摘要:

This article reviews our recent works on frequency control of semiconductor lasers. The magnitudes of quantum noise limited frequency modulation (FM) noise, realized by the negative electrical feedback, are given for four methods of using an external Fabry–Perot cavity as a frequency demodulator. It is shown that the theoretical expression for the quantum noise‐limited FM noise of the feedback laser contains a factor of 1/8 as compared with that of the free running laser, which is due to the different ways of injecting the vacuum fluctuations to the laser cavity and to the external Fabry–Perot cavity for negative electrical feedback. The FM sideband technique is shown to be an effective method to reject the contribution of laser power fluctuations to the FM noise detection for the negative electrical feedback system. As a candidate for a high reflectivity and frequency selective external reflector for the optical feedback, characteristics of the semiconductor laser as a phase conjugate mirror, i.e., the characteristics of the nearly degenerate four‐wave mixing and the nondegenerate four‐wave mixing in a semiconductor laser, are shown. Optical feedback by using a velocity selective optical pumping and polarization spectroscopy of an atomic vapor is proposed as an effective method to realize simultaneously the center frequency stabilization and linewidth reduction of the field spectrum of the laser, and also the fine detuning of the stabilized center frequency.For the heterodyne frequency locking between two lasers, a spectroscopic method of using a Doppler‐free spectrum of the three‐level atomic vapor, obtained by using the phenomenon of coherent population trapping, is shown. In order to realize a highly efficient nonlinear optical frequency conversion for wideband frequency sweep of semiconductor lasers, a method of adding the output powers of several lasers, i.e., the coherent addition, is presented. After emphasizing that the wideband frequency sweep (covering from the near‐infrared to the visible region) can be realized by using the techniques of nonlinear optical frequency conversions and the optical phase locking, relevant experimental results of nonlinear optical frequency conversions are presented which are the second harmonics generation, sum and difference frequency conversions. A highly accurate optical frequency measurement system is proposed using an optical frequency comb generator with a modulation sidebands up to several THz. Performances of the optical frequency comb generator used for this system are presented. As a candidate for an ultrafast and wavelength insensitive photodetector for optical frequency counting, nonbolometric optical response characteristics of a high transition temperature (Tc) oxide superconducting film are demonstrated.  

ISSN:0021-8979    

DOI:10.1063/1.353354

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The complex refractive index of SiGe alloys at 632.8 nm has been measured as a function of the Ge concentration usinginsituellipsometry while the material is slowly removed from a silicon substrate using reactive‐ion etching (RIE). Homogeneous, strained epitaxial SiGe films on silicon substrates were used. The Ge concentration was obtained by Rutherford backscattering. If an unknown SiGe structure is etched with RIE,insituellipsometry yields combinations of the ellipsometric angles &PSgr; and &Dgr; with time. Starting at the Si substrate, these points are, on a point‐to‐point basis, converted into combinations of complex refractive index and depth in a numerical procedure. For this inversion of the ellipsometry equations, the known relation between the real and the imaginary part of the refractive index of SiGe is used. Finally the refractive indices are converted into Ge concentrations. Thus the depth profile of the Ge concentration in an unknown epitaxial SiGe structure can be inferred from aninsituellipsometric measurement during RIE of the unknown structure. The obtained resolutions in depth and Ge concentration are 0.3 nm and 0.3%, respectively.

ISSN:0021-8979    

DOI:10.1063/1.353916

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The influences of cladding layer thicknesses on the performance of strained‐layer InGaAs/GaAs graded‐index separated confinement heterostructure quantum well lasers have been studied. The waveguiding property of the laser structure was analyzed using the transfer matrix method. In this work, experimental results and the calculated results showed that threshold current densities and external quantum efficiencies both were crucially dependent on the thicknesses of cladding layer for both single and multiple quantum well lasers. The minimum cladding layer thicknesses needed to maintain low threshold current densities and low internal total loss for both single and multiple quantum well devices were determined experimentally and theoretically.

ISSN:0021-8979    

DOI:10.1063/1.353917

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We theoretically calculate the line shapes of the third order, the cascaded third order, and the fifth order nonlinear processes in a femtosecond time‐resolved four‐wave mixing experiment. On the basis of the calculations, experimentally we distinguish the wavelength dependent contributions to the direct fifth order process and the cascaded third order process in bulk GaAs. Our results show that the cascaded process dominates at wavelengths near band gap resonance; however the direct process dominates away from resonance. The nonlinear susceptibilities &khgr;(3)and &khgr;(5)are also obtained.

ISSN:0021-8979    

DOI:10.1063/1.353918

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nonlinear optical properties of CdSe quantum dots are investigated using self‐saturation and degenerate four‐wave mixing techniques. The saturation of the room temperature absorption coefficient, for a wavelength in the vicinity of the first exciton peak, is measured. The measured data can be predicted from a description of the quantum dot as a two level, homogeneously broadened, saturating system. The variation of the four‐wave mixing reflectivity with intensity and with wavelength is reported. All four‐wave mixing data are also consistent with the homogeneously‐broadened two‐level model.

ISSN:0021-8979    

DOI:10.1063/1.353919

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The dynamics of the green (2H11/12,4S3/2) and red (4F9/2) upconversion emission excited by 15 ns pulses from an Er:fibre laser at 1500 nm are presented and analyzed. The upconversion process is found to fit a kinetic model, which includes both cross relaxation and energy transfer.  

ISSN:0021-8979    

DOI:10.1063/1.354092

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The dynamics of photorefractive diffraction in paraelectric KTa1−xNbxO3crystals during writing, reading, and erasing have been studied systematically. Experimental observations related not only to the diffraction from the first‐order photorefractive grating but also to that from the second‐order photorefractive grating, and where a writing beam with spots smaller than, as well as larger than, the entrance surface of the crystal was used. All the complicated behaviors observed have been explained qualitatively. An electron‐hole transport model and a nonequilibrium screening model have been applied, and the existence of an internal dc electric field induced during writing simultaneously by an optical field and an externally applied field has been suggested and demonstrated. The significant influence of this induced field is indicated.

ISSN:0021-8979    

DOI:10.1063/1.353920

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The high‐pressure atomic Ne laser operates on four visible transitions between the 3pand 3smanifolds. Oscillation at 585 nm (3p’[1/2]0→3s’[1/2]10) at efficiencies of ≳1% have been demonstrated by others. The upper laser level is believed to be populated by dissociative recombination of Ne2+, while state‐selective Penning reactions relax the lower laser levels. To investigate these pumping mechanisms, experimental and modeling studies have been performed on a short pulsee‐beam excited Ne laser using He/Ne/Ar mixtures. We found that the electron temperature in the afterglow following thee‐beam pulse largely determines the time at which oscillation starts. The electron temperature during the afterglow is partly controlled by a slow relaxation of excited states in Ar. Laser oscillation does not occur until these manifolds are depleted and the electron temperature decreases, thereby increasing the rate of dissociative recombination.

ISSN:0021-8979    

DOI:10.1063/1.353921

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In this article we present a study of a new class of optical fibers based on lead germanate glass. The maximum vibrational frequency of this glass is intermediate between silica and zirconium barium lanthanum aluminum fluoride glass, causing a beneficial change in nonradiative decay and therefore quantum efficiency for particular laser transitions. Fabrication of high‐strength, low‐loss fibers of this glass has been acheived by modification of the composition to produce optimal physical properties for fiber drawing, while retaining the useful vibrational properties of the original PbGeO2glass. Measurements of both the thermal and optical properties are described. The fibers produced are ideal for many applications in fiber devices.

ISSN:0021-8979    

DOI:10.1063/1.353922

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Nanosecond optical Kerr‐effect (OKE) measurements are reported using a modified apparatus, designed to enable rapid and precise data recording in pure liquids. Careful design of the apparatus enables measurements to be made at several inducing wavelengths without substantial apparatus modifications. The first measurement of the optical Kerr effect for benzene at an inducing wavelength of 532 nm is presented together with novel OKE data for the hitherto unstudied homologous alcohol series from methanol to 1‐dodecanol. Analysis of the results indicates for this series the existence of a linear relationship between the carbon chain length and the optically induced Kerr constant somewhat similar to the behavior previously observed in then‐alkanes.

ISSN:0021-8979    

DOI:10.1063/1.353923

出版商:AIP    

年代:1993

数据来源: AIP