CN114978320B - Optical fiber communication system performance optimization method and device based on direct-modulated laser - Google Patents

Abstract

The invention discloses a method for optimizing the performance of an optical fiber communication system based on a direct-tuning laser, which comprises the following steps: substituting the initial related physical parameters into a system transfer function to calculate and obtain an initial system frequency response curve; adjusting the injection current I ₀ or the optical fiber dispersion D ₀ value of the direct-tuning laser to enable the system frequency response curve to be as flat as possible; correcting the frequency response function of the direct-tuning laser according to the injection current I ₀ of the direct-tuning laser at the moment; correcting the transmission optical fiber according to the fiber dispersion D ₀ value at the moment; obtaining a new system frequency response curve according to the corrected parameters; and carrying out electric domain frequency domain equalization at the transmitting end to obtain a precompensated initial frequency response curve of the system, so that the performance of the system is optimal. The invention carries out preliminary compensation on the system transmission system frequency response curve, and further compensates the preliminarily compensated system frequency response curve by utilizing the electric domain frequency domain equalization technology, thereby improving the transmission performance of the system. The invention also provides a corresponding device for optimizing the performance of the optical fiber communication system based on the direct-tuning laser.

Description

Optical fiber communication system performance optimization method and device based on direct-modulated laser

Technical Field

The present invention belongs to the technical field of optical fiber communication, and more specifically, relates to a method and device for optimizing the performance of an optical fiber communication system based on a direct-modulated laser.

Background technique

In short-distance data communication systems and optical access network systems, low-cost, high-integration technology has always been the main research topic. Direct-modulation and direct-detection technology based on directly modulated lasers (DML) has been widely studied and applied to optical access networks in recent years as the mainstream transmission technology for optical short-distance and access networks.

In direct modulation and direct inspection systems, compared with Mach-Zehnder modulators (MZMs) or electro-absorption modulated lasers (EMLs), DMLs have the advantages of high output optical power, low implementation cost and small footprint, making them more popular. However, the chirp damage of DMLs is a major difficulty affecting their widespread application, especially when the transmission distance is long and the rate is high. In a direct modulation laser, the modulation signal is used as the driving current of the gain region to complete the electro-optical conversion. The change of current will also change the refractive index inside the optical cavity, which will affect the wavelength excitation of the optical cavity, causing the optical frequency to change and produce chirp. The chirp of a direct modulation laser can be divided into adiabatic chirp and transient chirp. For adiabatic chirp, the frequency of the output optical signal is related to the amplitude of the optical field. For transient chirp, the frequency of the output optical signal is related to the amplitude change of the optical field. When the signal is transmitted in the optical fiber, due to the existence of dispersion, signals of different optical frequencies will have different group delays, resulting in aliasing of different frequencies and serious signal damage. In order to improve transmission performance, chirp management technology is generally used. There are three main solutions: optical spectrum filtering, digital signal processing and complex modulation. The core idea of the optical spectrum filtering solution is to filter out the optical frequency corresponding to the 0 symbol. When the 0 symbol is filtered out by the optical filter, only the 1 symbol will remain in the optical signal, which makes the optical signal no longer affected by dispersion. In addition, the reduction of the 0 symbol power also means the increase of the extinction ratio, which will further improve the signal quality. At the same time, optical filtering can be regarded as a vestigial sideband (VSB) signal to a certain extent, which can avoid the frequency response attenuation of the direct detection system and is suitable for long-distance transmission. However, the cost of this solution comes from the additional optical filter, which will increase the cost to a certain extent. On the other hand, in order to achieve a better chirp filtering effect, the wavelength of the laser needs to be strictly aligned with the filter, which requires a more accurate feedback circuit correction, so the wavelength stability control will also bring cost. The core idea of the solution based on digital signal processing is to use nonlinear equalization technology to compensate for the nonlinear damage caused by chirp. Since optical signals of different intensities correspond to different optical frequencies, the damage caused by chirp is actually a nonlinear damage. Current DSP-based solutions all use nonlinear Volterra equalization technology to compensate. The cost of this solution mainly comes from two aspects. On the one hand, high-speed ADC is a relatively expensive chip. On the other hand, Volterra filter requires second-order and third-order taps, which requires a large number of multiplication operations, resulting in a significant increase in cost and power consumption. The core idea of the complex modulation scheme is to use the phase change caused by chirp as a modulation dimension, which can achieve two-dimensional modulation of coherent systems to a certain extent. The biggest limitation of this technology in access networks is the high complexity of coherent reception. In addition, the optical phase in this scheme is easily affected by modulation current and temperature, which will bring cost.

In summary, all three solutions will bring great cost. The cost of optical filtering lies in the additional optical filter and the corresponding wavelength control, the cost of Volterra digital signal processing lies in the complex second-order and third-order multiplication circuits, and the cost of complex modulation lies in the complexity of coherent reception. Due to the existence of these cost costs, it is particularly important to find a lower-cost solution to suppress the damage caused by chirp.

Summary of the invention

In order to overcome the defects in the above-mentioned prior art, the present invention provides a method for optimizing the performance of an optical fiber communication system based on a direct-modulated laser. The direct-modulated laser can be applied to short-distance data communication and access network systems, and can also be applied to metropolitan area networks with a transmission distance greater than 20 kilometers.

To achieve the above object, according to one aspect of the present invention, a method for optimizing the performance of an optical fiber communication system based on a directly modulated laser is provided, comprising the following steps:

S1: extracting initial relevant physical parameters of an optical fiber communication system based on a directly modulated laser, wherein the optical fiber communication system includes a directly modulated laser at a transmitting end and transmission optical fibers with different dispersion values;

S2: Mathematically model the optical fiber communication system based on the direct-modulated laser, establish the emission and transmission frequency response function model of the system except the receiving end, bring the obtained initial relevant physical parameters into the above frequency response function model to calculate the initial frequency response curve of the system except the receiving end;

S3: pre-compensate the initial frequency response curve of the above system, that is, adjust the injection current of the direct-modulated laser. The adjusted injection current must be in the linear region of the driving current of the direct-modulated laser and meet the extinction ratio requirement of the device.

S4: pre-compensate the initial frequency response curve of the above system, that is, adjust the fiber dispersion value so that the overall system frequency response curve meets the preset flatness requirement and achieves distortion-free transmission conditions;

S5: modifying the injection current value of the direct-modulated laser according to the injection current of the new direct-modulated laser obtained in step S3; performing dispersion compensation processing on the transmission optical fiber according to the new optical fiber dispersion value obtained in step S4;

S6: Substituting the parameters corrected in step S5 into the total amplitude response of the system to obtain an updated system frequency response curve;

S7: Optimize the updated system frequency response curve obtained in step S6 using the electrical domain frequency domain equalization technology to further flatten the system frequency response curve and achieve distortion-free transmission conditions for the overall transmission characteristics of the system.

In one implementation of the present invention, in step S1, the following physical parameters of the direct-modulated laser and the transmission optical fiber at the transmitting end of the system are obtained by pre-designing the system or measuring the actual system.

In one embodiment of the present invention, the physical parameters include: line width enhancement factor α ₀ of the directly modulated laser, adiabatic chirp parameter κ ₀ of the directly modulated laser, injection current I ₀ of the directly modulated laser, fiber dispersion D ₀ and fiber length L ₀ .

In one embodiment of the present invention, the mathematical model established in step S2 is:

In a transmission system based on a directly modulated laser, taking into account the injection current of the directly modulated laser and the fiber dispersion factor, the frequency response is expressed by the following formula:

In this formula, the first term on the right side is the frequency response caused by transient chirp, which is recorded as H _tst (f,L), and the second term is the frequency response caused by adiabatic chirp, which is recorded as _Hadb (f,L), f represents frequency, L represents transmission distance, I represents injection current, α represents linewidth enhancement factor, D represents fiber dispersion, λ represents wavelength of direct modulated laser, c represents speed of light in vacuum, ε represents gain limitation factor, Γ represents light limitation factor, _Ith represents threshold current, e represents electron charge, and V represents active area volume;

The total amplitude response of the system is the superposition of two frequency responses, namely:

Substitute the initial relevant physical parameters obtained in step S1 into the above system total amplitude response formula to obtain the system initial frequency response curve.

In one embodiment of the present invention, the system frequency response curve pre-compensation method is achieved by adjusting the physical parameters of the injection current of the directly modulated laser and the fiber dispersion value.

In one embodiment of the present invention, the system frequency response curve pre-compensation is divided into two cases:

(1) When the optical fiber dispersion value can be changed, that is, when the optical fiber can be replaced, the dispersion values of different existing optical fibers are measured and recorded as D _i , i = 1, 2, ..., n;

(2) When the fiber dispersion value cannot be changed, that is, when the fiber cannot be changed, the current fiber dispersion value is recorded as D ₀ ;

For different dispersion values D _i , substitute them into the total amplitude response formula of the system, adjust different injection current values I _i through simulation, obtain a series of system frequency response curves under different conditions, and find the flat system frequency response curve under limited conditions. Record the dispersion value and the injection current value of the direct-modulated laser at this time, and modify the physical parameters of the system accordingly.

In one embodiment of the present invention, the method of compensating the system frequency response curve by using the frequency domain equalization technology is implemented by digital signal processing technology, and the specific method is as follows:

① Perform Fourier transform on the original data x at the transmitter to obtain X;

② Perform Fourier transform on the data y received by the receiving end to obtain Y;

③ Obtain the system frequency response curve by converting the transformed data Y/X;

④Smooth the system frequency response curve;

⑤ Obtain new data by inverting the system frequency response curve;

⑥ Multiply the transmitted data with the constructed new data in the frequency domain and then convert it back to the time domain for transmission.

In one embodiment of the present invention, factors affecting system performance include: injection current of a directly modulated laser, dispersion of an optical fiber, and a digital signal processing algorithm.

In one embodiment of the present invention, the overall system frequency response curve of the system is made as flat as possible in step S4, specifically, the amplitude difference between the low-frequency part and the high-frequency part of the system frequency response curve is made less than 5 dBm.

According to another aspect of the present invention, there is also provided a device for optimizing the performance of an optical fiber communication system based on a direct-modulated laser, comprising at least one processor and a memory, wherein the at least one processor and the memory are connected via a data bus, and the memory stores instructions that can be executed by the at least one processor, and after being executed by the processor, the instructions are used to complete the above-mentioned method for optimizing the performance of an optical fiber communication system based on a direct-modulated laser.

In general, the above technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

The present invention conducts physical modeling on the communication system based on the direct-modulated laser and finds the physical parameters that affect its transmission performance. By combining the physical level optimization of the device and the optical fiber link with the digital level optimization of the digital signal processing algorithm, the performance of the system is further improved. At the same time, due to the pre-compensation of the system frequency response curve, the pressure of frequency domain equalization is reduced, the complexity of the digital signal processing algorithm is reduced, and the cost of the system is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic flow chart of a method for optimizing the performance of an optical fiber communication system based on a directly modulated laser according to the present invention;

FIG2 is a schematic diagram of a system frequency response curve in an initial state of the system according to an embodiment of the present invention;

FIG3 is a schematic diagram of a system frequency response curve after the system updates parameters in an embodiment of the present invention;

FIG4 is a flow chart of a frequency domain equalization algorithm according to an embodiment of the present invention;

FIG5 is a schematic diagram showing the principle of compensating a system frequency response curve using frequency domain equalization technology in an embodiment of the present invention;

FIG. 6 is a diagram showing the result of compensating the system frequency response curve using the frequency domain equalization technology in an embodiment of the present invention.

Detailed ways

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 the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Factors that affect system performance include: injection current of the directly modulated laser, dispersion of the optical fiber and digital signal processing algorithms.

As shown in FIG1 , the present invention provides a method for optimizing the performance of an optical fiber communication system based on a directly modulated laser, comprising the following steps:

S1: Extracting initial relevant physical parameters of an optical fiber communication system based on a direct-modulated laser, wherein the optical fiber communication system includes a direct-modulated laser at the transmitting end and transmission optical fibers with different dispersion values. The following physical parameters of the direct-modulated laser at the transmitting end of the system and the transmission optical fiber can be obtained by pre-designing the system or measuring the actual system, including: line width enhancement factor α ₀ of the direct-modulated laser, adiabatic chirp parameter κ ₀ of the direct-modulated laser, injection current I ₀ of the direct-modulated laser, optical fiber dispersion D ₀ and optical fiber length L ₀ and other parameters;

S2: Mathematically model the optical fiber communication system based on the direct-modulated laser, establish a system emission and transmission frequency response function model except for the receiving end, bring the obtained initial relevant physical parameters into the above frequency response function model to calculate the initial frequency response curve of the system except for the receiving end. The mathematical model established in step S2 is:

In a transmission system based on a directly modulated laser, taking into account the injection current of the directly modulated laser and the fiber dispersion factor, the frequency response is expressed by the following formula:

In this formula, the first term on the right is the frequency response caused by transient chirp, which is recorded as H _tst (f,L), and the second term is the frequency response caused by adiabatic chirp, which is recorded as _Hadb (f,L), f represents frequency, L represents transmission distance, I represents injection current, α represents linewidth enhancement factor, D represents fiber dispersion, λ represents direct-modulated laser wavelength, c represents light speed in vacuum, ε represents gain limitation factor, Γ represents light limitation factor, _Ith represents threshold current, e represents electron charge, and V represents active area volume. The total amplitude response of the system is the superposition of the two frequency responses. The total amplitude response formula of the system is:

Substituting the initial relevant physical parameters obtained in step S1 into the above system total amplitude response formula, the initial frequency response curve of the system as shown in FIG. 2 is obtained.

S3: Pre-compensate the initial frequency response curve of the above system, that is, adjust the injection current of the direct-modulated laser. The adjusted injection current must be in the linear region of the driving current of the direct-modulated laser and meet the extinction ratio requirement of the device.

S4: pre-compensating the initial frequency response curve of the above system, that is, adjusting the fiber dispersion value so that the overall system frequency response curve of the system meets the preset flatness requirement and achieves distortion-free transmission conditions (specifically, the amplitude difference between the low-frequency part and the high-frequency part of the system frequency response curve can be made less than 0dBm, as close to 0dBm as possible, or even equal to 0dBm).

The system frequency response curve pre-compensation method is achieved by adjusting the physical parameters of the injection current and fiber dispersion value of the direct-modulated laser, which can be divided into two cases:

(1) When the optical fiber dispersion value can be changed, that is, when the optical fiber can be replaced, the dispersion values of different existing optical fibers are measured and recorded as D _i , i = 1, 2, ..., n;

(2) When the fiber dispersion value cannot be changed, that is, when the fiber cannot be changed, the current fiber dispersion value is recorded as D ₀ ;

For different dispersion values D _i , substitute them into the total amplitude response formula of the system, adjust different injection current values I _i through simulation, obtain a series of system frequency response curves under different conditions, and find the flat system frequency response curve under limited conditions. Record the dispersion value and the injection current value of the direct-modulated laser at this time, and modify the physical parameters of the system accordingly.

S5: modifying the injection current value of the direct-modulated laser according to the injection current of the new direct-modulated laser obtained in step S3; and performing dispersion compensation processing on the transmission optical fiber according to the new optical fiber dispersion value obtained in step S4.

S6: Substituting the parameters corrected in step S5 into the total amplitude response of the system, an updated system frequency response curve as shown in FIG3 is obtained.

S7: Optimize the updated system frequency response curve obtained in step S6 using the electrical domain frequency domain equalization technology to further flatten the system frequency response curve and achieve distortion-free transmission conditions for the overall transmission characteristics of the system.

The method of using frequency domain equalization technology to compensate the system frequency response curve is implemented by digital signal processing technology, as shown in FIG4 , and the specific method is as follows:

① Perform Fourier transform on the original data x at the transmitter to obtain X;

② Perform Fourier transform on the data y received by the receiving end to obtain Y;

③ Obtain the system frequency response curve by converting the transformed data Y/X;

④Smooth the system frequency response curve;

⑤ Obtain new data by inverting the system frequency response curve;

⑥ Multiply the transmitted data with the constructed new data in the frequency domain and then convert it back to the time domain for transmission.

After pre-compensating the system frequency response curve, the present invention further compensates the system frequency response curve using the frequency domain equalization technology of the digital signal processing algorithm. FIG5 is a schematic diagram of the principle of compensating the system frequency response curve using the frequency domain equalization technology. FIG6 is a result of compensating the system frequency response curve using the frequency domain equalization technology. The optimization schemes shown in FIG6 are better than only optimizing the physical parameters of the device or only using the digital signal processing algorithm, and have a greater improvement in system performance.

It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A method for optimizing the performance of an optical fiber communication system based on a directly modulated laser, characterized in that it comprises the following steps: S1: extracting initial relevant physical parameters of an optical fiber communication system based on a directly modulated laser, wherein the optical fiber communication system includes a directly modulated laser at a transmitting end and transmission optical fibers with different dispersion values; S2: Mathematically model the optical fiber communication system based on the direct-modulated laser, establish the emission and transmission frequency response function model of the system except the receiving end, bring the obtained initial relevant physical parameters into the above frequency response function model to calculate the initial frequency response curve of the system except the receiving end; S3: pre-compensate the initial frequency response curve of the above system, that is, adjust the injection current of the direct-modulated laser. The adjusted injection current must be in the linear region of the driving current of the direct-modulated laser and meet the extinction ratio requirement of the device. S4: pre-compensate the initial frequency response curve of the above system, that is, adjust the fiber dispersion value so that the overall system frequency response curve meets the preset flatness requirement and achieves distortion-free transmission conditions; S5: modifying the injection current value of the direct-modulated laser according to the injection current of the new direct-modulated laser obtained in step S3; performing dispersion compensation processing on the transmission optical fiber according to the new optical fiber dispersion value obtained in step S4; S6: Substituting the parameters corrected in step S5 into the total amplitude response of the system to obtain an updated system frequency response curve; S7: Optimize the updated system frequency response curve obtained in step S6 using the electrical domain frequency domain equalization technology to further flatten the system frequency response curve and achieve distortion-free transmission conditions for the overall transmission characteristics of the system. 2. The method for optimizing the performance of an optical fiber communication system based on a direct-modulated laser according to claim 1, characterized in that, in step S1, the following physical parameters of the direct-modulated laser and the transmission optical fiber at the transmitting end of the system are obtained by pre-designing the system or measuring the actual system, and the physical parameters include: the line width enhancement factor α ₀ of the direct-modulated laser, the adiabatic chirp parameter κ ₀ of the direct-modulated laser, the injection current I ₀ of the direct-modulated laser, the optical fiber dispersion D ₀ and the optical fiber length L ₀ . 3. The method for optimizing the performance of an optical fiber communication system based on a directly modulated laser according to claim 1 or 2, wherein the mathematical model established in step S2 is: In a transmission system based on a directly modulated laser, taking into account the injection current of the directly modulated laser and the fiber dispersion factor, the frequency response is expressed by the following formula: In this formula, the first term on the right side is the frequency response caused by transient chirp, which is recorded as H _tst (f,L), and the second term is the frequency response caused by adiabatic chirp, which is recorded as _Hadb (f,L), f represents frequency, L represents transmission distance, I represents injection current, α represents linewidth enhancement factor, D represents fiber dispersion, λ represents wavelength of direct modulated laser, c represents speed of light in vacuum, ε represents gain limitation factor, Γ represents light limitation factor, _Ith represents threshold current, e represents electron charge, and V represents active area volume; The total amplitude response of the system is the superposition of two frequency responses, namely: Substitute the initial relevant physical parameters obtained in step S1 into the above system total amplitude response formula to obtain the system initial frequency response curve. 4. The method for optimizing the performance of an optical fiber communication system based on a direct-modulated laser as described in claim 1 or 2, wherein the system frequency response curve pre-compensation method is achieved by adjusting the physical parameters of the injection current and optical fiber dispersion value of the direct-modulated laser. 5. The method for optimizing the performance of an optical fiber communication system based on a directly modulated laser according to claim 4, wherein the pre-compensation of the system frequency response curve is divided into two cases: (1) When the optical fiber dispersion value can be changed, that is, when the optical fiber can be replaced, the dispersion values of different existing optical fibers are measured and recorded as D _i , i = 1, 2, ..., n; (2) When the fiber dispersion value cannot be changed, that is, when the fiber cannot be changed, the current fiber dispersion value is recorded as D ₀ ; For different dispersion values D _i , substitute them into the total amplitude response formula of the system, adjust different injection current values I _i through simulation, obtain a series of system frequency response curves under different conditions, find out the flat system frequency response curve under limited conditions, record the dispersion value and injection current value of the direct-modulated laser at this time, and modify the physical parameters of the system accordingly. 6. The method for optimizing the performance of an optical fiber communication system based on a directly modulated laser according to claim 1 or 2, wherein the method for optimizing by using the electrical domain and frequency domain equalization technology is implemented by digital signal processing technology, and the specific method is as follows: ① Perform Fourier transform on the original data x at the transmitter to obtain X; ② Perform Fourier transform on the data y received by the receiving end to obtain Y; ③ Obtain the system frequency response curve by converting the transformed data Y/X; ④Smooth the system frequency response curve; ⑤ Obtain new data by inverting the system frequency response curve; ⑥ Multiply the transmitted data with the constructed new data in the frequency domain and then convert it back to the time domain for transmission. 7. The method for optimizing the performance of an optical fiber communication system based on a direct-modulated laser as described in claim 1 or 2, characterized in that the factors affecting the system performance include: the injection current of the direct-modulated laser, the dispersion of the optical fiber and the digital signal processing algorithm. 8. The method for optimizing the performance of an optical fiber communication system based on a directly modulated laser according to claim 1 or 2, characterized in that in step S4, the overall system frequency response curve of the system is made to meet a preset flatness requirement, specifically: the amplitude difference between the low-frequency part and the high-frequency part of the system frequency response curve is made to be less than 5dBm. 9. A device for optimizing the performance of an optical fiber communication system based on a directly modulated laser, characterized in that: The method comprises at least one processor and a memory, wherein the at least one processor and the memory are connected via a data bus, and the memory stores instructions that can be executed by the at least one processor, and after being executed by the processor, the instructions are used to complete the method for optimizing the performance of an optical fiber communication system based on a direct-modulated laser according to any one of claims 1 to 8.