Reinhard Caspary

Four-Channel WDM Transmission Over 50-m SI-POF at 14.77 Gb/s Using DMT Modulation

Wavelength division multiplexing (WDM) is a promising solution for upgrading the capacity of polymer optical fiber (POF)-based telecommunication networks. In this letter, we report on the successful realization of a four-channel highspeed WDM transmission system for 1-mm diameter step-index POF (SI-POF). For combining the optical signals coming from 405-, 450-, 515-, and 639-nm laser diodes onto 1-mm SI-POF, a 4 × 1 coupler with low insertion loss (IL) has been developed. To spatially separate different wavelength channels, a fourchannel demultiplexer with low IL (<;5.7 dB) and high (non)adjacent channel isolation (>30 dB) has been realized in bulk optics. The 14.77-Gb/s data transmission based on the offline-processed discrete multitone modulation technique has been demonstrated over 50-m SI-POF at a bit-error rate of 10-3.

A Thermal Splicing Method to Join Silica and Fluoride Fibers

Even though the melting temperatures of silica and fluoride glass are very different, a new thermal splicing method to join these fibers is presented here. The lowest attenuation achieved was about 0.2 dB. Moreover, this thermal splice was stabilized, packed and inserted in a simple fiber laser setup.

Recent progress on S-band fiber amplifiers

The internet boom in the 1990s led to an exponential increase of the bandwidth demands on optical long-haul transmission links and the introduction of WDM and DWDM systems. However, the gain bandwidth of usual fiber amplifiers is limited to a maximum of 80 nm in the C- and L-band. Todays optical senders and receivers are limited to a spectral efficiency of not more than 1 bit/s/Hz which results in a total capacity of about 10 Tbit/s in the C- and L-bands. Meanwhile the crash of the telecom market damped the bandwidth growth somewhat, but it is still an important task to work on solutions for transmission systems at extremely high bitrates beyond 10 Tbit/s. One of these solutions is the use of larger parts of the low attenuation window of the transmission fibers. It seems to be consensus that the first step towards this direction will be the S- and S/sup +/-band at 1450-1530 nm. Here we will give an overview of the current status and new developments in the field of S-band fiber amplifier technologies. As usual, the term S-band will be used for Sand S/sup +/-band in this work.

Avalanche Pumping of Thulium Doped S-Band Fiber Amplifiers

In the last years a lot of different pump configurations were investigated for thulium doped fiber amplifiers (TDFA) in the S-band. Since the TDFA is using a four-level transition with long lifetime of the lower amplifier level, it turned out, that pumping with two wavelengths was most effective. Comparing the results of fluoride fibers doped with 2000 ppm and 5000 ppm thulium, we show that an avalanche effect significantly improves the efficiency of TDFAs with the highly thulium doped fiber when pumped at 1050 nm only and at the same time makes the dual-pump configuration 790/1050 nm inefficient. For the measurements we used self-made fluoride fibers

Thulium-doped fiber amplifier for the S-band

Two configurations of thulium-doped fiber amplifiers (TDFA) are presented and the performance of the amplifier in these configurations is discussed. The measurements are compared with a simulation using a self-written model and compared with results reported in the literature. The problems during the design, their solutions and the possibilities to improve the amplifier operation are presented.

Computer aided EDFA design, simulation and optimization

Six important programs of commercially available software for erbium-doped fiber amplifiers are described with attention to advanced simulations. A more detailed description is given of two programs, EDFA Design(R) and VPIComponentMaker(R). The models included in the software are discussed, and their implicit assumptions are explained and examined.

Eu-doped polymer fibers

Polymer optical fibers are a very good choice for flexible and robust short range optical data links. We have developed PMMA with Eu3+-doped polymer chains. From this optically active material we draw fibers. These fibers can be used for UV pumped polymer fiber amplifiers in cases where larger distances have to be bridged. This paper presents the fabrication of these fibers, their optical characteristics and results of first gain measurements.

Methacrylate-Based Copolymers for Polymer Optical Fibers

Waveguides made of poly-methyl-methacrylate (PMMA) play a major role in the homogeneous distribution of display backlights as a matrix for solid-state dye lasers and polymer optical fibers (POFs). PMMA is favored because of its transparency in the visible spectrum, low price, and well-controlled processability. Nevertheless, technical drawbacks, such as its limited temperature stability, call for new materials. In this work, the copolymerization technique is used to modify the properties of the corresponding homopolymers. The analytical investigation of fourteen copolymers made of methyl-methacrylate (MMA) or ethyl-methacrylate (EMA) as the basis monomer is summarized. Their polymerization behaviors are examined by NMR spectroscopy with subsequent copolymerization parameter evaluation according to Fineman-Ross and Kelen-Tüdös. Therefore, some r-parameter sets are shown to be capable of copolymerizations with very high conversions. The first applications as high-temperature resistant (HT) materials for HT-POFs are presented. Copolymers containing isobornyl-methacrylate (IBMA) as the comonomer are well-suited for this demanding application.

Alumina films as gas barrier layers grown by spatial atomic layer deposition with trimethylaluminum and different oxygen sources

Alumina layers were grown from trimethylaluminum (TMA) and water, ozone as well as an oxygen plasma as co-reactants in low temperature spatial atomic layer deposition (ALD). The influence of the amount of precursor, the precursor exposure duration, and substrate temperature were investigated with respect to the growth rate while employing different oxygen sources. The TMA/water process provided alumina (AlOx) films with superb film quality as shown by infrared measurements. Ozone-based processes allowed lower substrate temperatures. Nevertheless, carbon residuals in different binding states were found within the bulk material. However, the carbon impurities have no impact on the barrier performance, since 50 nm AlOx grown by TMA either with water or ozone exhibited a water vapor transition rate in the range of 10−6 g/m2/day. However, when our home-built microwave plasma source was applied in a remote configuration, the water vapor transition rate was one order of magnitude higher due to a reduction in fil...

High speed WDM transmission on standard polymer optical fibers

We have developed WDM multiplexer and demultiplexer in the visible spectral range for POF transmission links and have carried out transmission experiments using different lengths of standard SI-POF. Our 4-channel WDM system with laser diode sources is operated in the violet, blue, green and red spectral range. Using discrete multitone modulation (DMT), we demonstrated a total data rate of 14.77 Gbit/s over 50 m and 8.26 Gbit/s over 100 m of SI-POF.