CN111970221B - High noise immunity P-bit optical transmission method based on multi-probability distribution - Google Patents

Abstract

The invention discloses a high noise-resistant P bit optical transmission method based on multi-probability distribution, which divides subcarriers into signal streams with 6 modes, multiplexes the signal streams, transmits the multiplexed signal streams to one core of a 19-core 6-mode optical fiber through an optical fiber fan-in device, and transmits the multiplexed signal streams to different transmitters of the other 18 coresThe 18 pseudo-random binary signals of the same wavelength are modulated using different binary sequences. The 19 signals are sent out through a 19-core 6-mode optical fiber and received and processed by a signal receiving device; probability shaping is carried out on the optical signals by adopting Maxwell-Boltzmann distribution on subcarriers of different modes by multi-probability coding modulation, wherein probability shaping scaling factors of high-order modes

With values greater than the fundamental mode

And (4) taking values. The invention has the technical advantages of high transmission efficiency and strong noise resistance.

Description

High noise immunity P-bit optical transmission method based on multi-probability distribution

technical field

The present invention relates to the technical field of communication technology, in particular to a high anti-noise P-bit optical transmission method based on multi-probability distribution.

Background technique

With the rapid growth of Internet services and emerging bandwidth applications, traffic to data center networks, access networks and fiber backbones has grown exponentially in recent years, and this trend is expected to continue for the foreseeable future. However, previous research has shown that the transmission capacity of single-mode fibers is rapidly approaching its fundamental Shannon limit. In order to break through the capacity limitation of single-core single-mode fiber, researchers have introduced multi-core fiber and few-mode fiber in spatial multiplexing. Ultra-high-capacity space division multiplexing (SDM) can make the transmission capacity of optical transmission system reach P bit level. Multi-core multiplexing (MCM) and few-mode multiplexing (FMM) technologies are studied to realize signal multiplexing in the two dimensions of core and transmission mode in multi-core and few-mode fibers, and further improve the system spectral efficiency and transmission capacity.

The probability shaping technology can reduce the gap between the actual transmission signal information transmission rate and the Shannon capacity limit by redesigning the QAM signal constellation distribution, so as to achieve the purpose of improving the channel capacity. The key theory and application research of probabilistic shaping technology has received extensive attention at home and abroad. The principle of probability shaping is that when the constellation points obey the Maxwell-Boltzmann distribution, the average transmission energy can be minimized under the given transmission entropy, thereby obtaining the sensitivity gain and improving the tolerance of the system to nonlinear effects and noise. By assigning different probabilities to each symbol, the data bit stream is converted into non-uniformly distributed symbols, and through FEC coding and constellation point mapping, the final non-uniformly distributed modulation symbol stream is generated.

At present, no existing technology using probability shaping technology has been found in the P-bit optical transmission system. The traditional single-mode fiber T-bit is the limit, and only one channel, the transmission speed is low, but the optical signal quality is good, 19 cores The 6-mode fiber has 114 channels for parallel transmission, and the transmission rate is very high and can reach P bits. However, the problems brought by multi-mode fiber are that the high-order mode loss is high, the mode coupling strength is large, and the optical signal quality based on high-order mode transmission is poor. This results in insufficient bit error rate performance.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a high anti-noise P-bit optical transmission method based on multiple probability distributions in order to solve the problems mentioned in the background art.

In this patent, we propose a multi-probability distribution method for highly noise-resistant P-bit optical transmission.

In order to realize the above-mentioned technical purpose, the technical scheme adopted in the present invention is:

High noise immunity P-bit optical transmission method based on multi-probability distribution, where:

Step 1: Two lasers with a frequency difference of Δf in the odd-even channel respectively generate an optical frequency comb with an interval of 2Δf through the optical frequency comb module, and then interweave them together through a coupler to form a dense optical carrier with a frequency interval of Δf,

Step 2: The dense optical carriers pass through the beam splitter to form multiple sub-carriers, and the sub-carriers are orthogonally multiplexed, and then multi-probability matching is performed on the sub-carriers of different modes through multi-probability coding and modulation, so that the sub-carriers of different modes are matched. have different probability distributions;

Step 3. After multiplexing, the sub-carriers are transmitted to one of the cores of the 19-core 6-mode fiber through the fiber fan-in device. In the different transmitters of the other 18 cores, the signal is modulated by using different binary sequences. 18 pseudo-random binary signals of the same wavelength, these 19 signals are sent out through 19-core 6-mode optical fibers, and are received and processed by the signal receiving device;

Among them, the specific method for multi-probability coding modulation to perform multi-probability matching on sub-carriers of different modes is: using Maxwell-Boltzmann distribution to perform probability shaping on the optical signal, and the formula is:

P _X ( _xi ) represents the probability that point _xi appears, and x _k represents the constellation point after QAM modulation;

where v is a scaling factor, which represents the degree of probability shaping, and takes a value between 0 and 1, where the value of v of the higher-order mode is greater than the value of v of the fundamental mode.

In order to optimize the above technical solutions, the specific measures taken also include:

The value range of the scaling factor v is 0-0.35.

The optical frequency comb module is an optical frequency comb based on a single pump laser and a silicon-based integrated microring resonator.

In step 1, one laser passes through the optical frequency comb module to generate an optical frequency comb with a frequency interval of 25 GHz, and then uses an arbitrary waveform generator with a channel frequency interval of 25 GHz to separate each sub-carrier, and modulates the odd numbers of λ1, λ3 and λ5. Channel group; there is also a laser that also generates sub-carriers with a frequency interval of 25GHz. The sub-carriers generated here are λ2, λ4 and λ6 as an even-numbered channel group, since the frequency interval between the odd-channel laser and the even-channel laser is 12.5GHz , the odd-even channels are interleaved together through a 50:50 coupler to form a dense optical carrier with a frequency spacing of 12.5 GHz.

In step 3, the sub-carrier is divided into 6 ports, and 6 modes of signal streams are obtained through delay lines of different lengths. These 6 signal streams are multiplexed by the Photon Lantern 6-mode multiplexer and fan-in to the device through optical fibers. Launched into 19-core 6-mode fiber.

In step 3, the method for the signal receiving device to receive and process the signal is as follows: the signal sent by the 19-core 6-mode optical fiber passes through the fan-out device, and the mode demultiplexer decomposes the signal of the 6 modes. Then through the coherent receiver, use a 12×12 MIMO equalizer, and digitally process the signal, and then perform probability dematching on the signal; then perform parallel-serial change and decoding to obtain the received binary data, and finally the received binary data Perform bit error rate analysis to evaluate system performance.

The signals of the above 6 modes are processed simultaneously by a 12×12 MIMO equalizer with a half-symbol interval, and the tap size is set to 1000 to compensate for the frequency-dependent differential mode delay and to update the tap coefficients according to the least mean square algorithm.

The multi-probability coding modulation of the present invention performs the Maxwell-Boltzmann distribution on the sub-carriers of different modes to perform probability shaping on the optical signal, and adjusts the scaling factor v, where v is one of the key parameters of the Maxwell-Boltzmann distribution, which can represent The degree of probability shaping, a value between 0 and 1. Probability shaping increases the probability of a signal with a small amplitude, and reduces the probability of a signal with a large amplitude. The larger the v, the greater the degree of probability shaping. It is also the difference in v that causes the probability distribution of the probability shaping to be different. The entropy H is different. The present invention adopts the low-order mode optical transmission probability of the signal with a lower degree of shaping, and the high-order mode optical transmission probability of the signal with a higher degree of shaping, reduces the high-order mode loss, effectively improves the anti-noise capability of the modulation format, and improves the bit error of the system. rate performance, saving transmit power. At the same time, probability shaping provides unparalleled flexibility for optical communication systems without increasing the complexity of the system.

The multi-probability coding modulation of the present invention is matched with the 19-core 6-mode optical fiber, the 19-core 6-mode optical fiber has 6 modes, and can achieve P-bit transmission, but the corresponding optical signal quality of high-order mode transmission is poor. Coded modulation overcomes this problem by solving that the optical transmission probability shaping degree of the high-order mode is higher than that of the low-order mode, so that the present invention can simultaneously obtain the technical advantages of high transmission efficiency and strong anti-noise ability.

Description of drawings

Fig. 1 is a flowchart of a high anti-noise P-bit optical transmission system based on multiple probability distributions;

Figure 2 is a structural diagram of a 19-core 6-mode optical fiber;

Fig. 3 is multi-probability coding part flow chart;

Figures 4-9 are the constellation diagrams received after passing through the additive white Gaussian noise channel.

Detailed ways

The embodiments of the present invention will be described in further detail below.

As shown in Figure 1, this scheme uses a low-cost, energy-efficient optical frequency comb based on a single pump laser and a silicon-based integrated microring resonator. The optical frequency comb based on this structure only needs a single III-V group DC pump laser, and the frequency interval of the output spectral lines is determined by the effective refractive index and geometric size of the resonator waveguide, which can be obtained by adjusting the effective refractive index through temperature tuning technology Precise and stable wavelengths with high regulation consistency. First, a laser passes through the optical frequency comb module to generate an optical frequency comb with a frequency interval of 25GHz, and then uses an AWG with a channel frequency interval of 25GHz to separate each sub-carrier, and after modulation, an odd-numbered channel group of λ1, λ3, and λ5 is generated; there is also a The laser also generates sub-carriers with a frequency interval of 25 GHz, where the generated sub-carriers are λ2, λ4, and λ6 as an even-numbered channel group. But since the frequency separation between the odd and even channel lasers is 12.5GHz, interleaving the odd and even channels together through a 50:50 coupler will form an optical signal with a frequency separation of 12.5GHz. After passing through the beam splitter, multiple sub-carriers are formed, and the sub-carriers are orthogonally multiplexed, and then multi-probability matching is performed on the signals of different modes according to the requirements, so that the lights of different modes have different probability distributions; then the signals are divided into 6 6 ports, and 6 modes of signal flow are obtained through delay lines of different lengths. Next, these 6 signals are multiplexed by a Photon Lantern 6-mode multiplexer and launched into one of the cores through a fiber-optic fan-in device, the six modes are LP01, LP11a, LP11b, LP21a, LP21b, and LP02 , the core-to-core crosstalk is less than 38dB, the insertion loss is less than 0.4dB, and the fiber structure is shown in Figure 2. The 6 modes of light are launched into one of the cores of a 19-core 6-mode fiber through a fiber bundle fan-in device. In the different transmitters of the remaining 18 cores, 18 signals of the same wavelength are modulated by using different pseudo-random binary sequences. In our setup, the 6-mode multiplexed signal generated by the multiplexer is divided into 6 ports by a few-mode power divider and input into the core adjacent to the core under test, each The core is also decorrelated through a delay line. For other non-adjacent cores, the signal is sent out through graded-index multimode fiber to excite all 6 modes on the input side of the MCF. The signal sent from the test core then passes through a fan-out device and demultiplexes the 6 modes by a mode multiplexer. Then through the coherent receiver, it is used for 12×12 MIMO processing, and digital signal processing such as channel equalization and dispersion compensation can be performed on it, and the probability de-matching can be performed on multiple probabilities according to the system requirements; Finally, the bit error rate analysis is performed on the received binary data to evaluate the performance of the system. In this system, samples of all modes are processed simultaneously by a 12×12 MIMO equalizer with half-symbol spacing. Set the tap size to 1000 to compensate for the frequency-dependent differential mode delay and update the tap coefficients according to a least mean square (LMS) algorithm.

Since the loss of the higher-order mode is higher than that of the fundamental mode, the mode coupling strength is larger, and the optical signal quality based on the transmission of the higher-order mode is poor. Therefore, we take a greater degree of probability shaping for high-order modes, and the specific probability distribution uses the Maxwell-Boltzmann distribution, see the following formula

In the formula, v is the scaling factor, which is one of the key parameters, which can represent the degree of probability shaping, ranging from 0 to 1. The larger v is, the greater the degree of probability shaping is, and it is the difference in v that causes the probability distribution of probability shaping to be different, and the information entropy H is different. Probability shaping increases the probability of a signal with a small amplitude and reduces the probability of a signal with a large amplitude, which leads to a reduction in the average power of the signal and saves the transmission power. At the same time, probability shaping provides unparalleled flexibility for optical communication systems without increasing the complexity of the system. The flow chart of multi-probability coding is shown in Figure 3.

Figures 4 to 9 show the constellation diagrams received after passing through the additive white Gaussian noise channel, wherein Figure 4 is the constellation diagram of the 16QAM signal with the information entropy H=3.7864 when the transmission mode is LP01. The constellation diagram of the P-bit transmission system using multi-probability mapping in this patent is shown in Figures 5-9. Figure 5 is the signal constellation diagram of the information entropy H=3.5611 when the transmission mode is LP11a, Figure 6 is the signal constellation diagram of the information entropy H=3.3061 when the transmission mode is LP11b, and Figure 7 is the scaling factor information entropy H=3.3061 when the transmission mode is LP21a The signal constellation diagram of 3.0541, Figure 8 is the signal constellation diagram of the information entropy H=2.8265 when the transmission mode is LP21a, and Figure 9 is the signal constellation diagram of H=2.6335 when the transmission mode is LP21a. It can be seen from Figures 4-9 that the high anti-noise P-bit optical transmission system based on multi-probability distribution proposed in this patent is feasible.

The probability distribution of each constellation point under different scaling factors is as follows:

It can be seen from the probability distribution that when the scaling factor v increases continuously, the probability of the middle constellation point appearing is greater, and the probability of the constellation point farther from the center appearing is smaller.

Depend on

It can be calculated that the average relative powers of H=3.7864, H=3.5611, H=3.3061, H=3.0541, H=2.8265, H=2.6335 are 6.9604, 5.7036, 4.6877, 3.9072, 3.3308, 2.9172, respectively, as can be seen from the simulation data , the multi-probability mode multiplexing optical signal transmission method proposed in this patent can reduce the transmission power of the entire system, and the larger the scaling factor v, the smaller the average relative power. At the same time, the operation and maintenance cost of the system is reduced, and high spectral efficiency and high transmission capacity are obtained.

The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions that belong to the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention. protection range.

Claims (7)

1. High anti-noise P-bit optical transmission method based on multi-probability distribution, which is characterized by: Step 1: Two lasers with a frequency difference of Δf in the odd-even channel respectively generate an optical frequency comb with an interval of 2Δf through the optical frequency comb module, and then interweave them together through a coupler to form a dense optical carrier with a frequency interval of Δf, Step 2: The dense optical carriers pass through the beam splitter to form multiple sub-carriers, and the sub-carriers are orthogonally multiplexed, and then multi-probability matching is performed on the sub-carriers of different modes through multi-probability coding and modulation, so that the sub-carriers of different modes are matched. have different probability distributions; Step 3. After multiplexing the sub-carriers, they are transmitted to one of the cores of the 19-core 6-mode fiber through the fiber bundle fan-in device. In the different transmitters of the remaining 18 cores, different binary sequences are used. 18 pseudo-signals of the same wavelength are modulated, these 19 signals are sent out through 19-core 6-mode optical fibers, and are received and processed by the signal receiving device; Among them, the specific method for multi-probability coding modulation to perform multi-probability matching on sub-carriers of different modes is: using Maxwell-Boltzmann distribution to perform probability shaping on the optical signal, and the formula is:

P _X ( _xi ) represents the probability that point _xi appears, and x _k represents the constellation point after QAM modulation; where v is a scaling factor, which represents the degree of probability shaping, and takes a value between 0 and 1, where the value of v of the higher-order mode is greater than the value of v of the fundamental mode. 2 . The multi-probability distribution-based high anti-noise P-bit optical transmission method according to claim 1 , wherein the value range of the scaling factor v is 0-0.35. 3 . 3. the high anti-noise P-bit optical transmission method based on multi-probability distribution according to claim 1, is characterized in that: described optical frequency comb module is the light based on single pump laser and silicon-based integrated micro-ring resonator frequency comb. 4. The high anti-noise P-bit optical transmission method based on multi-probability distribution according to claim 1, is characterized in that: in step 1, one laser light passes through the optical frequency comb module to generate the optical frequency comb whose frequency interval is 25GHz, and reuses The arbitrary waveform generator with a channel frequency interval of 25 GHz separates each sub-carrier, and generates odd-numbered channel groups of λ1, λ3 and λ5 after modulation; there is also a laser that also generates sub-carriers with a frequency interval of 25 GHz. The sub-carriers generated here are respectively For λ2, λ4 and λ6 as an even-numbered channel group, since the frequency interval between the odd-channel laser and the even-channel laser is 12.5GHz, the odd-even channels are interleaved together through a 50:50 coupler to form a frequency interval of 12.5GHz. Dense optical carrier. 5. The high anti-noise P-bit optical transmission method based on multi-probability distribution according to claim 1, is characterized in that: in step 3, the subcarrier is divided into 6 ports, and 6 kinds of modes are obtained by delay lines of different lengths. Signal streams, these 6 signal streams are multiplexed together through a 6-mode multi-mode multiplexer based on photonic lanterns and fan-in into 19-core 6-mode fiber through a fiber fan-in device. 6. The high anti-noise P-bit optical transmission method based on multi-probability distribution according to claim 1, is characterized in that: in step 3, the method that the signal receiving device receives and processes the signal is: the signal sent by the 19-core 6-mode fiber passes through The fan-out device, demultiplexes the 6-mode signals by the mode demultiplexer; then passes through the coherent receiver, uses a 12×12 MIMO equalizer, and performs digital signal processing on the signal, and then probabilistically solves the signal Matching; then perform parallel-serial change and decoding to obtain the received binary data, and finally analyze the bit error rate of the received binary data to evaluate the performance of the system. 7. The multi-probability distribution-based high anti-noise P-bit optical transmission method according to claim 6, wherein the signals of the 6 modes are processed simultaneously by a 12×12 MIMO equalizer with a half-symbol interval, and the tap size is set to is 1000 to compensate for frequency-dependent differential mode delays and update tap coefficients according to the least mean squares algorithm.

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