Calculations reveal limit of microfiber thinness

When the diameter of a microfiber is smaller than the wavelength of light being transmitted through it, the presence of the evanescent field projecting outside the fiber allows such tapered fibers to be used for optical sensing, atom trapping, and other applications.

When the diameter of a microfiber is smaller than the wavelength of light being transmitted through it, the presence of the evanescent field projecting outside the fiber allows such tapered fibers to be used for optical sensing, atom trapping, and other applications. To determine the diameter of the microfiber below which evanescent light cannot propagate, a researcher from OFS Laboratories (Somerset, NJ) used the theory of nonadiabatic transitions-developed and used in quantum mechanics-and made the assumption that a fiber’s diameter changes smoothly and is adiabatically slow as a function of fiber length when using the taper-drawing technique.

For a fiber with diameter d0 at the center of a taper with length L, light propagates through the fiber when the transmission loss P of the fiber is much less than 1. Calculations show that the point at which P approximately equals 1 is the condition that determines the threshold value of diameter d0 below which the propagation of the evanescent field is impossible. The threshold diameter of the microfiber is only an order of magnitude smaller than the transmission wavelength, regardless of L. Contact Mikhail Sumetsky at sumetski@ofsoptics.com.

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