Optical signal amplifier
AssigneeFurukawa Electric Co., Ltd.
InventorsShunichi Matsushita, Shu Namiki, Yoshihiro Emori
Life of this patent
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Abstract
Abstract of Disclosure An optical signal amplifier comprises a light source, a depolarizer, and a gain medium that transfers energy from a pump beam output from the depolarizer to the optical signal. The depolarizer may comprise one or more birefringent optical fibers which support two polarization modes, a fast mode and a slow mode. The light propagates in the fast mode at a higher velocity than the light propagates in the slow mode so as to impart phase delay as the light propagates in the birefringent optical fibers, thereby at least partially depolarizing the beam.
Claims60
An optical signal amplifier comprising:
- at least one source of light;
- at least one depolarizer comprising one or more birefringent optical components coupled to receive said light as an input and having as an output a pump beam;
- and
- a Raman gain medium configured to receive said pump beam and optical signals as inputs and to transfer energy from said pump beam to said optical signals via stimulated Raman scattering.
The amplifier of Claim 1, wherein said birefringent optical components comprise birefringent optical fibers.
The amplifier of Claim 1, wherein said depolarizer comprises a birefringent optical fiber having fast and slow axes in a pre-selected non-parallel orientation with respect to a direction of polarization of said light from said at least one source of light.
The amplifier of Claim 2, wherein said source of light comprises a birefringent optical fiber having a fast axis oriented substantially parallel to a direction of polarization of said light from said at least one source of light.
The amplifier of Claim 2, wherein said depolarizer comprises at least two birefringent optical fibers, wherein a first one of said birefringent optical fibers has fast and slow axes in a first pre-selected orientation with respect to a direction of polarization of said light from said at least one source of light, and wherein a second one of said birefringent optical fibers has fast and slow axes in a second pre-selected orientation with respect to a direction of polarization of said light from said at least one source of light.
The amplifier of Claim 1, wherein said depolarizer comprises a LYOT type depolarizer.
The amplifier of Claim 1, wherein said birefringent optical components comprise birefringent optical crystals.
The amplifier of Claim 7, wherein said depolarizer comprises a Cornu depolarizer.
The amplifier of Claim 1, further comprising at least one fiber Bragg grating situated to receive light from at least one of said light sources to provide a narrow wavelength distribution for said light.
The amplifier of Claim 1, wherein said at least one source of light comprises a single semiconductor laser.
The amplifier of Claim 1, wherein said at least one source of light comprises a plurality of semiconductor lasers.
The amplifier of Claim 11, wherein each of said plurality of semiconductor lasers has a different center frequency.
The amplifier of Claim 11, further comprising a beam combiner configured to receive light from at least two of said semiconductor lasers and to direct said light to said depolarizer.
The amplifier of Claim 11, further comprising a beam combiner configured to receive said pump beam from at least two of said depolarizers, each of which are positioned to receive light from one of said semiconductor lasers.
An amplifier for amplifying an optical signal comprising:
- a light source having as an output a first beam of light characterized by a first degree of polarization;
- a depolarizer optically connected to said light source so as to receive said first light beam as an input, and having as an output a pump beam characterized by a second degree of polarization wherein said second degree of polarization is less than said first degree of polarization;
- and
- a Raman gain medium optically connected to said depolarizer so as to receive said optical signal and said pump beam as inputs and configured to transfer energy from said pump beam to said optical signal through Raman scattering.
The amplifier of Claim 16, wherein said depolarizer comprises one or more birefringent optical fibers.
The amplifier of Claim 17, wherein at least one of said one or more birefringent optical fibers has fast and slow axes in a pre-selected orientation with respect to a direction of polarization of said first beam of light.
The amplifier of Claim 18, wherein said light source comprises a semiconductor laser and said Raman gain medium comprises an optical fiber.
The amplifier of Claim 19, wherein said light source comprises a Bragg grating optically connected to said semiconductor laser so as to receive said light from said laser and to provide a narrow wavelength distribution for said light.
The amplifier of Claim 20 wherein said light source further comprises a polarization controller coupled between said semiconductor laser and said depolarizer, said polarization controller altering a polarization state of said light.
An optical signal amplifier comprising:
- at least one light source having an output beam comprising a linearly polarized component thereof;
- a birefringent optical fiber situated to receive said output beam, said birefringent optical fiber having a fast axis and a slow axis wherein linearly polarized light having an electric field oriented parallel to said fast axis propagates through said birefringent optical fiber faster than linearly polarized light having an electric field oriented parallel to said slow axis, said fast axis being perpendicular to said slow axis, wherein said birefringent optical fiber is oriented such that the electric field of said linearly polarized component of said output beam is nonparallel to both said fast and said slow axis;
- and
- a Raman gain medium situated to receive an output of said birefringent optical fiber and one or more optical signals, and configured to transfer energy from said output to said optical signals so as to amplify said optical signals.
The amplifier of Claim 23, wherein said birefringent optical fiber is oriented such that the electric field of said output beam is at an angle that is approximately 45º from said fast axis.
An optical signal amplifier comprising:
- a light source having an output light beam;
- a beamsplitter situated to receive and separate said output light beam into first and second beams,
- a first birefringent optical fiber that receives said first beam from said beamsplitter,
- a second birefringent optical fiber that receives said second beam from said beamsplitter;
- a beamcombiner situated to receive said first and second beams from said first and second birefringent optical fibers, said beamcombiner combining said beams into a pump beam;
- a Raman gain medium situated to receive said pump beam and one or more optical signals and configured to transfer energy from said pump beam to said optical signals so as to amplify said optical signals.
The amplifier of Claim 26, wherein said first and second birefringent optical fibers have lengths sufficient to impart phase delay between light in a fast polarization mode and light in a slow polarization mode in said first and second birefringent optical fibers to thereby cause said single pump beam output by said beamcombiner to at least partially comprise depolarized light.
The amplifier of Claim 27, wherein said length of said first birefringent optical fiber and said length of said second birefringent optical fiber are approximately equal.
The amplifier of Claim 27, wherein said length of said first birefringent optical fiber and said length of said second birefringent optical fiber are different.
The amplifier of Claim 26, wherein said Raman gain medium comprises an optical fiber gain medium that produces gain through stimulated Raman scattering.
The amplifier of Claim 26, wherein said beamsplitter couples substantially all of said first beam into said slow polarization mode of said first birefringent optical fiber and couples substantially all of said second beam into said slow mode of said second birefringent optical fiber.
The amplifier of Claim 31, wherein said length of said first birefringent optical fiber and said length of said second birefringent optical fiber are different.
The amplifier of Claim 26, wherein said beamsplitter couples substantially all of said first beam into said fast polarization mode of said first birefringent optical fiber and couples substantially all of said second beam into said fast polarization mode of said second birefringent optical fiber.
The amplifier of Claim 33, wherein said length of said first birefringent optical fiber and said length of said second birefringent optical fiber are different.
An optical apparatus comprising:
- at least one source of light radiating at least partially polarized light characterized by a first degree of polarization;
- a Raman gain medium having a signal input for accepting an optical signal beam, a pump input for accepting a pump beam, a signal output for outputting an optical signal beam amplified by energy from said pump beam;
- an optical path between said at least one source and said pump input of said Raman gain medium;
- and
- at least one depolarizer in said optical path that converts said at least partially polarized light into an at least partially depolarized pump beam characterized by a second degree of polarization that is less than said first.
The optical apparatus of Claim 35, wherein said Raman gain medium comprises an optical fiber Raman gain medium.
The optical apparatus of Claim 35, further comprising:
- a transmitter comprising an optical source that emits said optical signal;
- and
- an optical path between said transmitter and said signal input of said Raman gain medium.
An optical communications system comprising:
- a transmitter comprising an optical source that emits an optical signal;
- a receiver comprising an optical detector capable of sensing said optical signal;
- an optical path between said transmitter and said receiver that said optical signal follows;
- an optical amplifier inserted in said optical path between said transmitter and said receiver, said amplifier comprising:
- an optical pump comprising a light source producing at least partially polarized light;
- a Raman gain medium inserted in said optical path between said transmitter and said receiver, said Raman gain medium having a signal input for accepting said optical signal from said transmitter, a pump input for accepting a pump beam, and a signal output for outputting said optical signal beam amplified by energy from said pump beam to said receiver;
- an optical path between said optical pump and said pump input of said Raman gain medium;
- a depolarizer comprising at least one birefringent optical component inserted in said optical path between said optical pump and said pump input, said depolarizer outputting at least partially depolarized light.
The optical communications system of Claim 41, wherein said birefringent optical component comprises at least one birefringent optical fiber.
A method of pumping an optical signal amplifier comprising:
- collecting light from a light source that emits at least partially polarized light, said light divisible into light of two orthogonal linearly polarized states;
- at least partially depolarizing said light by imparting phase delay between said light of said two orthogonal linearly polarized states;
- and
- directing said at least partially depolarized light into a Raman gain medium of an optical signal amplifier.
The method of Claim 43, further comprising altering the polarization of said light collected from said laser such that said light is equally divided into said two orthogonal linearly polarized states.
The method of Claim 43, wherein said step of depolarizing comprises passing said light collected from said laser through a birefringent optical fiber that supports two polarization modes, a fast mode and a slow mode.
The method of Claim 45, wherein substantially all said light of one of said two orthogonal linearly polarized states is coupled into said fast mode and substantially all said light of the other of said two orthogonal linearly polarized states is coupled into said slow mode, said light propagating in said fast mode at a higher velocity than said light propagating in said slow mode so as to impart phase delay as said light propagates in said birefringent optical fiber.
The method of Claim 43, wherein said step of depolarizing comprises separating said light collected from said laser into first and second beams which are coupled into respective first and second birefringent optical fibers that supports two polarization modes, a fast mode and a slow mode, said light propagating in said fast mode at a higher velocity than said light propagating in said slow mode so as to impart phase delay as said light propagates in said birefringent optical fibers.
The method of Claim 43, wherein said step of depolarizing comprises separating said light collected from said laser into first and second beams which are coupled into respective first and second birefringent optical fibers that supports two polarization modes, a fast mode and a slow mode, such that both said first and second beams are coupled in the same mode in said fibers.
The method of Claim 43, wherein said light from said light source is combined with light from at least one other light source of at least partially polarized light prior to being at least partially depolarized.
A method of amplifying an optical signal comprising:
- routing a beam of light into one or more birefringent optical fibers configured to at least partially depolarize said beam of light;
- and
- routing an output of said one or more birefringent optical fibers to a Raman gain medium of an optical signal amplifier.
The method of Claim 51, comprising routing said beam of light to a beamsplitter, routing a first output of said beamsplitter to a first birefringent optical fiber, and routing a second output of said beamsplitter to a second birefringent optical fiber.
The method of Claim 51, comprising routing said beam of light to a single birefringent optical fiber having fast and slow axes which are non-parallel to a direction of polarization of said beam of light.
An optical signal amplifier comprising:
- at least one light source;
- means for at least partially depolarizing light emitted by said light source;
- and
- a Raman gain medium situated to receive said at least partially depolarized light.
A method of making an optical signal amplifier comprising:
- coupling a light source to an input of at least one birefringent optical element;
- and
- coupling an output of said at least one birefringent optical element to a Raman gain medium.
A method of minimizing polarization induced gain fluctuations in an optical signal amplifier comprising:
- at least partially depolarizing a beam of substantially polarized light from a first light source without combining said beam of light with a second beam of substantially polarized light from a second light source;
- and
- using said at least partially depolarized beam of light as a pump beam in a Raman gain medium in said optical signal amplifier.
A method of communicating between two locations with light comprising:
- generating an optical signal;
- coupling said optical signal into an optical fiber;
- amplifying said optical signal using Raman scattering;
- and
- sensing said optical signal,
- wherein said amplifying comprises:
- producing an at least partially polarized pump beam characterized by a degree of polarization,
- at least partially depolarizing said at least partially polarized pump beam thereby reducing said degree of polarization, and
- coupling said at least partially depolarized pump beam and said optical signal into a Raman gain medium, thereby inducing Raman scattering in said Raman gain medium and providing optical gain.
An optical signal amplifier comprising:
- at least one light source having an output beam comprising a linearly polarized component thereof;
- a birefringent optical fiber at least two meters in length situated to receive said output beam, said birefringent optical fiber having a fast axis and a slow axis wherein linearly polarized light having an electric field oriented parallel to said fast axis propagates through said birefringent optical fiber faster than linearly polarized light having an electric field oriented parallel to said slow axis, said fast axis being perpendicular to said slow axis, wherein said birefringent optical fiber is oriented such that the electric field of said linearly polarized component of said output beam is nonparallel to both said fast and said slow axis whereby the degree of polarization of light exiting said birefringent optical fiber is less than 40%;
- and
- a Raman gain medium situated to receive an output of said birefringent optical fiber and one or more optical signals, and configured to transfer energy from said output to said optical signals via stimulated Raman scattering so as to amplify said optical signals.
The optical signal amplifier of Claim 58, wherein said birefringent optical fiber is oriented such that the electric field of said linearly polarized component of said output beam is nonparallel to both said fast and said slow axis whereby the degree of polarization of light exiting said birefringent optical fiber is less than 20%.
The optical signal amplifier of Claim 59, wherein said birefringent optical fiber is oriented such that the electric field of said linearly polarized component of said output beam is nonparallel to both said fast and said slow axis whereby the degree of polarization of light exiting said birefringent optical fiber is less than 10%.
Dependencies are inferred from the claim text.