Biomedical Engineering Reference
In-Depth Information
IMAGING
AREA
Serial Output Register
Sense Node & Amplifier
Figure 6.2-5 Interface of a CCD array and the register for data output.
Modern light-wave communication systems had their
birth in the 1960s. The first demonstration of the ruby
laser in 1960 ( Maiman 1960 ) and a demonstration of
laser operations in semiconductor devices in 1962 ( Hall
et al. 1962 ; Nathan et al. 1962 ) were early stepping
stones that led to the continuous operation of room
temperature, long-lifetime, semiconductor lasers that are
in common use today. The laser made available a co-
herent optical frequency carrier of enormous communi-
cation capacity. If a communication system was built that
utilized only 0.01% of the laser carrier frequency, its
modulation bandwidth would be 30 GHz. In 1966
a parallel evolution of fiber technology was taking place.
Although the best existing fibers at that time had at-
tenuation greater than 1000 dB/km, researchers at
Standard Telecommunication Laboratories (STC) in
England ( Kao and Hockham 1966 ) speculated that losses
as low as 20 dB/km should be achievable and they further
suggested that such fibers would be useful in telecom-
munication applications, and they were correct. In 1970
workers at Corning Glass Works ( Kapron et al. 1970 )
produced the first fiber with loss under 20 dB/km. Since
that time, fiber technology has advanced to the point of
producing fibers with loss less than 0.25 dB/km at 1.55
m m. These fibers are approaching the Rayleigh scattering
limit of the glass being used to fabricate them. The big-
gest advantage of an optical fiber communication system
is its tremendous information-carrying capacity. There
are already many systems that can carry several thousand
simultaneous conversations over a pair of optical fibers
that are thinner than a human hair.
6.2.2.1 Classification and features
of optical fibers
Fibers that are used for optical communications are
waveguides made of transparent dielectrics whose func-
tion is to guide light over long distances. An optical fiber
consists of an inner cylinder of glass called the core,
Readout
Readout
Sense Node and
Amplifier
Sense Node and
Amplifier
SubArray
SubArray
SubArray
SubArray
Sense Node and
Amplifier
Sense Node and
Am plifier
Readout
Readout
Figure 6.2-6 CCD subarrays and hardware registers for reading data out.
Search WWH ::




Custom Search