New simple method for measuring the mode spot size in monomode fibres

The equivalent step index (ESI) parameters associated with single-mode fibres can be evaluated by observing the changes in transmitted power on the far field when a Ronchi ruling is inserted between the end face of the fibre and a detector collecting the output intensity. Measurements as a function of wavelength allow one to determine the cutoff wavelength, ESI parameters for short lengths of fibre and effective cutoff wavelength for long lengths.     

Dynamic simulations of the dipolar driven demagnetization process of magnetic multi-core nanoparticles

In this work, we investigate dynamically the dipolar driven demagnetization process of magnetic multi-core particles by solving the Landau-Lifshitz equation for single-domain particles distributed on a three-dimensional sphere. We analyze the relaxation time in respect to different geometry and material parameters. Further we show that the demagnetization times differ from the behaviour of a single magnetic sphere in the case of low damping. To explain these dynamics nanoparticular systems of different dimensions are investigated. We show that deviations can be attributed to a confinement of the relaxation dynamics to a lower dimensional submanifold of the k-space.     

Feasibility demonstration of low pump power operation for 1.48 mu m diode-pumped erbium-doped fibre amplifier module

An optimisation of the erbium-doped fibre greatly improves the 1.48 mu m pumping efficiency. The amplifier exhibits 26.2 dB fibre gain for 8 mW launched pump power and 20.2 dB gain for only 5.2 mW pump power, giving an outstanding 3.9 dB/mW gain coefficient.<>     

Determination of modal dispersion in monomode fibres from wavelength dependence of the mode spot size

It is demonstrated in this letter that the spectral mode spot size measurement is a useful means of determining the modal dispersion of monomode fibres used in the 1.3 ?m wavelength region.     

Electron beam lithography and ion implantation techniques for fabrication of high-Tc Josephson junctions

Established semiconductor process technologies are demonstrated to be suitable for the fabrication of high temperature superconductor (HTS) Josephson junctions. Single YBCO bridges were modified by local oxygen ion irradiation through a narrow slit in a PMMA mask which was formed by electron beam lithography. The influence of slit dimension and irradiation dose was investigated. The critical current and normal resistance ot the modified microbridges can be controlled by these two parameters. Proximity coupling across the modified region is observed up to a slit width of 250 nm. When exposed to microwave irradiation the microbridges exhibited Shapiro steps. In dc SQUIDs a voltage modulation as a function of an applied magnetic flux is observed.     

35 AM-VSB TV channels distribution with high signal quality using a1480 nm diode-pumped erbium-doped fiber postamplifier

In the system considered, the postamplifier, with an output power of +9.6 dBm, did not degrade the very high linearity of the isolated distributed-feedback (DFB) laser transmitter. A 51.2-dB weighted signal-to-noise ratio was obtained, and an optical power budget of 16 dB was achieved with a weighted signal-to-noise ratio higher than 48 dB. A larger power budget with a higher signal-to-noise ratio (SNR) is possible with an increase of DFB laser output power and erbium-doped fiber amplifier (EDFA) saturated output power, and with a minimization of the EDFA noise contribution     

Stress measurements of fibers and preforms

The authors point out the formation mechanism of axial stress, describes the method and the apparatus used for measurements, and presents the results obtained during a study of loss reduction on trapezoidal core 1.55-μm dispersion-shifted fibers manufactured by the MCVD technique. It is concluded that the stress measurements on fiber are less accurate than those on preform (experimental dispersion reaches 15% instead of 5%). The various observations made from measurements on preform show that the axial stress is related to the index profile and that the core axial stress increases with the GeO₂ content. The measurements performed on fiber show that the level of stress is linearly dependent on the drawing tension and that the stress profile is related to the glass-transition temperature of the different materials. Furthermore, this method of stress measurement is complementary to the more standard index profile measurement on fiber or on preform     

Photochemische Umwandlungen, 42 [1] Photoisomerisierungen im 5-Isopropyliden-tetracyclo-[4.3.0.02,4.03,7]non-8-en-System. Vorläufige mitteilung

Direct photochemical excitation of the tetracyclo[4.3.0.0.^2,4.0^3,7]non-8-enes 7a – d leads to a mixture of the isomers 8a – d and 10a – d , with the former being the main products. On sensitization by acetone the formation of 10a – d is clearly favored. The cis-bishomobenzenes 9a – d are the postulated intermediates. Spectral data and some thermal reactions are described.     

Parametric study of depressed inner cladding single-mode fibers

A parametric study on the depressed inner cladding (DIC) single-mode fibers shows the influence of the inner-cladding diameter on the effective cutoff wavelengths of the first two modes, determining a practical transmission window. The set of curves that is obtained can be considered universal, at least for a value of the inner-cladding/core index differences ratio close to 0.5. The behavior of the effective cutoff wavelengths is explained by studying the effective index of the modes and the fundamental mode diameter, this explanation being confirmed by a bending and microbending sensitivity test. It appears that DIC fibers optimized for long-range transmission should have an inner cladding to core diameter ratio greater than 3 and a relative depth of the inner cladding smaller than 0.5.