Polarization-maintaining fiber system and method of manufacturing the same

In an optical fiber system comprising first and second polarization-maintaining fibers (41. 42), a first orthogonal coordinate of the first polarization-maintaining fiber is azimuthally rotated relative to a second orthogonal coordinate of the second polarization-maintaining fiber by the use of an optical coupler (40) by a preselected angle between 0° and 90°, both exclusive. Preferably, the optical coupler is shorter than a beat length of each fiber and the preselected angle is equal to 45°. The optical fiber system is applicable to an optical sensor for sensing a variable physical parameter. In the sensor, a light beam is incident onto one end of the first polarization-maintaining fiber so that a plane of polarization of the light beam is matched to one of those planes of the first polarization-maintaining fiber which are determined by the first orthogonal coordinate. A third polarization-maintaining fiber is coupled through an additional optical coupler to the second polarization-maintaining fiber. The optical fiber system can be manufactured either by twisting and locally fusing a single polarization-maintaining fiber or by splicing two polarization-maintaining fibers.