Portable DWDM OSAs Advance to Short List of Essential Test Equipment

With DWDM systems now appearing in the field, it’s important to have the right testing equipment. Many contractors are finding that portable OSAs are advancing to the “short list” of essential test equipment for their DWDM system installation and maintenance activities.

To support DWDM applications, look for high-end grating monochromators with channel wavelength accuracy to within 1/10 of grid spacing and power-level accuracy to within +/- 0.02 dB including power tilt.

Optical Spectrum Analyzer (OSA)

An optical spectrum analyzer (OSA) is a test instrument that measures the spectral characteristics of light. This type of instrument is used in a wide variety of applications. OSAs measure the power and wavelength of a light signal and can display this information on a computer screen. They can also determine the Optical Signal-to-Noise Ratio (OSNR) of an optical signal. This information is useful for analyzing and optimizing optical systems.

OSAs use a tunable filter to separate different components of the optical signal and then a photodetector to convert the resulting electrical current into a measurement. The OSA can then calculate the Optical Signal-to-Noise-Ratio (OSNR) of a signal by comparing it to the background noise of the system.

The tunable filter used in an OSA is most often a Fabry-Perot interferometer. This technique filters incoming light by using parallel mirrors that create a resonant cavity to set the input wavelength. This type of filter has a very high wavelength resolution and a broad dynamic range, making it ideal for DWDM analysis.

A single mechanical sweeping mechanism in an OSA covers a range of wavelengths sometimes from 350 to 1700nm. The accuracy handheld-dwdm-osa of this span can vary depending on the internal error correction algorithms used to compensate for wavelength dependencies, gain blocks and polarization effects.

Most OSAs offer an automatic calibration feature to ensure that all measurements are performed in the same conditions. This allows them to detect and correct for factors that can affect the result, such as the temperature of the detector or polarization variations in the light source.

Optical Spectrum Analyzers are used in many different applications, including DWDM channel testing. They are able to identify and display multiple wavelength peeks within one sweep, which can be useful for assessing the DWDM ITU grid. In addition to this functionality, an OSA can also act as a multiwavelength meter and automatically scan and qualify the power levels of channels in a DWDM system. This can save time and effort when compared to manual wavemeter-based DWDM testing.

Optical Time-Domain Reflectometer (OTDR)

When light pulses travel through optical fiber, they encounter impurities that scatter and absorb the energy. This causes a certain amount of loss, which can be measured using an OTDR. The OTDR reads the level of the reflected signal and displays the data on a trace window. This allows the user to locate and identify the cause of a problem. This type of test instrument is used to verify inline splices on concatenated fiber cables and locate faults.

The OTDR uses a pulse of laser light to measure the backscatter signal. This can be used Internet of things to measure the loss of a single optical fiber. It can also be used to measure the distance between two points on a trace. OTDRs use a mathematical method called least squares to reduce the noise of the trace and provide accurate measurements.

There are some factors that influence the performance of an OTDR, such as its accuracy, measurement range, and ability to resolve events close together. The accuracy of an OTDR is defined as the difference between the measured value and the true value.

An OTDR’s accuracy is affected by the length of the test pulse, the size of the reflected peak, and the number of events within the trace window. A longer pulse increases the distance between events and improves the resolution of an OTDR’s display, but can also introduce more errors in the data. An OTDR’s resolution and accuracy are also affected by the shape of the reflected peak. A flat-topped peak can saturate the photodetector, reducing the OTDR’s ability to detect imperfections in the cable.

In addition to examining the OTDR’s display for events, you can compare two traces in the same window to see how the results differ. This can be useful when troubleshooting, especially if you have a trace from before the installation and want to find out what caused a change in the results. Most OTDRs offer this feature, which can help you troubleshoot problems quickly and efficiently.

Multiwavelength Meter (MWM)

The rapid rise of DWDM networks created an urgent need for test equipment that could detect wavelengths. Two kinds of instruments emerged to fill this need: optical spectrum analyzers (osa) and multiwavelength meters (mwm). Both are used in the field for system installation, maintenance, troubleshooting, and failure analysis. But they differ in some key ways.

A mwm is a specialized type of wavemeter that measures power in an optical channel. It samples the incoming signal by scanning the optical spectrum through a narrow bandpass filter, then performs a fast Fourier transform (fft) on the interference patterns to produce a channel table that gives you information about the underlying optical signal.

Unlike an OSA, which uses Michelson interferometry, a mwm uses the Fabry-Perot method to filter the input signal using parallel mirrors. This method has the advantage of requiring no moving parts and being able to detect closely spaced channels with very high resolution. But it also suffers from a limited dynamic range, which makes it less suitable for DWDM testing.

Like an osa, a mwm can measure a wide variety of optical signals and components, from basic CWDM channel checkers to fully populated DWDM systems. But mwms must be able to handle higher levels of incoming power and provide a better optical rejection ratio than osas. This is a critical specification that defines the instrument’s ability to reliably separate strong signals from weak ones and to detect overlapping channels.

For this reason, mwms are often more suitable than osas for use in the field. Despite their greater portability and durability than lab-oriented osas, however, some mwm models require special attention to calibration because they can easily get decalibrated by frequent handling. They are also physically larger and heavier than osas, so some users find them difficult to carry around, especially on long testing or sweeping trips.