We investigate the performance of two different all-optical wavelength conversion configurations: four-wave mixing in
highly nonlinear fiber and cascaded second harmonic and difference frequency generation in periodically poled Lithium
Niobate. Both configurations have the capability to convert phase-modulated signals with high data rates. Error free
wavelength conversion of up to 160 Gbit/s DPSK and 320 Gbit/s DQPSK data signals is demonstrated. The converter
using highly non-linear fiber can have advantages in network applications in which cascaded wavelength conversion are
requested due to its potentially higher conversion efficiency and OSNR. The Lithium Niobate converter generates no
phase distortion by wavelength conversion of phase-modulated signals. This could be useful for applications utilizing
PSK formats with 2 bit per symbol or more, like DQPSK or 8-PSK.
We report on components and techniques for single wavelength channel transmission at data rates up to 2.56 Tbit/s. The enabling technologies were OTDM technology, phase modulation formats, and precise dispersion management of the fiber link.
Today, commercial fiber optical transmission systems are operated at a data rate of 10 or 40 Gbit/s per wavelength channel. The optical time division multiplexing (OTDM) technique allows for the investigation of the next generation TDM data rate of 160 Gbit/s while electrical signal processing at 160 Gbit/s is not yet available. In an OTDM transmission system, the key functions of the transmission system are realized using ultrafast all-optical or electro-optical network elements. In this paper, the recent progress in ultrafast technologies for 160 Gbit/s OTDM transmission systems is reviewed. The focus will be on techniques to realize optical pulse sources and ultrafast optical gates which operate on a time scale of a few picoseconds to a few hundred femtoseconds. They are the key elements of a 160 Gbit/s OTDM transmission system and are applied for various functions in the system. The paper focuses in particular on the application of ultrafast optical technologies for measurement purposes. In an optical communication system the quality of the data signal can be inferred from the optical eye diagram of the data signal. Presently, the measurement of optical eye diagrams at a data rate of 160 Gbit/s is inhibited by the limited bandwidth of photodetectors and electrical sampling oscilloscopes. By realizing an all-optical sampling system using the ultrafast technologies discussed before, the bandwidth of such an optical sampling system exceeds 400 GHz and allows for eye diagram measurements up to 320 Gbit/s.
The structure evolution characteristics of single and stratified NdF3 optical thin films on amorphous quartz substrates have been investigated by cross sectional transmission electron microscopy, x-ray diffractometer measurements and atomic force microscopy. The films were deposited by physical vapor deposition under ultra high vacuum conditions. The morphology changes with substrate temperature from V shaped columnar (Zone T) to a columnar morphology corresponding to zone II. The zone boundary falls in the range above 300 °C. The surface roughness of the single films is lowest at 300 °C substrate temperature. The main texture components are <111<, <1 13< and <001< respectively for the three single films of increasing substrate temperature. The surface roughness is decreased by the stratification. The grain size is increased by stratification with CaF2 and decreased by stratification with MgF2 compared to the grain size ofthe single film at the same substrate temperature. Keywords: thin film, stratification, morphology, texture, surface roughness, extinction