Optical Wavelength Converter
As the name suggests wavelength converter converts optical signal with one wavelength to the other optical signal. These types of converters are widely used in WDM networks. Optical wavelength converters are of four types based on their input and output wavelength handling limits. They are fixed input fixed output, variable input fixed output, fixed input variable output and variable input variable output.
Fixed input fixed output converter takes fixed wavelength signal as input and converts it to the fixed wavelength output signal. Variable input fixed output converter takes arbitrary wavelength as input and provides fixed wavelength as output. Fixed input, variable output takes fixed wavelength signal as input and converts it to the variety of wavelengths as output signal. Variable input, variable output type converts variable wavelength signal input to the variable output signal.
Wavelength conversion methods
Wavelength conversion methods are optoelectronic, optical gating, interferometric, and wave mixing. These methods are described below.
Optoelectronic: This type of optical wavelength converter is variable input, fixed output type as mentioned above. It converts the input signal first to electrical form, regenerates it and transmits it using the laser device. Optical Receiver takes either 1310 or 1550 nm wavelength as input. Tunable laser device is used to obtain the desired wavelength.
optical gating: This method utilizes cross gain modulation and exploits nonlinear effect of the SOA (Semiconductor Optical Amplifier). It also takes variable input and will provide either fixed or variable optical signal as output. This optical gating method utilizes optical device whose characteristics varies based on intensity of the input optical signal to obtain the output.
interferometric: In this method also phase distortion of cross gain modulation is utilized to obtain wavelength signal conversion. This method is also referred as cross phase modulation. Carrier density varies based on input signal and in turn change refractive index and consecutively modulates the phase of the probe signal.
wave mixing: Here nonlinear phenomenon of the transmission medium is utilized to obtain wavelength conversion. Four wave mixing produces f1,f2,f3 and f1+f2-f3. This is exploited to obtain the conversion in this type of optical wavelength converter with the help of optical filter. If we take signal frequency as fs and probe frequency as fp then we will have 2fs-fp and 2fp-fs .