<P> Some special - purpose optical fiber is constructed with a non-cylindrical core and / or cladding layer, usually with an elliptical or rectangular cross-section . These include polarization - maintaining fiber and fiber designed to suppress whispering gallery mode propagation . Polarization - maintaining fiber is a unique type of fiber that is commonly used in fiber optic sensors due to its ability to maintain the polarization of the light inserted into it . </P> <P> Photonic - crystal fiber is made with a regular pattern of index variation (often in the form of cylindrical holes that run along the length of the fiber). Such fiber uses diffraction effects instead of or in addition to total internal reflection, to confine light to the fiber's core . The properties of the fiber can be tailored to a wide variety of applications . </P> <P> Attenuation in fiber optics, also known as transmission loss, is the reduction in intensity of the light beam (or signal) as it travels through the transmission medium . Attenuation coefficients in fiber optics usually use units of dB / km through the medium due to the relatively high quality of transparency of modern optical transmission media . The medium is usually a fiber of silica glass that confines the incident light beam to the inside . Attenuation is an important factor limiting the transmission of a digital signal across large distances . Thus, much research has gone into both limiting the attenuation and maximizing the amplification of the optical signal . Empirical research has shown that attenuation in optical fiber is caused primarily by both scattering and absorption . Single - mode optical fibers can be made with extremely low loss . Corning's SMF - 28 fiber, a standard single - mode fiber for telecommunications wavelengths, has a loss of 0.17 dB / km at 1550 nm . For example, an 8 km length of SMF - 28 transmits nearly 75% of light at 1,550 nm . It has been noted that if ocean water was as clear as fiber, one could see all the way to the bottom even of the Marianas Trench in the Pacific Ocean, a depth of 36,000 feet . </P> <P> The propagation of light through the core of an optical fiber is based on total internal reflection of the lightwave . Rough and irregular surfaces, even at the molecular level, can cause light rays to be reflected in random directions . This is called diffuse reflection or scattering, and it is typically characterized by wide variety of reflection angles . </P>

Explain the working principle of optical fiber transmission media
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