Construction of simulation model of the optical transmission module
The optical communication simulation analysis software OptiSystem is used to conduct test simulation, to verify the test principle of bit error rate, eye diagram, and signal bandwidth, and to predict the test results, from which the relationship between the design parameters of the optical transmission module and the electrical characteristic parameters is analyzed.
The research selects the SFP-10G-LR optical transmission module and builds a simulation model in the simulation software according to the module parameters, in which the parameters of each component are consistent with the design parameters of the actual optical transmission module. Each part of the optical transmission module in the simulation model corresponds to the functions of each part in the actual device, and the pulse transmitter and the directly modulated laser constitute the transmitter part of the optical transmission module. The pulse generator generates a pulse sequence consistent with the input signal, and the direct modulation laser directly modulates the optical signal according to the input signal while generating the optical signal, and transmitting the information in the input signal through the optical signal. The optical receiver part of the optical transmission module is composed of a detector, an amplifier and a filter. The detector detects the optical signal from the optical fiber and sends out a weak electrical signal, which is then amplified by the amplifier. The transmitted information is returned in the form of electrical signals. In the actual test experiment, the transmission fiber part in the middle is affected by the laboratory conditions, and the transmission fiber of different lengths can be selected for the experiment.
Simulation Model Verification of Optical Transmission Module
After completing the construction of the simulation model of the optical transmission module, the simulation model is verified. A simple comparison of the input and output signals collected shows that the signal distortion is within a reasonable range, and the basic functions of signal transmission can be completed. A spectrum analyzer is placed behind the optical transmitter to measure the emitted optical signal, and the center wavelength of the obtained measurement result is about 1310 nm.
Bit Error Rate Simulation Test
Select the test equipment required for the test plan, and build the corresponding experimental simulation model in the OptiSystem software. The bit error rate analyzer simultaneously collects the random sequence generated by the pseudo-random code generator, the sequence generated by the code pattern generator and the output signal of the final optical transmission module, and finally gives the corresponding bit error rate through comparison and calculation.
Eye Diagram Simulation Test
After completing the simulation of the bit error rate test principle, use the same process to simulate the eye diagram. According to the eye diagram test principle, select the test equipment required for the test plan, and build the corresponding experimental simulation model in the OptiSystem software. Similar to the bit error rate test, the pseudo-random code generator generates the pseudo-random code sequence required for the test and inputs it into the optical transmission module. and the output signal of the optical transmission module, and finally the eye diagram of the signal transmission of the optical transmission module is given. At the same time, the same experimental conditions as in the bit error rate test simulation experiment were selected to carry out the control experiment, and the simulation experiment results were obtained as shown in Figure 7, where the abscissa is the time represented by the bit period, and the ordinate is the amplitude. By analyzing the results of the two sets of control experiments, it can be concluded that under the condition of a certain transmit power, with the increase of the center wavelength, the eye diagram of the signal transmission is gradually clear, and the greater the opening degree of the “eye” means that the signal transmission is The overall quality improvement is more obvious. In the case of a fixed center wavelength, as the transmit power decreases, the eye diagram becomes more blurred, which means that the overall quality of the signal transmission is degraded.
Signal Bandwidth Simulation Test
Finally, carry out the simulation test of the signal bandwidth. According to the signal bandwidth test principle, select the test equipment required by the test plan, and build the corresponding experimental simulation model in the OptiSystem software. The simulation test is carried out under the same control experimental conditions as above, and the spectrum diagram of the measured signal is obtained. From the analysis of the simulation results, it can be concluded that the factor that has a greater impact on the signal bandwidth is the transmit power of the optical transmission module, while the center wavelength has less impact. When the transmit power is too low, problems such as signal transmission distortion and serious signal power consumption will occur.
Analysis of Test Results
Based on the above simulation test results, the influence of the working center wavelength of the optical transmission module and the transmit power of the optical transmitter on the quality of the transmitted signal can be analyzed. After a series of test results obtained by testing and simulating each electrical characteristic parameter under different experimental conditions, it can be concluded that the signal transmission quality of the optical transmission module is positively correlated with the center wavelength and the transmit power, that is, within the design range, the signal transmission performance It increases with the increase of center wavelength and transmit power, and vice versa. The maximum center wavelength of 1 355 nm, the maximum transmit power of 0.5 dBm and the minimum center wavelength of 1 260 nm and the minimum transmit power of -8.2 dBm were selected for control experiments.
This paper mainly focuses on an SFP+ optical module, selects the bit error rate, eye diagram and signal bandwidth as the main test parameters, investigates the test methods of each parameter and summarizes the test principles. On this basis, the OptiSystem software is used to conduct simulation experiments on the test of each parameter, which verifies the feasibility of the test principle, and the influence on the signal transmission quality can be quickly obtained by changing the design parameters. At the same time, according to the results of the simulation test, the influence of the design parameters of the optical transmission module on the signal transmission performance is analyzed.