A novel geometry of double phase conjugate mirror in photorefractive s
ingle crystal Bi12TiO20 fiber is proposed, when pump beams are repeate
dly internally reflected from the fiber faces. The phase conjugate wav
e reflectivities up to 18% and with response time of a few seconds wer
e obtained at lambda = 632.8 nm, supplying the fiber with an alternati
ng electric field of square wave form. Two possible effective configur
ations of mutually incoherent beam coupling inside the photorefractive
fiber were compared experimentally.