Operation Of Laser Diodes Research Articles

Exactness of simplified scalar optical approaches in modelling a threshold operation of possible nitride vertical‐cavity surface‐emitting diode lasers

AbstractModern small‐size vertical‐cavity surface‐emitting diode lasers (VCSELs) require principally fully vectorial optical modelling because their cavity sizes are of the order of the wavelength of emitted radiation. However, much simpler scalar approaches are often surprisingly exact even beyond the limits of their confirmed validity. Therefore, in the present paper, reasonable limits of an application of simplified scalar optical approaches (instead of more exact but also much more involved and time‐consuming rigorous vectorial ones) are determined to model threshold operation of possible nitride VCSELs equipped with tunnel junctions with the aid of a comparison of results of the scalar effective frequency method with those obtained using the fully vectorial three‐dimensional plane wave admittance method. Both these optical methods have been found to give usually quite close results for the fundamental transverse mode. Larger discrepancies between the results of both approaches have been found for first‐order transverse modes (and even larger are expected for higher‐order ones) and for larger (or very small) active regions. Some structural modifications of nitride VCSELs, which may enable their low‐threshold single‐fundamental‐mode room‐temperature continuous‐wave operation, are proposed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Bonding Temperature and Applied Load on the Bonding Integrity and Optical Performance of Face-Down Bonded Ridge-Waveguide Lasers

The effects of bonding temperature and applied load on the mechanical integrity of 80Au-20Sn solder joints and the optical performance of laser diodes (LDs) are presented. Insufficient solder wetting at 280°C and poor joint integrity at an applied load below 0.196 MPa resulted in solder failure during die shear test. As the bonding temperature and applied load increased, the joint integrity and the optical performance improved. Shear testing further showed fracture in the LD due to the high mechanical strength of 80Au-20Sn solder and good adhesion properties of the solder joint. Microstructure studies showed good metallurgical stability with little interfacial intermetallic compound (IMC) formed. However, beyond an applied load of 0.523 MPa, the LD performances degraded due to modification of the bandgap energy in the active region. From our experimentation, a bonding window with good bonding integrity and high optical performance was, nevertheless, achieved.

Infrared spectra of helium clusters seeded with nitrous oxide, HeN4–N2O, with N=1–80

High resolution infrared spectra of HeN-N2O clusters are studied in the 2200 cm(-1) region of the N2O nu1 fundamental band. The clusters are produced in a pulsed supersonic jet expansion from a cooled nozzle source and probed using a tunable diode laser operating in a rapid-scan mode. Three isotopic forms are used (14N14N16O, 15N14N16O, and 15N15N16O) in order to support the spectral analyses. For clusters up to N approximately 24, the individual spectra are resolved, assigned, and analyzed together with complementary microwave data. Assignments for larger clusters are uncertain due to overlapping transitions, but an approximate analysis is still possible for N approximately 25-80. Compared to helium clusters containing the related CO2 or OCS molecules, the rotational dynamics of HeN-N2O clusters show similarities but also important differences. In particular, HeN-N2O has more irregular behavior in the range of N=6-17, indicating that conventional molecular structure plays a greater role. In general terms, these differences can be attributed to a greater degree of angular anisotropy in the He-N2O intermolecular potential.

High-Temperature Continuous-Wave Operation of GaInAsN–GaAs Quantum-Dot Laser Diodes Beyond 1.3 $\mu$m

Internal laser parameters and characteristic temperature T0 of a GaInAsN-GaAs quantum-dot (QD) laser emitting above 1350 nm were determined. Continuous-wave operation of GaInAsN-GaAs QD ridge waveguide laser diodes with an emission wavelength of 1355 nm at room temperature (RT) is reported for the first time. Low threshold currents of 16 mA are achieved at RT. Ground state laser emission is observed up to temperatures of 75degC with a resulting laser emission wavelength of 1395 nm.

Experimental study of nonlinear mode mixing in dual-wavelength semiconductor lasers

New schemes for the generation of the sum, difference, and double frequencies in dual-wavelength injection lasers, based on an intracavity nonlinear mode mixing owing to a bulk nonlinearity, are experimentally investigated. Namely, the operation of the dual-wavelength laser diodes at the TE0 and TE1 modes, butt-joint laser diodes, and interband cascade lasers with tunnel junction are described.

Comparison of Exactness of Scalar and Vectorial Optical Methods Used to Model a VCSEL Operation

In the paper, a comparison between results of the optical scalar and vectorial optical methods, using the scalar effective frequency method and the vectorial method of lines, respectively, as their typical examples, applied for simulating an operation of vertical-cavity surface-emitting diode lasers (VCSELs) is presented. Both optical approaches has been applied to simulate an operation of the standard 1.3-mum GaAs-based oxide-confined GaInAsN double quantum-well VCSEL, but comparison conclusions seem to be more general and concerns all VCSELs. Validity limits of the simplified scalar approach have been determined by comparing its approximate results with more exact ones obtained with the aid of the accurate vectorial model. The scalar model has been found to be quite exact in the case of a determination of the wavelength of emitted radiation, whereas its exactness in the lasing threshold analysis is much worse, especially in the case of higher order modes, smaller aperture diameters and/or weak radial optical guidance. Our analysis leads also to more general designing conclusions concerning the optimal position and the thickness of the oxide layer assuring, respectively, the stable single mode operation and the lowest threshold gain

Cavity ring-down spectroscopy measurements of single aerosol particle extinction. I. The effect of position of a particle within the laser beam on extinction

A continuous wave distributed feedback diode laser operating in the near infrared at wavelengths close to 1650 nm has been used to measure the extinction of light by single aerosol particles. The technique of optical feedback cavity ring-down spectroscopy (CRDS) was used for measurement of CRDS events at a repetition rate of 1.25 kHz. This very high repetition rate enabled multiple measurements of the extinction of light by single aerosol particles for the first time and demonstrated the dependence of light scattering on the position of a particle within the laser beam. A model is proposed to explain quantitatively this phenomenon. The minimum detectable dimensionless extinction coefficient epsilonmin was determined to be 3x10(-6). Extinction values obtained for single spherical polymer beads from a monodisperse sample of particles of diameter of 4 microm are in near-quantitative agreement with the values calculated by the Mie scattering theory. The deviations from the Mie theory expected for measurement of extinction by CRDS using a continuous wave laser are discussed in the companion paper.

650-nm InGaP Broad Area Lasers With 5000-h Reliable Operation at 600 mW

Reliable operation of 650-nm broad area laser diodes with InGaP quantum-wells embedded in AlGaInP waveguide layers and n-AlInP and p-AlGaAs cladding layers is reported. Mounted on chemical vapor deposition (CVD)-diamond heat spreader and standard C-mounts, the 100-mum stripe width lasers showed reliable operation over 5000 h at 15 degC and 600 mW

Amplification and front facet reflectivity of broad area lasers

The effect of front-facet reflectivity on the amplification performance of Broad Area Laser (BAL) diodes in a double-pass configurationis studied experimentally. A method to measure the front facet reflectivities of laser diodes is generalized to BALs. The method is based on fitting a model, with front facet reflectivity as a parameter, to the threshold current vs. external feedback of the diode. Reflectivities of three BAL diodes are measured, and their amplification abilities have been assessed. The tested diodes had amplification factors of 0, 1, and 10 and front facet reflectivities of 12.7 +/-1%, 4.6 +/-0.4%, and 1.2 +/-0.2% respectively. It is concluded that a front facet modal reflectivity of less than 4.6% is necessary for a BAL to function as an amplifier.

Performance and optical characteristic of InGaN MQWs laser diodes

The performance of the InGaN multi-quantum wells (MQWs) laser diode structures has been numerically investigated by using ISE TCAD software. We investigated the effect of well numbers, barrier thickness and barrier doping on the output power, threshold current, and slope efficiency. All material parameters used in the model are evaluated based on the recent literature values. We observed the maximum output power and lower threshold current when the well number was two. Effective change in the output power and threshold current was observed with the variations in barriers thickness and doping level. Our results are in agreement with the experimental results observed by [S. Nakamura et al. Jpn. J. Appl. Phys. Part 2, 37, L1020 (1998) and S. Nakamura et al. Appl. Phys. Lett. 76, 22 (2000)].

Period-doubling and total mode-locking, and chaotic pulsations in a GaAs ridge wave-guide external-cavity diode laser

We report on the experimental observations of a period-doubling route to chaos and a total mode-locking between two lowest-order lateral modes of a GaAs ridge wave-guide diode laser at 795 nm. A self-starting passively mode-locking was achieved in an extended-cavity diode laser (ECDL) operating in a gain saturation regime. In the period-doubling mode-locked state, the RF spectra associated with the coherently coupled lateral TE(0) and TE(1) modes, consisted of harmonics (nf(rep)/2, n is an integer) of the half of pulse repetition rate f(rep)/2 and the period (2T) of the pulse train was two-times longer than the pulse round-trip time T. On the other hand, in the total mode-locked state, the RF spectra and the pulse train corresponding to the TE(0) and TE(1) modes had exactly the same features compared to those of the period-doubling mode-locked state, except the RF spectra and the pulse train of the TE(1) mode were shifted by f(ref)/4 in frequency and by T in time, respectively, indicating the pulses actually traveled alternatively through two lateral modes. The total mode-locking and also chaotic pulsations were observed at slightly different operation parameters, e.g. at different feedback angle of the grating, which was used as an output coupler of the ECDL.

Intrinsic Dynamic Properties of High-Characteristic Temperature GaInNAs Laser Diodes Operating at 1.3 $\mu$m

The properties of a high-characteristic temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =155K) 1.3-mum GaInNAs-GaAs laser are presented with an emphasis on laser dynamic characteristics evaluated by linewidth enhancement factor and relative intensity noise. It is found that the relatively high differential gain of GaInNAs-GaAs quantum wells leads to a small linewidth enhancement factor of 2.8, indicating a small magnitude of frequency modulation with modulation current. The relative intensity noise measurements indicate a relaxation frequency of 4.7 GHz at a moderate bias current, from which the maximum intrinsic modulation bandwidth was calculated to be 9.7 GHz. The experimental determination of the low linewidth enhancement factor and high relaxation frequency reinforce the potential of dilute nitride lasers for high-speed directly modulated fiber links

Hole-well antimonide laser diodes on GaSb operating near 2.93 µm

The operation of electrically-pumped type-II Sb-based laser diodes in which only the holes are quantum confined is reported. These laser structures were fabricated by molecular beam epitaxy on (001) GaSb substrates. In the multi-quantum well region, radiative recombinations originate from InGaSb hole wells embedded in InGaAsSb barriers lattice-matched to GaSb. Laser operation was demonstrated from such structures up to 243 K at 2.93 µm in the pulsed regime (200 ns, 5 kHz). A minimum threshold of about 12.8 kW/cm2 combined with a T0 around 70 K have been measured.

Low current operation of GaN-based blue-violet laser diodes fabricated on sapphire substrate using high-temperature-grown single-crystal AlN buffer layer

Low current laser operation at 405 nm has been demonstrated for the first time for the devices fabricated on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) using a high-temperature-grown single-crystal AlN buffer. The thick optical guiding layers were adopted to improve optical confinement. The device structure was the 2-μm-wide ridge-stripe type without facet coating. The minimum threshold current and current density were 60 mA and 3.8 kA/cm 2 for cavity lengths of 500 mm and 1 mm, respectively. These data were comparable to those reported using the special dislocation reduction techniques. The threshold current density linearly decreases with decreasing inverse of cavity length. It was expected that the low threshold current density ranging from 1 to 2 kA/cm 2 could be realized by adapting high reflection coating for laser facets. This expected current density was comparable to values realized for devices grown on the thick freestanding GaN as substrates. These findings support the promising potential of the HT-AlN buffer technique for production of advanced short-wavelength light-emitting devices on sapphire substrates.

Wavelength modulated off-axis integrated cavity output spectroscopy in the near infrared

A novel instrument based on an improved off-axis alignment of integrated cavity output spectroscopy (OA-ICOS) in conjunction with a wavelength modulation (WM) technique, was developed using a DFB diode laser operating in the near infrared at 1.573 μm (6357.3 cm-1). The laser-based sensor employed a 44 cm optical cavity that provided an effective absorption path length of ∼68 m. A minimum detectable absorption of approximately 3.6 ppmv Hz-1/2 or 2.3×10-7 Hz-1/2 per optical pass was obtained using second harmonic detection. We demonstrated that by implementation of the WM technique to OA-ICOS in the near infrared, the detection sensitivity was improved by a factor of 14 compared to that obtained with OA-ICOS. Measurements of CO2 mixing ratios in ambient air have been performed by using both OA-ICOS and WM-OA-ICOS techniques for performance comparison.

High Power Continuous Wave Blue InAlGaN Laser Diodes Made by Plasma Assisted MBE

Room temperature, continuous wave operation of InGaN multi-quantum wells laser diodes made by rf plasma assisted molecular beam epitaxy at 411 nm wavelength is demonstrated. The threshold current density and voltage were 4.2 kA/cm and 5.3 V, respectively. High optical power output of 60 mW was achieved. The lifetime of these laser diodes exceeds 5 h with 2 mW of optical output power. The laser diodes are fabricated on low dislocation density bulk GaN substrates, at growth conditions which resembles liquid phase epitaxy. We demonstrate that relatively low growth temperatures (600–700◦C) pose no intrinsic limitations for fabrication of nitride optoelectronic components by plasma assisted molecular beam epitaxy.

Control of an external-cavity laser diode operating in the regular pulse package regime with a frequency shift of the optical feedback

I demonstrate numerically that the regular pulse package regime observed in an external-cavity laser diode can be controlled by means of an adequate shift of the optical feedback frequency. This control leads to a stable pulsed behavior.

Monolithic integration of AlGaInP laser diodes on SiGe∕Si substrates by molecular beam epitaxy

Room temperature operation of visible AlGaInP laser diodes epitaxially integrated on Si was demonstrated. Compressively strained laser heterostructures were grown by molecular beam epitaxy (MBE) on low dislocation density SiGe∕Si substrates, where the threading dislocation density of the top relaxed Ge layers was measured in the range of 2×106cm−2. A threshold current density of Jth∼1.65kA∕cm2 for the as-cleaved, gain-guided AlGaInP laser grown on SiGe∕Si was obtained at the peak emission wavelength of 680nm under pulsed mode current injection. These results show that not only can high quality AlGaInP materials grown by MBE be achieved on Si via relaxed SiGe interlayers, but the prototype demonstration of laser diode operation on Si illustrates that very defect sensitive optoelectronics in the III-P system can indeed be integrated with Si substrates by heteroepitaxial methods.

Separate-confinement-oxidation vertical-cavity surface-emitting laser structure

In the present paper, a comprehensive self-consistent three-dimensional model is used to analyze physical aspects of the operation of oxide-confined vertical-cavity surface-emitting diode lasers (VCSELs) and to optimize their structures. The impact of the built-in radial confining mechanisms created by oxide apertures, i.e., the influence of their diameters and localizations on radial confinements of both the current injection into VCSEL active regions and electromagnetic fields of successive cavity modes, has been investigated. Basically, there are two extreme cases: the index-guided (IG) VCSELs with the aperture localized at the antinode position of the optical standing wave, characterized by a very low lasing threshold but exhibiting rather poor mode selectivity, and the gain-guided (GG) VCSELs with the aperture shifted to the node position, ensuring usually the single-fundamental-mode operation, but at the expense of much higher lasing threshold. In the present paper, the separate-confinement-oxidation VCSEL structure has been proposed exhibiting simultaneously advantages of both the IG VCSELs (the low lasing threshold) and the GG ones (the single-fundamental-mode operation).

60 mW continuous-wave operation of InGaN laser diodes made by plasma-assisted molecular-beam epitaxy

We demonstrate continuous-wave operation at 411nm of InGaN multi-quantum-well laser diodes (LDs) made by plasma-assisted molecular-beam epitaxy (PAMBE). The threshold current density and voltage for these LDs are 4.2kA∕cm2 and 5.3V, respectively. High optical output power of 60mW is achieved. The LDs are fabricated on low-dislocation-density bulk GaN substrates, at growth conditions which resemble liquid-phase epitaxy. We show that use of such substrates eliminates spiral growth, which is the dominant growth mechanism for PAMBE on high-dislocation-density substrates. Therefore, PAMBE opens new perspectives for next generation of InGaN LDs.