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The ratio (R) of the molecular density of emissive layer to the carrier density in exciton formation zone has been provided to weigh the electrical stability of organic light‐emitting diode and simulated via the general mode of carrier device lifetimes. With current density increasing from 1 to 500 mA cm−2, the molecular density of emissive layer enabling the largest R, that is, the best electrical stability of device, gradually increases from 7.5 × 1019 to 1.5 × 1021 cm−3. At a given current density, R increases with the average bandgap of emissive layer increasing. There is a power law dependence of R on current density. For host–guest emissive layer, the electrical stability of device decreases with guest concentration increasing, mostly because the average bandgap of the host–guest emissive layer decreases. The current research provides some deep insights into developing the emissive layers of organic light‐emitting diodes toward high luminance applications. [ABSTRACT FROM AUTHOR]

We present a model for quantum-well (QW) semiconductor optical amplifiers (SOAs) that considers bidirectional field propagation and the carrier densities in the barrier and QW regions. Carrier capture from the barriers into the QWs and carrier escape from the QWs to the barriers are included by means of effective capture and escape times. The model incorporates the wavelength dependence of the optical response of the active region and the effects of spectral hole burning via an analytical approximation to the susceptibility of the active material, which allows one to very effectively include the wavelength dependence of the output properties of the SOA. The model is used to analyze the experimental results obtained for a multiquantum-well SOA. The simulations results show a good agreement with the experimental data when a carrier-density dependent escape time from the QW to the barrier regions is considered. [ABSTRACT FROM PUBLISHER]

We present a numerical study of the noise of conventional and gain-clamped semiconductor optical amplifiers (SOAs), using a detailed device model. The model makes use of a density-matrix gain calculation, and takes into account the forward and backward amplified spontaneous emission (ASE) spectra and the spatial carrier hole-burning. The device is longitudinally divided into M sections and a rate equation for averaged photon and carrier densities is used for each section. We demonstrate that the accuracy on the calculated noise figure strictly depends on the number of sections M. We obtain a good tradeoff between the results accuracy and the computational complexity with M=8. The model is then applied to study the noise in a distributed Bragg reflector (DBR)-type gain-clamped SOA for varying signal power, pump current, and lasing wavelength. We show that changes in the spatial carrier profile caused by the input signal significantly affect the noise figure, even when the gain is constant. A slight dependence of the noise figure on lasing wavelength is also foreseen, while the dependence on the pump current is negligible. A new method for gain-clamped SOA noise figure reduction is proposed, based on unbalanced Bragg reflectors. An improvement of noise figure (NF) as large as 2 dB is devised [ABSTRACT FROM PUBLISHER]

Novel quantum-well lasers with a 100-Å GaAs quantum-well (QW) (λ~840 nm) and a higher energy 40-Å AlGaInAs QW (λ~810 nm) in a graded AlxGa1-xAs separate confinement heterostructure (SCH) with the bandgap increasing from the p- to the n-side are characterized. A sizeable variation in the QW carrier densities can be achieved as a function of well composition and placement due to the built-in electric field that forces carriers toward the p-side of the SCH and the different densities of states and carrier capture rates of the QW's. Transversely emitted spontaneous emission (SE) is measured through a windowed contact to determine the relative contribution from each QW to the total SE. Information from these measurements is incorporated into a detailed device model to determine the carrier density and evaluate the gain characteristics in a new way. Since the nonidentical wells emit different photon energies, it is shown for the first time that the carrier density can be determined at a specific location within the SCH of a semiconductor laser. By changing the placement of dissimilar QW's and the grading of the SCH, it is found that the gain spectrum can be substantially engineered [ABSTRACT FROM PUBLISHER]

We propose a novel bistable laser diode (BLD) with active multimode interference (MMI) cavity. Bistable switching can be realized between two cross-coupled modes by means of gain saturation. Static characteristics of the multimode interference (MMI)-BLD are analyzed using a finite-difference beam propagation method. The photon-carrier interactions are calculated using the carrier-rate equation. This model gives accurate distributions of photon and carrier densities, optical gain, and refractive index inside the cavity. We predict that the MMI-BLD shows bistable switching between the two cross-coupled modes by light injection, therefore allowing it to be used as all-optical flip-flop or optical memory. [ABSTRACT FROM PUBLISHER]

A general scheme for the determination of vital operating characteristics of semiconductor lasers from low intensity photoluminescence spectra is outlined and demonstrated. We describe a comprehensive model that allows us to determine properties of the running device like gain spectra, peak gain wavelengths, bandwidths or differential gains, as well as inhomogeneous broadening and actual carrier densities of PL-signals. This information can then be used to compute characteristics like the temperature dependence of the gain, threshold densities, optical field distributions or near-field and far-field outputs [ABSTRACT FROM PUBLISHER]

We present a theory which demonstrates how the diffusion of photogenerated carriers affects the impulse response of a resonant-cavity enhanced photodetector (RCE). Analytic expressions for carrier densities and short-circuit current are derived, The theory indicates that diffusion introduces a significant tail in the temporal response of photodetectors. The influence of diffusion rises as the absorption width decreases, and a discrepancy in bandwidth as high as 35% between our results and previous theoretical predictions is observed. Therefore, the effect should be taken into account while calculating the critical parameters of RCE photodetectors with thin absorption region [ABSTRACT FROM PUBLISHER]