Optical Phase Conjugation and All-Optical Demultiplexing using Four-Wave Mixing in Dispersion Shifted Fibers

Doctoral thesis, 1998

This thesis deals with two applications of four-wave mixing in optical dispersion-shifted fibers; optical phase conjugation and all-optical switching. The work is a part of an effort to study the upgradability of the existing fiber plant, which is of large economic interest. Present transmission capacities are generally limited by pulse broadening due to chromatic dispersion in the fiber, and by the bandwidths of the electro-optic and opto-electronic interfaces. Optical phase conjugation has been suggested as one technique for compensation of temporal distortion due to linear dispersion and nonlinear effects. It can be implemented via four-wave mixing in an optical fiber, so that the output wave is a true spectrally inverted replica of the input wave. We present experimental and theoretical results on the detrimental effects that undesired nonlinearities in the conjugator will induce, and how they are reduced when a shorter fiber is used. Furthermore, the conversion efficiency and the residual polarization dependence in a polarization-insensitive optical phase-conjugator, using two orthogonal pump-waves, are investigated. We also describe a noise characterization of the conjugator, and calculations of the noise figure indicating 3 dB quantum limit at conversion efficiencies >>100%. The capacity of a transmission system, based on single-mode fibers, is generally much higher than the bandwidth of the electronics at the transmitting and the receiving end. This is sometimes referred to as the "electronic bottleneck", and it can be overcome, e.g. by using several channels on different wavelengths, with a lower bit-rate on each, or with a high bit-rate at one wavelength and all-optical data-switching. In this thesis we present an all-optical demultiplexer with 20 dB inherent amplification, that utilizes four-wave mixing in a dispersion-shifted fiber. We also show how the extinction ratio is deteriorated in a saturated device, and evaluate the influence of variations in zero-dispersion wavelength and parametric noise amplification.