摘要:

We investigate electrical wavelength tuning of a cavity length dispersive fiber ring laser operated in the 1/2-rational harmonic mode-locking condition. By changing the modulator frequency around the optimum mode-locking frequency, a tuning range of 10.45 nm with a tuning rate of 0.067 nm/kHz is achieved. The repetition rate of the mode-locked pulses is twice the modulation frequency (∼1 GHz) and the extinction ratio of the laser spectrum during the full tuning range is above 30 dB. Compared with the conventionally harmonic mode locking, the tuning range is about half reduced but the tuning rate has a same value. The variation of the modulation frequency and the length of the dispersion compensation fiber has a same effect on the wavelength tuning as in the case of conventionally harmonic mode-locking. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122811

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A unipolar injection quantum cascade (QC) laser grown in an AlGaAs/GaAs material system by molecular beam epitaxy, is reported. The active material is a 30 period sequence of injectors/active regions made fromAl0.33Ga0.67As/GaAs-coupled quantum wells. For this device a special waveguide design, which complies with a GaAs heavily doped substrate and very shortAl0.90Ga0.10Ascladding layers, has been optimized. At a heat-sink temperature of 77 K, the laser emission wavelength is 9.4 &mgr;m with peak optical power exceeding 70 mW and the threshold current density is 7.3 kA/cm2. The maximum operating temperature is 140 K. This work experimentally demonstrates the general validity of QC laser principles by showing laser action in a heterostructure material different from the one used until now. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122812

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The electro-optic effect in helical ferroelectric liquid crystal deformed by transverse electric field is exploited to realize a diffraction-based light modulator. Experiments show that a contrast ratio better than 100:1 is easily achievable for the short-pitch liquid crystal aligned homeotropically with oblique readout breaking the initial symmetrical geometry. The modulation obtains low polarization sensitivity for selected directions of the readout. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122813

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Low thresholds (∼500 W/cm2) for amplified spontaneous emission (ASE) are reported in films of soluble poly(paraphenylene vinylene)-based conjugated polymer blends. Efficient Fo¨rster energy transfer from the absorbing host polymer to the emitting guest polymer is observed. Emission in the blends originates predominantly from the guest polymer. The large spectral shift between the absorption and emission wavelengths lowers the self-absorption losses and results in low ASE thresholds. Initial results show an enhancement in photoluminescence quantum efficiency of the blends. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122814

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Rough surfaces are proposed as a class of couplers for achieving high absorption in broadband quantum-well infrared photodetectors (QWIPs). The performance of these structures is predicted numerically using the steepest-descent fast-multipole method, a recently developed fast electromagnetic analysis technique. This method permits the efficient and accurate solution of the electric-field integral equation governing scattering from a quasiplanar structure. The scattered optical electric-field component along the growth direction at the device layer can be used to predict the QWIP absorption. It is demonstrated that rough-surface couplers exhibit very high absorption sustained over large spectral ranges, in contrast to quasirandom or periodic gratings that are characterized by tradeoffs between peak absorption and spectral range. It is expected that the excellent spectral absorption characteristics of rough-surface couplers will make them particularly suitable for broadband QWIP applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122815

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Time-resolved surface scattering imaging was performed for liquid benzyl chloride and liquid toluene under femtosecond KrF laser ablation conditions. No scattering image was obtained until 1 ns, while scattering started from 2 ns when the laser fluence exceeded25 mJ/cm2,and its intensity increased with the passage of time. The higher the laser fluence was, the steeper the increasing slope was. The scattering is due to surface roughness, which is the initial stage of macroscopic morphological changes. Root-mean-square surface roughness was estimated from the scattering intensity by using frosted fused-silica plates as reference samples. The induced surface roughness increases to a few hundred nm in 10 ns. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122816

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The identification of lasing modes in vertical-cavity surface-emitting lasers (VCSELs) is usually based on the polarization-resolved near-field pattern identification, a method difficult to apply in the presence of multiple transverse modes. We study lasing modes of a multitransverse mode index-guided VCSEL under dc pumping conditions by considering in detail the modes’ spectral positions. The experimentally observed spectra are compared with theoretical calculations, based on a recently developed method for vectorial VCSEL eigenmodes [D. Burak and R. Binder, Appl. Phys. Lett.72, 891 (1998)]. This allows for the identification of transverse lasing modes as a function of the pumping current. Two main effects that influence the spectral characteristics of the VCSEL are considered in our approach: temperature-induced linear shift of lasing wavelengths with increasing pumping current and switching of the lasing mode between different eigenmodes of the VCSEL cavity. The obtained temperature-dependent shift of the lasing frequencies agrees reasonably well with the value known from previous experimental estimations. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122817

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The monolithic integration of a SiGe/Si rib waveguide modulator and multiple quantum well photodetector prepared by molecular beam epitaxy is achieved. The low dark current of 49.8 nA at −5 V reverse bias is measured and a modulation depth of 90&percent; at 2.8 V modulation bias is obtained. The external quantum efficiency at&lgr;=1.55 &mgr;mis estimated to be 18.2&percent;. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122818

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report the observation of inhibited spontaneous emission of organic dye rhodamine 6G infiltrated in a polymer replica of synthetic opal as a photonic crystal. The morphology-dependent resonances, superimposed on the broadband emission of rhodamine 6G due to spherical wavelength-sized microcavity enhancement of dye emission, have also been observed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122819

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We study the near-field and the angular distribution of radiation resulting from the scattering of surface plasmon polaritons from a surface defect by means of numerical calculations based on the use of the impedance boundary condition. Maximum reflection (plasmon mirrors) is found for half widths on the order of the inverse of the surface plasmon wavevector, either protuberances or indentations, as predicted by a perturbation-theoretic argument. Maximum radiation (light emitters) occurs for wider protuberances, with coupling efficiencies beyond 80&percent;. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122820

出版商:AIP    

年代:1998

数据来源: AIP