Advancements in Silicon Photonics - Optical Signal Processing by Silicon Photonics - page 39

(d) By introducing the transparency in electromagnetically stimulate in which
absorption at a particular frequency is reduced by optically inducing the
destructive interference between the parallel quantum states [ 20 ].
(e) In Stimulated Raman scattering [ 21 ] where the photons are exchanged for
photons with shifted energy by means of the attendant excitation or relaxation
of the medium; and the modulation instability [ 22 ] in which small divergence
from a waveform are reinforced by nonlinearity, the foundation is to break up
into a chain of pulses.
(f) For exotic linear phenomena the nonlinearity can also be used to create an
environment. These include “slow light”, a process in which light can be con-
siderably slowed or even halted. The process “fast light” in which the group
velocity of light that exceeds the speed of light in a vacuum. It even becomes
more negative that is causing a pulse to move toward the source [ 23 ].
4.6 Nonlinear Optics
NLO is the branch of optics that explains the behavior of light in nonlinear media;
a medium in which the dielectric polarization ' P ' acts in response the nonlinearly
to the electric field ' E ' of the light. It is observed that the nonlinearity exhibits
characteristically at very high light intensities such as those provided by pulsed
lasers.
4.6.1 Frequency Mixing Processes
(a) Second-harmonic generation abbreviated as SHG or the process of frequency
doubling: In general, the light produced in this process is of double frequency
which means that the wavelength reduces to half.
(b) Sum frequency generation (SFG) is a process where the frequency of the gen-
erated light equals to the sum of two individual frequencies.
(c) Third harmonic generation (THG) is a process in which the frequency of gen-
erated light is a tripled frequency. This process is usually completed in two
steps: First step of SHG is followed by second step SFG of original and fre-
quency-doubled waves.
(d) Difference frequency generation (DFG) is the process in which light is purely
generated having frequency equals to the difference of two other frequencies.
(e) Parametric amplification is fundamentally the signal's amplification of a sig-
nal in which the input is present in occurrence of a higher-frequency pump
wave, and at the same time the generating of an idler wave that can be consid-
ered as DFG.