A preparation and coupling method of a 90-degree optical mixer based on thin film lithium niobate (TFLN)

Abstract

The application discloses a preparation and coupling method of a 90-degree optical mixer based on a TFLN. The preparation method comprises the following steps: cleaning a TFLN substrate, making a waveguide structure through photoetching and ion beam etching, making electrodes through electron beam evaporation and photoetching, and connecting an electrode control module; the coupling method comprises the following steps: optical input coupling, light splitting and combining coupling, and phase adjustment and coupling optimization. Through accurate control of process parameters and coupling steps, low-loss waveguide structure manufacturing, efficient optical coupling and accurate phase adjustment can be realized, the problems of complex preparation process, low coupling efficiency and large phase error of an existing mixer are solved, the performance of the optical mixer is improved, and the demand of high-speed optical communication is met.

Description

Technical Field

[0001] This invention relates to the field of optical communication device manufacturing technology, specifically to a method for fabricating and coupling a 90° optical mixer based on thin-film lithium niobate (TFLN). Background Technology

[0002] The 90° optical mixer is a key component in coherent optical communication systems, and its performance significantly impacts the signal processing quality and transmission efficiency of these systems. Traditional 90° optical mixers suffer from complex fabrication processes and difficulty in controlling precision, resulting in poor device consistency and stability. Furthermore, existing optical coupling methods suffer from low coupling efficiency and large phase errors, failing to meet the demands of high-speed, high-capacity optical communication.

[0003] Thin-film lithium niobate (TFLN) materials have attracted widespread attention in the field of optoelectronic devices due to their excellent optical and electro-optic properties. However, the fabrication process and coupling technology of TFLN-based 90° optical mixers still need improvement, and an efficient and precise fabrication and coupling method is urgently needed to enhance device performance. Summary of the Invention

[0004] The purpose of this invention is to provide a fabrication and coupling method for a 90° optical mixer based on TFLN, so as to solve the problems of complex fabrication process, low coupling efficiency and large phase error in the prior art, and improve the performance and reliability of the optical mixer.

[0005] The specific steps of the preparation method of the present invention are as follows:

[0006] 1. TFLN substrate preparation: Select a high-quality TFLN substrate and ultrasonically clean it sequentially with acetone, ethanol and deionized water. Each cleaning step lasts 15-20 minutes to remove oil, impurities and dust from the substrate surface, ensuring a clean substrate surface and providing a good foundation for subsequent processes.

[0007] 2. Waveguide Structure Fabrication: Photoresist is spin-coated onto the cleaned TFLN substrate at a speed of 3000-4000 rpm for 30-40 seconds, forming a uniform photoresist film with a thickness of approximately 1-1.5 μm. Then, a mask with the designed waveguide structure pattern is applied to the substrate, and exposure is performed using ultraviolet lithography for 10-15 seconds. After exposure, the substrate is developed in a developer solution for 1-2 minutes to remove unexposed photoresist. Next, the waveguide structure is fabricated using ion beam etching, with the ion beam energy controlled at 400-600 eV and the beam current density at 8-12 mA / cm². 2The etching time is determined according to the waveguide design depth, generally 20-30 minutes. After etching, soak in a photoresist remover for 10-15 minutes to remove residual photoresist.

[0008] 3. Electrode Fabrication: Electrodes are fabricated on the first and second phase shift arms of the waveguide using electron beam evaporation (EB / LD). The substrate is placed in an EB / LD apparatus, with the evaporation temperature set to 1000-1200℃, the titanium evaporation rate set to 0.5-1 nm / s, and a deposition thickness of 0.2-0.3 μm to form a titanium thin film. Photoresist is then coated again, and the photolithography and development steps are repeated to form the electrode pattern. Excess titanium is removed using wet or dry etching to create electrodes with a width of 2-5 μm and a spacing of 1-3 μm.

[0009] 4. Electrode control module integration: The fabricated electrodes are connected to a pre-designed and fabricated electrode control module containing a high-precision voltage source and feedback control circuit through gold wire bonding or other appropriate methods.

[0010] The specific steps of the coupling method of the present invention are as follows:

[0011] 1. Optical Input Coupling: The external signal light and local oscillator light are connected to the signal light input waveguide and local oscillator light input waveguide respectively via optical fibers using end-face coupling. An optical fiber alignment device is used to precisely align the optical fiber end face with the waveguide input end face, controlling the alignment accuracy within ±1μm. A three-dimensional micro-motion platform is used to adjust the position and angle of the optical fiber, and the optical power at the input waveguide output end is monitored in real time to optimize the coupling efficiency to over 85%.

[0012] 2. Beam Splitting and Combining: The signal light and the local oscillator light enter a directional coupler made of TFLN material for beam splitting and combining. Precise control of parameters such as the coupling length and waveguide spacing of the directional coupler ensures that the beam splitting ratio meets design requirements (e.g., close to 50:50), and guarantees low loss and high coupling efficiency during the combining process, controlling the output optical signal power consistency deviation within ±5%.

[0013] 3. Phase Adjustment and Coupling Optimization: The voltage on the electrodes of the first and second phase shift arms is adjusted using the electrode control module. A PID control algorithm is employed to adjust the voltage in real time based on the optical signal phase monitoring results, achieving precise phase adjustment. The coupling efficiency and power consistency of the output optical signal are monitored synchronously, and the coupling process is optimized to ensure that the phase error of the output optical signal is less than ±1° and the coupling efficiency reaches over 90%. Attached Figure Description

[0014] Figure 1 A schematic diagram of the fabrication process for a 90° optical mixer based on TFLN.

[0015] Figure 2 This is an enlarged schematic diagram of the TFLN substrate cleaning process.

[0016] Figure 3 This is a schematic diagram of the waveguide structure fabrication process.

[0017] Figure 4 This is a schematic diagram of the electrode manufacturing process.

[0018] Figure 5 A schematic diagram of the coupling process of a 90° optical mixer based on TFLN.

[0019] Figure 6 This is a detailed schematic diagram of optical input coupling.

[0020] Figure 7 This is a schematic diagram of the beam splitting and wave combining coupling structure.

[0021] Figure 8 This is a schematic diagram of phase adjustment and coupling optimization.

[0022] Figure 1 This diagram illustrates the overall fabrication process of a 90° optical mixer based on TFLN (Transient Fluorescent Laminate). From left to right, it shows the TFLN substrate preparation stage, including ultrasonic cleaning with acetone, ethanol, and deionized water; followed by the waveguide structure fabrication stage, encompassing photoresist coating, photolithography, development, ion beam etching, and residual photoresist removal; then the electrode fabrication stage, demonstrating the electron beam evaporation deposition of titanium metal, photolithography, and etching to form the electrodes; finally, the electrode control module integration stage, showcasing the connection between the electrodes and the electrode control module. This diagram visually presents the sequence and flow logic of each fabrication step, aiding in understanding the overall architecture of the fabrication method.

[0023] Figure 2 This document details the operational procedures for ultrasonic cleaning of TFLN substrates using acetone, ethanol, and deionized water. The figures clearly indicate the containers holding the different cleaning solutions, the substrate's placement within each container, and the operational status of the ultrasonic cleaning equipment. This highlights the importance of the cleaning process in ensuring substrate cleanliness and provides a solid foundation for subsequent processes.

[0024] Figure 3 The diagram details key processes in waveguide structure fabrication, including photoresist coating, photolithography, development, and ion beam etching. It shows the uniform thin film of photoresist after coating the substrate, the relative position of the mask and substrate during the photolithography step, the photoresist pattern formed after development, and the working principle of the ion beam etching equipment and the resulting waveguide structure morphology. The diagram clearly demonstrates the process details and technical key points of waveguide structure fabrication.

[0025] Figure 4The focus is on showcasing the electron beam evaporation deposition of titanium and the photolithography etching process for electrode fabrication. The figures illustrate the process of titanium evaporation and deposition on the substrate in the electron beam evaporation equipment, the electrode pattern formed after photolithography and development, and the final electrode structure obtained after etching to remove excess titanium, clearly demonstrating the specific processes and structural characteristics of electrode fabrication.

[0026] Figure 5 This diagram demonstrates the coupling process of a 90° optical mixer based on TFLN, starting with optical input coupling, proceeding to beam splitting and multiplexing coupling, and then to phase adjustment and coupling optimization. Arrows in the diagram indicate the optical signal transmission path, illustrating the connection method of the signal light and local oscillator light through the end-face coupling of the fiber and waveguide, the beam splitting and multiplexing process using a directional coupler made of TFLN material, and the principle of phase adjustment and coupling optimization achieved by the electrode control module adjusting the voltage of the phase shift arm electrodes. It showcases the overall process and working mechanism of the coupling method.

[0027] Figure 6 This diagram details the connection and alignment of the optical fiber and waveguide during optical input coupling. The positional relationships of the optical fiber, waveguide, fiber alignment equipment, and 3D micro-motion platform are shown, along with how the alignment accuracy between the optical fiber and waveguide is precisely controlled within ±1μm by adjusting the 3D micro-motion platform. The diagram also demonstrates the device and method for monitoring the optical power at the output end of the input waveguide, highlighting the key technical details and operational points of optical input coupling.

[0028] Figure 7 The diagram details the structure and working principle of the TFLN directional coupler during beam splitting and multiplexing. It shows key parameters such as the waveguide structure, coupling length, and waveguide spacing of the directional coupler, as well as the process of beam splitting and multiplexing of the signal light and local oscillator light within the coupler. Different colors of light represent the optical signals after splitting and multiplexing, clearly illustrating how precise control of the directional coupler parameters ensures the splitting ratio and coupling efficiency, and how to control the output optical signal power consistency deviation within ±5%.

[0029] Figure 8 This diagram illustrates the relationship between the electrode control module, the phase-shifting arm electrode, and the optical signal during phase adjustment and coupling optimization. The diagram shows the location and connection of the high-precision voltage source, feedback control circuit, phase-shifting arm electrode, and optical signal monitoring device in the electrode control module. It demonstrates the process of precisely adjusting the optical signal phase by regulating the electrode voltage using a PID control algorithm, and the principle of simultaneous monitoring of the output optical signal coupling efficiency and power consistency for coupling optimization. The diagram visually presents the core technology and working logic of this step. Detailed Implementation

[0030] Preparation method examples

[0031] 1. TFLN substrate cleaning: Select a TFLN substrate of suitable size, immerse it in acetone solution and ultrasonically clean it for 18 minutes to remove surface oil; then transfer it to ethanol solution and ultrasonically clean it for 18 minutes to further remove impurities; finally immerse it in deionized water and ultrasonically clean it for 20 minutes to remove residual ethanol and other small particles, and then dry it with nitrogen gas.

[0032] 2. Waveguide Structure Fabrication: On a clean TFLN substrate, photoresist was coated by rotating at 3500 rpm for 35 seconds to form a photoresist film with a thickness of approximately 1.2 μm. The designed waveguide structure mask was then placed on the substrate and exposed in a UV lithography apparatus for 12 seconds. After exposure, the substrate was developed in the accompanying developer for 1.5 minutes to obtain the photoresist pattern. The substrate was then placed in an ion beam etching apparatus, with the ion beam energy set to 500 eV and the beam current density to 10 mA / cm². 2 The waveguide structure was created by etching for 25 minutes, and then the residual photoresist was removed by soaking in a photoresist remover for 12 minutes.

[0033] 3. Electrode Fabrication: In the phase-shifting arm region of the waveguide, metallic titanium was deposited at 1100℃ and a rate of 0.8 nm / s using an electron beam evaporation apparatus, with a deposition thickness of 0.25 μm. Photoresist was then coated again, and after photolithography exposure and development, an electrode pattern was formed. Excess metallic titanium was removed using wet etching to fabricate electrodes with a width of 3 μm and a spacing of 2 μm.

[0034] 4. Electrode control module integration: The fabricated electrodes and electrode control module are connected by gold wire bonding to complete the fabrication process.

[0035] Coupling Method Examples

[0036] 1. Optical Input Coupling: The signal light and local oscillator light are respectively connected to optical fibers. An optical fiber alignment device is used to align the fiber end face with the waveguide input end face. The position and angle of the optical fiber are continuously adjusted using a three-dimensional micro-motion platform, and the optical power at the waveguide output end is monitored in real time. When the optical power reaches its maximum value, the optimal coupling state is determined, at which point the coupling efficiency reaches 88%.

[0037] 2. Beam splitting and multiplexing: The signal light and the local oscillator light enter the TFLN directional coupler for beam splitting and multiplexing. Based on the pre-designed and optimized parameters of the directional coupler, its manufacturing process is precisely controlled to ensure that the beam splitting ratio is close to 50:50 and the power consistency deviation of the output optical signal after multiplexing is controlled within ±4%.

[0038] 3. Phase Adjustment and Coupling Optimization: A voltage is applied to the phase-shifting arm electrodes using an electrode control module, and the voltage is monitored and adjusted in real time using a PID control algorithm. During the adjustment process, the phase and coupling efficiency of the output optical signal are continuously monitored, and parameters are continuously optimized, ultimately ensuring that the phase error of the output optical signal is less than ±1° and the coupling efficiency reaches 92%.

[0039] By implementing the above preparation and coupling methods, a high-performance 90° optical mixer based on TFLN can be fabricated, meeting the device performance requirements of optical communication systems.

[0040] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a 90° optical mixer based on TFLN, characterized in that, Includes the following steps: Prepare a TFLN substrate and ultrasonically clean it sequentially with acetone, ethanol and deionized water. Photoresist was coated on the cleaned TFLN substrate surface. After photolithography exposure and development, waveguide structure was fabricated using ion beam etching technology. After etching, residual photoresist was removed. Electrodes are fabricated on the first and second phase shift arms of the waveguide by depositing metallic titanium using electron beam evaporation technology, followed by photolithography and etching. Connect the fabricated electrodes to the electrode control module.

2. The preparation method according to claim 1, characterized in that, In the aforementioned ion beam etching technology, the ion beam energy is 400-600 eV, and the beam current density is 8-12 mA / cm². 2 The etching time is 20-30 minutes.

3. The preparation method according to claim 1, characterized in that, When depositing metallic titanium using the electron beam evaporation technique, the evaporation temperature is 1000-1200℃, the titanium evaporation rate is 0.5-1nm / s, and the deposition thickness is 0.2-0.3μm.

4. A coupling method for a 90° optical mixer based on TFLN, characterized in that, Includes the following steps: Optical input coupling: The external signal light and local oscillator light are connected to the signal light input waveguide and local oscillator light input waveguide respectively through optical fibers using end-face coupling. The optical fiber alignment equipment is used for precise alignment, and the position and angle of the optical fiber are adjusted by a three-dimensional micro-motion platform. Beam splitting and combining: A directional coupler made of TFLN material is used to split and combine the signal light and the local oscillator light. The splitting ratio and coupling efficiency are ensured by precisely controlling the parameters of the directional coupler. Phase adjustment and coupling optimization: The phase shift arm electrode voltage is adjusted using the electrode control module, and the voltage is adjusted in real time using a PID control algorithm. The coupling efficiency and power consistency of the output optical signal are monitored and optimized simultaneously.

5. The coupling method according to claim 4, characterized in that, In the optical input coupling, the alignment accuracy between the optical fiber and the waveguide is controlled within ±1μm to achieve a coupling efficiency of over 85%.

6. The coupling method according to claim 4, characterized in that, In the beam splitting and multiplexing coupling, the power consistency deviation of the output optical signal is controlled to be within ±5%.

7. The coupling method according to claim 4, characterized in that, In the phase adjustment and coupling optimization, the phase error of the output optical signal is made less than ±1°, and the coupling efficiency reaches more than 90%.

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