J.C.L. Yong

1.3-/spl mu/m quantum-well InGaAsP, AlGaInAs, and InGaAsN laser material gain: a theoretical study

Due to the keen interest in improving the high-speed and high-temperature performance of 1.3-/spl mu/m wavelength lasers, we compare, for the first time, the material gain of three different competing active layer materials, namely InGaAsP-InGaAsP, AlGaInAs-AlGaInAs, and InGaAsN-GaAs. We present a theoretical study of the gain of each quantum-well material system and present the factors that influence the material gain performance of each system. We find that AlGaInAs and InGaAsN active layer materials have substantially better material gain performance than the commonly used InGaAsP, both at room temperature and at high temperature.

Characterization of the temperature sensitivity of gain and recombination mechanisms in 1.3-/spl mu/m AlGaInAs MQW lasers

The potential of 1.3-/spl mu/m AlGaInAs multiple quantum-well (MQW) laser diodes for uncooled operation in high-speed optical communication systems is experimentally evaluated by characterizing the temperature dependence of key parameters such as the threshold current, transparency current density, optical gain and carrier lifetime. Detailed measurements performed in the 20/spl deg/C-100/spl deg/C temperature range indicate a localized T/sub 0/ value of 68 K at 98/spl deg/C for a device with a 2.8 /spl mu/m ridge width and 700-/spl mu/m cavity length. The transparency current density is measured for temperatures from 20/spl deg/C to 60/spl deg/C and found to increase at a rate of 7.7 A/spl middot/cm/sup -2//spl middot/ /spl deg/C/sup -1/. Optical gain characterizations show that the peak modal gain at threshold is independent of temperature, whereas the differential gain decreases linearly with temperature at a rate of 3/spl times/10/sup -4/ A/sup -1//spl middot//spl deg/C/sup -1/. The differential carrier lifetime is determined from electrical impedance measurements and found to decrease with temperature. From the measured carrier lifetime we derive the monomolecular ( A), radiative (B), and nonradiative Auger (C) recombination coefficients and determine their temperature dependence in the 20/spl deg/C-80/spl deg/C range. Our study shows that A is temperature independent, B decreases with temperature, and C exhibits a less pronounced increase with temperature. The experimental observations are discussed and compared with theoretical predictions and measurements performed on other material systems.

Material gain comparison for InGaAsP, AlGaInAs and InGaAsN for 1.3 micron laser diode

Summary form only given. Recently, AlGaInAs and InGaAsN have received much interest as materials for 1.3 micron laser applications in competition with traditional InGaAsP. Both AlGaInAs and InGaAsN have the advantage of large conduction band offsets leading to superior electron confinement. We compare the gain and transparency carrier density at two temperatures to determine best the modulation response as well as the lowest possible threshold carrier density for uncooled laser applications. It is predicted that AlGaInAs has the highest peak differential gain for both room temperature and high temperature operation hence showing much potential for high speed response. AlGaInAs also has the lowest predicted transparency carrier density that may lead to low threshold currents, further enhancing its promise for 1.3 micron laser diode applications.

In-plane strain modification of polarization behavior of vertical-cavity surface-emitting lasers

We demonstrate experimentally how an external mechanical stress applied to a VCSEL wafer results in an in-plane anisotropic strain, which dramatically alters the polarization behavior of our VCSELs. In the presence of in-plane strain, the VCSEL still emits linearly polarized light but its direction strongly depends on the magnitude and the orientation of the strain (with respect to the crystal co-ordinate system). The latter behavior can be understood by taking into account the elasto-optic effect and the proper strain distribution. Furthermore, for a specific range in magnitude and orientation of the externally induced strain, current induced polarization switching between the two fundamental modes (with orthogonal linear polarization) is present in a reproducible way. The current at which switching occurs strongly depends on the magnitude of the external stress and can be tuned in the whole region of single-mode operation. These effects can be explained by accounting for the anisotropy of the valence band. The latter is induced by the in-plane uniaxial strain, leading to a modification of density of states and effective masses for different directions in the plane of the QW, and henceforth to a gain anisotropy and a different gain curve for each of the two polarization modes. Furthermore, the frequency splitting between the two cavity eigenmodes (also a result of the stress via the elasto-optic effect) has to be taken into account. We will discuss how the gain anisotropy changes with current, lattice temperature and carrier density, and how all these determine the polarization behaviour of VCSELs.

Mode formation in 1.3 /spl mu/m GaInNAs VCSELs with unequal well filling

We report on the dynamics of the mode formation in a vertical cavity surface emitting laser (VCSEL). The work covers both the averaged and unequal filling (and hence gain) of the quantum wells.

Effect of nitrogen on the temperature induced wavelength shift of GaInNAs lasers

The temperature dependence of the lasing wavelength of GaInNAs quantum well laser is found to be 0.394 nm/K, which is smaller than conventional InGaAsP material system. The band anticrossing model is utilised to derive an understanding of this effect.

The evolution of transverse modes in GaInNAs VCSELs

In this work a circularly symmetric structure is assumed. The field, thermal, standard carrier diffusion and photon rate equations are solved accordingly. The model used for the material gain is both carrier and temperature dependent, with the nonlinear dependency introduced by the use of a phenomenological gain suppression factor. The model is flexible enough to be used for either gain-guided or index-guided structures, but at this initial stage of the work, gain-guided device whose operation is very much affected by thermal effects, composed of triple GaInNAs quantum wells with DBR stacks.

Temperature resolved 1.3 /spl mu/m AlGaInAs MQW laser measurements: transparency current density, gain and carrier lifetime

Summary form only given. To study the potential of this material system, results of threshold current variation, transparency current density and optical gain over temperature as well as the effective carrier lifetime of a 1.3 /spl mu/m ridge waveguide grating (RWG) AlGaInAs MQW laser are presented.

Investigation of 2D-lattice distributed reflector lasers

A detailed study of the InGaAsP-InP 2D-lattice MQW laser has been undertaken. Characterisation of the optical field intensity as a function of distance along the device cavity has shown that etching significantly alters the optical properties of the waveguide. A high value of coupling coefficient is obtained, with K/sub g/ >250cm/sup -1/. Modelling suggests that this high value is consistent with the mode-hop free single-mode emission found to hold in the etched device even under large-signal modulation at 10 Gb/s.

Feasibility of AlGaInAs lasers for high speed uncooled communication systems

Summary form only. There has recently been renewed interest in AlGaInAs 1.3/1.55 /spl mu/m lasers for high speed data communications. This laser system is an attractive alternative to the traditional GaInAsP lasers predominately because of higher characteristic temperature, T/sub 0/. For example, in the past year, T/sub 0/ values for AlGaInAs lasers have typically been observed to be around 80 K. This improved temperature sensitivity is crucial for future high speed uncooled data communications systems where active components may be required to operate at temperatures as high as 80-90/spl deg/C. To date however little analysis has considered the high temperature, high speed operation of InGaAsP devices. In this paper therefore we have evaluated the feasibility of AlGaInAs lasers for high-speed modulation at high temperatures.