• Switching is an essential operation in communication networks. It is also a basic operation in digital computers and signal processing systems. The current rapid development of high-data-rate fiber-optic communication systems has created a need for high-capacity repeaters and terminal systems for processing optical signals and, therefore, a need for high-speed photonic switches.

• A switch is characterized by the following parameters:

$\rightarrow$Size (number of input and output lines) and direction(s), i.e., whether data can be transferred in one or two directions.

$\rightarrow$ Switching time: (time necessary for the switch to be reconfigured from one state to another).

$\rightarrow$ Propagation delay time: (time taken by the signal to cross the switch).

$\rightarrow$ Throughput: (maximum data rate that can flow through the switch when it is connected).

$\rightarrow$ Switching energy: (energy needed to activate and deactivate the switch).

$\rightarrow$ Power dissipation: (energy dissipated per second in the process of switching).

$\rightarrow$ Insertion loss: (drop in signal power introduced by the connection).

$\rightarrow$ Crosstalk :( undesired power leakage to other lines).

$\rightarrow$ Physical dimensions. This is important when large arrays of switches are to be built.

• Optical signals may be switched by the use of electronic switches: the optical signals are converted into electrical signals using photodetectors, switched electronically, and are converted into electrical signals using photodetectors, switched electronically, and then converted back into light using LEDs or lasers (Fig. 4.10).

• These optical/electrical/ optical conversions introduce unnecessary time delays and power loss

• Figure 4.11 An optoelectronic 8*8 crossbar switch. Eight optical signals carried by eight optical fibers are detected by an array of photodetectors, switched using an 8 X 8 electronic crossbar switch, and regenerated using eight LEDs (or diode lasers) into eight outgoing optical fibers.

• The data rates that can be handled by silicon switches are currently a few hundred Mb/s, while GaAs switches can operate at rates exceeding 1 Gb/s.

Optical Switching Technologies :

$\rightarrow$ Optomechanical Switches

$\rightarrow$ Micro electrical mechanical system devices

$\rightarrow$ Electro optic switches

$\rightarrow$ Thermo optic switches

$\rightarrow$ Liquid Crystal switches

$\rightarrow$ Bubble switches

$\rightarrow$ Acousto optic switch

$\rightarrow$ Semiconductor amplifier switch