Wavelength converter

Details Wavelength converter Wavelength converter

1997-12-30

1999-08-17

Hellner, Mark

Optical: systems and elements

Optical amplifier

359326, H01S 300, G02F 135

Patent

active

059402075

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a wavelength converter for converting a first light signal of a first wavelength for transmitting data into a second light signal of a second wave-length, having signal input for receiving the first light signal, a signal output for emitting the second light signal, a modulatable optical semiconductor amplifier with an input, an output and modulation input, a first laser light source which with the semiconductor amplifier forms a first stage, with the input of the semiconductor amplifier being connected to the first laser light source and the modulation input of the semiconductor amplifier being connected to the signal input for cross amplification modulation and the first laser light source emitting light of a third wavelength, and wherein a second stage is connected to the output first stage by a coupling element, the second stage being provided with a second laser light source emitting light of the second wavelength and with a modulatable component.
Wavelength converters are required, inter alia, in optical data transmission systems in which data is transmitted by time or wavelength multiplexing.
In digital data transmission, data may be transmitted by light signals of two different levels, each corresponding to a binary signal. Since in data transmission, the error rate is influenced by the spacing between the two logic levels, it is desirable that the inter-level spacing of the input signal be not reduced by any wavelength conversion. In wavelength conversion the level spacing is determined by the so-called extinction factor, the extinction factor achievable with a single semiconductor amplifier being as a rule too low to maintain the level spacing of the input signal in the output signal. Cascading two semiconductor amplifiers for wavelength conversion will result in an increasing deterioration of the extinction, i.e., in a reduction of the extinction factor.
2. The Prior Art
In SIMON, J. C., et al.: Two-stages wavelength converter with improved extinction ratio, OFC 1995, San Diego, U.S.A., there is described a dual stage optical wavelength converter, by which a light signal may be converted from a first wavelength to a second wavelength.
The wavelength converter described in this prior publication is provided with two optical series-connected semiconductor amplifiers each of which amplifies a light signal applied to its input. A light signal from a laser light source having a wave-length of .lambda..sub.int and operating in a continuous wave is applied to the input of the first amplifier and does not, therefore, transmit any data. Furthermore, the two semiconductor amplifiers are each equipped with a modulation input connected to the signal input of the wavelength converter.
Hence, the light signal of wavelength .lambda..sub.in applied to the signal input of the wavelength converter modulates the amplification of the two semiconductor amplifiers, the amplification factors of which, because of saturation effects, will decrease as the level of the modulation signal increases.
The modulation signal of wavelength .lambda..sub.in and the light signal of wavelength .lambda..sub.int are coupled into the semiconductor amplifiers in opposite directions so that only the signal of wavelength .lambda..sub.int will leave the semiconductor amplifiers in the direction of the signal output.
If the level of the modulation signal of wavelength .lambda..sub.in is relatively high, the semiconductor amplifiers are driven to saturation so that the amplification factor and, hence, the levels of any output signals will be relatively low. If, by contrast, the level of the modulation signal of wavelength .lambda..sub.in in relatively low, then the amplification factor of the semiconductor amplifiers and the level of any output signals will be relatively high. That is to say that the polarity of the output signals of the two semiconductor amplifiers is inverted relative to the input signal of the wavelength converter.
Between the two semiconducto

REFERENCES:
patent: 5264960 (1993-11-01), Glance
patent: 5734493 (1998-03-01), Jopson
Simon, J.C. et al.: "Two-stages wavelength converter with improved extinction ration", OFC 1995, San Diego, CA.
Perino, J.S. et al.: Proceedings of 1994 Conference on Lasers and Electro-Optics and the International Electronics Conference CLEO/IQEC, Anaheim, CA, May 8-13 ?, pp. 298-299.

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