Optical multiplexers allow multiple signals to be transmitted simultaneously over a single optical fiber link. There are different optical multiplexing techniques, including wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). WDM assigns each signal a unique wavelength, while OTDM separates signals in the time domain. Optical multiplexers and demultiplexers use passive optical filters to combine and separate the wavelength signals. This increases bandwidth utilization and reduces transmission costs.

1. Optical Multiplexers
Presented by: Aizaz Ahmed Sahito

2. Multiplexing
 Multiplexing is an essential part in a communication system where
multiple users transmit data simultaneously through a single link,
whether the link is a coaxial cable, a fiber, radio or satellite.
 Multiplexing is widely employed in communication systems due to
its capability to increase the channel utilization or the transmission
capacity and decrease system costs.

3. Multiplexing in Fiber Optics
 The bandwidth properties of optical fiber are well known and make
it the media of choice for high-speed data and video applications.
However, various forms of multiplexing are required to take
advantage of this bandwidth.
 Optical multiplexer and de-multiplexer are basically passive optical filter
systems, which are arranged to process specific wavelengths in and out of
the transport system (usually optical fiber).
 Process of filtering the wavelengths can be performed using:
 Prisms
 Thin film filter
 Dichroic filters or interference filters

4.  There are different techniques in multiplexing light signals onto a single
optical fiber link.
 Optical Multiplexing Techniques
 Optical Time Division Multiplexing (OTDM)
Separating wavelengths in time
 Wavelength division multiplexing (WDM)
Each channel is assigned a unique carrier frequency
Channel spacing of about 50GHz
I. Coarse Wavelength Division Multiplexing (CWDM)
II. Dense Wavelength Division Multiplexing
Uses a much narrower channel spacing, therefore, many more wavelengths are
supported.

5. Optical Time Division Multiplexing
 Optical time division multiplexing (OTDM) has a similar concept to
electrical TDM, only that it is implemented in optical domain.
 OTDM (Optical Time-Division Multiplexing) is a very powerful optical
multiplexing technique that deliveries very high capacity of data
over optical fiber.
 The basic principle of this technology is to multiplex a number of
low bit rate optical channels in time domain.

6. Optical Time Division Multiplexing
 The overall OTDM system can be viewed as three big blocks
1. transmitter block
2. line system,
3. receiver block.
 The transmitter block is consist of Laser sources, modulators, channel
alignment systems, and multiplexer.
 The line system contains optical amplifiers and transmission fibers.
 The receiver block is made of synchronization/timing extraction circuit and
channel De-multiplexer.

8. Wavelength division Multiplexing
 Wavelength division multiplexing (WDM) is used to transmit more than one
high-speed digital data stream on a single optical fiber.
 Different wavelengths of light, (different colors) propagate in a single fiber
without interfering. The devices that do the optical combining and
separation are referred to as WDMs.
 These are passive optical devices that typically employ optical filters
 In wavelength-division multiplexing (WDM) systems, different independent
users transmit data over a single fiber using different wavelengths

9.  At the transmitter side, n independent user’s data are modulated onto n
high frequency carriers, each with a unique wavelength (λ).
 A wavelength multiplexer combines these optical signals and couples
them into a single fiber.
 At the receiving end, a De-multiplexer is required to separate the optical
signals into appropriate channels.
 This is done with n optical filters,

11.  Coarse wavelength division multiplexing
uses a relatively small number of channels, e.g. four or eight, and a large
channel spacing of 20 nm
The resulting total data rates are useful e.g. within metropolitan areas, as
long as broadband technologies are not widespread in households
 Dense wavelength division multiplexing
It extended method for very large data capacities, as required e.g. in the
Internet backbone. It uses a large number of channels (e.g. 40, 80, or
160), and a correspondingly small channel spacing

12.  Code Division Multiplexing
 Also used in microwave transmission.
 Spectrum of each wavelength is assigned a unique spreading
code.
 Channels overlap both in time and frequency domains but the
code guide each wavelength.

13. optical add-drop multiplexer (OADM)
 It is a device used in wavelength division multiplexing systems for
multiplexing and routing different channels of light into or out of a single
mode fiber (SMF).
 "Add" and "drop" here refer to the capability of the device to add one or
more new wavelength channels to an existing multi-wavelength WDM
signal. and/or to drop (remove) one or more channels, passing those
signals to another network path.
 An OADM may be considered to be a specific type of optical cross-
connect.

15. Applications
 The major scarce resource in telecommunication is bandwidth – users
want transmit at more high rate and service providers want to offer more
services, hence, the need for a faster and more reliable high speed
system.
 Reducing cost of hardware, one multiplexing system can be used to
combine and transmit multiple signals from Location A to Location B.
 Each wavelength, λ, can carry multiple signals.
 Mux/De-Mux serve optical switching of signals in telecommunication and
other field of signal processing and transmission.
 Future next generation internet.