378
9 Analog Optical Fiber Channels
processing at multiple-gigahertz sampling frequencies include signal filtering,
analog-to-digital conversion, frequency conversion and mixings, signal correlation,
generation of arbitrary waveforms, and beam-forming methodologies for phased
array radars.
9.7 Summary
Although digital transmission techniques have been used most widely in optical fiber
communication links, sometimes it is more advantageous to transmit information in
its original analog form instead of first converting it to a digital format. In fact, as a
result of the emerging use of broadband wireless communication devices, schemes
have been investigated and implemented for using analog optical fiber links for
distributing broadband microwave-frequency signals in a variety of applications.
The transition in the use of wireless devices from pure voice communications to
a wide selection of broadband services created much interest in developing radioover-fiber (ROF) links. The convergence of optical and wireless access networks is
driven by the need to have seamless connectivity between an access network and both
stationary and fast-moving mobile users at data rates of at least 2.5 Gb/s. The implementations of ROF links include the interconnection of antenna base stations with a
central controlling office in a wireless access network, access to wireless services for
indoor environments (e.g., large office buildings, airport departure lounges, hospitals, conference centers, hospitals, and hotel rooms), and connections to personal
area networks in homes. Services of interest to mobile users include broadband
Internet access, fast peer-to-peer file transfers, high-definition video, and online
multiparty gaming. Depending on the network type, the optical links can use singlemode fibers, 50- or 62.5-µm core-diameter multimode glass fibers, or large-core
multimode polymer optical fibers.
Problems
9.1 Commercially available wideband receivers have equivalent resistances R eq =
75 . With this value of R eq and letting the remaining transmitter and receiver
parameters be the same as in Example 9.1, plot the total carrier- to-noise ratio
and its limiting expressions, as given by Eq. (9.10) through Eq. (9.13), for
received power levels ranging from 0 to −16 dBm. Show that the thermal noise
of the receiver dominates over the quantum noise at all power levels when R eq
= 75 .
9.2 Consider a five-channel frequency-division-multiplexed (FDM) system having
carriers at f 1 , f 2 = f 1 + , f 3 = f 1 + 2, f 4 = f 1 + 3, and f 5 = f 1 +
4, where is the spacing between carriers. On a frequency plot, show the
number and location of the triple-beat and two-tone third-order intermodulation
products.
9.3 Suppose an engineer wants to frequency-division multiplex
60 FM signals. If 30 of these signals have a per-channel modulation index m i
9 Analog Optical Fiber Channels
processing at multiple-gigahertz sampling frequencies include signal filtering,
analog-to-digital conversion, frequency conversion and mixings, signal correlation,
generation of arbitrary waveforms, and beam-forming methodologies for phased
array radars.
9.7 Summary
Although digital transmission techniques have been used most widely in optical fiber
communication links, sometimes it is more advantageous to transmit information in
its original analog form instead of first converting it to a digital format. In fact, as a
result of the emerging use of broadband wireless communication devices, schemes
have been investigated and implemented for using analog optical fiber links for
distributing broadband microwave-frequency signals in a variety of applications.
The transition in the use of wireless devices from pure voice communications to
a wide selection of broadband services created much interest in developing radioover-fiber (ROF) links. The convergence of optical and wireless access networks is
driven by the need to have seamless connectivity between an access network and both
stationary and fast-moving mobile users at data rates of at least 2.5 Gb/s. The implementations of ROF links include the interconnection of antenna base stations with a
central controlling office in a wireless access network, access to wireless services for
indoor environments (e.g., large office buildings, airport departure lounges, hospitals, conference centers, hospitals, and hotel rooms), and connections to personal
area networks in homes. Services of interest to mobile users include broadband
Internet access, fast peer-to-peer file transfers, high-definition video, and online
multiparty gaming. Depending on the network type, the optical links can use singlemode fibers, 50- or 62.5-µm core-diameter multimode glass fibers, or large-core
multimode polymer optical fibers.
Problems
9.1 Commercially available wideband receivers have equivalent resistances R eq =
75 . With this value of R eq and letting the remaining transmitter and receiver
parameters be the same as in Example 9.1, plot the total carrier- to-noise ratio
and its limiting expressions, as given by Eq. (9.10) through Eq. (9.13), for
received power levels ranging from 0 to −16 dBm. Show that the thermal noise
of the receiver dominates over the quantum noise at all power levels when R eq
= 75 .
9.2 Consider a five-channel frequency-division-multiplexed (FDM) system having
carriers at f 1 , f 2 = f 1 + , f 3 = f 1 + 2, f 4 = f 1 + 3, and f 5 = f 1 +
4, where is the spacing between carriers. On a frequency plot, show the
number and location of the triple-beat and two-tone third-order intermodulation
products.
9.3 Suppose an engineer wants to frequency-division multiplex
60 FM signals. If 30 of these signals have a per-channel modulation index m i