Meeting the Challenge of Testing High-Performance Demultiplexers

Ruth A. Mendonsa

The advent of dense wavelength division multiplexed (DWDM) telecommunications systems has brought with it new development and production challenges. Among these is the configuration of test equipment that meets the requirements of the device to be tested. Although such configurations are possible with readily available instrumentation, the immediate limitation is to retain the required measurement performance and still meet the equally important need for fast throughput. Testing a 16-channel DWDM demultiplexer to its rigid specifications over all channels could easily take several hours per device, but such test time is unacceptable.
One major telecommunications company has turned to the HP 83464A DWDM measurement system from the Santa Rosa, Calif.-based Hewlett-Packard Lightwave Div. to solve its throughput requirements. The company's test system employs a flexible user interface that supports two modes of operation: engineering and production. It simultaneously measures multiple DWDM demultiplexers over temperature and offers performance beyond that available from the individual instruments that it comprises.
Hewlett-Packard's test system includes an amplified spontaneous emissions source for characterizing the noise properties of the demultiplexer, a tunable laser source and optical spectrum analyzer for accurate wavelength selectivity, a multiwavelength meter, a polarization controller, lightwave switching for automatic signal routing, a PC and customized software for system control and for meeting specific test routines and parameters.
Multichannel DWDM demultiplexers will offer wavelength channel spacing as narrow as 0.8 and even 0.4 nm with minimal insertion loss and substantial crosstalk isolation. The HP 83464A verifies these specifications as well as center wavelength, bandwidth, polarization dependence of center wavelength and bandwidth, and polarization-dependent loss.