When implementing DWDM networks, OSAs are important. The most critical specifications include optical signal-to-noise ratio (OSNR) and power-level accuracy. OSAs for DWDM networks must have accurate wavelength measurements within a tenth of a grid spacing. A high-end grating-based OSA can deliver a wavelength measurement accuracy of +/-0.02 nm and power-level accuracy of +/-0.5 dB.
Fabry-Perot interferometer
The Osa Fabry-PeroT interferometer is an optical device that produces parallel interference extrema at discrete positions. The oscillation frequency is controlled by the distance of the mirrors. This device is useful for determining optical frequencies, particularly in the presence of chromatic dispersion.
Its dual-amplitude modulation scheme is implemented in an optical fiber coupled to a piezoelectric transducer bar. This dynamic strain varies the difference between the two optical paths, and the Fabry-Perot interferometry demodulates the output voltage based on the difference in the optical path. This system is applicable to low-frequency displacement sensing applications, such as geophysics.
The Osa Fabry-PeroT interferometer’s scanning principle allows it to acquire high spectral resolution and lower wavelength ranges. The principle behind this method is simple: changing the length of the cavity leads to a change in the FPI output wavelength. Its length is mechanically adjusted by a piezoelectric actuator with submillimeter resolution. The scanning mechanism is synchronized with a photodetector that acquires an optical signal in each wavelength region.
The Osa Fabry-PeroT interferometer has several advantages. In addition to allowing for highly accurate and precise measurements, it is flexible enough to switch wavelengths. It can also be adjusted by rotating the interferometer. The wedge angle is exaggerated in the illustration, but it’s still a fraction of a degree.
The Osa Fabry-PeroT interferometer is capable of detecting temperature in a wide range of temperature. Its temperature-sensitive nature makes it ideal for detecting temperature changes in optical fibers. The Osa Fabry-Perat interferometer uses a silicon film that crystallizes by a laser annealing process. The film is then coated with aluminum.
A unique characteristic of the Osa Fabry-PeroT interferometer is that it can be tuned to control the spatial location of the concentric interference fringes. Its tunable liquid crystal etalon allows it to be used for Rayleigh scattering experiments at NASA Glenn Research Center.
The OSA is very flexible and inexpensive. It can measure the power of different spectral components by sweeping the center wavelength of a narrowband optical filter. Various implementations of the Osa interferometer have been described elsewhere. The accuracy of power measurement is typically 0.1-0.5 dB, and the resolution bandwidth depends on the channel plan. In a typical DWDM system with 100-G/50-G spacing, this resolution is sufficient.
The Osa Fabry-PeroT interferometer is a very effective spectrometer for measuring CO2. It is also a good tool for atmospheric CO2 monitoring. It is a valuable research tool. So, if you want to measure CO2, you can easily create an Osa Fabry-Pero T-Scanner.
Fast Fourier transform (FFT)-based analysis
In the DWDM network, a dense wavelength division multiplexer (DWDM) splits a broadband spectral into multiple optical paths, each with a specific frequency range. Each channel of the DWDM is then sampled by a high-speed synchronous ADC. The data are uploaded to a computer, where they are processed in real time. A joint algorithm of MLE and FFT is then used to determine the cavity length.
DWDM systems typically have a channel offset of 10%, limiting their wavelength range to 1528–1565 nm. One newer technology, the BOSA Phase High-Resolution Complex OSA, uses an inverse Fourier transform to measure wavelengths in real time with a dynamic range of 80 dB. The method also provides real-time measurements of relative phase, amplitude, and power. It is intended for use in 40G/100G networks.
A Fast Fourier transform (FFT) analyzer can also measure the amplitude of individual spectral lines, called spectral line amplitude. The FFT method relies on the use of a time-weighted window function, which can reduce spectral leakage, which is a systematic error in the frequency spectrum caused by the spread of energy across multiple spectral lines.
FFT analysis can help identify mechanical parts that require maintenance. With FFT analysis, engineers can also measure sound pressure levels in noisy environments. This can help them take steps to mitigate the impact of loud tonal components and critical frequency ranges.
The authors of a new paper describe the FFT-based analysis of an OTDM add-drop multiplexer. This technology makes use of a saw-tooth pulse shaper and superstructured fibre Bragg grating.
The FFT-based method can greatly improve demodulation accuracy. By allowing a higher frequency range, a FFT-based method can produce higher resolution. Furthermore, FFT-based analysis can be used to improve the update rate.
The FFT-based method is an alternative to spectral analysis. The FFT-based OSA method enables the use of multiwavelength meters and emphasizes high-performance wavelength certainty and low uncertainties in power measurement. The multiwavelength meters are manufactured by Bristol Instruments and incorporate a scanning Michelson interferometer (SMIC) with a wavelength axis calibrated to 0.0001 nm. In contrast, direct-measurement OSA uses a wavelength axis calibrated to 0.01 nm. Generally, the FFT-based OSA method measures relative power and not absolute power.
FFT-based analysis is a good option for Osa DWDM, because it has a high frequency resolution and a low computational burden. However, the disadvantage is that the FFT-based analysis will result in a slower response time. The FFT method relies on the idea of interpreting two endpoints of a time waveform as connected. In reality, random signals are rarely equal at both ends of a time interval, so FFT analysis can lead to unwanted noise in the frequency spectrum.
Before performing FFT-based analysis, time data must be acquired. This may have been collected in the past or could be collected during the analysis. FFT-based analysis uses digital signal processing techniques to transform time-domain data into a frequency domain.
Field-deployable design
Field-deployable OSA devices are a new class of optical signal processing devices. They can be used to measure optical signals in both CWDM and DWDM networks. These instruments are based on the Michelson interferometric method. In this method, an input signal is split into two paths, each of which is reflected back by a pair of mirrors. This creates a sequence of sequential interference, which is mathematically analyzed with fast Fourier transform algorithms. The resultant electrical signal is then analyzed to reveal the input signal’s wavelength range. The Michelson interferometer design is also shock-resistant and has a small dynamic range.
Field-deployable OSAs are available for benchtop and cellular applications. JDSU announced two new OSAs for next-generation networks in 2010. The OSA 500 is dedicated to DWDM spectra and the OSA 500R is dedicated to ROADM networks with 40/100 Gbit/50 GHz channel spacing.
CWDM is a popular technology in DWDM monitoring, but it lacks some important properties. It has a low dynamic range and a low spectral resolution. It also has poor sensitivity for noise measurements. Nonetheless, it provides good wavelength accuracy and is widely used in wavelength meters. In addition, it is also scalable, and it can be easily field-deployed.
The FTBx-5245 OSA was developed for DWDM network analysis. This new DWDM-based optical test instrument is housed in the highly scalable LTB-8 platform. This platform can support eight 100G modules simultaneously. It also houses the FTBx-88200NGE multiservice transport module. Additionally, it provides complete lab testing capabilities.
DWDM systems are increasingly being deployed in many locations, which has resulted in the development of more sophisticated optical spectrum analyzers. These devices are crucial for ensuring proper system operation and characterizing individual optical components. They can be used during the development, manufacturing, installation, commissioning, and maintenance of optical networks. Depending on the application, there are three main types of OSA: benchtop, embedded, and portable.
Osa DWDM uses multiple wavelengths. The Osa DWDM design combines two separate wavelengths. These wavelengths are used to transmit the signals. These wavelengths are not directly adjacent to each other, which results in an improved system performance.
Using the FFT method, an optical spectrum analyzer measures the power of an optical source over a defined wavelength range. Using a rotating filter, this device presents different wavelengths sequentially to a photodetector. This method is accurate and accommodates a wide spectral range. However, this method is sensitive and requires protection against shock.
In the DWDM network, an automatic power reduction mechanism is required to ensure that the laser power does not exceed the Class 1 limits. This feature is important in metro core networks. The ONS 15454 standard defines the Metro Core Network (MCN) application for this technology. Gain flatness is an important parameter for erbium-doped fiber amplifiers.