Chapter 5
Optical Power Coupling
Abstract Having examined the characteristics of optical fibers and the associated
light sources used with them, the next step is to investigate how to launch optical
power into a particular fiber efficiently from some type of luminescent source. In
conjunction with this topic is the question is how to couple optical power from one
fiber into another. Each jointing technique is subject to certain conditions, which can
cause varying degrees of optical power loss at the joint. The purpose of this chapter
is to highlight these conditions and determine methods for minimizing the joint loss.
In implementing an optical fiber link, two of the major system questions are how to
launch optical power into a particular fiber from some type of luminescent source and
how to couple optical power from one fiber into another. Launching optical power
from a source into a fiber entails considerations such as the numerical aperture, core
size, refractive-index profile, and core-cladding index difference of the fiber, plus the
size, radiance, and angular power distribution of the optical source.
A measure of the amount of optical power emitted from a source that can be
coupled into a fiber is usually given by the coupling efficiency η defined as
η =
P F
P S
Here P F is the power coupled into the fiber and P S is the power emitted from the
light source. The launching or coupling efficiency depends on the type of fiber that
is attached to the source and on the coupling process; for example, whether lenses
or other coupling improvement schemes are used.
In practice, many source suppliers offer devices with a short length of optical
fiber (1 m or less) already attached in an optimum power-coupling configuration.
This section of fiber is generally referred to as a flylead or a pigtail. The powerlaunching problem for these pigtailed sources thus reduces to a simpler one of
coupling optical power from one fiber into another. The effects to be considered
in this case include fiber misalignments; different core sizes, numerical apertures,
and core refractive-index profiles; plus the need for clean and smooth fiber end faces
© 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_5
209
Optical Power Coupling
Abstract Having examined the characteristics of optical fibers and the associated
light sources used with them, the next step is to investigate how to launch optical
power into a particular fiber efficiently from some type of luminescent source. In
conjunction with this topic is the question is how to couple optical power from one
fiber into another. Each jointing technique is subject to certain conditions, which can
cause varying degrees of optical power loss at the joint. The purpose of this chapter
is to highlight these conditions and determine methods for minimizing the joint loss.
In implementing an optical fiber link, two of the major system questions are how to
launch optical power into a particular fiber from some type of luminescent source and
how to couple optical power from one fiber into another. Launching optical power
from a source into a fiber entails considerations such as the numerical aperture, core
size, refractive-index profile, and core-cladding index difference of the fiber, plus the
size, radiance, and angular power distribution of the optical source.
A measure of the amount of optical power emitted from a source that can be
coupled into a fiber is usually given by the coupling efficiency η defined as
η =
P F
P S
Here P F is the power coupled into the fiber and P S is the power emitted from the
light source. The launching or coupling efficiency depends on the type of fiber that
is attached to the source and on the coupling process; for example, whether lenses
or other coupling improvement schemes are used.
In practice, many source suppliers offer devices with a short length of optical
fiber (1 m or less) already attached in an optimum power-coupling configuration.
This section of fiber is generally referred to as a flylead or a pigtail. The powerlaunching problem for these pigtailed sources thus reduces to a simpler one of
coupling optical power from one fiber into another. The effects to be considered
in this case include fiber misalignments; different core sizes, numerical apertures,
and core refractive-index profiles; plus the need for clean and smooth fiber end faces
© 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_5
209