摘要:

Optical waveguiding LiNbO3film was grown on (001)‐oriented crystalline SiO2substrate by pulsed laser deposition. The film is highly (012) textured and has smooth surface. Its photoluminescence (PL) spectra were obtained by using the 514.4 nm line excitation of Ar+laser, displaying a broad band peaked at 2.2 eV at room temperature and three well‐resolved luminescent bands peaked at 2.3, 2.2, and 2.14 eV at liquid nitrogen temperature with different polarization properties. Spectral analysis indicates that these obtained PL bands arise from the self‐trapped excitons and theE′ defect pairs connected with oxygen vacancies in the LiNbO3film. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117981

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Volume holograms are thermally fixed in a pure and an iron doped potassium niobate crystal through the screening of a photorefractive space‐charge field by a nonphotoactive species at elevated temperature (110 °C). The nonphotoactive species is identified as the hydrogen ion. Fixed holograms are reconstructed at different temperatures. A diffraction efficiency of 16% in a 6 mm thick KNbO3:Fe sample is measured. The time constant and activation energy associated with the thermal induced decay of the hologram are determined to be 2.9×10−7s and 0.81 eV for the KNbO3:Fe sample, and 1.35×10−7s and 0.79 eV for the pure KNbO3sample. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117982

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The noise characteristics of a polarization additive pulse mode‐locked erbium‐doped fiber soliton ring laser are examined. Relaxation oscillations are found only when the cw background copropagates with the soliton and not when the soliton operates alone. This observation proves that the mode‐locked pulse stream has a strong self‐stabilization that exempts the soliton from the relaxation oscillations, leading to extremely quiet operation. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117983

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Carrier localization in a disordered potential was studied in type‐I strained Si1−xGex/Si superlattices (SLs) where layer widths have been artificially pseudorandomized. The photoluminescence (PL) intensity under a transverse bias voltage varies monotonically and exhibits a folded increase as the bias is increased as opposed to an ordered SL where only steady drop‐off of PL intensity, symmetric with respect to bias polarity, was observed with increasing field strength. The results indicate that electron and hole wave functions are located spatially apart at zero bias due to disorder‐induced localization. We point out that such a wave‐function displacement is even pronounced for type‐II SL potentials in the presence of monolayer thickness fluctuation. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117984

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Experimental studies of InAs heterostructures illuminated by far‐infrared (FIR) radiation reveal an abrupt increase in the charge density for FIR intensities above a threshold value that rises with increasing frequency. We attribute this charge density rise to interband impact ionization in a regime in which &ohgr;&tgr;m∼1, where &tgr;mis the momentum relaxation time, andf=&ohgr;/2&pgr; is the FIR frequency. The dependence of the density rise on the FIR field strength supports this interpretation, and gives threshold fields of 3.7–8.9 kV/cm for the frequency range 0.3–0.66 THz. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117842

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A technique for measuring optical pulses, using heterodyne autocorrelation rather than a nonlinear process, is proposed. This method gives not only the pulse width, but also information about optical phase in a simple way. Practical measurement is demonstrated with linearly chirped weak optical pulse train from an actively model‐locked external‐cavity semiconductor laser. Pulse width and chirp are quantified. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117843

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The potential of optical near‐field photocurrent spectroscopy for analyzing microscopic aging processes in optoelectronic devices is demonstrated. The technique combines the subwavelength spatial resolution of near‐field optics with tunable laser excitation, allowing for selective investigation of specific parts of the device structure. Experiments on GaAs/(AlGa)As high power laser diodes before and after accelerated aging provide direct visualization of defect growth within thep‐i‐njunction and information on aging‐enhanced recombination processes close to the laser facet. The effect of wave guiding of the exciting light on the image formation is discussed. The nondestructiveness makes this technique a particularly attractive method forinsituanalysis in high power laser diodes. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117844

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A multiple cross switching phenomenon is observed in a two‐mode semiconductor laser in an external cavity. Its physical origins are investigated. The changing temperature or injection current causes the variation of the refractive index and the length of the laser diode, leading to the shift of the modulated gain peaks of the anti‐reflection‐coated laser diode in the external cavity. Consequently, the two modes experience different gains periodically and the strong gain competition then leads to the multiple cross switching. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117845

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have used multilayer mirror optimization methods to enhance the coupling of pump light into vertical‐cavity surface‐emitting lasers (VCSELs). With previously reported devices, pump light was coupled into VCSEL cavities through interference notches in the mirror reflectance spectrum. This approach is sensitive to temperature dependent reflectance spectrum shifts. We have created devices with a wide pump‐band window of low reflectance. We report the simulation, growth, and optically pumped lasing of such optimized low‐ripple VCSELs. Further, broadband pump windows open the possibility of spectrally‐broad optical pumps and they eliminate need for costly tunable pump lasers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117846

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a 3×3 surface‐normal wavelength‐selective crossbar using polymer‐based volume holograms. A prototype device is demonstrated using the center wavelength of 775 nm and &Dgr;&lgr;=10 nm. Employment of 1/4‐pitch graded‐index rod lenses reduces the required nine wavelengths to three while maintaining the 3×3 interconnects. The diffraction efficiencies of 75%, 83%, and 75% are experimentally confirmed for wavelength 765, 775, and 785 nm, respectively. Surface‐normal configuration eliminates the conventional edge‐coupling scheme which is vulnerable in a harsh environment. A 3×3 crossbar is demonstrated with a two‐way system insertion loss less than 3 dB and channel‐to‐channel cross talk less than 20 dB. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117847

出版商:AIP    

年代:1996

数据来源: AIP