Photonic-crystal fiber

Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is now finding applications in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas.

Other arrangements include concentric rings of two or more materials, first proposed as "Bragg fibers" by Yeh and Yariv,[8] bow-tie, panda, and elliptical hole structures (used to achieve higher birefringence due to irregularity in the relative refractive index), spiral[9] designs which allow for better control over optical properties as individual parameters can be changed.

[13] A combination of a polymer and a chalcogenide glass was used by Temelkuran et al.[14] in 2002 for 10.6 μm wavelengths (where silica is not transparent).

These photonic crystal fibers operate on the same index-guiding principle as conventional optical fiber—however, they can have a much higher effective refractive index contrast between core and cladding, and therefore can have much stronger confinement for applications in nonlinear optical devices, polarization-maintaining fibers.

PCF can also be modified by coating the holes with sol-gels of similar or different index material to enhance the transmittance of light.

The term "photonic-crystal fiber" was coined by Philip Russell in 1995–1997 (he states (2003) that the idea dates to unpublished work in 1991).

SEM micrographs of a photonic-crystal fiber produced at US Naval Research Laboratory . (left) The diameter of the solid core at the center of the fiber is 5 μm, while (right) the diameter of the holes is 4 μm
Diagram of a photonic crystal fiber in perspective and cross-sectional views. A solid-core fiber is shown with a periodic air hole cladding and a solid blue coating.
Diagram in cross-sectional view of two types of photonic crystal fibers: index guide (left) and photonic bandgap (right).