USA As Represented by Secretary of the Navy

Michael J Marrone

Alan D Kersey

Anthony Dandridge

Ronald D Esman

Charles G Askins

A method and apparatus for overcoming polarization induced signal fading in both heterodyne communication and interferometric sensing. An adjustable birefringent element in series with a linear-polarization beam splitter forms an elliptical-polarization beam splitter. The birefringent element controllably evolves the states of polarization of two input signals thereby controlling the power contribution of each signal onto the orthogonal axes used by the linear beam splitter. When the states of polarization are evolved such that there are equal signal to reference power ratios on the beam splitter axes, subsequent detectors generate a constant, optimum amplitude signal without the need for weighting or decision circuits.

Adaptive polarization diversity detection scheme for coherent

A sensor system includes a sensor head, an optical source, and a measurement apparatus. The sensor head includes a beamsplitter having first, second, third, and fourth ports, the beamsplitter being responsive to light selectively applied to the first, second and third ports for passing light of a first input polarization state from the first port to the second port, for passing light of a second input polarization state orthogonal to the first input polarization state from the first port to the third port, and for collectively passing light of a first output polarization state and light of a second output polarization state orthogonal to the first output polarization state from the third port to the fourth port. The optical source means provides light to the first port. The sensor head further includes a bidirectional polarimetric sensor responsive to polarized light output by the beamsplitter at the second and third ports and to an electromagnetic field applied to the polarimetric sensor for producing first polarized light at said third port and for producing second polarized light at said second port. The first and second polarized light have polarization states each of which varies as a function of the electromagnetic field and the polarization state of the light output by the beamsplitter at the other one of the second and third ports. The measurement means is responsive to light from the fourth port for producing an output signal indicative of the electromagnetic field strength.

Polarization insensitive current and magnetic field optic sensor

A sensor system includes a sensor head, an optical source, and a measurement apparatus. The sensor head includes a beamsplitter having first, second, third, and fourth ports, the beamsplitter being responsive to light selectively applied to the first, second and third ports for passing light of a first polarization state from the first port to the second port, for passing light of a second polarization state from the first port to the third port, for passing light of the second polarization state from the second port to the fourth port, and for passing light of the first polarization state from the third port to the fourth port. The optical source means provides light to the first port. The sensor head further includes a bidirectional polarimetric sensor responsive to polarized light output by the beamsplitter at the second and third ports and to an electromagnetic field applied to the polarimetric sensor for producing first polarized light at said third port and for producing second polarized light at said second port. The first and second polarized light have polarization states each of which varies as a function of the electromagnetic field and the polarization state of the light output by the beamsplitter at the other one of the second and third ports. The measurement means is responsive to light from the fourth port for producing an output signal indicative of the electromagnetic field strength.

A technique and apparatus for detecting the internal rotation of the principal axes in the fabrication of birefringent fibers is based upon a new method for producing and interpreting the interference fringe pattern backscattered power from a birefringent fiber side-illuminated with a laser light source to determine the internal orientation of the strain-inducing axes. An apparatus employing this technique for controlling internal rotation of the principal axes provides for adjustment of the orientation of at least one of the traction surfaces pulling the fiber during drawing fabrication to maintain parallel alignment of the planes of rotation of the surfaces to reduce the fiber rotation-inducing motion which leads to internal rotation of the fiber's principal axes.

Method and apparatus for controlling internal rotation of principal axes

A system and method for minimizing polarization-induced phase noise in an interferometric fiber sensor is disclosed. The system includes an optical source of light; a single mode input fiber; means coupled between the optical source and the input fiber for scrambling the polarization state of the light from the optical source at a first frequency to effectively produce and pass depolarized light to the input fiber; an interferometric fiber sensor responsive to light from the input fiber for producing at its output an interference pattern proportional to a phase shift produced by a field being sensed by the interferometric fiber sensor; detection means responsive to the interference pattern for developing a photocurrent signal averaged over a period of time longer than the period of the first frequency; and demodulation means responsive to the photocurrent signal for producing an electrical output signal substantially proportional to the phase shift produced by the field being sensed by the interferometric sensor.

System and method for minimizing input polarization-induced phase noise

An apparatus for minimizing polarization-induced signal fading in an interferometric fiber-optic sensor is disclosed. The apparatus includes an optical source for providing an input light beam, a polarization modulator for modulating the state of polarization of the input light beam into at least three states represented by mutually perpendicular polarization vectors on a Poincare Sphere. The apparatus further includes means for conveying the input light beam with the at least three mutually perpendicular modulated states of polarization to the fiber-optic sensor, the interferometric fiber-optic sensor being responsive to the input light beam with modulated polarization states for developing an interference pattern output, wherein the interference pattern output has at least three visibilities corresponding to the input states of polarization. A photodetector is responsive to the interference pattern output for developing an electrical signal having at least three amplitudes corresponding to the at least three states of polarization. An output circuit is responsive to the electrical photodetector signal for time-sampling the photodetector signal having three amplitudes corresponding to the at least three mutually perpendicular input states of polarization and selecting the one having maximum visibility. A method for minimizing polarization-induced signal fading is also disclosed.

Apparatus and method for minimizing polarization-induced signal fading

An optical fiber dosimeter for monitoring by luminescence the presence of ionizing radiation and measuring a cumulative dose from around reactors, accelerators and waste storage areas. A length of silica core optical fiber in the presence of ionizing radiation has been found to luminesce in two distinct emission bands, one with a peak around 450 nm (blue) and the other with a peak around 650 nm (red). The intensity of the red luminescence is proportional to the intensity of ionizing radiation on the fiber whereas the intensity of blue luminescence is proportional to both the intensity of ionizing radiation on the fiber and the accumulated ionizing radiation history or dosage on the fiber. A device constructed according to the invention may be employed to surround an area of a human body tissue or organ undergoing radiation treatment as an aid in directing the radiation.

Growing community of inventors

Severna Park, MD, United States of America

Michael J Marrone