New Fiber Optic Source Speeds Component Testing

Ruth A. Mendonsa

Lightwave telecommunication systems are meeting today's spiraling demand for increased bandwidth by adding multiple wavelength channels to each fiber. Wavelength division multiplexed (WDM) systems deliver 10- to 40-Gb performance on a single fiber, and 100-Gb performance is not far off.
For all their advantages, WDM systems require advanced fiber optic components and related production test instrumentation. Typical performance requirements for these components include tight center wavelength tolerance, low insertion loss, high channel-to-channel isolation and high wavelength stability. Many fiber optic component manufacturers are using high-power, broadband amplified spontaneous emission (ASE) sources to test WDM components such as multiplexers, demultiplexers, add-drop filters and fiber Bragg gratings.
DiCon Fiberoptics Inc. of Berkeley, Calif., automates its production testing of WDM filter components using the MPS-8033/55 Broadband ASE Source from ILX Lightwave of Bozeman, Mont., in conjunction with an optical spectrum analyzer.
First, the broadband source is connected to the optical spectrum analyzer via a fiber patch cord to obtain a reference spectrum, which is stored digitally in the analyzer. The filter is then inserted between the broadband source and the analyzer, and a second spectrum is stored. The filter's transmission properties can be obtained by figuring the ratio of the second spectrum to the first.
The reference spectrum is typically measured and stored only once or twice a day. For production testing, the user can simply connect a component and start a test program. The actual measurement of the transmission vs. wavelength takes only seconds. DiCon Fiberoptics has found the wavelength scanning speed of an optical spectrum analyzer to be faster than that of a tunable laser.
For accuracy and speed in this application, the broadband source must provide a stable, high-power output spectrum that is spread over the wavelength range. For dense WDM component testing, this range is typically from 1540 to 1570 nm. The source incorporates 10 m of erbium-doped fiber that is pumped with a high-power 980-nm laser diode. This emission generally has a smooth spectrum spread over the 1520- to 1570-nm wavelength region. Proper selection of erbium fiber and pump laser power allows total output powers of 10 to 20 mW. The output spectrum is also stable and intrinsically unpolarized.
The MPS-8033/55 broadband ASE source is also being used in fiber optic sensor work.