Optical Spectrum Analyzer function | OSA Application Note

This page covers application note on Optical Spectrum Analyzer(OSA). It mentions function of Optical Spectrum Analyzer(OSA) including block diagram. Popular vendors of Optical Spectrum Analyzer are also mentioned.

As we know RF spectrum analyzer is used to view and diagnose RF signals over frequency bands. Here X-axis is electromagnetic radio frequency and Y-axis is the power.

Similarly for measurement of optical signal, optical spectrum analyzer(OSA) is needed. It is basically an optical instrument. It measures properties of light over range of electromagnetic spectrum. The measured variable of OSA is usually light intensity. It can also be polarization state.

Optical Spectrum Analyzer

Figure-1 depicts Optical Spectrum Analyzer model number AQ6375B from Yokogawa Electric Corporation.

The main application of OSA is to troubleshoot problems in DWDM systems.
Refer DWDM tutorial to know more on DWDM.

Optical Spectrum Analyzer Block Diagram

The figure-2 depicts simple block diagram of Optical Spectrum Analyzer. Let us understand functions of each of the modules of OSA.

• Incoming optical signal to be measured is passed through wavelength tunable filter. This optical filter resolves different spectral components individually.

• Photodetector converts optical signal into electrical equivalent signal. This electrical current magnitude is proportional to incident optical power.

• The current is converted into equivalent voltage using transimpedance amplifier.

• Later this is digitized using ADC converter in the Optical Spectrum Analyzer. This signal is applied to vertical part of display unit as amplitude.

• Ramp tunes optical filter such that its resonant wavelength is proportional to horizontal position.

Optical Spectrum Analyzer Vendors

There are different Vendors of Optical Spectrum Analyzer (OSA). It include YOKOGAWA, Keysight Technologies, Thorlabs, Anritsu, Finisar, EXFO, APEX technologies etc. Following table summarizes popular vendors or manufacturers of OSA.

Vendors Model, Features or Specifications
YOKOGAWA Model#1: Long wavelength (1200 to 2400 nm) OSA AQ6375B
Model#2: Visible wavelength (350nm to 1200nm) OSA AQ6373B
Model#3: Telecom OSA AQ6370B (600nm to1700nm) , for single and multi-mode optics
FINISAR Model:WaveAnalyzer 1500S
It has 4 measurements per sec across C-band or
10 Hz across any 200GHz frequency window
Anritsu Model: MS9740A Benchtop OSA
Wavelength: 600 nm to 1750 nm
EXFO Model: IQS-5240S-BP
Supports 1250 nm to 1650 nm

Fiber Optic Network and Optical Components Related Links

DWDM system basics   Fibre optic communication   What is PDMA?   What is WDM?  SONET SDH tutorial   SDH Networks   SDH Frame structure   SDH Modulation   PDH Frame structure   Optical Components  Optical Isolator   Optical Circulator   Optical Amplifier   Optical Filter   Optical Coupler   Optical MUX DEMUX   Optical Equalizer   Optical Switch   Wavelength converter  

What is Difference between

PDH vs SDH  SONET versus SDH   CAS vs CCS  Types of WDM   Single vs multimode fiber  

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