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Optical Switching
The need for Optical Switching
 High bit rate transmission must be matched by switching capacity
 Optical or Photonic switching can provide such capacity
What is Optical Switching?
Switching is the process by which the destination of a individual optical information signal is controlled
Optical Switching Overview
Switching is the process by which the destination of a individual optical information signal is controlled
Switch control may be:
 Purely electronic (present situation)
 Hybrid of optical and electronic (in development)
 Purely optical (awaits development of optical logic, memory etc.)
Switching In Optical Networks. Electronic switching
Most current networks employ electronic processing and use the optical fibre only as a transmission medium. Switching and processing of data are performed by converting an optical signal back to electronic form.
Electronic switches provide a high degree of flexibility in terms of switching and routing functions.
The speed of electronics, however, is unable to match the high bandwidth of an optical fiber (Given that fibre has a potential bandwidth of approximately 50 Tb/s – nearly four orders of magnitude higher than peak electronic data rates).
An electronic conversion at an intermediate node in the network introduces extra delay.
Electronic equipment is strongly dependent on the data rate and protocol (any system upgrade results in the addition/replacement of electronic switching equipment).
Switching In Optical Networks. All-Optical switching
All-optical switches get their name from being able to carry light from their input to their output ports in its native state – as pulses of light rather than changes in electrical voltage.
All-optical switching is independent on data rate and data protocol.
Results in a reduction in the network equipment, an increase in the switching speed, a decrease in the operating power.
Generic forms of Optical Switching
 The forms above represent the domains in which switching takes place
 Net result is to provide routing, regardless of form
 Switch control may be:
 Purely electronic (present situation)
 Hybrid of optical and electronic (in development)
 Purely optical (awaits development of optical logic, memory etc.)
Network Applications
Protection switching
Optical Cross-Connect (OXC)
Optical Add/Drop Multiplexing (OADM)
Optical Spectral Monitoring (OSM)
Protection Switching
Protection switching allows the completion of traffic transmission in the event of system or network-level errors.
Usually requires optical switches with smaller port counts of 1X2 or 2X2.
Protection switching requires switches to be extremely reliable.
Switch speed for DWDM, SONET, SDH transport and cross connect protection is important, but not critical, as other processes in the protection scheme take longer than the optical switch.
It is desirable in the protection applications to optically verify that the switching has been made (optical taps that direct a small portion of the optical signal to a separate monitoring port can be placed at each output port of the switch).