Lithium niobate optical transceiver and method of forming the same

Abstract

The embodiment of the present disclosure provides a lithium niobate optical transceiver and a forming method thereof, wherein the lithium niobate optical transceiver comprises a lithium niobate modulator chip, and a detector chip, a laser chip, an electric driving chip and a transimpedance amplifier chip which are inversely stacked on the lithium niobate modulator chip; wherein: the electric driving chip is used for providing a modulation driving voltage to a modulation electrode in the lithium niobate modulator chip, so that the lithium niobate modulator modulates an optical signal generated by the laser chip; the detector chip is used for detecting the modulated optical signal and converting the modulated optical signal into an electric signal; and the transimpedance amplifier chip is used for amplifying the electric signal.

Description

Technical Field

[0001] This disclosure relates to the field of photonic integrated chip technology, and to, but is not limited to, a lithium niobate optical transceiver and a method for forming the same. Background Technology

[0002] Lithium niobate (LiNbO3, LN) materials possess excellent properties, including high electro-optic response, high intrinsic bandwidth, wide transparency window (0.35 μm to 5 μm), and good thermal stability, making them widely studied and applied in electro-optic modulators. In particular, with the rapid development of thin-film lithium niobate in recent years and the resolution of the etching problem in lithium niobate waveguides, thin-film lithium niobate modulators have received extensive research. Compared to traditional lithium niobate modulators, thin-film lithium niobate modulators offer advantages such as high modulation bandwidth, small structural size, and high modulation efficiency.

[0003] However, most lithium niobate thin-film optical modulators are currently standalone devices, with few heterogeneous integration with light sources, photodetectors, and electric drive chips, which is insufficient in practical applications. Summary of the Invention

[0004] This disclosure provides a lithium niobate optical transceiver and a method for forming the same.

[0005] In a first aspect, embodiments of this disclosure provide a lithium niobate optical transceiver, comprising: a lithium niobate modulator chip, and a detector chip, a laser chip, an electric drive chip, and a transimpedance amplifier chip flip-chip stacked on the lithium niobate modulator chip; wherein: the electric drive chip is used to provide a modulation drive voltage to the modulation electrode in the lithium niobate modulator chip, so that the lithium niobate modulator modulates the optical signal generated by the laser chip; the detector chip is used to detect the modulated optical signal and convert it into an electrical signal; and the transimpedance amplifier chip is used to amplify the electrical signal.

[0006] In some embodiments, the lithium niobate modulator chip includes: a substrate, a ridge waveguide on the substrate, and the modulation electrode; wherein the ridge waveguide includes: a lithium niobate thin film and a silicon nitride waveguide on the lithium niobate thin film, or a lithium niobate ridge waveguide in the lithium niobate thin film.

[0007] In some embodiments, the electric drive chip and the modulation electrode are interconnected via flip-chip bonding; the transimpedance amplifier chip and the metal electrode on the detector chip are interconnected via flip-chip bonding; and the laser chip is connected to the peripheral power supply circuit via wire bonding.

[0008] In some embodiments, the ridge waveguide includes a 2×2 beam splitter, a Mach-Zehnder waveguide, and a 2×2 beam combiner; wherein the output of the 2×2 beam splitter is connected to the input of the 2×2 beam combiner through the Mach-Zehnder waveguide.

[0009] In some embodiments, the modulation electrode includes a differential driving electrode; the lithium niobate film is Z-cut, and the radio frequency electric field passes perpendicularly through the ridge waveguide; or, the modulation electrode includes a single-ended push-pull GSG driving electrode, and the lithium niobate film is X-cut.

[0010] In some embodiments, the differential driving electrode includes a differential GGSSG driving electrode or a differential GGSSG driving electrode; wherein, S + Electrode and S - The electrodes are respectively located directly above the two optical waveguide arms of the Mach-Zehnder waveguide, with the G electrode located on both sides of the optical waveguide arm, and the optical waveguide arm and the S electrode... + Electrode or the S - The vertical distance between the differential electrodes ranges from 500 nm to 2 μm.

[0011] In some embodiments, the lithium niobate modulator chip further includes: a heated metal thin film for bias point control of the lithium niobate modulator, and / or termination resistor matching of the lithium niobate modulator.

[0012] In some embodiments, the ridge waveguide further includes a 2×4 multimode interferometer mixer for demodulating coherent optical signals.

[0013] Secondly, embodiments of this disclosure provide a method for forming a lithium niobate optical transceiver, comprising: providing a lithium niobate modulator chip; flip-chipping a detector chip, a laser chip, an electric drive chip, and a transimpedance amplifier chip onto the lithium niobate modulator chip; wherein the electric drive chip is used to provide a modulation drive voltage to the modulation electrode in the lithium niobate modulator chip, so that the lithium niobate modulator modulates the optical signal generated by the laser chip; the detector chip is used to detect the modulated optical signal and convert it into an electrical signal; and the transimpedance amplifier chip is used to amplify the electrical signal.

[0014] In some embodiments, flip-chipping a detector chip, a laser chip, an electric drive chip, and a transimpedance amplifier chip on the lithium niobate modulator chip includes: sequentially forming a first pad and the electric drive chip connected to the first pad on the modulation electrode; forming the laser chip and the detector chip in a capping layer of the lithium niobate modulator chip; forming a metal electrode connected to the detector chip on the capping layer; and sequentially forming a second pad and the transimpedance amplifier chip connected to the second pad on the metal electrode.

[0015] In this embodiment, the electric drive chip, detector chip, laser chip, transimpedance amplifier chip, and lithium niobate modulator chip are integrated together using a flip-chip process. This achieves several advantages: firstly, it integrates other key functional chips, enabling three-dimensional stacking integration to form a lithium niobate optical transceiver, characterized by high process tolerance, high integration, small size, and high speed; secondly, it reduces the length of high-frequency traces, improving signal quality and integrity, and fully leveraging the performance advantages of each component; furthermore, it integrates the optical signal transmitter and receiver, enabling interconnection between the light source, detector, and modulator. Attached Figure Description

[0016] In the accompanying drawings (which are not necessarily drawn to scale), similar reference numerals may describe similar parts in different views. Similar reference numerals with different letter suffixes may indicate different examples of similar parts. The drawings illustrate, by way of example and not limitation, the various embodiments discussed herein.

[0017] Figure 1 A schematic diagram illustrating the implementation process of a method for forming a lithium niobate optical transceiver provided in this embodiment of the disclosure;

[0018] Figures 2 to 9 This is a schematic diagram of the composition and structure of a lithium niobate optical transceiver provided in an embodiment of this disclosure. Detailed Implementation

[0019] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0020] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this disclosure. However, it will be apparent to those skilled in the art that this disclosure may be practiced without one or more of these details. In other instances, to avoid confusion with this disclosure, certain technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and structures described in detail.

[0021] In the accompanying drawings, for clarity, the dimensions of layers, areas, and elements, as well as their relative dimensions, may be exaggerated. The same reference numerals denote the same elements throughout.

[0022] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this disclosure, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion. And the discussion of a second element, component, area, layer, or portion does not imply that the first element, component, area, layer, or portion necessarily exists in this disclosure.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprise” and / or “comprising,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0024] Before introducing the embodiments of this disclosure, the relevant technologies will be introduced first.

[0025] Silicon photonics is a next-generation technology based on silicon and silicon-based substrate materials such as silicon-germanium / silicon (SiGe / Si) and silicon-on-insulator (SOI). It utilizes existing complementary metal-oxide-semiconductor (CMOS) processes for the development and integration of optical devices. Combining the ultra-large-scale, ultra-high-precision manufacturing capabilities of integrated circuit technology with the ultra-high speed and ultra-low power consumption advantages of photonics, it represents a disruptive technology for addressing the failure of Moore's Law. This combination benefits from the scalability of semiconductor wafer manufacturing, enabling large-scale production and cost reduction. Optical modulators and detectors are core active devices in silicon photonics.

[0026] The bandwidth limit of pure silicon optical modulators based on carrier dispersion effects is approximately 80 GHz, with limited room for improvement at present. Lithium niobate thin-film optical modulators, on the other hand, theoretically have a bandwidth of up to 500 GHz, showing promising prospects and experiencing rapid development both domestically and internationally in recent years. III-V group and germanium-silicon photodetectors have higher bandwidth limits, with 265 GHz already reported. Therefore, integrating lithium niobate thin-film optical modulators and photodetectors into photonic chips will be a technological trend, effectively addressing the current bandwidth limitations. Furthermore, heterogeneous integration of photonic chips, electrical chips, and laser chips through three-dimensional stacking will further improve the overall chip performance.

[0027] Among the related technologies, there are two heterogeneous integration schemes for LN thin film optical modulators: Scheme (1) directly flip-chips the unetched LN thin film onto the silicon-based chip processed by CMOS technology to form a heterogeneous integration of other silicon-based passive devices and germanium-silicon photodetectors; Scheme (2) flip-chips the etched LN thin film onto the silicon-based chip processed by CMOS technology. The two have certain similarities.

[0028] Most lithium niobate thin-film optical modulators in related technologies are single devices, with few heterogeneous integration schemes with light sources, photodetectors, and electric drive chips, resulting in shortcomings in practical applications. Specifically: (1) Although a single lithium niobate thin-film optical modulator has excellent performance, performance degradation, process compatibility, and large-scale production need to be addressed when integrated with other photonic chips; (2) The integration method of lithium niobate thin-film optical modulators with electric drive chips is limited to gold wire bonding, which introduces high-frequency loss and signal quality degradation; (3) When lithium niobate thin-film optical modulators are integrated with other photonic chip structures, the process error tolerance is low, and the performance degradation is severe; (4) Lasers have not yet been integrated.

[0029] This disclosure provides a method for forming a lithium niobate optical transceiver, with reference to... Figure 1The method includes steps S101 and S102, wherein:

[0030] Step S101: Provide a lithium niobate modulator chip;

[0031] Here, lithium niobate crystals exhibit good thermoelectric, piezoelectric, elasto-optic, and electro-optic effects. The electro-optic effect refers to a phenomenon where a material's refractive index changes significantly under the influence of a DC electric field (or a low-frequency electric field); in other words, the applied electric field alters the optical properties of the medium. In some materials, the change in refractive index is linearly related to the intensity of the applied electric field, known as the linear electro-optic effect, also called the Pockels effect. The linear electro-optic effect can be considered as a second-order nonlinear polarization produced by the combined action of the incident light field and the DC electric field in the material. Since the linear electro-optic effect is described by second-order nonlinear polarizability, it can only occur in crystals with spatial asymmetry. Because higher-order effects are much weaker than first-order effects, in lithium niobate crystals, we only need to consider the linear electro-optic effect.

[0032] The lithium niobate modulator chip includes a lithium niobate modulator; wherein, the lithium niobate modulator utilizes the electro-optic effect of lithium niobate crystals to convert electrical signals into optical signals. The lithium niobate modulator can be a lithium niobate optical modulator, and the lithium niobate optical modulator can also be used to construct coherent optical modulator chips, phase modulator chips, and polarization optical modulator chips, and the embodiments disclosed herein are not limited thereto.

[0033] In lithium niobate phase modulators, appropriate crystal orientations should be selected for different electric field directions to obtain the maximum electro-optic coefficient. When the electrode electric field direction is parallel to the lithium niobate film surface, an X-cut (crystal cross-section parallel to the X-axis) Y-direction lithium niobate film should be selected, or a Y-cut (crystal cross-section parallel to the Y-axis) X-direction lithium niobate film should be selected. When the electrode electric field direction is perpendicular to the lithium niobate film surface, a Z-cut (crystal cross-section parallel to the Z-axis) lithium niobate film should be selected. This allows for full utilization of the maximum electro-optic coefficient γ of lithium niobate. 33 This achieves the optimal modulation efficiency.

[0034] A lithium niobate modulator chip may include a substrate, a ridge waveguide on the substrate, and modulation electrodes. The ridge waveguide may be formed using methods such as dry etching, wet etching, strip deposition to form an equivalent ridge waveguide, or ion thermal diffusion and ion exchange. In some embodiments, the ridge waveguide may include a lithium niobate thin film and a silicon nitride waveguide on the lithium niobate thin film. In some embodiments, the ridge waveguide may also include a lithium niobate ridge waveguide located within the lithium niobate thin film.

[0035] In some embodiments, when the ridge waveguide includes a lithium niobate film and a silicon nitride waveguide located on the lithium niobate film, the implementation of step S101 may include steps S1011 to S1014, wherein:

[0036] Step S1011: Provide a substrate;

[0037] Here, the substrate can be a silicon substrate; of course, the substrate can also be a quartz substrate, a lithium niobate substrate, or other suitable substrates.

[0038] Step S1012: Form a lithium niobate thin film on the substrate;

[0039] Here, the thickness of the lithium niobate film can be from 200 nanometers (nm) to 800 nanometers, for example, the thickness of the lithium niobate film is 500 nm.

[0040] Step S1013a: A silicon nitride optical waveguide is formed on a lithium niobate thin film to form a ridge-type optical waveguide;

[0041] Here, a silicon nitride thin film can be formed on a lithium niobate thin film using deposition processes such as chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), and plasma-enhanced chemical vapor deposition (PECVD). Subsequently, the silicon nitride thin film is etched to form a silicon nitride optical waveguide. The ridge-shaped optical waveguide in this embodiment includes a lithium niobate planar optical waveguide and a silicon nitride optical waveguide. In practice, the silicon nitride optical waveguide can transfer the light field to the lithium niobate planar optical waveguide for continued transmission, thereby achieving light modulation.

[0042] In some embodiments, silicon nitride optical waveguides and lithium niobate films can also be combined by bonding, thereby combining high refractive index materials, mature optical waveguide etching processes, and unetched lithium niobate films. Such a combination not only avoids the difficulties caused by directly etching lithium niobate films, but also better utilizes the electro-optic and nonlinear properties of lithium niobate films.

[0043] In some embodiments, where the ridge waveguide includes a lithium niobate ridge waveguide located in a lithium niobate thin film, step S1013a can be replaced by step S1013b, forming a lithium niobate waveguide in the lithium niobate thin film to form a ridge waveguide.

[0044] Here, a mask layer can be formed on the lithium niobate film first. The material of the mask layer can be silicon dioxide or silicon nitride. Next, optical waveguide mask windows are etched on the mask layer, that is, optical waveguide patterns are etched on the mask layer. Then, an optical waveguide is formed on the lithium niobate film using a suitable method such as annealing proton exchange or titanium diffusion process.

[0045] Step S1014: A modulation electrode is formed on the ridge-shaped optical waveguide to form a lithium niobate modulator chip.

[0046] Here, a metal thin film can be formed through a deposition process, and then a modulation electrode can be formed by electroplating on the metal thin film. The material of the modulation electrode can include gold or aluminum, or other suitable materials. The modulation electrode can be a traveling wave electrode, which can include a differential drive electrode or a single-ended push-pull GSG drive electrode.

[0047] The differential driving electrode is either a metallic microwave signal waveguide or a non-metallic conductor waveguide. In implementation, the differential driving electrode can be constructed from a metallic microwave signal waveguide or a non-metallic conductor material. The metallic microwave signal waveguide can be a GGSSG (ground-signal-ground-signal-ground) structure, or a differential electrode structure such as SS (signal-signal) or GSSG (ground-signal-signal-ground). In some embodiments, the differential driving electrode structure can also be a variant electrode structure, such as adding a track portion to an SS differential electrode structure to form a tracked differential electrode structure. Similarly, various derived structures can be added, and this disclosure does not limit the specific embodiments.

[0048] Step S102: Flip-chip the detector chip, laser chip, electric drive chip and transimpedance amplifier chip onto the lithium niobate modulator chip.

[0049] The laser chip is used to generate laser light. A laser chip can include a single laser generator; a laser chip can integrate multiple lasers, enabling the output of multi-wavelength light through a single chip.

[0050] The laser chip is flip-chip mounted on the lithium niobate modulator chip. The laser chip can be coupled to the silicon nitride optical waveguide in the lithium niobate modulator chip. The laser generated by the laser chip is coupled to the silicon nitride optical waveguide through evanescent wave coupling or other methods. In this embodiment, other methods can also be used to efficiently couple the laser to the silicon nitride optical waveguide.

[0051] The electric driver chip provides a modulation drive voltage to the modulation electrodes, enabling the lithium niobate modulator to modulate the optical signal. By changing this drive voltage, the refractive index of the interferometer arms of the Mach-Zehnder structure within the lithium niobate modulator can be controlled, thereby altering the phase of the laser signal and ultimately changing its intensity.

[0052] Detector chips are used for photoelectric conversion, converting received high-speed modulated optical signals into electrical signals; detector chips can be semiconductor photodiode detector chips. Trans-impedance amplifier (TIA) chips are used in scenarios where current is amplified to voltage, such as amplifying the detection signal of a photodetector. Because it amplifies current to voltage, the gain is defined as the output voltage divided by the input current, and the unit of gain is resistance; therefore, this type of amplifier is called a transimpedance amplifier.

[0053] The electrical signal obtained by the detector chip is input to the TIA chip through an inductor and capacitor. After being amplified by the TIA, it is input to the external circuit through leads. By selecting appropriate inductors and capacitors, the detector chip in this embodiment can greatly increase its effective receiving bandwidth, thereby realizing the reception of high-speed optical signals using a low-cost and low-bandwidth detector chip.

[0054] Flip-chip refers to a chip that is connected to the substrate via wire bonding and ball-mounting processes. In traditional wire bonding, the electrical surface of a chip faces upwards, while in a flip-chip, the electrical surface faces downwards, essentially flipping the chip over; hence the name "flip-chip."

[0055] In practice, metal pads can be formed on the modulation electrodes in the lithium niobate modulator chip, and the modulation electrodes and the electric drive chip can be connected through the metal pads to form a lithium niobate optical transceiver, which can reduce the length of high-frequency traces.

[0056] In some embodiments, step S102 may include steps S1021 to S1024, wherein:

[0057] Step S1021: A first pad and an electrically driven chip connected to the first pad are sequentially formed on the modulation electrode.

[0058] Here, suitable processes such as chemical vapor deposition, physical vapor deposition, plasma-enhanced chemical vapor deposition, sputtering, and electroplating can be used to form the conductive material to form the first pad. The conductive material may include one of gold (Au), indium (In), and gold-tin alloy (AuSn). In other embodiments, a gold wire ball-forming machine can also be used to form the first pad on the modulation electrode, which is simple to manufacture, has high process efficiency, low cost, and is conducive to mass production.

[0059] Step S1022: Form a laser chip and a detector chip in the capping layer of the lithium niobate modulator chip;

[0060] Here, two grooves can be formed in the capping layer of the lithium niobate modulator chip, with a laser chip formed in one groove and a detector chip formed in the other groove.

[0061] Step S1023: Form a metal electrode on the cover layer that is connected to the detector chip;

[0062] Here, the material of the metal electrode can be a suitable metal such as gold, titanium, or platinum.

[0063] Step S1024: A second pad and a transimpedance amplifier chip connected to the second pad are sequentially formed on the metal electrode.

[0064] The method and materials for forming the second pad can be referenced from those for the first pad, and will not be repeated here.

[0065] During implementation, the detector chip is positioned 0 to 500 nm away from the ridge waveguide to ensure high coupling efficiency. The distance between the lithium niobate modulator chip and the metal electrode should be greater than 30 μm to reduce crosstalk in the radio frequency signal.

[0066] In this embodiment, the electric drive chip, detector chip, laser chip, transimpedance amplifier chip, and lithium niobate modulator chip are integrated together using a flip-chip process. This achieves several advantages: firstly, it integrates other key functional chips, enabling three-dimensional stacking integration to form a lithium niobate optical transceiver, characterized by high process tolerance, high integration, small size, and high speed; secondly, it reduces the length of high-frequency traces, improving signal quality and integrity, and fully leveraging the performance advantages of each component; furthermore, it integrates the optical signal transmitter and receiver, enabling interconnection between the light source, detector, and modulator.

[0067] This disclosure also provides a lithium niobate optical transceiver, see reference. Figure 2 The lithium niobate optical transceiver includes: a lithium niobate modulator chip 21, and an electric drive chip 22, a laser chip 23, a detector chip 24, and a transimpedance amplifier chip 25, which are flip-chip mounted on the lithium niobate modulator chip 21.

[0068] The electric drive chip 22 is used to provide a modulation drive voltage to the modulation electrode 201 in the lithium niobate modulator chip 21, so that the lithium niobate modulator modulates the optical signal generated by the laser chip 23.

[0069] The detector chip 24 is used to detect the modulated optical signal and convert it into an electrical signal.

[0070] The transimpedance amplifier chip 25 is used to amplify electrical signals.

[0071] In this embodiment, the electric drive chip, lithium niobate modulator chip, detector chip, laser chip, and transimpedance amplifier chip are integrated together using a flip-chip process. On one hand, this integrates other key functional chips, achieving three-dimensional stacking integration of these chips to form a lithium niobate optical transceiver, characterized by high process tolerance, high integration, small size, and high speed. On the other hand, reducing the length of high-frequency traces improves signal quality and integrity, and fully leverages the performance advantages of each component. Furthermore, the integration of the optical signal transmitter and receiver enables interconnection between the light source, detector, and modulator.

[0072] In some embodiments, reference Figure 4 The electric drive chip 22 and the modulation electrode 201 are interconnected via flip-chip bonding; the transimpedance amplifier chip 25 and the metal electrode 26 on the detector chip 24 are interconnected via flip-chip bonding; the laser chip 23 is connected to the peripheral power supply circuit via wire bonding. Wire bonding, also known as bonding, bonding, or wire welding, refers to the connection of internal interconnections in solid-state circuits of microelectronic devices using metal wires such as gold or aluminum wires, utilizing heat pressing or ultrasonic energy; that is, the connection between the chip and the circuit or lead frame.

[0073] Because lithium niobate films are relatively hard, etching them is difficult. In practice, a high-refractive-index material, such as silicon nitride, can be formed on the lithium niobate film, allowing light to propagate within the silicon nitride. By adjusting the dimensions (width and thickness) of the silicon nitride, a ridge-type optical waveguide structure can be formed. Initially, the silicon nitride waveguide contains more energy, which is then split into two beams. Since lithium niobate films exhibit electro-optic effects, while silicon nitride does not, it is desirable to concentrate more energy in the lithium niobate film. In practice, the width of the silicon nitride can be adjusted to gradually concentrate more energy in the lithium niobate film. This results in greater overlap between the optical and electric fields, higher interaction strength, and higher modulation efficiency.

[0074] Also refer to Figure 2 and Figure 3 ,in, Figure 3 for Figure 2 A slice diagram of the ridge waveguide is shown. The lithium niobate modulator chip 21 includes: a substrate 202, a ridge waveguide 203 located on the substrate 202, and a modulation electrode 201; wherein, the ridge waveguide 203 includes: a lithium niobate thin film 2031 and a silicon nitride waveguide 2032 located on the lithium niobate thin film 2031. In this way, the interconnection of the light source, detector, and ridge waveguide can be realized, and the optical transparency window of the lithium niobate waveguide supports the range of 400nm to 3um, with strong scalability.

[0075] In some embodiments, continue to refer to Figure 2 The lithium niobate modulator chip 21 also includes a capping layer 204 located on the ridge waveguide 203. Here, the refractive index difference between the lithium niobate thin film material and the capping layer material can be 0.1 to 1.2, for example, 1.0. The capping layer can be a silicon dioxide layer or other materials that meet the refractive index requirements.

[0076] The capping layer protects the ridge waveguide from physical damage and prevents other materials with refractive indices higher than or close to that of lithium niobate from covering the surface of the ridge waveguide. This prevents the formation of light-limiting structures in the lithium niobate ridge waveguide, which could cause normal transmitted light to radiate out of the ridge waveguide, increasing its loss. In practice, the modulation electrode can be located on the capping layer.

[0077] In this embodiment, a ridge-type optical waveguide is formed by heterogeneous integration of a lithium niobate thin film and a silicon nitride optical waveguide. This means that the optical waveguide structure is constructed by depositing silicon nitride material without etching the lithium niobate thin film. This not only avoids the difficulties associated with directly etching the lithium niobate thin film but also better utilizes the electro-optic and nonlinear properties of the lithium niobate thin film. Furthermore, it meets process requirements, thereby enabling large-scale production.

[0078] Also refer to Figure 4 and Figure 5 ,in, Figure 5 for Figure 4 A slice of the ridge waveguide in the image. The lithium niobate modulator chip 21 includes: a substrate 202, a ridge waveguide 203 located on the substrate 202, and a modulation electrode 201; wherein, the ridge waveguide 203 includes: a lithium niobate ridge waveguide located in the lithium niobate thin film 2031.

[0079] In some embodiments, reference Figure 3 or Figure 5The ridge-type optical waveguide 203 includes a 2×2 beamsplitter 31, a Mach-Zehnder waveguide 32, and a 2×2 combiner 33; the Mach-Zehnder waveguide 32 includes two optical waveguide arms 321. The output of the 2×2 beamsplitter 31 is connected to the input of the 2×2 combiner 33 via the Mach-Zehnder waveguide 32. In other words, the 2×2 beamsplitter 31 and the 2×2 combiner 33 are connected by two optical waveguide arms 321.

[0080] Here, both the 2×2 beam splitter and the 2×2 beam combiner include Y-branch waveguides, used to construct the Mach-Zehnder Interferometer (MZI) structure in the lithium niobate modulator. The Y-branch waveguide is an important device unit in integrated optics. It is not only the foundation for optical integrated devices such as beam splitters, combiners, optical modulators, MZIs, and optical switches, but can also function independently as a power divider or combiner, and can be integrated with other discrete components such as lasers. A typical Y-branch waveguide consists of an incident waveguide, a transition waveguide, and a pair of output waveguides. Structurally, due to differences in refractive index distribution and waveguide width selection, it can be divided into symmetrical and asymmetrical types.

[0081] In some embodiments, the Y-branch waveguide can employ a symmetrical bi-branch waveguide structure. The materials and widths of the two branch waveguides can be identical, ensuring that the optical transmission characteristics of both branches are the same. To prevent large radiation losses, the arm angles of the bi-branch waveguides can be relatively small. In some embodiments, the Y-branch waveguide can be designed as a sine / cosine or double-circular arc shape, thereby effectively reducing the transmission loss of waveguide splitting / combining and achieving higher integration.

[0082] Both 2×2 beamsplitters and 2×2 beam combiners can be 2×2 multimode interferometers. In implementation, light waves enter through the input grating and are split into two beams by the 2×2 beamsplitter. One beam passes through the upper waveguide arm of the Mach-Zehnder waveguide 32, and the other through the lower waveguide arm. An electrically driven chip applies a voltage to the differential electrodes, causing a change in the refractive index of the lithium niobate. Therefore, the two beams, after passing through the upper and lower waveguide arms of the Mach-Zehnder waveguide 32, will have a phase difference. After passing through the 2×2 beam combiner, interference causes a change in the amplitude of the output light, thus achieving intensity modulation. When the upper and lower optical waveguide arms are completely symmetrical, if no voltage is applied to the modulation electrode, a direct laser output is generated after the two optical waveguide arms converge. If a voltage is applied to the modulation electrode, a phase difference will occur between the two branch signals due to electro-optic induction. The two laser outputs can be coherently constructive or coherently destructive depending on whether the phase difference is 0 or π, thereby completing the modulation of the laser output, which is finally output from the output end.

[0083] In some embodiments, the vertical height between the modulation electrode and the ridge waveguide ranges from 500 nm to 3 μm.

[0084] In some embodiments, reference Figure 2 In the case where the ridge waveguide 203 includes a lithium niobate thin film 2031 and a silicon nitride waveguide 2032 located on the lithium niobate thin film 2031, the modulation electrode 201 includes a differential GSGSG driving electrode, the lithium niobate thin film is Z-cut, and the radio frequency electric field passes perpendicularly through the ridge waveguide 203. This results in a high degree of overlap between the optical and electric fields, which can improve modulation efficiency.

[0085] During implementation, the S in the differential GGSSG drive electrode + Electrode and S - The electrodes are located directly above the two optical waveguide arms of the Mach-Zehnder waveguide, with the G electrode located on both sides of the waveguide arms, and the optical waveguide arms and S... + Electrode or S - The vertical distance between the differential electrodes ranges from 500 nm to 2 μm.

[0086] In implementation, S + The centerline of the electrode can be aligned with the centerline of the waveguide. In some embodiments, S + Electrode (S) - The width of the electrode can be the same as the width of the waveguide, so that S + Electrode (S) - The electrode is positioned directly above the waveguide, which reduces bandwidth absorption and improves modulation efficiency. In other embodiments, S + Electrode (S) - The width of the electrode can be different from the width of the waveguide.

[0087] In some embodiments, the width of the G electrode can be greater than that of the S electrode. + Electrode or S - Electrodes are used to reduce microwave loss of high-frequency signals.

[0088] In addition, from Figure 2 As can be seen, the G electrode penetrates the cladding layer 204 and connects to the ridge waveguide 203, S + Electrode and S - The electrodes are all located on the capping layer 204. This allows the radio frequency electric field to penetrate the lithium niobate thin film region as much as possible, thereby improving the operating efficiency of the lithium niobate modulator chip.

[0089] In some embodiments, where the ridge waveguide includes a lithium niobate film and a silicon nitride waveguide located on the lithium niobate film, the lithium niobate modulator chip further includes a vertical thermally adiabatic coupler. The vertical thermally adiabatic coupler guides light from the silicon nitride waveguide into the lithium niobate film and guides light from the lithium niobate film back to the silicon nitride waveguide.

[0090] In other embodiments, reference is made to Figure 4 In the case where the ridge waveguide 203 includes a lithium niobate ridge wave located in the lithium niobate thin film 2031, the lithium niobate thin film is X-cut, and the modulation electrode 201 includes a single-ended push-pull GSG drive electrode.

[0091] The single-ended push-pull GSG drive electrodes are located on both sides of the two optical waveguide arms of the Mach-Zehnder waveguide. (Continue to reference...) Figure 4 The waveguide arm is located between the G electrode and the S electrode, meaning the G electrode and S electrode are located on opposite sides of the waveguide arm. The vertical height between the single-ended push-pull GSG driving electrode and the ridge waveguide ranges from 500 nm to 3 μm. The horizontal distance between the ridge waveguide and the single-ended push-pull GSG driving electrode is greater than 400 nm.

[0092] When the modulation electrode uses a single-ended push-pull GSG driving electrode, the electric field polarities of the upper and lower optical waveguide arms are opposite, resulting in opposite phase shifts. This makes the total phase change of the device twice that of a single-arm phase modulator, thereby accelerating the modulation speed of the laser.

[0093] In other embodiments, reference is made to Figure 6 In the case where the ridge waveguide 203 includes a lithium niobate ridge wave located in the lithium niobate thin film 2031, the lithium niobate thin film is Z-cut, and the radio frequency electric field passes perpendicularly through the ridge waveguide 203; the modulation electrode 201 includes a differential GGSSG driving electrode. This results in a high degree of overlap between the optical and electric fields, which can improve modulation efficiency. In implementation, the S in the differential GGSSG driving electrode... + Electrode and S - The electrodes are located directly above the two optical waveguide arms of the Mach-Zehnder waveguide, with the G electrode located on both sides of the waveguide arms, and the optical waveguide arms and S... + Electrode or S - The vertical distance between the differential electrodes ranges from 500 nm to 2 μm.

[0094] In some embodiments, reference Figure 7 The modulation electrode 201 includes a differential GSSG drive electrode. The electric drive chip 22 is flip-chip mounted on the G electrode and S electrode. + Electrode and S - On the electrodes.

[0095] In other embodiments, reference is made to Figure 8 The modulation electrode 201 includes a differential GGSG driving electrode. The G electrode is located in a groove in the capping layer 204, and the top surface of the G electrode is lower than the top surface of the capping layer 204. + Electrode and S - The electrodes are located on the protruding structure in the capping layer 204. The electrically driven chip 22 is flip-chip mounted on the S... + Electrode and S - On the electrodes. This allows for compatibility with different types of electrical chips.

[0096] In some embodiments, reference Figure 9 The lithium niobate modulator chip 21 also includes: a heated metal film 205 for bias point control of the lithium niobate modulator and / or matching of the lithium niobate modulator termination resistor.

[0097] Here, the material for heating the metal thin film can be metals such as gold, copper, lithium, platinum, and titanium, and can have a certain resistance value, such as 50 ohms (Ω) or 100 Ω, so as to achieve heating of the waveguide and matching of the terminating resistor.

[0098] In practical applications, the bias operating point of a lithium niobate modulator drifts with changes in charging time and ambient temperature. Therefore, a control circuit is needed to adjust and control the magnitude of the DC voltage applied to the heated metal film (i.e., the bias electrode). By applying a DC voltage to the heated metal film on the lithium niobate modulator chip, a suitable phase difference can be applied to the transmitted light in the first branch waveguide (i.e., the upper optical waveguide arm) and the second branch waveguide (i.e., the lower optical waveguide wall), thereby controlling the operating point of the lithium niobate modulator to operate at the linear operating point (i.e., bias phase of π / 2), the minimum power point (i.e., bias phase of π), or the maximum power point (i.e., bias phase of 0).

[0099] In some embodiments, the ridge waveguide further includes a 2×4 multimode interferometer mixer for demodulating the coherent optical signal. The 2×4 multimode interferometer mixer is suitable for detecting coherent optical signals and extracting the phase information of the light.

[0100] This disclosure provides a lithium niobate optical transceiver that integrates a laser, a lithium niobate thin-film modulator, a photodetector, and a driver and TIA chip in a three-dimensional stacked configuration. It features high process tolerance, high integration, small size, and high speed. (Reference) Figure 2 , Figure 4 , Figure 6 , Figure 7 , Figure 8 or Figure 9The optical transceiver includes a lithium niobate thin film region (i.e., lithium niobate modulator chip 21), a detector chip region (i.e., detector chip 24), a laser chip region (i.e., laser chip 23), and an electrical chip region (i.e., electrical drive chip 22 and transimpedance amplifier chip 25).

[0101] The detector chip area, laser chip area, and electrical chip area are flip-chip stacked on the lithium niobate thin film area to form a three-dimensional integrated optical transceiver.

[0102] The lithium niobate thin film region includes a ridge waveguide 203, a modulation electrode 201, and a heating metal thin film 205 (reference). Figure 9 The system includes a substrate 202 (e.g., a quartz substrate); a ridge waveguide 203 is coupled to a laser chip 23 to guide continuous light to the lithium niobate waveguide, constructing an MZI architecture. This is then combined with a modulation electrode 201 and an electrically driven chip 22 to form a modulation region, enabling optical signal transmission. The optical signal modulation end can also be used to transmit coherent optical modulator signals.

[0103] At the optical signal receiving end, the ridge waveguide 203 couples the optical signal to the detector chip area, and then, in conjunction with the TIA chip, realizes the conversion and amplification of the optical signal into an electrical signal.

[0104] For specific ridge waveguide types, modulation electrode types and locations, and lithium niobate thin film cutting methods, please refer to other embodiments.

[0105] The working process of the lithium niobate optical transceiver in the embodiments of this disclosure will be described in detail below:

[0106] First, a laser chip generates laser light. Second, the generated laser light is efficiently coupled into a silicon nitride optical waveguide using methods such as evanescent wave coupling. The laser light is split in two within the silicon nitride optical waveguide, and the light is gradually transmitted into a lithium niobate thin film.

[0107] Subsequently, a voltage is applied to the modulation electrode by an electric drive chip to change the refractive index of the lithium niobate film, thereby causing a phase difference between the two beams of light passing through the upper and lower optical waveguide arms of the Mach-Zehnder waveguide. After passing through a 2×2 beam combiner, the amplitude of the output light changes due to interference, thus achieving intensity modulation.

[0108] Finally, the detector chip detects the modulated optical signal and converts it into an electrical signal; the transimpedance amplifier chip amplifies the electrical signal.

[0109] In the several embodiments provided in this disclosure, it should be understood that the disclosed devices and methods can be implemented in a non-target manner. The device embodiments described above are merely illustrative; for example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components may be combined, or integrated into another system, or some features may be ignored or not executed. Furthermore, the various components shown or discussed may be coupled or directly coupled to each other.

[0110] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units may be selected to achieve the purpose of this embodiment according to actual needs.

[0111] The features disclosed in the several method or device embodiments provided in this disclosure can be arbitrarily combined without conflict to obtain new method or device embodiments.

[0112] The above descriptions are merely some embodiments of this disclosure, but the protection scope of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this disclosure should be included within the protection scope of this disclosure. Therefore, the protection scope of this disclosure should be determined by the scope of the claims.

Claims

1. A lithium niobate optical transceiver, characterized in that, include: A lithium niobate modulator chip, and a detector chip, a laser chip, an electric drive chip, and a transimpedance amplifier chip flip-chip stacked on the lithium niobate modulator chip; wherein: The electric drive chip is used to provide a modulation drive voltage to the modulation electrode in the lithium niobate modulator chip in a direction perpendicular to the lithium niobate modulator, so that the lithium niobate modulator modulates the optical signal generated by the laser chip; The detector chip is used to detect the modulated optical signal and convert it into an electrical signal; The transimpedance amplifier chip is used to amplify the electrical signal; The detector chip, the laser chip, the electric drive chip, and the transimpedance amplifier chip are all located on the ridge waveguide in the lithium niobate modulator chip.

2. The optical transceiver according to claim 1, characterized in that, The lithium niobate modulator chip includes: A substrate, a ridge-shaped optical waveguide located on the substrate, and the modulation electrode; The ridge waveguide includes: a lithium niobate thin film and a silicon nitride waveguide located on the lithium niobate thin film, or a lithium niobate ridge waveguide located in the lithium niobate thin film.

3. The optical transceiver according to claim 1, characterized in that, The electric drive chip and the modulation electrode are interconnected via flip-chip bonding; The transimpedance amplifier chip and the metal electrodes on the detector chip are interconnected via flip-chip bonding. The laser chip is connected to the external power supply circuit via metal wire bonding.

4. The optical transceiver according to claim 2, characterized in that, The ridge-type optical waveguide includes a 2×2 beam splitter, a Mach-Zehnder waveguide, and a 2×2 beam combiner. The output of the 2×2 beam splitter is connected to the input of the 2×2 beam combiner via the Mach-Zehnder waveguide.

5. The optical transceiver according to claim 4, characterized in that, The modulation electrode includes a differential drive electrode; the lithium niobate thin film is Z-cut, and the radio frequency electric field passes perpendicularly through the ridge-shaped optical waveguide; Alternatively, the modulation electrode may include a single-ended push-pull GSG drive electrode, and the lithium niobate film may be X-cut.

6. The optical transceiver according to claim 5, characterized in that, The differential driving electrode includes a differential GGSSG driving electrode or a differential GGSSG driving electrode; Among them, S + Electrode and S - The electrodes are respectively located directly above the two optical waveguide arms of the Mach-Zehnder waveguide, with the G electrode located on both sides of the optical waveguide arm, and the optical waveguide arm and the S electrode... + Electrode or the S - The vertical distance between the electrodes ranges from 500 nm to 2 μm.

7. The optical transceiver according to any one of claims 2 to 6, characterized in that, The lithium niobate modulator chip further includes: a heated metal film for bias point control of the lithium niobate modulator, and / or matching of the terminal resistor of the lithium niobate modulator.

8. The optical transceiver according to claim 4, characterized in that, The ridge-type optical waveguide also includes a 2×4 multimode interferometer mixer for demodulating coherent optical signals.

9. A method for forming a lithium niobate optical transceiver, characterized in that, include: Provide lithium niobate modulator chips; A detector chip, a laser chip, an electric drive chip, and a transimpedance amplifier chip are flip-chip mounted on the lithium niobate modulator chip. The electric drive chip is used to provide a modulation drive voltage to the modulation electrode in the lithium niobate modulator chip in a direction perpendicular to the lithium niobate modulator, so that the lithium niobate modulator modulates the optical signal generated by the laser chip. The detector chip is used to detect the modulated optical signal and convert it into an electrical signal; The transimpedance amplifier chip is used to amplify the electrical signal; The detector chip, the laser chip, the electric drive chip, and the transimpedance amplifier chip are all located on the ridge waveguide in the lithium niobate modulator chip.

10. The forming method according to claim 9, characterized in that, A detector chip, a laser chip, an electric drive chip, and a transimpedance amplifier chip are flip-chip mounted on the lithium niobate modulator chip, including: A first pad and an electrically driven chip connected to the first pad are sequentially formed on the modulation electrode; The laser chip and the detector chip are formed in the overlay layer of the lithium niobate modulator chip; A metal electrode connected to the detector chip is formed on the cover layer; A second pad and the transimpedance amplifier chip connected to the second pad are sequentially formed on the metal electrode.

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