When optical communications systems were initially deployed, it was fairly easy to verify physical-layer performance since the entire network was owned and installed by one company. If the system worked, testing of the subcomponents was no longer necessary. However, today’s optical networks often use components from various suppliers, so the customer needs a test strategy and a specification to ensure all the components satisfy the system-level requirements.
A digital communications system – whether it is a an interface bus or a telecommunications link within a laptop computer, must run with an acceptable Bit-Error Ratio (BER), typically one error in 1,012 bits. If a transmitter is paired with a single receiver via fiber and the system does not achieve the desired BER, the machine operator must determine if the error is on the receiver, the transmitter or both.
Network specifications should assure that receivers will interoperate with a worst-case transmitter. Transmitters must also offer a signal with enough quality to interoperate with a worst-case receiver.
Wide-bandwidth oscilloscopes allow the operator to perform optical eye-mask tests. The instruments are available in several names, such as digital communications analyzers. These oscilloscope can do the test to determine if any waveform samples fall on the mask.
Several laser manufacturers wanted the lasers to pass the mask test without violations and look for measurements with great margin. Expanding the dimensions of the mask as large as possible without incurring mask hits delivers the maximum margin.
Leave a Reply
You must be logged in to post a comment.