Optical wavelength conversion using four wave mixing in fiber

Details Optical wavelength conversion using four wave mixing in fiber Optical wavelength conversion using four wave mixing in fiber

1999-08-11

2001-12-11

Lee, John D. (Department: 2874)

Optical: systems and elements

Optical frequency converter

Dielectric optical waveguide type

C359S327000, C359S330000

Reexamination Certificate

active

06330104

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to an optical wavelength conversion and, more particularly, to a method of and apparatus for providing optical wavelength conversion using four wave mixing in fiber.
BACKGROUND OF THE INVENTION
Increasingly, communication networks are using optical fiber links to interconnect switches, routers and multiplexer nodes of the networks. On each optical fiber link, Wavelength Division Multiplexing(WDM) is being used to increase bandwidth utilization of the optical fiber link. When a network includes many nodes, the blocking probability increases due to wavelength contention which occurs when two channels require the use of the same wavelength. This wavelength contention problem is often overcome by using wavelength conversion whereby one of the channels is converted to another unused wavelength. Wavelength conversion for WDM networks is described in the article entitled “Wavelength Conversion Technologies for WDM Network Applications” by S. J. B. Yoo, Journal of Lightwave Technology, Vol. 14, No. 6, Jun. 1, 1996.
One technique uses four wave mixing effects of a semiconductor optical amplifier to accomplish wavelength conversion. However, many of the existing wavelength conversion techniques require expensive components and/or are complicated to implement. Thus, there is a continuing need for a simple, low cost wavelength conversion apparatus.
SUMMARY OF THE INVENTION
In accordance with the present invention, we disclose a wavelength conversion apparatus and method which uses four wave mixing of a first wavelength and a control wavelength in an optical fiber to convert the first wavelength to a desired wavelength. Four wave mixing is produced by operating the optical fiber at a predetermined input power density and by using a fiber length which provides substantial Raman gain. The first wavelength is converted to a higher wavelength by using the higher wavelength four wave mixing signal and converted to a lower wavelength by using the lower wavelength four wave mixing signal.
More particularly, in accordance with our invention, an optical wavelength converter apparatus comprises (1) a first input optical wavelength signal coupled to a first end of an optical fiber; (2) a second input optical wavelength signal coupled to the first end of the optical fiber; (3) the optical fiber having a length suitable to provide substantial Raman gain to optical wavelength signals produced by four wave mixing of the first input optical wavelength signal and the second input optical wavelength signal in the optical fiber, the Raman gain using at least one pump signal selected from a group including the first input optical wavelength signal, the second input optical wavelength signal, and a third input optical wavelength signal having a wavelength substantially below the four wave mixing optical wavelength signals produced in the optical fiber; (4) wherein the power levels of the first and second optical wavelengths are selected to produce a predetermined power density in the optical fiber; and (5) an optical filter connected to a second end of the optical fiber for filtering all optical wavelengths except for one of the four wave mixing optical wavelength signals.
In accordance with our invention, when the first wavelength is to be increased, the higher wavelength of the four wave mixing optical wavelength signals is used and no third input wavelength is used as a pump signal to provide Raman gain. When the first wavelength is to be decreased, the lower wavelength of the four wave mixing optical wavelength signals is outputted from the filter and the third input wavelength is used as a pump signal to provide Raman gain.
According to another aspect of our invention, the optical fiber is erbium doped at a level which enables the optical fiber to be an erbium doped fiber amplifier (EDFA), using a suitable pump wavelength (e.g., 1480 nm). One embodiment includes an adjustable polarization controller for controlling the polarization of one of the first and second input optical wavelengths being coupled to the optical fiber. Other embodiments provide different techniques for coupling the first and second input optical wavelengths to the optical fiber by splicing, tapered splicing, or by using a graded-index (GRIN) lens. Other embodiments enable the optical fiber to be a polarization maintaining optical fiber, a single mode fiber, or a multimode fiber.
Our method of converting an optical wavelength to another wavelength comprises the steps of (1) receiving a first input optical wavelength to be converted; (2) receiving a second input optical wavelength; (3) coupling the first and second input optical wavelengths to a first end of an optical fiber; (4) selecting the optical fiber to have a length suitable to provide substantial Raman gain optical wavelength signals produced by four wave mixing of the first input optical wavelength signal and the second input optical wavelength signal in the optical fiber; (5) pumping the Raman gain using at least one pump signal selected from a group including the first input optical wavelength signal, the second input optical wavelength signal, and a third input optical wavelength signal having a wavelength substantially below the four wave mixing optical wavelength signals produced in the optical fiber; (6) selecting the power level of the first and second input optical wavelengths to produce a predetermined power density in the optical fiber; and (7) filtering all optical wavelengths exiting from the second end of the optical fiber except for one of the four wave mixing optical wavelength signals.


REFERENCES:
patent: 5386314 (1995-01-01), Jopson
patent: 5532868 (1996-07-01), Gnauck et al.
patent: 5754334 (1998-05-01), Artiglia et al.
patent: 6101024 (2000-08-01), Islam et al.
“Wavelength Conversion Technologies for WDM Network Applications” by S.J. B. Yoo, Journal of Lightwave Technology, vol. 14, No. 6, Jun. 1, 1996, pp. 955-966.

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