2.8 Photonic Crystal Fiber Concepts
77
Table 2.4 Sample
characteristics of PMMA and
PF polymer optical fibers
Characteristic
PMMAPOF
PFPOF
Core diameter
0.4 mm
0.050–0.30 mm
Cladding diameter
1.0 mm
0.25–0.60 mm
Numerical aperture
0.25
0.20
Attenuation
150 dB/km at
650 nm
<40 dB/km at
650–1300 nm
Bandwidth
2.5 Gb/s over
200 m
2.5 Gb/s over
550 m
crystal fiber (PCF) or a microstructured fiber [45–48]. The difference between this
new structure and that of a conventional fiber is that the cladding and, in some cases,
the core regions of a PCF contain air holes, which run along the entire length of the
fiber. Whereas the material properties of the core and cladding define the light transmission characteristics of conventional fibers, the structural arrangement of the hole
channels in a PCF creates an internal microstructure, which offers extra dimensions
in controlling the optical properties of light, such as the dispersion, nonlinearity, and
birefringence effects in optical fibers.
The sizes of the holes and the hole-to-hole spacing (known as the pitch) in the
microstructure and the refractive index of its constituent material determine the lightguiding characteristics of photonic crystal fibers. The two basic PCF categories are
index-guiding fibers and photonic bandgap fibers. The light transmission mechanism
in an index-guiding fiber is similar to that in a conventional fiber as it has a highindex core surrounded by a lower-index cladding. However, for a PCF the effective
refractive index of the cladding depends on the wavelength and the size and pitch
of the holes. In contrast, in a photonic bandgap fiber light is guided by means
of a photonic bandgap effect in either a hollow or microstructured core, which is
surrounded by a microstructured cladding.
2.8.1 Index-Guiding PCF
Figure 2.26 shows the two-dimensional cross-sectional end view of a basic structure
of an index-guiding PCF. The fibers have a solid core that is surrounded by a cladding
region, which contains air holes that run along the length of the fiber and can have
a variety of different shapes, sizes, and distribution patterns. As an illustration, in
Fig. 2.26 the air holes are arranged in a uniform hexagonal array. The holes all have
a diameter d and a hole-to-hole spacing or pitch .
The values of the hole diameter and the pitch are important for determining the
operational characteristics of an index-guiding PCF. For a diameter-to-pitch ratio
d/ < 0.4 the fiber exhibits single-mode properties over a wide range of wavelengths
(from about 300 to 2000 nm). This characteristic is not possible to achieve in standard
77
Table 2.4 Sample
characteristics of PMMA and
PF polymer optical fibers
Characteristic
PMMAPOF
PFPOF
Core diameter
0.4 mm
0.050–0.30 mm
Cladding diameter
1.0 mm
0.25–0.60 mm
Numerical aperture
0.25
0.20
Attenuation
150 dB/km at
650 nm
<40 dB/km at
650–1300 nm
Bandwidth
2.5 Gb/s over
200 m
2.5 Gb/s over
550 m
crystal fiber (PCF) or a microstructured fiber [45–48]. The difference between this
new structure and that of a conventional fiber is that the cladding and, in some cases,
the core regions of a PCF contain air holes, which run along the entire length of the
fiber. Whereas the material properties of the core and cladding define the light transmission characteristics of conventional fibers, the structural arrangement of the hole
channels in a PCF creates an internal microstructure, which offers extra dimensions
in controlling the optical properties of light, such as the dispersion, nonlinearity, and
birefringence effects in optical fibers.
The sizes of the holes and the hole-to-hole spacing (known as the pitch) in the
microstructure and the refractive index of its constituent material determine the lightguiding characteristics of photonic crystal fibers. The two basic PCF categories are
index-guiding fibers and photonic bandgap fibers. The light transmission mechanism
in an index-guiding fiber is similar to that in a conventional fiber as it has a highindex core surrounded by a lower-index cladding. However, for a PCF the effective
refractive index of the cladding depends on the wavelength and the size and pitch
of the holes. In contrast, in a photonic bandgap fiber light is guided by means
of a photonic bandgap effect in either a hollow or microstructured core, which is
surrounded by a microstructured cladding.
2.8.1 Index-Guiding PCF
Figure 2.26 shows the two-dimensional cross-sectional end view of a basic structure
of an index-guiding PCF. The fibers have a solid core that is surrounded by a cladding
region, which contains air holes that run along the length of the fiber and can have
a variety of different shapes, sizes, and distribution patterns. As an illustration, in
Fig. 2.26 the air holes are arranged in a uniform hexagonal array. The holes all have
a diameter d and a hole-to-hole spacing or pitch .
The values of the hole diameter and the pitch are important for determining the
operational characteristics of an index-guiding PCF. For a diameter-to-pitch ratio
d/ < 0.4 the fiber exhibits single-mode properties over a wide range of wavelengths
(from about 300 to 2000 nm). This characteristic is not possible to achieve in standard