Chapter 4
Light Sources for Fiber Links
Abstract Semiconductor-based light-emitting diodes and laser diodes are the two
basic types of light sources that are compatible with the dimensions of optical fibers.
These components are suitable light sources for optical communications because of
their optical power output levels, the ability to directly modulate the light level with an
information signal, and their high efficiency. To understand the applications of these
optical sources, this chapter first presents some basic concepts of semiconductor
physics and then describes the operational characteristics of light-emitting diodes
and laser diodes.
Two classes of semiconductor-based light sources that are widely used for fiber
optic communications are heterojunction-structured semiconductor laser diodes
(also referred to as injection laser diodes or ILDs) and light-emitting diodes (LEDs).
A heterojunction consists of two adjoining semiconductor materials with different
bandgap energies. Note that as described below, the bandgap energy represents the
minimum energy that is required to boost an electron in a semiconductor material
to a higher energy state in which it can participate in electrical conduction. These
devices are suitable for fiber transmission systems because they have adequate output
power for a wide range of applications, their optical power output can be directly
modulated by varying the input current to the device, they have a high efficiency,
and their dimensions are compatible with those of the optical fiber. Comprehensive
treatments of the major aspects of LEDs, laser diodes, and their underlying semiconductor principles are presented in various books and review articles [1–6]. Chapter 11
addresses optical fiber lasers and pump lasers used for optical amplifiers.
The intent of this chapter is to give an overview of the pertinent characteristic
of fiber-compatible semiconductor luminescent sources. The first section discusses
semiconductor material fundamentals that are relevant to light source operation. The
next two sections present the output and the operating characteristics of LEDs and
laser diodes. Next are sections concerning the temperature responses and linearity
characteristics of optical sources.
In this chapter first Sect. 4.1 shows that the light-emitting region of both LEDs
and laser diodes consists of a pn junction constructed of direct-bandgap III–V semiconductor materials. When this junction is forward biased, electrons and holes are
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
G. Keiser, Fiber Optic Communications,
https://doi.org/10.1007/978-981-33-4665-9_4
147
Light Sources for Fiber Links
Abstract Semiconductor-based light-emitting diodes and laser diodes are the two
basic types of light sources that are compatible with the dimensions of optical fibers.
These components are suitable light sources for optical communications because of
their optical power output levels, the ability to directly modulate the light level with an
information signal, and their high efficiency. To understand the applications of these
optical sources, this chapter first presents some basic concepts of semiconductor
physics and then describes the operational characteristics of light-emitting diodes
and laser diodes.
Two classes of semiconductor-based light sources that are widely used for fiber
optic communications are heterojunction-structured semiconductor laser diodes
(also referred to as injection laser diodes or ILDs) and light-emitting diodes (LEDs).
A heterojunction consists of two adjoining semiconductor materials with different
bandgap energies. Note that as described below, the bandgap energy represents the
minimum energy that is required to boost an electron in a semiconductor material
to a higher energy state in which it can participate in electrical conduction. These
devices are suitable for fiber transmission systems because they have adequate output
power for a wide range of applications, their optical power output can be directly
modulated by varying the input current to the device, they have a high efficiency,
and their dimensions are compatible with those of the optical fiber. Comprehensive
treatments of the major aspects of LEDs, laser diodes, and their underlying semiconductor principles are presented in various books and review articles [1–6]. Chapter 11
addresses optical fiber lasers and pump lasers used for optical amplifiers.
The intent of this chapter is to give an overview of the pertinent characteristic
of fiber-compatible semiconductor luminescent sources. The first section discusses
semiconductor material fundamentals that are relevant to light source operation. The
next two sections present the output and the operating characteristics of LEDs and
laser diodes. Next are sections concerning the temperature responses and linearity
characteristics of optical sources.
In this chapter first Sect. 4.1 shows that the light-emitting region of both LEDs
and laser diodes consists of a pn junction constructed of direct-bandgap III–V semiconductor materials. When this junction is forward biased, electrons and holes are
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
G. Keiser, Fiber Optic Communications,
https://doi.org/10.1007/978-981-33-4665-9_4
147