Precision length standard for coherent laser radar
This disclosure presents a version of a coherent laser radar system that is immune to environmental effects on Mach-Zehnder-configured interferometers and reference length standards comprising such systems. The present disclosure also describes methods and materials which alleviate interferometer drift due to vapor absorption using a polyimide coated polarization maintaining fiber to reduce the change in the length of a reference arm.
1. A measurement system comprising:
two optical fibers, each optical fiber from said two optical fibers being coated with a substantially hydrophobic and substantially non-outgassing substance; one optical fiber from said two optical fibers having a length different from another optical fiber from said two optical fibers;
a first fiber optic coupler for
receiving electromagnetic (EM) radiation; and
splitting the EM radiation into a measurement path and a reference path;
said reference path including
a second fiber optic coupler for
receiving said EM radiation from the reference path; and
splitting said EM radiation into each of said two optical fibers;
a third fiber optic coupler for
receiving EM radiation from said two optical fibers; and
providing said received EM radiation to a single fiber; and
a detector for
calibrating, from said single fiber, a difference in length between said two optical fibers; and
calculating a distance along said measurement path as a function of said difference in length, wherein said reference path is in a Mach-Zehnder configuration, and said substantially hydrophobic and substantially con-outgassing substance is selected from polyimide, ultraviolet cured acrylate, teflon, tefzel, hytrel, or nylon.
2. A method for rendering the measurement of distance along an electromagnetic (EM) radiation measurement path insensitive to temperature variations and environmental fluctuations comprising the steps of:
coating two optical fibers, said two optical fibers disposed between a first fiber optic coupler and a second fiber optic coupler, with a substantially hydrophobic and substantially non-outgassing substance;
receiving EM radiation into a third fiber optic coupler;
splitting the received EM radiation into a measurement EM radiation and a reference EM radiation;
receiving the reference EM radiation into the first fiber optic coupler;
splitting, by the second fiber optic coupler, the received reference EM radiation into the two optical fibers;
receiving the two optical fibers into the second fiber optic coupler;
combining, by the second fiber coupler, combined EM radiation received from the two optical fibers and providing the combined EM radiation to a single fiber;
calibrating, from the combined EM radiation, a difference in length of between the two optical fibers; and
calculating a distance of the measurement EM radiation as a function of the difference in Length, wherein said reference path is in a Mach-Zehnder configuration, and said substantially hydrophobic and substantially con-outgassing substance is selected from polyimide, ultraviolet cured acrylate, teflon, tefzel, hytrel, or nylon.