Abstract: A laser radiation arrives at a separating plate, after which a first part of the radiation is applied to a fibre optic wound with N turns to end at a phase conjugating mirror which returns the radiation into the same fibre optic. The other part of the radiation, reflected by the plate, travels in a fibre optic defining another optical path, very close to the first, and wound in the opposite direction for N turns, terminating at the same phase conjugating mirror or at another mirror of the same type, which returns the incident wave through the same fibre optic. The state of interference, detected at the separating plate by a detector, represents any rotation of the gyrometer. The phase conjugating mirror or mirrors is or are advantageously defined by optically non-linear media energized by two plane pump waves and travelling in opposite directions but on a colinear basis.