Handheld DWDM OSA – Essential Field Test Equipment for Installers
DWDM systems have created a demand for test equipment that is no longer confined to the lab. The handheld OSA has taken its place on the list of essential field instruments for installers, alongside loss test sets and OTDRs. A grating monochromator design makes these portable devices highly durable and suitable for rugged field use, says Lynn Mason, outside-plant product manager at exfo Electro-Optical Engineering Inc.
Optical Spectrum Analyzers (OSAs)
OSAs are designed to filter and display a wide spectral range of light at a time, applying the spectrum analysis principles developed for radio waves to a closely related form of electromagnetic radiation. They do this by splitting an input signal into two beams that travel different paths before recombining. This creates sequentially constructive and destructive interference patterns that are measured by a photodetector, with the intensity of the interference corresponding to the wavelengths present in the signal. The output of the photodetector is then converted to an electrical signal, which is displayed on a screen.
A wide variety of OSAs are available, with many based on Michelson interferometer technology. These use mirrors to measure the path lengths of two distinct beams, and then perform fast Fourier transforms to reveal the signals in a wavelength range (see Figure 2).
Another option is the Littman monochromator design. WWG notes that this type of OSA can measure a wide range of wavelengths with a single sweep, so it’s ideal for testing passive devices such as CWDM filters. It also has a small footprint, which makes it more portable.
Whether a slit or grating monochromator is used, most manufacturers agree that the most important specifications for an OSA are wavelength measurement accuracy and power reading accuracy. For DWDM applications, each center wavelength needs to be within 1/10 of the ITU grid tolerance, and most high-end field OSAs have wavelength accuracy down to 10 pm.
Optical Time-Domain Reflectometers (OTDRs)
When troubleshooting a fiber optic link, OTDRs conduct timed measurements of reflected light to evaluate factors like attenuation and distance. This information helps pinpoint impurities and defects in handheld-dwdm-osa the optical fiber, enabling efficient maintenance and repair of optical fiber networks.
An OTDR uses a high-power laser transmitter to send a test pulse down the optical fiber. The reflected and scattered light returns to the OTDR, which detects it using a sensitive receiver. The OTDR measures the reflected power at each point along the optical trace and calculates loss based on the declining intensity of the returned signal.
The OTDR’s display unit visualizes the results as distance-vs.-attenuation graphs, event tables and traces, helping technicians pinpoint the location of defects and make informed decisions about network maintenance. Depending on the type of optical fiber and measurement range, an OTDR can measure both multimode and single-mode optical fibers.
When using an OTDR, the distance range should be at least twice the length of the cable under test. A shorter range may produce poorer resolution in the trace or create distortions from reflections and splices. Choosing the proper distance Internet of things range is especially important when locating events that require precise measurement, such as macrobends and microbends. Likewise, the OTDR should be kept away from reflective and nonreflective events that can obscure trace measurement data, such as connectors, splices and splitters.
Optical Network Analyzers (ONAs)
A network analyzer determines a circuit’s responses to signals and outputs them in either s-parameter or impedance (Smith Chart) format. Some modern network analyzers also can display polar or cartesian formats of magnitude related measurements.
The basic measurement system consists of four sections, the signal source, signal separation device, receiver or detector and the signal processor/display section. The signal separation device separates the incident, reflected and transmitted signals. The receiver converts the microwave frequency of the reflected or transmitted signals to a lower IF frequency for further processing. The signal processor or display section then processes the IF signal and produces information to be displayed on CRT.
In addition to determining the snr, an important parameter in DWDM testing is the optical rejection ratio (orr). This specification describes how well a powerful signal can be distinguished from weaker adjacent signals. The higher the orr, the more power that can be transmitted without degrading the quality of the transmission.
While the snr and orr are critical for measuring the performance of a DWDM metropolitan network, other tests are required to provide an overall picture of a DWDM metro network. A scalar network analyzer (SNA) and vector network analyzer (VNA) help to perform the more comprehensive measurements needed for an overall network picture. These field instruments have replaced many bulky lab units in field testing applications.
Optical Multiwavelength Meters (OMMs)
Optical multiwavelength meters (OMMs) are Michelson interferometer-based instruments that simultaneously measure wavelength and power of optical signals, laser lines and light sources. They provide a compact, cost-effective test solution for the development and manufacturing of optical communication devices and components.
Keysight’s OMM 6810B and OMH-6700B series Optical Measurement Heads provide precise power and wavelength measurements with the same instrument. They capitalize on ILX’s unique power and wavelength measurement technique based on integrating sphere technology, eliminating problems such as detector saturation, alignment beam profile, polarization and back reflection.
Power only heads provide precision power measurement of laser diodes with an 80 dB dynamic range while wavelength only heads feature a temperature-controlled semiconductor detector to ensure high sensitivity, stability and low noise. These heads require no manual calibration and can be used with either a power or wavelength spectrum analyzer.