A CWDM optical transmitting chip

Abstract

The application discloses a CWDM optical transmitting chip, which comprises a SiNx grating coupler, a SiNx mode spot converter, a waveguide converter, a SiNx-thin film lithium niobate electro-optical modulator, a SiNx-thin film lithium niobate waveguide device and a SiNx-thin film lithium niobate CWDM wavelength division multiplexer, wherein SiNx material is deposited on a silicon dioxide substrate layer to form a SiNx waveguide device layer, thin film lithium niobate is directly bonded on the SiNx waveguide device layer, the SiNx waveguide device layer is used for etching the SiNx-thin film lithium niobate waveguide device, and a silicon dioxide thin film layer and a thin film lithium niobate layer are sequentially covered on the SiNx waveguide device layer; the application utilizes the electro-optical modulation characteristics of the thin film lithium niobate material, adopts an inverted ridge waveguide structure, can realize high-speed electro-optical modulation, integrates wavelength division multiplexing and electro-optical modulation, and realizes high-speed and large-capacity signal transmission.

Description

Technical Field

[0001] This invention relates to the field of silicon-based optoelectronics, and more particularly to a CWDM optical transmission chip. Background Technology

[0002] With the development of big data and the internet, the demand for data centers and high-performance computing is constantly increasing. However, traditional electrical interconnects are limited by bandwidth and power consumption, making it difficult to meet the ever-growing capacity demands. The need for high-capacity, reliable, and low-cost optical data links has driven the development of photonic integrated circuits. Traditional transceiver devices composed of discrete optical components typically have a single-channel transmission rate of 50-100 Gbit / s. As data capacity continues to grow, the performance of a single modulator is insufficient to meet application requirements. Therefore, combining modulators with multiplexing technology is a promising solution to address future data capacity growth. Optical modules are one of the core components of fiber optic communication systems and the most important part of optical communication equipment. Their main function is to achieve photoelectric conversion, serving as the interconnection channel between the optical and electrical worlds.

[0003] Optical transceiver chips are a crucial component of optical modules, integrating optical couplers, electro-optic modulators, wavelength division multiplexers, and other passive devices. While silicon-based optical transceiver chip technology is relatively mature and commercially available, the limited bandwidth of silicon-based grating couplers and the restricted modulation bandwidth of silicon-based electro-optic modulators hinder the implementation of higher-speed transmission systems. Lithium niobate materials, with their lower propagation loss and ultra-high bandwidth, are favored by researchers for their ability to achieve high data rate transmission. However, the stable chemical properties of thin-film lithium niobate materials prevent the formation of low-loss waveguides using common chemical etching methods. Therefore, thin-film lithium niobate optical transceiver chips are currently still in the research stage.

[0004] Existing technical solutions:

[0005] Patent application number 202010245273.8 discloses a heterogeneous integrated CWDM4 optical transmitter chip, comprising a laser, an electro-optic modulator, and a wavelength division multiplexer. The laser of the optical transmitter chip is bonded to a substrate and aligned with the chip via end-face coupling. The substrate has a silicon dioxide layer, and the silicon dioxide layer has a silicon layer. The electro-optic modulator includes a waveguide combiner, a waveguide splitter, and a silicon waveguide phase shifter. The waveguide combiner and waveguide splitter are both disposed within the silicon dioxide layer, while the silicon waveguide phase shifter is disposed on the silicon layer. The wavelength division multiplexing device is disposed within the silicon dioxide layer. The entire heterogeneously integrated CWDM4 optical transmitter chip exhibits low transmission loss, and the mode field mismatch between the silicon dioxide waveguide and the single-mode fiber is small. Low-loss end-face coupling can be directly achieved between the output end of the optical transmitter chip and the single-mode fiber.

[0006] Because its heterogeneous integrated CWDM optical emission chip is designed on a three-layer structure consisting of a substrate, a silicon dioxide layer, and a silicon layer, the performance of electro-optic modulation is always limited by the silicon material.

[0007] The paper with DOI 10.1002 / adpr.202200121 presents a monolithic photonic integrated circuit based on a hybrid insulator platform using silicon nitride and lithium niobate. The circuit includes optical couplers, a ring resonant modulator, and a mode divider (MDD). This is the first demonstration on a Si3N4-LNOI hybrid platform of a photonic integrated circuit composed of a high-speed electro-optic modulator and a (de)multiplexer. The MDD is positioned centrally, with four optical couplers on each side connected to the corresponding input / output ports of the MDD. A ring resonant modulator is also placed between the input optical coupler and the MDD interface to modulate the optical signal. The final result achieves a single-channel data communication rate of 70 Gbps and a total data capacity of 280 Gbps.

[0008] However, the aforementioned photonic integrated circuit uses a resonator structure for the modulator, which is very sensitive to temperature. Secondly, the multiplexing device uses mode division multiplexing, which has a limited application range. Furthermore, the entire circuit has a total of eight optical interfaces, four input interfaces and four output interfaces, making the structure complex. Summary of the Invention

[0009] This invention overcomes the shortcomings of the prior art and provides a CWDM optical transmission chip.

[0010] To achieve the above objectives, the technical solution adopted by this invention is as follows: a CWDM optical transmission chip, comprising: a SiNx grating coupler, a SiNx mode converter, a waveguide converter, a SiNx-thin-film lithium niobate electro-optic modulator, a SiNx-thin-film lithium niobate waveguide device, and a SiNx-thin-film lithium niobate CWDM wavelength division multiplexer, characterized in that SiNx material is deposited on a silicon dioxide substrate to form a SiNx waveguide layer, and thin-film lithium niobate is directly bonded to the SiNx waveguide layer without etching, wherein a silicon dioxide thin film layer and a thin-film lithium niobate layer are sequentially covered on the SiNx waveguide layer, and the SiNx waveguide layer is etched and then bonded to the substrate. A silicon dioxide layer and a thin-film lithium niobate layer together form a SiNx-thin-film lithium niobate waveguide device; the SiNx grating coupler is the coupling interface between the chip and the optical fiber; the SiNx mode converter is used to transmit the optical mode field of the grating region to the optical waveguide for transmission; the waveguide converter is used to transmit the optical mode field transmitted inside the SiNx waveguide to the SiNx-thin-film lithium niobate waveguide layer for transmission; the SiNx-thin-film lithium niobate electro-optic modulator confines the optical mode field as much as possible within the thin-film lithium niobate material through the SiNx mode converter, and uses the secondary electro-optic coefficient γ33 of the thin-film lithium niobate material to achieve high-speed electro-optic modulation.

[0011] In a preferred embodiment of the present invention, the electrode structure of the SiNx-thin film lithium niobate electro-optic modulator adopts a push-pull structure, which can simultaneously achieve opposite phase shifts on both arms of the SiNx-thin film lithium niobate electro-optic modulator.

[0012] In a preferred embodiment of the present invention, the SiNx-thin lithium niobate CWDM wavelength division multiplexer is fabricated using a single-step etching process.

[0013] In a preferred embodiment of the present invention, the SiNx grating coupler is disposed at the interface between the input optical fiber and the output optical fiber.

[0014] In a preferred embodiment of the present invention, the SiNx mode converter is a tapered optical waveguide.

[0015] In a preferred embodiment of the present invention, the light wave is split and input into the two arms of the phase shifter by a SiNx-thin thin-film lithium niobate multimode interference coupler for transmission, or the light waves from the two arms of the phase shifter are combined and output after transmission.

[0016] In a preferred embodiment of the present invention, the SiNx is made of ordinary silicon nitride material, silicon-rich silicon nitride, or nitrogen-rich silicon nitride material.

[0017] In a preferred embodiment of the present invention, the SiNx waveguide device layer is formed by depositing SiNx material on a silicon dioxide substrate using plasma-enhanced chemical vapor deposition (PECVD).

[0018] In a preferred embodiment of the present invention, the SiNx waveguide is left on the SiNx waveguide device layer through a one-step full etching process.

[0019] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0020] This invention employs full etching on a SiNx platform followed by bonding of a thin-film lithium niobate layer, avoiding etching the lithium niobate film and reducing process complexity. Furthermore, using SiNx to fabricate grating-coupled devices enables a wider bandwidth, providing a foundation for CWDM (Central Wavelength Division Multiplexing). Utilizing the electro-optic modulation characteristics of thin-film lithium niobate material, and employing the proposed inverted ridge waveguide structure, high-speed electro-optic modulation can be achieved. Integrating wavelength division multiplexing with electro-optic modulation enables high-speed, high-capacity signal transmission.

[0021] SiNx has low material loss and an optically transparent window similar to thin-film lithium niobate, and the performance of photonic integrated circuits based on this hybrid platform is not reduced by the introduction of load materials. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the overall structure of Example 1;

[0024] Figure 2 This is a schematic diagram of the structure after removing the lithium niobate thin film in Example 1;

[0025] Figure 3 This is a structural diagram of a SiNx-thin lithium niobate electro-optic modulator;

[0026] Figure 4 This is a cross-sectional view of a SiNx-thin lithium niobate phase shifter;

[0027] Figure 5 This is a schematic diagram of the overall structure of Example 2;

[0028] Figure 6 This is a schematic diagram of the overall structure of Example 3;

[0029] In the picture:

[0030] 101: SiNx grating coupler;

[0031] 102: SiNx mode converter;

[0032] 103: Waveguide converter;

[0033] 104: SiNx-thin film lithium niobate electro-optic modulator;

[0034] 105-1: SiNx-thin film lithium niobate waveguide 1;

[0035] 105-2: SiNx-thin film lithium niobate waveguide 2;

[0036] 105-3: SiNx-thin film lithium niobate waveguide 3;

[0037] 105-4: SiNx-thin film lithium niobate waveguide 4;

[0038] 106: SiNx-thin-film lithium niobate CWDM wavelength division multiplexer;

[0039] 107: SiNx-thin lithium niobate bent waveguide;

[0040] 108: Thin film lithium niobate layer;

[0041] 109: Silica thin film layer;

[0042] 1010: Silicon dioxide substrate;

[0043] 1011: Silicon substrate layer;

[0044] 1012-1: Silica cladding;

[0045] 1012-2: Silicon dioxide layer surrounding SiNx after etching;

[0046] 1013: SiNx waveguide device layer;

[0047] 104-1: 1×2SiNx-thin lithium niobate multimode interference coupler (MMI);

[0048] 104-2: SiNx-thin lithium niobate bent waveguide;

[0049] 104-3: SiNx-thin lithium niobate straight waveguide;

[0050] 104-4: SiNx-thin lithium niobate mode converter;

[0051] 104-5: SiNx-thin lithium niobate phase shifter;

[0052] 104-6: Electrode. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. In the description of the present invention, the reference to "embodiment", "one embodiment" or "other embodiments" indicates that a specific feature, structure or characteristic described in connection with the embodiment is included in at least some 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.

[0054] like Figure 1 As shown, a CWDM optical transmitter chip includes four grating couplers (101) at the input end and one grating coupler (101) at the output end, five SiNx mode converters (102), five ridge waveguide converters (103), four SiNx-thin film lithium niobate electro-optic modulators (104), four SiNx-thin film lithium niobate waveguides connected to the input channel of the wavelength division multiplexer, one SiNx-thin film lithium niobate CWDM wavelength division multiplexer (106), one SiNx-thin film lithium niobate waveguide (107) connected to the output channel of the wavelength division multiplexer, a silicon dioxide substrate (108), a silicon dioxide thin film layer (109), and a thin film lithium niobate layer (1010).

[0055] The specific structure of the SiNx-thin film lithium niobate electro-optic modulator (104) is as follows: Figure 3 As shown, it consists of two 1×2 SiNx-thin-film lithium niobate multimode interference couplers (104-1), eight SiNx-thin-film lithium niobate bent waveguides (104-2), four SiNx-thin-film lithium niobate straight waveguides (104-3), four SiNx-thin-film lithium niobate mode converters (104-4), two SiNx-thin-film lithium niobate phase shifters (104-5), and electrodes (104-6).

[0056] The CWDM optical transmitter chip proposed in this paper is characterized by:

[0057] The SiNx grating coupler (101) is located at the interface between the input and output optical fibers. It is used to couple the signal light from the input fiber into the waveguide or to couple the light passing through the chip to the output fiber. Both the input and output optical fibers are single-mode fibers.

[0058] The SiNx mode converter (102) is a tapered optical waveguide, in which four SiNx mode converters complete the optical transmission from the SiNx grating coupler (101) to the four-way waveguide converter (103), and another SiNx mode converter completes the optical transmission from the waveguide converter (103) to the SiNx grating coupler.

[0059] The waveguide converter (103) has a SiNx waveguide on one side and a SiNx-thin-film lithium niobate waveguide on the other side, which completes the optical transmission from the SiNx waveguide to the SiNx-thin-film lithium niobate waveguide.

[0060] The SiNx-thin-film lithium niobate electro-optic modulator (104) consists of a SiNx waveguide layer fabricated on a silicon dioxide substrate (108), a thin-film lithium niobate layer on top (109), and a silicon dioxide thin-film layer (1010) in between. Light waves are input through a 1×2 SiNx-thin-film lithium niobate multimode interference coupler (104-1), propagating through the SiNx-thin-film lithium niobate curved waveguide (104-2) and straight waveguide (104-3). At this point, the optical mode field is mostly confined within the SiNx. Under the action of the SiNx-thin-film lithium niobate mode converter (104-4), the waveguide width of the SiNx is narrowed, further confining the optical mode field within the thin-film lithium niobate layer. Utilizing the electro-optic effect of the thin-film lithium niobate material, the phase of the light wave in the region of the SiNx-thin-film lithium niobate phase shifter (104-5) can be controlled by applying a voltage to the signal electrode (104-6). The modulated light wave is confined within SiNx by a SiNx-thin-film lithium niobate mode converter (104-4) for propagation. It then continues to propagate through SiNx-thin-film lithium niobate curved waveguides (104-2) and straight waveguides (104-3) before being coupled out at the output by a 1×2 SiNx-thin-film lithium niobate multimode interference coupler (104-1).

[0061] The SiNx-thin-film lithium niobate electro-optic modulator (104) contains a SiNx-thin-film lithium niobate mode converter (104-4) that transitions the optical mode field confined within the SiNx to the SiNx-thin-film lithium niobate layer. If the SiNx is ordinary silicon nitride, this device is unnecessary; the optical mode field can directly transition to the SiNx-thin-film lithium niobate layer and is mostly confined within it. If the SiNx is silicon-rich silicon nitride or nitrogen-rich silicon nitride, the waveguide widths at both ends of the silicon nitride need to be carefully set to achieve the transition of the optical mode field.

[0062] The SiNx-thin film lithium niobate waveguide (105) connects the SiNx-thin film lithium niobate electro-optic modulator (104) to the corresponding input channel of the SiNx-thin film lithium niobate CWDM wavelength division multiplexer (106) to achieve low-loss transmission of optical signals.

[0063] The SiNx-thin thin-film lithium niobate CWDM wavelength division multiplexer (106) has four input channels and one output channel, realizing the coupling of the optical input of the four channels into one channel and output.

[0064] The SiNx thin-film lithium niobate bent waveguide (107) connects the output port of the SiNx-thin-film lithium niobate CWDM wavelength division multiplexer (106) to the waveguide converter (103).

[0065] The thin-film lithium niobate layer (108) is directly bonded to the silicon nitride waveguide layer without etching, with only a thin silicon dioxide layer at the interface to improve device uniformity. Its main function is to achieve high-speed electro-optic modulation in the SiNx-thin-film lithium niobate electro-optic modulator (104) region. To improve modulation efficiency, the direction along the electrode signal is the Z-axis of the thin-film lithium niobate.

[0066] The silicon dioxide thin film layer (109) is a very thin layer of silicon dioxide, which enables the thin film lithium niobate to achieve good flatness when bonded to SiNx, thus ensuring device performance.

[0067] The SiNx waveguide device layer (1013) refers to the etched SiNx platform, which can realize the various devices mentioned above through etching process and bonding with lithium niobate material.

[0068] The input signal enters the SiNx grating coupler (101) through the input optical fiber, and is converted by the SiNx mode converter (102) to be transmitted in the waveguide converter (103). The waveguide converter (103) converts the optical mode field from SiNx waveguide transmission to SiNx-thin thin-film lithium niobate transmission. The output light wave is split by a 1×2 SiNx-thin thin-film lithium niobate multimode interference coupler (104-1) and modulated by a SiNx-thin thin-film lithium niobate electro-optic modulator. The modulator adopts a push-pull method, and by applying a voltage to the electrode (104-6), opposite phase shifts can be achieved on the SiNx-thin thin-film lithium niobate phase shifter (104-5). The optical mode field is then confined within the SiNx waveguide layer by a waveguide converter (103). After transmission through the SiNx thin-film lithium niobate bent waveguide (104-2) and straight waveguide (104-3), the light is combined and output by a 1×2 SiNx-thin-film lithium niobate multimode interference coupler (104-1). The output light wave is connected to the corresponding input channel of the SiNx-thin-film lithium niobate CWDM wavelength division multiplexer (106). Under the multimode interference of the SiNx-thin-film lithium niobate CWDM wavelength division multiplexer (106), the four input light waves are coupled into one and output from the output waveguide to the SiNx-thin-film lithium niobate bent waveguide (107). Then, the optical mode field in the SiNx-thin-film lithium niobate is converted into the optical mode field in the SiNx waveguide by the waveguide converter (103). Finally, the light wave is transmitted to the SiNx grating coupler (101) by the SiNx mode converter (102) and coupled to the output fiber. It achieves the integration of high-speed electro-optic modulation and high-capacity wavelength division multiplexing technology.

[0069] Figure 4 This is a cross-sectional view of a SiNx-thin lithium niobate phase shifter, where:

[0070] The SiNx waveguide device layer (1013) was deposited on a silicon dioxide substrate (1010) using plasma-enhanced chemical vapor deposition (PECVD). A one-step full etching process was then used to leave the desired width of the SiNx waveguide, which was then covered with a very thin silicon dioxide film layer (109) to improve material uniformity. A thin lithium niobate layer (108) was then bonded, and a silicon dioxide overlayer (1012-1) was placed on top. Figure 4 As can be seen, the final waveguide resembles an inverted ridge structure, with the thin-film lithium niobate waveguide layer (108) equivalent to the planar waveguide and the SiNx waveguide device layer (1013) equivalent to the ridge waveguide. Outside the SiNx-thin-film lithium niobate phase shifter (104-5), the SiNx waveguide device layer (1013) is used to fabricate passive devices. In the SiNx-thin-film lithium niobate phase shifter (104-5) region, to maximize the utilization of the electro-optic properties of the thin-film lithium niobate material, the optical mode field is mostly confined within the thin-film lithium niobate layer (108) of the SiNx-thin-film lithium niobate waveguide. Figure 4 The electrode (104-6) shown is only in the SiNx-thin thin-film lithium niobate phase shifter (104-5) region and is not present in other areas of the chip.

[0071] Example 1

[0072] refer to Figure 1 , Figure 2 , Figure 3 as well as Figure 4 As shown, the optical transmitting chip has a silicon substrate layer (1011), a silicon dioxide substrate layer (1010), a SiNx waveguide layer (1013), a silicon dioxide thin film layer (109), and a thin film lithium niobate thin film layer (108).

[0073] The optical transmitting chip integrates five SiNx grating couplers (101), five SiNx mode converters (102), five waveguide converters (103), four SiNx-thin-film lithium niobate electro-optic modulators (104), five SiNx-thin-film lithium niobate waveguides (105, 107), and one SiNx-thin-film lithium niobate CWDM wavelength division multiplexer (106). Among them, the SiNx grating couplers (101) and SiNx mode converters (102) are disposed in the SiNx waveguide layer (1013), and the other devices are converted into the integrated SiNx-thin-film lithium niobate waveguide layer through the waveguide converters (103).

[0074] The SiNx grating coupler (101) is used as the coupling interface with the external optical fiber.

[0075] The five SiNx mode converters (102) mentioned above are used to realize mode conversion and optical transmission between the SiNx grating coupler (101) and the waveguide converter (103).

[0076] The five waveguide converters (103) are used: one side is a SiNx waveguide and the other side is a SiNx thin film lithium niobate waveguide to realize optical transmission from the SiNx waveguide to the SiNx thin film lithium niobate waveguide.

[0077] The four SiNx-thin-film lithium niobate electro-optic modulators (104) are adopted: the SiNx-thin-film lithium niobate phase shifter (104-5) region has an inverted ridge structure, the SiNx waveguide layer (1013) is fully etched, and a silicon dioxide thin film layer (109) and a thin film lithium niobate layer (108) are covered on it. In order to achieve high-speed electro-optic modulation, the optical mode field is confined to the thin film lithium niobate material as much as possible through the SiNx-thin-film lithium niobate mode converter, and the secondary electro-optic coefficient γ33 of the thin film lithium niobate material is used for electro-optic modulation.

[0078] The four SiNx-thin-film lithium niobate electro-optic modulators (104) are used: the SiNx-thin-film lithium niobate mode converters (104-4) inside them are used to transmit the optical mode field inside SiNx to the inside of SiNx-thin-film lithium niobate, and most of the optical mode field is confined in the thin-film lithium niobate to achieve high-speed electro-optic modulation.

[0079] The four SiNx thin-film lithium niobate waveguides (105, 107) are respectively connected to the four input channels and one output channel of the SiNx thin-film lithium niobate CWDM wavelength division multiplexer (106). They can be straight waveguides, curved waveguides, or a combination of straight and curved waveguides.

[0080] The aforementioned SiNx thin-film lithium niobate CWDM wavelength division multiplexer (106) couples four optical signals into one output through multimode interference, meeting the requirements of CWDM transmission and realizing high-capacity information transmission.

[0081] Example 2

[0082] like Figure 5 As shown, the thin-film lithium niobate layer covers the electro-optic modulator region, the wavelength division multiplexer region, and part of the SiNx optical waveguide transmission region. Alternatively, the thin-film lithium niobate layer can cover only the phase shifter region of the electro-optic modulator. In this case, by redesigning the 104-4 mode converter in this design, the optical mode field can be converted from the SiNx waveguide to the SiNx-thin-film lithium niobate waveguide. The waveguide converter 103 can be replaced with a regular SiNx waveguide.

[0083] Example 3

[0084] like Figure 6 As shown, the thin-film lithium niobate covers the entire chip. Therefore, the grating coupler and the mode converter connected to the grating coupler in this design need to be redesigned to be SiNx-thin-film lithium niobate grating coupler and SiNx-thin-film lithium niobate mode converter. To achieve higher transmission efficiency for the grating coupler, a reflector can be added to the substrate or an opening can be made in the grating substrate to allow the optical fiber to enter from below.

[0085] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A CWDM optical transmitter chip comprising: SiNx grating coupler, SiNx mode spot converter, waveguide converter, SiNx-thin film lithium niobate electro-optical modulator, SiNx-thin film lithium niobate waveguide device, SiNx-thin film lithium niobate CWDM wavelength division multiplexer, characterized in that, SiNx material is deposited on the silicon dioxide substrate layer to form a SiNx waveguide layer, the thin film lithium niobate is directly bonded on the SiNx waveguide layer without etching, the SiNx waveguide layer is covered with a silicon dioxide film layer and a thin film lithium niobate layer in sequence, and the SiNx waveguide layer and the silicon dioxide layer and the thin film lithium niobate layer covering thereon form a SiNx-thin film lithium niobate waveguide device after etching; The SiNx grating coupler is a coupling interface of a CWDM optical transmitting chip and an optical fiber, the SiNx mode spot converter is used to transfer the optical mode field in the grating region to the optical waveguide for transmission, and the waveguide converter is used to transfer the optical mode field transmitted in the SiNx waveguide to the SiNx-thin film lithium niobate waveguide layer for transmission; the SiNx-thin film lithium niobate electro-optical modulator limits the optical mode field in the thin film lithium niobate material as much as possible through the SiNx mode spot converter, and uses the secondary electro-optical coefficient γ33 of the thin film lithium niobate material, so as to realize high-speed electro-optical modulation.

2. The CWDM optical transmitter chip of claim 1, wherein: The electrode structure of the SiNx-thin film lithium niobate electro-optical modulator adopts a push-pull structure, which can realize opposite phase shifts on the two arms of the SiNx-thin film lithium niobate electro-optical modulator at the same time.

3. The CWDM optical transmitter chip of claim 1, wherein: The SiNx-thin film lithium niobate CWDM wavelength division multiplexer is prepared by a single-step etching process.

4. The CWDM optical transmitter chip of claim 1, wherein: The SiNx grating coupler is arranged at the interface of the input optical fiber and the output optical fiber.

5. The CWDM optical transmitter chip of claim 1, wherein: The SiNx mode spot converter is a tapered optical waveguide.

6. The CWDM optical transmitter chip of claim 1, wherein: The optical wave is split by the SiNx-thin film lithium niobate multimode interference coupler and input into the two arms of the phase shifter for transmission, or the optical wave in the two arms of the phase shifter after transmission is combined and output.

7. The CWDM optical transmitter chip of claim 1, wherein: The SiNx is a common silicon nitride material or a silicon-rich silicon nitride or a nitrogen-rich silicon nitride material.

8. The CWDM optical transmitter chip of claim 1, wherein: The SiNx waveguide layer is formed by depositing SiNx material on the silicon dioxide substrate layer by plasma enhanced chemical vapor deposition (PECVD).

9. The CWDM optical transmitter chip of claim 1, wherein: The SiNx waveguide is left on the SiNx waveguide layer by a one-step full etching process.

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