2.2.

3 Optical
multiplexers and
Photonic Switches
Presented by Natalie-Ann Ndebele
 Optical Multiplexers Basics
• Definition :- the combination of data signals from different Sources over a
single pair of optical fiber.
• Optical multiplexing is the art of combining multiple optical signals into
one to make full use of the immense bandwidth potential of an optical
channel. It can perform additional roles like providing redundancy,
supporting advanced topologies, reducing hardware and cost, etc. The idea is
to divide the huge bandwidth of optical fiber into individual channels of
lower bandwidth, so that multiple access with lower-speed electronics is
achieved
 WDM
(Wavelength Division Multiplexing)
• Definition:- Wavelength Division Multiplexing (WDM) is a fiber-optic
transmission technique that enables the use of multiple light
wavelengths (or colors) to send data over the same medium.
• Used to increase capacity of single standard fiber by assigning many
channels to the fiber which helps increase data transmission rate
• Using multiplexer , all signals are transmitted by a single fiber.
• At the receiving side , the Demultiplexer separates the different
wavelengths and assigns them to different receivers
WDM Architecture

• Ultimately in WDM , we are

increasing the capacity of the fiber by
using this fiber with different
wavelengths
• Multiple signals from multiple
transmitters are combined and
forwarded to multiple receivers. Hence
data rate is increased.
 Advantages and disadvantages of WDM

Advantages Disadvantages,
• Easier to reconfigure • Cost of the system increases
• Full duplex transmission is with the addition of optical
possible components

• It provides higher bandwidth

 OTDM
Optical time division Multiplexing
• A technique that can combine multiple low
bit rate channel in to single high bit rate
channel in time basis. each channel can be
multiplexed in to multiplexer for given period
of time. In OTDM, only one wavelength of
light is used instead of Different wavelength
of light in WDM and same frequency
• This happens when the data transmission rate
of media is greater than that of the source,
and each signal is allotted a definite amount
of time. These slots are so small that all
transmissions appear to be parallel
Advantages and disadvantages of OTDM
• System is very simple to • OTDM is synchronization
implement dependent
• faster single-channel access times • Lack of synchronization may
for high-data-rate end users. result in collision on the
channel
 FDM
Frequency division Multiplexing
• In FDM, the total bandwidth is divided to a set of
frequency bands that do not overlap. Each of these
bands is a carrier of a different signal that is generated
and modulated by one of the sending devices. The
frequency bands are separated from one another by
strips of unused frequencies called the guard bands, to
prevent overlapping of signals.
• The modulated signals are combined together using a
multiplexer (MUX) in the sending end. The combined
signal is transmitted over the communication channel,
thus allowing multiple independent data streams to be
transmitted simultaneously. At the receiving end, the
individual signals are extracted from the combined
signal by the process of demultiplexing (DEMUX ).
 Advantages and disadvantages of FDM
• It does not need synchronization • FDM requires more hardware
between its transmitter as well as than TDM
receiver. • A large number of modulator
• FDM is simpler and easy and filter required hence it is
demodulation. costly
 Photonic Switches
• Photonics simply refers to the study of light as well as its properties
• A photonic switch is a device that selectively switches optical signals from one
channel to another.
• The switching can be temporal or spatial.
• Temporal switching is known as optical (time domain) switch or an optical modulator
• While the spatial switching is called an optical space switch or optical router.
• Networking equipment today is still based on electronic signals, meaning optical
signals must converted to electrical signals , for amplification , regeneration and
switching, then reconverted to optical signals (optical-to-electronic-to-optical OEO
conversion)
• Information arriving at then node is forwarded on towards its final destination via
best possible path, which may be determined by factors such as distance, cost and
reliability of specific routes
Operation of an optical switch
• An optical switch may operate by mechanical
means such as physically shifting an optic fiber to
drive one or more alternative fibers or by electro-
optic effects, magneto-optic effects etc.
• Slow optic switch, e.g. those using moving fibers
may be used for alternate routing of an optical
switch transmission path e.g. routing around a fault
• Fast optic switches , e.g. those using magneto-optic
and electro-optic effects are used to perform logic
operations
• Also included in this category are semiconductor
optical amplifiers which are optoelectronic devices
used as optical switches and can be integrated with
discrete circuits
Switching node
• An optical packet-switching node is shown in the diagram on the
side. The idea is to create packet-switching nodes with much
higher capacities than can be envisioned with electronic packet
switching.
• Such a node takes a packet coming in, reads its header, and
switches it to the appropriate output port. The node may also
impose a new header on the packet.
• It must also handle contention for output ports. If two packets
coming in on different ports need to go out on the same output
port, one of the packets must be buffered, or sent out on another
port.
• In summary,the node buffers the incoming packets, looks at the
packet header, and routes the packets to an appropriate output
port based on the information contained in the header.
 Importance and application of photonic
switches
Importance Applications
• less crowded network • Computer and networking
• Reduced protocol issues purposes

• Increased bandwidth • Phone systems

• Increased distance • Drop multiplexing