All-Optical Frequency Shifting - Optical Signal Processing by Silicon Photonics - page 91

is an intensity modulation (IM-DD).The XPM effect is a process having two steps:
First, the signal is modulated when its phase modulation is done by the co-prop-
agating second signal, whereas in the second step, transformation of the phase
modulation into a power variation dispersion leads to a. Further, the cut-off con-
nection can occur between the channels due to dispersion and thereby XPM-effect
is reduced.
7.11 Self-Phase Modulation
Self-phase modulation, aka SPM, is defined as a nonlinear optical effect of inter-
action of light and matter. A varying refractive index of the medium due to the
optical Kerr effect will induce when an ultrashort pulse of light is traveling in a
medium. This refractive index variation will produce a phase shift in the pulse.
This phase shift also leads to a change in the pulse's frequency spectrum. Self-
phase modulation is an important effect in optical systems that uses short intense
pulses of light, for example, laser and optical fiber communications systems.
7.12 Free Carrier Absorption
Theoretically, FCA occurs when a material absorbs a photon and a carrier is
excited from a filled state to an unoccupied state in the same band. FCA is very
different from interband absorption in semiconductors. The reason behind this is
that the electron being excited is a conduction electron that can move freely, hence
FCA.
7.13 Optical Detectors
A monolithically scaled optical interconnect system based on SOI technology
requires four major components:
• A light source,
• An optical modulator for encoding data into light pulses,
• A waveguide for eficiently transporting light across the chip, and
• A photodetector for converting optical signals into electrical signals.
One of the necessary components of an optical fiber communication system is
decoder, which is also a fundamental element dictating the overall performance of
the system. The function it performs is converting the received signal from optical
to electrical, then this signal is amplified before processing it further. A detector
must satisfy the criteria and stability of performance characteristics.