GaAs Waveguide Research Articles

The optical gain and radiative current density of GaInNAs/GaAs/AlGaAs separate confinement heterostructure quantum well lasers

The optical gain and radiative current density of GaInNAs/GaAs/AlGaAs separate confinement heterostructure quantum well (QW) lasers with an emission wavelength of 1.3 μm have been theoretically investigated. The effect of carrier leakage from the GaInNAs QW to the GaAs waveguide layer is studied, and its influence on the optical gain and radiative current density is identified. The hole filling caused by an injected carrier has a strong impact on the optical gain and radiative current density, while the effect of electron filling is negligible, reflecting the smaller band-gap discontinuity in the valence band than in the conduction band. Hole occupation in the waveguide layer decreases the optical gain, and increases the radiative and threshold current densities of the laser. Our calculated threshold current density (659.6 A/cm2) at T=300 K is in good agreement with the experimental value (650.9 A/cm2) reported in literature [R. Fehse et al., IEEE J. Sel. Top. Quantum Electron. 8, 801 (2002)].

Characterization and analysis of two-dimensional GaAs-based photonic crystal nanocavities at room temperature

This paper describes the design and fabrication process of a two-dimensional GaAs-based photonic crystal nanocavity and analyzes the optical characterization of cavity modes at room temperature. Single InAs/InGaAs quantum dots (QDs) layer was embedded in a GaAs waveguide layer grown on an Al 0.7Ga 0.3As layer and GaAs substrate. The patterning of the structure and the membrane release were achieved by using electron-beam lithography, reaction ion etching, inductively coupled plasma etching and selective wet etching. The micro-luminescence spectrum is recorded from the fabricated nanocavities, and it is found that some high-order cavity modes are clearly observed besides the lowest-order resonant mode is exhibited in spite of much high rate of nonradiative recombination. The variance of resonant modes is also discussed as a function of r/ a ratio and will be used in techniques aimed to improve the probability of achieving spectral coupling of a single QD to a cavity mode.

Near Field Imaging of a GaAs Photonic Crystal Cavity and Waveguide Using a Metal Coated Fiber Tip

We report optical near field characterization of a GaAs photonic crystal waveguide which is side coupled to a nano cavity. We observe the effect of the metal coated probe on the resonance wavelength and the intensity distribution. The measurements fit well to finite difference time domain simulations.

55 W peak power from 1100 nm wavelength 60 µm broad-area laser diodes enabled by reduced carrier accumulation in the waveguide

Optical power from 1100 nm broad-area laser diodes is found to be limited by the accumulation of minority carriers in the waveguide layer, caused by a small effective barrier between the quantum wells and the GaAs waveguide. This effect is visible as enhanced spontaneous emission at high currents. We show that increasing the number of QWs mitigates this effect and leads to higher emitted powers. Optimized devices deliver more than 55 W per 60 µm stripe width under 300 ns pulse operation. In this paper we present the experimental results of our study.

DIRECT IMPRINTING OF SiO2 WAVEGUIDE STRUCTURES ON GaAs AND ITS APPLICATION IN InAs/GaAs QUANTUM DOT INTERMIXING

A novel approach for intermixing of InAs / GaAs quantum dot (QD) structure by direct imprinting of SiO 2 strips using silicafilm is presented. The silicafilm SiO 2 strips were imprinted on a InAs / GaAs QD structure by an Obducat nanoimprinter using a polyethylene terepthalate soft mold. Inductively coupled plasma etching of GaAs waveguide structures using the imprinted SiO 2 strips as hard mask has been demonstrated. By using the silicafilm SiO 2 as a capping layer, the effects of impurity-free vacancy disordering intermixing on optical characteristics of the InAs / GaAs QD structure have been examined. The measured photoluminescence spectra of the InAs / GaAs QD structure suggest that differential wavelength blueshift of up to 105 nm for region with and without the SiO 2 film can be achieved. A cost effective one step SiO 2 hard mask with graded thickness profile for quantum well or QD intermixing by imprinting technique is proposed for application in broadband lasers and superluminescent diodes.

High-power laser diodes emitting light above 1100 nm with a small vertical divergence angle of 13°

Laser diodes with highly strained InGaAs quantum wells, emitting at 1130 nm, embedded in a GaAs waveguide were investigated. This Letter reviews the design of the vertical structure for enclosing high output power in angles smaller than 18 degrees . Example designs were processed to 200 microm stripe-width lasers with an 8-mm-long optical cavity. When these are mounted on C mounts, they give an output power of 38 W under quasi-cw operation from a single emitter.

High-Q factor single mode circular photonic crystal nano-resonator

In this work, the analysis, fabrication and optical characterization of a two-dimensional circular photonic crystal (2D-CPC) nano-resonator based on an air/GaAs/air slab waveguide are presented. Four InAs/InGaAs quantum dots (QDs) stacked layers emitting around 1300 nm at room temperature were embedded in a GaAs waveguide layer grown on an Al0.7Ga0.3As layer and GaAs substrate. The patterning of the structure and the membrane release were achieved by using electron beam lithography, ICP plasma etching and selective wet etching of the AlGaAs sacrificial layer. The micro-luminescence spectrum recorded from the fabricated nano-cavity shows a narrow optical transition at the resonance wavelength of about 1282 nm with a FWHM and Q-factor of 6.2 Å and more than 2000, respectively.

Enhanced In(Ga)As∕GaAs quantum dot based electro-optic modulation at 1.55μm

The authors report a study of the linear electro-optic coefficient in waveguides containing InGaAs∕GaAs quantum dots with a band gap at 1.3μm. The Pockels effect is investigated in the 1.55μm telecommunication window. The measured linear electro-optic coefficient for InGaAs∕GaAs is ∼3.4×10−11m∕V, much higher than that of the bulk or quantum well material. An ∼35% enhancement of the phase variation is achieved compared to that obtained in bulk GaAs waveguides. Finally, a spectral bandwidth of ∼100nm is demonstrated in the 1.5–1.6μm window.

Quantum dot nano-cavity emission tuned by a circular photonic crystal lattice

In this work the analysis, fabrication and optical characterization of a circular two-dimensional photonic crystal (2D-CPC) nano-resonator based on a air/GaAs/air slab waveguide are presented. Four InAs/InGaAs quantum dots (QDs) stacked layers emitting around 1300 nm were embedded in a GaAs waveguide layer grown on an Al 0.7Ga 0.3As sacrificial layer. The nano-resonator was realized by drilling 2D-PC air holes arranged in a circular lattice configuration through electron beam lithography (EBL), inductively coupled plasma (ICP) etching and wet selective etching of the Al 0.7Ga 0.3As sacrificial layer in order to release the membrane. The spectral response of the active circular nano-cavity has been simulated by using a three dimensional finite-difference time-domain method (3D-FDTD) as a function of both the inner and outer holes radius/period ratios of the photonic crystal structure. Good agreement between the calculated resonance and the experimental results, recorded from the nano-cavity by a μPL setup, has been achieved.

InGaAs/GaAs QD-based electro-optic modulator with over 100 nm bandwidth at 1.55 µm

The potential of an InGaAs/GaAs quantum-dot-based phase modulator for broadband (>100 nm) applications at 1.55 µm is demonstrated. A ∼35% enhancement of the phase variation (Vπ ∼ 3.5 V for 4 mm-long devices) is achieved compared to that obtained with bulk GaAs waveguides.

The intrinsic frequency response of 1.3-/spl mu/m InGaAsN lasers in the range T=10/spl deg/C-80/spl deg/C

Optical modulation response experiments above threshold are carried out in ridge waveguide InGaAs and InGaAsN (N=0.5%) in a temperature span of 10 degC-80 degC. The modulation traces are analyzed with a complete rate equation model that allows extraction of the resonance frequency and damping that are intrinsic to the carrier and photon processes occurring in the laser active region. This analysis enables calculation of the K-factor and its temperature behavior. K-values for InGaAsN lasers are larger and show a more pronounced dependence on temperature than in InGaAs lasers. This behavior is ascribed to a decrease in the effective differential gain with nitrogen content

Fabrication and Characterization of Molecular Beam Epitaxy Grown Thin-Film GaAs Waveguides for Mid-Infrared Evanescent Field Chemical Sensing

Thin-film GaAs waveguides were designed and fabricated by molecular beam epitaxy for use in mid-infrared (MIR) evanescent field liquid sensing. Waveguides were designed to facilitate the propagation of a single mode at a wavelength of 10.3 microm emitted from a distributed feedback quantum cascade laser, which overlaps with molecular selective absorption features of acetic anhydride. The characterization of the waveguides shows transmission across a broad MIR band. Evanescent field absorption measurements indicate a significant sensitivity enhancement in contrast to multimode planar silver halide waveguides.

THz sideband generation at telecom wavelengths in a GaAs-based quantum cascade laser

Terahertz sideband generation is demonstrated by using the nonlinear intracavity interaction between far-infrared and near-infrared modes in a GaAs waveguide. A low power near-infrared beam at 1.32μm is coupled into a quantum cascade laser operating at 104μm (2.9 THz), which acts as both the THz source and the nonlinear medium. The conversion efficiency of the resulting sidebands is found to be approximately 4.5×10−6.

High-power highly strained InGaAs quantum-well lasers operating at 1.2 μm

High-power highly strained In/sub x/Ga/sub 1-x/As quantum-well lasers operating at 1.2 μm are demonstrated. The edge emitting broad area (BA) laser diode structures are grown by metal organic vapor phase epitaxy at low growth temperatures using trimethylgallium, trimethylindium, and arsine sources. In the laser structure, an InGaAs QW is sandwiched between the GaAs waveguide and AlGaAs cladding layers. The operating wavelength for the laser diode at room temperature (20/spl deg/C) is about 1206 nm, which redshifts to 1219 nm at 46/spl deg/C. The transparency current density for the BA laser diodes is as low as 52 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the characteristic temperature value is 76 K. High-power laser operation in the pulse mode (about 1.6 W) at room temperature was achieved.

Ferromagnetic resonance and microstructural studies of Ag/Fe–GaAs waveguide structures

We report the growth and characterization of ferromagnetic iron/silver (Ag/Fe) multilayer structures on gallium arsenide (GaAs) (100) substrates by molecular beam epitaxy. The samples have been characterized by x-ray diffraction and ferromagnetic resonance (FMR) techniques. X-ray read-camera studies have demonstrated the epitaxial nature of crystalline Fe film grown on GaAs substrate, while x-ray rocking curve measurements reveal a narrow linewidth of only 0.3°. On the FMR technique, we focused specifically on the information contained in FMR linewidth ΔH(f ). Experimental results on ultrathin Fe/Ag films have been obtained with sufficient resolution to measure the linewidth broadening due to intrinsic damping. FMR linewidth is resolved to vary between 0.5 and 1.1 GHz in a frequency range of 20 GHz. Frequency-dependent FMR linewidth ΔHpp(ω) shows a typical linear dependence with a zero frequency offset ΔH(0) of almost zero value, indicating a near-perfect crystalline quality of the deposited magnetic film. The Gilbert damping parameter G is extracted to be 1.45×108 s−1 from the slope of the curve.

Fabrication of ferromagnetic/semiconductor waveguide structures and application to microwave bandstop filter

We studied the propagation of a microwave signal in Fe/Ag–GaAs waveguide structures. In an ultrahigh frequency ferromagnetic resonance measurement, maximum coupling and thus strong attenuation of the microwave power occur near the ferromagnetic resonance frequency fres of Fe film. Magnetostatic wave (MSW)-based microwave devices have been achieved in the form of a bandstop filter utilizing single crystal Fe/Ag structures grown on GaAs (100) substrate. MSW-based microwave devices possess the unique capability of electronically tunable operating carrier frequency via a magnetic field. The peak absorption frequency for an Fe easy axis case has been tuned in a range from 10.6 to 36 GHz. For a hard axis case, the tuning frequency ranges from 8 to 22 GHz. The experimental results show that Fe/Ag–GaAs waveguide structures are very promising systems for use in future microwave magnetoelectronics as they have well-defined magnetic properties, as well as favorable electrical properties.

Effect of growth conditions and strain compensation on indium incorporation for diode lasers emitting above 1050 nm

Diode lasers with an emission wavelength of up to 1150 nm have been grown by metalorganic vapor-phase epitaxy (MOVPE). For the growth of the highly strained InGaAs/GaAs quantum wells low growth temperatures are found favorable to suppress defect formation. An incorporation of GaAsP strain compensating layers reduces indium carry-over effects but the defect formation in the InGaAs quantum well starts at lower indium content. At high TMIn/(TMIn+TMGa) ratio in the vapor phase no temperature dependence of indium incorporation efficiency was obtained. Broad-area (1 mm long, 100 μm wide) diode lasers using such QWs in GaAs waveguide and AlGaAs cladding layers show very low threshold current densities ( jth=93 A/cm 2 at 1102 nm and jth=85 A/cm 2 at 1152 nm). Ridge-waveguide diode lasers (750 μm long, 3 μm wide) with a low threshold current of 9 mA and an efficiency of more than 90% were fabricated.

Improved catastrophic optical mirror damage levelinInGaAs/AlGaAs laser diodes

9.2 W continuous wave (CW) optical power at a heatsink temperature 10°C and 12.2 W in a regime with stabilised temperature of the laser chip is demonstrated from a 100 µm aperture InGaAs/AlGaAs (λ = 1.03 µm) laser diode with 0.4 µm wide GaAs waveguide. Thus, record-high optical power densities of 30 MW/cm2 and 40 MW/cm2 correspondingly are achieved at the front facet without catastrophic optical mirror damage (COMD).

BAND GAP RESONANT FEMTOSECOND PULSE PROPAGATION IN NONLINEAR DISPERSIVE SEMICONDUCTOR WAVEGUIDES

A detailed numerical analysis has been made for a femtosecond not-too-strong Gaussian pulse propagating through a millimeter size GaAs waveguide. The role of weakly bound 1s-excitonic structure below the fundamental absorption edge has been incorporated in the time dependent perturbation treatment of the coherent pulse-semiconductor interaction. The analysis reveals the occurrence of both self-steepening and spectral broadening arising due to the inherent intensity dependence of the complex optical susceptibility in GaAs waveguide structures.

180 mW DBR lasers with first-order grating in GaAsemitting at 1062 nm

Distributed Bragg reflector (DBR) lasers emitting at 1062 nm using a first-order grating fabricated by holographic lithography in a GaAs waveguide layer have been realised for the first time. At room temperature the DBR lasers show excellent characteristics with a monomode output power of 180 mW at 300 mA.