DP-PAMx film lithium niobate-based photon integrated modulator

Abstract

The invention discloses an integrated optical modulator for realizing a DP-PAMx (polarization multiplexing-x-order optical pulse amplitude modulation, x = 2, 4, 8, 16) modulation format based on a TFLN (thin film lithium niobate) photon integration technology, which comprises a light beam splitter based on a thin film lithium niobate base, a Mach-Zehnder structured light intensity modulator, a heating light phase shifter and a light polarization rotation beam combiner, and a matched high-speed modulation circuit and the like. Advanced light modulation units such as optical power beam splitting, polarization rotation beam combination, multi-order light intensity modulation, heating of an optical phase shifter and additional arrangement of a high-speed modulation circuit are achieved through the thin film lithium niobate photon integration technology, and the functional units are integrated into a prototype chip through the LNOI (thin film lithium niobate on insulator) wafer technology and a process processing platform. And optical and electrical function units are integrated through a high-speed packaging technology and an electromagnetic compatibility design, so that the ultra-high-speed optical modulator module of the next-generation optical communication system of the data center, which meets the requirements of single-wave (or single-path) 400Gb / s and above speed, is finally realized.

Description

Technical Field

[0001] The present invention relates to the field of optical communication and photon information processing, and in particular to a thin-film lithium niobate-based electro-optic modulator used for loading an electrical signal to be transmitted onto an optical carrier in optical communication. Background Art

[0002] Optical communication is a communication method that uses light waves as information carriers, and mainly uses optical fiber as a transmission medium to achieve information transmission between users. Compared with the traditional electrical signal transmission mode using copper cables, optical communication has a larger transmission bandwidth and transmission capacity, lower transmission loss, stronger anti-electromagnetic interference ability and higher transmission quality.

[0003] Data center optical communication technology is a key technology that supports high-speed information transmission in modern data centers. The internal network of data centers is also undergoing a transformation from copper cables to optical cables. In recent decades, with the rapid development of Internet big data and cloud computing, the number and scale of data centers have continued to grow, and the demand for efficient, high-speed and reliable data transmission has also increased. In particular, the current new round of scientific and technological revolution and industrial transformation is accelerating, and the emergence of AI large models represented by ChatGPT has accelerated digital technology into the era of artificial intelligence.

[0004] The explosion of AI big models has driven the continuous development of new computing infrastructure construction, and traditional data centers have accelerated their transformation into intelligent computing centers. This has put forward higher requirements for high-speed data transmission within data centers, and the market demand for higher network bandwidth and capacity has increased rapidly. Considering the technical advantages, economy and compatibility, artificial intelligence cluster data centers are upgrading from 400G optical modules to 800G optical modules. At the same time, the optical modulator technology for high-speed optical modules has also moved from single-channel (or single-wave) 100Gb / s to single-channel (or single-wave) 200Gb / s, and the next-generation ultra-high-speed single-channel (or single-wave) 400Gb / s optical modulator technology has also entered the industry's research and development vision.

[0005] At present, the optical modules used in the internal optical network of the data center mainly adopt the PAMx (x=4) modulation mode. When the modulation rate reaches 200Gb / s per channel (or single wave), the modulation baud rate is required to reach more than 100GBaud, and the 3dB bandwidth supported by the modulator is required to reach more than 50GHz; if the modulation rate is further upgraded to 400Gb / s per channel (or single wave), if the PAMx (x=4) modulation mode is continued to be used, the 3dB bandwidth requirement of the modulator needs to reach more than 100GHz, which is an insurmountable limit for the DML and VCSEL that currently use direct modulation. Therefore, it is urgent to find new material systems and modulation methods to achieve breakthroughs in modulator technology, meet the high bandwidth requirements of artificial intelligence cluster data centers, and achieve industrial chain economy and technical backward compatibility.

[0006] At present, in backbone networks and core networks, single-wavelength 400Gb / s coherent optical communication systems have begun to be commercialized and deployed on a large scale, and the optical system mainly adopts DP-IQ modulation. Because the DP-IQ modulation mode of coherent optical communication systems requires high-order complex modulation formats (DP-QPSK, DP-16QAM, etc.) and powerful DSP digital signal processing technology, its implementation cost and power consumption far exceed the maximum tolerable value of the current internal optical network of the data center. Therefore, the coherent optical modulation technology of the traditional backbone network and core network cannot be directly transplanted to the internal optical network of the data center.

[0007] As a new type of photonic integrated material, thin-film lithium niobate is known as optical silicon. It has many superior properties and is particularly suitable for the new generation of photonic integrated chips and optical communication systems. It supports a variety of new photonic signal processing and optical modulation modes. Its main advantages are high electro-optical coefficient, large bandwidth, high linearity, low optical loss, low driving voltage, small size and high performance. Modulators and photonic integrated chips based on thin-film lithium niobate materials and processes will play an increasingly important role in ultra-high-speed trunk optical communication networks, ultra-high-speed data centers, artificial intelligence, supercomputing centers, submarine optical networks and other fields. Summary of the invention

[0008] The purpose of the present invention is to provide a DP-PAMx optical modulator based on a Mach-Zehnder structure, which makes it very suitable for realizing the various optical functional units of a single-channel (or single-wavelength) 400Gb / s and above advanced modulation format optical modulator, and integrates electrical control and data transmission units to form an optical modulator integrated module.

[0009] To achieve the above object, the present invention proposes a waveguide structure modulator based on a thin film lithium niobate-based material, which realizes PAMx (x=2, 4, 8, 16) modulation of an optical carrier in two perpendicular polarization states. The basic modulation unit of the thin film lithium niobate-based modulator includes: 1) An optical beam splitter with a thin-film lithium niobate-based micro-nano waveguide structure, used to split an input optical carrier beam into two independent optical carrier beams for output; 2) The intensity modulator of the thin-film lithium niobate-based Mach-Zehnder interferometer structure and the matching high-speed modulation circuit are used to load the electrical signal onto the optical carrier and perform amplitude modulation on two independent optical carriers respectively; 3) Heated phase shifters applied to the two arms of the thin-film lithium niobate-based Mach-Zehnder interferometer to achieve precise adjustment of the operating phase point of the modulator unit; 4) A polarization rotation combiner based on a thin-film lithium niobate-based micro-nano waveguide structure realizes polarization rotation and beam combining of two modulated optical signals. The polarization states of the two optical beams are first made perpendicular to each other, and then the two optical beams are coupled to an optical carrier output.

[0010] The light output by the laser is first coupled into a thin-film lithium niobate-based micro-nano waveguide beam splitter, which is used to split the input optical carrier into two independent optical carriers and make the output power of the two beams roughly equal. The two independent light beams enter two Mach-Zehnder structure optical intensity modulators respectively. When the light beam passes through the thin-film lithium niobate-based waveguide arm of this intensity modulator, if the electrical signal to be transmitted is loaded at the RF input port, then these electrical data signals can amplitude modulate the input optical carrier, and the modulation rate of the modulator can reach 200Gb / s or above through a specially designed high-speed modulation circuit that matches the thin-film lithium niobate-based modulator. This is the modulation process of the optical carrier by the electrical data signal of one of the light beams, and the data modulation process of the other light beam is similar. After modulation, the two independent optical signals are then passed through a polarization rotation combiner to adjust the polarization states of the two light beams to be perpendicular to each other, and then combined into one optical output. At the same time, the output light can be coupled to an optical fiber or other optical transmission medium for transmission. At this time, the output single-channel (or single-wave) optical signal rate reaches 400Gb / s or above.

[0011] The present invention also proposes a preparation method for a DP-PAMx thin-film lithium niobate-based photonic integrated modulator, which integrates the functional unit into a prototype chip using an LNOI (thin-film lithium niobate on insulator) design and manufacturing process platform, and combines optical and electrical functional units through high-speed packaging technology and electromagnetic compatibility design. The optical and electrical functional units are processed using a photolithography process compatible with a CMOS process, and the geometric structure of the modulator waveguide is first depicted on a photoresist layer using exposure and development, and then the pattern on the photomask is transferred to an LNOI wafer substrate through an etching process.

[0012] It can be seen from the above technical solution that the present invention has the following beneficial effects: 1. The most significant innovation of this invention is to use thin-film lithium niobate-based materials and process platforms to modulate the electrical signal data of two independent optical carriers, and then realize the next generation of single-channel (or single-wave) 400Gb / s and above photonic integrated modulators through optical polarization multiplexing. This new modulation method not only improves the capacity of data center optical communication systems, but also effectively reduces data processing delays, and is expected to reduce the power consumption, volume and cost of next-generation high-speed optical modules, meeting the optical communication needs of future artificial intelligence cluster data centers; 2. The present invention realizes high-performance integrated optical modulation chip through DP-PAMx modulation mode, so that the modulated electrical signal format remains compatible with the traditional PAM modulation format, realizes the reuse of industrial chain technology resources, and promotes the economy and compatibility of data center optical communication system deployment; 3. The use of photolithography compatible with CMOS technology reduces the cost and complexity of the manufacturing process. This step uses exposure and development to depict the geometric structure on the photoresist layer, and then transfers the pattern on the photomask to the LNOI wafer through an etching process. The LNOI wafer mentioned here contains not only a thin-film lithium niobate layer, but also other metal layers and dielectric layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings, wherein: Figure 1 It is a schematic diagram of the structure of the DP-PAMx modulator based on thin-film lithium niobate-based materials provided by the present invention; Figure 2 It is a schematic diagram of the optical power transfer function curve based on the Mach-Zehnder structured light intensity modulator. DETAILED DESCRIPTION

[0014] Figure 1 This is a schematic diagram of the structure of the DP-PAMx modulator based on thin-film lithium niobate-based materials provided by the present invention. As shown in the figure, the basic unit of the modulator mainly includes: an optical beam splitter 1, a Mach-Zehnder structure light intensity modulator 2 (2-a, 2-b), an optical polarization rotation combiner 3, a heated optical phase shifter 4 (4-a, 4-b, 4-c, 4-d), and an external modulated electric field signal 5 (5-a, 5-b, 5-c, 5-d, 5-e, 5-f, 5-g, 5-h).

[0015] The optical beam splitter 1 is used to split the input optical carrier into two independent optical carriers X and Y, which are then input into two Mach-Zehnder structure optical intensity modulators 2-a and 2-b respectively.

[0016] The two Mach-Zehnder structure optical intensity modulators 2-a and 2-b are used to modulate the intensity of two independent optical carriers. When a voltage is applied to one arm of the thin-film lithium niobate-based Mach-Zehnder interferometer, the refractive index in the waveguide of the arm will change, so that when the light propagates in it, an additional phase shift caused by the applied voltage will occur. When the two arms form a Mach-Zehnder interferometer structure, the output light intensity will change with the applied voltage.

[0017] The principle of amplitude modulation using the Mach-Zehnder interferometer structure can be used Figure 2 The optical power transfer function curve of the Mach-Zehnder structure intensity modulator shown in FIG. 1 is used to illustrate. From this curve, it can be seen that when different bias voltages (given by the external modulated electric field signal 5) are applied to the modulation arm of the Mach-Zehnder structure intensity modulator, its output optical power will change. When the external bias voltage is zero, the output optical power is maximum, and when the external bias voltage is Vπ, the output optical power is minimum, that is, the optical carrier amplitude changes with the external bias voltage. In this way, when the high and low levels of the input electrical signal change between 0 and Vπ, the amplitude modulation of the light wave is achieved. By encoding the external modulated electric field signal 5 (5-a, 5-b, 5-c, 5-d, 5-e, 5-f, 5-g, 5-h), optical pulse amplitude modulation (PAMx, x=2, 4, 8, 16) can be achieved.

[0018] The heated optical phase shifters 4 (4-a, 4-b, 4-c, 4-d) applied to the modulation arms of the Mach-Zehnder structure intensity modulators 2-a and 2-b are used to achieve fine-tuning of the working phase points of the Mach-Zehnder structure intensity modulators 2-a and 2-b so that the modulator as a whole can achieve the best modulation performance.

[0019] The modulated X-beam and Y-beam optical signals are input to the optical polarization rotation combiner 3. The main function of the optical polarization rotation combiner 3 is to first adjust the polarization states of the two light beams so that the polarization states of the two light beams are perpendicular to each other, and then combine the two light beams into one light beam, and couple this light beam into an optical fiber or other optical transmission medium, thereby realizing single-channel (or single-wave) polarization multiplexing-optical pulse intensity modulation (DP-PAMx, x=2, 4, 8, 16).

[0020] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A thin-film lithium niobate-based photonic integrated modulator based on the DP-PAMx modulation mode, wherein the basic modulation unit of the modulator comprises: 1) An optical beam splitter based on a thin-film lithium niobate-based micro-nano waveguide structure, which is used to split the input optical carrier into two independent optical carrier outputs; 2) Based on the Mach-Zehnder structure intensity modulator of thin-film lithium niobate-based micro-nano waveguide structure and the matching high-speed modulation circuit, the electrical signal is loaded onto the optical carrier and the amplitude of the optical carrier is modulated; 3) A thermal effect optical phase shifter based on a thin film lithium niobate-based micro-nano waveguide structure is used to fine-tune the working phase point of the two modulation arms of the Mach-Zehnder structure intensity modulator; 4) A polarization rotation combiner based on a thin-film lithium niobate-based micro-nano waveguide structure is used to rotate the polarization states of two independent optical signals to be perpendicular to each other and couple the two optical signals into one optical carrier output.

2. The DP-PAMx thin film lithium niobate based optical modulator according to claim 1, characterized in that: At the input end, the optical beam splitter based on the thin-film lithium niobate-based micro-nano waveguide structure splits an input light beam into two light beams of approximately equal power; at the output end, the polarization rotation beam combiner based on the thin-film lithium niobate-based micro-nano waveguide structure can adjust the polarization states of the two light beams so that the polarization states of the two light beams are perpendicular to each other, and then combine the two beams of light with perpendicular polarization states into one.

3. The DP-PAMx thin-film lithium niobate-based optical modulator according to claim 2, characterized in that: Two intensity modulators of Mach-Zehnder interferometer structure are respectively formed in two perpendicular polarization states.

4. The DP-PAMx thin-film lithium niobate-based optical modulator according to claim 3, characterized in that: The multiple electric field signals applied to the arms of the Mach-Zehnder structure intensity modulator can perform multi-order pulse amplitude modulation on the optical carrier.

5. The DP-PAMx thin-film lithium niobate-based optical modulator according to claim 3, characterized in that: The phase shifter based on the thermal effect of thin film lithium niobate based micro-nano waveguide structure fine-tunes the working phase point of the two arms of the Mach-Zehnder structure intensity modulator.

6. The DP-PAMx thin-film lithium niobate-based optical modulator according to claim 1, characterized in that: Based on this basic modulation unit, photonic integration technology can be used for series and parallel connection to achieve optical modulator chips and modules with more complex modulation formats and higher communication capacity.

7. According to the preparation method of the DP-PAMx thin-film lithium niobate-based optical modulator according to claim 1, the functional unit is integrated into a prototype chip using a CMOS compatible process platform, and the optical and electrical functional units are combined through high-speed packaging technology and electromagnetic compatibility design, and processed using a photolithography process. First, a geometric structure is engraved on a photoresist layer by exposure and development, and then the pattern on the photomask is transferred to a wafer substrate by an etching process.

8. The DP-PAMx optical modulator according to claim 1, wherein implementation methods include but are not limited to thin-film lithium niobate-based wafers and photonic integrated platforms, and also include silicon-based, indium phosphide-based, and other wafers and photonic integrated platforms that can implement the modulation method described in the present invention.

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