A wide-bandwidth, low-insertion-loss Mach-Zehnder modulator based on thin-film lithium niobate

Abstract

The present invention discloses a high-efficiency, ultra-wideband, low-insertion-loss Mach-Zehnder modulator, which belongs to the fields of microwave photonics, optoelectronic modulators, and high-efficiency optoelectronic conversion. The present invention comprises a SiO2 substrate, on which are disposed dual-parallel Mach-Zehnder modulators, each with a pattern spot converter at either end. Based on the process technology of lithium niobate thin film modulators, the present invention optimizes the pattern spot conversion waveguide structure, achieves low insertion loss, and increases the modulation bandwidth through dual-parallel modulators. The present invention can effectively improve the linearity and operating bandwidth of microwave photonic links, meeting the widespread application requirements of broadband satellite communications and high-frequency RF front-ends in various fields.

Description

Technical Field

[0001] The present invention belongs to the fields of microwave photons, optoelectronic modulators, and high-efficiency optoelectronic conversion, and specifically relates to a large-bandwidth, low-insertion-loss Mach-Zehnder modulator based on thin-film lithium niobate. Background Art

[0002] RF front-ends, transmission links, and signal processing systems are core functional modules in radar, communications, and other systems. The growing demand for wide-bandwidth, multi-band, and reconfigurable signal processing in electronic information equipment poses new challenges to microwave technology. Traditional microwave technology suffers from numerous bottlenecks, including high-frequency losses, narrow bandwidth, low processing speeds, and inflexible modulation, making it difficult to meet the evolving needs of these equipment.

[0003] Microwave photonics combines the advantages of microwaves and light waves, and has the advantages of large bandwidth and high speed. It is expected to break through the bottleneck problem of traditional electrical domain and meet the needs of electronic information equipment. Microwave photonic technology mainly involves three types of devices: lasers, electro-optical modulators and detectors. The electro-optical modulator is a key unit for realizing electro-optical conversion. It refers to a device that modulates the electrical signal carrying information onto an optical carrier. The characteristic parameters of the optical carrier used to carry information mainly include intensity, phase, frequency and polarization state. It is a core component for realizing optical domain processing. The most typical modulator structure is the Mach-Zehnder modulator, which has the advantages of significant electro-optical effect, low waveguide loss, and mature process manufacturing. It can effectively improve transmission linearity, increase the bandwidth and operating frequency band of microwave photonic links, and can be used in ultra-wideband signal receiving systems in ultra-wideband radar, large-capacity communications, high-performance electronic countermeasures and other fields.

[0004] Currently, all mature modulators are based on traditional bulk lithium niobate processing, which is large in size and power consumption. Furthermore, research on this type of modulator is limited in China, resulting in a high reliance on imports. While leading international modulators can achieve modulation bandwidths exceeding 60 GHz, domestic modulators exceeding 20 GHz are still unavailable. The emergence of thin-film lithium niobate materials is expected to replace traditional bulk lithium niobate modulators, significantly reducing modulator size and power consumption and catching up with world-class standards.

[0005] In response to the rapid development of communication technology towards multi-band, large bandwidth, multi-beam, and flexible configuration, as well as the demand for satellite multi-functional integration technology, which is currently widely used in various fields of satellite communication bandwidth and high-frequency RF front-end requirements, we are researching modulators to achieve low insertion loss and waveguide structures, modulators to achieve high modulation bandwidth, lithium niobate thin film modulator process technology research, high-reliability packaging design and technology research, and other key technologies such as breakthroughs in the design of low-loss optical structures such as waveguides and couplers, modulator bandwidth theory and traveling wave electrode design, reliability and uniformity process manufacturing technology, optical waveguide mode conversion technology, and high-reliability packaging to achieve the ability to enhance the bandwidth and frequency band of traditional satellite communications.

[0006] Therefore, the research on high-efficiency, ultra-wideband, low-insertion-loss Mach-Zehnder modulators is of great value and significance for promoting the next generation of higher-capacity optical communication systems, faster data centers, and analog fiber-optic communication systems. It also plays an important role in promoting and facilitating the communication application industry related to high-speed modulators, and has high-value scientific significance. Summary of the Invention

[0007] In light of this, the present invention proposes a high-bandwidth, low-insertion-loss Mach-Zehnder modulator based on thin-film lithium niobate. This modulator features ultra-wideband operation, low insertion loss, and high modulation efficiency, and is widely applicable to multi-band, high-bandwidth, and high-capacity communication systems.

[0008] To achieve the above object, the technical solution of the present invention is:

[0009] A large-bandwidth, low-insertion-loss Mach-Zehnder modulator based on thin-film lithium niobate comprises a SiO2 substrate on which dual parallel Mach-Zehnder modulators are disposed, with a mode spot converter at each end of the dual parallel Mach-Zehnder modulator. The mode spot converter has a double-tapered structure, comprising a bottom inverted-tapered waveguide and a top inverted-tapered waveguide. The bottom inverted-tapered waveguide comprises a bottom rectangular section and a bottom conical section. The width of the bottom conical section is smaller than the width of the bottom rectangular section. A straight waveguide section extends from the end of the bottom conical section. The top inverted-tapered waveguide comprises a top rectangular section and a top conical section. The width of the top rectangular section is smaller than the width of the bottom conical section. The length of the top rectangular section is equal to the length of the bottom rectangular section. The width of the top conical section is equal to the width of the top rectangular section. The end of the top conical section is flat, and the end of the top conical section is located at a distance between 1 / 5 and 3 / 5 of the length of the bottom conical section.

[0010] The dual-parallel Mach-Zehnder modulator includes a waveguide network and five high-frequency electrodes. There is a gap between two adjacent high-frequency electrodes. There is a straight waveguide at each end of the waveguide network. The straight waveguide at one end of the waveguide network is divided into four waveguides, namely the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, through a two-stage one-to-two structure. The four waveguides pass through four gaps respectively and then form a straight waveguide at the other end of the waveguide network through a two-stage two-in-one structure. The first waveguide and the second waveguide are combined into the fifth waveguide, and the third waveguide and the fourth waveguide are combined into the sixth waveguide. A DC electrode is provided at each of the first waveguide, the third waveguide, and the fifth waveguide.

[0011] The spot size converters at both ends of the dual-parallel Mach-Zehnder modulator are mirror-symmetrical. The straight waveguide at each end of the dual-parallel Mach-Zehnder modulator is connected to the bottom rectangular section and the top rectangular section of the spot size converter at this end. The width of the straight waveguide of the dual-parallel Mach-Zehnder modulator is equal to the width of the bottom rectangular section of the spot size converter. The height of the straight waveguide of the dual-parallel Mach-Zehnder modulator is equal to the height of the double-taper structure of the spot size converter.

[0012] Furthermore, a silicon dioxide upper cladding layer is provided above the double-cone structure of the spot converter.

[0013] Furthermore, the waveguides in the dual parallel Mach-Zehnder modulator and the spot size converter are both made of lithium niobate.

[0014] The beneficial effects of the present invention are:

[0015] 1. The present invention realizes a high-efficiency, high-bandwidth pattern converter and a dual-parallel Mach-Zehnder modulator, thereby realizing a high-efficiency, ultra-wideband, low-insertion-loss Mach-Zehnder modulator.

[0016] 2. The present invention can be implemented by adopting a high-uniform processing technology and a high-reliability packaging method, and can achieve indicators of modulation bandwidth ≥ 60.83 GHz, insertion loss ≤ 4.6 dB, and extinction ratio ≥ 24 dB.

[0017] 3. The present invention can solve the problems of microwave photonic link linearity, ultra-wideband, low insertion loss, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of a high-efficiency and high-bandwidth spot converter in an embodiment of the present invention.

[0019] Figure 2 Schematic diagram of the structure of a dual parallel Mach-Zehnder modulator in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] A large-bandwidth, low-insertion-loss Mach-Zehnder modulator based on thin-film lithium niobate comprises a SiO2 substrate on which a dual-parallel Mach-Zehnder modulator is arranged. Two ends of the dual-parallel Mach-Zehnder modulator are each provided with a high-efficiency, high-bandwidth pattern converter.

[0022] like Figure 1As shown, the high-efficiency, high-bandwidth spot converter uses a dual-tapered spot converter, which mainly includes a top inverted tapered waveguide and a bottom inverted tapered waveguide. The spot converter has a dual-tapered structure, including a bottom inverted tapered waveguide LN1 and a top inverted tapered waveguide LN2. The bottom inverted tapered waveguide includes a bottom rectangular section and a bottom tapered section. The width of the bottom tapered section is smaller than the width of the bottom rectangular section. A straight waveguide section extends from the end of the bottom tapered section. The top inverted tapered waveguide includes a top rectangular section and a top tapered section. The width of the top rectangular section is smaller than the width of the bottom tapered section. The length of the top rectangular section is equal to the length of the bottom rectangular section. The width of the top tapered section is equal to the width of the top rectangular section. The top tapered section has a flat end, and the end of the top tapered section is located between 1 / 5 and 3 / 5 of the length of the bottom tapered section.

[0023] In addition, a silicon dioxide upper cladding layer is provided on the double-tapered structure of the spot converter.

[0024] In this high-efficiency, high-bandwidth spot converter, the top and bottom inverted-tapered waveguides, along with the silica upper cladding structure above, effectively confine light waves and prevent them from dispersing in the air. To guide light waves from the optical fiber into the bottom inverted-tapered waveguide, a straight waveguide with a width of W4 extends from the tip of the bottom inverted-tapered waveguide. This also prevents damage to the tip of the bottom inverted-tapered waveguide during the actual process, which can occur during polishing.

[0025] like Figure 2 As shown, the dual-parallel Mach-Zehnder modulator includes a waveguide network and five high-frequency electrodes (ground electrodes G and signal electrodes S arranged alternately). There is a gap between two adjacent high-frequency electrodes. There is a straight waveguide at each end of the waveguide network. The straight waveguide at one end of the waveguide network is divided into four waveguides, namely the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, through a two-stage one-to-two structure. The four waveguides pass through four gaps respectively and then form a straight waveguide at the other end of the waveguide network through a two-stage two-in-one structure. The first waveguide and the second waveguide are combined into the fifth waveguide, and the third waveguide and the fourth waveguide are combined into the sixth waveguide. A DC electrode DC1, DC2, and DC3 are provided at the first waveguide, the third waveguide, and the fifth waveguide.

[0026] The dual-parallel Mach-Zehnder modulator (MZM1) and MZM2 are intensity modulators with identical performance. The modulating signals and DC bias applied to their upper and lower arms have the same amplitude but opposite phases. These signals are embedded in the two arms of the main modulator, MZM3.

[0027] In a high-efficiency ultra-wideband low insertion loss Mach-Zehnder modulator, the spot size converters at both ends of the dual-parallel Mach-Zehnder modulator are mirror-symmetrical, the straight waveguide at each end of the dual-parallel Mach-Zehnder modulator is connected to the bottom rectangular segment and the top rectangular segment of the spot size converter at the local end, the width of the straight waveguide of the dual-parallel Mach-Zehnder modulator is equal to the width of the bottom rectangular segment of the spot size converter, the height of the straight waveguide of the dual-parallel Mach-Zehnder modulator is equal to the height of the double-taper structure of the spot size converter, and the waveguides in the dual-parallel Mach-Zehnder modulator and the spot size converter are both made of lithium niobate.

[0028] The working principle of the present invention is as follows:

[0029] In a bi-tapered mode spot converter, light waves initially propagate through a ridged single-mode waveguide. As the waveguide narrows, its ability to confine the light wave weakens, and the mode field area gradually expands. Simultaneously, the waveguide is confined by the cladding, preventing it from dispersing into the air. As the waveguide width shrinks with transmission distance, its mode field gradually expands. The small-scale mode field in the ridged single-mode waveguide gradually diffuses into the cladding through the double-layer inverted tapered waveguide, transforming into a large-scale mode field.

[0030] In a thin-film lithium niobate Mach-Zehnder modulator, the optical signal output by the biconical spot size converter enters the modulator and is then split into two equal-power paths via a beam splitter waveguide and injected into MZM1 and MZM2, where intensity modulation is performed on each of the two sub-modulators. Furthermore, adjusting the DC bias on MZM3 introduces a phase difference into the signals on the two arms (applying a DC bias to the modulation electrode on one arm of the main modulator introduces a phase shift, determined by the DC bias, into the intensity-modulated optical signal on that arm). Finally, the two signals are coupled out of the modulated optical signals on the two arms via the beam splitter waveguide.

[0031] The functional components are assembled in a certain order in the photolithography, and the principle of assembling electrical components first and then optical components is adopted. A fully functional modulator module is constructed through gradient solder, auxiliary fixtures and metal brackets.

[0032] In summary, this invention, based on lithium niobate thin-film modulator technology, optimizes the spot conversion waveguide structure, achieves low insertion loss, and increases modulation bandwidth through dual parallel modulators. This invention achieves modulation bandwidth ≥ 60.83 GHz, insertion loss ≤ 4.6 dB, and extinction ratio ≥ 24 dB. This effectively improves the linearity and operating bandwidth of microwave photonic links, meeting the widespread application needs of broadband satellite communications and high-frequency RF front-ends across various fields.

[0033] The above description is only a specific implementation of the present invention in the embodiment, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with the field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A high-bandwidth, low-insertion-loss Mach-Zehnder modulator based on thin-film lithium niobate, comprising a SiO2 substrate, characterized in that: A dual-parallel Mach-Zehnder modulator is provided on a SiO2 substrate, with a mode spot converter at each end of the dual-parallel Mach-Zehnder modulator; the mode spot converter is a dual-taper structure, comprising a bottom inverted-taper waveguide and a top inverted-taper waveguide, the bottom inverted-taper waveguide comprising a bottom rectangular section and a bottom conical section, the width of the bottom conical section being smaller than the width of the bottom rectangular section, a straight waveguide extending from the end of the bottom conical section, the top inverted-taper waveguide comprising a top rectangular section and a top conical section, the width of the top rectangular section being smaller than the width of the bottom conical section, the length of the top rectangular section being equal to the length of the bottom rectangular section, the width of the top conical section being equal to the width of the top rectangular section, the end of the top conical section being flat, and the end of the top conical section being located at a position between 1 / 5 and 3 / 5 of the length of the bottom conical section; The dual-parallel Mach-Zehnder modulator includes a waveguide network and five high-frequency electrodes. There is a gap between two adjacent high-frequency electrodes. There is a straight waveguide at each end of the waveguide network. The straight waveguide at one end of the waveguide network is divided into four waveguides, namely the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide, through a two-stage one-to-two structure. The four waveguides pass through four gaps respectively and then form a straight waveguide at the other end of the waveguide network through a two-stage two-in-one structure. The first waveguide and the second waveguide are combined into the fifth waveguide, and the third waveguide and the fourth waveguide are combined into the sixth waveguide. A DC electrode is provided at each of the first waveguide, the third waveguide, and the fifth waveguide. The spot size converters at both ends of the dual-parallel Mach-Zehnder modulator are mirror-symmetrical. The straight waveguide at each end of the dual-parallel Mach-Zehnder modulator is connected to the bottom rectangular section and the top rectangular section of the spot size converter at this end. The width of the straight waveguide of the dual-parallel Mach-Zehnder modulator is equal to the width of the bottom rectangular section of the spot size converter. The height of the straight waveguide of the dual-parallel Mach-Zehnder modulator is equal to the height of the double-taper structure of the spot size converter.

2. The thin-film lithium niobate-based high-bandwidth, low-insertion-loss Mach-Zehnder modulator according to claim 1, characterized in that: The spot converter also has a silicon dioxide upper cladding layer above the double-tapered structure.

3. The high-bandwidth, low-insertion-loss Mach-Zehnder modulator based on thin-film lithium niobate according to claim 1, characterized in that: The waveguides in the dual parallel Mach-Zehnder modulator and the spot size converter are both made of lithium niobate.

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