PAM4 modulation chip and modulation method thereof

Abstract

The invention provides a PAM4 modulation chip and a modulation method thereof, and belongs to the technical field of optical fiber communication. Comprising a transmitting end and a receiving end which are both in a transistor shape. The transmitting end comprises a DML laser and an auxiliary circuit; the emitting laser adopts a DML laser to emit a modulated PMA4 signal; a DML laser and an auxiliary circuit are integrated into a transmitting module; the receiving end comprises a 25G PIN detector and a transimpedance amplifier TIA chip; the TIA chip converts a weak current signal output by the PIN detector into a voltage signal and amplifies the voltage signal. The PAM4 is embedded in the optical module, so that the dispersion problem is solved to a certain extent, and the transmission distance of a single optical module is increased by four times.

Description

Technical Field

[0001] The present invention provides a PAM4 modulation chip and a modulation method thereof, belonging to the technical field of optical fiber communication. Background Art

[0002] In the 1980s, the birth of EDFA optical devices successfully solved the problem of signal attenuation in optical fiber communication systems and significantly improved the quality and distance of signal transmission. However, optical signals are still affected by many adverse factors during transmission. At present, among the many adverse effects, the dispersion problem of optical signals occupies a dominant position. The dispersion of optical signals will cause the pulse signal to gradually broaden as the transmission distance continues to increase, and at the same time, the signal will lose its cross-sectional symmetry, which will cause extremely serious signal overlap and distortion. In addition, the higher the transmission rate of the optical module, the greater the limitation on its transmission distance. For example, the current commercial 25Gbps optical module has a transmission distance of only 10-15km in the C band. In order to further improve the transmission capacity of optical fiber communication systems, the key problem of dispersion must be effectively solved. Summary of the invention

[0003] This invention takes the SFP28 DWDM optical module as the basis for in-depth research, and the theory as a solid research support. By cleverly embedding advanced technologies such as PAM4 in the optical module, it strives to successfully solve the dispersion problem to a certain extent, so that the transmission distance of the optical module can be greatly increased to 40km. This can not only meet the growing demand for information transmission, but also effectively promote the continuous development of optical fiber communication systems in a more efficient and stable direction, providing a solid technical guarantee for the rapid development of the information age.

[0004] First, the present invention provides a PAM4 modulation chip, including a transmitter and a receiver, both of which are in transistor shape; the transmitter includes: a DML laser and an auxiliary circuit; the transmitting laser uses a DML laser to transmit a modulated PMA4 signal; the DML laser and the auxiliary circuit are integrated into a transmitting module;

[0005] The receiving end includes a 25G PIN detector and a transimpedance amplifier TIA chip; the TIA chip converts the weak current signal output by the PIN detector into a voltage signal and amplifies it.

[0006] Secondly, the present invention provides a PAM4 modulation method, which uses the PAM4 modulation chip described above, and includes the following steps:

[0007] Conversion between S1, NRZ signal and PAM4 signal:

[0008] At the transmitting end, DSP / Gearbox converts two 12.5G NRZ signals into 25G PAM4 signals, realizing signal synthesis and encoding conversion; and realizes NRZ to PAM4 mapping to ensure correct transmission and encoding of information;

[0009] At the receiving end, the DSP / Gearbox converts the processed PAM4 signal back to an NRZ signal so that it can be output to subsequent equipment for processing; it implements PAM4 to NRZ decoding;

[0010] S2, shaping the signal;

[0011] DSP / Gearbox performs signal shaping operations to improve signal quality and reliability; including pre-emphasis and equalization: pre-emphasis compensates for high-frequency attenuation during transmission by enhancing the high-frequency part of the signal and improves the signal-to-noise ratio of the high-frequency component of the signal; equalization eliminates the distortion generated by the signal during transmission by adjusting the frequency response of the signal;

[0012] S3, realize clock data recovery:

[0013] At the receiving end, the clock signal is extracted from the received signal, and the data is sampled and recovered according to the clock signal to ensure that the data at the receiving end is synchronized with the sending end;

[0014] S4, implement forward error correction FEC of data:

[0015] FEC (forward error correction) is used to detect and correct errors generated during transmission. In the test, the forward error correction function of DSP / Gearbox data improves the reliability of data transmission. FEC encodes the data at the sending end and adds redundant information, so that the receiving end can use this redundant information to correct errors when errors are detected, without requesting the sending end to resend the data.

[0016] The present invention solves the dispersion problem to a certain extent by embedding PAM4 technology in the optical module, which increases the transmission distance of a single optical module by 4 times. The key lies in solving the dispersion problem of optical signals. The dispersion of optical signals will cause the pulse signal to broaden and lose cross-sectional symmetry as the transmission distance increases, resulting in serious signal overlap and distortion and limiting the transmission rate and distance of the optical module. PAM4 technology improves the transmission capacity of the optical fiber communication system to address this problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a hardware block diagram of the 25G PAM4 optical module of the present invention. DETAILED DESCRIPTION

[0018] This embodiment uses the SFP28 DWDM optical module as the basis for in-depth research, and theory as a solid research support. By embedding advanced technologies such as PAM4 in the optical module, it strives to successfully solve the dispersion problem to a certain extent, so that the transmission distance of the optical module can be greatly increased to 40km. This can not only meet the growing demand for information transmission, but also effectively promote the continuous development of optical fiber communication systems in a more efficient and stable direction, providing a solid technical guarantee for the rapid development of the information age.

[0019] like Figure 1 The following is a block diagram of the hardware design of a 25G PAM4 optical module, which includes the following two parts:

[0020] (1) The implementation steps of the transmitter (TOSA) include:

[0021] 1.1. Prepare two 12.5GNRZ signals of different levels:

[0022] First, two 12.5G NRZ (Non-Return-to-Zero) signals with different levels are prepared at the transmitter, which will serve as input sources for subsequent processing.

[0023] 1.2. Synthesis through digital signal processing chip (DSP) with PAM4 line coding technology:

[0024] The prepared two-channel 12.5G NRZ signal is input into a digital signal processing chip (DSP) with PAM4 (Pulse Amplitude Modulation 4-level) line coding technology.

[0025] The DSP chip uses its internal specific algorithms and circuits to combine the two NRZ signals into a 25G PAM4 signal. By combining two low-rate NRZ signals into a high-rate PAM4 signal, it prepares for subsequent signal processing and transmission without changing the amount of transmitted information.

[0026] 1.3. Convert voltage signal to current signal through laser driver chip:

[0027] The synthesized 25G PAM4 signal is then reconstructed through the laser driver chip.

[0028] The laser driver chip converts the voltage signal of the PAM4 signal into a current signal. This conversion process is to be able to directly drive the DML (Directly Modulated Laser) laser, because the laser is usually modulated by current.

[0029] 1.4. Drive and modulate the DML laser and send optical signals:

[0030] The current signal converted by the laser driver chip directly drives and modulates the DML laser.

[0031] Under the action of the current signal, the DML laser will generate and emit an optical signal with a specific wavelength and intensity. The baud rate of the optical signal emitted here is 12.5G. Although the rate of the PAM4 signal is 25G, since PAM4 is a multi-level modulation technology, each symbol can carry more information, so the baud rate of the optical signal is 12.5G.

[0032] Finally, the laser sends a 12.5G baud rate optical signal into the optical fiber for transmission, and the optical signal is transmitted along the optical fiber to the receiving end.

[0033] (2) Implementation steps of the receiving end (ROSA)

[0034] 2.1. Photodetectors convert light signals into electrical signals:

[0035] At the receiving end, a photodetector with a baud rate of 12.5G is responsible for receiving the optical signal from the optical fiber.

[0036] Photoelectric detectors use the photoelectric effect to convert received optical signals into distorted electrical signals. Since the transmission of optical signals may be affected by various factors, such as optical fiber loss and dispersion, the converted electrical signals will have certain distortion.

[0037] 2.2. Transimpedance amplifier amplifies the electrical signal:

[0038] The distorted electrical signal is then amplified by a transimpedance amplifier, which converts the weak current signal output by the photodetector into a voltage signal and amplifies it to increase the signal strength and signal-to-noise ratio.

[0039] 2.3. Enter the DSP chip for signal shaping and clock recovery:

[0040] The amplified signal enters the DSP chip for further processing.

[0041] The DSP chip first shapes the signal, including pre-emphasis and equalization. Pre-emphasis is a common technology in signal transmission, which enhances the high-frequency part of the signal at the transmitting end to compensate for the high-frequency attenuation during the transmission process. Equalization adjusts the frequency response of the signal to eliminate the distortion generated by the signal during transmission.

[0042] In addition to signal shaping, the DSP chip also implements clock data recovery, which is one of the key technologies at the receiving end. Its function is to extract the clock signal from the received signal and sample and recover the data according to the clock signal to ensure that the data at the receiving end is synchronized with the sending end.

[0043] 2.4. Convert digital signal to analog signal and output two NRZ signals:

[0044] After being processed by the DSP chip, a relatively complete digital signal is obtained.

[0045] Finally, the digital signal is converted into an analog signal, and two NRZ signals are output from the original rate of the gold finger. This process is to restore the signal processed by the receiving end to the same format as the input signal of the transmitting end so that it can be processed and used by subsequent equipment.

[0046] The DSP / Gearbox function implementation of the present invention includes the following process:

[0047] S1. Conversion between NRZ signal and PAM4 signal:

[0048] At the transmitting end, DSP / Gearbox converts two 12.5G NRZ signals into 25G PAM4 signals, realizing signal synthesis and encoding conversion. It realizes the mapping from NRZ to PAM4 and ensures the correct transmission and encoding of information.

[0049] At the receiving end, the DSP / Gearbox converts the processed PAM4 signal back to an NRZ signal so that it can be output to subsequent equipment for processing, thus achieving PAM4 to NRZ decoding.

[0050] S2. Shaping the signal (pre-emphasis, equalization, etc.):

[0051] DSP / Gearbox shapes the signal to improve its quality and reliability. Pre-emphasis technology improves the signal-to-noise ratio of the high-frequency component of the signal by enhancing the high-frequency part of the signal, compensating for the high-frequency attenuation during transmission. Equalization technology adjusts the frequency response of the signal to eliminate the distortion generated during transmission, making the signal closer to the original signal.

[0052] S3.Realize clock data recovery:

[0053] Clock data recovery is one of the important functions of DSP / Gearbox. At the receiving end, the clock signal is extracted from the received signal, and the data is sampled and recovered according to the clock signal to ensure that the data at the receiving end is synchronized with the sending end. This process requires accurate clock recovery algorithms and circuits to ensure the correct reception and processing of data.

[0054] S4. Implement forward error correction (FEC) of data (mostly used for testing):

[0055] FEC (Forward Error Correction) is a technology commonly used in data transmission to detect and correct errors generated during the transmission process. In the test, DSP / Gearbox can implement the forward error correction function of data to improve the reliability of data transmission. FEC technology encodes the data at the sending end and adds some redundant information so that the receiving end can use this redundant information to correct errors when errors are detected without requesting the sending end to resend the data.

[0056] The packaging and integration of PAM4 modulation chip are as follows:

[0057] 1. Choose TO package:

[0058] Both the transmitter and receiver adopt TO (Transistor Outline) packaging. TO packaging has good stability and reliability, and can protect the internal chips and circuits from the influence of the external environment. At the same time, TO packaging is also easy to install and use, which can improve the production efficiency and reliability of optical modules.

[0059] 2. Transmitter integration:

[0060] The transmitting laser uses a DML laser to transmit the modulated PMA4 signal. The DML laser has the characteristics of direct modulation, which can quickly respond to changes in electrical signals and achieve high-speed data transmission. At the transmitting end, the DML laser is integrated with other circuits to form a complete transmitting module.

[0061] 3. Receiver integration:

[0062] The receiving end integrates 25G PIN (Positive-Intrinsic-Negative) and transimpedance amplifier (TIA) chips. PIN detector is a commonly used photodetector with high sensitivity and fast response. TIA chip is used to convert the weak current signal output by PIN detector into voltage signal and amplify it. The receiving end integrates PIN detector and TIA chip to form a complete receiving module.

[0063] Through the above detailed steps, the design of optical modules based on PAM4 coding technology can be realized, and the transmission distance limit of SFP28 optical modules can be increased to 40 kilometers. It has the advantages of mature technology, low cost, low power consumption, and easy mass production.

Claims

1. A PAM4 modulation chip, comprising a transmitter and a receiver, both of which are in transistor shape; characterized in that: The transmitting end includes: a DML laser and an auxiliary circuit; the transmitting laser uses the DML laser to transmit the modulated PMA4 signal; the DML laser and the auxiliary circuit are integrated into a transmitting module; The receiving end includes a 25G PIN detector and a transimpedance amplifier TIA chip; the TIA chip converts the weak current signal output by the PIN detector into a voltage signal and amplifies it.

2. A PAM4 modulation method, characterized in that: Using the PAM4 modulation chip described in claim 1, comprising the following steps: Conversion between S1, NRZ signal and PAM4 signal: S2, shaping the signal; S3, realize clock data recovery: S4. Implement forward error correction (FEC) of data.

3. A PAM4 modulation method according to claim 2, characterized in that: The specific method of S1 is: At the transmitting end, DSP / Gearbox converts two 12.5G NRZ signals into 25G PAM4 signals, realizing signal synthesis and encoding conversion; and realizes NRZ to PAM4 mapping to ensure correct transmission and encoding of information; At the receiving end, the DSP / Gearbox converts the processed PAM4 signal back to an NRZ signal so that it can be output to subsequent equipment for processing; Implement PAM4 to NRZ decoding.

4. A PAM4 modulation method according to claim 2, characterized in that: The specific method of S2 is: DSP / Gearbox performs signal shaping operations to improve the quality and reliability of the signal; including pre-emphasis and equalization: pre-emphasis compensates for the high-frequency attenuation during transmission by enhancing the high-frequency part of the signal, thereby improving the signal-to-noise ratio of the high-frequency component of the signal; Equalization eliminates signal distortion during transmission by adjusting the signal's frequency response.

5. A PAM4 modulation method according to claim 2, characterized in that: The specific method of S3 is: at the receiving end, a clock signal is extracted from the received signal, and data is sampled and restored according to the clock signal to ensure that the data at the receiving end is synchronized with the sending end.

6. A PAM4 modulation method according to claim 2, characterized in that: The specific methods of S4 are: FEC forward error correction, used to detect and correct errors generated during transmission; in the test, the forward error correction function of DSP / Gearbox data improves the reliability of data transmission; FEC encodes the data at the sending end and adds redundant information so that the receiving end can use the redundant information to correct errors when errors are detected without requesting the sending end to resend the data.

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