Thin-film lithium niobate linear electro-optical modulator based on double-injection structure

Abstract

The invention discloses a thin-film lithium niobate linear electro-optical modulator based on a double-injection structure, relates to the technical field of optical communication, and aims to solve the problems that an electro-optical overlapping factor of a traditional structure is low and is easily influenced by dispersion of microwave signals during high-frequency modulation, and the technical scheme is that the thin-film lithium niobate linear electro-optical modulator comprises a silicon dioxide substrate, a waveguide and a silicon dioxide cladding; the waveguide comprises an input waveguide, a Y beam splitter, a first connecting waveguide, a first directional coupler, a dissipater, a second connecting waveguide, a first straight waveguide, a second straight waveguide, a gold electrode, a second directional coupler and an output waveguide. Different transmission coefficients and coupling coefficients are set for the first directional coupler and the second directional coupler, and transmission responses of square waves, sine waves and similar triangular waves can be obtained. Through the synergistic effect of the two independent injection regions, three-signal resonance of a double-main-line waveguide signal and a micro-ring signal is realized, accurate regulation and control of an electric signal can be completed, a high-order nonlinear effect is inhibited, and the linearity is improved.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, specifically to a thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure. Background Technology

[0002] Lithium niobate ( Lithium niobate (LN), as a typical ferroelectric oxide crystal, has become a core substrate material for electro-optic modulators in optical communication, optical sensing, and other fields due to its excellent linear electro-optic effect, wide transmission band (0.4μm-5μm), high optical damage threshold, and good thermal stability. The linear electro-optic effect refers to the characteristic that the refractive index of a material changes linearly with an applied electric field. This effect is the physical basis for achieving efficient conversion of electrical signals to optical signals—when an electrical signal is applied to a lithium niobate optical waveguide, the waveguide's refractive index changes, thereby modulating the phase, amplitude, or polarization state of the optical signal to complete the modulation function.

[0003] Early lithium niobate electro-optic modulators mostly used traditional titanium diffusion or proton exchange single waveguide structures. Although they achieved basic modulation functions, they exposed significant limitations in high-speed, low-power application scenarios.

[0004] On the one hand, the electro-optic overlap factor of traditional structures is low—the applied modulation electric field is mainly distributed in the semiconductor or dielectric region near the electrodes, and the degree of overlap with the optical field transmitted in the waveguide is limited, resulting in low modulation efficiency. In order to achieve the target modulation depth, a higher driving voltage (usually 5V-10V) needs to be applied, which increases the system power consumption and driving circuit complexity.

[0005] On the other hand, single waveguide structures are susceptible to microwave signal dispersion during high-frequency modulation: the speed of the microwave signal transmitted by the modulation electrode is difficult to match with the speed of the optical signal in the optical waveguide. When the frequency exceeds tens of GHz, the speed mismatch leads to limited modulation bandwidth, which cannot meet the THz-level bandwidth requirements of ultra-high-speed communication.

[0006] In addition, the parasitic capacitance between the waveguide and the electrode in the traditional structure is relatively large, which further aggravates the attenuation of high-frequency signals and restricts the response speed and operating frequency of the modulator. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the existing defects and provide a thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure, which can effectively solve the problems in the background art.

[0008] To achieve the above objectives, this invention discloses a thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure. The technical solution adopted includes a silicon dioxide substrate, Waveguide and silicon dioxide cladding, the The waveguide is located between the silicon dioxide substrate and the silicon dioxide cladding; The The waveguide includes an input waveguide, a Y-beam splitter, a racetrack-shaped microring, and an output waveguide, wherein the input waveguide and the output waveguide are... The input and output terminals of the waveguide; The output end of the input waveguide is connected to the input end of the Y beam splitter. The output end of the Y beam splitter includes two sets, namely an upper port and a lower port, which split a single-mode light wave into two single-mode waves of equal power. The upper port of the Y beam splitter is connected to the racetrack-shaped micro-ring and the dissipation in sequence through the first connecting waveguide, which is responsible for dissipating the transmitted light energy and preventing the influence caused by light reflection. The lower port of the Y beam splitter is connected to the racetrack-shaped micro-ring and the output waveguide through the second connecting waveguide. The racetrack-shaped microring is also equipped with a gold electrode; The design of a lithium niobate electro-optic modulator with a dual-injection structure improves the electro-optic overlap factor and microwave-optic speed matching degree by optimizing the spatial distribution of waveguides and electrodes.

[0009] As a preferred embodiment of the present invention, the runway-shaped microring includes a first directional coupler, a second directional coupler, a first straight waveguide, and a second straight waveguide, wherein the first directional coupler is located between the first connecting waveguide and the dissipation waveguide; and the second directional coupler is located between the second connecting waveguide and the output waveguide. By introducing precise control over the phase of the dual-injection microring, a triangular wave-like transmission response can be achieved, thereby enabling efficient suppression of the third-order intermodulation term.

[0010] As a preferred embodiment of the present invention, the coupling coefficient and transmission coefficient of the first directional coupler and the second directional coupler are different, and their parameters can be adjusted according to requirements to achieve different output waveform requirements.

[0011] As a preferred embodiment of the present invention, the gold electrodes are distributed on both sides of the second straight waveguide to regulate the refractive index change of the racetrack-shaped microring.

[0012] As a preferred embodiment of the present invention, the first connecting waveguide is a 90-degree curved waveguide, and the waveguide length is less than that of the second connecting waveguide; the electric field distribution formed by the symmetrical double waveguide and the intermediate electrode can highly overlap with the optical field, thereby improving the electro-optic overlap factor and significantly reducing the driving voltage, thus achieving low-power modulation.

[0013] As a preferred embodiment of the present invention, the second connecting waveguide includes three 90-degree circular arc waveguides and one straight waveguide. The bending radius of the circular arc waveguides ranges from 15µm to 100µm, which is used to reduce bending loss.

[0014] Compared with the prior art, the beneficial effects of the present invention are: by introducing precise control of the phase of the dual-injection microring, the present invention can achieve a triangular wave-like transmission response, thereby achieving efficient suppression of the third-order intermodulation term.

[0015] SFDR based on lithium niobate linear electro-optic modulator with dual injection structure is Compared to traditional Mach-Zehnder interferometer electro-optic modulators, this modulator offers an improvement of nearly 14 dB at a center frequency of 10 GHz. While maintaining high bandwidth, it effectively improves modulation linearity, laying a solid foundation for its widespread application in high-speed, high-precision optical communication and microwave photonics systems.

[0016] The electric field distribution formed by the symmetrical double waveguides and the intermediate electrode can highly overlap with the optical field, thereby improving the electro-optic overlap factor and significantly reducing the driving voltage, thus achieving low-power modulation. The symmetrical structure of the double waveguides facilitates the control of the characteristic impedance of the microwave transmission line (such as 50Ω matching). By optimizing the electrode width, spacing, and waveguide size, speed matching between microwave signals and optical signals can be achieved over a wide frequency range. Attached Figure Description

[0017] Figure 1 For the present invention Schematic diagram of waveguide structure; Figure 2 This is a cross-sectional schematic diagram of the overall structure of the present invention; Figure 3 This is a schematic diagram of the square wave response simulation results of the present invention with adjusted transmission coefficient and coupling coefficient; Figure 4 This is a schematic diagram of the sinusoidal response simulation results of the present invention with adjusted transmission coefficient and coupling coefficient; Figure 5 This is a schematic diagram of the simulation results of the triangular wave response with adjusted transmission coefficient and coupling coefficient according to the present invention; Figure 6 The transmission characteristic curves of square waves, sine waves and triangular waves generated under different voltages in this invention are shown. Figure 7 This paper compares the SFDR performance of a conventional MZ modulator with that of the DI modulator proposed in this invention.

[0018] In the figure: 1. Input waveguide; 2. Y-beam splitter; 3. First connecting waveguide; 4. First directional coupler; 5. Dissipation; 6. Second connecting waveguide; 7. First straight waveguide; 8. Second straight waveguide; 9. Gold electrode; 10. Second directional coupler; 11. Output waveguide. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0020] like Figures 1 to 7 As shown, this invention discloses a thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure. The technical solution adopted includes a silicon dioxide substrate, Waveguide and silicon dioxide cladding; Figure 2 The upper and lower layers in the diagram represent the silica substrate and the silica cladding, respectively, used to protect the substrate disposed between them. Waveguide structure.

[0021] The waveguide includes an input waveguide 1, a Y-beam splitter 2, a first connecting waveguide 3, a first directional coupler 4, a dissipation 5, a second connecting waveguide 6, a first straight waveguide 7, a second straight waveguide 8, a gold electrode 9, a second directional coupler 10, and an output waveguide 11. The input waveguide 1 is directly connected to the Y-beam splitter 2. The upper port of the Y-beam splitter 2 is sequentially connected to the first connecting waveguide 3, the first directional coupler 4, and the dissipation 5. The lower port of the Y-beam splitter 2 is sequentially connected to the second connecting waveguide 6, the second directional coupler 10, and the output waveguide 11.

[0022] The first directional coupler 4, the first straight waveguide 7, the second straight waveguide 8, and the second directional coupler 10 constitute a ring resonator (runway-shaped micro-ring). The two waves, separated by the Y-beam splitter 2, travel towards the resonator through the first connecting waveguide 3 and the second connecting waveguide 6. These two waves are injected into the runway with the same amplitude and phase. Since these two waves have the same wavelength, they interfere with each other within the runway. The dual-injection structure achieves three-signal resonance between the dual main waveguide signal and the micro-ring signal through the synergistic effect of the two independent injection regions. This enables precise control of the electrical signal, suppresses higher-order nonlinear effects, and improves linearity.

[0023] Y-beam splitter 2 splits a single-mode light wave into two single-mode waves of equal power, with lower loss and larger manufacturing tolerance, thereby improving the linearity of the device.

[0024] The second connecting waveguide 5 includes three 90-degree circular arc waveguides and one straight waveguide. The bending radius of the circular arc waveguides ranges from 15um to 100um, which is used to reduce bending loss.

[0025] The light at the output waveguide 11 is contributed by a combination of two nearly identical ring resonators. The first ring is associated with the light at the upper port of the Y beam splitter 2, and the second ring is associated with the light at the lower port of the Y beam splitter 2. This device has the special property of operating independently in two FSR states. The expected FSR value of this design is twice that of a conventional ring FSR, which is also beneficial for detection because it can provide a larger operating bandwidth.

[0026] Working principle of the invention: The dual-injection structure achieves three-signal resonance of the dual main waveguide signals and the micro-ring signal through the synergistic effect of two independent injection regions. This enables precise control of the electrical signal, suppresses higher-order nonlinear effects, and improves linearity. Furthermore, requiring only a single ring and electrode, the relative simplicity of this configuration increases the possibility of improving SFDR in practice.

[0027] The linearity of electro-optic modulators is typically quantified as spurious-free dynamic range (SFDR), usually expressed as the fundamental frequency signal versus third-order intermodulation distortion. )exist The power ratio at the intersection of the noise floor and the ground truth.

[0028] In the formula, V is the input voltage, I is the output optical power, and Vb is the bias voltage. Let f1 and f2 be the amplitudes of two RF frequencies; the formula shows that... The amplitude of the component consists of all odd-order nonlinear terms, with cubic terms dominating. Suppression is achieved by optimizing the structural parameters of the electro-optic modulator. The cubic term can significantly improve the linearity of the electro-optic modulator.

[0029] The dual-injection structure plays a crucial role in suppressing third-order intermodulation distortion. To verify the beneficial effects of this invention, the following simulation experiment was conducted: This experiment uses the finite-difference time-domain method for calculation and analysis. The main parameters used in the simulation calculation include: the lithium niobate waveguide width is 2... Thickness is 600 To ensure the light field is concentrated in the modulation region, the racetrack-shaped microring includes a first directional coupler 4 and a second directional coupler 10. Both coupling units have the same length, requiring the gold electrode 9 to not interact with the first directional coupler 4 and the second directional coupler 10. The gold electrode 9 has a characteristic impedance close to 50Ω to reduce resistive loss, and its length is... To meet the demand for 10GHz bandwidth.

[0030] Reference Figure 3As shown in the diagram, by adjusting the transmission coefficients of the first directional coupler 4 and the second directional coupler 10, setting the transmission coefficient of the first directional coupler 4 to 0.1 and the transmission coefficient of the second directional coupler to 0.75, a square wave transmission response can be obtained at the output waveguide 11.

[0031] Reference Figure 4 As shown in the diagram, by adjusting the transmission coefficients of the first directional coupler 4 and the second directional coupler 10, setting the transmission coefficient of the first directional coupler 4 to 0.99 and the transmission coefficient of the second directional coupler to 0.1, a sinusoidal transmission response can be obtained at the output waveguide 11.

[0032] Reference Figure 5 As shown in the diagram, by adjusting the transmission coefficients of the first directional coupler 4 and the second directional coupler 10, setting the transmission coefficient of the first directional coupler 4 to 0.1 and the transmission coefficient of the second directional coupler to 0.75, a triangular wave transmission response can be obtained at the output waveguide 11.

[0033] Reference Figure 6 The diagram illustrates the transmission characteristic curves of three states—triangular wave, square wave, and sine wave—generated under different voltages at 1550nm. The square wave structure exhibits the highest modulation efficiency and fastest response speed, making it suitable for scenarios with high requirements for optical signal modulation speed and amplitude, such as ultra-high-speed optical communication and fast logic gate operations in optical computing. However, it requires extremely high voltage control precision, as even a small voltage deviation can lead to significant changes in transmission. Sine wave modulation ensures stable measurement signals even with small voltage variations, but its modulation efficiency is relatively low, requiring a larger voltage variation range to achieve large modulation. The triangular wave structure offers a moderate balance between modulation speed and voltage control difficulty, enabling efficient modulation of optical transmission and achieving a high SFDR.

[0034] Reference Figure 6 As shown, under dual-tone signal modulation, the SFDR of this lithium niobate electro-optic modulator is obtained as follows: It is nearly 14dB better than regular MZM. In summary, the high linearity lithium niobate electro-optic modulator based on a dual-injection structure proposed in this invention achieves the following simulated SFDR under a 10GHz modulation signal: Compared with traditional MZI modulators, it achieves an improvement of nearly 14dB. The larger spurious-free dynamic range enables the dual-injection modulator to extract and process useful signals more effectively in complex scenarios with multiple superimposed signals and interference signals, reducing signal distortion and bit error rate, and improving the overall performance and reliability of the modulator. It has significant advantages in signal processing accuracy and stability, can adapt to a wider range of signal strengths, and meets the needs of application scenarios with high signal quality requirements. It is an attractive candidate for large-scale integration in RF analog applications.

[0035] The circuits and mechanical connections involved in this invention are conventional methods used by those skilled in the art, and technical inspiration can be obtained through a limited number of experiments; they are common knowledge.

[0036] Components not described in detail in this article are existing technologies.

[0037] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure, characterized in that: Including silica substrate, Waveguide and silicon dioxide cladding, the The waveguide is located between the silicon dioxide substrate and the silicon dioxide cladding; The The waveguide includes an input waveguide (1), a Y-beam splitter (2), a racetrack-shaped microring, and an output waveguide (11), wherein the input waveguide (1) and the output waveguide (11) are... The input and output terminals of the waveguide; The output end of the input waveguide (1) is connected to the input end of the Y beam splitter (2). The output end of the Y beam splitter (2) includes two sets, namely the upper port and the lower port, which split a single-mode light wave into two single-mode waves with equal power. The upper port of the Y beam splitter (2) is connected to the racetrack-shaped micro-ring and the dissipation (5) in sequence through the first connecting waveguide (3). The lower port of the Y beam splitter (2) is connected to the racetrack-shaped micro-ring and the output waveguide (11) through the second connecting waveguide (6). The racetrack-shaped microring is also provided with a gold electrode (9).

2. The thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure according to claim 1, characterized in that: The racetrack-shaped microring includes a first directional coupler (4), a second directional coupler (10), a first straight waveguide (7), and a second straight waveguide (8). The first directional coupler (4) is located between the first connecting waveguide (3) and the dissipation (5); the second directional coupler (10) is located between the second connecting waveguide (6) and the output waveguide (11).

3. The thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure according to claim 2, characterized in that: The coupling coefficient and transmission coefficient of the first directional coupler (4) and the second directional coupler (10) are different, and their parameters can be adjusted as needed.

4. A thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure according to claim 2, characterized in that: The gold electrodes (9) are distributed on both sides of the second straight waveguide (8) to regulate the refractive index change of the racetrack-shaped microring.

5. A thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure according to claim 1, characterized in that: The first connecting waveguide (3) is a 90-degree curved waveguide, and its waveguide length is less than that of the second connecting waveguide (6).

6. A thin-film lithium niobate linear electro-optic modulator based on a dual-injection structure according to claim 1, characterized in that: The second connecting waveguide (6) includes three 90-degree circular arc waveguides and one straight waveguide. The bending radius of the circular arc waveguide is in the range of 15um-100um, which is used to reduce bending loss.

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