Optical fiber distributed feedback laser
AssigneeOptoplan AS
InventorJon Thomas Kringlebotn
Life of this patent
Estimating the term…
Abstract
An optical end-pumped fiber laser doped with one or more rare-earths and with distributed feedback (DFB) via a fiber Bragg-grating, which is oscillating on two orthogonally polarized wavelengths. The distance between the wavelengths may be tuned by changing the birefringence of the fiber. The laser may be applied as a polarimetric sensor in which an asymmetrical force changes the wavelength separation, or as a tunable two-wavelength source. A particular preferred field of application is for measuring the pressure in pipes, to determine the flow.
Claims23
A method for application of a fiber-optic distributed feedback (DFB) fiber laser with distributed feedback via one single fiber Bragg-grating along the whole laser length with at least one phase-shift in the core of an optical fiber doped with at least one rare-earths, which operates robustly without mode hopping, at two orthogonally polarized fundamental laser modes which have different wavelengths .lambda..sub.Bx and .lambda..sub.By, as a fiber-optic sensor, for the measurement of an externally applied parameter;
- said method comprising the steps of:
- propagating light through the DFB laser to cause interaction with the Bragg-grating;
- exposing the Bragg-grating to an external parameter causing alternation of the wavelength .lambda..sub.Bx and .lambda..sub.By, and
- determining the difference between the altered wavelengths, said difference being a measure of the external parameter.
A method for application of a fiber-optic distributed feedback via one single fiber Bragg-grating along the whole laser length with at least one phase-shift in the core of an optical fiber doped with at least one rare-earths, which operates as a fiber-optic sensor for the measurement of an externally applied parameter;
- said method comprising the steps of:
- propagating light through the DFB laser to cause normal operation without mode hopping at first and second polarized laser modes with first and second wavelength .lambda..sub.Bx and .lambda..sub.By ;
- applying differential gain to suppress the second of the laser modes and thus the second wavelengths;
- exposing the Bragg-grating to an external parameter causing a change in the first wavelength, and determining the difference between the first wavelength and the first changed wavelength, said difference being a measure of the externally applied parameter.
A system for measuring at least one externally applied parameter, said system comprising:
- a distributed feedback fiber-optic laser (DFB) having a first predetermined length with a fiber Bragg-grating engraved into a core of active fiber, said Bragg-grating having a second predetermined length;
- said active fiber being doped with at least one rare earth;
- said Bragg-grating including a phase-change means for achieving interference on only one wavelength in each of a pair of orthogonal polarization states;
- a source of laser light;
- a transmission fiber and means for transmitting laser light through the transmission fiber;
- said distributed Bragg-grating responding to the transmitted laser light and emitting light in a first and a second wavelength, the difference between the first and the second wavelength being proportional to the change in birefringence in the active fiber which is caused by the externally applied parameter.
In a measuring system;
- an optical, end-pumped fiber laser with distributed feedback means including a fiber-optic Bragg-grating in a fiber core;
- an amplifying optical fiber being doped with at least one rare earth element;
- said Bragg-grating being arranged on at least a portion of said amplifying optical fiber and including a phase-discontinuity;
- a light source causing lasing of the laser in a first and a second orthogonally polarized mode outputting a first and a second wavelength, and
- means for exposing said Bragg-grating to an external parameter causing birefringence of the laser operation and thus changes in said first and said second wavelength.
Dependencies are inferred from the claim text.