Hole lifetime in electroabsorption modulator integrated laser diode (EAM-LD) has been reduced to 7ps by employing a shallow quantum well (QW) absorption layer. 10Gbps-80km SMF transmission has been achieved at +5.3dBm fiber launched power.
Recording characteristics of partially oxidized Fe-Co media were improved remarkably by the introduction of an Fe-Co under-layer. In this paper, the effects of the coercive force of the Fe-Co under-layer on recording characteristics were investigated using a ring-type head. The stronger the coercive force of the under-layer, the higher the reproduced voltage and recording density D50, and the superior C/N and overwrite characteristics. Waveforms of a medium whose Fe-Co under-layer possessed a high coerclve force were sharper than those of a medium with low coercive force. We consider that the broadening of the waveforms depends mainly on interactions between the head and Fe-Co under-layer.
A low power consumption tunable DFB laser diode array, integrated with backside waveguides, is experimentally demonstrated. Fiber output power of 14 dBm was obtained in full L-band with module power consumption less than 3 W.
Low-temperature Seebeck coefficient S/T measurements have been performed on Pr-based 1-2-20 system, PrTr2X20 (Tr = Ti, Ta, V, Ir, X = Al, Zn) with non-Kramers doublet ground states. For PrTr2X20 with X = Al, we find a large S/T, which amounts to those of heavy fermion metals. By contrast, S/T for PrIr2Zn20 is found to be considerably small as the same order of magnitude as those of ordinary metals, despite the commonly enhanced Sommerfeld coefficient γ throughout the system. A satisfactory of the quasi-universal relation between S/T and γ as well as the Kadowaki-Woods relation demonstrates that the mass enhancement is realized in PrTr2Al20 due to the hybridization between f-electrons and the conduction electrons. We also find that the small S/T of PrIr2Zn20 is enhanced at low temperatures under the fields on the verge of quadrupole ordered phase, and in the same regime, the electrical resistivity follows the quadratic temperature dependence with a steep slope as a characteristic of Fermi liquid. The results imply an emergence of a nontrivial coherent state with sizable mass enhancement associated with the quadrupole degree of freedom.
A wave-number domain information theoretical analysis proposed previously is applied to studying dynamical structures of chaotic multi-mode oscillations exhibited by homogeneously broadened Maxwell- Bloch (M-B) model. Most of radiation energy is concentrated at the gain center, but turbulent disturbances are generated in two off resonant wave- number regions we call Rabi chaotic bands, and they propagate toward other regions in the wave-number space. The analysis further reveals that there is a close interplay between the gain center and the Rabi bands, which yields a ‘chaotic itinerancy’ over the ruins of local chaotic attractors. This phenomenon results in self-induction of mode partition noise and mode hopping, which have been often observed in multi-mode laser oscillations.
Abstract Turbo pumps for rocket engines often equipped balance piston (BP) systems at the back-shroud of the impellers for cancelling their axial thrust. The BP system is self-balancing and stable under quasi-static conditions, but it is known that the BP systems can be unstable under certain dynamic conditions. The performance characteristics of turbo pumps equipped with unshrouded impellers might be affected by the axial position of the rotor. Thus it is necessary to consider this effect when calculating the balance of axial thrust. Few experiments have determined the characteristics of unshrouded impellers equipped with BP systems yet. In this research, an experimental study of a model turbo pump for rocket engines was carried out. This pump had an unshrouded impeller, a BP system, a vaned diffuser, and a volute. Axial forced oscillations were applied on the rotor of the pump by an active magnetic bearing (AMB) test facility. This setup can oscillate with freely-selected amplitude and frequency applying thrust to the rotor. During the oscillations, the fluctuation of axial thrust under the operating conditions was monitored using strain gauges. The axial thrust compensation ability and the response of the BP system were evaluated by analyzing the magnitude, amplitude and phase delay of the axial position of the rotor. Moreover, 3D simulations and 1D simulations were carried out for the model pump. In the 3D simulations, computational fluid dynamics (CFD) was used to calculate the internal flow of the model pumps. The BP system was equipped with an impeller on which were applied forced oscillations. The impeller movement was modeled using a mesh morphing method. The 1D simulation predicted the axial thrust by calculating the mass flow balance using the geometry of the model pump. The phase lag between the axial position and the thrust was dominated by the pressure fluctuation at the BP chamber caused by the mass flow balance. The 3D simulations well predicted the fluctuation, but the characteristics of the BP system estimated by the 3D simulations were more stable than those determined by the experiments. On the other hand, the characteristics estimated by the 1D simulation was less stable than those by the experiments. However, these simulations grasped the tendency of the BP system to become unstable as the oscillation frequency increases, and are effective in predicting the characteristics.
A high-power, ultralow-chirp electroabsorption modulator (EAM) integrated with a distributed-feedback laser diode (EML) having ultrashort lifetime of photogenerated holes in the EAM quantum-well (QW) structure is reported for the first time. A shallow QW structure having a small valence band offset to enhance the sweepout of photogenerated holes was employed as EAM absorption layer. The measured hole lifetimes were 7-11 ps, and the measured frequency chirp (/spl alpha/-parameter) was low or negative at low EAM reverse bias voltages even under high optical output power conditions. Successful 10-Gb/s 80-km normal-dispersion single-mode fiber transmission (chromatic dispersion D=1600 ps/nm) and the record average fiber optical output power (P/sub f/) of +5.3 dBm were achieved at 25/spl deg/C. In addition, semicooled operation of EML at enhanced bit rates has been demonstrated for application in small-form-factor protocol-agnostic optical transceivers. A 10.7-Gb/s 1600-ps/nm transmission was achieved at 45/spl deg/C and P/sub f/=+3.0 dBm.
