Patent ID: 11960042
Assignee: NEC CORPORATION
Field: Measurement (Instruments)
Classification: CPC G  H | IPC G  H

Claim 0:
1. An improved laser interferometric arrangement for detecting low frequency vibrations comprising:
a pair of optical fibers;
an optical fiber sensing interrogator including a laser source, a coherent receiver, and a signal processor, the interrogator in optical communication with the optical fibers at a near end of the fibers, the interrogator having an input port and an output port, the input port optically connected to one of the fibers and the output port connected to the other one of the fibers; and
a fiber turnaround optically connecting the optical fibers at a point near a far end of the fibers;
wherein the interrogator generates optical interrogation signals and outputs them to the fiber optically connected to its output port, and receives a portion of the output signals at its input port after such received signals traverses the fiber turnaround;
wherein the received signals are coherently detected using the same laser source as a local oscillator by the coherent receiver.