摘要:

A significantly improved recovery time of 130 ps has been achieved in an all‐optical zero‐gap directional coupler containing multiple quantum wells. The mechanism for the all‐optical switching is due to free‐carrier induced refractive nonlinearities at near‐band‐gap resonant frequencies. The large reduction in the switch recovery time was obtained by the application of an external dc bias which sweeps out the carriers from the quantum wells. From our experimental results on the laser pulse width limited switch‐up time of 2 ps, we <m1;&37>deduce that the contribution of self‐electro‐optic effect nonlinearity is negligible in this case.

ISSN:0003-6951    

DOI:10.1063/1.105008

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Stable index‐guided operation of variable stripe strained‐layer InGaAs‐GaAs‐AlGaAs lasers achieved by MeV oxygen implantation‐induced disorder of the active region is demonstrated. Well‐behaved near‐ and far‐field patterns for lasers implanted with 5×1016cm−2and 1×1017cm−2oxygen are observed to be stable with increasing drive current. Comparison with unimplanted, oxide‐defined stripe lasers fabricated from the same wafer indicates a dramatic improvement in emission characteristics as a result of the presence of a lateral real‐index waveguide in the oxygen‐disordered regions which is stronger than the carrier‐induced antiguide present in unimplanted InGaAs‐GaAs strained‐layer lasers.

ISSN:0003-6951    

DOI:10.1063/1.105009

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have built a self‐mode‐locked Ti:sapphire cw oscillator delivering up to 2 W of average output power. This oscillator provides 100 fs pulses tunable in the 770–807 nm range. Using a fiber‐prism compressor at the cavity output, the pulses have been compressed down to 27 fs at 785 nm, while keeping 200 mW average power.

ISSN:0003-6951    

DOI:10.1063/1.105010

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We experimentally demonstrate the importance of two‐dimensional carrier confinement for picosecond dynamics in gain‐switched quantum well lasers, measuring time‐resolved spectra of gain‐switched quantum well (QW) lasers with coupled QWs and uncoupled QWs. The result indicates that an extremely short pulse (<2 ps) is generated in the uncoupled QW lasers. On the other hand, the pulse duration is about 10 ps in the coupled QW lasers in which the two‐dimensional confinement effect is significantly reduced owing to the miniband formation. These results demonstrate the importance of the two‐dimensional confinement of carriers for the short pulse generation in the semiconductor lasers. The measured dynamic spectral shift of the gain‐switched QW lasers also confirm the significant role of the two‐dimensional carrier confinement.

ISSN:0003-6951    

DOI:10.1063/1.105011

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Probe beam intensities more than an order of magnitude larger than pump beam intensities do not erase photorefractive gratings during nondegenerate four‐wave mixing in photorefractive GaAs/AlGaAs quantum wells. The pump and probe laser wavelengths are absorbed in spatially separated regions of the multilayer structure. The photoconductivity of a probe beam around 840 nm is confined to the GaAs quantum wells and cannot easily erase the trapped space‐charge gratings in the AlGaAs barriers written by an above‐band‐gap HeNe laser at 633 nm. This allows a weak visible control beam to modulate a strong infrared signal beam.

ISSN:0003-6951    

DOI:10.1063/1.105012

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Twenty‐element near‐resonant AlGaAs/GaAs arrays of antiguides have been optimized for maximum intermodal discrimination and large Strehl ratio. It is found that 1000‐&mgr;m‐long devices with two intracavity Talbot‐type spatial filters, and a 3 to 1 ratio between element core and interelement spacing provide the best results. The intermodal discrimination is discussed for both Talbot and uniform devices. For devices with two Talbot‐type spatial filters, diffraction‐limited‐beam operation is obtained to 1 W pulsed power, and operation in a beam with lobewidth 1.5× diffraction limit is obtained to 2 W and 19× threshold. cw diffraction‐limited‐beam operation is obtained to 0.5 W, limited by thermal considerations. Uniform devices operate in beams with lobewidth ≊3× diffraction limit to 5 W and 45× threshold. At 5 W total output the coherent uniphase power is 1.6 W, and the coherent power in the main lobe is 0.94 W.

ISSN:0003-6951    

DOI:10.1063/1.105013

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Optical switching in a thermally expanding Si e´talon has been demonstrated. In this experiment a pulsed CO2laser beam is used to heat a Si e´talon and shift the interference fringe of a 1.5 &mgr;m probe beam. It is shown that the switching time can be greatly reduced from ms to &mgr;s by choosing a probe beam of shorter wavelength in an external switching configuration. By aligning one e´talon at switch‐on and another at switch‐off, we have demonstrated a write and erase logic system.

ISSN:0003-6951    

DOI:10.1063/1.105014

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have observed current‐controlled wavelength switching in narrow oxide stripe In0.17Ga0.83As‐GaAs‐Al0.20Ga0.80As strained‐layer single quantum well heterostructure lasers. Laser emission switches from the lowest (n=1) quantized state transition in the quantum well at low currents to the first excited state transition (n=2) at higher currents, with an energy difference of ≊50 meV. For currents near the switching point, we have also observed time‐dependent lasing behavior, with a switch in the laser emission from then=1 to then=2 transition. The order of this temporal switching (fromn=1 ton=2) is opposite that observed in narrow stripe gain‐guided GaAs‐AlGaAs quantum well lasers, due to strong antiguiding in InGaAs lasers, which negates the effect of a thermal guide.

ISSN:0003-6951    

DOI:10.1063/1.105015

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Aluminum oxide thin films were prepared by a low‐temperature atmospheric‐pressure chemical vapor deposition method. The raw material was aluminum 2‐ethylhexanoate, which is nontoxic and easy to handle. At a reaction temperature above 480 °C, an amorphous film can be obtained on glass and silicon (100) substrates. The reaction temperature and the deposition rate are comparable to the corresponding values in the low‐temperature chemical vapor depositions of Al2O3. In addition, the deposition can be carried out in air. Aluminum 2‐ethylhexanoate appears to offer a viable alternative to alkylaluminum, aluminum &bgr;‐diketonate, and alkoxide for low‐temperature Al2O3production.

ISSN:0003-6951    

DOI:10.1063/1.105016

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Computer simulations of unsupported (111), (001), and (011) thin films of gold, using an embedded‐atom‐method potential, demonstrate a direct correlation between the bulk‐surface stress and the film dimensions. The considerably more complex elastic behavior, by contrast, appears to be dominated by the atomic structure of the film surfaces, and not by the stress‐induced anisotropic lattice parameter changes.

ISSN:0003-6951    

DOI:10.1063/1.105017

出版商:AIP    

年代:1991

数据来源: AIP