At&t Bell Laboratories

Bell Telephone Laboratories

Akira Hasegawa

Yuji Kodama

Dietrich Marcuse

In soliton optical fiber communication systems that comprise a multiplicity of spaced-apart intermediate non-electronic amplifiers, pulse arrival time jitter can be substantially reduced by incorporation into the transmission path of spaced-apart bandwidth-limiting elements. Exemplarily, the bandwidth-limiting elements are optical filters of bandwidth B.sub.f, with a filter associated with each intermediate amplifier, and with B.sub.f chosen to fall within the range B.sub.sol (N.sub.f /3).sup.1/2, where B.sub.sol is the FWHM spectral width of the soliton pulses, and N.sub.f is the number of intermediate filters in the system. More generally, the bandwidth-limiting elements are selected such that &gt;.delta.t.sup.2 &gt;, the variance of the jitter, is at most 90% of the variance associated with an, otherwise identical, comparison system that does not contain the bandwidth-limiting elements. Systems according to the invention thus can overcome the Gordon-Haus limit on the bit rate/distance product.

Soliton optical fiber communication system

Pulses of electromagnetic radiation having predetermined spacing between pulses can be generated by coupling amplitude modulated carrier radiation into an appropriate nonlinear transmission medium that has anomalous dispersion in some spectral region. The amplitude modulation is to be such that the amplitude has peaks with the predetermined spacing, and the carrier wavelength is to be in the anomalous dispersion region of the medium. Interaction between the medium and the radiation then results in contraction of the width of the amplitude peaks, which can result in formation of narrow pulses. A preferred transmission medium is monomode fiberguide, e.g., silica-based single mode optical fiber. In addition to the method for producing a sequence of pulses, a communication system using the inventive method is disclosed. Furthermore, a communication system comprising Raman amplification of the signal is disclosed.

Generation of pulses of electromagnetic radiation by use of the induced

Pulses of electromagnetic energy of appropriate peak power can form soliton pulses in monomode fiber. The width of such pulses changes during propagation, and can decrease for certain ranges of peak power, e.g., between about P.sub.o and 9/4 P.sub.o, where P.sub.o is the 'balanced' peak power. Using this property, repeaterless transmission of soliton pulses is possible if the pulses are non-electronically amplified by appropriate amounts at appropriate intervals. Exemplary amplifying means are glass laser, Raman laser, semiconductor laser medium, and cw injection.

Soliton fiber telecommunication systems

The data transmission rate link length product of monomode fiberguide telecommunication systems can be increased above values possible in 'linear' systems by appropriate use of the non-linear dependence of the fiber refractive index on electric field. In particular, selecting the appropriate pulse peak power and center wavelength can result in creation of a soliton, i.e., a pulse capable of substantially dispersionless transmission. The center wavelength is to be close to, but larger than, the wavelength of zero first-order chromatic dispersion of the fiberguide, and the latter wavelength is to be within the anomalous dispersion regime of the fiberguide. Criteria for determining the appropriate peak power, center wavelength, fiber loss, and minimum link length, as well as the asymptotic pulse width and soliton spread due to the power loss in the fiber are given, and facilitate design of a system according to the invention.

Monomode fiberguide telecommunication system utilizing soliton pulses

A multimode fiber lightwave communication system using pulses of center wavelength in the region of anomalous dispersion of the fiber material. For instance, in silica-based fiber, this implies a wavelength greater than about 1.3 .mu.m. In such a system, modal dispersion can be reduced by using the nonlinear properties of the fiber material. In particular, by adjusting the pulse amplitude to satisfy the expression ##EQU1## where v.sub.gj is the group velocity of the j-th mode,

Multimode fiber lightwave communication system utilizing pulse

Method for achieving phase matching for electromagnetic radiation propagating through single mode transmission media, such as, for instance, single mode optical fiber. When coherent, monochromatic radiation of essentially constant amplitude, the carrier, is propagating through such a medium, and if the frequency of the carrier is chosen to be within a region of anomalous dispersion of the medium, then, provided the medium has a finite nonlinear coefficient of the index of refraction, the carrier wave is subject to a modulational instability. This instability results in the generation and exponential growth of sidebands, the two closest to the carrrier frequency being the dominant ones. The modulation frequency is proportional to the square root of the power in the carrier wave. Apparatus for using the method is also disclosed, such as apparatus for using the method to tunably generate coherent radiation in the far infrared, apparatus for tunably generating coherent radiation relatively close to the carrier frequency, and apparatus for using the method for amplifying radiation at a frequency relatively close to the carrier frequency.

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New Providence, NJ, United States of America

Akira Hasegawa