Displacement detection apparatus

A displacement detection apparatus comprising:

• a low-coherence light source that emits light and has a coherence length;
• a lens that condenses the light from the light source;
• a polarization maintaining fiber that transmits the light condensed by the lens, the polarization maintaining fiber having a length longer than a length obtained by dividing, by a wavelength of the light source, a product of the coherence length of the light source and a beat length obtained from a difference between propagation constants of two polarization modes;
• and
• a displacement detector that divides a beam transmitted by the polarization maintaining fiber into two beams and converts the respective beams to an interference signal by causing the respective beams to interfere with each other, in order to set a variation of a phase applied to each of the divided beams to an amount of displacement.

A displacement detection apparatus, comprising:

• a low-coherence laser light source that emits light;
• a lens that condenses the light from the laser light source;
• a polarization maintaining fiber that transmits the light condensed by the lens, the polarization maintaining fiber having a length avoiding an interference between a beam via an X polarization mode axis and a beam via a Y polarization mode axis;
• and
• a displacement detector that divides a beam transmitted by the polarization maintaining fiber into two beams and converts the respective beams to an interference signal by causing the respective beams to interfere with each other, in order to set a variation of a phase applied to each of the divided beams to an amount of displacement.