Judy M Rorison

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.

Multi-weight unipolar codes for multimedia spectral-amplitude-coding optical CDMA systems

A novel balanced detection scheme for multi-access interference cancellation in multimedia spectral-amplitude-coding optical code-division multiple-access system is proposed. The receiver is capable of handling both equal and unequal in-phase cross correlation of optical orthogonal codes. A novel class of constant-length variable-weight optical orthogonal codes able to support multimedia services with different quality-of-service requirements is proposed as well. The construction is based on the pairwise balanced designs, or more specifically, on an incidence structure defined on an integer sub-lattice.

Investigations of Repetition Rate Stability of a Mode-Locked Quantum Dot Semiconductor Laser in an Auxiliary Optical Fiber Cavity

We have investigated experimentally the pulse train (mode beating) stability of a monolithic mode-locked multi-section quantum-dot laser with an added passive auxiliary optical fiber cavity. Addition of the weakly coupled (¿ -24 dB) cavity reduces the current-induced shift d¿/dI of the principal peak in the RF spectrum (the effective pulse repetition frequency) by more than an order of magnitude, from -39.5 to -2.3 kHz/mA. The rms timing jitter of the pulse train is simultaneously reduced from 1.4 to 0.9 ps.

Calculation of losses in 2-D photonic Crystal membrane waveguides using the 3-D FDTD method

The three-dimensional finite-difference time-domain method is used to obtain loss per unit length in a two-dimensional photonic crystal membrane waveguide by simulating three different length guides. Results are shown for propagation both above and below the light line. The results are compared with a Fourier expansion method and good agreement is obtained above and below the light line.

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.

Design of multiweight unipolar codes for multimedia optical CDMA applications based on pairwise balanced designs

A novel class of constant-length variable-weight optical orthogonal codes is proposed that can support multimedia services with different data rates and quality-of-service requirements. The construction is based on the pairwise balanced designs, or more specifically, on an incidence structure defined on an integer lattice. Proposed codes are suitable for spectral-amplitude coding, fast-frequency hopping, and time-spreading encoding in multimedia environment. A novel dual-balanced decoder is proposed capable of canceling multiuser interference in multimedia applications for spectral-amplitude-coding schemes employing the unipolar codes having nonfixed in-phase cross correlation.

Investigations of mode control in proton-implanted and oxide-confined VCSELs using PBGs: modelling and experiment

We have investigated theoretically the influence on transverse optical modes of a two-dimensional photonic crystal (PC) defect waveguide embedded into a vertical-cavity surface-emitting laser. In gain-guided structures, where the index profile is weak, the effect of the PC is efficient. In the oxide-confined structures, where the index guidance provided by the oxide is larger, this is not the case, but the efficiency of the PC can be increased by oxide in the node position. It is shown that the thermal lensing effect leads to increased sensitivity of the single-mode conditions on the current injection change.

Optical transitions in GaInNAs/GaAs multi-quantum wells with varying N content investigated by photoluminescence excitation spectroscopy

We report on the nitrogen-concentration dependence of optical transitions between quantized states of electrons and holes in GaInNAs/GaAs multi-quantum wells. Using low-temperature photoluminescence excitation spectroscopy, systematic studies have been performed on a series of samples with nitrogen concentrations in the range 0%‐1.14%. The observed data were compared with theoretical fitting based on the band anticrossing model in which the localized N states interact with the extended states in the conduction band, taking strain effects into account. Our results are consistent with the band anticrossing model, but with differing coupling strength between different quantum states of electrons in the quantum wells.

Optical gain in GaAsBi/GaAs quantum well diode lasers

Optical gain, absorption and spontaneous emission spectra for GaAs_0.978Bi_0.022/GaAs laser diodes are measured experimentally and compared with theory. Internal optical losses of 10-15 cm^-1 and peak modal gain of 24 cm^-1 are measured at threshold. The results of calculations showed excellent agreement with the experiment, key for future laser design.

Optical characteristics of 1.55 μm GaInNAs multiple quantum wells

We report the optical characterization of high-quality 1.55μm GaxIn1−xNyAs1−y multiquantum wells (MQWs), grown on GaAs with Ga(In)N0.01As spacer layers. The transitions between the quantized QW states of the electrons and holes have been identified using photoluminescence excitation spectroscopy. Their energies are consistent with theoretical fitting based on the band anticrossing model. It is also confirmed by detailed spectroscopic measurements that the addition of even a small amount of In to GaN0.01As barriers remarkably improves the optical characteristics of the QWs. The results imply that although strain-compensated GaInNAs MQWs provide a feasible approach to realizing 1.55μm optical emission, the relative lattice mismatch between the wells and barriers is critical to the optical quality of the related QWs.