A double loop of optical fiber as a spectral-balanced reflector of broadband radiation

New scheme of whole-fiber interferometer based on directed branched-guides that is a double loop with balanced interferometer shoulders is proposed. It is shown that transmission of radiation in such optical device due to repeated passage through directed branches becomes independent on their division coefficient. In particular, at passage through a double loop the broadband radiation is divided on two practically equal spectral-closed parts. Spectral characteristics of laser radiation at passage through a double loop are experimentally studied. (authors)