Ultrafast all-optical switch has been demonstrated by inserting Fe-doped multiple quantum wells (MQWs) in asymmetric Fabry-Perot microcavities. Heavy Fe doping during the InGaAs∕InP MQW epitaxial growth is a well-controlled technique to reach subpicosecond optical time constants. An asymmetric Fabry-Perot microcavity using gold metal as a back mirror and air/InP interface as a front mirror is realized. Pump-probe experiments using a conventional scheme on such switching devices are investigated. The device reveals an ultrafast response time, as low as 290fs, for an iron concentration of 2×1019cm−3, a contrast ratio of 8dB, a threshold switching fluence of 3.5μJ∕cm−2, and a 37-nm 3-dB bandwidth in the 1.55-μm telecommunication spectral range.
Articles you may be interested in290 fs switching time of Fe-doped quantum well saturable absorbers in a microcavity in 1.55 μ m range Appl. Phys. Lett. 85, 5926 (2004); 10.1063/1.1804239 Ultrashort, nonlinear, optical time response of Fe-doped InGaAs/InP multiple quantum wells in 1.55-μm range Appl. Phys. Lett. 82, 1670 (2003); 10.1063/1.1557333 High-speed 1.55 μm Fe-doped multiple-quantum-well saturable absorber on InP Appl. Phys. Lett. 78, 4065 (2001); 10.1063/1.1381410 Time-frequency spectroscopy of an InGaAs/InP quantum-well exciton Bragg reflector Appl. Phys. Lett. 74, 2569 (1999); 10.1063/1.123900Carrier lifetime and exciton saturation in a strain-balanced InGaAs/InAsP multiple quantum well GaInAs/InP multiple quantum wells ͑MQWs͒ are used as saturable absorbers for all-optical signal regeneration at a 1.55-m wavelength. These MQWs are doped during their growth by molecular-beam epitaxy with Fe to improve their temporal response. The present work develops a theoretical description of the carrier recombination dynamics in these MQWs. Temporal evolution of the populations of excitons, holes, electrons, and iron traps is determined by coupled evolution equations. The model describes the optical temporal nonlinearity of the saturable absorbers near the excitonic peak transition. Furthermore, pump-probe experiments have been performed to measure the recovery time of these structures having different Fe doping concentrations. A good agreement between the experimental measurements and the model predictions of the optical temporal behaviors of the saturable absorbers is obtained. The control of the recovery time ͑nanoseconds to picoseconds͒ with the Fe traps in a large concentration range (10 15 to 10 19 cm Ϫ3 ) is particularly well highlighted by this model. The Fe doping concentration prescribed to reach a targeted fast recovery time is predicted with good accuracy by the model, which leads us to propose an attractive way to design ultra-high-speed, all-optical signal regenerators based on saturable absorbers.
A new technique (division of the film into very many small squares) allows the observation of supercooling and superheating of superconducting layers under both parallel and perpendicular fields. The possible existence of "edge" nucleation in thick films, analogous to surface nucleation for semiinfinite samples, is shown. The superconducting parameters determined for films extrapolate correctly to known bulk values. Critical thicknesses for passage from type I to type II behavior agree with theoretical predictions. Nonlocal corrections to the penetration depth allow one to explain deviations from the Gorkov-Goodman relation for bulk metals.
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