TABLE OF CONTENTS The light sources and receivers which we consider in this chapter are hybrids of semiconductor components. Most of them are manufactured industrially and used in multimode and single mode optical fiber links: they are already manufactured and available commercially at low cost in great quantities.
This chapter is built on the differences between:
the essential ratings and characteristics of transmitters and receivers optimized for digital transmissions at high data rates along single mode optical fibers over long distances,
the essential characteristics of the semiconductor transmitters and receivers dedicated to digital transmission in free-space optical links.
The first characteristic common to both light emitter and detector is the optical spectral range.
In the two spectral windows centered on 0.8 and 1.55 ?m wavelengths:
specific attenuations of multimode and single mode fibers are small,
manufacturing technologies, materials and single mode fiber structures allow excellent dispersion and amplification performances to be attained,
passive components - couplers, filters and photo-incorporated Bragg network reflectors - are already industrial realities,
erbium-doped optical fiber amplifiers (Er 3+), high power lasers for optical pumping at 1.48 ?m, are available.
And furthermore:
in ophthalmology, the components of this infrared spectral window are considered less dangerous to high power densities than those centered on shorter wavelengths such as 0.85 ?m. They are primarily absorbed by the cornea and do not seem to cause irreversible pathological damage to human eye constituents,
all the sources, components, couplers and filters quoted previously and used in optical fiber...
