摘要:

We describe measurements of dynamic wavelength shift in single mode vertical cavity surface emitting lasers operating at 850 nm. Small signal modulation experiments yield a linewidth enhancement factor 3.7<&agr;<4.5, depending on the modulation frequency. Under large signal modulation we measure &Dgr;&ngr;×&Dgr;&tgr;∼3.6 for gain switched pulses. The dependence of dynamic chirp on the pulse width is accurately modeled by numerical solution of rate equations. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113390

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A unipolar cascade laser operating at 8.4 &mgr;m wavelength is reported. The structure, grown by molecular beam epitaxy in the AlInAs/GaInAs material system, contains a 25‐stage coupled‐quantum‐well active region. The waveguide design is optimized to enhance optical confinement and reduce losses associated with the interface plasmon mode, by taking advantage of the dispersion of the refractive index of the contact layer near the plasma frequency. The peak optical power is 30 mW and the threshold current density 2.8 kA/cm2, at a heat‐sink temperature of 100 K and the highest operating temperature is 130 K. The slope efficiency at 100 K is ∼0.1 W/A, corresponding to a differential quantum efficiency of 5.4% per stage. This work, combined with previous results on shorter wavelength quantum cascade lasers, demonstrates that the wavelength of these new light sources can be tailored over a wide range by changing the active layers’ thicknesses using the same materials. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113391

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The scanning near‐field optical microscopy imaging of specimens in liquid and of cultured cells in aqueous solutions is reported. A scanning near‐field optical/atomic‐force microscope (SNOM‐AFM) was developed, in which the scanning of an optical‐fiber probe cantilever over the specimen was controlled by noncontact mode AFM (dynamic mode AFM). This imaging mode reduces damage to the probe and soft specimens. The resonant frequency of the probe cantilever decreased 20% to ≊14 kHz and theQfactor decreased by a factor of 8 to ≊30 in water, compared with these values in air, which was sufficient to perform SNOM‐AFM imaging in liquid. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113392

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A model is proposed for the kinetics of photoinduced defects and the photorefractivity in germanosilicate fibers. It is based on the existence of short lived large energy fluctuations which produce transient traps for carriers that release their energy and enhance defects creation. The enhancement of the photorefractivity with the presence of hydrogen is explained as a result of two mechanisms, that involve the increase in the number of weak bonds and the stabilization of the created defects. In some special cases analytic solutions are found that explain reasonably well the experiments. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113393

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The optimized structure for the InGaAsP/GaAs quaternary material lasers (&lgr;=0.808 &mgr;m) is investigated for the most efficient high‐power operation through an experiment and theoretical study. A comparative study is performed of threshold current densityJthand differential efficiency &eegr;ddependence on cavity length (L) for two different laser structures with different active layer thickness (150 and 300 A˚) as well as for laser structures with different multiple quantum well structures. A theoretical model with a more accurate formulation for minority leakage phenomenon provides explanation for the experimental results and sets general optimization rules for other lasers with similar restrictions on the band gap and refractive index difference between the active layer and the cladding layers. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113394

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have fabricated a two‐dimensional photonic band structure based on macroporous silicon with individual gaps for both polarizations in the infrared region between 250 and 500 cm−1(20–40 &mgr;m). A square lattice of circular air rods with a lattice constant of 8 &mgr;m was etched 340 &mgr;m deep in ann‐type silicon substrate by electrochemical pore formation in hydrofluoric acid. The transmission spectra between 50 and 650 cm−1were in good agreement with the theoretical calculated structure. The pore formation technique should allow the fabrication of photonic lattices with a complete two‐dimensional band gap in the middle and near infrared. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113395

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a method to determine the dielectric relaxation time using a phase‐modulation technique. The predictions were checked using a GaAs crystal. The experimental results agree well with the theory. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113396

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Imaging of topography and locally induced photoluminescence of anodically etched porous silicon is performed using a force regulated near field scanning optical microscope. The photoluminescence signal on as‐prepared wafers shows strong evidence for inherent, rather than purely geometrically induced, variations. Images of small particles display distributions of regions of relatively strong luminescence on the 100 nm lateral scale. Highly localized photoluminescence spectra obtained on these particles show spectral shifts as high as 50 nm compared with those obtained on as‐prepared porous silicon wafer. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113397

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe a single frequency, unidirectional erbium fiber ring laser. Wavelength selection is performed by a ‘‘continuous fiber’’ filter of the fiber to planar waveguide coupler type. Varying the refractive index experienced by the exposed surface of the filter allowed the single longitudinal mode output from the laser to be tuned, discretely, from 1556–1561 nm with a resolution limited linewidth of 52 kHz. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113398

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This letter investigates the effects of band‐structure, band‐filling, and many‐body interactions on the temperature behavior of a vertical‐cavity surface‐emitting laser. Significant improvement in temperature stability of the laser output is predicted in the presence of gain arising from high lying quantum well subbands. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113399

出版商:AIP    

年代:1995

数据来源: AIP