Optical waveguides – Polarization without modulation
Patent
1998-01-29
1999-08-31
Sanghavi, Hemang
Optical waveguides
Polarization without modulation
385 28, 385 29, 372 6, 372 19, 359341, G02B 626, H01S 300
Patent
active
059464283
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally to a fiber optic system and more particularly, to a fiber optic system which can concurrently amplify and switch an input signal via a pump signal.
BACKGROUND OF THE INVENTION
Historically, fiber optic systems have separately addressed the problems of switching of an input signal and amplifying the input signal.
For example, one type of optical switch for an input signal uses a birefringent fiber switch which has an optical fiber with a birefringence that preserves polarization. When an input signal is coupled into the birefringent optical fiber, the input signal propagates in one of two, perpendicular, polarized modes in the optical fiber. To switch the input signal to propagate in the other polarized mode in the birefringent optical fiber, a gating signal of sufficient energy is coupled into the optical fiber to propagate in the same polarized mode as the input signal initially. The gating signal induces a non-linear birefringence in the optical fiber which causes the input signal to switch and propagate in the other polarized mode. However, the gating signal in the birefringent fiber switch does not amplify the input signal.
One example of a type of optical amplifier for amplifying an input signal uses an optical fiber and a phenomenon known as Raman gain. Again, the input signal propagates in the optical fiber. To amplify the input signal using Raman gain, a pump signal whose wavelength is less than the wavelength of the input signal is coupled into the optical fiber which is carrying the input signal. The pump signal amplifies the input signal, but does not switch the polarization or propagation of the input signal.
SUMMARY OF THE INVENTION
A fiber optic system in accordance with the present invention includes an optical fiber, a coupling device, and a system for generating a pump signal. The optical fiber has a birefringence which preserves polarization and has a first polarization mode which is substantially perpendicular to a second polarization mode. The coupling device couples an input signal having an input wavelength into the optical fiber so that the input signal propagates in the first polarization mode in the optical fiber. The system for generating a pump signal generates a pump signal with a pump wavelength which is within a range of 50 nm to 300 nm less than the input wavelength and which and has a first amount of pump power which is enough power to switch the input signal polarization, but not enough power to create higher order solitons. The coupling device also couples the pump signal into the optical fiber so that the pump signal propagates in the first polarization mode in the optical fiber. The pump signal alters the birefringence of the optical fiber which causes the input signal to switch polarization modes and propagate in the second polarization mode and amplifies the input signal as it propagates through the optical fiber. Accordingly, with the fiber optic system of the invention, an input signal can be amplified and switched concurrently, and thus separate stages for amplification and switching are not required.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a fiber optic system in accordance with the present invention; and
FIG. 2 is a cross-sectional view of the optical fiber taken along lines 2--2 of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of a fiber optic system 10 in accordance with the present invention is illustrated in FIG. 1. Fiber optic system includes an optical fiber 12, a coupler 14, and a pump laser 18. With fiber optic system 10, an input signal can be both amplified and switched concurrently, and thus separate stages for amplification and switching are not required.
Referring more specifically to FIG. 1, fiber optic system 10 includes optical fiber 12 which has a birefringence that preserves polarization. Since optical fiber 12 is birefringent, optical fiber 12 has a first polarization mode which is substantially perpendicular to a second polarization mode.
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Aleksandrov Igor Vladimirovitch
Nestrova Zinaida Vasylevna
Nolan Daniel Aloysius
Corning Incorporated
Greener William
Sanghavi Hemang
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