The phrase “PC load letter” is a printer error message on some mostly obsolete types of HP laserjet printers. Here, “PC” stands for “paper cassette” and the error indicates that no letter-sized paper is available for a print job with a letter size. The error message is instructing the user to load a letter-sized paper into the printer.
Photonic crystal fiber (PCF) is a kind of optical fiber that uses photonic crystals to form the cladding around the core of the cable. Photonic crystal is a low-loss periodic dielectric medium constructed using a periodic array of microscopic air holes that run along the entire fiber length. In PCFs, photonic crystals with photonic band gaps are constructed to prevent light propagation in certain directions with a certain range of wavelengths. Contrary to normal fiber optics, PCFs use total internal reflection or light confinement in hollow core methods to propagate light. Light propagation in PCFs is far superior to standard fiber, which uses constant lower refractive index cladding. Applications for photonic crystal fibers include spectroscopy, metrology, biomedicine, imaging, telecommunication, industrial machining and military technology.Photonic crystal fiber is also known as microstructured, or holey, fiber.
Fiber-optic cables are constructed with a core and a cladding of constant refractive index difference. Light travels through the core as a result of the refraction property of light, which occurs as a result of the difference between the refractive indexes of the core and cladding. This refracted light bears much higher loss during propagation over extended distances, and thus requires repeaters and amplifiers for extended distance communications. In PCF, on the other hand, light is trapped in the core, providing a much better wave guide to photons than standard fiber optics. The polymers used instead of glass in PCF provide the advantage of a more flexible fiber, which allows for easier and less expensive installation. Various photonic crystals conforming to various photonic lattices are manufactured depending on the required properties of the propagated light. Photonic crystal fibers are generally divided into two main categories:
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