Patent ID: 9250118
Filing Date: 2016-02-02
CPC Classification: G01H

Claim Text:
1. A seismometer based optical sensing, comprising: a seismometer frame; a mass of a seismometer suspended to the seismometer frame and responsive to vibrations to move relative to the seismometer frame; a first optical retroreflector attached to and fixed in position relative to the mass; a second optical retroreflector attached to and fixed in position relative to the seismometer frame; optical components including at least one beam splitter and at least one birefringent plate attached to the seismometer frame and configured with the first and second optical retroreflectors to form an optical interferometer; a first optical detector that detects a first optical output of the optical interferometer; a second optical detector that detects a second optical output of the optical interferometer; a first optical path between the optical interferometer and the first optical detector; a second optical path between the optical interferometer and the second optical detector; and a processing unit that processes the detector outputs from the first and second optical detectors to extract seismic information indicated by the motion of the mass of the seismometer, wherein the at least one beam splitter, the first and second optical retroreflectors, and the at least one birefringent plate are operable to alter a light beam to form fringe signals including sine and cosine values of the phase of optical output of the optical interferometer, wherein the seismometer frame includes a base, a first extension arm attached to the base and extending in a direction away from the base, a second extension arm attached to the base at a separate position with respect to the first extension arm and extending away from the base, and a support arm moveably coupled to the first extension arm at a joint, wherein the second optical retroreflector and the optical components are attached to the second extension arm, wherein the mass is attached to the support arm such that it moves with the support arm, and the mass is suspended by a leaf spring, wherein the leaf spring is fixed at one end to the first extension arm of the seismometer frame and engaged at the other end to the support arm so that the mass is suspended by the leaf spring above the base of the seismometer frame, and wherein the first optical retroreflector is attached to the first extension arm and optically aligned with at least some of the optical components on the second extension arm.