Optical: systems and elements – Optical frequency converter
Reexamination Certificate
1997-12-23
2001-03-27
Negash, Kinfe-Michael (Department: 2633)
Optical: systems and elements
Optical frequency converter
C359S199200, C359S332000
Reexamination Certificate
active
06208454
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to a wavelength converter for use in wavelength division multiplexed optical communications systems. More particularly, the present invention is directed to an interferometer wavelength converter having an integrated continuous wave probe source and/or integrated optical pre-amplifier(s).
II. Description of the Related Art
Wavelength division multiplex (WDM) networks benefit from the flexibility of wavelength converters due to the reduction in network blocking probability that such converters provide and because wavelength conversion at selected nodes in the network enables decentralized wavelength allocation management. One of the most-practical all-optical wavelength conversion schemes is cross-phase modulation in an interferometric configuration containing semiconductor optical amplifiers (SOA). Essentially, such a configuration consists of a three-port interferometer device, such as a Michelson or Mach-Zehnder interferometer, wherein an input optical signal is provided to a first port, a continuous wave beam from a light source such as a laser is provided to a second port, and an output signal is generated from a third port. The wavelength of the input optical signal is converted to the wavelength of the light source and is delivered, as so converted, from the third port of the device. The benefits of such a wavelength conversion scheme include conversion efficiency, extinction ratio enhancement and low chirp characteristics. However, it suffers from coupling losses resulting from coupling the continuous wave input to the interferometer, and from polarization variations of the continuous wave input. Furthermore, its input signal dynamic range, i.e., the range of input signal powers that is acceptable, is fairly small, typically 3 or 4 dB.
A goal of the present invention is to ameliorate the disadvantages, while retaining the benefits of an interferometric design. This is accomplished by monolithic integration, i.e. fabrication on the same chip of an interferometer, a continuous wave laser, and a pre-amplifier for the input signal. By the very nature of monolithic integration, such a fabrication removes the need for a fiber connection between the continuous wave laser and the interferometer, and therefore diminishes coupling losses between these components. The preamplifier not only provides gain, but also allows controlled gain for adjusting the input signal power available to the power required by the interferometer.
SUMMARY OF THE INVENTION
The present invention is directed to a device for converting an optical signal having a wavelength and translating a data signal to a different wavelength. The inventive device includes a first port for receiving the optical signal and an interferometer having first and second branches, receiving the optical signal at one of those branches. A continuous wave optical power source, such as a DFB laser, is formed on a common substrate with the interferometer. The laser provides optical power to the interferometer at a particular wavelength and, in use, the wavelength of the optical signal is converted by the interferometer to the wavelength of the optical power source. The resulting optical signal can then be output on an optic fiber.
In a preferred embodiment, a semiconductor optical amplifier is also formed on the substrate with the interferometer and laser. The amplifier enables adjustment of the optical signal power so that it remains within the operating range of the interferometer.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.
REFERENCES:
patent: 5978129 (1999-11-01), Jourdan et al.
patent: 6005708 (1999-12-01), Leclerc et al.
patent: 08334796 (1996-12-01), None
Danielsen et al., “Wavelength converters: network applications and systems experiments”, Lasers and Electro-Optics, 1997. CLEO '97, vol: 11, pp. 26-26.*
Vodjdani et al., “Integrated Optics interferometric devices with Semiconductor Optical Amplifiers for wavelength conversion”, Lasers and Electro-Optics Society Annual Meeting, 1995. 8th Annual Meeting Conference Proceedings, vol. 1., IEEE. pp. 243-244.
Koren Uziel
Spiekman Leonard Henri
Wiesenfeld Jay M.
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