Polarization independent prism coupling method and waveguide structure

Abstract

The application 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 layer in a prism coupling waveguide, the refractive index distribution of the optical anisotropic material is adjusted, the transverse electric mode and the transverse magnetic mode in the waveguide have the same effective refractive index, different polarization states in the same light beam can be coupled into the optical waveguide at the same time, the prism coupling is no longer limited by the polarization sensitivity problem, the problem that a traditional prism coupling mode is limited by phase matching constraints is overcome, and the light with different polarization states in the same light beam has the optimal coupling angle.

Description

Technical Field

[0001] The present 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 are rapidly developing towards miniaturization and integration. Guided by this trend, integrated optics has garnered widespread attention, with optical waveguides forming the foundation and core of integrated optics. A key issue in integrated optics is how to couple light from free space into waveguides. Existing solutions include fiber end-face coupling, grating coupling, and prism coupling. Prism coupling offers unique advantages, including a simple structure and the ability to excite selectable waveguide modes.

[0003] However, due to the constraints of phase matching conditions, traditional prism coupling means that light with different polarization states has different optimal coupling angles. Therefore, different polarization states in the same 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 the simultaneous coupling of different polarization states in the same light beam, and overcomes the limitations 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:

[0006] The present invention provides a polarization-independent prism coupling method. An optically anisotropic material is used in a waveguide provided with a prism coupling structure. 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.

[0007] Preferably, one or more layers among the substrate layer, the core layer and the cladding layer in the waveguide are made of optically anisotropic material.

[0008] Preferably, the optically anisotropic material is liquid crystal or lithium niobate.

[0009] Another aspect of the present 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 an optically anisotropic material, 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.

[0010] 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.

[0011] Preferably, it further comprises an electrode layer and a glass cover plate arranged on the outer surface.

[0012] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0013] By introducing optically anisotropic materials into a prism-coupled waveguide structure and engineering its refractive index profile, this invention achieves polarization-independent optical coupling. This allows light of different polarization states to be efficiently and simultaneously coupled into the waveguide, resolving the polarization sensitivity issue inherent in conventional prism coupling. By achieving polarization-independent coupling, the present invention effectively improves the coupling efficiency of light from free space into the waveguide structure, which is crucial for improving the performance of optical communication systems and reducing optical losses. Furthermore, the implementation of polarization-independent coupling overcomes the drawbacks of conventional polarization-sensitive coupling, such as the need for complex polarization control and alignment.

[0014] Since traditional prism coupling is limited by phase matching conditions, it is difficult to achieve same-beam polarization-independent light beam coupling. Therefore, it 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 to promote the advancement of integrated optics and photonics technology, and promotes innovation in optical communications, optical computing and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0016] Figure 1 2 is a schematic structural diagram of a prism-coupled waveguide introducing an optical anisotropic material according to an embodiment of the present invention;

[0017] Figure 2 Schematic diagram of birefringence and orientation angle under polarization-independent coupling conditions provided by an embodiment of the present invention;

[0018] Figure 3 1 is a schematic diagram comparing the coupled light fields in the TE mode and the TM mode according to an embodiment of the present invention;

[0019] Figure 4 is a coupling efficiency curve diagram of the simultaneous coupling of the TE mode and the TM mode provided by an embodiment of the present invention;

[0020] Figure 5 Schematic diagram of the light beam transmission path in the waveguide after the TE mode and the TM mode are simultaneously coupled according to an embodiment of the present invention;

[0021] Figure 6 1 is a schematic diagram of the change of TE mode and TM mode coupling efficiency over time according to an embodiment of the present invention.

[0022] Reference numerals include:

[0023] 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

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present 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 present invention and do not constitute a limitation to the present invention. Similar elements in different embodiments use associated similar element numbers. In the following embodiments, many detailed descriptions are intended to enable the present 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 elements, materials, or methods. In some cases, some operations related to the present invention are not shown or described in the specification. This is to avoid the core part of the present invention being overwhelmed by too much description. For those skilled in the art, it is not necessary to describe these related operations in detail. They can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0025] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention 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 orders in the description and the drawings are only for the purpose of clearly describing a certain embodiment and are not intended to be a required order, unless otherwise specified that a certain order must be followed.

[0026] In the description of the present 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" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present 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 present 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 the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0027] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0028] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0029] In one embodiment of the present invention, a polarization-independent prism coupling method is provided, which is mainly aimed at existing waveguides that use prism coupling structures for optical coupling. An optically 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 optically anisotropic materials. Optically 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 optically anisotropic material, the transverse electric mode and the transverse magnetic mode in the waveguide can have the same effective refractive index, thereby achieving polarization-independent prism coupling. For light with different polarization states in the same light beam, this design can simultaneously couple light with different polarization states, completing the mutual conversion of the light beam between free space and the waveguide structure.

[0030] See also Figure 1In one embodiment of the present invention, a waveguide structure is designed based on the aforementioned 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 7. The coupling prism 1 is used to couple light from free space into the waveguide structure. Through the principle of total internal reflection, the coupling prism 1 can guide incident light 8 into the waveguide structure and excite a waveguide mode 9. The coupling prism 1 is made of a high-refractive-index material, specifically heavy lanthanum flint glass, with a refractive index of 1.89. An electrode layer 6 is provided on the top surface of the coupling prism 1. This electrode layer 6, in combination with another electrode layer 6, applies an electric field to control the alignment of liquid crystal molecules within the cladding layer 5. The electrode layer 6 is typically made of a conductive material, such as indium tin oxide (ITO). In this embodiment of the present invention, the thickness of the ITO is designed to be 30 nm.

[0031] A substrate layer 2 is provided above the upper electrode layer 6 of the coupling prism 1. This layer primarily supports the foundation and functional layers of the waveguide structure. It is made of silicon dioxide with a refractive index of 1.47 and a gradual thickness distribution, increasing from 0 to 2 microns.

[0032] 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.

[0033] The upper surface of the core layer 3 is provided with a cladding layer 5, with orientation layers 4 on both sides. The refractive index of the cladding layer 5 is lower than that of the core layer 3, ensuring that incident light 8 coupled into the core layer 3 is effectively transmitted through total internal reflection, thereby realizing a waveguide mode 9. The material of the cladding layer 5 must have low refractive index and low loss properties. In this embodiment of the present invention, to achieve polarization-independent prism coupling, the cladding layer 5 is made of an optically anisotropic material. Common optically anisotropic materials include liquid crystal or lithium niobate. In this embodiment of the present invention, negative optically anisotropic liquid crystal is specifically used, with a refractive index of 1.48 for ordinary light and a refractive index of 1.69 for extraordinary light. The thickness of the cladding layer 5 is 6 microns. The orientation layers 4 on the upper and lower sides of the cladding 5 are primarily used to control the alignment of the liquid crystal molecules in the cladding layer 5, thereby achieving light modulation and control. The orientation layers 4 are rubbed, with a refractive index of 1.58 for light. Each orientation layer 4 is 50 nm thick.

[0034] To realize polarization-independent prism coupling, the refractive index distribution of the optical anisotropic material of the cladding layer 5 is adjusted to make the effective refractive index of the transverse electric mode and the transverse magnetic mode in the waveguide mode 9 of the waveguide the same. When the polarization-independent prism coupling condition is met, the required birefringence and orientation angle of the negative liquid crystal of the cladding layer 5 satisfy the curve as shown in Figure 2 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 decreases to about 0.2.

[0035] An electrode layer 6 is arranged on the upper surface of the orientation layer 4 above the cladding layer 5, which forms a pair of electrodes with the electrode layer 6 above the coupling prism 1, and the arrangement of the negative liquid crystal in the cladding layer 5 is controlled by applying an electric field. The upper surface of the electrode layer is also provided with a glass cover plate 7, which is located at the top of the waveguide structure and mainly plays a protective and supporting role.

[0036] As an optional embodiment, the substrate layer 2 or the core layer 3 can also be made of an optical anisotropic material. Optionally, one of the substrate layer 2, the core layer 3 or the cladding layer 5 is made of an optical anisotropic material, or multiple layers of the substrate layer 2, the core layer 3 or the cladding layer 5 are made of an optical anisotropic material at the same time.

[0037] To verify the effectiveness of the embodiment of the present application, the waveguide structure provided above is verified, and the verification results are as follows:

[0038] Please refer to Figure 3 , which shows the comparison of the coupling of light field in TE mode and TM mode of the waveguide structure. The coupling efficiency can be calculated by the overlap integral of the Gaussian light beam and the best coupling light field. The larger the overlap integral is, the higher the coupling efficiency is.

[0039] Please refer to Figure 4 , which shows the coupling efficiency of the waveguide structure in TE mode and TM mode. Both modes can achieve a coupling efficiency of up to 91%. This result shows that by introducing an optical anisotropic material, efficient coupling of light with different polarization states is realized, which is of great significance for polarization-independent prism coupling.

[0040] Please refer to Figure 5 , which 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 TE mode and TM mode at the same time. Different polarization states of the same light beam can be coupled into the waveguide from free space at the same time and achieve stable propagation.

[0041] Please refer to Figure 6, shows how the coupling efficiency of light with different polarization states changes with time in TE mode and TM mode after the light beam is coupled into the core layer 3. The coupling efficiency of these two modes changes with time by less than 1%, indicating that the coupling efficiency has good stability.

[0042] The above results demonstrate the effectiveness of the polarization-independent prism coupling method and corresponding optical waveguide proposed in this embodiment of the present invention. By introducing optically anisotropic materials, efficient and stable coupling of light with different polarization states is achieved. This not only improves the efficiency and stability of optical coupling, but also simplifies the complexity of existing designs.

[0043] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the scope of protection of this specification. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this specification shall be included in the scope of protection of this specification.

[0044] 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 smartphone, 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.

[0045] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0046] The various embodiments in this specification are described in a progressive manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiments are generally similar to the method embodiments, so the description is relatively simple. For relevant parts, refer to the description of the method embodiments.

[0047] The foregoing description of this specification describes specific embodiments. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in an order different from that described in the embodiments and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order shown or the sequential order to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A polarization-independent prism coupling method, characterized in that: Optically anisotropic materials are used in a waveguide provided with a prism coupling structure. The waveguide includes: a coupling prism, a substrate layer, a core layer, and a cladding layer. Among them, one or more layers of the substrate layer, the core layer, and the cladding layer are made of optically anisotropic materials. By adjusting the refractive index distribution of the optically anisotropic materials, 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, wherein: One or more layers among the substrate layer, the core layer and the cladding layer in the waveguide are made of the optically anisotropic material.

3. The polarization-independent prism coupling method according to claim 1, wherein: 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 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.

5. The waveguide structure according to claim 4, wherein: 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 with orientation layers on both the upper and lower sides.

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

Images