Module 19 : WDM Components
Lecture     : WDM Components - II
  Various types of OXCs are made depending on the type of function. Fiber Cross Connects (FXC) s are those which connect one fiber channel to another. For wavelength switching Wavelength Switching Cross Connects (WSXC) switch wavelength from one port to a port which might be carrying a different wavelength without having to resort to wavelength conversion. WIXCs are switches which provide for wavelength conversion in switching from one fiber to another.
   
  Wavelength Converters
  Wavelength converters are devices which changes the wavelength of an input signal. There are several ways in which a wavelength conversion can occur. Usually, wavelength conversion takes place from a shorter wavelength to a longer wavelength. For instance, certain material can absorb radiation and re-radiate at a lower frequency.
In WDM network, frequency converters are used in conjunction with OXCs for better utilization of available wavelengths. The most commonly used techniques of wavelength conversion are
Electro-optic conversion
Cross - Gain Modulators (XGM)
Cross-Phase Modulation (XPM)
Four-wave mixing
   
 

Electro-optic conversion In electro-optic conversion an input light signal is converted into an electrical signal, regenerated and re-transmitted at a different wavelength using a tunable laser.

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Cross-Gain Modulation (XGM)

Semiconductor Optical Amplifiers (SOA) are used in WDM systems for switching and wavelength conversion. The active medium in SOAs have homogeneously broadened gain, i.e., change in carrier density in the medium affects all input signals. Thus a strong signal at a wavelength $ \lambda_1$will affect a weak signal at a different wavelength.

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