Ring-assisted Mach-Zehnder modulator based on thin film lithium niobate platform

Abstract

The invention belongs to the technical field of integrated electro-optical modulators, and discloses a ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform, and the modulator comprises optical waveguide arms which comprise a first optical waveguide arm and a second optical waveguide arm, the first optical waveguide arm comprises a first modulation arm part, a second modulation arm part, and a cross arm part, the optical wave signal transmission directions of the first modulation arm part and the second modulation arm part are the same, and the cross arm part is connected with the output end of the first optical waveguide arm and the output end of the second optical waveguide arm; the micro-ring resonator is coupled with the second optical waveguide arm; wherein the cross arm part is configured as follows: when the light transmitted by the first modulation arm part is allowed to be output through the cross arm part, the light transmitted by the second modulation arm part is allowed to be output through the cross arm part in a delayed manner; or when the light transmitted by the second modulation arm part is allowed to be output through the cross arm part, the light transmitted by the first modulation arm part is allowed to be output through the cross arm part in a delayed manner.

Description

Technical Field

[0001] This invention belongs to the field of integrated electro-optic modulator technology, specifically relating to a ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform. Background Technology

[0002] With the increasing demand for high-precision detection, broadband signal processing, and anti-interference performance in modern communication systems, their technological systems are developing towards higher frequency bands. Existing data center interconnects and broadband telecommunications networks typically utilize optical communication modules to handle high-data-rate Internet services. Electro-optic modulators are one of the core components in the field of optical communication, and researching electro-optic modulators with high modulation bandwidth, high extinction ratio, low power consumption, easy integration, and low cost is of significant practical importance.

[0003] Electro-optic modulators are typically based on the linear electro-optic effect (Pockels effect) of crystals, which means that the change in the refractive index of a crystal under the influence of an electric field is proportional to the change in the applied electric field. Currently, the most widely used electro-optic modulator is the waveguide-type electro-optic modulator made of lithium niobate crystal material. Its principle is that an applied modulation voltage causes a change in the refractive index of the lithium niobate optical waveguide, thereby changing the phase of the light wave passing through the waveguide, thus achieving phase modulation. Lithium niobate waveguide electro-optic phase modulators are characterized by simple structure, small size, mature manufacturing process, and ease of use (encapsulated with fiber optic pigtails).

[0004] Based on the key optical structure of electro-optic modulators, electro-optic modulators can also be classified into the following types:

[0005] 1. Modulator based on dual-signal MZI. Its structure is a modulator, but two optical signals are injected into the device. The amplitude and phase of the two input signals must be matched with predetermined values ​​of the amplitude and phase of the radio frequency signal. The two injected optical signals can be implemented using two polarizations, two wavelengths, and bidirectional signals. The main advantages of this modulator are its relatively simple structure and low cost. Its disadvantages are inflexible design, unsatisfactory performance, and strict manufacturing tolerance requirements.

[0006] 2. Cascaded modulator. It consists of two or more standard MZI modulators connected in series or parallel to eliminate IMD3 / IMD5. However, the complex compensation of multiple modulators leads to disadvantages such as stricter manufacturing tolerance requirements, higher manufacturing costs, and higher optical loss.

[0007] 3. RAMZI Modulator. This modulator uses ring resonators (RRs) instead of the standard phase modulator (PM) coupled in the MZI arm. Resonant phase tuning compensates for the inherent nonlinear transfer function of the MZI, thereby improving the spurious-free dynamic range. However, this modulator is still a straight waveguide phase modulator. Traditional straight waveguide phase modulators typically reduce half-wave voltage by increasing the device length. However, increasing the waveguide length is detrimental to device fabrication, packaging, and application, resulting in existing RAMZI modulators still having a slightly larger size, hindering integration and mass production. Summary of the Invention

[0008] In view of this, in order to solve the problems mentioned in the background art, the object of the present invention is to provide a ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform, comprising:

[0011] An optical waveguide arm includes a first optical waveguide arm and a second optical waveguide arm. The first optical waveguide arm includes a first modulation arm, a second modulation arm, and a cross arm. The optical wave signal transmission directions of the first modulation arm and the second modulation arm are the same. The cross arm connects the output end of the first optical waveguide arm and the output end of the second optical waveguide arm.

[0012] A micro-ring resonator is coupled to the second optical waveguide arm;

[0013] The cross arm portion is configured as follows:

[0014] When light propagating through the first modulation arm is allowed to exit through the cross arm, a delay is made to allow light propagating through the second modulation arm to exit through the cross arm.

[0015] Alternatively, when light propagating through the second modulation arm is allowed to exit through the cross arm, a delay is made to allow light propagating through the first modulation arm to exit through the cross arm.

[0016] Preferably, the cross arm includes a first cross arm and a second cross arm, the first cross arm being connected to the output terminal of the first modulation arm, and the second cross arm being connected to the output terminal of the second modulation arm.

[0017] Preferably, the optical waveguide arm further includes a connecting arm that connects the second cross arm portion to the input end of the first optical waveguide arm, so that the first modulation arm portion and the second modulation arm portion are configured to sequentially deliver modulation.

[0018] Preferably, the modulator further includes a first electrode group, comprising a signal electrode disposed between the first modulation arm and the second modulation arm, and two ground electrodes disposed outside the first modulation arm and the second modulation arm, respectively, to coordinately modulate the light propagating in the first modulation arm and the second modulation arm.

[0019] Preferably, the microring resonator includes a coupling straight arm, a modulation straight arm, and a microring arm, and the microring resonator is coupled to the second optical waveguide arm through the coupling straight arm.

[0020] Preferably, the modulator further includes a second electrode group, comprising a signal electrode and a ground electrode disposed on both sides of the modulation straight arm, to coordinately modulate the light propagating in the modulation straight arm.

[0021] Preferably, the phase modulation region of the modulation straight arm has a length of 536 μm, and the radius of the micro-ring arm is 85 μm.

[0022] Preferably, the phase modulation region lengths of the first modulation arm and the second modulation arm are not less than the phase modulation region length of the modulation straight arm.

[0023] Preferably, the first optical waveguide arm, the second optical waveguide arm, and the modulation straight arm each include a first waveguide layer, a second waveguide layer, and a lithium niobate layer; wherein the lithium niobate layer is bonded between the first waveguide layer and the second waveguide layer.

[0024] Preferably, the modulator further includes a beam splitter and an optical combiner respectively connected to the input and output ends of the optical waveguide arm.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] In the modulator of this invention, the first optical waveguide arm integrates a cross-waveguide phase modulation structure, which forms two modulation arms. Through delay control, the optical signal passes through the two modulation arms in a staggered manner, effectively achieving the superposition of modulation effects, increasing the phase modulation length, and significantly reducing the half-wave voltage without increasing the overall chip length. The second optical waveguide arm couples a microring resonator, utilizing the interaction between Mach-Zehnder interference and microring resonance to generate a special Fano resonance. This enables strong suppression of the IMD3 term, thereby significantly improving the spurious-free dynamic range.

[0027] In summary, the modulator provided by this invention can reduce the half-wave voltage and decrease the device size without increasing the device length, which is conducive to integration, has good practicality, and has practical application value. Attached Figure Description

[0028] Figure 1This is a schematic diagram of the structure of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of the first optical waveguide arm in this invention;

[0030] Figure 3 This is a schematic diagram of the coupling structure between the second optical waveguide arm and the micro-ring resonator in this invention;

[0031] Figure 4 This is a schematic diagram of the structure of the first waveguide layer, the second waveguide layer, and the lithium niobate layer in this invention.

[0032] Figure 5 This is a comparison chart of the simulation results of the optical link between the modulator of this invention and the MZI modulator;

[0033] In the diagram: Optical waveguide arm-100; First optical waveguide arm-110; First modulation arm-111; Second modulation arm-112; Cross arm-113; Connecting arm-114; Second optical waveguide arm-120; Micro-ring resonator-200; Coupled straight arm-201; Modulated straight arm-202; Micro-ring arm-203; First electrode group-300; Second electrode group-400; Beam splitter-500; Optical combiner-600; First waveguide layer-1; Second waveguide layer-2; Lithium niobate layer-3. Detailed Implementation

[0034] To further understand the content of this invention, a detailed description of the invention is provided in conjunction with the accompanying drawings and embodiments. The structures, proportions, sizes, etc., depicted in the accompanying drawings are merely for illustrative purposes and to aid those skilled in the art, and are not intended to limit the implementation conditions of the invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effects and objectives of the invention, should still fall within the scope of the technical content disclosed in this invention. Furthermore, terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity and not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention. It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein.

[0035] Figure 1This is a schematic diagram of the structure of a ring-assisted Mach-Zehnder interferometer modulator based on a lithium niobate thin film according to an embodiment of the present invention. As shown in the figure, the structure of the ring-assisted Mach-Zehnder interferometer modulator based on a lithium niobate thin film includes: a beam splitter 500, an optical waveguide arm 100, and an optical combiner 600. The optical waveguide arm 100 includes a first optical waveguide arm 110 and a second optical waveguide arm 120. Each optical waveguide arm 100 has an optical waveguide core comprising an electro-optic material, i.e., a material whose optical properties (e.g., refractive index) can be altered by an electric field (e.g., the Pockels effect). In the example embodiment described below, the electro-optic material is lithium niobate (LiNbO3, "LN"), but other suitable electro-optic materials may also be used. The optical waveguide arm 100 is configured to receive light from the beam splitter 500 and, after traveling along the optical waveguide arm 100, transmit the light to the optical combiner 600 for recombination. In some embodiments, the beam splitter 500 and the optical combiner 600 may be formed of a different material than the optical waveguide arm 100; for example, the beam splitter 500 and the optical combiner 600 may be formed of a silicon waveguide, while the optical waveguide arm 100 may be an LN waveguide.

[0036] Figure 2 This is a schematic diagram of the structure of the first optical waveguide arm 110 in the ring-assisted Mach-Zehnder interferometer modulator based on lithium niobate thin film according to an embodiment of the present invention. As shown in the figure, the first optical waveguide arm 110 includes a first modulation arm 111, a second modulation arm 112, a cross arm 113, and a connecting arm 114. The cross arm 113 includes a first cross arm and a second cross arm that cross each other. The first cross arm is connected to the output end of the first modulation arm 111, and the second cross arm is connected to the output end of the second modulation arm 112. The connecting arm 114 connects the second cross arm and the input end of the first optical waveguide arm 110, thereby constructing the first modulation arm 111 and the second modulation arm 112 into a sequential transmission structure with the same optical signal transmission direction. In some embodiments, the ring-assisted Mach-Zehnder interferometer modulator based on a lithium niobate thin film of the present invention further includes a first electrode group 300, which includes a signal electrode and two ground electrodes, the signal electrode being located between the two ground electrodes, and a first modulation arm 111 being disposed between the signal electrode and one of the ground electrodes, and a second modulation arm 112 being disposed between the signal electrode and the other ground electrode. The signal electrode and the ground electrodes are configured to co-modulate light propagating in the first optical waveguide arm 110 in response to a voltage applied between the first electrode group 300. In a typical embodiment, the first electrode group 300 is configured as a traveling wave electrode structure (“RF waveguide”).

[0037] For example, such as Figure 2 As shown, the configuration of the cross arm 113 and the connecting arm 114 allows light in the first optical waveguide arm 110 to sequentially pass through the first modulation arm 111 and the second modulation arm 112 in the same direction. Specifically, when light passes through the first modulation arm 111, a voltage is applied between the upper ground electrode and the intermediate signal electrode to modulate the light propagating in the first modulation arm 111; when light passes through the second modulation arm 112, a voltage is applied between the lower ground electrode and the intermediate signal electrode to modulate the light propagating in the second modulation arm 112. In a typical embodiment, the cross arm 113 is configured such that when light propagating in the first modulation arm 111 is allowed to exit through the cross arm 113, a delay is allowed before light propagating in the second modulation arm 112 is allowed to exit through the cross arm 113; or, when light propagating in the second modulation arm 112 is allowed to exit through the cross arm 113, a delay is allowed before light propagating in the first modulation arm 111 is allowed to exit through the cross arm 113. Therefore, the cross arm 113 itself does not directly increase the physical waveguide length, but rather, through optical path design and timing control, allows light to pass through the first modulation arm 111 and the second modulation arm 112 at staggered times, thereby achieving the superposition of modulation effects. When the delay time... When u is an integer, the modulation effects of the first modulation arm 111 and the second modulation arm 112 are superimposed in the same direction, and the total modulation amount is twice that of a single arm. This is equivalent to doubling the effective modulation length while the actual chip length remains unchanged. In addition to increasing the phase modulation length, the cross waveguide structure constructed by the first optical waveguide arm 110 can also achieve modulation enhancement or modulation cancellation by adjusting the microwave frequency or delay time, and has reconfigurability.

[0038] It should be noted that the first optical waveguide arm 110 maintains a stable half-wave voltage of around 3V within the wavelength range of 1510–1600nm, which is beneficial for integration with lasers of different wavelengths. The cross-waveguide structure constructed by the first optical waveguide arm 110 is compact and has low crosstalk, making it suitable for high-density photonic integrated chips.

[0039] Figure 3This is a schematic diagram of the coupling between the second optical waveguide arm 120 and the microring resonator 200 in a ring-assisted Mach-Zehnder interferometer modulator based on a lithium niobate thin film according to an embodiment of the present invention. As shown in the figure, a racetrack-shaped microring resonator 200 is provided, comprising a coupling straight arm 201, a modulation straight arm 202, and a microring arm 203. The microring resonator 200 is coupled to the second optical waveguide arm 120 through the coupling straight arm 201. In some embodiments, the ring-assisted Mach-Zehnder interferometer modulator based on a lithium niobate thin film according to the present invention further includes a second electrode group 400, which includes a signal electrode and a ground electrode extending along the modulation straight arm 202. In this arrangement, a signal electrode and a ground electrode are respectively disposed on both sides of the modulation straight arm 202. The signal electrode and the ground electrode are configured to modulate light propagating in the modulation straight arm 202 in response to a voltage applied between the second electrode group 400. In a typical embodiment, the second electrode group 400 is configured to adopt a traveling wave electrode structure (“RF waveguide”).

[0040] It should be noted that the phase modulation region length of the modulation straight arm 202 is 536μm, and the radius of the micro-ring arm 203 is 85μm, so as to ensure a FSR (Free Spectrum Range, FSR) close to 100GHz while taking into account reasonable micro-ring loss.

[0041] In an exemplary embodiment, the transmission characteristics of the micro-ring resonator 200 are commonly analyzed using a transfer matrix. The transfer function expression for the all-pass single-ring resonator is as follows:

[0042] In the formula, Indicates the transmission coefficient of the resonator. It is the loss coefficient of the resonator. This indicates the round-trip phase of the resonator.

[0043] exist Figure 3 In the structure shown where the microring resonator 200 is coupled to the second optical waveguide arm 120, the coupling region is characterized using the transfer matrix method. For a structure using the transfer coefficient... and coupling coefficient The input-output transformation of the ideal, lossless coupling region can be controlled by the following matrix:

[0044] ;

[0045] In the formula, and The relationship between them can be represented as ; Representing the round-trip phase shift at zero output voltage, the normalized transfer function of a specific resonator can be derived:

[0046] ;

[0047] in, By comparing the transmission matrix of the all-pass single-ring resonator with this specific transmission matrix, the specific transmission coefficients in the specific transmission matrix can be obtained. Equivalent to transmission coefficient The conclusion.

[0048] The loss in the pre-defined waveguide is negligible, and the frequency response of the micro-ring resonator 200 is expressed as: ;

[0049] Therefore, the output electric field of the ring-assisted Mach-Zehnder interferometer modulator based on lithium niobate thin film of the present invention can be expressed as: ;in, It is represented as the phase difference between the first optical waveguide arm 110 and the second optical waveguide arm 120.

[0050] Generally, under radio frequency excitation, since the excitation signal contains multiple frequencies (in analog, such as...), Figure 1 As shown and Therefore, electro-optical conversion naturally generates IMD3 products, which cannot be eliminated by conventional filtering techniques. Similar to the traditional MZI architecture, the ring-assisted Mach-Zehnder interferometer modulator based on lithium niobate thin film operates in an orthogonal state, with the microring resonator 200 in a deeply overcoupled state and biased at a non-resonant point. Fano resonance can be achieved by adjusting the phase difference between the first optical waveguide arm 110 and the second optical waveguide arm 120, as well as the coupling coefficient between the second optical waveguide arm 120 and the microring resonator 200. The IMD3 component in the modulated optical field originates from the third-order Taylor coefficient of the RAMZI transfer function at the bias point v=Vp, which corresponds to the orthogonal operating point:

[0051] ;

[0052] in, This indicates the amplitude of IMD3. It is a two-tone signal injected into the electrode ( ),Will Defined as the amplitude of the RF signal. DC bias voltage, and For closely spaced modulated signals, It is the change in the effective refractive index of the waveguide under the applied voltage. This indicates the output field strength.

[0053] In summary, the key transmission coefficient in the microring resonator 200 This setting is to ensure that the microring resonator 200 eliminates the IMD3 component under operating conditions;

[0054] To eliminate IMD3, the following conditions must be met:

[0055] ;

[0056] in, It is the slope constant. and or Under these conditions, and by deriving the formula, we can obtain the transmission coefficient when achieving high linearity. The conclusion.

[0057] Figure 4 This is a cross-sectional view of the modulation arms (first modulation arm 111, second modulation arm 112, and modulation straight arm 202) in a ring-assisted Mach-Zehnder interferometer modulator based on a lithium niobate thin film according to an embodiment of the present invention. As shown in the figure, the first optical waveguide arm 110, the second optical waveguide arm 112, and the modulation straight arm 202 each include a first waveguide layer 1, a second waveguide layer 2, and a lithium niobate layer 3; wherein the lithium niobate layer 3 is bonded between the first waveguide layer 1 and the second waveguide layer 2. In some embodiments, the first waveguide layer 1 and the second waveguide layer 2 may be formed of a different material than the lithium niobate layer 3; for example, the first waveguide layer 1 and the second waveguide layer 2 may be formed of silicon or germanium. In a typical embodiment, both the first waveguide layer 1 and the second waveguide layer 2 comprise SiO2. Furthermore, the phase modulation region lengths of the first modulation arm 11 and the second modulation arm 12 are defined to be no less than the phase modulation region length of the modulation straight arm 202.

[0058] It should be noted that the lithium niobate layer 3 can form a slit mode. For the mode field distribution of the ring-assisted Mach-Zehnder interferometer modulator based on lithium niobate thin film of the present invention, the optical field can be mainly concentrated in the lithium niobate layer 3 with a high electro-optic modulation coefficient (e.g., electro-optic modulation coefficient r33≥30pm / V). Therefore, the ring-assisted Mach-Zehnder interferometer modulator based on lithium niobate thin film of the present invention has optical field phase modulation performance with low half-wave voltage-length product, high modulation rate, and low insertion loss.

[0059] like Figure 4The lithium niobate (LN) waveguide shown is obtained as follows: The structure of the lithium niobate layer 3 can be defined within a wafer plane (corresponding to the unthinned lithium niobate material). First, the lithium niobate layer 3 needs to be fabricated on the wafer plane using physical or chemical etching on an insulator. Then, amorphous silicon deposition is performed to obtain the initial first waveguide layer 1 and the initial second waveguide layer 2, thus obtaining the LN waveguide with a slit structure provided by this invention. In this embodiment, by constructing a slit waveguide structure of the first waveguide layer-lithium niobate layer-second waveguide layer, the ring-assisted Mach-Zehnder interferometer modulator based on the lithium niobate thin film of this invention can be ensured to have low half-wave voltage-length product, high modulation rate, and low insertion loss optical field phase modulation performance. It should be noted that the etching depth is half the thickness of the thick lithium niobate layer 3, the top width of the etched LN ridge waveguide is 1.2 μm, and the waveguide sidewall angle is 60°.

[0060] Furthermore, in various embodiments, one or more other material layers may be present above and / or below the optical waveguide core and / or electrodes (signal electrodes and ground electrodes), including those embodiments that provide an optical cladding for the optical waveguide of the modulation arm.

[0061] Figure 5 This figure compares the simulation results of the ring-assisted Mach-Zehnder interferometer modulator and the MZI modulator based on lithium niobate thin film of this invention in the simulated optical link. As shown in the figure, strong suppression of IMD3 is achieved through Fano resonance, and the SFDR of the modulator designed in this invention reaches 125.5 dB∙Hz at a frequency of 5 GHz. 4 / 5 It is 19.5 dB higher than the reference MZI modulator.

[0062] Specifically:

[0063] A common metric for defining the nth-order SFDR is the nth-order output intercept (OIPn), which represents the output power point at the extrapolated intersection of the small-signal response of the fundamental signal and the nth-order distortion component. OIPn is an assumed output power point and cannot be physically realized. SFDR is normalized to a 1Hz bandwidth and can be expressed in units of [dB·Hz(n−1) / n] as follows:

[0064] ;

[0065] The validity of this formula requires two basic assumptions:

[0066] (i) In the small signal range, the linear response is maintained for the fundamental harmonic (FH), and the nth order distortion term also retains its nth order characteristics;

[0067] (ii) Throughout the specified analysis bandwidth Maintain frequency independence.

[0068] By simulating an analog optical link at a noise floor of -164.0 dBm / Hz, mathematical calculations and physical modeling were performed using the expressions for SFDR and OIPn (a common metric for defining the nth-order SFDR is the nth-order output intercept (OIPn), which represents the output power point at the extrapolated intersection of the small-signal response of the fundamental signal and the nth-order distortion component). This yielded a linear graph of the designed modulator of this invention and the IMD3 of the reference MZI structure on a double logarithmic scale at a specific frequency. The SFDR value was then calculated using their respective output intercepts. Figure 5 As can be seen, in the modulator of this invention, the IMD3 signal shows a slope of 5 on the double logarithmic scale at both frequencies, indicating that the cubic term of IMD3 is strongly suppressed. In the reference MZI, the IMD3 signal shows a slope of 3 on the double logarithmic scale at both frequencies, indicating that the cubic term of IMD3 is dominant (i.e., not suppressed).

[0069] In the description of this invention, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform, comprising: The optical waveguide arm (100) includes a first optical waveguide arm (110) and a second optical waveguide arm (120). The first optical waveguide arm (110) includes a first modulation arm (111), a second modulation arm (112), and a cross arm (113). The optical wave signal transmission directions of the first modulation arm (111) and the second modulation arm (112) are the same. The cross arm (113) connects the output end of the first optical waveguide arm (110) and the output end of the second optical waveguide arm (120). The microring resonator (200) is coupled to the second optical waveguide arm (120); The cross arm portion (113) is configured as follows: When light propagating through the first modulation arm (111) is output through the cross arm (113), light propagating through the second modulation arm (112) is output through the cross arm (113) after a delay. Alternatively, when light propagating through the second modulation arm (112) is allowed to be output through the cross arm (113), a delay is allowed for light propagating through the first modulation arm (111) to be output through the cross arm (113).

2. The ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 1, characterized in that: The cross arm (113) includes a first cross arm and a second cross arm, the first cross arm is connected to the output end of the first modulation arm (111), and the second cross arm is connected to the output end of the second modulation arm (112).

3. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 2, characterized in that: The optical waveguide arm (100) further includes a connecting arm (114) that connects the second cross arm to the input end of the first optical waveguide arm (110), so that the first modulation arm (111) and the second modulation arm (112) are configured to deliver modulation sequentially.

4. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 1, 2, or 3, characterized in that, Also includes: The first electrode group (300) includes a signal electrode disposed between the first modulation arm (11) and the second modulation arm (12) and two ground electrodes disposed outside the first modulation arm (11) and the second modulation arm (12) respectively, so as to coordinately modulate the light propagating in the first modulation arm (11) and the second modulation arm (12).

5. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 1, characterized in that: The microring resonator (200) includes a coupling straight arm (201), a modulation straight arm (202), and a microring arm (203). The microring resonator (200) is coupled to the second optical waveguide arm (120) through the coupling straight arm (201).

6. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 5, characterized in that, Also includes: The second electrode group (400) includes a signal electrode and a ground electrode disposed on both sides of the modulation straight arm (202) to coordinately modulate the light propagating in the modulation straight arm (202).

7. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 5, characterized in that: The phase modulation region of the modulation straight arm (202) is 536 μm long, and the radius of the micro-ring arm (203) is 85 μm.

8. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 7, characterized in that: The phase modulation region length of the first modulation arm (11) and the second modulation arm (12) is not less than the phase modulation region length of the modulation straight arm (202).

9. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 5, characterized in that: The first optical waveguide arm (110), the second optical waveguide arm (120) and the modulation straight arm (202) all include a first waveguide layer (1), a second waveguide layer (2) and a lithium niobate layer (3); wherein the lithium niobate layer (3) is bonded between the first waveguide layer (1) and the second waveguide layer (2).

10. A ring-assisted Mach-Zehnder modulator based on a thin-film lithium niobate platform according to claim 1, characterized in that: It also includes a beam splitter (500) and an optical combiner (600) respectively connected to the input and output ends of the optical waveguide arm (100).

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