Fiber polarisation scrambler
AssigneeNufern
InventorMitchell Underwood, III
Life of this patent
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Abstract
An optical apparatus for depolarizing a laser beam within a fiber MOPA laser is disclosed. The apparatus includes a first phase modulator for spectral broadening, a linear polarizer, an optical coupler, a second phase modulator for depolarizing the laser beam, and a polarization-maintaining optical fiber. The optical coupler divides a linearly-polarized portion of the laser beam equally between fast and slow axes of the second phase modulator. The laser beam delivered by the polarization-maintaining optical fiber is truly unpolarized. The apparatus provides independent control of the spectral broadening and the depolarization to mitigate stimulated Brillouin scattering during subsequent amplification. A method for depolarizing a laser beam, using this apparatus, is also disclosed.
Claims20
An optical apparatus for depolarizing a laser beam, comprising:
- a linear polarizer receiving the laser beam and transmitting a portion thereof that is linearly polarized;
- a polarization-scrambling phase modulator having fast and slow axes, the polarization-scrambling phase modulator driven by a random rapidly-modulated electrical signal from a source thereof;
- an optical coupler receiving the linearly-polarized laser beam, dividing the linearly-polarized laser beam into two polarization components having equal power, and separately delivering the two polarization components to the fast and slow axes of the polarization-scrambling phase modulator;
- and
- a birefringent element having fast and slow axes, the polarization component in the slow axis of the polarization-scrambling phase modulator coupled into the fast axis of the birefringent element and the polarization component in the fast axis of the polarization-scrambling phase modulator coupled into the slow axis of the birefringent element;
- wherein, the polarization-scrambling phase modulator produces a random differential phase modulation and a time delay between the two polarization components therein;
- wherein the birefringent element has a length selected to compensate for the time delay.
A MOPA laser, comprising:
- a seed laser providing a laser beam;
- a linear polarizer receiving the laser beam and transmitting a portion thereof that is linearly polarized;
- a polarization-scrambling phase modulator having fast and slow axes;
- an optical coupler receiving the linearly-polarized laser beam, dividing the linearly-polarized laser beam into two polarization components having equal power, and separately delivering the two polarization components to the fast and slow axes of polarization-scrambling phase modulator;
- a birefringent element having fast and slow axes, the polarization component in the slow axis of the polarization-scrambling phase modulator coupled into the fast axis of the birefringent element and the polarization component in the fast axis of the polarization-scrambling phase modulator coupled into the slow axis of the birefringent element;
- and
- an amplifier that does not have birefringence, the two polarization components delivered from the birefringent element to the amplifier, the amplifier generating an amplified laser beam;
- wherein, the polarization-scrambling phase modulator produces a differential phase modulation and a time delay between the two polarization components therein;
- wherein the birefringent element has a length selected to compensate for the time delay.
A method for depolarizing a laser beam, comprising the steps of:
- transmitting a portion of the laser beam that is linearly polarized through a linear polarizer;
- dividing the linearly-polarized laser beam into two polarization components having equal power;
- delivering the polarization components into different axes of a polarization-scrambling phase modulator having fast and slow axes;
- driving the polarization-scrambling phase modulator with a random rapidly-modulated electrical signal that preferentially modulates one of the polarization components, thereby producing a random differential phase modulation between the polarization components;
- coupling the polarization component in the slow axis of the polarization-scrambling phase modulator into a fast axis of a birefringent element;
- and
- coupling the polarization component in the fast axis of the polarization-scrambling phase modulator into a slow axis of the birefringent element;
- wherein, the polarization-scrambling phase modulator produces a time delay between the two polarization components therein and the birefringent element has a length selected to compensate for the time delay.
Dependencies are inferred from the claim text.