Lithium niobate thin film integrated chip, optoelectronic device and fiber-optic gyroscope

Abstract

The embodiment of the present application discloses a lithium niobate thin film integrated chip, an optoelectronic device and an optical fiber gyroscope, the integrated chip comprises a substrate, a lower cladding layer, a lithium niobate thin film waveguide core layer and an upper cladding layer from bottom to top, wherein the lithium niobate thin film waveguide core layer comprises an incident unit, a polarizing unit, a Y-branch coupling unit, a mode filtering unit, a Y-branch beam splitting unit, a phase modulation unit and a resonance unit connected in sequence. The embodiment of the present application realizes monolithic integration of multiple functions such as polarization, beam splitting, beam combining, modulation and resonance by using the advantages of low loss, small size, high electro-optic performance and the like of the lithium niobate thin film, solves the problems of thermal matching, optical coupling loss and the like existing in the mixed integration technology of multiple heterogeneous materials, improves the integration degree and reliability of chip integration, and simplifies the process flow.

Description

Technical Field

[0001] This invention relates to the field of chip integration, and more particularly to a lithium niobate thin-film integrated chip, optoelectronic devices, and fiber optic gyroscopes. Background Technology

[0002] Fiber optic gyroscopes are angular velocity sensors based on the Sagnac effect. They offer advantages such as no moving parts, high precision, resistance to electromagnetic interference, and small size, making them more promising for applications than laser gyroscopes or other electromechanical gyroscopes. With the development of inertial technology, application fields are placing increasingly stringent requirements on the size and weight of inertial systems, making integrated, miniaturized, and low-cost fiber optic gyroscope designs inevitable. Traditional fiber optic gyroscope optical systems consist of various discrete optical components, mainly including a broadband light source, fiber optic coupler, Y-waveguide phase modulator, polarization-maintaining fiber loop, photodetector, and signal processing circuitry. These optical components form a closed optical path through optical fibers, resulting in complex manufacturing processes, large system size, and poor reliability, failing to meet the growing demand for miniaturized and integrated inertial systems.

[0003] The main goal of integrated optical gyroscopes is to achieve high-precision sensing while reducing the size of the optical gyroscope. Currently, the core component of fiber optic gyroscopes—the Y-waveguide phase modulator, which integrates polarization, coupling, beam splitting, and modulation—is still fabricated using traditional lithium niobate bulk materials. This is primarily achieved through proton exchange, resulting in a small refractive index difference between the waveguide core and cladding. This leads to large device size, incompatibility with semiconductor processes, and consequently, large fiber optic gyroscope system dimensions, making integration difficult and a major challenge for miniaturization. To improve integration, passive photonic chip technologies such as silicon-based silicon dioxide and silicon nitride have been proposed for hybrid integration with lithium niobate bulk material modulator chips. However, problems such as poor thermal matching and optical coupling efficiency exist between different chips, making it difficult to meet the demands for high-performance, high-reliability, and highly integrated systems.

[0004] In summary, fiber optic gyroscopes can be integrated using photonic devices. However, due to the large size of each functional chip in photonic devices and the low integration of multiple chips, it is difficult to achieve high integration of each functional chip. Therefore, how to achieve high integration of functional chips is an urgent problem to be solved. Summary of the Invention

[0005] In a first aspect, the present invention provides a lithium niobate thin film integrated chip, which, from bottom to top, comprises a substrate, a lower cladding layer, a lithium niobate thin film waveguide core layer, and an upper cladding layer;

[0006] The lithium niobate thin-film waveguide core layer includes an incident unit, a polarization unit, a Y-branch coupling unit, a mode filtering unit, a Y-branch beam splitting unit, a phase modulation unit, and a resonant unit connected in sequence.

[0007] The incident unit is used to connect to the light source and input the incident light source into the polarization unit to polarize the light source and obtain single-polarized light;

[0008] The Y-branch beam splitter is used to split the coupled output single-polarized light into two equal paths, and then the phase modulation unit modulates the two single-polarized lights to obtain two modulated signal lights.

[0009] The resonant unit is used to control the phase shift of the two modulated signal lights, return the two modulated signal lights to the Y-branch beam splitter, and re-modulate them through the phase modulation unit;

[0010] The Y-branch beam splitter is also used to combine the two modulated signal beams after re-modulation to generate an interference signal.

[0011] The mode filtering unit is used to reduce noise in the single-polarized light and the modulated signal light;

[0012] The other branch of the Y-branch coupling unit is used to output the interference signal.

[0013] In an optional embodiment, the polarization unit includes a first through waveguide, a wide ridge waveguide, a first circular arc waveguide, and a first conical waveguide. The wide ridge waveguide is disposed on one side of the first through waveguide and is sequentially connected to the first circular arc waveguide and the first conical waveguide.

[0014] The resonant unit includes a second circular arc waveguide, a second straight waveguide, a third circular arc waveguide, a third straight waveguide, a fourth circular arc waveguide, a fourth straight waveguide, a fifth circular arc waveguide connected in sequence, and an optical microcavity waveguide disposed on one side of the third straight waveguide.

[0015] In an optional embodiment, the first to fourth through waveguides and the second to fifth circular arc waveguides all adopt a single-mode ridge waveguide structure made of lithium niobate thin film material;

[0016] The wide ridge waveguide and the first circular arc waveguide are respectively adopted as multimode ridge waveguide structures made of lithium niobate thin film.

[0017] The wide-ridge waveguide and the first through waveguide satisfy a preset phase matching condition in TM transmission mode, but do not satisfy the preset phase matching condition in TE transmission mode.

[0018] The first conical waveguide, the single-mode ridge waveguide structure, and the multi-mode ridge waveguide structure all adopt a shallow ridge structure with the same ridge height.

[0019] In an optional embodiment, the incident unit includes a second conical waveguide and a fifth through waveguide connected in sequence, with the small end of the second conical waveguide connected to the fifth through waveguide;

[0020] The Y-branch coupling unit includes a sixth through waveguide, a seventh through waveguide, a Y-branch coupling waveguide, and an eighth through waveguide connected in sequence.

[0021] The Y-branch beam splitter unit includes a ninth through waveguide, a Y-branch beam splitter, a tenth through waveguide, and an eleventh through waveguide;

[0022] The mode filtering unit includes two reverse-connected sixth and seventh arc waveguides, the sixth arc waveguide being connected to the eighth through waveguide, and the seventh arc waveguide being connected to the ninth through waveguide;

[0023] The phase modulation unit includes a first electrode and a second electrode. The first electrode is symmetrically disposed on both sides of the tenth through waveguide, and the second electrode is symmetrically disposed on both sides of the eleventh through waveguide.

[0024] In an optional embodiment, the first circular arc waveguide, the second circular arc waveguide, the fifth circular arc waveguide, the sixth circular arc waveguide, and the seventh circular arc waveguide all adopt a 90° circular arc structure;

[0025] Both the third and fourth circular arc waveguides adopt a 180° circular arc structure;

[0026] The radius of the arc of the first to fifth circular arc waveguides and the seventh circular arc waveguide is greater than or equal to 50 μm.

[0027] In an optional embodiment, the substrate is made of lithium niobate crystal, the lower cladding is made of silicon dioxide, the lithium niobate thin-film waveguide core is made of lithium niobate thin film, and the upper cladding is made of silicon dioxide with a refractive index less than a preset refractive index threshold.

[0028] In an optional embodiment, the optical microcavity waveguide adopts a microring structure, and the radius of the microring is not less than 200 μm; or,

[0029] The optical microcavity waveguide adopts a microdisk structure, and the radius of the microdisk is not less than 200 μm.

[0030] In a second aspect, the present invention provides an optoelectronic device, including the aforementioned lithium niobate thin-film integrated chip.

[0031] Thirdly, the present invention provides a fiber optic gyroscope, including a light source, a photodetector, and optoelectronic devices as described above.

[0032] Fourthly, the present invention provides an optoelectronic system, including the fiber optic gyroscope as described above.

[0033] The embodiments of the present invention have the following beneficial effects:

[0034] The lithium niobate thin-film integrated chip provided in this embodiment comprises, from bottom to top, a substrate, a lower cladding layer, a lithium niobate thin-film waveguide core layer, and an upper cladding layer. The lithium niobate thin-film waveguide core layer includes, in sequence, an incident unit, a polarization unit, a Y-branch coupling unit, a mode filtering unit, a Y-branch beam splitting unit, a phase modulation unit, and a resonant unit. This embodiment utilizes the advantages of lithium niobate thin films, such as low loss, small size, and high electro-optic performance, to monolithically integrate optoelectronic devices with multiple functions including polarization, beam splitting, beam combining, modulation, and resonance. This solves the problems of thermal matching and optical coupling loss inherent in hybrid integration technologies using various heterogeneous materials, improves the integration density and reliability of the chip, simplifies the process flow, and saves on the cost of integrated chip fabrication. Attached Figure Description

[0035] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope of protection of the present invention. In the various drawings, similar components are numbered similarly.

[0036] Figure 1 A waveguide cross-sectional view of a multifunctional thin-film lithium niobate integrated chip according to an embodiment of the present invention is shown.

[0037] Figure 2 A top view of the multifunctional thin-film lithium niobate integrated chip structure in an embodiment of the present invention is shown;

[0038] Figure 3 A schematic diagram of the fiber optic gyroscope in an embodiment of the present invention is shown.

[0039] Key component symbols: 10-Substrate; 20-Lower cladding; 30-Lithium niobate thin-film waveguide core; 40-Upper cladding; 31-Incident unit; 32-Polarization unit; 33-Y-branch coupling unit; 34-Mode filtering unit; 35-Y-branch beam splitter; 36-Phase modulation unit; 37-Resonant unit; 311-Second conical waveguide; 312-Fifth straight-through waveguide; 321-First straight-through waveguide; 322-Wide ridge waveguide; 323-First circular arc waveguide; 324-First conical waveguide; 331-Sixth straight-through waveguide; 332-Seventh straight-through waveguide; 333-Y-branch coupling waveguide; 3 34-Eighth straight-through waveguide; 341-Sixth circular arc waveguide; 342-Seventh circular arc waveguide; 351-Ninth straight-through waveguide; 352-Y-branch beam splitter waveguide; 353-Tenth straight-through waveguide; 354-Eleventh straight-through waveguide; 361-First electrode; 362-Second electrode; 371-Second circular arc waveguide; 372-Second straight-through waveguide; 373-Third circular arc waveguide; 374-Third straight-through waveguide; 375-Fourth circular arc waveguide; 376-Fourth straight-through waveguide; 377-Fifth circular arc waveguide; 378-Optical microcavity waveguide; 50-Light source; 60-Photodetector; 70-Signal processing circuit. Detailed Implementation

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0041] The components of the embodiments of the invention described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0042] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0043] Furthermore, the terms "first," "second," and "third" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0044] Unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the invention pertain. Terms (such as those defined in commonly used dictionaries) shall be interpreted as having the same meaning as in their contextual meaning in the relevant technical field and shall not be interpreted as having an idealized or overly formal meaning, unless clearly defined in the various embodiments of the invention.

[0045] Traditional fiber optic gyroscope optical systems consist of discrete optical components, primarily a broadband light source, fiber coupler, Y-waveguide phase modulator, polarization-maintaining fiber loop, photodetector, and signal processing circuitry. These components form a closed optical path via optical fibers, resulting in complex manufacturing processes, large system size, and poor reliability, failing to meet the growing demand for miniaturized integration in inertial systems. Integrated fiber optic gyroscopes, on the other hand, are large and difficult to integrate, hindering the high-performance, high-reliability requirements of high-integration systems. With the development of photonic devices, emerging thin-film lithium niobate photonic devices inherit the excellent electro-optic properties of lithium niobate bulk materials and possess a strongly confined optical structure, effectively reducing device size and demonstrating strong photonic integration potential, making high-integration of fiber optic gyroscopes possible. Based on this, this embodiment provides a multifunctional lithium niobate thin-film integrated chip to meet the high-integration requirements of hybrid chip integration.

[0046] Please refer to Figure 1 and Figure 2 The multifunctional lithium niobate thin-film integrated chip provided in this embodiment includes, from bottom to top, a substrate 10, a lower cladding layer 20, a lithium niobate thin-film waveguide core layer 30, and an upper cladding layer 40.

[0047] Preferably, the substrate 10 is made of lithium niobate crystal with a thickness of 500 μm; the lower cladding layer 20 is made of silicon dioxide with a thickness of 4 μm; the lithium niobate thin-film waveguide core layer 30 is made of lithium niobate thin film with a thickness ranging from 400 nm to 600 nm; and the upper cladding layer 40 is made of low-refractive-index (refractive-index less than a preset refractive-index threshold) silicon dioxide with a thickness of 0.8 μm. This embodiment effectively improves the thermal matching of the integrated device by using lithium niobate for both the substrate 10 and the lithium niobate thin-film waveguide core layer 30. Figure 1 (W indicates width, H indicates thickness).

[0048] Exemplarily, the lithium niobate thin-film waveguide core layer 30 includes an incident unit 31, a polarization unit 32, a Y-branch coupling unit 33, a mode filtering unit 34, a Y-branch beam splitting unit 35, a phase modulation unit 36, and a resonant unit 37 connected in sequence.

[0049] In this embodiment, the incident unit is used to connect to the light source and input the incident light source to the polarization unit to polarize the light source and obtain single-polarized light; one branch of the Y-branch coupling unit is used to couple and output the single-polarized light; the Y-branch beam splitting unit is used to split the coupled single-polarized light into two equal paths, and then modulates the two single-polarized lights through the phase modulation unit to obtain two modulated signal lights; the resonant unit is used to control the phase shift of the two modulated signal lights, return the two modulated signal lights to the Y-branch beam splitting unit, and re-modulate them through the phase modulation unit; the Y-branch beam splitting unit is also used to combine the two modulated signal lights after re-modulation to generate an interference signal; the mode filtering unit is used to perform noise reduction processing on the single-polarized light and modulated signal light passing through the mode filtering unit; the other branch of the Y-branch coupling unit is used to output the interference signal.

[0050] It can be understood that the beam of the external light source is transmitted sequentially through the incident unit 31, the polarization unit 32, the Y-branch coupling unit 33, the mode filtering unit 34, the Y-branch beam splitting unit 35, the phase modulation unit 36 ​​and the resonant unit 37, and then returns sequentially through the phase modulation unit 36, the Y-branch beam splitting unit 35 and the mode filtering unit 34, and finally output through the Y-branch coupling unit 33.

[0051] The incident unit 31 includes a second conical waveguide 311 and a fifth straight-through waveguide 312 connected in sequence; the polarization unit 32 includes a first straight-through waveguide 321, a wide-ridge waveguide 322, a first circular arc waveguide 323, and a first conical waveguide 324. The small end of the second conical waveguide 311 is connected to the fifth straight-through waveguide 312, and the fifth straight-through waveguide 312 is connected to the first straight-through waveguide 321; the wide-ridge waveguide 322 is disposed on one side of the first straight-through waveguide 321 and is connected in sequence to the first circular arc waveguide 323 and the first conical waveguide 324. The polarization unit 32 is used to polarize the incident light (the light source incident through the incident unit 31) to obtain single-polarized light, thereby reducing optical path transmission crosstalk; the first straight-through waveguide 321 in the polarization unit 32 is used to output the optical signal. Additionally, the incident unit 31 can also integrate a mode converter to improve the coupling efficiency between the incident unit 31 and the light source.

[0052] The Y-branch coupling unit 33 includes a sixth through waveguide 331, a seventh through waveguide 332, a Y-branch coupling waveguide 333, and an eighth through waveguide 334 connected in sequence. The sixth through waveguide 331 is connected to the first through waveguide 321. One branch of the Y-branch coupler unit is used to couple the single-polarized light output from the polarization unit 32, and the other branch is used to couple the returned optical signal.

[0053] Y-branch beam splitter unit 35 includes a ninth straight waveguide 351, a Y-branch beam splitter 352, a tenth straight waveguide 353, and an eleventh straight waveguide 354.

[0054] The mode filtering unit 34 includes two counter-connected sixth arc waveguides 341 and seventh arc waveguides 342. The sixth arc waveguide 341 connects to the eighth straight waveguide 334, and the seventh arc waveguide 342 connects to the ninth straight waveguide 351. The mode filtering unit 34 is used to employ a curved waveguide design to eliminate crosstalk and noise effects of the radiation modes in the Y-branch coupling unit 33 and the Y-branch beam splitter unit 35 in the optical path.

[0055] The phase modulation unit 36 ​​includes a first electrode 361 and a second electrode 362. The first electrode 361 is symmetrically disposed on both sides of the tenth through waveguide 353, and the second electrode 362 is symmetrically disposed on both sides of the eleventh through waveguide 354. The phase modulation unit 36 ​​is used to perform phase modulation on the two single-polarized lights output from the Y-branch beam splitter 35 to correspond to the output modulated signal light. The phase modulation unit 36 ​​has advantages such as low half-wave voltage, high modulation efficiency, and high bandwidth.

[0056] The resonant unit 37 includes a second arc waveguide 371, a second straight waveguide 372, a third arc waveguide 373, a third straight waveguide 374, a fourth arc waveguide 375, a fourth straight waveguide 376, and a fifth arc waveguide 377 connected in sequence, as well as an optical microcavity waveguide 378 disposed on one side of the third straight waveguide 374. The second arc waveguide 371 is connected to the tenth straight waveguide 353, and the fifth arc waveguide 377 is connected to the eleventh straight waveguide 354. This resonant unit 37 is used to control the phase shift of two modulation signal lights propagating clockwise and counterclockwise, respectively. The resonant unit 37 provided in this embodiment has advantages such as small size and large phase shift.

[0057] The two modulated signal lights transmitted through the resonant unit 37 are re-modulated by the phase modulation unit 36 ​​and returned to the Y-branch beam splitting unit 35 to be combined to form an interference signal. The interference signal is output to the photodetector 60 through the Y-branch coupling unit 33.

[0058] Exemplary examples include the first straight waveguide 321, the second straight waveguide 372, the third straight waveguide 374, the fourth straight waveguide 376, the fifth straight waveguide 312, the sixth straight waveguide 331, the seventh straight waveguide 332, the eighth straight waveguide 334, the ninth straight waveguide 351, the tenth straight waveguide 353, the eleventh straight waveguide 354, the Y-branch coupling waveguide 333, the second circular arc waveguide 371, the third circular arc waveguide 373, the fourth circular arc waveguide 375, the fifth circular arc waveguide 377, the sixth circular arc waveguide 341, the seventh circular arc waveguide 342, and the Y-branch beam splitter waveguide 352, all of which are single-mode ridge waveguide structures made of lithium niobate thin film material and only support the TE0 and TM0 modes of electromagnetic wave propagation.

[0059] The wide-ridge waveguide 322 and the first circular arc waveguide 323 are both multimode ridge waveguide structures made of lithium niobate thin film, which can support the transmission of four electromagnetic wave propagation modes: TE0, TE1, TM0, and TM1. By adjusting the ridge width of the wide-ridge waveguide 322, a preset phase matching condition is met between the wide-ridge waveguide 322 in the higher-order mode TM1 and the first through waveguide 321 in the TM fundamental mode: neff TM1 =neff TM0 In TE mode, this phase matching condition is not met: neff TM1 ≠neff TM0 This causes the TM0 fundamental mode in the first through waveguide 321 and the TM1 higher-order mode in the wide ridge waveguide 322 to hybridize and couple, so that the TM0 fundamental mode gradually transforms into the TM1 higher-order mode and couples into the wide ridge waveguide 322 for transmission.

[0060] It can be understood that the polarization unit 32 adopts a single-mode ridge waveguide structure corresponding to the wide ridge waveguide 322 and the first through waveguide 321 to form an asymmetric directional coupler structure design. This allows the TE mode, which does not meet the phase matching condition, to transmit normally in the single-mode ridge waveguide structure, while the TM mode, which meets the phase matching condition, is gradually coupled from the single-mode ridge waveguide structure to the wide ridge waveguide 322. Combined with the curved waveguide and the tapered waveguide, the TM mode light is finally dissipated in the cladding, thereby achieving the TM mode elimination effect and realizing the polarization function. Moreover, the polarization unit 32 has a simple structure and compact size.

[0061] Preferably, the first circular arc waveguide 323, the second circular arc waveguide 371, the fifth circular arc waveguide 377, the sixth circular arc waveguide 341 and the seventh circular arc waveguide 342 all adopt a 90° circular arc structure; the third circular arc waveguide 373 and the fourth circular arc waveguide 375 both adopt a 180° circular arc structure.

[0062] In this embodiment, the sixth circular waveguide 341 and the seventh circular waveguide 342 can be combined to form a mode filter. This mode filter is used to eliminate the radiation modes of the substrate 10 in the Y-branch coupling unit 33 and the Y-branch beam splitter 35, so as to avoid them from disturbing the output signal.

[0063] Optionally, the radii of the arcs in the first, second, third, fourth, fifth, and seventh circular arc waveguides 373, 375, 377, and 342 are all greater than or equal to 50 μm to reduce transmission loss to below 0.1 dB / cm. Additionally, the radius of the arc in the first circular arc waveguide 323 can be greater than or equal to 100 μm.

[0064] The large end of the second conical waveguide 311 is used for coupling the input incident light, and optionally, the ridge width ranges from 3μm to 6μm; the ridge width at the small end of the second conical waveguide 311 is the same as the ridge width of the fifth through waveguide 312; the ridge width of the second conical waveguide 311 decreases linearly from the large end to the small end; optionally, the length of the second conical waveguide 311 ranges from 200μm to 500μm.

[0065] The first circular arc waveguide 323 and the first positive tapered waveguide 324 are used to filter out TM mode light coupled from the first through waveguide 321 into the wide ridge waveguide 322; the first circular arc waveguide 323 is also used to deflect the light in the wide ridge waveguide 322 away from the TM mode transmission optical path by means of transmission path deflection; the first positive tapered waveguide 324 adopts a tapered structure to gradually dissipate the light in the waveguide core layer into the cladding for elimination.

[0066] The large end of the first positive conical waveguide 324 has the same ridge width as the wide ridge waveguide 322; the small end of the first positive conical waveguide 324 has a ridge width of 0; optionally, the length of the first positive conical waveguide 324 ranges from 50μm to 300μm.

[0067] In this embodiment, the optical microcavity waveguide 378 adopts a microring or microdisk structure with a radius greater than or equal to 200 μm. The optical microcavity waveguide 378 is used for time delay. The microdisk has a high Q-value because the Q-value (quality factor) of the optical microcavity directly characterizes the ability of the resonant cavity to confine the resonant optical field and is proportional to the photon lifetime, resulting in a long delay time. However, the resonant modes are complex, leading to more complex subsequent signal processing. The microring, on the other hand, has a relatively lower Q-value than the microdisk, resulting in purer modes and easier subsequent signal processing. Therefore, the structure of the optical microcavity waveguide 378 can be selected according to actual conditions, and this embodiment does not impose any limitations.

[0068] Because lithium niobate films are difficult to etch, conventional etching results in high sidewall roughness and high scattering loss. Consequently, when deep ridge waveguides are designed in lithium niobate waveguide chips, the confinement is strong and the loss is high. Therefore, in order to reduce the waveguide loss of lithium niobate films, preferably, the second positive conical waveguide 311, the wide ridge waveguide 322, the first positive conical waveguide 324, and other ridge waveguides, as well as dual-mode ridge waveguides and single-mode ridge waveguides, can all adopt shallow ridge structure design with equal ridge height. Therefore, the etching depth is consistent, and the waveguide structure only needs to be prepared by a single dry etching process, which can effectively reduce optical transmission loss.

[0069] This embodiment also provides an optoelectronic device, including the lithium niobate thin-film integrated chip described above.

[0070] This embodiment also provides a fiber optic gyroscope, including a light source 50, a photodetector 60, and the aforementioned optoelectronic devices, wherein, see [link to documentation]. Figure 3When fabricating a fiber optic gyroscope using the multifunctional lithium niobate thin-film integrated chip of this embodiment, it is only necessary to connect the second positive conical waveguide 311 to the light source 50, and the first through waveguide 321 to the photodetector 60 using optical fiber or a hybrid integration method, respectively. The first electrode 361 and the second electrode 362 are electrically connected to the signal processing circuit 70, and the photodetector 60 is connected to the signal processing circuit 70. This enables the miniaturization and integration of the fiber optic gyroscope. The integrated fiber optic gyroscope is a reentry fiber optic gyroscope. In this embodiment, one branch of the Y-branch coupler unit is used to couple the single-polarized light output from the polarization unit 32 into the phase modulation unit 36. After being transmitted through the resonant unit 37, the two modulated signal lights are modulated again by the phase modulation unit 36 ​​and return to the Y-branch beam splitting unit 35 to be combined to form an interference signal. The interference signal is output to the photodetector 60 through the other branch of the Y-branch coupling unit 33.

[0071] Furthermore, in this embodiment, an optical microcavity waveguide 378 and a third through waveguide 374 are used to form a coupled resonator, replacing the traditional long optical fiber, to form a reentry optical gyroscope. This makes the Sagnac phase shift generated by the optical microcavity waveguide 378 n times the length of a single optical microcavity, where n is the number of cycles of the optical signal in the optical microcavity, which is determined by the Q value of the resonator. n can be increased by optimizing the radius and loss of the optical microcavity waveguide 378 and the coupling distance between the optical microcavity waveguide 378 and the third through waveguide 374, thereby increasing the detection sensitivity.

[0072] This embodiment also provides an optoelectronic system, including the fiber optic gyroscope described above.

[0073] In the first aspect of this embodiment, by employing a single-film lithium niobate material platform with strong optical field confinement capabilities, multi-functional monolithic integration of polarization, coupling, beam splitting, modulation, and resonance is achieved, significantly reducing the size of the integrated chip and the coupling loss between different functional chips, and improving the device integration density. In the second aspect, the polarization unit 32 adopts an asymmetric directional coupler structure design composed of a wide-ridge waveguide 322 and a single-mode ridge waveguide. This allows the TE mode, which does not meet the phase matching condition, to transmit normally in the single-mode ridge waveguide, while the TM mode, which meets the phase matching condition, gradually transmits from the single-mode ridge waveguide. Coupled to the wide ridge waveguide 322, and combined with the curved waveguide and the tapered waveguide, the TM mode light is ultimately dissipated in the cladding, thereby achieving the TM mode elimination effect and realizing the polarization function. Moreover, the polarization unit 32 has the characteristics of simple structure and compact size. Thirdly, the fabrication process of the multifunctional thin-film lithium niobate chip provided in this embodiment is simple. The ridge waveguide height is consistent in the lithium niobate waveguide chips with different functions designed and integrated, and only the waveguide width is different. Therefore, only one dry etching is required, which greatly simplifies the process flow. Moreover, the processing technology is compatible with the semiconductor processing technology, which can effectively reduce the fabrication cost.

[0074] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium niobate thin-film integrated chip, characterized in that, From bottom to top, it includes a substrate, a lower cladding layer, a lithium niobate thin-film waveguide core layer, and an upper cladding layer; wherein, both the substrate and the lithium niobate thin-film waveguide core layer are made of lithium niobate material to improve the thermal matching of the integrated chip; The lithium niobate thin-film waveguide core layer includes an incident unit, a polarization unit, a Y-branch coupling unit, a mode filtering unit, a Y-branch beam splitting unit, a phase modulation unit, and a resonant unit connected in sequence. The incident unit is used to connect to the light source and input the incident light source into the polarizing unit to polarize the light source and obtain single-polarized light. The polarizing unit includes a first through waveguide, a wide-ridge waveguide, a first circular arc waveguide, and a first conical waveguide. The wide-ridge waveguide is disposed on one side of the first through waveguide and is sequentially connected to the first circular arc waveguide and the first conical waveguide. The wide-ridge waveguide and the single-mode ridge waveguide structure corresponding to the first through waveguide form an asymmetric directional coupler structure to achieve the polarization function. One branch of the Y-branch coupling unit is used to couple and output the single-polarized light; The Y-branch beam splitter is used to split the coupled output single-polarized light into two equal paths, and then the phase modulation unit modulates the two single-polarized lights to obtain two modulated signal lights. The resonant unit is used to control the phase shift of the two modulated signal lights, return the two modulated signal lights to the Y-branch beam splitter, and re-modulate them through the phase modulation unit; The Y-branch beam splitter is also used to combine the two modulated signal beams after re-modulation to generate an interference signal. The mode filtering unit is used to reduce noise in the single-polarized light and the modulated signal light; The other branch of the Y-branch coupling unit is used to output the interference signal.

2. The lithium niobate thin-film integrated chip according to claim 1, characterized in that, The resonant unit includes a second circular arc waveguide, a second straight waveguide, a third circular arc waveguide, a third straight waveguide, a fourth circular arc waveguide, a fourth straight waveguide, a fifth circular arc waveguide connected in sequence, and an optical microcavity waveguide disposed on one side of the third straight waveguide.

3. The lithium niobate thin-film integrated chip according to claim 2, characterized in that, The first to fourth through waveguides and the second to fifth circular arc waveguides all adopt a single-mode ridge waveguide structure made of lithium niobate thin film material; The wide ridge waveguide and the first circular arc waveguide are respectively adopted as multimode ridge waveguide structures made of lithium niobate thin film. The wide-ridge waveguide and the first through waveguide satisfy a preset phase matching condition in TM transmission mode, but do not satisfy the preset phase matching condition in TE transmission mode. The first conical waveguide, the single-mode ridge waveguide structure, and the multi-mode ridge waveguide structure all adopt a shallow ridge structure with the same ridge height.

4. The lithium niobate thin-film integrated chip according to claim 2, characterized in that, The first circular arc waveguide, the second circular arc waveguide, and the fifth circular arc waveguide all adopt a 90° circular arc structure; Both the third and fourth circular arc waveguides adopt a 180° circular arc structure; The radius of the arc of the first to fifth circular arc waveguides is greater than or equal to 50µm.

5. The lithium niobate thin-film integrated chip according to claim 1, characterized in that, The incident unit includes a second conical waveguide and a fifth through waveguide connected in sequence, with the small end of the second conical waveguide connected to the fifth through waveguide; The Y-branch coupling unit includes a sixth through waveguide, a seventh through waveguide, a Y-branch coupling waveguide, and an eighth through waveguide connected in sequence. The Y-branch beam splitter unit includes a ninth through waveguide, a Y-branch beam splitter, a tenth through waveguide, and an eleventh through waveguide; The mode filtering unit includes two reverse-connected sixth and seventh arc waveguides, the sixth arc waveguide being connected to the eighth through waveguide, and the seventh arc waveguide being connected to the ninth through waveguide; The phase modulation unit includes a first electrode and a second electrode. The first electrode is symmetrically disposed on both sides of the tenth through waveguide, and the second electrode is symmetrically disposed on both sides of the eleventh through waveguide.

6. The lithium niobate thin-film integrated chip according to claim 1, characterized in that, The substrate is made of lithium niobate crystal, the lower cladding is made of silicon dioxide, the lithium niobate thin film waveguide core is made of lithium niobate thin film, and the upper cladding is made of silicon dioxide with a refractive index less than a preset refractive index threshold.

7. The lithium niobate thin-film integrated chip according to claim 2, characterized in that, The optical microcavity waveguide adopts a microring structure, and the radius of the microring is not less than 200µm; or, The optical microcavity waveguide adopts a microdisk structure, and the radius of the microdisk is not less than 200µm.

8. An optoelectronic device, characterized in that, Including the lithium niobate thin-film integrated chip as described in any one of claims 1-7.

9. A fiber optic gyroscope, characterized in that, It includes light sources, photodetectors, and optoelectronic devices as described in claim 8.

10. A photoelectric system, characterized in that, Including the fiber optic gyroscope as described in claim 9.

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