Generation and optimum control of picosecond optical pulses fromgain-switched semiconductor lasers

The generation of picosecond pulses from gain-switched semiconductor laser diodes is studied. Theoretically, common-rate equations are used to give pulse width and amplitude as a function of external parameters. The numerical predictions are compared with experimental results. It is found that optimum conditions can be achieved by an appropriate choice of the bias current     

Gel-combustion synthesis of nanocrystalline spinel catalysts for VOCs elimination

Gel-combustion synthesis (GCS) in self-sustaining mode was used for preparation of mixed oxide with spinel structure AB₂O₄ (where A = Co, Cu and B = Cr, Co). To support these mixed oxides on CeO₂ and ZrO₂ powders, the GCS technique in self-propagating mode was developed. The synthesized materials were characterized by IR-spectroscopy, X-ray diffraction and transmission electron microscopy. The GCS preparation leads to the formation of nanocrystalline, single-phase spinel catalysts, which showed high activity in VOCs (hexane) elimination. The best catalytic performance was obtained over copper cobaltite catalyst prepared by GCS from glycerin-chelated precursor.     

Balanced phase diversity receiver in 565 Mbit/s DPSK transmission system

565 Mbit/s DPSK optical transmission experiments with a balanced phase diversity receiver are reported. by employing a bulk optical 90 degrees hybrid in the input stage and a silicon bipolar multiplier IC in the demodulator and AFC stages, a system with a receiver sensitivity of -48.5 dBm and long-term stability was realised.<>     

Integrated optics 90° hybrid on LiNbO3 for phasediversity receivers

Present an integrated optic eight-port 90° hybrid on LiNbO₃ comprising four tunable directional couplers and two phase shifters for adjusting the phases between the output ports. Measurements on the phase stability show phase fluctuations of <±5° and a temperature dependence of ≈15°/°C     

Operation of a 100-bit, 2.6 µm bubble shift register

Complete circuit operation for a small 100-bit serial shift register memory with a 10.6 μm period fabricated on a garnet wafer using electron beam lithography and single level all-permalloy technology is reported. Overall circuit operation including generation, propagation, and detection was achieved with a 6 Oe bias margin using a 1 kHz rotating field. Although the circuit design and fabrication techniques were not optimized, we believe that this is the first published report of complete circuit operation for a single level device with bubbles as small as 2.6 μm. The performance of two different types of chevron expander detectors and two different generators was evaluated and circuits combining disk generators with herringbone detectors were found to provide the best overall operating margin. At low speeds (∼5 Hz) high-bias failures were caused by failure of the domains to strip out fully in the detector while the low bias limit was determined by the introduction of spurious bubbles into the track near the generator.     

UV Raman imaging--a promising tool for astrobiology: comparative Raman studies with different excitation wavelengths on SNC Martian meteorites

The great capabilities of UV Raman imaging have been demonstrated on the three Martian meteorites: Sayh al Uhaymir, Dar al Gani, and Zagami. Raman spectra without disturbing fluorescence and with high signal-to-noise-ratios and full of spectral features were derived. This result is of utmost importance for the development of powerful instruments for space missions. By point scanning the surfaces of the meteorite samples, it was possible for the first time to construct UV-Raman images out of the array of Raman spectra. Deep-UV Raman images are to the best of our knowledge presented for the first time. The images were used for a discussion of the chemical-mineralogical composition and texture of the meteorite surfaces. Comparative Raman studies applying visible and NIR Raman excitation wavelengths demonstrate a much better performance for UV Raman excitation. This comparative study of different Raman excitation wavelengths at the same sample spots was done by constructing a versatile, robust sample holder with a fixed micro-raster. The overall advantages of UV resonance Raman spectroscopy in terms of sensitivity and selectivity are demonstrated and discussed. Finally the application of this new technique for a UV Raman instrument for envisaged astrobiological focused space missions is suggested.     

Investigation of crosstalk interference in a fibre loop opticalbuffer

Experimental and theoretical investigations of crosstalk interference in a fibre loop optical buffer are reported. Up to 23 circulations of a 622Mbit/s data packet at a bit error rate BER<10 ^-9 were demonstrated experimentally. A contrast ratio of 29 dB of the input/output 2×2 space switch of the fibre loop is required. This value is in very good agreement with theoretical predictions     

Fiber loop optical buffer

Fiber loop optical buffers enable data storage for discrete time intervals and therefore appear suitable for applications in optical asynchronous transfer mode (OATM)-based networks where data are transmitted in cells of fixed length. In this paper, the feasibility and the limitations of optical data storage in a fiber loop optical buffer are studied theoretically and experimentally, A model of a fiber loop buffer, incorporating semiconductor laser amplifiers (SLA) as switching gates, is described. The two major interfering quantities are cross talk and amplified spontaneous emission of the SLA gates. To limit the impact of cross talk on the signal quality, an on/off ratio of the SLA gates of at least 30 dB is required. The paper describes the optimum operation conditions, which enable data storage for more than 100 circulations even for data rates in the range from 10 to 160 Gb/s     

Bandwidth efficient operation of phase diversity reception compared with heterodyne reception

In two-channel 2 Gbit/s and 565 Mbit/s transmission experiments the operation of a balanced phase diversity receiver and of a balanced heterodyne receiver is examined with regard to bandwidth efficiency in multichannel and high bit rate transmission.<>