Modern Optical Networks - Optical Signal Processing by Silicon Photonics - page 28

There are two types of devices that are currently more frequent; frequency doublers
are generally made up of lithium niobate (LN), potassium titanyl phosphate (KTP),
lithium tantalate (LT), or lithium triborate (LBO), and frequency triplers usually
are made of potassium dihydrogen phosphate (PTP) or KTP. The two of them are
extensively usable in optical experiments that include lasers as a light source.
Two processes are frequently used to attain the conversion, second harmonic
generation (SHG) sometimes also known as frequency doubling, or summing of
frequency generation which sums two different frequencies. Direct third harmonic
generation (THG), also called frequency tripling exists, but famous examples of
these devices are less efficient and are generally not used in practice. “Real world”
triplers use a two-stage process that combines two photons using SHG, and then
addition of a third using summing.
Optical frequency multipliers are more frequent in high-power lasers, markedly
those that are used for inertial confinement fusion (ICF) experiments.
3.9 Optical Network
A network can be defined as a collection of transmission links and other utensils
which provides a means of information interchange within a group of end users.
The purpose of the network is to provide a means of information interchange
between end users. The network usually contains some shared resources. That is,
links and switching nodes are shared between many users. The term “network” also
usually implies a geographic separation between end users. This is not always true in
the sense that communicating end users may be across the room or across the world.
Networks may be characterized by their geographic extent such as:
• Local Area Network (LAN).
• Metropolitan Area Network (MAN).
• Wide Area Network (WAN).
Figure 3.7 illustrates the main concept of a network that is subdivided into three
parts;
• Access/edge-network (used to provide the connectivity to user to the nearest
node, 1-10 km distances)
• Regional/metro optical network (provide interconnectivity between regional and
metropolitan domains)
• Long-haul optical networks (ranges about 10-500 km)
Optical communication networks can support high bandwidth as the WDM tech-
niques are mature enough. The optical industry must observe the different quali-
ties and types of service enabled by different infrastructure configurations and then
decide which services to offer over those infrastructures. The optical network can
be considered from various geographical domains, multiplexing technologies and
transport capacity [ 16 ] (Fig. 3.8 ).