Four Wave Mixing in Silicon Photonics - Optical Signal Processing by Silicon Photonics - page 98

P T Transmitted power

α Attenuation

dB Decibel

χ Tensor

P 0 Output power

µ m Micro meter

∆ Index contrast

1 D One dimentional

2 D Two dimentional

3 D Three dimentional

η Efficiency

A eff Effective area

λ Wavelength

ω Frequency

nm Nano meter

P NL Nonlinear polarization

Ω s Frequency shift

K Propagation constant

8.1 Four-Wave Mixing

In optical fibers, the scattering processes depend on molecular vibrations or
density variations of silica. In a separate class of nonlinear phenomena, optical
fibers play a passive role except for mediating interaction among several optical
waves. Such nonlinear processes are referred to as parametric processes because
they involve modulation of medium parameters, such as the refractive index,
and require phase matching before they can build up along the fiber. Among
these, FWM plays the dominant role. Although four-wave mixing (FWM)
can be detrimental for wavelength division multiplexing (WDM) systems that
must be designed to reduce its impact, it is also useful for a variety of applica-
tions e.g., designing light wave systems, generating a spectrally inverted signal
through the process of optical phase conjugation, wavelength conversion. FWM
can also be applied for phase conjugation, holographic imaging, and optical
image processing.

8.2 Basis of FWM

The source of FWM lies in the nonlinear response of bound electrons of a mate-
rial to an electromagnetic field. The polarization induced in the medium contains
terms whose magnitude is governed by the nonlinear susceptibilities [ 1 - 3 ]. The
resulting nonlinear effects can be classified as second- or third-order parametric