Thin-film lithium niobate electro-optical modulator and preparation method thereof

Abstract

The invention relates to the technical field of electrooptical modulators, and discloses a thin-film lithium niobate electrooptical modulator and a preparation method thereof.The thin-film lithium niobate electrooptical modulator comprises a substrate layer, a buried insulating layer, a thin-film lithium niobate layer and a covering layer, and the thin-film lithium niobate layer is etched to form a Mach-Zehnder interferometer waveguide structure; the Mach-Zehnder interferometer waveguide structure comprises an input waveguide, a 3dB coupler, a modulation arm waveguide 3dB beam combiner, an output waveguide, a signal electrode and a temperature compensator, a substrate layer is made of silicon, sapphire or quartz materials, and the method comprises the steps of wafer pretreatment, waveguide structure preparation, covering layer deposition, temperature compensator preparation and post-treatment and testing. And the performance stability of the device is guaranteed by accurately controlling technological parameters of photoetching, etching, deposition and the like. The device has the advantages of high electro-optical response speed, low transmission loss, high environmental adaptability, good integration compatibility and the like, and can be widely applied to the fields of high-speed optical communication, optical sensing and the like.

Description

Technical Field

[0001] This invention relates to the field of electro-optic modulator technology, specifically to a thin-film lithium niobate electro-optic modulator and its preparation method. Background Technology

[0002] As a core device in modern optoelectronic technologies such as optical communication, optical interconnection, optical computing, and optical sensing, the core function of electro-optic modulators is to accurately convert electrical signals into amplitude, phase, or polarization state changes of optical signals. They are the key hubs for realizing high-speed signal transmission and processing. With the rapid development of technologies such as 5G communication, high-speed interconnection of data centers, and quantum communication, the market has put forward higher requirements for the performance of electro-optic modulators, including higher modulation bandwidth, faster response speed, lower transmission loss, better environmental stability, and stronger integration compatibility.

[0003] The crystal orientation design of the thin-film lithium niobate layer in some existing devices is unreasonable, resulting in the electro-optic coefficient not being fully utilized. The electro-optic coefficient r of conventional devices is low. 33 The voltage is mostly below 25 pm / V, which is insufficient to meet the requirements of ultra-high-speed signal modulation. At the same time, the poor design of the modulation arm waveguide structure results in high transmission loss, which causes severe attenuation of optical signal energy, affecting transmission distance and modulation accuracy. The refractive index of thin-film lithium niobate crystal is sensitive to temperature changes, and existing devices lack an effective temperature compensation mechanism. Significant phase drift is easily generated in the wide operating temperature range of -40℃ to 85℃, which leads to distortion of the modulation signal and makes it difficult to guarantee stability. Summary of the Invention

[0004] The purpose of this invention is to provide a thin-film lithium niobate electro-optic modulator and its preparation method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a thin-film lithium niobate electro-optic modulator, comprising a substrate layer, a buried insulating layer, a thin-film lithium niobate layer, and a capping layer, wherein a Mach-Zehnder interferometer waveguide structure is etched in the thin-film lithium niobate layer; The Mach-Zehnder interferometer waveguide structure includes an input waveguide, a 3dB coupler, a modulation arm waveguide 3dB combiner, an output waveguide, signal electrodes, and a temperature compensator.

[0006] Preferably, the substrate is made of silicon, sapphire, or quartz and has a thickness of 300-500 μm, and the buried insulating layer is made of silicon dioxide and has a thickness of 1-5 μm.

[0007] Preferably, the thickness of the thin-film lithium niobate layer is 300-800 nm, the crystal orientation is X, and the electro-optic coefficient r is... 33 ≥28pm / V.

[0008] Preferably, the modulation arm waveguide is a strip waveguide with a width of 1-3 μm, a height of 200-500 nm, and a transmission loss of ≤0.5 dB / cm.

[0009] Preferably, a temperature compensator is also etched into the thin-film lithium niobate layer. The temperature compensator is a titanium diffusion resistor or a metal heater, used to compensate for phase drift in the range of -40℃ to 85℃.

[0010] Preferably, the procedure includes the following steps: S1, Wafer Preprocessing A lithium niobate wafer on an insulator was selected, and the surface of the thin-film lithium niobate layer was cleaned and dried. S2, Waveguide Structure Fabrication Waveguide patterning masks are fabricated on the surface of thin-film lithium niobate layers using electron beam lithography or deep ultraviolet lithography. Mach-Zehnder interferometer waveguide structures, polarization beam splitters, and polarization rotators are then formed by reactive ion etching. S3, Overburden deposition A capping layer was deposited on the surface of the etched thin film lithium niobate layer using plasma-enhanced chemical vapor deposition technology. S4. Temperature Compensator Preparation A temperature compensator was fabricated in a designated area of ​​a thin-film lithium niobate layer using a titanium diffusion process. S5, Post-processing and Testing After cutting, grinding, and polishing the device and completing the fiber optic coupling packaging, optical and electrical performance tests are performed.

[0011] Preferably, in step S1, the acetone and isopropanol are used for ultrasonic cleaning for 10-15 minutes, followed by rinsing with deionized water for 5-10 minutes, and then drying in an oven at 100-120°C for 30-60 minutes.

[0012] Preferably, in step S2, the etching gas is a mixture of CF4 and O2, with a gas flow ratio of 3:1-5:1, an etching power of 100-200W, an etching pressure of 1-5Pa, and an etching depth of 200-500nm.

[0013] Preferably, in step S3, the capping layer material is silicon dioxide or aluminum nitride, with a thickness of 0.5-2 μm, a deposition temperature of 200-300℃, and the difference between the refractive index of the deposited capping layer and the refractive index of the thin film lithium niobate layer is ≤0.1.

[0014] Preferably, in step S4, the diffusion temperature is 900-1000℃, the diffusion time is 1-3h, the diffusion depth is 100-200nm, and the material of the metal heater is gold or platinum with a thickness of 0.5-1μm.

[0015] Compared with the prior art, the present invention provides a thin-film lithium niobate electro-optic modulator and its preparation method, which has the following beneficial effects: This invention relates to a thin-film lithium niobate electro-optic modulator and its fabrication method. The thin-film lithium niobate layer is designed with an X-crystal orientation, and the electro-optic coefficient r is [missing information]. 33 With a performance of ≥28pm / V, far exceeding the performance indicators of conventional electro-optic materials, it can achieve high-speed electro-optic conversion, significantly improve modulation bandwidth and signal response rate, and meet the needs of high-frequency signal processing in fields such as optical communication and optical sensing. At the same time, the modulation arm waveguide is designed as a strip structure with a width of 1-3μm and a height of 200-500nm, and the transmission loss is ≤0.5dB / cm, which effectively reduces energy attenuation during optical signal transmission and ensures the integrity and stability of signal transmission.

[0016] This thin-film lithium niobate electro-optic modulator and its fabrication method, by integrating a temperature compensator in the form of a titanium diffusion resistor or a metal heater into the thin-film lithium niobate layer, can accurately compensate for phase drift over a wide temperature range of -40℃ to 85℃, avoiding the influence of ambient temperature changes on modulation accuracy. This allows the device to maintain stable operation even under complex environments such as extreme high and low temperatures and temperature and humidity fluctuations. The substrate layer is made of high-strength and high-stability materials such as silicon, sapphire, or quartz, with a thickness controlled at 300-500μm. Combined with a 1-5μm thick silicon dioxide buried insulating layer, it not only ensures the mechanical structural strength of the device but also effectively isolates external interference, improving the long-term reliability of the device.

[0017] This thin-film lithium niobate electro-optic modulator and its fabrication method utilize a lithium niobate-on-insulator wafer as a substrate. Through a layered design of an embedded insulating layer and a thin-film lithium niobate layer, efficient confinement of the optical field and low-loss transmission are achieved. The Mach-Zehnder interferometer waveguide structure integrates the input waveguide, 3dB coupler, modulation arm waveguide, 3dB beam combiner, output waveguide, and signal electrode into one compact structure, which is easy to integrate with other optoelectronic devices and meets the requirements of large-scale applications of optical integrated chips. The cover layer is made of silicon dioxide or aluminum nitride, and the refractive index difference between the cover layer and the thin-film lithium niobate layer is ≤0.1, which can reduce light reflection loss and effectively protect the waveguide structure, extending the device's service life. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort: Figure 1 This is a three-dimensional schematic diagram of the structure of the present invention; Figure 2This is a three-dimensional schematic diagram of the waveguide structure of the Mach-Zehnder interferometer of the present invention; Figure 3 This is a three-dimensional schematic diagram of the 3dB coupler and modulation arm waveguide of the present invention; Figure 4 This is a schematic diagram of the structural process of the present invention.

[0019] In the figure: 1. Substrate layer; 2. Buried insulating layer; 3. Thin-film lithium niobate layer; 31. Mach-Zehnder interferometer waveguide structure; 311. Input waveguide; 312. 3dB coupler; 313. Modulation arm waveguide; 314. 3dB beam combiner; 315. Output waveguide; 316. Signal electrode; 317. Temperature compensator; 4. Cover layer. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] This invention provides the following technical solutions: Example 1: Please refer to Figure 1-4 The present invention provides a technical solution: a thin-film lithium niobate electro-optic modulator, comprising a substrate layer 1, a buried insulating layer 2, a thin-film lithium niobate layer 3, and a capping layer 4, wherein a Mach-Zehnder interferometer waveguide structure 31 is etched in the thin-film lithium niobate layer 3; The Mach-Zehnder interferometer waveguide structure 31 includes an input waveguide 311, a 3dB coupler 312, a modulation arm waveguide 313, a 3dB beam combiner, an output waveguide 315, a signal electrode 316, and a temperature compensator 317.

[0023] The substrate layer 1 is made of silicon, sapphire, or quartz material with a thickness of 300-500 μm, and the buried insulating layer 2 is made of silicon dioxide material with a thickness of 1-5 μm.

[0024] The thickness of the thin-film lithium niobate layer 3 is 300-800 nm, the crystal orientation is X, and the electro-optic coefficient r is... 33 ≥28pm / V.

[0025] The modulation arm waveguide 313 is a strip waveguide with a width of 1-3μm, a height of 200-500nm, and a transmission loss of ≤0.5dB / cm.

[0026] A temperature compensator 317 is also etched into the thin-film lithium niobate layer 3. The temperature compensator 317 is a titanium diffusion resistor or a metal heater, used to compensate for phase drift in the range of -40℃ to 85℃.

[0027] Example 2: Please refer to Figure 1-4 Furthermore, based on Example 1, a method for preparing a thin-film lithium niobate electro-optic modulator was obtained.

[0028] Includes the following steps: S1, Wafer Preprocessing A lithium niobate wafer on an insulator was selected, and the surface of the thin-film lithium niobate layer 3 was cleaned and dried. S2, Waveguide Structure Fabrication A waveguide patterning mask is fabricated on the surface of a thin lithium niobate layer 3 using electron beam lithography or deep ultraviolet lithography. The Mach-Zehnder interferometer waveguide structure 31, polarization beam splitter and polarization rotator are formed by reactive ion etching. S3, capping layer 4 deposition A capping layer 4 was deposited on the surface of the etched thin film lithium niobate layer 3 using plasma-enhanced chemical vapor deposition technology; S4, Temperature Compensator 317 Preparation A temperature compensator 317 was fabricated in a designated area of ​​the thin-film lithium niobate layer 3 using a titanium diffusion process. S5, Post-processing and Testing After cutting, grinding, and polishing the device and completing the fiber optic coupling packaging, optical and electrical performance tests are performed.

[0029] In step S1, the equipment is ultrasonically cleaned with acetone and isopropanol for 10-15 minutes, rinsed with deionized water for 5-10 minutes, and then dried in an oven at 100-120℃ for 30-60 minutes.

[0030] In step S2, the etching gas is a mixture of CF4 and O2, with a gas flow ratio of 3:1-5:1, an etching power of 100-200W, an etching pressure of 1-5Pa, and an etching depth of 200-500nm.

[0031] In step S3, the material of the capping layer 4 is silicon dioxide or aluminum nitride, with a thickness of 0.5-2 μm and a deposition temperature of 200-300℃. The difference between the refractive index of the deposited capping layer 4 and the refractive index of the thin film lithium niobate layer 3 is ≤0.1.

[0032] In step S4, the diffusion temperature is 900-1000℃, the diffusion time is 1-3h, the diffusion depth is 100-200nm, and the metal heater is made of gold or platinum with a thickness of 0.5-1μm.

[0033] In actual operation, when this device is in use, the incident light signal enters the device through the input waveguide 311 and is first transmitted to the 3dB coupler 312. Based on the principle of light coupling and splitting, the 3dB coupler 312 splits the input light signal into two coherent beams with equal power. These beams are then injected into two completely symmetrical modulation arm waveguides 313. The modulation arm waveguides 313 adopt a strip structure design and utilize the refractive index difference between the thin-film lithium niobate layer 3, the buried insulating layer 2, and the capping layer 4 to achieve strong confinement of the light field, reduce light signal leakage, ensure the coherence of the two split beams, and achieve a transmission loss ≤0.5dB / cm, ensuring the transmission of the light signal. To ensure energy stability during transmission, after an external electrical signal is applied to the signal electrode 316, a uniform electric field is formed in the thin lithium niobate layer 3 in the region where the modulation arm waveguide 313 is located. According to the Pockels effect, the refractive index of the lithium niobate crystal changes linearly with the applied electric field. When the electrical signal is applied to the modulation arm waveguide 313 through the signal electrode 316, the refractive index of the lithium niobate crystal in the two modulation arms is differentially modulated, resulting in a phase difference between the two coherent beams during transmission. The magnitude of the phase difference is proportional to the intensity of the applied electric field, thus realizing the conversion of the electrical signal into a phase change of the optical signal. Since the thin lithium niobate layer 3 adopts an X-crystal orientation, its electro-optic coefficient r 33With a voltage ≥28 pm / V, it possesses excellent electro-optical response characteristics. The temperature compensator 317 operates synchronously: by sensing changes in ambient temperature, it actively adjusts its own heating power to compensate for the temperature in the modulation arm waveguide 313 region. Its principle is to utilize the slight influence of temperature changes on the refractive index of the lithium niobate crystal to offset the additional phase drift caused by ambient temperature fluctuations, ensuring that the phase difference between the two split beams is determined only by the external electrical signal, thus guaranteeing the stability of the modulation accuracy. After passing through the modulation arm waveguide 313, the two coherent beams with a phase difference are transmitted to the 3dB combiner 314. According to the principle of light interference, the two beams interfere and superimpose in the combiner. When the phase difference between the two beams is 0 or an integer multiple of 2π, a phase difference is generated. Constructive interference produces the strongest output light signal. When the phase difference is an odd multiple of π, destructive interference occurs, resulting in the weakest output light signal. When the phase difference is between these two values, the output light intensity varies with the phase difference in a cosine manner. The interfered light signal is led out of the device through the output waveguide 315, completing the modulation of the light signal amplitude by the electrical signal. If phase modulation is required, the electrical signal can be controlled to generate a specific phase difference between the two beams. After beam combining, the phase-modulated light signal is directly output. In addition, the polarization beam splitter and polarization rotator integrated into the waveguide structure fabrication process can preprocess the polarization state of the incident light, ensuring that the electro-optic modulation process is not affected by the polarization state of the incident light, thus achieving polarization-independent modulation.

[0034] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A thin-film lithium niobate electro-optic modulator, comprising a substrate layer (1), a buried insulating layer (2), a thin-film lithium niobate layer (3), and a capping layer (4), characterized in that: The thin-film lithium niobate layer (3) is etched to form a Mach-Zehnder interferometer waveguide structure (31). The Mach-Zehnder interferometer waveguide structure (31) includes an input waveguide (311), a 3dB coupler (312), a modulation arm waveguide (313), a 3dB combiner, an output waveguide (315), a signal electrode (316), and a temperature compensator (317).

2. The thin-film lithium niobate electro-optic modulator according to claim 1, characterized in that: The substrate layer (1) is made of silicon, sapphire or quartz and has a thickness of 300-500 μm. The buried insulating layer (2) is made of silicon dioxide and has a thickness of 1-5 μm.

3. The thin-film lithium niobate electro-optic modulator according to claim 1, characterized in that: The thickness of the thin-film lithium niobate layer (3) is 300-800 nm, the crystal orientation is X, and the electro-optic coefficient r 33 ≥28pm / V.

4. The thin-film lithium niobate electro-optic modulator according to claim 1, characterized in that: The modulation arm waveguide (313) is a strip waveguide with a width of 1-3μm, a height of 200-500nm, and a transmission loss of ≤0.5dB / cm.

5. The thin-film lithium niobate electro-optic modulator according to claim 1, characterized in that: A temperature compensator (317) is also etched in the thin film lithium niobate layer (3). The temperature compensator (317) is a titanium diffusion resistor or a metal heater, used to compensate for phase drift in the range of -40℃ to 85℃.

6. A method for fabricating a thin-film lithium niobate electro-optic modulator according to claims 1-5, characterized in that: The process includes the following steps: S1, Wafer Preprocessing Select a lithium niobate wafer on an insulator and clean and dry the surface of the thin-film lithium niobate layer (3); S2, Waveguide Structure Fabrication Waveguide patterning masks are fabricated on the surface of thin lithium niobate layer (3) using electron beam lithography or deep ultraviolet lithography. Mach-Zehnder interferometer waveguide structure (31), polarization beam splitter and polarization rotator are formed by reactive ion etching. S3, Overburden deposition A capping layer (4) was deposited on the surface of the etched thin film lithium niobate layer (3) using plasma-enhanced chemical vapor deposition technology. S4, Preparation of temperature compensator (317) A temperature compensator (317) was fabricated in a designated area of ​​the thin-film lithium niobate layer (3) using a titanium diffusion process. S5, Post-processing and Testing After cutting, grinding, and polishing the device and completing the fiber optic coupling packaging, optical and electrical performance tests are performed.

7. The method for fabricating a thin-film lithium niobate electro-optic modulator according to claim 6, characterized in that: In step S1, the equipment is ultrasonically cleaned with acetone and isopropanol for 10-15 minutes, rinsed with deionized water for 5-10 minutes, and then dried in an oven at 100-120℃ for 30-60 minutes.

8. The method for fabricating a thin-film lithium niobate electro-optic modulator according to claim 6, characterized in that: In step S2, the etching gas is a mixture of CF4 and O2, with a gas flow ratio of 3:1-5:1, an etching power of 100-200W, an etching pressure of 1-5Pa, and an etching depth of 200-500nm.

9. The method for fabricating a thin-film lithium niobate electro-optic modulator according to claim 6, characterized in that: The material of the capping layer (4) in step S3 is silicon dioxide or aluminum nitride, with a thickness of 0.5-2μm and a deposition temperature of 200-300℃. The difference between the refractive index of the deposited capping layer (4) and the refractive index of the thin film lithium niobate layer (3) is ≤0.

1.

10. The method for fabricating a thin-film lithium niobate electro-optic modulator according to claim 6, characterized in that: In step S4, the diffusion temperature is 900-1000℃, the diffusion time is 1-3h, the diffusion depth is 100-200nm, and the metal heater is made of gold or platinum with a thickness of 0.5-1μm.

Images