After installing the optical module, testing its performance is an essential step. When the optical components in the entire network system are supplied by one supplier, if the network system can work normally, then there is no need to test the sub-components of the system separately. However, most of the subcomponents in network systems now come from different suppliers, so it is very important to test the compatibility and interoperability of optical components, especially individual optical modules. So how to test the compatibility of optical modules?

We know that the optical module is composed of a transmitter and a receiver. When the transmitter is connected to the receiver through optical fiber, if the bit error rate of the whole system does not achieve the expected effect, is it the problem of the transmitter or the receiver? Or maybe there’s a problem with both the transmitter and receiver. In fact, the transmitter and receiver of the optical module will affect each other. Therefore, the qualified standard of the optical module is that any receiver can receive the optical signal from the transmitter with the worst performance, and any transmitter can emit the optical signal that can be detected by the receiver. The light signal received by the worst performing receiver.

Accurately defining the worst performance of a transmitter or receiver is a complex task. If the receiver needs to receive a certain power to meet the system’s bit error rate requirements, then this power is the minimum transmit power of the transmitter; if The receiver can only tolerate a certain amount of jitter capacity, then, the jitter capacity is the maximum jitter tolerance of the transmitter.

Testing optical modules is generally divided into 4 steps (as shown in the figure below), which are mainly divided into testing the transmitter and receiver.

transmitter test

When testing, you need to pay attention to the wavelength and shape of the transmitter output waveform, as well as the jitter tolerance and bandwidth of the receiver. When testing the transmitter, you need to pay attention to the following two points:

1. The quality of the input signal used to test the transmitter must be good enough. In addition, the quality of the electrical measurements must be confirmed by jitter measurements and eye diagram measurements. Eye diagram measurements are a common way to examine the output waveform of a transmitter because the eye diagram contains a wealth of information that reflects the overall performance of the transmitter.

2. The output optical signal of the transmitter must be measured with optical quality indicators such as eye diagram test, optical modulation amplitude and extinction ratio.

receiver test

When testing the receiver, you also need to pay attention to the following two points:

3. Unlike testing transmitters, when testing receivers, the quality of the optical signal must be sufficiently poor, therefore, an optical stress eye diagram must be created that represents the worst signal that must pass the jitter measurements and optical power tests for calibration.

4. Finally, it is necessary to test the electronic output signal of the receiver. There are three main types of this test:

• 　　 Eye diagram test, which can ensure that the “eye” of the eye diagram is in an open state. Eye diagram testing is usually achieved by the depth of bit error rate

Jitter test , test different types of jitter

• 　　 Jitter tracking and tolerance, test the tracking of internal clock recovery circuit to jitter

All in all, testing optical transceivers is a complex task, but it is also an indispensable step to ensure its good performance. As a widely used measurement method, eye diagram measurement can effectively test the transmitter of the optical module. The receiver test of the optical module is more complicated and requires more test methods.