Cross-sectional scanning tunneling microscopy and spectroscopy of strain in buried heterostructure lasers

Cross-sectional scanning tunneling microscopy and spectroscopy have been used to probe the unreconstructed (1 1 0) surface of a commercially available buried heterostructure laser in ultra high vacuum. Complex re-growth above the non-linear blocking layers is shown to induce tensile strain in the device. Spectroscopic measurements show an increase in both the density of filled valence band states and empty conduction band states as a result of the strain, with a particularly large increase at −3.1 V. Current imaging tunneling spectroscopy measurements show an increase in the tunneling current in to and out of the strained regions at both gap voltage polarities, consistent with the spectroscopy. Moving towards tensile strain, InP is known to maintain much the same bandgap, with the split-off level and lower lying states being drawn up towards the valence band edge, consistent with the data.     

A nonlinear circuit model for studying the frequency response in buried heterostructure lasers

An equivalent-circuit model of a semiconductor laser is developed. The model includes diffusion and uses the parabolic gain approximation. It can be applied to various buried heterostructure (BH) devices to simulate optical response characteristics. The values of the circuit elements versus injection current clearly indicate that the parabolic gain approximation and carrier diffusion play an important role in obtaining a more accurate frequency response, especially for (BH) lasers with stripe widths greater than the diffusion length.     

Modes in buried planar optical waveguides with graded-index profiles

The refractive index profile of buried graded-index planar optical waveguides fabricated by ion migration can be described by a buried secant hyperbolic function. Using such a profile, we have obtained the exact propagation characteristics for such buried optical waveguides. We have also shown that profiles which deviate slightly from the above profile can be treated as perturbations and a first-order perturbation correction gives very accurate results.     

Dielectric constant and optical confinement in homostructure PbSnTe diode lasers

The refractive index of PbSnTe is calculated as a function of carrier concentration, wavelength and temperature. The derived values are used in the determination of the electric field distribution and the optical confinement in homostructure Pb_0.85Sn_0.15Te lasers. It is shown that large refractive index steps and efficient optical confinement can be achieved in homostructure lasers having an appropriate carrier concentration profile.     

Direct modulation and optical confinement factor modulation of semiconductor lasers

A method for modulation of semiconductor lasers is demonstrated. The method is based on the modulation of the optical confinement factor. Using this method an enhanced—3-dB bandwidth is observed in agreement with the small signal rate equation analysis. A modulation response that drops at high frequencies slower than the conventional direct current modulation response is achieved. This supports the theoretical predictions, showing an intrinsic 1/f decay rate for the optical confinement factor modulation scheme versus an intrinsic 1/f² decay for direct modulation.     

Direct modulation and optical confinement factor modulation of semiconductor lasers

Abstract

A method for modulation of semiconductor lasers is demonstrated. The method is based on the modulation of the optical confinement factor. Using this method an enhanced—3-dB bandwidth is observed in agreement with the small signal rate equation analysis. A modulation response that drops at high frequencies slower than the conventional direct current modulation response is achieved. This supports the theoretical predictions, showing an intrinsic 1/f decay rate for the optical confinement factor modulation scheme versus an intrinsic 1/f² decay for direct modulation.     

Improved model of optical phonon confinement in silicon nanocrystals

We develop a model for calculating the Raman scattering spectra from phonons confined in for silicon nanocrystals, which is based on the familiar approach taking into account the uncertainty in the quasi-momentum of phonons localized in the nanocrystals. The model is considerably improved by taking into account dispersion of phonons not only in the magnitude of the quasi-momentum, but also in its direction. A significant refinement of the model is also due to the fact that phonon dispersion is calculated using the widely approved Keating model instead of being approximated by empirical expressions as was done in earlier approaches. The calculations based on this model make it possible to determine the sizes of silicon nanocrystals more precisely from analysis of the experimental Raman spectra.     

Improved planar optical branching elements for multimode fibre transmission systems

The optical tapping and fan-out elements which we had previously fabricated for multimode fibre transmission systems all suffered from the serious drawback that the aging of the light-sensitive foil used in our simple planar technology resulted in a deterioration in the performance of structures using such foil as a planar waveguide. This paper introduces improved optical structures in which this drawback has been avoided while stil retaining the simple technique by which high fibre positioning accuracy is assured. In addition the overall insertion loss of the structures has been reduced to about 2 dB for the fan-out structure and 1.2 dB–1.5 dB for the access coupler.     

Strain-tunable electronic and optical properties of h-BN/BC_3 heterostructure with enhanced electron mobility

By using first-principles calculation, we study the properties of h-BN/BC_3 heterostructure and the effects of external electric fields and strains on its electronic and optical properties. It is found that the semiconducting h-BN/BC_3 has good dynamical stability and ultrahigh stiffness, enhanced electron mobility, and well-preserved electronic band structure as the BC_3 monolayer. Meanwhile, its electronic band structure is slightly modified by an external electric field. In contrast,applying an external strain can mildly modulate the electronic band structure of h-BN/BC_3 and the optical property exhibits an apparent redshift under a compressive strain relative to the pristine one. These findings show that the h-BN/BC_3 hybrid can be designed as optoelectronic device with moderately strain-tunable electronic and optical properties.     

Realization of high performance LDA-systems using optical amplifiers, high power semiconductor lasers and optical fiber lasers

Advanced novel techniques for sophisticated LDA applications are presented in this paper. By applying laser sources with high output powers like MOPA-lasers (master oscillator power amplifier), fiber lasers and booster fiber amplifiers to increase the laser power in the measuring volume and by amplifying the scattered light power with optical fiber preamplifiers to increase the sensitivity of the receiving units, the signal-to-noise-ratio of laser Doppler signals is drastically improved and the overall performance of a laser Doppler anemometer is significantly enhanced.     

Technology of the (Al,Ga)As/GaAs double heterostructure lasers

Conclusion Even thqugh the LPE growth of (Al,Ga)As layers is now largely a matter of industrial development or routine, there still remain some problems that need fundamental study. We have pointed to two of them: growth of very thin layers and the influence of ambient atmosphere. The problem of automation of the growth process, while being connected with industrial LPE installations, also has a bearing on the fundamental research, e.g. it is important for reproducible preparation of very thin layers.We did not include in this paper work done in our laboratories in the field of integrated optics. A hybrid combination of DH coherent source with a MESFET GaAs device has been tested; integrated version of this optoelectronic circuit is in preparation.Invited talk at the International Conference on Radiative Recombination and Related Phenomena in III–V Compound Semiconductors, Prague, 4–7 October, 1983.     

Modal analysis of IncGaAsP-InP, GaAs/AlGaAs-GaAs, and InGaAsP/AlGaAs-GaAs MIS heterostructure lasers

The transverse modal behavior of Metal-Insulator (Oxide)-Semiconductor (MIS) heterostructure injection lasers is analyzed. MIS structures have been proposed by Jain and Marciniec as an alternate approach to p-n heterojunctions to obtain minority carrier injection and subsequent lasing action. In the modal analysis the MIS structure is treated as an asymmetrical three-layer slab waveguide with appropriate boundary conditions. Numerical computations of electric field strength, intensity and confinement factor P are presented for various GaAs and InP based MIS structures. A comparison of the output characteristics of a GaAs MIS laser with a conventional GaAs p-n double heterostructure laser is also reported.     

Plasmonically enhanced optical transmission through a metalized nanostructured photonic crystal fiber taper

A subwavelength holey plasmonic structure was proposed by adiabatically tapering a photonic crystal fiber (PCF) and subsequently metalizing the cleaved end facet. By coupling a white light into the PCF side, we experimentally observed an enhanced optical transmission in the spectral domain through the plasmonic structure at the tapered end. We further showed numerically that the proposed device renders a focused directional beam, due to its Fresnel-zone-like configuration and the plasmonic lensing effects.     

Multi-state optical flip-flop memory based on ring lasers coupled through the same gain medium

We investigate a system consisting of multiple ring lasers coupled by a single gain medium. All the ring lasers share a common feedback arm. The output power of an individual laser shows periodic oscillations as a function of time. The periodicity of the oscillation is determined by the ratio of the roundtrip times of the feedback arm and the ring cavity. In the case that two of such ring lasers are coupled, either their oscillation periodicities are synchronized, or the system is bi-stable. In the latter operation regime, the system can act as an optical flip-flop memory whose state be switched by injection of external light. The concept can be extended to multi-state operations; an eight-state optical flip-flop memory is experimentally demonstrated.     

Optical locking of two semiconductor lasers through high-order Brillouin Stokes components in optical fiber

A novel technique for optical injection locking of two semiconductor lasers through high-order Brillouin Stokes components in optical fiber is proposed and experimentally demonstrated. The configuration potentially provides microwave signals generation at manifold Brillouin frequency without high-frequency external modulator and generator. Significant narrowing of the locked slave semiconductor laser linewidth was recorded.     

Point and planar ultraviolet excitation/detection of hydroxyl-radical laser-induced fluorescence through long optical fibers

We demonstrate an all-fiber-coupled, UV, laser-induced-fluorescence (LIF) detection system of the hydroxyl radical (OH) in flames. The nanosecond-pulsed excitation of the (1,0) band of the OH A(2)∑(+)-X(2)Π system at ～283 nm is followed by fluorescence detection from the (0,0) and (1,1) bands around 310 nm. The excitation-laser beam is delivered through a 400 μm core UV-grade optical fiber of up to 10 m in length, and the fluorescence signal collected is transmitted through a 1.5 mm core 3 m long fiber onto the remote detector. Single-laser-shot planar LIF (PLIF) imaging of OH in flames is also demonstrated using fiber-based excitation. The effects of delivering intense UV beams through long optical fibers are investigated, and the system improvements for an all-fiber-coupled OH-PLIF imaging system are discussed. Development of such fiber-based diagnostics and imaging systems constitutes a major step in transitioning laser diagnostic tools from research laboratories to reacting flow facilities of practical interest.     

Kerr-lens, mode-locked lasers as transfer oscillators for optical frequency measurements

We introduce a novel concept for optical frequency measurement and division which employs a Kerr-lens, mode-locked laser as a transfer oscillator whose noise properties do not enter the measurement process. We experimentally demonstrate that this method opens up the route to phase-link signals with arbitrary frequencies in the optical or microwave range while their frequency stability is preserved. Received: 23 July 2001 / Published online: 29 November 2001