Specialty Optical Fibers Handbook

(2) those whose inner wall material has a refractive index less than one (attenu-

ated total reflectance, i.e. ATR, guides). Leaky or n > 1 guides have metallic and

dielectric films deposited on the inside of metallic [43], plastic [44], or glass tubing

[45]. ATR guides are made from dielectric materials with refractive indices less

than one in the wavelength region of interest [46]. Therefore, n < 1 guides are

fiber-like in that the core index (n  1) is greater than the clad index. Hollow

sapphire fibers operating at 10.6 mm(n ¼ 0:67) are an example of this class of

hollow guide [47].

13.6.1 Hollow Metal and Plastic Waveguides

The earliest circular cross-section hollow guides were formed using metallic

and plastic tubing as the structural members. ...