4,881 research outputs found
MQW tuned semiconductor lasers with uniform frequency response
No full textA tunable semiconductor laser with an intrinsically wideband uniform frequency response has been developed, using the quantum confined Stark effect in quantum well material as the tuning mechanism. A frequency response uniform within 3 dB from 20 kHz to 1.2 GHz was achieved, limited by the measuring system at low frequencies and by device capacitance at high frequencies. Analysis shows that with optimised tuning elements an uniform frequency response to over 50 GHz should be achievable with this technique
High-performance Heterodyne Optical Injection Phase-lock Loop Using Wide Linewidth Semiconductor Lasers
No full textThe requirements for narrow linewidth lasers or short-loop propagation delay limit optical phase-lock loop realizability with semiconductor lasers. Although optical injection locking can provide low-phase-error variance, its locking range is limited by stability considerations. The first experimental results for an heterodyne optical injection phase-lock loop are reported. Phase-error variance as low as 0.003 rad 2 in a bandwidth of 100 MHz, single-sideband (SSB) noise density of -94 dBc/Hz at 10-kHz offset and mean time to cycle slip of 3 × 10 10 s have been achieved using DFB lasers of 36-MHz summed linewidth, a loop propagation delay of 20 ns and an injection ratio of -30 dB.103427429Kazovsky, L.G., Balanced phase-locked loops for homodyne receivers (1986) J. Lightwave Technol, LT-4, pp. 182-195Lidoyne, O., Gallion, P., Erasme, D., Analysis of a homodyne receiver using an injection-locked semiconductor laser (1991) J. Lightwave Technol., 9, pp. 659-665. , MayRamos, R.T., Seeds, A.J., Fast heterodyne optical phase-lock loop using double quantum well laser diodes (1992) Electron. Lett., 28 (1), pp. 82-83Gliese, U., Nielsen, T.N., Bruun, M., Christensen, E.L., Stubkjaer, K.E., Lindgren, S., Broberg, B., A wideband heterodyne optical phase-locked loop for generation of 3-18 GHz microwave carriers (1992) IEEE Photon. Technol. Lett., 4, pp. 936-938. , AugGoldberg, L., Taylor, H.F., Weller, J.F., Bloom, D.M., Microwave signal generation with injection-locked laser diodes (1983) Electron. Lett., 19 (13), pp. 491-493Ramos, R.T., Seeds, A.J., Delay, linewidth and bandwidth limitations in optical phase-locked loop design (1990) Electron. Lett., 26 (6), pp. 389-391Lidoyne, O., Gallion, P., Chabran, C., Debarge, G., Locking range, phase noise and power spectrum of an injection-locking semiconductor laser (1990) Proc. Inst. Elect. Eng., 137 (3 PART J), pp. 147-154Bordonalli, A.C., Walton, C., Seeds, A.J., High-performance homodyne optical injection phase-lock loop using wide linewidth semiconductor lasers (1996) IEEE Photon. Technol. Lett., 8, pp. 1217-1219. , SeptGardner, F.M., (1979) Phaselock Techniques, , New York: WileyRamos, R.T., Gallion, P., Erasme, D., Seeds, A.J., Bordonalli, A.C., Optical injection locking and phase-lock loop combined systems (1994) Opt. Lett., 19 (1), pp. 4-6Hui, R., D'Ottavi, A., Mecozzi, A., Spano, P., Injection locking in distributed feedback semiconductor lasers (1991) IEEE J. Quantum Electron., 27, pp. 1688-1695. , Jun
High-performance Phase Locking Of Wide Line Width Semiconductor Lasers By Combined Use Of Optical Injection Locking And Optical Phase-lock Loop
No full textThe requirement for narrow linewidth lasers or short-loop propagation delay makes the realization of optical phase-lock loops using semiconductor lasers difficult. Although optical injection locking can provide low phase error variance for wide linewidth lasers, the locking range is restricted by stability considerations. Theoretical and experimental results for a system which combines both techniques so as to overcome these limitations, the optical injection phase-lock loop (OIPLL), are reported. Phase error variance values as low as 0.006 rad 2 (500 MHz bandwidth) and locking ranges exceeding 26 GHz were achieved in homodyne OIPLL systems using DFB lasers of summed linewidth 36 MHz, loop propagation delay of 15 ns and injection ratio less than -30 dB. Phase error variance values as low as 0.003 rad 2 in a bandwidth of 100 MHz, a mean time to cycle slip of 3 × 10 10 s and SSB noise density of -94 dBc/Hz at 10 kHz offset were obtained for the same lasers in an heterodyne OIPLL configuration with loop propagation delay of 20 ns and injection ratio of -30 dB.172328342Kahn, J.M., L Ghit/s PSK homodyne transmission system using phase-locked semiconductor lasers (1989) IEEK Photon. Electron. Lett., 1, pp. 340-342. , OctKazovsky, L.G., Atlas, D.A., A 1320-nm experimental optical phase-locked loop: Performance investigation and PSK homodyne experiments at 140 Mb/s and 2 Gb/s (1990) J. Lightwave Technol., 8, pp. 1415-1425. , SeptRamos, R.T., Seeds, A.J., Fast heterodyne optical phase-lock loop using double quantum well laser diodes (1992) Electron. Lett., 28 (1), pp. 82-83Bordonalli, A.C., Cai, B., Seeds, A.J., Williams, P.J., Generation of microwave signals by active mode locking in a gain bandwidth restricted laser structure (1996) IEEE Photon. Technol. Lett., 8, pp. 151-153. , JanWendt, K.R., Fredendall, G.L., Automatic frequency and phase control of synchronization in television receivers (1943) Proc. IRE, 31, pp. 7-15Peter, M., Strandberg, M.W.P., Phase stabilization of microwave oscillators (1955) Proc. IRE, (43), pp. 869-873Bykovskii, Y.A., Use of a Fabry-Perot resonator for the stabilization of the frequency of an injection laser (1970) Sov. Phys. - Semiconductors, 4, pp. 580-583Yamaguchi, S., Suzuki, M., Frequency stabilization of a diode laser by use of the optogalvanic effect (1982) Appl. Phys. Lett., 11, pp. 597-598Gliese, U., Nielsen, N.T., Bruun, M., Christensen, E.L., Stubkjaer, K.E., Lindgren, S., Broberg, B., A wideband heterodyne optical phase-locked loop for generation of 3-18 GHz microwave carriers (1992) IEEE Photon. Technol. Lett., 4, pp. 936-938. , AugKobayashi, S., Kimura, T., Coherence of injection phase-locked AlGaAs semiconductor laser (1980) Electron. Lett., 16 (7), pp. 668-670Hui, R., Mecozzi, A., D'Ottavi, A., Spanno, P., Injection locking in distributed feedback semiconductor lasers (1991) IEEE J. Quantum Electron., 27, pp. 1688-1695. , JuneLidoyne, O., Gallion, P., Chabran, C., Debarge, G., Locking range, phase noise and power spectrum of an injection-locked semiconductor laser (1990) Inst. Elec. Eng. Proc., 137 (3 PART J), pp. 147-154Bordonalli, A.C., Seeds, A.J., Ramos, R.T., Low phase noise optical phase-lock loops using combined injection locking and phase locking (1994) Inst. Elec. Eng. Colloquium on Microwave Opto-Electronics, pp. 61-65. , London, U.K., Dig. 1994/022Ramos, R.T., Gallion, P., Erasme, D., Seeds, A.J., Bordonalli, A.C., Optical injection locking and phase-lock loop combined systems (1994) Opt. Lett., 19 (1), pp. 4-6Bordonalli, A.C., Walton, C., Seeds, A.J., High performance homodyne optical injection phase-lock loop using wide linewidth semiconductor lasers (1996) IEEE Photon. Technol. Lett., 8 (9), pp. 1217-1219Hodgkinson, T.G., Phase-locked-loop analysis for pilot carrier coherent optical receivers (1985) Electron. Lett., 21 (25-26), pp. 1202-1203Kazovsky, L.G., Performance analysis and linewidth requirements for optical PSK heterodyne communication systems (1986) J. Lightwave Technol., LT-4, pp. 415-425. , AprOhtsu, M., (1992) Highly Coherent Semiconductor Lasers, 1st Ed., , Boston, MA: Artech HouseGardner, F.M., (1979) Phaselock Techniques, 2nd Ed., , New York: WileyAgrawal, G.P., Dutta, N.K., (1993) Semiconductor Lasers, 2nd Ed., , New York: Van Nostrand ReinholdCai, B., Wake, D., Seeds, A.J., Microwave frequency synthesis using injection locked laser comb line selection (1995) Proc. LEOS Summer Topical Meetings, pp. 13-14. , Keystone, Digest no. 95TH8031, Paper WD2Lidoyne, O., Gallion, P., Erasme, D., Analysis of a homodyne receiver using injection-locked semiconductor laser (1991) J. Lightwave Technol., 9, pp. 659-665. , MayRamos, R.T., Seeds, A.J., Delay, linewidth and bandwidth limitations in optical phase-locked loops (1990) Electron. Lett., 26 (6), pp. 389-391Walton, C., Bordonalli, A.C., Seeds, A.J., High performance heterodyne optical injection phase-lock loop using wide linewidth semiconductor lasers (1998) IEEE Photon. Technol. Lett., 10, pp. 427-429. , Ma
Drag Reduction by Applying Speedstrips on Rowing Oars
No full textAbstractThe objective of this study was to determine the advantage of the application of speedstrips to rowing oars for a lightweight single sculler. The research method comprehended three steps: (1) the analysis of the rowing oar movement, (2) the determination of the change in drag and (3) the composition of a rowing model to establish the advantage that could be achieved. The parameters needed for the model: boat velocity, oar angle velocity and power delivered by the rower, were recorded on a real single sculler. The change in drag due to speedstrips on cylinders was determined by performing wind tunnel experiments. The rowing model (Matlab) simulates a race by using real stroke data of a world-class rower as input, while calculating the drag with the coefficients determined by the wind tunnel experiments. The output of the model is the final advantage by the application of speedstrips to rowing oars. Speedstrips induce a 0.1% advantage over a 2000 m race under calm wind conditions. The advantage increases up to .4% with a headwind velocity of 5 m s-1. For bigger boats, the advantage could be even more significant
Drag and Power-loss in Rowing Due to Velocity Fluctuations
No full textAbstractThe flow motions in the turbulent boundary layer between water and a rowing boat initiate a turbulent skin friction. Reducing this skin friction results in better rowing performances. A Taylor-Couette (TC) facility was used to verify the power losses due to velocity fluctuations PV′ in relation to the total power , as a function of the velocity amplitude A. It was demonstrated that an increase of the velocity fluctuations results in a tremendous decrease of the velocity efficiency eV . The velocity efficiency eV for a typical rowing velocity amplitude A of 20 – 25% was about 0.92 – 0.95%. Suppressing boat velocity fluctuations with 60% will increase boat speed with 1.6%. Riblet surfaces were applied on the inner and outer cylinder wall to indicate the drag reducing ability of such surfaces. The results of the measurements at constant velocity are identical as the results reported earlier, while the experimental configuration was different. This confirms once more the consistency of the TC-system for drag studies. The maximum drag reduction DR was 3.4% at a Reynolds number Res 4.7 × 104, which corresponds to a shear velocity in this TC-system with water of V 4.7 m/s. For typical rowing velocity fluctuations, the riblets maintain to reduce the drag with 2.8% and corresponds to a averaged velocity increase of 0.9%. The drag reducing ability of riblets is partly lost due to velocity fluctuations with high amplitudes (A > 20%). From these results, it is concluded that the friction coefficient Cf will vary within one cycle. Higher acceleration/deceleration leads to a additional level of turbulent kinetic energy
Direct extraction of oil from sunflower seeds by twin-screw extruder according to an aqueous extraction process: Feasibility study and influence of operating conditions
No full textThe objective of this study was to evaluate the feasibility of an aqueous process to extract sunflower seed oil using a co-rotating twin-screw extruder. Aqueous extraction was carried out using whole seeds and the influence of the operating conditions on oil yield was examined. Operating conditions included screw profile, screw rotation speed, and input flow rates of sunflower seeds and water. Liquid/solid separation required the addition of a lignocellulosic residue upstream from the filtration zone. However, even with maximum fiber input flow, drying of the cake meal did not improve. The lixiviation of the sunflower seeds was also incomplete. The aqueous extraction of the oil was more efficient in the twin-screw extruder than the reference trial conducted in a batch reactor. The best oil extraction yield obtained was approximately 55% and the residual oil content of the cake meal was approximately 30%. The hydrophobic phases produced were oil-in-water emulsions. These emulsions were stabilized by phospholipids and proteins at the interface, which are natural surface-active agents co-extracted during the process
A.J. Cronin. A doctor into lifelong writer
No full textReality and fiction might be strictly coexistent in the narrative world. The author of this article, after a deep reading of A.J. Cronin’s novels, has tried to find out the right key to penetrate into the novelist’s intricate world. After many interrogatives on A.J. Cronin both as a man and writer, the author , finally, has been able to grasp from the pages of the novelist, the suffering of a man who has made of his romance the history of his own life
Diode-pumped self-starting passively mode-locked neodymium-doped fibre laser
No full textA Nd3+-fibre laser pumped by a single stripe laser diode has been passively mode-locked using a semiconductor saturable absorbed end mirror as the mode-locking element. A 6 cm length of heavily doped fibre was used to minimise the effects of positive group velocity dispersion, and stable mode-locking with pulses of 4 psec duration was obtained at the laser wavelength of 1053 nm. <br/
Quantum well modulators for thulium-doped fibre lasers
No full textRare-earth doped single-mode optical fibres are ideal sources for producing mode locked pulses of very short duration since they have large fluorescence linewidths. To make full use of the linewidth very fast modulators or saturable absorbers are necessary. This work investigates the use of Multiple Quantum Well (MQW) modulators for modelocking and Q-switching fibre lasers. The particular attraction of this approach is that MQW modulators offer good on/off ratios for low voltage drive and are compact in size. Work carried out by Whitehead et al [1] led to the development of the Asymmetric Fabry Perot modulator (AFPM) structure which can achieve very high contrast by using MQW electro-absorption to obtain complete destructive interference of light reflected from the device
Passively mode-locked Er<sup>3+</sup> fibre laser using a semiconductor nonlinear mirror
No full textA nonlinear mirror consisting of InGaAs / InP multiple-quantum-wells integrated with a Bragg reflector stack has been used to passively mode-lock a fiber laser in an extremely simple and advantageous linear-cavity configuration. To date, pulses as short as 7.6 ps have been observed
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