A tunable electro-optic grating coupler

Abstract

The application provides a tunable electro-optic grating coupler, which comprises a first grating layer with light reflection and lower electrode functions arranged below an electro-optic material layer and a second grating layer with light coupling and upper electrode functions arranged above the electro-optic material layer, so that the device can form a longitudinal electric field tuning structure perpendicular to the plane of the electro-optic material layer without additional preparation of independent tuning electrodes, thus fundamentally avoiding direct etching process of the electro-optic material layer and completely solving the problems of lattice damage, scattering loss and electro-optic performance degradation caused by the etching process; meanwhile, the tunable electro-optic grating coupler utilizes the excellent conductive processing performance of the second grating layer and the high reflection performance of the first grating layer, so that the device has excellent comprehensive performance of high coupling efficiency, large working bandwidth, low driving voltage and picosecond-level ultra-high-speed electric control tuning.

Description

Technical Field

[0001] This invention relates to the field of integrated photonic chip technology, and more particularly to a tunable electro-optic grating coupler. Background Technology

[0002] Grating couplers have become the standard optical input / output interface for mainstream integrated photonics platforms such as silicon-based, silicon nitride, and lithium niobate thin films due to their significant advantages, including large alignment tolerance, on-chip testing at any location on the wafer, no need for end-face polishing, and simple packaging process. With the evolution of optical communication towards ultra-high speeds of 800G / 1.6T, the continuous increase in optical interconnect density in data centers, and the rapid development of microwave photonics processing technology, integrated optoelectronic chips place higher demands on the performance of grating couplers: they not only need high coupling efficiency and large operating bandwidth, but also urgently require the integration of dynamically tunable functions to achieve wavelength matching in wavelength division multiplexing systems, dynamic routing of reconfigurable photonic chips, and online compensation for device process deviations.

[0003] Existing mainstream grating coupler material systems all have inherent limitations: while silicon-based and silicon nitride grating couplers offer advantages such as low transmission loss, wide bandwidth transparency, and compatibility with CMOS (Complementary Metal-Oxide-Semiconductor) processes, their materials themselves lack linear electro-optic effects and can only achieve tuning through thermo-optic effects. This results in fatal flaws such as high power consumption (mW level) and slow response speed (μs level), failing to meet the demands of high-speed dynamic applications. Lithium niobate thin-film grating couplers can achieve nanosecond-level tuning by utilizing the linear electro-optic effect of lithium niobate, but its linear electro-optic coefficient is only about 30 pm / V, leading to high driving voltage (typically >10V) and a limited tuning range, making it difficult to meet the needs of next-generation low-power photonic chips.

[0004] Barium titanate (BaTiO3, BTO), a typical perovskite-structured ferroelectric material, possesses the highest linear electro-optic coefficient among known oxide materials. The experimental effective electro-optic coefficient of high-quality epitaxial films can reach 923 pm / V, more than 30 times that of conventional lithium niobate. Electro-optic modulators based on BTO films have achieved voltages as low as 0.16V. With a half-wave voltage-length product of 1 cm and a modulation rate exceeding 100 Gbit / s, BTO-based optoelectronic devices demonstrate enormous application potential. However, current research on BTO-based optoelectronic devices mainly focuses on the core electro-optic modulator unit, lacking systematic research on the essential optical input / output coupling interface of the BTO platform. A grating coupler scheme that efficiently integrates with BTO waveguides and simultaneously possesses electro-optic tuning capabilities has not yet been developed. More critically, the direct etching process for BTO thin films is complex and prone to lattice damage during etching, introducing significant scattering loss and electro-optic performance degradation, severely limiting its application in grating couplers.

[0005] Therefore, how to fully utilize the ultra-high electro-optic material properties of BTO to construct a BTO-based grating coupler with high coupling efficiency, large bandwidth, and low power consumption electro-optic tuning function while avoiding direct etching of BTO thin films has become a key technical problem that urgently needs to be solved in the field of integrated photonics. Summary of the Invention

[0006] The purpose of this invention is to provide a tunable electro-optic grating coupler to address the technical problems of existing BTO-based grating couplers, such as slow tuning speed, high driving voltage, complex direct etching process of BTO thin films, and the introduction of severe optical losses and electro-optic performance degradation. This invention achieves efficient optical coupling and low-power, high-speed electronic tuning by employing a dual-layer grating dual-function synergistic design, completely avoiding direct etching of BTO material. Ultimately, it yields a device that combines high coupling efficiency, large operating bandwidth, and CMOS process compatibility.

[0007] To solve the above-mentioned technical problems, the present invention provides a tunable electro-optic grating coupler, comprising: Substrate; A buffer layer is disposed on the substrate; The first grating layer, located on the buffer layer, serves both as a light reflection layer and a lower electrode layer. The first buried oxide layer is disposed above the buffer layer and completely covers the first grating layer; An electro-optic material layer is disposed on the first buried oxide layer and is used to transmit light waves and has electro-optic refractive index modulation characteristics. The second grating layer is disposed on the electro-optic material layer and has both grating coupling function and upper electrode function. The second buried oxide layer is disposed above the electro-optic material layer and completely covers the second grating layer; The upper cladding layer is disposed on the second buried oxygen layer; When a voltage is applied to the first grating layer and the second grating layer, a longitudinal electric field perpendicular to its plane is formed in the electro-optic material layer. The refractive index of the electro-optic material layer is modulated through the electro-optic effect, thereby realizing the electronically controlled tuning of the grating coupling wavelength.

[0008] Preferably, the material of the first grating layer is Au, the material of the second grating layer is TiN, and the material of the electro-optic material layer is BaTiO3.

[0009] Preferably, the sum of the thicknesses of the first grating layer, the electro-optic material layer, and the second grating layer is ≤0.4μm.

[0010] Preferably, the period of the first grating layer is a positive integer multiple of the period of the second grating layer.

[0011] Preferably, the first grating teeth of the first grating layer and the second grating teeth of the second grating layer are aligned at their edges in the grating period direction, or maintain a preset phase offset.

[0012] Preferably, an insulating spacer layer is provided between the second grating layer and the electro-optic material layer. The insulating spacer layer is made of SiO2 and has a thickness of 10-30 nm.

[0013] Preferably, the duty cycle of the second grating layer gradually changes linearly or nonlinearly along the direction of light propagation, so that its coupled light field approximates a Gaussian distribution to achieve mode field matching.

[0014] Preferably, the tunable electro-optic grating coupler further includes a first waveguide electrode and a second waveguide electrode, the first waveguide electrode being connected to a side lead-out terminal of the first grating layer, and the second waveguide electrode being connected to a side lead-out terminal of the second grating layer; the materials of the first waveguide electrode and the second waveguide electrode both include any one of Cu, Pt, Ag and Au.

[0015] Preferably, the substrate is made of Si, and the buffer layer, the first buried oxide layer, the second buried oxide layer, and the upper cladding layer are all made of SiO2.

[0016] Preferably, the operating parameters of the tunable electro-optic grating coupler are as follows: operating voltage not exceeding 5V, center operating wavelength around 1550nm, compatible with TE polarized light, and fiber incident angle of 8° to 12°.

[0017] The beneficial effects of this invention are as follows: Unlike the prior art, this invention provides a tunable electro-optic grating coupler. It features a first grating layer below the electro-optic material layer, serving as both a light reflection and lower electrode, and a second grating layer above the electro-optic material layer, serving as both a light coupling and upper electrode. This allows the device to form a longitudinal electric field tuning structure perpendicular to the plane of the electro-optic material layer without the need for additional independent tuning electrodes. This fundamentally avoids the direct etching process of the electro-optic material layer, completely solving the problems of lattice damage, scattering loss, and electro-optic performance degradation caused by etching. Simultaneously, the tunable electro-optic grating coupler utilizes the excellent conductivity of the second grating layer and the high reflectivity of the first grating layer, enabling the device to possess excellent comprehensive performance, including high coupling efficiency, large operating bandwidth, low driving voltage, and nanosecond-level high-speed electronically controlled tuning. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cross-sectional structure of the tunable electro-optic grating coupler provided in Embodiment 1. Figure 2 This is a top view of the tunable electro-optic grating coupler provided in Embodiment 1; Figure 3 This is a schematic diagram of the first cross-sectional structure of the tunable electro-optic grating coupler provided in Embodiment 2. Figure 4 This is a schematic diagram of the second cross-sectional structure of the tunable electro-optic grating coupler provided in Embodiment 2. Figure 5 This is a schematic diagram of the cross-sectional structure of the tunable electro-optic grating coupler provided in Embodiment 3. Figure 6 This is a schematic diagram of the cross-sectional structure of the tunable electro-optic grating coupler provided in Embodiment 4. In the accompanying drawings: 100—tunable electro-optic grating coupler; 101—substrate; 102—buffer layer; 103—first grating layer; 104—first buried oxide layer; 105—electro-optic material layer; 106—second grating layer; 107—second buried oxide layer; 108—upper cladding layer; 109—insulating spacer layer. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] To address the shortcomings of existing technologies, this invention provides a tunable electro-optic grating coupler based on titanium nitride-barium titanate-gold heterostructure integration. It employs a dual-layer grating multifunctional design combined with a longitudinal electric field tuning mechanism, and does not perform etching on the BTO thin film throughout the process, thereby achieving efficient optical coupling of the grating coupler. At the same time, it has low-voltage, high-speed, and wide-range electrically controlled wavelength tuning capabilities. The entire structure and process are compatible with CMOS systems and can meet the practical application requirements of high-density photonic integration.

[0021] In this embodiment of the invention, a tunable electro-optic grating coupler is provided, comprising: a substrate; a buffer layer disposed on the substrate; a first grating layer disposed on the buffer layer, serving as both a light reflection function and a lower electrode function; a first buried oxide layer disposed above the buffer layer and completely covering the first grating layer; an electro-optic material layer disposed on the first buried oxide layer, used for transmitting light waves and possessing electro-optic refractive index modulation characteristics; a second grating layer disposed on the electro-optic material layer, serving as both a grating coupling function and an upper electrode function; a second buried oxide layer disposed above the electro-optic material layer and completely covering the second grating layer; and an upper cladding layer disposed on the second buried oxide layer. When a voltage is applied to the first grating layer and the second grating layer, an electric field perpendicular to the plane of the electro-optic material layer is formed in the electro-optic material layer. The refractive index of the electro-optic material layer is modulated through the electro-optic effect, thereby realizing the electronic control tuning of the grating coupling wavelength.

[0022] Specifically, the aforementioned tunable electro-optic grating coupler employs a dual-layer grating composite function design. The upper grating serves as both grating coupling and the upper electrode, while the lower grating acts as both a reflective layer and the lower electrode, together forming a vertical electrode system. This electrode system can apply a vertical electric field perpendicular to the thin-film plane to the intermediate electro-optic functional layer, utilizing the excellent linear electro-optic effect of the electro-optic material to achieve electrically controlled tuning of the center wavelength of the grating coupler. This design, through the synergistic cooperation of multiple functional structures, effectively avoids optical losses caused by direct etching of electro-optic materials, achieving integrated grating coupling and electro-optic tuning functions. This device features high coupling efficiency, large operating bandwidth, low driving voltage, and good compatibility with CMOS processes, making it widely applicable in wavelength division multiplexing optical communication systems and reconfigurable photonic integrated chips.

[0023] In this embodiment of the invention, the substrate is selected as single-crystal silicon with a thickness of several hundred micrometers, which can provide stable mechanical support for the entire optoelectronic device. This material is also a commonly used standard substrate for semiconductor micro-nano processing and CMOS technology. The buffer layer is prepared on the substrate surface and is made of silicon dioxide with a thickness of 200-500 nm. It can flatten the substrate surface and buffer the interlayer stress, thereby improving the adhesion effect and crystal quality of the upper film.

[0024] In this embodiment of the invention, the first grating layer is fabricated above the buffer layer. The main material is highly reflective metallic gold with a thickness of 100-200 nm. It is patterned to form a periodic grating structure. The period of the first grating layer is 600-1000 nm, and the grating duty cycle is 0.3-0.7. This periodic grating structure, on the one hand, performs directional reflection of the downward diffracted beam and optimizes the optical coupling efficiency of the device by combining the optical field constructive interference effect. On the other hand, it serves as the lower electrode and together with the upper second grating layer, forms a longitudinal electric field application system.

[0025] In this embodiment of the invention, the first buried oxide layer is also made of silicon dioxide material with a thickness of 200-1500 nm. The first buried oxide layer completely covers the first grating layer, which can not only flatten the surface structure, but also isolate the first grating layer from the upper electro-optic material layer, avoid the absorption loss caused by metal from interfering with the optical signal transmission, and can also precisely control the optical field transmission path and optical path difference, providing a structural basis for the reflection light to achieve constructive interference.

[0026] In this embodiment of the invention, the electro-optic material layer is a continuous, unetched BTO thin film with a thickness of 100–150 nm. This electro-optic material layer, grown above the first buried oxide layer, is the core active structure for optical transmission and electro-optic modulation. Maintaining the integrity of the thin film morphology avoids lattice damage, scattering loss, and electro-optic performance degradation caused by etching processes. Barium titanate, a perovskite ferroelectric material, has an effective electro-optic coefficient of up to 923 pm / V, far exceeding the performance of traditional lithium niobate materials. It can support high-sensitivity electro-optic tuning under low-voltage conditions and can also function as a low-loss optical waveguide for optical signal transmission.

[0027] In this embodiment of the invention, the second grating layer is fabricated on the surface of the electro-optic material layer. TiN material, highly compatible with CMOS processes, is selected, with a thickness of 100nm–200nm. After etching, a periodic grating structure is formed, consisting of periodically arranged TiN grating teeth, used to achieve diffraction coupling between the fiber beam and the BTO waveguide mode. The period of the second grating layer is 600–900nm, and the grating duty cycle is 0.3–0.7. The refractive index of TiN material in the 1550nm operating band is approximately 2.0, and its refractive index value is between that of BTO and SiO2, which can form a reasonable refractive index gradient, ensuring efficient diffraction coupling between the single-mode fiber Gaussian beam and the BTO waveguide mode. TiN material itself has good conductivity and can directly serve as the upper electrode of the device, eliminating the need for additional independent electrodes, effectively simplifying the device structure and processing flow. The etching process for this material is mature, resulting in smooth grating sidewalls, low overall optical loss, and excellent process stability.

[0028] In this embodiment of the invention, both the second buried oxide layer and the upper cladding layer are made of silicon dioxide. The thickness of the second buried oxide layer is 200–600 nm, and the thickness of the upper cladding layer is 200–400 nm. The second buried oxide layer completely covers the second grating layer, serving as an isolation and protection layer. The upper cladding layer covers the outside of the second buried oxide layer, protecting the overall structure of the device and adjusting the effective refractive index of the device to reduce the impact of the external environment on the light transmission process.

[0029] In this embodiment of the invention, the tunable electro-optic grating coupler is further configured with a first waveguide electrode and a second waveguide electrode. The first waveguide electrode is connected to the side lead-out end of the first grating layer, and the second waveguide electrode is connected to the side lead-out end of the second grating layer. The first waveguide electrode and the second waveguide electrode can be made of any one of copper, platinum, silver, or gold. They have stable conductivity and can continuously and smoothly apply a driving voltage.

[0030] In this embodiment of the invention, the sum of the thicknesses of the first grating layer, the electro-optic material layer, and the second grating layer is ≤0.4μm; this design is beneficial for high-density photonic integration.

[0031] The specific working process of the tunable electro-optic grating coupler provided in this embodiment of the invention to achieve electrically controlled tuning of the grating coupling wavelength is as follows: (1) Optical coupling process: The beam output from the single-mode fiber irradiates the surface of the second grating layer (TiN upper grating) in the tunable electro-optic grating coupler at an incident angle of 8° to 12°. The TE (transverse electric wave) polarized light in the beam can complete the mode conversion through the grating diffraction effect and accurately couple into the electro-optic material layer (lower BTO thin film waveguide) to realize the effective transmission and introduction of free space light to thin film waveguide light.

[0032] (2) Reflection Enhancement Process: Part of the beam diffracted downwards through the second grating layer penetrates the BTO thin film and the first buried oxide layer (SiO2) and is transmitted to the first grating layer (Au grating) at the bottom of the device. With the help of the reflection characteristics of the periodic Au grating, the beam is reflected back to the core region of the BTO waveguide. By precisely controlling and optimizing the thickness parameters of the first buried oxide layer, the bottom reflected beam and the upward diffracted beam of the grating can meet the constructive interference condition, effectively reducing optical signal loss and significantly improving the optical coupling efficiency of the grating coupler.

[0033] (3) Electro-optic tuning process: A DC voltage or modulation voltage is applied between the second grating layer and the bottom first grating layer, which can form a potential difference between the two layers, thereby generating a uniform longitudinal electric field perpendicular to the thin film plane inside the BTO thin film. Based on the Pockels electro-optic effect, the refractive index of the BTO thin film will change linearly with the intensity of the applied electric field, changing the effective refractive index of the grating coupling region, causing the Bragg wavelength of the tunable electro-optic grating coupler to drift in a controllable manner, and finally realizing high-precision electro-optic tuning of the device's operating center wavelength.

[0034] Specifically, the operating parameters of the tunable electro-optic grating coupler are as follows: operating voltage not exceeding 5V, center operating wavelength around 1550nm, suitable for coupling and transmission of TE polarized light, and fiber incident angle of 8° to 12°. The wavelength tuning range can reach over 10nm, and the tuning response speed can reach sub-nanosecond to picosecond levels (limited by the intrinsic response speed of the Pockels effect of BTO material and the bandwidth of the driving circuit), featuring low-voltage driving and high-speed tuning.

[0035] In summary, this invention achieves two core functions—grating coupling and electro-optic tuning—without increasing the number of device layers or process complexity. First, the bottom-periodically matched Au grating reflects downward-diffracted light back to the BTO waveguide region. Combined with the optimized thickness of the second buried oxide layer, this forms constructive interference of the optical field, effectively improving coupling efficiency. Furthermore, compared to continuous metal films, this structure exhibits lower guided-mode absorption and more controllable optical path directionality. Second, the longitudinal electrode pair formed by the second and first grating layers can create a large-area uniform electric field within the BTO thin film, with the electric field distribution and optical path directionality being highly compatible. The field overlaps significantly, and the linear electro-optic effect of BTO enables electrically controlled tuning of the Bragg wavelength, resulting in higher tuning sensitivity compared to traditional lateral electrodes under the same driving voltage. Furthermore, the heterogeneous waveguide composed of a TiN grating and a BTO thin film allows for flexible control of the effective refractive index and mode field energy distribution by adjusting parameters such as grating height, film thickness, period, and duty cycle, further enhancing electro-optic tuning capabilities while ensuring coupling efficiency. Finally, the various materials used in the device, as well as the fabrication processes such as sputtering, PECVD (Plasma-Enhanced Chemical Vapor Deposition), and photolithography, are all compatible with standard CMOS processes, resulting in low integration difficulty and promising conditions for large-scale mass production and industrial application.

[0036] The technical solution of this application will now be described in conjunction with specific embodiments.

[0037] Example 1: Please see Figure 1 and Figure 2 This embodiment 1 provides a tunable electro-optic grating coupler 100 based on titanium nitride-barium titanate-gold heterostructure integration, comprising: a substrate 101; a buffer layer 102 disposed on the substrate 101; a first grating layer 103 disposed on the buffer layer 102, serving as both a light reflection function and a lower electrode function; a first buried oxide layer 104 disposed above the buffer layer 102 and completely covering the first grating layer 103; an electro-optic material layer 105 disposed on the first buried oxide layer 104, used for transmitting light waves and possessing electro-optic refractive index modulation characteristics; a second grating layer 106 disposed on the electro-optic material layer 105, serving as both a grating coupling function and an upper electrode function; a second buried oxide layer 107 disposed above the electro-optic material layer 105 and completely covering the second grating layer 106; and an upper cladding layer 108 disposed on the second buried oxide layer 107. When a voltage is applied to the first grating layer 103 and the second grating layer 106, an electric field perpendicular to the plane of the electro-optic material layer 105 is formed in the electro-optic material layer 105. The refractive index of the electro-optic material layer 105 is modulated through the electro-optic effect, thereby realizing the electronic control tuning of the grating coupling wavelength.

[0038] In this embodiment 1, the substrate 101 is made of Si and has a thickness of several hundred micrometers; the buffer layer 102 is made of SiO2 and has a thickness of 300 nm; the first grating layer 103 is made of Au and has a thickness of 120 nm, a grating period of 800 nm, and a duty cycle of 0.5; the first buried oxide layer 104 is made of SiO2 and preferably has a thickness of 300 nm; the electro-optic material layer 105 is made of BTO and has a thickness of 100 nm; the second grating layer 106 is made of TiN and has a thickness of 120 nm, a grating period of 800 nm, and a duty cycle of 0.5; the second buried oxide layer 107 is made of SiO2 and has a thickness of 300 nm; and the upper cladding layer 108 is made of SiO2 and has a thickness of 300 nm.

[0039] The complete fabrication process of the tunable electro-optic grating coupler 100 provided in Example 1 is fully compatible with standard CMOS production lines. The core processes include sputtering deposition, PECVD thin film deposition, photolithography, dry etching, and metal stripping. The process flow is standardized and mass-producible. The specific fabrication steps are as follows: Step (1) Pretreatment of substrate 101: Select single crystal silicon as substrate and thoroughly clean substrate 101 using standard cleaning process to remove surface impurities and native oxide layer; then dry and keep warm for 15 min to complete surface passivation treatment, effectively improving the interface adhesion and film growth quality of subsequent film deposition.

[0040] Step (2) Preparation of the first grating layer 103: A buffer layer 102 of silicon dioxide is deposited on the surface of the pretreated silicon substrate 101 using PECVD process, and then an Au thin film is deposited by magnetron sputtering process. Finally, a periodic Au grating bottom layer structure with uniform period is prepared by combining photolithography, dry etching or metal stripping process, which is the first grating layer 103.

[0041] Step (3) Deposition and surface planarization of the first buried oxide layer 104: Continue to use PECVD process to deposit silicon dioxide film to fully cover the bottom Au grating structure and obtain the first buried oxide layer 104; then use chemical mechanical polishing process to planarize the surface film to ensure the device surface is flat.

[0042] Step (4) Deposition of electro-optic material layer 105: A barium titanate (BTO) ferroelectric thin film is grown on the flat surface of the first buried oxide layer 104 using pulsed laser deposition or magnetron sputtering. The deposition temperature is controlled at 550℃~650℃ to prepare a continuous, flat, and defect-free BTO thin film. The BTO thin film is not etched throughout the process, so its crystal structure is completely preserved, ensuring the excellent electro-optic performance of the film.

[0043] Step (5) Preparation of the second grating layer 106: Titanium nitride (TiN) thin film is deposited by magnetron sputtering, and then a periodic TiN grating structure is prepared by high-precision photolithography combined with dry etching process to obtain the second grating layer 106 with the same period as the first grating layer 103.

[0044] Step (6) Deposition and encapsulation: Sequentially deposit the second buried oxide layer 107 and the upper cladding layer 108 made of silicon dioxide to encapsulate the core optoelectronic functional structure of the device, which not only achieves structural protection, but also allows for precise control of the waveguide refractive index distribution of the device and optimizes the optical field transmission characteristics.

[0045] Step (7) Electrode fabrication and device forming: Waveguide electrodes are fabricated by photolithography, metal sputtering and stripping processes to complete the electrode lead-out of the bottom Au grating and the upper TiN grating, and finally a CMOS-compatible tunable electro-optic grating coupler 100 with complete structure and stable performance is obtained.

[0046] In this embodiment 1, the operating voltage of the tunable electro-optic grating coupler 100 is controlled within 5V, the operating wavelength is set in the optical communication band around 1550nm, and the optical fiber is incident at an angle of 8° to 12°. The device mainly completes the coupling and transmission of TE polarized light signals. After FDTD simulation optimization, the coupling efficiency is expected to reach over 60%.

[0047] In this embodiment, TiN material is used to fabricate the grating structure. Leveraging the ease of etching TiN and the high flatness of its sidewalls after etching, the process difficulties of directly etching BTO material are perfectly avoided, significantly reducing device fabrication difficulty and improving yield. Simultaneously, this embodiment uses a BTO thin film as the waveguide core layer, ensuring low-loss optical signal transmission while fully utilizing the excellent electro-optic coefficient of BTO material. Utilizing the Pockels effect, it achieves core performance characteristics of low driving voltage and wide-range center wavelength electro-optic tuning, demonstrating significant advantages in tuning efficiency and operating range. Furthermore, the Au reflective layer structure added to the bottom of the device reflects the diffracted optical signal back into the waveguide, reducing optical energy loss and significantly improving the overall coupling efficiency of the grating coupler, thus optimizing the device's optical performance. Finally, the device uses a transverse electrode to apply pressure to form a longitudinal electric field, which can precisely control the refractive index of the BTO waveguide, thereby stably changing the Bragg wavelength of the grating coupler. The tuning method is precise and highly controllable. In addition, the overall fabrication materials of this device are highly compatible with CMOS back-end processes, and it can be adapted to existing semiconductor integration process systems, enabling miniaturization and array integration of the device, and possessing the potential for large-scale optoelectronic integrated chip applications.

[0048] Example 2: Please see Figure 3 and Figure 4This embodiment 2 provides a tunable electro-optic grating coupler 100 based on titanium nitride-barium titanate-gold heterostructure integration. Its structure is roughly the same as that of embodiment 1, except that: this embodiment 2 adjusts the period parameter of the bottom first grating layer 103 based on the structure of embodiment 1. The period of the gold first grating layer 103 is set to twice the period of the top titanium nitride second grating layer 106. Figure 3 ) or three times ( Figure 4 When the period of the second grating layer 106 is 800nm, the period of the bottom first grating layer 103 is set to 1.6μm or 2.4μm. The two grating layers can maintain edge alignment in the vertical direction, or a corresponding phase offset (1 to 2 period offset) can be set.

[0049] In this embodiment, the use of an integer multiple (≥2 times) period design reduces the equivalent fill factor of the Au grating, thereby reducing the lateral optical absorption loss of the Au metal material on the BTO guided mode. When the two grating layers can maintain edge alignment in the vertical direction, a light-transmitting window without metal obstruction is formed below the grating teeth of the second grating layer 106. Downward diffracted light can pass through the light-transmitting window into the first buried oxide layer 104 and reach the first grating layer 103 for reflection, widening the vertical migration channel of the light field and optimizing the lateral overlap effect of the reflected light and the waveguide mode. After simulation optimization, the coupling efficiency is expected to be improved to over 70%. The first grating layer 103 can also form a smoother reflection phase response, avoiding excessively strong narrowband resonant coupling between the upper and lower grating layers, thus effectively improving the operating bandwidth of the device. At the same time, this structural design reduces the alignment accuracy requirements of the photolithography process, improving process tolerance and product yield. On this basis, the duty cycle of the first grating layer 103 can be increased to enhance the reflection intensity and further improve the coupling efficiency.

[0050] Example 3: Please see Figure 5 , Figure 5 This is a schematic cross-sectional view of the tunable electro-optic grating coupler 100 provided in Embodiment 3. In Embodiment 3, based on the structure of Embodiment 1, an ultrathin silicon dioxide insulating spacer layer 109 is added between the second grating layer 106 and the electro-optic material layer 105. The thickness of the insulating spacer layer 109 is maintained between 10 nm and 30 nm. In Embodiment 3, the thickness of the insulating spacer layer 109 is preferably 20 nm. The second grating layer 106 is fabricated above the insulating spacer layer 109, and the BTO thin film electro-optic material layer 105 remains completely flat throughout.

[0051] Specifically, the sputtering deposition and photolithography etching processes of TiN thin films can easily cause physical damage to the surface of the underlying BTO thin film, disrupting the original crystal structure and introducing additional optical scattering losses. The newly added silicon dioxide insulating spacer layer 109 can provide physical isolation and protection, fully preserving the high crystallinity and low transmission loss of the BTO thin film. By adjusting the thickness of the insulating spacer layer 109, those skilled in the art can change the energy distribution ratio of the light field between the upper and lower grating structures, optimizing the mode field overlap state. The entire process does not require changes to the grating tooth height or the BTO thin film thickness. The insulating spacer layer 109 uses a CMOS-compatible dielectric material, requiring no additional process equipment or procedures, simplifying the fabrication process. Furthermore, it does not significantly weaken the longitudinal electric field tuning performance of the device, minimizing optical losses while ensuring tuning capability.

[0052] Example 4: Please see Figure 6 , Figure 6 This is a schematic cross-sectional view of the tunable electro-optic grating coupler 100 provided in Embodiment 4. In this embodiment 4, the design of the second grating layer 106 is further optimized based on the structure of Embodiment 1. The traditional uniform duty cycle grating is abandoned. A linear or nonlinear gradually changing duty cycle is set according to the light propagation direction (from the optical fiber incident end to the waveguide output end). The duty cycle increases linearly from about 0.3 at the optical fiber incident end to about 0.7 at the waveguide output end, so that the light radiation intensity of TiN grating teeth at different positions in the second grating layer 106 gradually changes. All TiN grating teeth are kept at the same potential through the peripheral connection structure to ensure the overall electrical connectivity.

[0053] Specifically, the radiation intensity of traditional uniform grating couplers is mismatched with the Gaussian mode field distribution of single-mode optical fibers, limiting theoretical coupling efficiency. The tunable electro-optic grating coupler 100 provided in Example 4, by designing the grating parameters of the second grating layer 106 to a graded duty cycle, can control the radiation intensity of each TiN grating tooth, making the optical field coupled to the fiber approximate Gaussian, thereby achieving mode field matching optimization and further improving coupling efficiency. This design does not change the electrical continuity of the TiN grating as the upper electrode (all TiN grating teeth are still connected to the same potential through peripheral connections), therefore it does not affect the electrical tuning function, and all TiN grating teeth remain at the same potential. Only the width of the TiN grating teeth is changed through photolithography, without adding additional process steps, making it fully compatible with standard TiN etching processes. Furthermore, the design is flexible and scalable, and the distribution function of the non-uniform duty cycle is not limited to a linear gradient.

[0054] Compared with existing technologies, the technical solution of this invention has the following advantages: (1) High coupling efficiency: The present invention achieves high coupling efficiency through mode field matching design of TiN / BTO heterostructure waveguide and coherent reflection enhancement of bottom Au grating.

[0055] (2) Electro-optic tunable function: This invention applies the ultra-high electro-optic coefficient (923 pm / V) of BTO to the dynamic tuning of the grating coupler, which can achieve the center wavelength tuning range under low voltage and the tuning response speed is on the order of nanoseconds.

[0056] (3) Large operating bandwidth: This invention achieves a large operating bandwidth by optimizing the TiN / BTO double-layer waveguide structure.

[0057] (4) Low loss: This invention avoids the scattering loss caused by direct etching of BTO and makes full use of the low loss characteristics of TiN material and the low transmission loss of BTO film.

[0058] (5) Process compatibility: The TiN deposition and etching process in this invention is highly compatible with CMOS production lines, paving the way for large-scale, low-cost monolithic integration with silicon-based electronic devices in the future.

[0059] (6) Reduced packaging cost: The design of the TiN grating teeth in this invention makes the device no longer dependent on precise end face processing.

[0060] (7) Small size and high integration: The total thickness of the two grating layers and the BTO film does not exceed 0.4 μm, which is conducive to high-density photonic integration.

[0061] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0062] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A tunable electro-optic grating coupler, characterized in that, include: Substrate; A buffer layer is disposed on the substrate; The first grating layer is disposed on the buffer layer and has both light reflection and lower electrode functions; The first buried oxide layer is disposed above the buffer layer and completely covers the first grating layer; An electro-optic material layer is disposed on the first buried oxide layer, used to transmit light waves and having electro-optic refractive index modulation characteristics; The second grating layer is disposed on the electro-optic material layer and has both grating coupling and upper electrode functions; The second buried oxide layer is disposed above the electro-optic material layer and completely covers the second grating layer; The upper cladding layer is disposed on the second buried oxygen layer; When a voltage is applied to the first grating layer and the second grating layer, a longitudinal electric field perpendicular to its plane is formed in the electro-optic material layer. The refractive index of the electro-optic material layer is modulated through the electro-optic effect, thereby realizing the electronically controlled tuning of the grating coupling wavelength.

2. The tunable electro-optic grating coupler according to claim 1, characterized in that, The material of the first grating layer is Au, the material of the second grating layer is TiN, and the material of the electro-optic material layer is BaTiO3.

3. The tunable electro-optic grating coupler according to claim 2, characterized in that, The sum of the thicknesses of the first grating layer, the electro-optic material layer, and the second grating layer is ≤0.4μm.

4. The tunable electro-optic grating coupler according to claim 2, characterized in that, The period of the first grating layer is a positive integer multiple of the period of the second grating layer.

5. The tunable electro-optic grating coupler according to claim 4, characterized in that, The first grating tooth of the first grating layer and the second grating tooth of the second grating layer are aligned at their edges in the grating period direction, or maintain a preset phase offset.

6. The tunable electro-optic grating coupler according to claim 2, characterized in that, An insulating spacer layer is provided between the second grating layer and the electro-optic material layer. The insulating spacer layer is made of SiO2 and has a thickness of 10-30 nm.

7. The tunable electro-optic grating coupler according to claim 2, characterized in that, The duty cycle of the second grating layer gradually changes linearly or nonlinearly along the direction of light propagation, so that its coupled light field approximates a Gaussian distribution to achieve mode field matching.

8. The tunable electro-optic grating coupler according to claim 2, characterized in that, The tunable electro-optic grating coupler further includes a first waveguide electrode and a second waveguide electrode. The first waveguide electrode is connected to a side lead-out of the first grating layer, and the second waveguide electrode is connected to a side lead-out of the second grating layer. The materials of the first waveguide electrode and the second waveguide electrode include any one of Cu, Pt, Ag and Au.

9. The tunable electro-optic grating coupler according to claim 1, characterized in that, The substrate is made of Si, and the buffer layer, the first buried oxide layer, the second buried oxide layer, and the upper cladding layer are all made of SiO2.

10. The tunable electro-optic grating coupler according to any one of claims 1 to 9, characterized in that, The operating parameters of the tunable electro-optic grating coupler are as follows: operating voltage not exceeding 5V, center operating wavelength around 1550nm, compatible with TE polarized light, and fiber incident angle of 8° to 12°.

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