Four-wave mixing (FWM) is a non-linear optical process where two other waves are produced by the interaction of two wavelengths. Four-wave mixing can take place in any kind of material.
Four-wave mixing is also referred to as degenerate four-wave mixing when there are three components involved and all the waves have the same frequency.
Four-wave mixing describes the wave interaction via a non-linear polarization. The generation of waves having the same frequency but different wave vectors is due to the non-linear refractive index of the medium.
Phase conjugation is the most frequently used FWM configuration. This article will provide details on the working, experimental set up and applications of four-wave mixing.
Experimental Set Up
The experimental set up for FWM consists of two incident beams, called the writing beam 1 and 2. A third beam called the probe beam is directed towards the interaction of the two writing beams via anon-linear medium. As a result a fourth beam called the signal beam is created.
Theory Behind Four-Wave Mixing
Four-wave mixing is a third-order parametric process in which two photons (writing beams) having frequencies f1 and f2 are annihilated by being made to pass through a non-linear medium. As a result two photons (probe and signal beams) having frequencies f3 and f4 are generated.
The relation between the frequencies of the four waves is f3+f4 = f1+f2.
Applications of Four-Wave Mixing
Some of the main application areas of FWM include:
- Fiber optic communication
- Wavelength conversion
- Parametric amplification
- Optical regeneration
- Optic phase conjugation
- Correction of aberrations of images.
References and Further Reading