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2 Optical Fiber Structures and Light Guiding Principles
2.7.3 Active Glass Optical Fibers
Incorporating rare-earth elements (atomic numbers 57–71) into a normally passive
glass gives the resulting material new optical and magnetic properties. These new
properties allow the material to perform amplification, attenuation, and phase retardation on the light passing through it [40, 41]. Doping (i.e., adding impurities) can
be carried out for silica, telluride, and halide glasses.
Two commonly used doping materials for fiber lasers are erbium and neodymium.
The ionic concentrations of the rare-earth elements are low (on the order of 0.005–
0.05 mol %) to avoid clustering effects. To make use of the absorption and fluorescence spectra of these materials, one can use an optical source that emits at an
absorption wavelength of the doping material to excite electrons to higher energy
levels in the rare-earth dopants. When these excited electrons are stimulated by a
signal photon to drop to lower energy levels, the transition process results in the emission of light in a narrow optical spectrum at the fluorescence wavelength. Chapter 11
discusses the applications of fibers doped with rare-earth elements to create optical
amplifiers.
2.7.4 Plastic Optical Fibers
The growing demand for delivering high-speed services directly to the workstation
has led fiber developers to create high-bandwidth graded-index polymer (plastic)
optical fibers (POF) for use on customer premises [42–44]. The core of these fibers
is either polymethylmethacrylate or a perfluorinated polymer. These fibers are hence
referred to as PMMA POF and PF POF, respectively. Although they exhibit considerably greater optical signal attenuations than glass fibers, plastic fibers are tough
and durable. For example, since the modulus of these polymers is nearly two orders
of magnitude lower than that of silica, even a 1-mm-diameter graded-index POF is
sufficiently flexible to be installed in conventional fiber cable routes. Standard optical
connectors can be used on plastic fibers having core sizes that are compatible with the
core diameters of standard multimode glass telecom fibers. Thus coupling between
similar sized plastic and glass fibers is straightforward. In addition, for the plastic
fibers inexpensive plastic injection-molding technologies can be used to fabricate
connectors, splices, and transceivers.
Table 2.4 gives sample characteristics of PMMA and PF polymer optical fibers.
2.8 Photonic Crystal Fiber Concepts
In the early 1990s researchers envisioned and demonstrated a new optical fiber structure. Initially this was called a holey fiber and later became known as a photonic
2 Optical Fiber Structures and Light Guiding Principles
2.7.3 Active Glass Optical Fibers
Incorporating rare-earth elements (atomic numbers 57–71) into a normally passive
glass gives the resulting material new optical and magnetic properties. These new
properties allow the material to perform amplification, attenuation, and phase retardation on the light passing through it [40, 41]. Doping (i.e., adding impurities) can
be carried out for silica, telluride, and halide glasses.
Two commonly used doping materials for fiber lasers are erbium and neodymium.
The ionic concentrations of the rare-earth elements are low (on the order of 0.005–
0.05 mol %) to avoid clustering effects. To make use of the absorption and fluorescence spectra of these materials, one can use an optical source that emits at an
absorption wavelength of the doping material to excite electrons to higher energy
levels in the rare-earth dopants. When these excited electrons are stimulated by a
signal photon to drop to lower energy levels, the transition process results in the emission of light in a narrow optical spectrum at the fluorescence wavelength. Chapter 11
discusses the applications of fibers doped with rare-earth elements to create optical
amplifiers.
2.7.4 Plastic Optical Fibers
The growing demand for delivering high-speed services directly to the workstation
has led fiber developers to create high-bandwidth graded-index polymer (plastic)
optical fibers (POF) for use on customer premises [42–44]. The core of these fibers
is either polymethylmethacrylate or a perfluorinated polymer. These fibers are hence
referred to as PMMA POF and PF POF, respectively. Although they exhibit considerably greater optical signal attenuations than glass fibers, plastic fibers are tough
and durable. For example, since the modulus of these polymers is nearly two orders
of magnitude lower than that of silica, even a 1-mm-diameter graded-index POF is
sufficiently flexible to be installed in conventional fiber cable routes. Standard optical
connectors can be used on plastic fibers having core sizes that are compatible with the
core diameters of standard multimode glass telecom fibers. Thus coupling between
similar sized plastic and glass fibers is straightforward. In addition, for the plastic
fibers inexpensive plastic injection-molding technologies can be used to fabricate
connectors, splices, and transceivers.
Table 2.4 gives sample characteristics of PMMA and PF polymer optical fibers.
2.8 Photonic Crystal Fiber Concepts
In the early 1990s researchers envisioned and demonstrated a new optical fiber structure. Initially this was called a holey fiber and later became known as a photonic