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What is an Optical Spectrum Analyzer used for?

Optical Spectrum Analyzer (OSA) - An Overview


An optical spectrum analyzer measures the quantity of the input optic signal against the frequency within the range of the instrument. For analyzing, it uses reflective or refractive techniques to differentiate the wavelength of light. The intensity of the light gets measured by an electro-optical detector, depending on which you get the reading displayed on the screen, quite similar to that of any other spectrum analyzer.


  • Process in use:


The optical input comes through an aperture in the instrument’s case from where an optical fiber or connector gets attached to the unit. The optical spectrum analyzer or OSA precisely measures the optical spectra, depending on the different wavelengths associated with the medium in use. The frequency range also varies for the change in wavelength in use.


  • Spectral analysis application


The use of spectral analysis is relevant in multiple applications of general science. Various statistical evaluations are possible through the advantage of displaying the possible autocorrelation over different time lags. It has a wide application in detecting cycles and trends in the data. Some typical application fields to notice are the following:

  1. Light sources: Light sources like laser systems or light-emitting diodes, popularly called LEDs, require certain characterizing resources. The OSA help in analyzing and characterizing the optical spectra involved in these sources.
  2. Testing networks: Multiple optical fibers communicating networks require the optical analyzer to evaluate the involved wavelength division multiplexing systems. The OSA tests the optical powers to the channels featuring distinct wavelengths and then signifies the noise ratio signal.
  3. Testing systems: Optical systems that have a dependency on the wavelengths to determine transmissivity or reflectivity necessitates the use of the OSA for comparing the optical spectra in different ways. The comparison takes place by considering both conditions of inclusion and exclusion of the concerned device.
  4. Telecom services: In telecom amplifiers, the characterization of the fiber amplifiers occurs with the help of the optical analyzer, where the result depends on noise figures and wavelength-dependent gain. Depending on the range of telecom wavelength bands, the analyzing instruments vary alongside their functioning aspects.


  • Application in stand-alone units


Optical spectrum analyzers are often in use for personal application, other than the usual functioning domains. Generally, you find similar examples in laboratory use, where the instrument control and display get carried out on a regular medium of output, like a personal computer. In such stationary setups, the optical input gets injected in two ways by considering the analyzing source.


  • Variations:


In some cases, you will find the fiber-optic input, with a fiber connector like one physical connection to another, subscriber connector (SC), or straight tip (ST), for connecting to a fiber patch cable. While other systems feature free-space optical input, the focus is on the input light to an optical slit, having the beam direction almost perpendicular to the slit surface.


  • Fundamental determining application:


The operational principle and techniques used in the optical spectrum analyzers largely define their functioning domain. Some instruments depend on the wavelength angles to analyze the diffractions, while others contain the interferometer for distinct purposes. The resultant you obtain varies at large depending on the concerned device and technicalities.


  • Application-based on Diffraction Gratings:


You can find some OSA that has the fundamental functioning based on that of a spectrograph. The polychromatic light gets spatially dispersed with a diffraction grating, from where it gets sent to a multi-channeled photodetector. There is a use of different gratings depending on the distinct wavelength range and resolutions.


  • Scanning Instruments:


The spectrum analyzers in the scanning instruments have the input light coming from the tunable bandpass filter. The single and high-dynamic ranged light detector detects the optical power for analysis. After systematic analysis, the input coming from the tunable filter gets displayed on the digital screen of the connected device. The display obtained results from the analyzing technicalities of the OSA installed, where the sensitivity varies as per the controlling unit.


  • In Tunable laser source:


As an alternate option, you can use the built-in laser source as an independent one, where the source output and control software can get integrated into the equipment. The user can synchronize the laser source output with the OSA to measure the active and passive components. It is a highly useful application in the field of Fiber brag grating transfer and functional characterization.


  • In dark fiber pair field trial:


Compared to the other discussed aspects, the said instrument is simpler for the lesser attached restrictions. The setup and placement of the active test channels, bulk moderated channels, or power management channels is much simpler. The OSA gets placed in each end for measuring the launch, power, and gain concerned in the undersea fiber communication.


Wrapping up


There are multiple optical spectrum analyzers available for distinct uses that feature different wavelength offerings. Usually, 600nm to 1700nm ranged OSA is suitable for both the purposes of telecommunication and general field applications.