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1 Perspectives on Lightwave Communications
consoles for 3D online games has created a growing demand for more bandwidth from applications such as video-on-demand, cloud computing, online gaming,
music streaming, and social networking. To accommodate this growing bandwidth
demand, network providers are continuously seeking new methods for increasing
the information-handling capacity of optical links. This is especially important in
the links running between a customer and a nearby traffic switching facility (known
as the central office). These methods include wavelength division, polarization division, mode division, and space division multiplexing techniques that combine many
individual information channels onto a single fiber.
1.5.1 Basis of WDM
The basis of wavelength division multiplexing (WDM) is to use multiple sources
operating at slightly different wavelengths to transmit several independent information streams simultaneously over the same fiber. Figure 1.9 shows the basic WDM
concept. Here N independent optically formatted information streams, each transmitted at a different wavelength, are combined by means of an optical multiplexer
and sent over the same fiber. Note that each of these streams could be at a different
data rate. Each information stream maintains its individual data rate after being
multiplexed with the other traffic streams, and still operates at its unique wavelength.
Although researchers started looking at WDM techniques in the 1970s, during the
ensuing years it generally turned out to be easier to transmit only a single wavelength
on a fiber using high-speed electronic and optical devices, than to invoke the greater
system complexity called for in WDM. However, a dramatic surge in WDM popularity started in the early 1990s owing to several factors. These include new fiber
types that provide better performance of multiple-wavelength operation at 1550 nm,
advances in producing WDM devices that can combine and separate closely spaced
wavelengths, and the development of optical amplifiers that can boost optical signal
Optical
multiplexer
Individual fiber
input lines
Single fiber
output line
λ 1 , λ 2 , …, λ N
λ 1
λ 2
λ N
Fig. 1.9 Basic concept of wavelength division multiplexing
1 Perspectives on Lightwave Communications
consoles for 3D online games has created a growing demand for more bandwidth from applications such as video-on-demand, cloud computing, online gaming,
music streaming, and social networking. To accommodate this growing bandwidth
demand, network providers are continuously seeking new methods for increasing
the information-handling capacity of optical links. This is especially important in
the links running between a customer and a nearby traffic switching facility (known
as the central office). These methods include wavelength division, polarization division, mode division, and space division multiplexing techniques that combine many
individual information channels onto a single fiber.
1.5.1 Basis of WDM
The basis of wavelength division multiplexing (WDM) is to use multiple sources
operating at slightly different wavelengths to transmit several independent information streams simultaneously over the same fiber. Figure 1.9 shows the basic WDM
concept. Here N independent optically formatted information streams, each transmitted at a different wavelength, are combined by means of an optical multiplexer
and sent over the same fiber. Note that each of these streams could be at a different
data rate. Each information stream maintains its individual data rate after being
multiplexed with the other traffic streams, and still operates at its unique wavelength.
Although researchers started looking at WDM techniques in the 1970s, during the
ensuing years it generally turned out to be easier to transmit only a single wavelength
on a fiber using high-speed electronic and optical devices, than to invoke the greater
system complexity called for in WDM. However, a dramatic surge in WDM popularity started in the early 1990s owing to several factors. These include new fiber
types that provide better performance of multiple-wavelength operation at 1550 nm,
advances in producing WDM devices that can combine and separate closely spaced
wavelengths, and the development of optical amplifiers that can boost optical signal
Optical
multiplexer
Individual fiber
input lines
Single fiber
output line
λ 1 , λ 2 , …, λ N
λ 1
λ 2
λ N
Fig. 1.9 Basic concept of wavelength division multiplexing