A Comparison of Small Signal Modulation Parameter Extraction Techniques for Vertical-Cavity, Surface-Emitting Lasers

The small signal modulation characteristics of a vertical-cavity, surface-emitting laser (VCSEL) are determined using three different measurements: relative intensity noise, frequency response, and high resolution optical spectra. The resonant and damping frequencies were measured, and related rate equation parameters were extracted; excellent agreement was found both between experiment and theory, and amongst the different measurement techniques. The results and procedures are compared, and the findings are presented below

Electrical and Optical Simulation of Tris(8-hydroxyquinoline) Aluminium-Based Microcavity Organic Light Emitting Diode (MOLED)

A detailed examination of the emitted radiation spectrum from tris(8-hydroxyquinoline) aluminum (Alq) based OLEDs on optical and electrical models have been presented. The OLED structure is examined as a function of choice of anode material and position of the NPB/Alq interface. The simulation results have been compared to those obtained from experiments, showing good agreement in both electrical and optical characteristics. The enhancement in light emission by aligning antinode of the stand wave pattern with effective carrier recombination region has been observed

Device optimization Based on Electrical and Optical Simulation of Tris(8-hydroxyquinoline) Aluminium Based Microacavity Organic Light Emitting Diode (MOLED)

OLED has emerged as a potential candidate for applications in display devices due to its prominent advantages in size, brightness and wide viewing angle. Following our previous work, where optical analysis of the OLED has been documented1 we present in this work detailed examination optical and electrical analysis of the performance of an OLEDs based on two organic layers: N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as the hole transport layer and tris (8-hydroxyquinoline) aluminium (Alq3) as the emitting layer, and two metallic mirrors. Our optical model fully takes into account dispersion in glass substrate, organic layers as well as the dispersion in metal contacts/mirrors. Influence of the incoherent transparent glass substrate is also accounted for. Two metal contacts Ag and Cu have been considered for anode and cathode respectively. For the hole transport layer NPB was used. The OLED structure is examined as a function of: thickness of the organic layers, and position of the hole transport layer/Alq3 interface. In order to obtain better agreement with EL experimental data, electrical models was developed in conjunction with the existing optical model to facilitate accurate optimisation of the OLED structure. The electrical model developed considers the metal contact as Schottky contact, the carrier mobility is taken to be field dependent with the Poole-Frenkel-like form and Langevin recombination model is used. The carrier transport was simulated using one-dimensional time-independent drift-diffusion model using device simulation software ATLAS.2 Finally, the optimised devices were fabricated and characterised and experimental and calculated optical emission spectra were compared together with results obtained from electrical transport model

The Effect of the Higher Order Modes on the Optical Crosstalk in Free-Space Optical Interconnect

In this paper we investigate the effect of the crosstalk introduced due to laser beam imaging in a free-space optical interconnect (FSOI) system. Due to the overfill of the transmitter microlens array by the vertical-cavity surface-emitting laser (VCSEL) beam, one part of the signal is imaged by the adjacent microlens to another channel, possibly far from the intended one. Furthermore, it is known that in practice, VCSELs tend to operate in several transverse modes simultaneously. This will cause even more increase in the interchannel and intersymbol interference, to our knowledge this issue has been neglected so far. The numerical simulation has been performed using a combination of exact ray tracing and the beam propagation methods. The results show that the stray-light crosstalk will increase significantly with either greater system density or higher order modes. The diffraction-caused crosstalk is mainly affected primarily by interconnection distance, channel density

Displacement and Distance Measurement using the Change in Junction Voltage Across a Laser Diode Due to the Self-Mixing Effect

The conventional self-mixing sensing systems employ a detection scheme utilizing the photocurrent from an integrated photodiode. This work reports on an alternative way of implementing a Vertical-Cavity Surface-Emitting Laser (VCSEL) based self-mixing sensor using the laser junction voltage as the source of the self-mixing signal. We show that the same information can be obtained with only minor changes to the extraction circuitry leading to potential cost saving with reductions in component costs and complexity. The theoretical linkage between voltage and photocurrent within the self-mixing model is presented. Experiments using both photo current and voltage detection were carried out and the results obtained show good agreement with the theory. Similar error trends for both detection regimes were observed

A status report on the observability of cosmic bubble collisions

In the picture of eternal inflation as driven by a scalar potential with multiple minima, our observable universe resides inside one of many bubbles formed from transitions out of a false vacuum. These bubbles necessarily collide, upsetting the homogeneity and isotropy of our bubble interior, and possibly leading to detectable signatures in the observable portion of our bubble, potentially in the Cosmic Microwave Background or other precision cosmological probes. This constitutes a direct experimental test of eternal inflation and the landscape of string theory vacua. Assessing this possibility roughly splits into answering three questions: What happens in a generic bubble collision? What observational effects might be expected? How likely are we to observe a collision? In this review we report the current progress on each of these questions, improve upon a few of the existing results, and attempt to lay out directions for future work.Comment: Review article; comments very welcome. 24 pages + 4 appendices; 19 color figures. (Revised version adds two figures, minor edits.

Optimization of Organic Light Emitting Diode Structures

In this work we present detailed analysis of the emitted radiation spectrum from tris(8-hydroxyquinoline) aluminum (Alq3) based OLEDs as a function of: the choice of cathode, the thickness of organic layers, and the position of the hole transport layer/Alq3 interface. The calculations fully take into account dispersion in glass substrate, indium tin oxide anode, and in the organic layers, as well as the dispersion in the metal cathode. Influence of the incoherent transparent substrate (1 mm glass substrate) is also fully accounted for. Four cathode structures have been considered: Mg/Ag, Ca/Ag, LiF/Al, and Ag. For the hole transport layer, N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) was considered. As expected, emitted radiation is strongly dependent on the position of the emissive layer inside the cavity and its distance from the metal cathode. Although our optical model for an OLED does not explicitly include exciton quenching in vicinity of the metal cathode, designs placing emissive layer near the cathode are excluded to avoid unrealistic results. Guidelines for designing devices with optimum emission efficiency are presented. Finally, the optimized devices were fabricated and characterized and experimental and calculated emission spectra were compared

Cavity Design and Optimization for Organic Microcavity OLEDs

We report on detailed simulations of the emission from microcavity OLEDs consisting of widely used organic materials, n,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq3) as emitting and electron transporting layer. The thick silver film was considered as a top mirror, while silver or copper films on quartz substrate were considered as bottom mirrors. The electroluminescence emission spectra, electric field distribution inside the device, carrier density and recombination rate were calculated as a function of the position of the emission layer, i.e. interface between NPB and Alq3. In order to achieve optimum emission from a microcavity OLED, it is necessary to align the position of the recombination region with the antinode of the standing wave inside the cavity. Once the optimum structure has been determined, the microcavity OLED devices were fabricated and characterized. The experimental results have been compared to the simulations and the influence of the emission region width and position on the performance of microcavity OLEDs was discussed

Correction to "Mode Selection and Tuning Mechanisms in Coupled-Cavity Terahertz Quantum Cascade Lasers"

In [1], the affiliation for Andrew Grier was incorrect. The correct affiliation where his contribution was made is as follows: A. T. Grier was with the School of Electronic and Electrical Engineering, University of Leeds, LS2 9JT Leeds, U.K. (e-mail: [email protected])