  in fiber-optic communication, a single-mode optical fiber (smf) is an optical fiber designed to carry light only directly down the fibre - the transverse mode. modes are the possible solutions of the helmholtz equation for waves, which is obtained by combining maxwell's equations and the boundary conditions. these modes define the way the wave travels through space, i.e. how the wave is distributed in space. waves can have the same mode but have different frequencies. this is the case in single-mode fibers, where we can have waves with different frequencies, but of the same mode, which means that they are distributed in space in the same way, and that gives us a single ray of light. although the ray travels parallel to the length of the fiber, it is often called transverse mode since its electromagnetic vibrations occur perpendicular (transverse) to the length of the fiber. the 2009 nobel prize in physics was awarded to charles k. kao for his theoretical work on the single-mode optical fiber.nobel prize citation http://www.nobelprize.org/nobel_prizes/physics/laureates/2009/kao-facts.html ==history== professor huang hongjia of the chinese academy of sciences, developed coupling wave theory in the field of microwave theory. he led a research team that successfully developed single-mode optical fiber in 1980.hongjia huang (1998). microwave approach to highly-irregular fiber optics. wiley. isbn 978-0-471-31023-5. retrieved 12 january 2011."hong-jia huang". the electromagnetics academy of zhejiang univserityhongjia huang (1984). coupled mode theory: as applied to microwave and optical transmission. vsp. isbn 978-90-6764-033-6 ==characteristics== like multi-mode optical fibers, single mode fibers do exhibit modal dispersion resulting from multiple spatial modes but with narrower modal dispersion. single mode fibers are therefore better at retaining the fidelity of each light pulse over longer distances than multi-mode fibers. for these reasons, single-mode fibers can have a higher bandwidth than multi-mode fibers. equipment for single mode fiber is more expensive than equipment for multi-mode optical fiber, but the single mode fiber itself is usually cheaper in bulk.  a typical single mode optical fiber has a core diameter between 8 and 10.5 Âµm and a cladding diameter of 125&nbsp;Âµm. there are a number of special types of single-mode op
Optical_fiber