Thin film lithium niobate electro-optical modulator with sectional type electrode structure

Abstract

The invention provides a thin film lithium niobate electro-optical modulator with a segmented electrode structure, which belongs to the field of photoelectric integrated devices and is composed of a lithium niobate substrate, a silicon dioxide buffer layer, a thin film waveguide layer and a segmented electrode layer from bottom to top. Impedance matching is optimized, loss is reduced, and high-speed data transmission under low energy consumption is achieved. Through the segmented electrode design, the bandwidth and efficiency of the modulator are improved, stray capacitance and resistance are reduced, and electric field distribution is optimized. The device has remarkable advantages in the fields of high-speed optical communication, photoelectric integrated circuits and the like, and has huge application potential in the emerging fields of quantum communication and the like. The preparation process relates to a plurality of processes, such as SMART CUT, buffer proton exchange, photoetching and the like, so that the performance and the stability of the device are ensured.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic integrated devices and relates to a segmented electrode structure thin-film lithium niobate electro-optic modulator. Background Technology

[0002] Electro-optic modulators play a crucial role in the optoelectronic field, widely used in high-speed optical communication and optoelectronic integrated circuits. Lithium niobate (LNiO) is widely considered an ideal material for optoelectronic devices due to its unique electro-optic effect, wide spectral transmittance, and excellent mechanical and thermal stability. In electro-optic modulator applications, these properties make LNiO excel in high-speed data transmission and signal processing. In recent years, advancements in thin-film technology have further enhanced the performance of LNiO modulators, improving device integration and response speed, driving miniaturization and low-power design, and playing a particularly critical role in modern optical communication systems.

[0003] Traditional electrode designs often limit device bandwidth and modulation efficiency due to high capacitance and significant losses. By dividing the electrode into multiple independent sections, a segmented electrode design can significantly reduce parasitic capacitance and resistance, lowering overall losses and capacitive load, thereby improving modulator bandwidth and efficiency. Furthermore, the segmented electrode structure can optimize electric field distribution, improve modulation depth and linearity, while reducing drive voltage requirements and power consumption, giving it a clear advantage in high-speed and low-power applications.

[0004] With the rapid development of optical communication technology, the demand for high-bandwidth, high-speed, and low-latency devices is increasing, further driving the research and development of high-performance optoelectronic devices. Segmented electrode thin-film lithium niobate electro-optic modulators offer unparalleled advantages in speed, power consumption, and integration compared to traditional electrode thin-film lithium niobate electro-optic modulators. Simultaneously, with the gradual advancement of optoelectronic hybrid integration technology, this modulator will also demonstrate enormous application potential in emerging fields such as quantum communication, coherent communication, and optoelectronic integrated circuits. Its superior performance gives it a crucial position and significant influence in the future development of optoelectronic technology. Summary of the Invention

[0005] The present invention proposes a segmented electrode structure thin-film lithium niobate electro-optic modulator, which mainly includes a lithium niobate thin-film optical waveguide and a segmented electrode structure. By segmenting the excitation of electrical signals, impedance matching is optimized to ensure effective signal transmission and reduce losses, thereby achieving high-speed data transmission with low power consumption.

[0006] The technical solution of this invention:

[0007] The segmented electrode structure of the thin-film lithium niobate electro-optic modulator consists of, from bottom to top, a bulk lithium niobate substrate, a silicon dioxide buffer layer, a lithium niobate thin film layer containing the MZ optical waveguide, and segmented electrodes made of gold on the outermost layer of the device. The segmented electrode structure comprises two main parts: a ground electrode and a center electrode. The ground electrode is divided into two symmetrical parts, each containing a signal introduction region, a signal transmission region, and a segmented modulation region. The center electrode connects the two segments of the modulation region into a single unit via the signal introduction region. Each layer is fabricated layer-by-layer using different processes, including SMART CUT, buffer proton exchange, photolithography, and deposition processes, corresponding to the fabrication of each layer.

[0008] Furthermore, the lithium niobate film has a thickness of 600 nm and is prepared using the SMART CUT process.

[0009] Furthermore, the preparation steps of the lithium niobate thin film include:

[0010] Step S1: Raw material preparation and selection of high-quality lithium niobate single crystals as starting material.

[0011] Step S2 involves placing the lithium niobate single crystal in an ion implanter. High-energy hydrogen ions (H+) are implanted into the lithium niobate single crystal, forming a damage layer of a certain depth within the single crystal.

[0012] Step S3 involves heat-treating the ion-implanted lithium niobate single crystal to promote the diffusion of implanted ions and form layer separation.

[0013] Step S4 uses a mechanical method to separate the implanted layer from the original lithium niobate single crystal. The separated lithium niobate film is then transferred and bonded to the target substrate. In this example, a bulk lithium niobate coated with silicon dioxide is used as the substrate.

[0014] Step S5 involves chemical mechanical polishing (CMP) of the transferred lithium niobate film to reduce surface roughness and thickness inhomogeneity.

[0015] Furthermore, the fabrication steps of the MZ optical waveguide include:

[0016] Step S6 uses photolithography to define the MZ optical waveguide pattern on the lithium niobate film. Photoresist is coated onto the surface of the lithium niobate film. The channel pattern of the MZ optical waveguide is transferred onto the photoresist by exposure using a photolithography machine.

[0017] After development in step S7, reactive ion etching (RIE) is used to transfer the channel pattern onto the lithium niobate film. The remaining photoresist is removed to obtain the channel structure of the MZ optical waveguide.

[0018] Step S8 involves immersing the etched lithium niobate film in a buffered proton exchange solution. The solution temperature is controlled between 150-200°C. During the exchange process, protons in the solution exchange with lithium ions in the lithium niobate, causing a change in refractive index and forming a waveguide.

[0019] Step S9 involves removing the buffered proton-exchanged lithium niobate membrane from the solution. The membrane is then thoroughly rinsed with deionized water to remove acidic substances and residual ions from its surface.

[0020] Step S10: Place the cleaned lithium niobate film into an annealing furnace. Annealing is performed at an appropriate temperature (230°C) to eliminate internal stress in the waveguide and stabilize the refractive index distribution.

[0021] Furthermore, the fabrication steps of the segmented electrode include:

[0022] Step S11 involves fabricating segmented electrode patterns on a lithium niobate thin film using photolithography. The specific steps are as follows: a. Coating the thin film surface with photoresist. b. Transferring the electrode pattern onto the photoresist through photolithography. c. Developing to remove unexposed photoresist. d. Transferring the electrode pattern onto the lithium niobate thin film using wet etching. e. Removing the remaining photoresist to obtain the electrode pattern.

[0023] Step S12 uses magnetron sputtering to grow a metal electrode on the electrode pattern.

[0024] Furthermore, the segmented electrode structure is integrally formed, and the fabrication of all sections of the ground electrode and the center electrode is completed in one photolithography deposition.

[0025] Furthermore, the ground electrode of the segmented electrode consists of two symmetrical comb-shaped fingers, one above the other, with each finger corresponding to the other.

[0026] Furthermore, the segmented electrode has a signal introduction area, and the signal is introduced into the device through a probe or gold wire during encapsulation coupling.

[0027] Furthermore, the segmented electrode center electrode is divided into upper and lower arms corresponding to the upper and lower ground electrodes respectively, and the MZ optical waveguide is located between the center electrode and the ground electrode.

[0028] The present invention has the following beneficial effects:

[0029] 1) The segmented design optimizes impedance matching, ensuring effective signal transmission and reducing losses. Through a more precise electric field distribution, the segmented electrodes not only enhance electro-optic interaction but also increase modulation depth, thereby improving the overall efficiency of the modulator.

[0030] 2) Segmented electrodes effectively reduce transmission loss and greatly improve the signal quality of the modulator by reducing the excitation of higher-order modes and multimode interference.

[0031] 3) The segmented electrode structure provides greater flexibility, allowing designers to customize modulators for different application needs and achieve optimal performance.

[0032] 4) The segmented electrode design can also effectively improve modulation efficiency. By making more efficient use of the input electrical energy for optical signal modulation, the ineffective consumption of energy is reduced, which enhances high-speed optical communication and optical information processing applications and enables high-speed data transmission with low energy consumption. Attached Figure Description

[0033] The present invention will now be described in further detail with reference to the accompanying drawings.

[0034] Figure 1 This is a top view of the segmented electrode of the present invention.

[0035] Figure 2 This is a top view of the waveguide portion of the present invention.

[0036] Figure 3 This is a side view of the present invention.

[0037] Among them, 1. Lithium niobate thin film; 2. Segmented electrode; 21. Ground electrode signal introduction area; 22. Ground electrode signal transmission area; 23. Ground electrode segmented modulation area; 24. Center electrode signal introduction area; 25. Center electrode upper and lower segmented modulation arms; 3. MZ optical waveguide; 4. Silicon dioxide buffer layer; 5. Bulk lithium niobate substrate. Detailed Implementation

[0038] like Figure 3 As shown, the segmented electrode structure thin-film lithium niobate electro-optic modulator comprises, from bottom to top, a bulk lithium niobate substrate 5, a silicon dioxide buffer layer 4, a lithium niobate thin film 1, and segmented electrodes 2 stacked together. The segmented electrode structure is as follows: Figure 1 As shown, a complete ground electrode is composed of two symmetrical ground electrode signal introduction areas 21, a ground electrode signal transmission area 22, and a ground electrode segmented modulation area 23; a complete center electrode is composed of a center electrode signal introduction area 24 and two segmented modulation arms above and below the center electrode; and a complete segmented electrode structure is formed by the complete ground electrode and the center electrode. Figure 2 The image shows the MZ optical waveguide 3, which is shielded by segmented electrodes. The overall length of the MZ optical waveguide 3 is the same as the length of the entire device. The lengths of the upper and lower arm active regions of the MZ optical waveguide 3 are the same as the lengths of the upper and lower segmented modulation arms 25 of the center electrode.

[0039] In this embodiment, the silicon dioxide buffer layer 4 is deposited on the bulk lithium niobate substrate 5 using a coating machine, with a coating thickness of 500 nm. The lithium niobate thin film 1 is bonded to the surface of the silicon dioxide buffer layer 4 using a bonding process. The MZ optical waveguide 3 is fabricated on the lithium niobate thin film 1 using photolithography and buffer proton exchange processes. After the stability of the MZ optical waveguide 3 is completed and tested, segmented electrodes 2 are fabricated on the surface of the lithium niobate thin film 1 containing the MZ optical waveguide 3 using photolithography and coating processes.

[0040] Specifically, the steps include the following:

[0041] Step S1: Raw material preparation and selection of high-quality lithium niobate single crystals as starting material.

[0042] Step S2 involves placing the lithium niobate single crystal in an ion implanter. High-energy hydrogen ions (H+) are implanted into the lithium niobate single crystal, forming a damage layer of a certain depth within the single crystal.

[0043] Step S4 involves heat-treating the ion-implanted lithium niobate single crystal to promote the diffusion of implanted ions and form layer separation.

[0044] Step S4 uses a mechanical method to separate the implanted layer from the original lithium niobate single crystal. The separated lithium niobate film is then transferred and bonded to the target substrate. In this example, a bulk lithium niobate coated with silicon dioxide is used as the substrate.

[0045] Step S5 involves chemical mechanical polishing (CMP) of the transferred lithium niobate film to reduce surface roughness and thickness inhomogeneity.

[0046] Step S6 uses photolithography to define the MZ optical waveguide pattern on the lithium niobate film. Photoresist is coated onto the surface of the lithium niobate film. The channel pattern of the MZ optical waveguide is transferred onto the photoresist by exposure using a photolithography machine.

[0047] After development in step S7, reactive ion etching (RIE) is used to transfer the channel pattern onto the lithium niobate film. The remaining photoresist is removed to obtain the channel structure of the MZ optical waveguide.

[0048] Step S8 involves immersing the etched lithium niobate film in a buffered proton exchange solution. The solution temperature is controlled between 150-200°C. During the exchange process, protons in the solution exchange with lithium ions in the lithium niobate, causing a change in refractive index and forming a waveguide.

[0049] Step S9 involves removing the buffered proton-exchanged lithium niobate membrane from the solution. The membrane is then thoroughly rinsed with deionized water to remove acidic substances and residual ions from its surface.

[0050] Step S10: Place the cleaned lithium niobate film into an annealing furnace. Annealing is performed at an appropriate temperature (230°C) to eliminate internal stress in the waveguide and stabilize the refractive index distribution.

[0051] Step S11 involves fabricating segmented electrode patterns on a lithium niobate thin film using photolithography. The specific steps are as follows: a. Coating the thin film surface with photoresist. b. Transferring the electrode pattern onto the photoresist through photolithography. c. Developing to remove unexposed photoresist. d. Transferring the electrode pattern onto the lithium niobate thin film using wet etching. e. Removing the remaining photoresist to obtain the electrode pattern.

[0052] Step S12 uses magnetron sputtering to grow a metal electrode on the electrode pattern.

[0053] Step S13: Align the prepared thin-film lithium niobate electro-optic modulator with the optical fiber. Secure the optical fiber and electro-optic modulator using UV-curable adhesive or other encapsulation materials. Connect the electrode leads and perform performance testing.

[0054] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the specification of the present invention should still fall within the scope of the patent of the present invention.

Claims

1. A segmented electrode structure thin film lithium niobate electro-optic modulator, characterized by: From bottom to top, it consists of bulk lithium niobate substrate, silicon dioxide buffer layer, lithium niobate thin film layer containing MZ optical waveguide and segmented electrode made of gold located at the surface layer of the device. The segmented electrode structure includes two parts of ground electrode and center electrode, the ground electrode is divided into two symmetrical parts, both containing signal introduction area, signal transmission area and segmented modulation area. The center electrode is connected by the signal introduction area to form a whole with the two arms of segmented modulation. Each layer is prepared by different processes from bottom to top, including SMART CUT process, buffer proton exchange process, photolithography process, plating process and so on, which correspond to each layer preparation respectively.

2. A thin film lithium niobate electro-optic modulator of segmented electrode structure according to claim 1, characterized in that: The preparation steps of the lithium niobate thin film include: Step S1 raw material preparation, select high-quality lithium niobate single crystal as starting material. Step S2, place the lithium niobate single crystal in the ion implanter. Implant high-energy hydrogen ions (H+) into the lithium niobate single crystal to form a damage layer of a certain depth in the single crystal. Step S3, heat treatment of the lithium niobate single crystal after ion implantation to promote the diffusion of implanted ions and form layer separation. Step S4, separate the implanted layer from the original lithium niobate single crystal by mechanical method. And transfer and bond the separated lithium niobate thin film to the target substrate. The substrate used in this example is bulk lithium niobate coated with silicon dioxide as the substrate. Step S5, chemical mechanical polishing (CMP) is performed on the transferred lithium niobate thin film to reduce surface roughness and thickness unevenness.

3. A thin film lithium niobate electro-optic modulator of segmented electrode structure according to claim 1, characterized in that: The preparation steps of the MZ optical waveguide include: Step S6, define the MZ optical waveguide pattern on the lithium niobate thin film using photolithography technology. Coat photoresist on the surface of the lithium niobate thin film. Expose the photoresist to light through the photolithography machine to transfer the channel pattern of the MZ optical waveguide to the photoresist. Step S7, after development, use reactive ion etching (RIE) to transfer the channel pattern to the lithium niobate thin film. Remove the remaining photoresist to obtain the channel structure of the MZ optical waveguide. Step S8, immerse the etched lithium niobate thin film in a buffer proton exchange solution. Control the temperature of the solution between 150-200℃. During the exchange process, the protons in the solution will exchange with the lithium ions in the lithium niobate, causing a change in refractive index and forming a waveguide. Step S9, take the lithium niobate thin film after buffer proton exchange out of the solution. Use deionized water to thoroughly clean the thin film to remove surface acidic substances and residual ions. Step S10, place the cleaned lithium niobate thin film in an annealing furnace. Perform annealing treatment at an appropriate temperature (230℃) to eliminate internal stress in the waveguide and stabilize the refractive index distribution.

4. The thin-film lithium niobate bend electro-optic modulation network of claim 1 or 2 or 3, wherein: The preparation steps of the electromagnetic shielding layer include: Step S11, use photolithography technology to make a segmented electrode pattern on the lithium niobate thin film. The specific steps are as follows: a. Coat photoresist on the surface of the thin film. b. Expose the photoresist to light through the photolithography machine to transfer the electrode pattern to the photoresist. c. Develop to remove the unexposed photoresist. d. Use wet etching method to transfer the electrode pattern to the lithium niobate thin film. e. Remove the remaining photoresist to obtain the electrode pattern. Step S12, use magnetron sputtering method to grow metal electrode on the electrode pattern.

5. A thin film lithium niobate electro-optic modulator of segmented electrode structure according to claim 1, characterized in that: The ground electrode is composed of two symmetrical comb-shaped finger strips, and the upper and lower finger strips correspond to each other in one-to-one correspondence.

6. A thin film lithium niobate electro-optic modulator of segmented electrode structure according to claim 1, characterized in that: The segmented electrode has a signal introduction area, and a signal introducer is introduced into the device through a probe or a gold wire when encapsulation coupling is performed.

7. A thin film lithium niobate electro-optic modulator of segmented electrode structure according to claim 1, characterized in that: The central electrode of the segmented electrode is divided into two arms corresponding to the upper and lower ground electrodes, and the MZ optical waveguide is located between the central electrode and the ground electrode.

8. A thin film lithium niobate electro-optic modulator of segmented electrode structure according to claim 1, characterized in that: The electrode is a segmented electrode structure, which realizes high-speed data transmission under the condition of ensuring low energy consumption.

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