Four Wave Mixing Wavelength Conversion

In addition to data buffering, wavelength conversion is often necessary when optical signals travel in between networks. This process could also be significantly faster if it was done optically. Four wave mixing is one such method of all optical wavelength conversion, made possible by nonlinear effects between two closely spaced wavelengths of laser light. Two wavelengths separated by a spacing delta₁ produce conjugate outputs spaced delta₁ from both initial wavelengths. This effect can be used to convert an input signal at a specific wavelength to an exact copy of the signal at a different wavelength. Two methods of implementing four wave mixing - single pump and dual pump - are shown below. We have studied the properties of four wave mixing in DFB lasers and modulators, and plan to further study the high speed characteristics, efficiency, and polarization dependencies of different four wave mixing schemes.

Representations of single pump four wave mixing (left) and dual pump four wave mixing (right). The outputs “OBA” and “OAB” in the dual pump case are not used, since they are independent of the input wavelength.

Spectral output of four wave mixing with single pump (left) and dual pump (right) configurations. Note the much cleaner output signals in the dual pump case.