A hybrid integrated electro-optical modulated diffraction grating filter device

Abstract

The present invention belongs to the field of electro-optical modulation devices. More specifically, it relates to a diffraction grating filter device that is a hybrid integration of optical fiber and lithium niobate. A lithium niobate thin film structure is attached to the cross section of the optical fiber, and an electrode structure is prepared on both sides of the lithium niobate thin film. At the same time, a diffraction grating structure is etched on the lithium niobate thin film. The electro-optical effect of the lithium niobate crystal and the diffraction effect of the diffraction grating are used to achieve an optical filtering function. The present invention proposes for the first time to integrate the lithium niobate thin film into the end face of the optical fiber. By utilizing the electro-optical effect of the lithium niobate crystal, high-speed electrically controlled tuning of the diffraction wavelength (reflection / transmission) of the diffraction grating can be achieved. The present invention overcomes the problem of the difficulty in coupling the optical fiber structure with the integrated optical waveguide.

Description

Technical Field

[0001] The present invention belongs to the field of electro-optical modulation devices, and more specifically, relates to a hybrid integrated electro-optical modulation diffraction grating filter device. The device adopts a hybrid integration of lithium niobate film and optical fiber, can realize electrically controlled optical filtering function, and can be applied to fields such as optical communications. Background Art

[0002] Optical filters have received widespread attention in recent years, and their important role in optical communications, optical sensing and other fields has gradually been recognized. The performance and cost of optical filters depend on the principles and methods of filtering. A diffraction grating is a spectroscopic element based on the diffraction phenomenon, which is often used as a core component to form an optical filter. Filters composed of diffraction gratings usually have the characteristics of simple structure and stable performance. As an excellent spectroscopic element, diffraction gratings are widely used in modern spectrometers. For example, grating diffraction can be used for spectral analysis and measurement of light wavelength.

[0003] While common fiber-based diffraction gratings can tune the grating's diffraction properties using the elastic-optical and thermo-optical effects, they suffer from slow tuning speeds, low tuning accuracy, and a complex tuning process. Lithium niobate crystals, on the other hand, exhibit excellent electro-optical effects, enabling high-speed, electrically controlled tuning of diffraction gratings. However, conventional diffraction gratings based on lithium niobate crystals suffer from low coupling efficiency when used in communication systems using optical fiber as the transmission medium.

[0004] In recent years, hybrid integrated devices combining lithium niobate thin films with semiconductor materials have been widely proposed. These devices fully utilize the electro-optical effect of lithium niobate crystals to achieve the design and fabrication of high-speed electro-optical modulation devices. Furthermore, the high refractive index contrast of lithium niobate thin film waveguides effectively reduces device size, laying the foundation for the development of future highly integrated optical devices. However, currently used communication devices and communication systems are still primarily based on optical fiber media, and due to mode matching issues, coupling these hybrid integrated devices with optical fiber devices remains a significant challenge. Summary of the Invention

[0005] To address the problems of low tuning speed and complex tuning methods of diffraction gratings based on optical fiber structures, as well as low coupling efficiency between lithium niobate devices and optical fiber devices, the present invention proposes an electro-optical modulation filter device that integrates a lithium niobate thin film diffraction grating structure and an optical fiber structure.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A hybrid integrated electro-optically modulated diffraction grating filter device comprises an optical fiber, a lithium niobate thin-film diffraction grating, and a pair of electrodes. A section of the optical fiber is stripped of its cladding to expose the core. The lithium niobate thin-film diffraction grating is fixedly mounted on the core cross-section, and the pair of electrodes are located on either side of the core and the lithium niobate thin-film diffraction grating, respectively. By varying the voltage applied to the electrodes, the refractive index of the lithium niobate thin-film diffraction grating is altered, thereby achieving tuning of the diffraction wavelength.

[0008] In a further optimization of this technical solution, the angle between the lithium niobate thin film diffraction grating and the transverse axis of the fiber core is 0 to 90 degrees. The cross section of the fiber core can be perpendicular to the direction of light propagation or tilted, so the angle of inclination of the cross section of the fiber core to the direction of light propagation can be 0 to 90 degrees.

[0009] This technical solution is further optimized, and the lithium niobate thin film diffraction grating is a Bragg grating.

[0010] This technical solution is further optimized, and the optical fiber is a single-mode optical fiber.

[0011] This technical solution is further optimized, and the core diameter of the single-mode optical fiber is 9 to 10 μm.

[0012] In a further optimization of the technical solution, the optical fiber is a few-mode optical fiber.

[0013] This technical solution is further optimized, and the core diameter of the few-mode optical fiber is 20 to 80 μm.

[0014] This technical solution is further optimized, and the optical fiber is a multimode optical fiber.

[0015] This technical solution is further optimized, and the core diameter of the multimode optical fiber is greater than 100 μm.

[0016] Distinguished from existing technologies, the above-mentioned technical solution has the following beneficial effects: The hybrid integrated electro-optically modulated diffraction optical device proposed in this invention utilizes the electro-optical effect of lithium niobate crystals and the high refractive index contrast of lithium niobate thin-film diffraction waveguides to effectively enhance the diffraction efficiency of the diffraction grating and reduce device size. Furthermore, this invention is the first to integrate a lithium niobate thin-film diffraction grating at the end face of an optical fiber, effectively resolving the issue of low coupling efficiency between lithium niobate devices and optical fiber components, and presenting a new approach for hybrid integrated applications based on lithium niobate thin-film waveguide devices and other materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of a hybrid integrated electro-optical modulated diffraction grating filter device;

[0018] Figure 2 Schematic diagram of the lithium niobate film diffraction grating structure;

[0019] Figure 3 Schematic diagram of the optical fiber end face.

[0020] Description of reference numerals:

[0021] 1 is the first optical fiber cladding; 2 is the fiber core; 3 is the lithium niobate thin film diffraction grating; 4 is the second optical fiber cladding; 5 is the positive electrode; and 6 is the negative electrode. DETAILED DESCRIPTION

[0022] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0023] See also Figure 1 The figure shows a schematic diagram of the structure of a hybrid integrated electro-optical modulated diffraction grating filter device. The hybrid integrated electro-optical modulated diffraction grating filter device includes a first optical fiber cladding 1, a fiber core 2, a lithium niobate thin film diffraction grating 3, a second optical fiber cladding 4, a positive electrode 5 and a negative electrode 6. The lithium niobate thin film diffraction grating 3 divides the fiber core 2 into two left and right sections, and the left and right sections of the fiber core 2 are core structures with the cladding stripped off. The electrode structure is placed on both sides of the bare fiber and the diffraction grating at both ends. Here, the electrodes can be prepared on both sides of the optical fiber core by coating so that the electric field can cover the diffraction grating structure. Alternatively, an external electrode can be used to cover the entire structure. According to the electro-optical effect of the lithium niobate crystal, the refractive index of the lithium niobate crystal can be changed by changing the voltage on the electrode, thereby changing the diffraction characteristics of the diffraction grating.

[0024] Currently, lithium niobate thin film waveguide gratings are usually integrated with silicon-based waveguides and then coupled to optical fibers. The structure proposed in the present invention directly integrates lithium niobate thin film waveguide gratings and optical fibers, solving the coupling loss problem.

[0025] See Figure 2 The figure shows the structure of the lithium niobate thin film diffraction grating. Figure 3 Figure 2 shows a schematic diagram of an optical fiber end face. The end face of the fiber core 2 is cut by the lithium niobate thin film diffraction grating 3 at a right angle or at a certain angle offset from the core 2 axis. The offset angle can range from 0 to 90 degrees. This offset angle determines the angle of incidence of the incident light on the lithium niobate thin film diffraction grating 3. The diffraction wavelength of the lithium niobate thin film diffraction grating 3 is related to this incident angle. By adjusting the incident angle, a specific diffraction wavelength can be designed.

[0026] The lithium niobate thin film diffraction grating 3 is prepared on the end face of the core 2 using bonding technology. The core 2 can be a single-mode optical fiber (core diameter 9-10μm) or a few-mode optical fiber (core diameter 20-80μm) or a multimode optical fiber (core diameter greater than 100μm).

[0027] The lithium niobate thin film diffraction grating 3 is a Bragg grating, and the diffraction wavelength is related to the refractive index of the material. For the x-tangential lithium niobate crystal, when the electric field is applied in the z direction, its refractive index satisfies:

[0028]

[0029] Among them, n e is the initial refractive index of lithium niobate crystal, γ 33 is the maximum electro-optic coefficient of lithium niobate, which is a constant, V is the voltage applied to the electrodes, and d is the electrode spacing.

[0030] As the voltage V applied to the electrode changes, the refractive index n of the lithium niobate crystal will also change. Through this electric field control method, the diffraction characteristics of the diffraction grating can be tuned.

[0031] It should be noted that, in this document, relational terms such as first and second, etc., are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "include," "comprise," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or terminal device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or terminal device. Without further limitation, elements defined by the phrase "include..." or "comprising..." do not exclude the presence of additional elements in the process, method, article, or terminal device comprising the elements. Furthermore, in this document, "greater than," "less than," "exceeding," etc., are understood to exclude the number itself; "above," "below," "within," etc., are understood to include the number itself.

[0032] Although the above embodiments have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concepts. Therefore, the above descriptions are merely embodiments of the present invention and do not limit the scope of patent protection of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the scope of patent protection of the present invention.

Claims

1. A hybrid integrated electro-optical modulated diffraction grating filter device, characterized in that: The invention comprises an optical fiber, a lithium niobate thin film diffraction grating and a pair of electrodes. The cladding of a section of the optical fiber is stripped to expose the fiber core. The lithium niobate thin film diffraction grating is fixedly arranged on the cross section of the fiber core. The pair of electrodes are respectively located on both sides of the fiber core and the lithium niobate thin film diffraction grating. The angle between the lithium niobate thin film diffraction grating and the transverse axis of the fiber core is greater than 0 degrees and less than or equal to 90 degrees.

2. The hybrid integrated electro-optical modulated diffraction grating filter device according to claim 1, characterized in that: The lithium niobate thin film diffraction grating is a Bragg grating.

3. The hybrid integrated electro-optical modulated diffraction grating filter device according to claim 1, characterized in that: The optical fiber is a single-mode optical fiber.

4. The hybrid integrated electro-optical modulated diffraction grating filter device according to claim 3, characterized in that: The core diameter of the single-mode optical fiber is 9-10 μm.

5. The hybrid integrated electro-optical modulated diffraction grating filter device according to claim 1, characterized in that: The optical fiber is a few-mode optical fiber.

6. The hybrid integrated electro-optical modulated diffraction grating filter device according to claim 5, characterized in that: The core diameter of the few-mode optical fiber is 20-80 μm.

7. The hybrid integrated electro-optical modulated diffraction grating filter device according to claim 1, characterized in that: The optical fiber is a multimode optical fiber.

8. The hybrid integrated electro-optical modulated diffraction grating filter device according to claim 7, characterized in that: The core diameter of the multimode optical fiber is greater than 100 μm.

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