Mzm and vsb based pam4 signal generation and transmission system

Abstract

The application belongs to the technical field of optical fiber communication, and particularly relates to a PAM4 signal generation and transmission system based on MZM and VSB. The application utilizes a single MZM, inputs two OOK electrical signals, and generates a PAM4 optical signal in push-pull mode, so that the generation of the optical signal after the synthesis of the two OOK electrical signals into PAM4 and the modulation of the optical signal by the MZM can be avoided. The differential working mode of the MZM is utilized to directly generate the PAM4 optical signal by using the two electrical signals. Meanwhile, the generated PAM4 signal is processed by using a VSB filter, and the processed optical signal still maintains good signal quality after being transmitted through a 5km standard single-mode optical fiber at a speed of 100Gb / s. The system of the application has simple structure, low cost and strong stability. The application is based on the differential working principle of the MZM, and can be used to conveniently and quickly generate the PAM4 optical signal in an optical communication system.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber communication technology, specifically relating to a PAM4 signal generation and transmission system based on MZM and VSB. Background Technology

[0002] With the advent of the 5G, big data, cloud computing, and IoT era, the demand for data traffic is increasing dramatically, making it increasingly difficult to improve the bandwidth of optical devices. This necessitates the adoption of complex modulation methods. Among the upgrade schemes for Non-Return-to-Zero (NRZ) modulation, Pulse Amplitude Modulation (PAM4) is one of the most promising high-order modulation methods, supporting optical communication towards higher speeds. PAM4 technology will be widely used in future 5G high-speed optical modules. PAM4 modulation uses four different signal levels for data transmission, with each symbol period representing 2 bits of information. Because PAM4 signals can transmit 2 bits of information per symbol period, to achieve the same signal transmission capacity, the symbol rate of PAM4 signals is only half that of NRZ signals. Under the same bandwidth, PAM4 signals can transmit more information.

[0003] Traditionally, PAM4 signals can be generated directly using digital modulation. However, by using the MZM (Mach-Zehnder modulator) push-free mode, we can directly perform intensity modulation to synthesize two OOK signals into a PAM4 signal.

[0004] Furthermore, long-distance fiber optic transmission suffers from severe signal distortion due to loss, dispersion, and nonlinear distortion. Dispersion is particularly pronounced in long-distance transmission. High-speed optical signals also exacerbate dispersion. Applying VSB filtering to the optical signal can remove half of the frequency components, effectively reducing the impact of dispersion and ensuring the quality of the received signal's eye diagram. Summary of the Invention

[0005] The purpose of this invention is to provide a PAM4 signal generation and transmission system based on MZM and VSB that is simple in structure, low in cost, highly stable and efficient.

[0006] The present invention provides a PAM4 signal generation and transmission system based on MZM and VSB, which includes PAM4 signal generation based on MZM and high-speed transmission of PAM4 signal in a 5km standard single-mode optical fiber through VSB filtering.

[0007] The PAM4 signal generation and transmission system based on MZM and VSB provided by this invention specifically includes:

[0008] An offline software uses digital modulation to generate two OOK signals as input to send data. The two signals have different amplitudes, so it is necessary to pull the level high to ensure that the MZM works in the linear range.

[0009] A single-mode laser is used to provide continuous wave light, which is input into the MZM;

[0010] A Mach-Zehnder modulator, set to operate in push-pull mode, for intensity modulation;

[0011] A VSB filter processes the optical signal generated by MZM, giving it better anti-dispersion characteristics;

[0012] A 5km standard single-mode optical fiber is used to transmit optical signals;

[0013] A photodiode is used to convert the optical signal generated by MZM into an electrical signal;

[0014] An oscilloscope that recovers the original transmitted data from the received signal.

[0015] The workflow of the system of this invention is as follows:

[0016] At the transmitting end, two OOK signals with different amplitudes carrying modulation information are generated using offline software and input into the two arms of the MZM respectively; at the same time, the continuous optical signal output from a single laser also enters the MZM. The MZM modulates the information of the two OOK signals onto the optical signal through intensity modulation to generate a PAM4 optical baseband signal; then the optical signal is processed through a VSB filter to improve its anti-dispersion capability; finally, the optical signal enters a 5km standard single-mode optical fiber and is converted into an electrical signal by a photodiode.

[0017] This invention utilizes only a single MZM to synthesize a PAM4 optical signal from two OOK electrical signals in push-pull mode. Simultaneously, VSB filtering reduces the impact of dispersion on the signal at high transmission rates. This technique avoids the need to synthesize PAM4 from two OOK electrical signals and then modulate it with an MZM. Instead, it directly generates the PAM4 optical signal using the differential operation mode of the MZM. The VSB filtering further enhances the signal's anti-dispersion capability in standard single-mode fiber at high transmission rates, resulting in higher signal quality.

[0018] This invention is based on the MZM differential working principle and can be used to conveniently and quickly generate PAM4 optical signals in optical communication systems.

[0019] This invention uses a VSB filter to process the generated PAM4 signal. The processed optical signal maintains good signal quality even after being transmitted through a 5km standard single-mode fiber at a speed of 100Gb / s.

[0020] The main features of this invention are:

[0021] It can directly convert two OOK electrical signals into PAM4 optical signals;

[0022] Two OOK signals carrying modulation information can be generated separately using offline software;

[0023] Four-level optical signals can be generated using only a single laser and a single MZM;

[0024] The generated PAM4 signal can carry more information than the NRZ signal;

[0025] It can transmit high-speed PAM4 signals over long distances;

[0026] It can reduce the impact of fiber dispersion in long-distance transmission;

[0027] The effective transmission distance of PAM4 signals can be significantly increased by using only one VSB filter;

[0028] Good dispersion management can be achieved using only a simple VSB filter.

[0029] The system of this invention has a simple structure, low cost, and high stability. It can be used in optical communication systems to conveniently and quickly generate PAM4 optical signals. Attached Figure Description

[0030] Figure 1 This is a framework diagram of the PAM4 signal generation and transmission system based on MZM and VSB of the present invention.

[0031] Figure 2 It is a simulation system built in VPI software.

[0032] Figure 3 It is a PAM4 signal eye diagram directly formed through MZM.

[0033] Figure 4 This is the receive eye diagram without VSB filtering.

[0034] Figure 5 This is the receive eye diagram after VSB filtering. Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings.

[0036] Figure 1 The diagram shows the framework of a PAM4 signal generation and transmission system based on MZM and VSB.

[0037] The first laser is an external cavity modulated laser, the MZM is a Mach-Zehnder optical modulator, the MZM generates the PAM4 optical signal, the VSB filter is a vestigial sideband filter, and the 5km optical fiber is a standard single-mode fiber. After passing through the optical fiber, the optical signal is converted into an electrical signal by a photodiode. The PAM4 signal can then be detected by an oscilloscope or processed using digital software.

[0038] At the transmitting end, offline software generates two OOK signals of different amplitudes carrying modulation information, which are then input into the two arms of the MZM. Simultaneously, a laser generates a continuous-wave optical signal, which is input into the MZM. The MZM operates in push-free mode for intensity modulation, modulating the two OOK signals onto the amplitude of the optical signal to form a four-level PAM4 optical signal. A VSB filter is then used to filter the PAM4 optical signal before it is transmitted through a standard single-mode fiber. At the receiving end, a photodiode converts the received optical signal into a PAM4 electrical signal.

[0039] The system of this invention was simulated and tested using VPI. The system framework is as follows: Figure 2 As shown, with Figure 1 Maintain consistency. Figure 2 The system framework diagram of the VPI software is given. The two small human figures represent simulators that work in conjunction with MATLAB. These simulators convert the OOK bitstream generated by MATLAB into electrical signals and input them into the system. Two OOK signals of different amplitudes carrying modulation information are simultaneously input into the two arms of the MZM. A PAM4 signal is generated through differential modulation. The eye diagram of the PAM4 signal is shown below. Figure 3 As shown in the diagram. In the fiber optic transmission stage, this study employed a comparative method, splitting the fiber into two paths using a splitter. One path underwent VSB filtering, and both paths were simultaneously transmitted through a 5km standard single-mode fiber. At the receiving end, a photodiode converted the signal into an electrical signal. It is worth noting that a low-pass filter was also applied at the end to reduce noise interference. Figure 4 , Figure 5 It is the eye diagram of the last received signals from both. Figure 4 This is the receive eye diagram without VSB filtering. Figure 5 This is the receive eye diagram after VSB filtering, and it can be clearly seen that... Figure 4 The signal eye diagram is severely distorted, the bit error rate is high, and the signal is almost unrecoverable. Figure 5 The decision threshold is clearly visible in the signal eye diagram, and the bit error rate is within acceptable limits.

Claims

1. A PAM4 signal generation and transmission system based on MZM and VSB, characterized in that, This includes MZM-based PAM4 signal generation, and high-speed transmission of the PAM4 signal in a 5km standard single-mode fiber using VSB filtering; specifically including: An offline software uses digital modulation to generate two OOK signals as input to send data. The two signals have different amplitudes, so it is necessary to pull the level high to ensure that the MZM works in the linear range. A single-mode laser is used to provide continuous wave light, which is input into the MZM; A Mach-Zehnder modulator, set to operate in push-pull mode, for intensity modulation; A VSB filter processes the optical signal generated by MZM, giving it better anti-dispersion characteristics; A 5km standard single-mode optical fiber is used to transmit optical signals; A photodiode is used to convert the optical signal generated by MZM into an electrical signal; An oscilloscope that recovers the original transmitted data from the received signal; Its workflow is as follows: At the transmitting end, two OOK signals with different amplitudes carrying modulation information are generated using offline software and input into the two arms of the MZM respectively; at the same time, the continuous optical signal output from a single laser also enters the MZM. The MZM modulates the information of the two OOK signals onto the optical signal through intensity modulation to generate a PAM4 optical baseband signal; then the optical signal is processed through a VSB filter to improve its anti-dispersion capability; finally, the optical signal enters a 5km standard single-mode optical fiber and is converted into an electrical signal by a photodiode.

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