Transmitting device, communication system and communication method for optical communication transmission

Abstract

The invention discloses a transmitting device for optical communication transmission, and the device comprises a modulator which generates four-level amplitude modulation PAM4 signals in X and Y polarization states; the marker tone provider is used for respectively embedding low-frequency marker tone signals with preset frequencies into the four-level amplitude modulation PAM4 signals in the X and Y polarization states; and the beam combiner is used for carrying out beam combination on the four-level amplitude modulation PAM4 signals in the X polarization state and the Y polarization state which are respectively embedded into the low-frequency marking sound signals, and introducing a path of synthesized DP-PAM4 signals into a transmission optical fiber. According to the invention, the PAM4 signal is subjected to polarization multiplexing without depending on a phase recovery technology, and the requirement on a receiving side of optical communication transmission is greatly reduced through an IM-DD intensity modulation mode and polarization multiplexing transmission. Polarization state self-identification is achieved by combining low-frequency marks, polarization state identification and separation are achieved by monitoring mark signal differences, a complex polarization tracking algorithm is replaced, and a high-cost modulator and a local oscillator needed by high-order coherent modulation are avoided.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and more specifically, to a transmitting device, a communication system, and a communication method for optical communication transmission. Background Art

[0002] With the rapid development of 5G, cloud computing, artificial intelligence (AI), and the Internet of Things (IoT), global data traffic is experiencing explosive growth, placing higher demands on optical communication networks with high bandwidth, low latency, and low power consumption. Current single-channel communication systems based on PAM4 (Pulse Amplitude Modulation, 4-level) technology are limited by technical bottlenecks such as materials and signal noise, and are gradually unable to meet the demand for 3.2T and even higher channel capacities. Consequently, the demand for more efficient modulation methods will greatly meet the demand for optical communication equipment with low power consumption, high speed, and high switching capacity.

[0003] Traditional single-polarization IM-DD (Intensity Modulation-Direct Detection) systems struggle to break through the single-wavelength 100G rate limit, while coherent optical communication systems are costly and complex. Furthermore, polarization mode dispersion (PMD) and four-wave mixing (FWM) effects significantly degrade the performance of multi-wavelength systems. Summary of the Invention

[0004] In response to at least one defect or improvement need in the prior art, the present application provides a transmitting device, a communication system, and a communication method for optical communication transmission, so as to solve the current problem of too low single-channel transmission rate, reduce the hardware requirements on the receiving side, and maximize technical and economic benefits.

[0005] To achieve the above objectives, in a first aspect, the present application provides a transmitting device for optical communication transmission, comprising:

[0006] Modulator, generating a four-level amplitude modulated PAM4 signal in X and Y polarization states;

[0007] A marker tone provider, which embeds a low-frequency marker tone signal of a preset frequency into the generated four-level amplitude modulation PAM4 signal of the X and Y polarization states;

[0008] The combiner combines the four-level amplitude modulated PAM4 signals in the X and Y polarization states of the low-frequency marker tone signals embedded with the preset frequency, and introduces the synthesized DP-PAM4 signal into the transmission optical fiber.

[0009] Furthermore, the modulator is a Mach-Zehnder modulator.

[0010] Furthermore, the attribute information of the low-frequency marker tone signal of the preset frequency is 1 MHz±Δf, the amplitude accounts for 2%, and the frequency is lower than the lower limit of the signal bandwidth of 100 kHz.

[0011] Furthermore, the modulator includes multiple polarization branches, and each polarization branch includes two corresponding sub-modulators;

[0012] Each polarization branch performs PAM4 signal modulation on the two polarized lights received, generating corresponding four-level amplitude modulated PAM4 signals in the X and Y polarization states.

[0013] The modulator is configured in the form of a double-electrode nested Mach-Zehnder modulator.

[0014] Furthermore, the sub-modulator is an external modulator.

[0015] Furthermore, each sub-modulator is correspondingly provided with a digital-to-analog converter and a differential amplifier;

[0016] The digital-to-analog converter performs digital-to-analog conversion on the received PAM4 driving electrical signal and outputs it to the differential amplifier, which performs differential amplification and outputs it to the corresponding sub-modulator to provide it with a driving voltage with sufficient swing amplitude.

[0017] In a second aspect, the present application provides a communication system for optical communication transmission, comprising:

[0018] The transmitting device according to any of the preceding items, configured to transmit the synthesized DP-PAM4 signal;

[0019] Transmission optical fiber, used to transmit the synthesized DP-PAM4 signal;

[0020] The receiving device is used to identify and receive the synthesized DP-PAM4 signal.

[0021] In a third aspect, the present application provides a communication method, comprising:

[0022] Generates four-level amplitude modulation PAM4 signals in X and Y polarization states;

[0023] Embedding low-frequency marker tone signals of preset frequencies into the generated four-level amplitude modulation PAM4 signals of the X and Y polarization states respectively;

[0024] Furthermore, a Mach-Zehnder modulator is used to generate a four-level amplitude modulated PAM4 signal in X and Y polarization states.

[0025] The four-level amplitude modulated PAM4 signals in the X and Y polarization states, each embedded with a low-frequency marker tone signal at a preset frequency, are combined, and the synthesized DP-PAM4 signal is introduced into the transmission optical fiber.

[0026] Furthermore, the attribute information of the low-frequency marker tone signal of the preset frequency is 1 MHz±Δf, the amplitude accounts for 2%, and the frequency is lower than the lower limit of the signal bandwidth of 100 kHz.

[0027] In general, the above technical solutions conceived by this application can achieve the following beneficial effects compared with the existing technology:

[0028] This application introduces optical polarization multiplexing PAM4 signal transmission into the optical communication transmission system, and doubles the single-channel transmission rate without increasing the demand for transmission hardware equipment, achieving better transmission performance. It also realizes self-identification of polarization state through low-frequency marking, and realizes identification and separation of polarization state by monitoring the difference of mark signal, avoiding complex digital signal synchronization algorithm. This application multiplexes polarization PAM4 technology without relying on phase recovery technology. Through IM-DD intensity modulation and polarization multiplexing transmission, the requirements for the receiving side of optical communication transmission are greatly reduced, replacing complex polarization tracking algorithms, and avoiding the use of high-cost modulators and local oscillators required for high-order coherent modulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 Schematic diagram of orthogonal polarization signal transmission at the transmitter end of the DP-PAM4 system provided in an embodiment of the present application;

[0031] Figure 2 A schematic diagram of adding a low-frequency marker tone to a transmitter to identify X and Y polarizations in a separate receiver according to an embodiment of the present application;

[0032] Figure 3 This is a schematic diagram of the structure of the DP-PAM4 signal transmitter under silicon photonic integrated modulation provided in an embodiment of the present application;

[0033] Figure 4 This is a schematic diagram of the structure of the DP-PAM4 signal transmitter under electro-absorption direct drive modulation provided in an embodiment of the present application;

[0034] Figure 5This is a schematic diagram of the structure of an 800G LR4 single-channel DP-PAM4 signal transmitter provided in an embodiment of the present application;

[0035] English translation of the attached figure:

[0036] 1. Modulator: modulator;

[0037] 2. Pol.Rotator: Polarization Rotator, polarization rotation device;

[0038] 3. PBC: Polarization Beam Couple, polarization beam combiner;

[0039] 4. Tone: marked tone;

[0040] 5. Integrated Muxes: integrated multiplexers;

[0041] 6. EML: Electro-Absorption Modulated Laser; EML modulation is an externally modulated laser technology that modulates the output of the laser through an electro-absorption modulator (EAM) to achieve intensity changes in the optical signal;

[0042] 7. FSO Muxes: Free Space Optics Muxes, multiplexing of free space optical signals;

[0043] 8. DAC CH: Channel of the digital-to-analog converter (DAC), that is, the independent unit in the DAC module used to output analog signals;

[0044] 9. RF Amp: radio frequency amplifier;

[0045] 10. MZM: Mach-Zehnder Modulator, a device that splits the input light into two equal signals that enter the two optical branches of the modulator respectively;

[0046] 11. EDFA: Erbium-doped fiber amplifier, is an optical amplifier that directly amplifies optical signals by doping optical fibers with erbium ions (Er3+). Its core principle is based on the stimulated emission effect.

[0047] 12. SMF: Single-Mode Fiber;

[0048] 13. Laser: laser;

[0049] 14. TE: Transverse electric mode, which means the direction of the electric field is perpendicular to the propagation direction;

[0050] 15. TM: transverse magnetic mode, which means the direction of the magnetic field is perpendicular to the propagation direction;

[0051] TE and TM can be collectively referred to as LP, or linear polarization mode. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of explaining this application and are not intended to limit this application. In addition, the technical features involved in the various embodiments of this application described below may be combined with each other as long as they do not conflict with each other.

[0053] The terms "including" or "having" and any variations thereof in the specification, claims, or drawings of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units inherent to the process, method, product, or apparatus.

[0054] As described in the background technology section of the specification, the current single-channel communication system based on PAM4 (Pulse Amplitude Modulation, 4-level) four-level amplitude modulation technology is limited by technical bottlenecks such as materials and signal noise, and is gradually unable to meet the needs of 3.2T or even higher channel capacity. The traditional single-polarization IM-DD (Intensity Modulation-Direct Detection) intensity modulation direct detection system is difficult to break through the single-wavelength 100G rate limit, and the coherent optical communication system is costly and complex. In addition, the polarization mode dispersion (Polarization Mode Dispersion) and four-wave mixing (FWM) effects will significantly reduce the performance of the multi-wavelength system. In view of this, the present application provides a transmitting device, a communication system and a communication method for optical communication transmission, which are used to solve the current problem of too low single-channel transmission rate, reduce the hardware requirements on the receiving side, and maximize technical and economic benefits.

[0055] refer to Figure 1 and Figure 2 An embodiment of the present application provides a transmitting device for optical communication transmission, which may include components such as a laser, a modulator, a marker tone provider, and a combiner.

[0056] The modulator generates a four-level amplitude modulated PAM4 signal in X and Y polarization states. The schematic diagram of orthogonal polarization signal transmission at the transmitter (transmitter) of the DP-PAM4 system is shown in the figure. Figure 1 Specifically, the transmitting device uses a highly integrated dual-polarization silicon photonic integrated Mach-Zehnder modulator (MZM) to generate four-level amplitude modulated PAM4 signals in X and Y polarization states. The two orthogonal polarized lights, X and Y, pass through a polarization beam splitter rotator (PBSR, which is a device that integrates the functions of a polarization beam splitter (PBS) and a polarization rotator (PR). It can achieve low transmission loss and high extinction ratio performance over a wide spectral range. The main function of the PBSR is to separate two orthogonally polarized optical signals at the input port and output them to different ports, while performing a 90° polarization rotation on one of the input signals.) The polarization rotation device (Pol.Rotator) rotates the TE polarization in the optical fiber into TM polarization and outputs it in split beams. It is then combined into a DP-PAM4 signal through a polarization beam combiner (PBC) and sent to the transmission optical fiber for transmission. Theoretically, the power of the two polarization states is basically equal, and the power after combining is the sum of the power of the X polarization state and the Y polarization state. DP-PAM4 relies on changes in light intensity for direct detection, without the need for phase information, thus simplifying the design of the receiving end (receiving device); traditional DP-QPSK (Dual-Polarization Quadrature Phase Shift Keying, which is a modulation technology mainly used in optical communications. DP-QPSK combines polarization multiplexing (PM) and quadrature phase shift keying (QPSK) technologies. It uses two polarization states (X and Y polarization waves) to carry different signals, and each polarization state uses QPSK modulation to achieve higher data transmission rates.) requires capturing the phase and amplitude of the light field, and requires a complex coherent receiver for precise phase recovery and carrier synchronization.

[0057] The marker tone provider embeds a low-frequency marker tone signal of a preset frequency into the generated four-level amplitude modulation PAM4 signal of the X and Y polarization states. The transmitter adds a low-frequency marker tone signal to identify the X and Y polarization signals in the separate receiving device. Figure 2 Specifically, marker tones can simplify polarization tracking and demultiplexing, such as Figure 2As shown, a low-frequency marker tone (1 MHz ± Δf) is embedded in the X / Y polarization signals of the transmitter. The amplitude accounts for 2% and the frequency is below the lower limit of the signal bandwidth (100 kHz). The receiver can directly identify the X / Y polarization signals by detecting the amplitude and frequency differences of the low-frequency marker tones. Dynamic tracking of the marker tones provides real-time feedback on the polarization rotation state (such as polarization changes caused by fiber bending or temperature changes), driving phase modulators (such as silicon photonic phase shifters) to compensate for polarization drift. Compared to traditional DP systems that require complex algorithms for polarization signal separation and phase recovery, marker tones provide a priori information, simplifying the demultiplexing process. DP-PAM4 (Dual-Polarization Pulse Amplitude Modulation, 4-level) is a high-efficiency modulation scheme based on traditional PAM4. It uses the horizontal and vertical polarizations of the optical signal to transmit independent data streams, thereby increasing transmission capacity. Through dual-polarity modulation and multi-level signal encoding, bandwidth utilization is significantly improved without significantly increasing hardware complexity. Compared to coherent communication technologies (such as DP-QPSK), DP-PAM4 eliminates the need for complex optoelectronic mixers and local oscillator lasers, resulting in lower hardware implementation costs and energy consumption. It is suitable for short-distance, high-density data center interconnection applications. DP-PAM4 significantly reduces DSP complexity through IM-DD and low-frequency marker tones, reducing hardware costs by over 50% compared to coherent systems.

[0058] Specifically, the polarization beam combiner (PBC) combines the four-level amplitude-modulated PAM4 signals in the X and Y polarization states of a low-frequency marker tone signal embedded at a preset frequency, and then directs the synthesized DP-PAM4 signal into the transmission fiber for transmission.

[0059] In some embodiments, a single channel of 800G LR4 with polarization multiplexing (MZ) modulation using silicon photonics is used as an example to illustrate the specific implementation of DP-PAM4 in a transmitter. A transmitter using DP-PAM4 transmission technology can consist of the following core modules: a light source module, an electro-optical modulation module, a polarization control and multiplexing module, and a drive and control circuit. The specific structure and key technologies are described below.

[0060] The light source module can use a narrow linewidth tunable laser (wavelength range covers C band (radio wave frequency band with frequency of 4.0-8.0GHz, widely used in satellite communication and optical communication fields), typical linewidth <100kHz), outputting continuous laser to the beam splitter. Through the symmetric design of the optical path, the input light beam is evenly divided into two beams, in which each polarization branch is equipped with an independent MZM array, and PAM4 signal modulation is performed on the two polarized lights respectively, with a data rate of up to 56Gbs / panel. A dual-electrode nested MZM (Dual-Drive MZM) is used in conjunction with a precoding circuit to achieve four-level optical signal output, reference Figure 3 and Figure 5 .

[0061] In some embodiments, EML modulation can also be used as the modulation method. The intensity change of the optical signal can be achieved by an external modulator (for example, an electro-absorption modulator). The light source signal in different polarization output directions is loaded with high and low levels to form a light absorption strength state, thereby achieving optical signal modulation and introducing polarization orthogonal states. Figure 4 .

[0062] In some embodiments, the input terminal receives the generated PAM4 driving electrical signal, which is output by the analog-to-digital converter (DAC) and then connected to an ultra-wideband differential amplifier (bandwidth ≥ 35 GHz) to provide sufficient swing amplitude (typical peak-to-peak value V pp =4~6V) driving voltage. By applying feedforward equalization (FFE) to the original electrical signal, the high-frequency response attenuation of the modulator and the transmission channel can be compensated to ensure the power balance (deviation <0.5dB) and phase noise consistency of the two polarized lights to improve signal integrity. In view of the nonlinear characteristics of the voltage-light intensity conversion of MZM (such as cosine square response), a pre-distortion algorithm is added to optimize the symmetry of the PAM4 eye diagram. Two polarized lights (TE and TM polarization states) are input into the polarization combiner. Through high-precision waveguide alignment technology, the orthogonality of the polarization state and the phase noise suppression are maintained to achieve spatial overlap of the two light fields. Figure 5 .

[0063] In some embodiments, a calibration tone injection method is used to measure the gain difference between the two driver amplifiers. Hybrid digital-analog regulation (DAC output amplitude scaling + analog attenuator fine-tuning) is then used to control the gain imbalance to within ±5%, thus preventing power mismatch from hindering polarization demultiplexing in the receiving device. Furthermore, a dynamic polarization controller (DPC) is used to correct polarization state orthogonality in real time, ultimately outputting a dual-polarization PAM4 composite optical signal after spectrum shaping to the fiber link.

[0064] This application introduces optical polarization multiplexing PAM4 signal transmission into the optical communication transmission system, and doubles the single-channel transmission rate without increasing the demand for transmission hardware equipment, achieving better transmission performance. It also realizes self-identification of polarization state through low-frequency marking, and realizes identification and separation of polarization state by monitoring the difference of mark signal, avoiding complex digital signal synchronization algorithm. This application multiplexes polarization PAM4 technology without relying on phase recovery technology. Through IM-DD intensity modulation and polarization multiplexing transmission, the requirements for the receiving side of optical communication transmission are greatly reduced, replacing complex polarization tracking algorithms, and avoiding the use of high-cost modulators and local oscillators required for high-order coherent modulation.

[0065] Another embodiment of the present application provides a communication system for optical communication transmission, which includes the transmitting device, transmission optical fiber and receiving device mentioned in the above embodiment.

[0066] The transmitting device mentioned in the above embodiment is used to transmit the synthesized DP-PAM4 signal.

[0067] Transmission optical fiber, used to transmit the synthesized DP-PAM4 signal.

[0068] The receiving device is used to identify and receive the synthesized DP-PAM4 signal.

[0069] DP-PAM4 relies on changes in light intensity for direct detection and does not require phase information, thereby simplifying the design of the receiving end (receiving device); while traditional DP-QPSK needs to capture the phase and amplitude of the light field, and requires a complex coherent receiver for precise phase recovery and carrier synchronization. Therefore, the receiving device in this embodiment does not require a very complex design, thereby reducing the communication cost of the communication system. Compared with the traditional DP system that requires complex algorithms to separate polarization signals and phase recovery algorithms, the marker tone provides prior information, thereby simplifying the demultiplexing process. The specific technical details and technical efficacy of the communication system used for optical communication transmission can be referred to the specific embodiments of the transmitting device mentioned above, and will not be repeated here.

[0070] Another embodiment of the present application provides a communication method, which may specifically include the following steps.

[0071] Step 1: Generate a four-level amplitude modulated (PAM4) signal in X and Y polarization states through a Mach-Zehnder modulator.

[0072] Step 2: Use a marker tone provider to embed a low-frequency marker tone signal of a preset frequency into the generated four-level amplitude-modulated PAM4 signals for the X and Y polarization states. The attribute information of the low-frequency marker tone signal of the preset frequency is 1 MHz ± Δf, the amplitude accounts for 2%, and the frequency is lower than the lower limit of the signal bandwidth of 100 kHz.

[0073] Step 3: Combine the four-level amplitude modulation PAM4 signals in the X and Y polarization states of the low-frequency marker tone signal embedded with the preset frequency through a polarization combiner, and introduce the synthesized DP-PAM4 signal into the transmission optical fiber.

[0074] The specific technical details and technical effects of this communication method can be referred to the specific embodiments of the transmitting device mentioned above, which will not be repeated here.

[0075] Those skilled in the art will appreciate that the technical features described in the various embodiments and / or claims of this application may be combined and / or coupled in various ways, even if such combinations and / or couplings are not explicitly described in this application. In particular, without departing from the spirit and teachings of this application, the technical features described in the various embodiments and / or claims of this application may be combined and / or coupled in various ways, and all such combinations and / or couplings fall within the scope of this application.

[0076] Although the present application has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made to the present application without departing from the spirit and scope of the present application as defined by the appended claims and their equivalents. Therefore, the scope of the present application should not be limited to the above-described embodiments, but should be determined not only by the appended claims but also by the equivalents of the appended claims.

Claims

1. A transmitting device for optical communication transmission, characterized in that: include: Modulator, generating a four-level amplitude modulated PAM4 signal in X and Y polarization states; A marker tone provider, which embeds a low-frequency marker tone signal of a preset frequency into the generated four-level amplitude modulation PAM4 signal of the X and Y polarization states; The combiner combines the four-level amplitude modulated PAM4 signals in the X and Y polarization states of the low-frequency marker tone signals embedded with the preset frequency, and introduces the synthesized DP-PAM4 signal into the transmission optical fiber.

2. The transmitting device according to claim 1, wherein The modulator is a Mach-Zehnder modulator.

3. The transmitting device according to claim 1, wherein The attribute information of the low-frequency marker tone signal of the preset frequency is 1 MHz±Δf, the amplitude accounts for 2%, and the frequency is lower than the lower limit of the signal bandwidth of 100 kHz.

4. The transmitting device according to claim 1, wherein The modulator includes multiple polarization branches, and each polarization branch includes two corresponding sub-modulators; Each polarization branch performs PAM4 signal modulation on the two polarized lights received, generating corresponding four-level amplitude modulated PAM4 signals in the X and Y polarization states. The modulator is configured in the form of a double-electrode nested Mach-Zehnder modulator.

5. The transmitting device according to claim 4, characterized in that The sub-modulator is an external modulator.

6. The transmitting device according to claim 4, characterized in that Each sub-modulator is correspondingly provided with a digital-to-analog converter and a differential amplifier; The digital-to-analog converter performs digital-to-analog conversion on the received PAM4 driving electrical signal and outputs it to the differential amplifier, which performs differential amplification and outputs it to the corresponding sub-modulator to provide it with a driving voltage with sufficient swing amplitude.

7. A communication system for optical communication transmission, characterized in that: include: The transmitting device according to any one of claims 1 to 6, configured to transmit the synthesized DP-PAM4 signal; Transmission optical fiber, used to transmit the synthesized DP-PAM4 signal; The receiving device is used to identify and receive the synthesized DP-PAM4 signal.

8. A communication method, characterized in that: include: Generates four-level amplitude modulation PAM4 signals in X and Y polarization states; Embedding low-frequency marker tone signals of preset frequencies into the generated four-level amplitude modulation PAM4 signals of the X and Y polarization states respectively; The four-level amplitude modulated PAM4 signals in the X and Y polarization states, each embedded with a low-frequency marker tone signal at a preset frequency, are combined, and the synthesized DP-PAM4 signal is introduced into the transmission optical fiber.

9. The communication method according to claim 8, wherein: A Mach-Zehnder modulator is used to generate a four-level amplitude modulated PAM4 signal with X and Y polarization states.

10. The communication method according to claim 8, wherein: The attribute information of the low-frequency marker tone signal of the preset frequency is 1 MHz±Δf, the amplitude accounts for 2%, and the frequency is lower than the lower limit of the signal bandwidth of 100 kHz.

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