The quasi-optical transmission line with optical contrast close to 1 is considered. Such devices can be used to study the effect of laser radiation on biological media, in microwave, terahertz, optical and X-ray wavelength ranges, as well as in acoustics. The use of composite refractive lenses, which are a set of identical spherical lenses arranged one after another on the same optical axis and with a refractive index close to one, reduces the loss of reflection in such a lens. Reducing the focal length in such refractive lenses is possible by increasing the number of refractive surfaces.
Parallel-chain optical transmission line for a low-loss ultraconfined light beam