent coupling solves the drawbacks of traditional polarization-sensitive coupling, such as the need for complex polarization control and alignment.

[0012] Since traditional prism coupling is limited by phase matching conditions, it is difficult to achieve same-beam polarization-independent light beam coupling, and therefore has high requirements for the incident light, which greatly limits the application of prism-coupled waveguides. The invention makes prism coupling no longer limited by polarization sensitivity issues, improves the scope of application and system robustness of prism coupling, provides an effective solution to polarization problems in integrated optical devices, helps promote the advancement of integrated optics and photonics technology, and promotes innovations in optical communications, optical computing and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 is a schematic structural diagram of a prism-coupled waveguide introducing an optical anisotropic material according to an embodiment of the present invention; Figure 2 is a schematic diagram of birefringence and orientation angle under polarization-independent coupling conditions provided by an embodiment of the present invention; Figure 3 is a schematic diagram comparing the coupled optical fields in the TE mode and the TM mode provided according to an embodiment of the present invention; Figure 4 is a coupling efficiency curve diagram of simultaneous coupling of TE mode and TM mode provided by an embodiment of the present invention; Figure 5 is a schematic diagram of a light beam transmission path in a waveguide after a TE mode and a TM mode are simultaneously coupled according to an embodiment of the present invention; Figure 6 It is a schematic diagram of the variation of the coupling efficiency of the TE mode and the TM mode over time according to an embodiment of the present invention.

[0014] Reference numerals include: Coupling prism 1, substrate layer 2, core layer 3, orientation layer 4, cladding layer 5, electrode layer 6, glass cover 7, incident light 8, waveguide mode 9. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0016] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.

[0017] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0018] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0019] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0020] In one embodiment of the present invention, a polarization-independent prism coupling method is provided, which is mainly aimed at the existing waveguide using a prism coupling structure for optical coupling, and an optical anisotropic material is introduced into the waveguide structure, and its light propagation characteristics change with different directions. Specifically, one or more layers of the substrate layer, core layer and cladding layer in the waveguide structure can be made of optical anisotropic materials. Optical anisotropic materials have refractive index anisotropy, and such materials include but are not limited to liquid crystal, lithium niobate, etc. By adjusting the refractive index distribution of the optical anisotropic material, the transverse electric mode and the transverse magnetic mode in the waveguide can have the same effective refractive index, so that polarization-independent prism coupling can be achieved. For light of different polarization states in the same light beam, this design can couple light of different polarization states simultaneously, and complete the mutual conversion of the light beam between free space and the waveguide structure.

[0021] See also Figure 1In one embodiment of the present invention, a waveguide structure is designed according to the above polarization-independent prism coupling method, comprising: a coupling prism 1, a substrate layer 2, a core layer 3, an orientation layer 4, a cladding layer 5, an electrode layer 6 and a glass cover plate 7, wherein the coupling prism 1 is used to couple light from free space into the waveguide structure, and through the principle of total internal reflection, the coupling prism 1 can guide the incident light 8 into the waveguide structure and excite the waveguide mode 9. The coupling prism 1 is made of a high refractive index material, specifically heavy lanthanum flint glass, and the refractive index of light is 1.89. An electrode layer 6 is provided on the upper surface of the coupling prism 1, and the electrode layer 6 is combined with another electrode layer 6 to apply an electric field to control the arrangement of liquid crystal molecules in the cladding layer 5. The electrode layer 6 is usually made of a conductive material, such as indium tin oxide (ITO), and the thickness of the indium tin oxide is designed to be 30nm in the embodiment of the present invention.

[0022] The upper surface of the electrode layer 6 on the upper surface of the coupling prism 1 is provided with a substrate layer 2, which mainly supports the base layer and the functional layer of the waveguide structure. The substrate layer 2 is made of silicon dioxide material, and its refractive index to light is 1.47, and its thickness distribution changes gradually, and the thickness gradually increases from 0 microns to 2 microns.

[0023] A core layer 3 is provided on the upper surface of the substrate layer 2. The core layer 3 is the main channel for light transmission in the waveguide structure. Its refractive index is usually higher than that of the surrounding materials to achieve total reflection and guidance of light. The core layer material needs to have high refractive index and low loss characteristics. Silicon oxynitride material is commonly used, which has a refractive index of 1.85 and a thickness of 580nm.

[0024] The upper surface of the core layer 3 is provided with a cladding 5 with an orientation layer 4 on both the upper and lower sides. The refractive index of the cladding 5 is lower than that of the core layer 3 to ensure that the incident light 8 coupled into the core layer 3 is effectively transmitted through total reflection in the core layer 3 to realize the waveguide mode 9. The material of the cladding 5 needs to have low refractive index and low loss characteristics. In the embodiment of the present invention, in order to realize polarization-independent prism coupling, the material of the cladding 5 uses an optically anisotropic material. Common optically anisotropic materials include liquid crystal or lithium niobate. In the embodiment of the present invention, negative liquid crystal with optical anisotropy is specifically used, and its refractive index for ordinary light is 1.48 and its refractive index for extraordinary light is 1.69. The thickness of the cladding 5 is 6 microns. The orientation layers 4 arranged on the upper and lower sides of the cladding 5 are mainly used to control the arrangement direction of the liquid crystal molecules in the cladding 5 to realize the modulation and control of light. The orientation layer 4 is a friction orientation, and the refractive index for light is 1.58. The thickness of each orientation layer 4 is 50nm.

[0025] In order to realize polarization-independent prism coupling, the refractive index distribution of the optical anisotropic material of the cladding 5 is adjusted so that the transverse electric mode and the transverse magnetic mode in the waveguide mode 9 of the waveguide have the same effective refractive index. When the polarization-independent prism coupling condition is met, the birefringence and orientation angle required by the negative liquid crystal of the cladding 5 meet the following conditions: Figure 2 As shown in the curve, when the orientation angle is small (such as 45°), the required birefringence is high (about 0.36); as the orientation angle increases, the birefringence gradually decreases; when the orientation angle approaches 90°, the birefringence drops to about 0.2.

[0026] Another electrode layer 6 is arranged on the upper surface of the orientation layer 4 above the cladding layer 5. The electrode layer 6 and the electrode layer 6 above the coupling prism 1 form a pair of electrodes, and an electric field is applied to control the arrangement of the negative liquid crystal in the cladding layer 5. A glass cover plate 7 is also arranged on the upper surface of the electrode layer. The glass cover plate 7 is located at the top of the waveguide structure and mainly plays a role of protection and support.

[0027] As an optional embodiment, the substrate layer 2 or the core layer 3 may be made of an optically anisotropic material. Optionally, one of the substrate layer 2, the core layer 3 or the cladding layer 5 may be made of an optically anisotropic material, or multiple layers of the substrate layer 2, the core layer 3 or the cladding layer 5 may be made of an optically anisotropic material at the same time.

[0028] In order to verify the effectiveness of the embodiment of the present invention, the waveguide structure provided above was verified, and the verification results are as follows: See also Figure 3 , which shows the comparison of the coupled light fields of the waveguide structure in the TE mode and the TM mode respectively. The coupling efficiency can be calculated by the overlap integral of the Gaussian beam and the optimal coupling light field. The larger the overlap integral, the higher the coupling efficiency.

[0029] See also Figure 4 , showing the coupling efficiency of the waveguide structure in the TE mode and the TM mode simultaneously coupled, both modes can simultaneously achieve a coupling efficiency of up to 91%. This result shows that by introducing optical anisotropic materials, efficient coupling of light in different polarization states is achieved, which is of great significance for polarization-independent prism coupling.

[0030] See also Figure 5 , shows the transmission path of the light beam in the core layer 3 after the incident light 8 is coupled into the core layer 3 in the TE mode and the TM mode at the same time. Lights of different polarization states in the same light beam can be coupled into the waveguide from the free space at the same time and achieve stable propagation.

[0031] See also Figure 6, shows the variation of coupling efficiency over time for light in different polarization states in TE mode and TM mode after the light beam is coupled into the core layer 3. The coupling efficiency of these two modes varies with time by less than 1%, indicating that the coupling efficiency has good stability.

[0032] The above results demonstrate the effectiveness of the polarization-independent prism coupling method and the corresponding optical waveguide proposed in the embodiment of the present invention. By introducing optical anisotropic materials, efficient and stable coupling of light in different polarization states is achieved. This not only improves the efficiency and stability of optical coupling, but also simplifies the complexity of existing designs.

[0033] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.

[0034] The systems, devices, modules or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0035] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0036] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0037] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A polarization-independent prism coupling method, characterized in that: An optical anisotropic material is used in a waveguide provided with a prism coupling structure, and the refractive index distribution of the optical anisotropic material is adjusted so that the transverse electric mode and the transverse magnetic mode in the waveguide have the same effective refractive index.

2. The polarization-independent prism coupling method according to claim 1, characterized in that: One or more layers among the substrate layer, the core layer and the cladding layer in the waveguide are the optically anisotropic material.

3. The polarization-independent prism coupling method according to claim 1, characterized in that: The optically anisotropic material is liquid crystal or lithium niobate.

4. A waveguide structure, characterized in that: include: A coupling prism, a substrate layer, a core layer and a cladding layer; wherein one or more layers of the substrate layer, the core layer and the cladding layer are made of optical anisotropic materials, and the refractive index distribution of the optical anisotropic materials is adjusted so that the transverse electric mode and the transverse magnetic mode in the waveguide have the same effective refractive index.

5. The waveguide structure according to claim 4, characterized in that The coupling prism is arranged below the substrate layer, the core layer is arranged on the upper surface of the substrate layer, and the upper surface of the core layer is provided with the cladding layer having the orientation layer arranged on the upper and lower sides.

6. The waveguide structure according to claim 5, characterized in that It also includes an electrode layer and a glass cover plate arranged on the outer surface.

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