J. Sarma

Spatial holeburning effects on the dynamics of vertical cavity surface-emitting laser diodes

Calculations are reported of the dynamic evolution of transverse modes in vertical cavity surface emitting lasers (VCSELs). It is shown that the spatial distribution of the modal fields plays an important role in determining the steady-state operating characteristics of the device. It is found that spatially separated modes can coexist by sharing the available gain, whereas strong competition occurs between modes that have a strong spatial overlap. The influence of carrier diffusion and spatial holeburning during the turn-on transient of the laser is elucidated, and the implications for the steady-state modal properties of the device are indicated. >

Lasing mode selection in vertical-cavity surface emitting-laser diodes

A detailed model, including current spreading, carrier diffusion, and corresponding modal gains, is developed for a well-defined vertical-cavity surface-emitting laser structure. Above-threshold-operation (hole burning) is also analyzed by the model to quantitatively demonstrate the influence of injecting contact geometry and size in determining monomode operation. Results from this model demonstrate the importance of modal gain dynamics in establishing stable operation of such devices and hence the model may be used for improved device design.<<ETX>>

Dynamics of transverse mode competition in vertical cavity surface emitting laser diodes

Abstract Calculations have been performed of transverse mode competition during the turn-on transient of VCSELs. Taking account of the interplay between the transverse mode structure and the gain medium it is shown that the spatial holeburning plays an important role in determining which transverse mode will be sustained under steady-state operating conditions.

Novel design of a hybrid-cavity surface-emitting laser

A new type of vertical-cavity surface-emitting laser (VCSEL) is proposed and analyzed to show the possibility of optical pumping from an integrated edge-emitting laser. With this scheme, it may be possible to make VCSELs of very small dimensions and VCSEL arrays. The laser design utilizes dopant induced intermixing of quantum wells (QWs) to provide different gain regions for the surface and edge-emitting sections. The multimode rate equations are used to evaluate the possibility of such a laser and the roles of the various design parameters are discussed. It is seen that efficient surface photon emission is possible for high vertical-cavity mirror reflectivities and sufficient separation of bandgap energies for the two QW gain regions.

Secondary pulsations driven by spatial hole burning in modulated vertical-cavity surface-emitting laser diodes

It is shown that significant optical power is generated in secondary pulsations after switch-off of vertical-cavity surface-emitting laser diodes (VCSEL’s) when the laser is modulated from an above-threshold state to a current that is at or below the threshold value. It is found from simulations that the optical power in the secondary pulsations can be as much as 25% of the power in the lasing state. The initial reduction of optical output power subsequent to the switch-off permits a spatial redistribution of charge carriers that in turn permits a transient recovery of the modal gain above the threshold value, thus enabling the secondary pulsations to occur. The phenomenon occurs as a result of the interplay between the transverse-mode structure and the gain medium and, as such, cannot be predicted by spatially independent rate equation models. Implications of the phenomenon for practical applications of VCSEL’s with pseudorandom nonreturn-to-zero modulation formats are pointed out.

1.3-W ripple-free superluminescent diode

This letter presents the experimental characterization of tapered and stripe superluminescent diodes fabricated from 980-nm high-power triple quantum-well InGaAs-AlGaAs semiconductor material. Record output powers in excess of 1.3 W pulsed have been measured, with 0.1-dB spectral modulation and maximum wall-plug efficiency 16%. Almost 1-W optical power into multimode optical fibers has been achieved with preliminary measurements of coupling efficiency.

Effects of spatial hole burning on polarization dynamics in edge-emitting and vertical-cavity surface-emitting laser diodes

The dynamical evolution of polarization states in vertical-cavity surface-emitting lasers (VCSELs) and ridge-waveguide edge-emitting laser diodes (RWEELD) has been studied, taking into account the interplay between the mode structure and the gain medium. The role of spatial hole burning in determining polarization switching properties of both device geometries is demonstrated.

PIEZOELECTRIC FIELD EFFECTS IN INGAAS (111)B QUANTUM WELLS

Strained In0.21Ga0.79As/GaAs quantum well structures have been grown by molecular beam epitaxy on (111)B GaAs substrates. Well widths between 20 and 160 A, separated by 500 A barriers were grown sequentially on the same substrate and subsequently characterized by low‐temperature (10 K) photoluminescence. The variation of the e‐hh transition energy with well width is markedly different for samples grown simultaneously on (100) and (111)B substrates due to the strain induced piezoelectric field. Using the envelope function approximation, the dependence of n=1 e‐hh transitions of (111)B samples on well width can be interpreted by the presence of a built‐in electric field of magnitude of 1.45×107 V/m. In contrast to the (100) sample, exciton lifetimes in the (111)B sample depend strongly on well width because of spatial separation of electrons and holes in the triangular wells. In the 160 A well, the exciton lifetime increases to 755 ns corresponding to a reduction of about three orders of magnitude in the el...

A versatile method for analyzing paraxial optical propagation in dielectric structures

This paper presents a fast and accurate quasi-analytic model for studying optical field propagation in weakly guiding dielectric structures. The proposed efficient and versatile computational scheme is obtained by merging the Hermite-Gauss (HG) total field expansion with the numerical collocation method and is particularly suited for longitudinally nonuniform structures. By means of a quasilinearization scheme, the same procedure has also been successfully applied to the analysis of field propagation in Kerr-nonlinear media. The latter achievement gives an indication of the great potentialities offered by this straight forward method. Several examples are discussed in the paper and in all cases the results computed by the proposed method favorably compare with those from alternative methods.

A new method for computing nonlinear carrier diffusion in semiconductor optical devices

The solution of carrier diffusion equations typically associated with semiconductor optical devices has been achieved by combining a function expansion scheme, using the Hermite-Gauss functions as the basis set, with the collocation numerical procedure. Results for a wide range of cases obtained by this new scheme compare very favorably with those calculated with other methods. Not only is the present process computationally fast and efficient, but it has the added attraction of providing the basis for conveniently solving also the nonlinear electromagnetic wave equation for the self-consistent modeling of such devices.