SFP+ Optical Transmission Module Electrical Parameter Test Principle
SFP+ is a hot-pluggable, communication protocol-independent optical transceiver that typically transmits light at wavelengths of 850nm, 1310nm, or 1550nm for SONET/SDH at 10G bps, Fibre Channel, gigabit Ethernet, 10 gigabit Ethernet and In other applications, it also includes DWDM links. SFP modules (the volume is reduced by half compared to GBIC modules, and more than double the number of ports can be configured on the same panel. This article is mainly for an SFP+ optical module, select the bit error rate, eye Figure and signal bandwidth are used as the main test parameters, the test methods of each parameter are investigated and the test principles are summarized.
The optimal optical transmission module design usually needs to meet four basic indicators: suitable spectral response range, suitable bandwidth, lowest possible noise and large dynamic range. These four basic indicators are generally measured by electrical characteristic parameters such as bit error rate, eye diagram and signal bandwidth. Among them, bit error rate is used to measure the accuracy of signal transmission, eye diagram is used to measure the overall quality of signal transmission, and signal is used to measure signal transmission capability and dynamic range.
The Principle of Bit Error Rate Test
The bit error rate is the frequency of bit errors. In an optical transmission system, the bit error rate is usually defined as the ratio of the number of pulses Ne and the total number of transmission pulses Nt within a certain time interval t. Sending through an external signal source A test code sequence is sent to the optical module, and the transmitted output signal and the test code sequence generated by the signal source are collected at the same time, the input signal and the output signal are compared bit by bit, and the total number of errors and the total number of transmitted pulses are counted. The bit error rate of the optical module can be obtained.
Eye Diagram Test Principle
Eye diagram refers to an eye-like graph formed by superimposing different random sequences collected on the oscilloscope after the period of the oscilloscope is adjusted to be consistent with the period of the transmitted random sequence, so it is called “eye diagram”. The test principle of the eye diagram is to connect the signal source, the module under test and the eye diagram in turn, and use the external signal source to generate a series of random code sequences and send them to the module under test. Random code sequence, superimpose the different random sequences obtained to obtain the eye diagram of the tested module.
Signal Bandwidth Test Principle
The test principle of the signal bandwidth is to connect the signal source, the module under test and the spectrum analyzer in sequence, and use the external signal source to generate a series of random code sequences and send them to the module under test. The random code sequence obtains the spectrogram of the signal under test, thereby obtaining the signal bandwidth of the component under test.