Sagnac Interferometer

Sagnac interferometer circuit

The Sagnac interferometer is a single-pass interferometer in which rays propagate along the same optical path in opposite directions. Distinguish designs using an even and odd number of mirrors . The Sagnac interferometer is characterized by high stability and ease of alignment.

In a typical Sagnac interferometer circuit, the light is separated by a translucent divider plate into two beams that propagate in a circle and are reduced by mirrors back to the divider. Due to the symmetry of the circuit, regardless of the position of the mirrors between the beams, a constant travel difference is maintained${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\Delta </span></span>}\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\varphi </span></span>}<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">=</span></span>\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">0</span></span>}}$ {\ displaystyle \ Delta \ phi = 0} . Create a nonzero phase shift${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\Delta </span></span>}\mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\varphi </span></span>}}$ {\ displaystyle \ Delta \ phi} between the rays can be the rotation of the interferometer. Based on this principle, fiber-optic gyroscopes are built .