Introduction
Optical fiber communication test refers to the test work to verify the characteristics of optical fiber communication system. Broadly speaking, the test objects include optical fibers, optical cables, light-emitting devices, photodetectors, optical transmitters, optical receivers, etc. There are many items to be carried out. Considering the system installation and operation, the side test of optical fiber line and equipment mainly includes the whole process attenuation of optical fiber line, optical transmitter output optical power, optical receiver sensitivity, dynamic range, signal jitter, bit error rate test, etc. The following introduces 4 test items including the entire attenuation of the optical fiber line, the average output optical power of the digital optical transmitter, the sensitivity of the digital optical receiver, and the signal jitter.
Optical fiber line attenuation test
After the optical fiber line is installed in the field, the cut-off method can be used to test the entire attenuation. The optical signal output by the standard light source is injected into the optical fiber line. At the end of the line The optical power meter measures the lifted optical power. Then cut off the optical fiber at the beginning of the line and measure the output optical power of the light source. The difference between the two is the attenuation of the optical fiber line, expressed in dB. This method is highly accurate and requires simple equipment, but the original optical fiber line needs to be cut off during the test. This is a destructive test method. Another non-destructive test method is based on the principle of backscatter, using a light-time city reflectometer to test the full attenuation. It can also measure the distribution of attenuation along the length of the line, joint attenuation, etc., which is easy to operate. But the accuracy is low.
Measurement of average output optical power of digital optical transmitter
Use a pattern generator to send the pseudo-random code electrical signal to the optical transmitter, and use optical The power meter measures the output optical power, that is, the average output optical power. When measuring. The light pulse should be a good rectangular wave. The pulse width should be basically the same, and there should be no phase jitter.
Digital optical receiver sensitivity test
The sensitivity of digital optical receiver is the minimum input optical power of the receiver under the premise of meeting the bit error rate requirements. During the test, the optical transmitter sends out a pseudo-random code optical pulse signal, enters the optical receiver through an optical attenuator, and measures the bit error rate of the output signal of the receiver. Increase the optical attenuation value until the received signal bit error rate rises to the technical index requirements, calculate the actual received optical power of the receiver according to the average output optical power of the optical transmitter, the attenuation of the optical attenuator, and the attenuation of the optical fiber and the optical fiber connection piano. Sensitivity, generally expressed in dBm.
Signal jitter test
The jitter of a digital signal is the time deviation between the width and interval of the signal pulse and its expected value. The signal jitter of the optical fiber communication system mainly includes the maximum jitter of the box and The allowable limit of the input jitter is twofold. The former is to send a jitter-free pseudo-random code optical signal at the transmitting end of the system, and measure the maximum jitter peak value of its output signal with a pulse code modulation signal analyzer at the receiving end. The latter is to send a pseudo-random code optical signal with variable jitter at the transmitting end. Monitor the bit error rate of the output signal at the receiving end, and test the allowable limit of signal jitter at the transmitting end when the bit error rate meets the index.