US 5,636,053 AGranted

Fiberoptic amplifier system with noise figure reduction

AssigneeE-Tek Dynamics, Inc.

InventorJing-Jong Pan

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Abstract

A fiberoptic amplifier system having an optical amplifier, which receives an input signal and generates an amplified signal and amplified spontaneous emission noise, and a variable polarization beam splitter, which receives the amplified signal and amplified spontaneous emission noise from the optical amplifier. The amplified spontaneous emission (ASE) noise is a broadband optical noise with a random polarization state in a rare earth-doped fiber optical amplifier. In a semiconductor laser diode optical amplifier, the ASE noise is partially polarized depending upon the waveguide structure of the laser diode. In the rare earth-doped fiber optical amplifier noise figure reduction configuration, the variable polarization beam splitter is responsive to the polarization of the amplified input signal to split one-half of the amplified spontaneous emission noise away from the amplified input signal and remaining one-half of the amplified spontaneous emission noise into a first port and the amplified input signal and the remaining one-half of the amplified spontaneous emission noise passes to an output port. This significantly reduces the noise figure of the fiberoptic amplifier system.

Claims22

Dependent claims

A fiberoptic amplifier system comprising

an optical amplifier receiving an input signal and generating an amplified input signal and an amplified spontaneous emission noise;
a variable polarization beam splitter receiving said amplified signal and amplified spontaneous emission noise from said optical amplifier, said variable polarization beam splitter responsive to polarization of said amplified input signal to split one-half of said amplified spontaneous emission noise away from said amplified input signal and one-half of said amplified spontaneous signal into a first port, said amplified input signal and one-half of said amplified spontaneous emission noise passing to an output port, said variable polarization beam splitter having
a first collimator subassembly holding an end of a first optical fiber in coaxial relationship with a first collimator, said first optical fiber carrying said amplified input signal and said amplified spontaneous emission noise from said optical amplifier;
a second collimator subassembly holding an end of a second optical fiber in coaxial relationship with a second collimator, said second optical fiber connected to said output port;
a third collimator subassembly holding an end of a third optical fiber in coaxial relationship with a third collimator, said third optical fiber connected to said first port;
means for directing light from said first collimator subassembly toward said second collimator subassembly or third collimator subassembly responsive to the polarization of said light signals from said first collimator subassembly;
and
first and second liquid crystal cells are interposed between said first collimator subassembly and said directing means, each of said liquid crystal cells having an optical axis at 45.degree. with respect to the other, said cells controllably rotating the polarization of light from said first collimator subassembly toward said directing means responsive to control signals;
a means for monitoring light intensity at one of said ports;
a control unit responsive to said monitoring means for controlling said variable polarization beam splitter such that light intensity at said output port is maximized;
whereby a noise figure of said fiberoptic amplifier system is reduced.

8 more elements

A fiberoptic amplifier system comprising

an optical amplifier receiving an input signal and generating an amplified input signal and an amplified spontaneous emission noise;
a variable polarization beam splitter receiving said amplified signal and amplified spontaneous emission noise from said optical amplifier, said variable polarization beam splitter responsive to polarization of said amplified input signal to split one-half of said amplified spontaneous emission noise away from said amplified input signal and one-half of said amplified spontaneous signal into a first port, said amplified input signal and one-half of said amplified spontaneous emission noise passing to an output port, said variable polarization beam splitter having
a first collimator subassembly holding an end of a first optical fiber in coaxial relationship with a first collimator, said first optical fiber carrying said amplified input signal and said amplified spontaneous emission noise from said optical amplifier;
a second collimator subassembly holding an end of a second optical fiber in coaxial relationship with a second collimator, said second optical fiber connected to said output port;
means for directing light from said first collimator subassembly toward said second collimator subassembly responsive to the polarization of said light signals from said first collimator subassembly;
and
first and second liquid crystal cells are interposed between said first collimator subassembly and said directing means, each of said liquid crystal cells having an optical axis at 45.degree. with respect to the other, said cells controllably rotating the polarization of light from said first collimator subassembly toward said directing means responsive to control signals;
a means for monitoring light intensity at said output port;
a control unit responsive to said monitoring means for controlling said variable polarization beam splitter such that light intensity at said output port is maximized;
whereby a noise figure of said fiberoptic amplifier system is reduced.

7 more elements

A fiberoptic amplifier system comprising

an optical amplifier receiving an input signal and generating an amplified input signal and an amplified spontaneous emission noise;
a variable polarization beam splitter receiving said amplified signal and amplified spontaneous emission noise from said optical amplifier, said variable polarization beam splitter responsive to polarization of said amplified input signal to split one-half of said amplified spontaneous emission noise away from said amplified input signal and one-half of said amplified spontaneous signal into a first port, said amplified input signal and one-half of said amplified spontaneous emission noise passing to an output port, said variable polarization beam splitter having
a first collimator subassembly holding an end of a first optical fiber in coaxial relationship with a first collimator, said first optical fiber carrying said amplified input signal and said amplified spontaneous emission noise from said optical amplifier;
a second collimator subassembly holding an end of a second optical fiber in coaxial relationship with a second collimator, said second optical fiber connected to said output port;
a third collimator subassembly holding an end of a third optical fiber in coaxial relationship with a third collimator, said third optical fiber connected to said first port;
a light director located between said first, second and third collimator subassemblies, said light director directing light from said first collimator subassembly toward said second collimator subassembly or third collimator subassembly responsive to the polarization of said light signals from said first collimator subassembly;
and
first and second liquid crystal cells are interposed between said first collimator subassembly and said light director, each of said liquid crystal cells having an optical axis at 45.degree. with respect to the other, said cells controllably rotating the polarization of light from said first collimator subassembly toward said light director means responsive to control signals;
a light intensity monitor at one of said ports;
a control unit responsive to said light intensity monitor for controlling said variable polarization beam splitter such that light intensity at said output port is maximized;
whereby a noise figure of said fiberoptic amplifier system is reduced.

8 more elements

A fiberoptic amplifier system comprising

an optical amplifier receiving an input signal and generating an amplified input signal and an amplified spontaneous emission noise;
a variable polarization beam splitter receiving said amplified signal and amplified spontaneous emission noise from said optical amplifier, said variable polarization beam splitter responsive to polarization of said amplified input signal to split one-half of said amplified spontaneous emission noise away from said amplified input signal and one-half of said amplified spontaneous signal into a first port, said amplified input signal and one-half of said amplified spontaneous emission noise passing to an output port, said variable polarization beam splitter having
a first collimator subassembly holding an end of a first optical fiber in coaxial relationship with a first collimator, said first optical fiber carrying said amplified input signal and said amplified spontaneous emission noise from said optical amplifier;
a second collimator subassembly holding an end of a second optical fiber in coaxial relationship with a second collimator, said second optical fiber connected to said output port;
a light director located between said first, and second collimator subassemblies, said light director directing light from said first collimator subassembly toward said second collimator subassembly responsive to the polarization of said light signals from said first collimator subassembly;
and
first and second liquid crystal cells are interposed between said first collimator subassembly and said light director, each of said liquid crystal cells having an optical axis at 45.degree. with respect to the other, said cells controllably rotating the polarization of light from said first collimator subassembly toward said light director responsive to control signals;
a light intensity monitor at one of said ports;
a control unit responsive to said light intensity monitor for controlling said variable polarization beam splitter such that light intensity at said output port is maximized;
whereby a noise figure of said fiberoptic amplifier system is reduced.

7 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/490,938Filed 15 Jun 1995
Granted: 3 Jun 1997
Term ends: Not estimatedThe source records don’t support an estimate.

Classification12 codes

H04B 10/291
Repeaters: in which processing or amplification is carried out without conversion of the main signal from optical form
G02F 1/13471
Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two…
H01S 3/10023
In optical amplifiers: by functional association of additional optical elements, e.g. filters, gratings, reflectors
H04B 10/2507
Arrangements specific to fibre transmission: for the reduction or elimination of distortion or dispersion