A 90° optical hybrid based on thin film lithium niobate (TFLN)

Abstract

The application discloses a 90-degree optical frequency mixer based on TFLN and relates to the technical field of optical communication.The purpose of the application is to solve the problems of large phase error and sensitivity to process fluctuation of the existing 90-degree optical frequency mixer.The mixer comprises an input waveguide module, a light splitting and phase shift module, a light combining module and an electrode control module; the input waveguide module introduces signal light and local oscillator light; the light splitting and phase shift module realizes light splitting and 90-degree phase difference modulation; the light combining module outputs four beams of interference light with a 90-degree phase interval; and the electrode control module accurately adjusts the phase of the optical signal.The waveguide structure of the TFLN substrate is made by using an ion beam etching technology; the light splitter and the light combiner are TFLN directional couplers with optimized parameters; the phase shift arm electrode is made of metal titanium; and the electrode control module adopts a PID algorithm.The application has the advantages of low loss, high-precision phase adjustment and high stability and can meet the demand of high-speed and large-capacity optical communication.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a 90° optical mixer based on thin-film lithium niobate (TFLN). Background Technology

[0002] In modern optical communication systems, the 90° optical mixer is a key component used to mix the input optical signal with a local oscillator optical signal to generate an output signal with a specific phase relationship. It is widely used in coherent optical communication, optical signal processing, and other fields. However, traditional 90° optical mixers have certain performance limitations. For example, they suffer from large phase errors, leading to low signal demodulation accuracy; they are sensitive to process variations, resulting in poor device consistency and stability; and as the demand for high speed and large capacity in optical communication systems continues to increase, traditional structures are struggling to meet the ever-growing performance requirements.

[0003] In recent years, thin-film lithium niobate (TFLN) materials have shown great application potential in the field of optoelectronic devices due to their excellent optical properties, such as high electro-optic coefficient, wide transparency window, and low optical loss. Applying TFLN materials to the design of 90° optical mixers is expected to break through the performance bottlenecks of traditional devices and improve the overall performance of optical communication systems. However, there are still many problems to be solved in the structural design and performance optimization of TFLN-based 90° optical mixers. Summary of the Invention

[0004] The purpose of this invention is to provide a 90° optical mixer based on TFLN to solve the problems of large phase error, sensitivity to process fluctuations, and difficulty in meeting the requirements of high-speed, high-capacity optical communication in existing 90° optical mixers. To achieve the above objective, this invention adopts the following technical solution:

[0005] A 90° optical mixer based on TFLN, comprising:

[0006] Input waveguide module: This includes a signal light input waveguide and a local oscillator light input waveguide, both fabricated using TFLN material. These waveguides are used to introduce externally input signal light and local oscillator light into the mixer, respectively. The signal light input waveguide and local oscillator light input waveguide are precisely fabricated on the TFLN substrate using photolithography, etching, and other processes. Their waveguide structure parameters are optimized to achieve low-loss optical transmission.

[0007] The beam splitting and phase shifting module, connected to the input waveguide module, includes a first beam splitter, a second beam splitter, a first phase shifter arm, and a second phase shifter arm. The first and second beam splitters equally divide the input signal light and local oscillator light into two beams. Both beam splitters utilize directional coupler structures made of TFLN material. By precisely controlling parameters such as the coupling length and waveguide spacing of the directional couplers, a high-precision beam splitting ratio is achieved. The first and second phase shifter arms modulate the phase of the two split beams, creating a 90° phase difference. The first and second phase shifter arms utilize the electro-optic effect of TFLN material; by placing electrodes on the phase shifter arms and applying different voltages, the phase of the optical signal is precisely adjusted.

[0008] The beam combining module, connected to the beam splitting and phase shifting module, includes a first beam combiner and a second beam combiner. It combines the phase-shifted signal light and the local oscillator light to output four interference beams with a 90° phase gap. Both the first and second beam combiners utilize directional coupler structures made of TFLN material. By rationally designing the coupler parameters, low loss and high coupling efficiency are ensured during the beam combining process.

[0009] Electrode control module: Connected to the electrodes on the first and second phase shift arms of the beam splitting and phase shifting module, it precisely controls the voltage applied to the electrodes, thereby achieving precise adjustment of the optical signal phase. The electrode control module employs a high-precision voltage source and feedback control circuit, enabling real-time monitoring of the phase information of the mixer output signal and automatically adjusting the voltage applied to the electrodes according to preset phase requirements to compensate for phase errors caused by factors such as temperature changes and process fluctuations.

[0010] In some embodiments of the present invention, the TFLN substrate is fabricated using ion beam etching technology to improve the sidewall roughness of the waveguide and reduce optical loss. During the waveguide fabrication process, by precisely controlling parameters such as the energy of the ion beam, the beam current density, and the etching time, the sidewalls of the waveguide are made smooth and perpendicular, effectively reducing scattering loss of light during waveguide transmission.

[0011] In some embodiments of the present invention, in the directional coupler structures of the first beam splitter, the second beam splitter, the first multiplexer, and the second multiplexer, the waveguide width is 0.5µm-2µm, the waveguide spacing is 0.2µm-1µm, and the coupling length is 10µm-100µm. By optimizing these parameters, precise control of the splitting ratio and coupling efficiency is achieved. For example, when the waveguide width is 1µm, the waveguide spacing is 0.5µm, and the coupling length is 50µm, the directional coupler can achieve a splitting ratio close to 50:50 and high-efficiency coupling.

[0012] In some embodiments of the present invention, the electrodes on the first and second phase shift arms are made of titanium, with an electrode width of 2-5 μm and an electrode spacing of 1-3 μm. By optimizing the electrode structure parameters, the electro-optic modulation efficiency is improved. Titanium has good conductivity and compatibility with TFLN materials. Within the aforementioned electrode width and spacing range, an electric field can be effectively applied, and efficient phase modulation can be achieved using the electro-optic effect of TFLN materials.

[0013] In some embodiments of the present invention, the electrode control module employs a proportional-integral-derivative (PID) control algorithm to adjust the voltage applied to the electrodes in real time and compensate for phase errors. The PID control algorithm can quickly and accurately calculate the voltage value to be adjusted based on the deviation between the output signal phase and the preset phase, and automatically adjust the voltage applied to the electrodes through a feedback control circuit, so that the phase of the mixer output signal is always maintained at a precise 90° interval. Attached Figure Description

[0014] Figure 1 It is the input waveguide and beam splitter module.

[0015] Figure 2 It is a phase shift module.

[0016] Figure 3 It consists of a wave combiner module and an electrode control module. Detailed Implementation

[0017] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] Example 1:

[0019] 1. Fabrication of TFLN Substrate: High-quality TFLN substrates were selected, and waveguide structures including the signal light input waveguide, local oscillator input waveguide, first beam splitter, second beam splitter, first phase shifter, second phase shifter, first combiner, and second combiner were fabricated on the substrate according to the designed waveguide structure parameters using ion beam etching technology. During the etching process, the ion beam energy was strictly controlled at 500 eV, and the beam current density was 10 mA / cm². 2 The etching time is 30 minutes to obtain smooth and vertical waveguide sidewalls.

[0020] 2. Electrode Fabrication: Electrodes were fabricated on the first and second phase shift arms using electron beam evaporation (EB / LD). The electrode width was set to 3 μm, and the electrode spacing was set to 2 μm to ensure good contact between the electrodes and the TFLN waveguide and effective electric field application.

[0021] 3. Connect the electrode control module: Connect the fabricated electrodes to the electrode control module. The electrode control module uses a high-precision voltage source and can output an adjustable voltage ranging from 0 to 10V. The control module uses a PID control algorithm to monitor the phase information of the mixer output signal in real time and automatically adjust the voltage applied to the electrodes according to the preset 90° phase interval requirement.

[0022] 4. Performance Testing: External signal light and local oscillator light are input into the mixer through the signal light input waveguide and local oscillator light input waveguide, respectively. After beam splitting, phase shifting, and combining, four interferometric beams are output. The phase of the output optical signal is tested using a high-precision optical phase detector. The results show that under different temperature and optical power input conditions, the phase error of the output optical signal is less than ±1°, meeting the requirements of a high-performance optical communication system.

[0023] Example 2:

[0024] 1. Optimize waveguide structure parameters: Optimize and adjust the structural parameters of the directional couplers for the first beam splitter, second beam splitter, first beam combiner, and second beam combiner. Adjust the waveguide width to 1.5µm, the waveguide spacing to 0.6µm, and the coupling length to 60µm.

[0025] 2. Re-fabricate the mixer: According to the optimized parameters, re-fabricate the 90° optical mixer based on TFLN on the TFLN substrate. The fabrication process is the same as in Example 1.

[0026] 3. Performance Comparison Test: The mixer fabricated in this embodiment was compared with the mixer fabricated in Embodiment 1. Under the same test conditions, the mixer fabricated in this embodiment showed further improvements in splitting ratio accuracy and coupling efficiency, with a splitting ratio deviation of less than ±0.5%, a 5% increase in coupling efficiency, and better power consistency of the output optical signal. This further proves that the present invention can effectively improve the performance of the mixer by optimizing the waveguide structure parameters.

[0027] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A 90° optical mixer based on TFLN, characterized in that, include: The input waveguide module includes a signal light input waveguide and a local oscillator light input waveguide, both of which are made of TFLN material and are used to introduce the externally input signal light and local oscillator light into the mixer respectively. The beam splitting and phase shifting module is connected to the input waveguide module and includes a first beam splitter, a second beam splitter, a first phase shifter arm, and a second phase shifter arm. The first beam splitter and the second beam splitter split the input signal light and the local oscillator light into two beams of light, respectively. The first phase shifter arm and the second phase shifter arm respectively modulate the phase of the two beams of light after beam splitting, so that they produce a phase difference of 90°. The beam combining module, connected to the beam splitting and phase shifting module, includes a first beam combiner and a second beam combiner, used to combine the phase-shifted signal light and the local oscillator light to output four beams of interference light with a 90° phase interval; The electrode control module is connected to the electrodes on the first and second phase shift arms of the beam splitting and phase shifting module, and is used to precisely control the voltage applied to the electrodes, thereby achieving precise adjustment of the phase of the optical signal.

2. The 90° optical mixer based on TFLN according to claim 1, characterized in that, The TFLN substrate is used to fabricate waveguide structures using ion beam etching technology.

3. The 90° optical mixer based on TFLN according to claim 1, characterized in that, The first beam splitter, the second beam splitter, the first beam combiner, and the second beam combiner are all directional coupler structures made of TFLN material, wherein the waveguide width is 0.5μm-2μm, the waveguide spacing is 0.2μm-1μm, and the coupling length is 10μm-100μm.

4. The 90° optical mixer based on TFLN according to claim 1, characterized in that, The electrodes on the first and second phase shift arms are made of titanium, with an electrode width of 2μm-5μm and an electrode spacing of 1μm-3μm.

5. The 90° optical mixer based on TFLN according to claim 1, characterized in that, The electrode control module employs a proportional-integral-derivative (PID) control algorithm to adjust the voltage applied to the electrode in real time and compensate for phase errors.

6. The 90° optical mixer based on TFLN according to claim 1, characterized in that, The waveguide structure parameters in the input waveguide module, the beam splitting and phase shifting module, and the beam combining module have been optimized to achieve low-loss optical transmission.

7. The 90° optical mixer based on TFLN according to claim 1, characterized in that, The first and second beam splitters achieve a high-precision splitting ratio by precisely controlling parameters such as the coupling length of the directional coupler and the waveguide spacing.

8. The 90° optical mixer based on TFLN according to claim 1, characterized in that, The first and second multiplexers ensure low loss and high coupling efficiency during the multiplexing process by rationally designing the parameters of the coupler.

9. The 90° optical mixer based on TFLN according to claim 1, characterized in that, The electrode control module employs a high-precision voltage source and feedback control circuit, which can monitor the phase information of the mixer output signal in real time and automatically adjust the voltage applied to the electrodes according to the preset phase requirements.

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