Optical Spectrum Analyzers (OSA DWDM)
DWDM systems offer the potential for ultra-fast, high-capacity connections. A key test instrument for DWDM is the optical spectrum analyzer (OSA).
OSAs divide light signals into their constituent wavelengths and measure the power of each. Their results are graphically displayed as power versus wavelength.
Optical Spectrum Analyzers
Optical spectrum analyzers (osa dwdm) are laboratory-based instruments used to measure the optical power of an electrical input signal. These instruments can be a standalone unit or one that is controlled and synchronized by a computer connected to it, and may also display the measured spectra in real time.
Several types of optical spectrum analyzers exist, including devices that utilize diffraction gratings, Fabry-Perot interferometers and Michelson interferometer technology to determine the power of an electrical signal. Those that utilize diffraction gratings are the most common type and provide high resolution in a relatively small wavelength range, as well as fast acquisition times for testing spectral properties of an optical input signal.
In a diffraction grating-based optical spectrum analyzer, the polychromatic light signal is spatially dispersed with a diffraction grating and then sent to a multi-channel photodetector array that detects the dispersed signal as an individual component. This allows for the analysis of wavelengths that would otherwise be unsuitable due to interferences.
These diffraction grating-based spectral analyzers typically offer wavelength resolution between 0.1 nm and 5 nm for standard measurements, and higher performance instruments can reach the order of 0.01 nm resolution. Similarly, Fabry-Perot interferometers can provide extremely high wavelength resolution – although they are limited by their very small free spectral range, which means they can only be used for specific applications that require a narrow, fixed frequency.
The spectral accuracy of an optical spectrum analyzer, in terms of the full width at half maximum (FWHM), is a very important feature to consider, because it affects both the dynamic range and acquisition speed. It also depends on the filter shape, how steeply the filter function drops with increasing wavelength offset and on the sensitivity of the detecting electronics.
Another important feature of an optical spectrum analyzer is its power spectral density (PSD), which can be displayed on a vertical axis, in a logarithmic scale osa dwdm or as a dBm value, which indicates decibels relative to 1 mW. This is a much better suited measurement method than simply dividing the total optical power through the detection bandwidth, since that can be inaccurate for many reasons, especially if coupling efficiency in the delivery path is unknown.
DWDM Technology
DWDM technology is an extension of optical networking that allows carriers to transmit information through multiple virtual fibers. Rather than installing new fiber cables, DWDM channels are added to existing telecommunications networks to meet bandwidth demands. These additional wavelength channels can carry a total capacity of up to 100 Gbps per pair, which is a significant increase in the maximum bandwidth available from existing telecommunications networks.
Compared to time-division multiplexing (TDM), dense wavelength-division multiplexing (DWDM) offers greater capacity at lower cost by fitting more wavelengths onto a single fiber cable. The technology is popular with telecommunications and cable companies because of its ability to handle vast amounts of data in high-bandwidth applications.
In addition, DWDM systems can be installed at a faster rate than traditional TDM equipment because they require less labor and can be installed without having to reconfigure the network. This makes them an ideal option for metropolitan area networks, which face a rapid demand for service provisioning.
A DWDM system typically consists of five key components: Optical transmitters and receivers, DWDM multixers and demultiplexers, erbium-doped fiber amplifiers (EDFAs), and optical add/drop multiplexers (OADMs). These devices combine the output from several optical channels for transmission across a single optical fiber and then separate the individual optical channels into two distinct streams or channels. The individual streams or channels do not interfere with each other due to light properties, allowing them to share the same physical fiber and data format without interfering with each other.
Because of the sensitivity of DWDM technology to light wave dispersion, optical spectrum analyzers are often used for testing DWDM systems. These devices divide a light signal into its constituent wavelengths and measure the power of each of them, with results displayed graphically.
Another type of instrument, called a multiwavelength meter, has an even stronger impact on testing DWDM systems. These meters measure each of the individual wavelengths to determine if they are within specified ranges. They also measure inter-channel noise to ensure that the optical signal is not smothering other wavelengths, which can lead to inaccurate snr measurements.
DWDM Applications
DWDM technology is used to transmit densely packed optical signals. It offers increased capacity and reduced costs by enabling the deployment of large numbers of channels within the same transmission medium without requiring expensive re-cabling or upgrading. However, these systems are not immune to performance limitations and require care to ensure they operate as expected.
Optical spectrum analyzers (OSA) are an essential part of the test instrument suite for DWDM applications. They are able to divide light signals into their constituent wavelengths, measure the power of each wavelength and display the results graphically. OSAs are available in diffraction-grating, Fabry-Perot and Michelson interferometer architectures.
Diffraction-grating-based OSAs use a rotating filter to present different wavelengths sequentially to the photodetector. Typical resolutions are between 0.1 and 10 nm. Diffraction-grating-based OSAs are popular for measurement of LED and laser chirp.
Another common design is the Fabry-Perot interferometer, which filters incoming light using parallel mirrors to form a resonant cavity. The mirrors are then tuned to set the input wavelength. The Fabry-Perot design provides high wavelength accuracy, although the dynamic range is limited.
In addition to wavelength and level measurements, DWDM OSAs are also used for other measurements including Erbium-Doped Fiber Amplifier gain tilt measurement. EDFAs typically have gain that is tilted toward the low side of the channel, so OSAs can help determine the gain tilt of individual channels.
To avoid spectral distortions, the OSAs are equipped with advanced filtering algorithms. Some OSAs can even detect noise in the signal to be measured, which is especially useful for determining channel-to-noise ratios in DWDM systems.
DWDM OSAs can also be configured with features such as Channel Search and Peak Search/Hold to facilitate fast and efficient channel identification and level characterization. This allows operators to quickly determine valid DWDM channels and verify power levels before and after signal amplification.
VIAVI also offers a compact range of broadband OSAs designed osa dwdm to perform spectral measurements on CWDM systems in access networks as well as DWDM systems in the backbone and for Next Generation 40G or 100G high-speed networks. These models offer true OSNR measurements for CWDM, DWDM and ROADM-based systems as well as for 40G networks with narrow channel spacing.
DWDM Spectrum Analyzers
Dense wavelength-division multiplexing (DWDM) technology is a promising technology for increasing bandwidth in optical fiber networks. The technology can help improve information transfer capacity and reduce spectral interference from other signals. However, this technology requires testing equipment that is able to accurately measure key DWDM test parameters such as channel power and wavelength/frequency.
Optical spectrum analyzers are used to measure the distribution of power over a specific wavelength domain and can be found in a wide variety of sizes. They typically feature a tunable optical filter that allows the analyzer to select a specific wavelength and route it to a monitor output. They also feature a photodetector that converts the optical signal into an electrical current that can be digitized for measurement.
The analyzers resolution is determined by the density of lines on the diffraction gratings surface, the distance from the detector and the configuration of the optical circuit. The higher the resolution, the better the accuracy of the spectrum analyzers measurements.
A Fabry-Perot interferometer is an optical spectrum analyzer that filters incoming light using parallel mirrors and piezo elements. This type of spectrum analyzer is ideal for detecting closely spaced channels and can be used to detect multiplexed optical signals in dense DWDM systems.
For high-speed data transmission in dense wavelength division multiplexing (DWDM) systems, optical spectrum analyzers are needed to detect and measure the individual waveforms that make up a single channel. DWDM is an emerging technology that offers unprecedented bandwidth in fiber optics and presents many test challenges.
These challenges include determining the maximum optical input power that an osa can tolerate without damage and ensuring that the analyzer can distinguish between channels. It also needs to be able to measure the optical rejection ratio (orr), which is how robust an osas signal-to-noise ratio is at different distances from the channel.
DWDM testing equipment should be able to perform accurate measurements over a wide range of conditions, including ambient temperature change and vibrations. It should also be able to display the measured wavelength/frequency, channel power and occupied bandwidth in a format that can be interpreted by a network operator.
