When optical transceivers was first deployed, verifying the performance of it was straightforward. The entire network was installed and owned by a single company, and if the system worked, extensive testing of the subcomponents was unnecessary. Today, however, most optical networks use components that may come from a variety of suppliers. Therefore, to test the compatibility and interoperability of each fiber optic transceiver becomes particularly important. How to test a fiber optic transceiver? This article may give you the answer.
As we all know, basically, a fiber optical transceiver consists of a transmitter and a receiver. When a transmitter through a fiber to connect with a receiver but the system doesn’t achieve your desired bit-error-ratio (BER), is the transmitter at fault? Or, is it the receiver? Perhaps both are faulty. A low-quality transmitter can compensate for by a low-quality receiver (and vice versa). Thus, specifications should guarantee that any receiver will interoperate with a worst-case transmitter, and any transmitter will provide a signal with sufficient quality such that it will interoperate with a worst-case receiver.
Precisely defining worst case is often a complicated task. If a receiver needs a minimum level of power to achieve the system BER target, then that level will dictate the minimum allowed output power of the transmitter. If the receiver can only tolerate a certain level of jitter, this will be used to define the maximum acceptable jitter from the transmitter. In general, there are four basic steps in testing an optical transceiver, as shown in the following picture, which mainly includes the transmitter testing and receiver testing.
Transmitter parameters may include wavelength and shape of the output waveform while the receiver may specify tolerance to jitter and bandwidth. There are two steps to test a transmitter:
1. The input signal used to test the transmitter must be good enough. Measurements of jitter and an eye mask test must be performed to confirm the quality using electrical measurements. An eye mask test is the common method to view the transmitter waveform and provides a wealth of information about overall transmitter performance.
2. The optical output of the transmitter must be tested using several optical quality metrics such as a mask test, OMA (optical modulation amplitude), and Extinction Ratio.
To test a receiver, there are also two steps:
3. Unlike testing the transmitter, where one must ensure that the input signal is of good enough quality, testing the receiver involves sending in a signal that is of poor enough quality. To do this, a stressed eye representing the worst case signal shall be created. This is an optical signal, and must be calibrated using jitter and optical power measurements.
4. Finally, testing the electrical output of the receiver must be performed. Three basic categories of tests must be performed:
- A mask test, which ensures a large enough eye opening. The mask test is usually accompanied by a BER (bit error ratio) depth.
- Jitter budget test, which tests for the amount of certain types of jitter.
- Jitter tracking and tolerance, which tests the ability of the internal clock recovery circuit to track jitter within its loop bandwidth.
In summary, testing a fiber optic transceiver is a complicated job, but it is an indispensable step to ensure its performance. Basic eye-mask test is an effective way to test a transmitter and is still widely used today. To test a receiver seems more complex and requires more testing methods. Fiberstore provides all kinds of transceivers, which can be compatible with many brands, such as Cisco, HP, IBM, Arista, Brocade, DELL, Juniper etc. In Fiberstore, each fiber optic transceiver has been tested to ensure our customers to receive the optics with superior quality. For more information about the transceivers or compatible performance test, please visit www.fs.com or contact us over firstname.lastname@example.org.
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