Now, the optical fiber to the home (HTTP) has been closer and closer to us, some time ago China telecom is vigorously laying communications cable, and issued a series of EPON standard specifications, which shows that optical fiber communication will soon be connected to tens of thousands of households, users can enjoy the unprecedented speed and pleasure brought by optical communication.
Optical transmission signals have great advantages over electrical transmission signals, such as: good confidentiality of optical transmission, large channel capacity, low cost and other advantages. An optical fiber can transmit about 1,000 times more power than a wire.Such a fast speed makes us all excited.Now the basic structure of optical communication system is o-e-o conversion process. The core component of photoelectric transceiver is commonly known as optical module, which determines whether the signal transmission is good or bad.
Therefore, it is necessary to test the channel transfer quality of optical module. The existing method is to judge the channel quality of the module by the quality of the observation signal eye map. As you may know, the principle of eye map is to use TRIGGER signal of signal source to synchronously sample and detect DATA signal, and form a group of points on the timeline, from which the graph like eyes is displayed on the oscilloscope. Tektronix is commonly used in the industry to test the eye chart to further adjust the impedance matching or bias of the module and to modulate the current to observe the eye chart to the desired level.
Various parameters can be tested by eye map, such as average power,EXR,rise time,fall time,jitter, etc. The attachment is an eye map tested by an oscilloscope, and the optical module has a wavelength of 1.25g 850nm. As can be seen from the figure, the rising edge and falling edge of the signal are asymmetric, which indicates that the impedance does not match well, and too thick line indicates that it is disturbed by relatively large noise.We can further improve the transmission performance of the module by adjusting the matching resistance. On the right side of the oscilloscope is the data display area. We can see the average optical power and EXR value emitted by the optical module. Meanwhile, we can select other options to test.