Handheld DWDM OSAs Move From the Lab to the Field

The rapid growth of DWDM has brought with it a new requirement for test equipment that is not confined to the laboratory. As a result, portable OSAs have moved from the lab to the field alongside loss test sets and OTDRs.

To meet the challenges of DWDM testing, handheld OSAs handheld-dwdm-osa must have excellent dynamic range and power-angle measurement capability.

What is an OSA?

OSAs divide a light signal into its component wavelengths, measure the power of each wavelength, and display results graphically. They are used to characterize the performance of CWDM and DWDM networks. The most basic units have a rotatable grating and a fixed detector; as the grating rotates and the detector moves, the OSA “sweeps” across the spectral range, allowing it to measure power-level distributions at every wavelength in the spectrum.

High-end diffraction-grating-based units for DWDM applications can achieve wavelength accuracy of +-0.02 nm and power-level accuracy of +-0.5 dB including the PDL error, says Hiroshi Goto, optical product specialist at Anritsu. Michelson interferometer-based OSAs display a multiwavelength spectrum by calculating the Fourier transform of a measured interference pattern.

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What are the key features of an OSA?

The detector-based technology at the core of a handheld DWDM OSA has long been in use as part of power meters, and its high wavelength accuracy, resolution and power dynamic range reflect this ancestry. It’s an ideal piece of equipment to have on hand when performing field tests in the field, as it offers a simple, intuitive user interface and twice-a-second scan rate.

Increasing demand for larger wavelength ranges, higher ORR at 0.4 nm and smaller resolution bandwidth (RBW) — mainly for lab purposes — has pushed designers to improve the OSA. To do this, they’ve improved the design of the device by incorporating double- and quadruple-pass gratings. These structures separate the spectrum into individual wavelengths by reflecting a section of the diffracted light back on itself multiple times before reaching the detector, giving a much better orr and wavelength resolution.

Other features of an OSA to consider are the wavelength accuracy and resolution, power level and optical signal-to-noise ratio (OSNR). An OSA with 20 pm wavelength accuracy or less and a resolution bandwidth under 70 pm makes it easy to detect weak signals that might be obscured by strong ones.

The OSNR is a measure of how robust the adjacent channels are to noise from the strong signal. An OSA with a high orr means that the powerful signal doesn’t smother its neighbors.

How do OSAs work?

As DWDM systems have become more sophisticated, the need for test equipment that can measure wavelengths as precisely as power levels has grown. That’s led to the development of OSAs, which divide a signal into its constituent wavelengths and display their power-level distributions.

The type of OSA you choose depends Internet of things on your DWDM testing requirements. For example, you may need to measure power density in a 0.1-nm slice of the spectrum or you may need to find the exact wavelength of the channel within a coarse WDM device (WDM coupler, switch or attenuator).

Anritsu’s OSAs use either a slit in a diffraction grating or a Michelson interferometer, which displays a spectrum by calculating the Fourier transform of a measured interference pattern. Both approaches have advantages and disadvantages, but the grating-based approach provides the best wavelength range, accuracy and dynamic range for DWDM applications.

The latest OSAs also include a DWDM-specific attenuation trace function that helps you optimize fiber-loss compensation in your network. This allows you to measure the loss of a single DWDM component and compensate for it in other fiber links, helping you avoid service outages due to poor attenuation. Good field OSAs also provide a number of automatic tools to help you characterize important component characteristics such as insertion loss, bandwidth and center wavelength. They also allow you to compare traces from multiple OSAs, which helps you identify the source of performance problems.