Optimum Injection Current Waveform for a Laser Range Finder Based on the Self-Mixing Effect

In a self-mixing type laser range finder the current of the laser is modulated with a triangle wave to produce a range of optical frequencies. However, the electrical signal does not produce a perfect linear sweep in optical frequency due to thermal and other effects in the laser. This leads to errors in the accuracy and resolution of the range finder. In this paper, we describe and implement a method in software to systematically determine the optimal shape of the injected waveform needed to eliminate these thermally induced measurement errors. With this method we do not require the more complicated and expensive optical techniques used by other researchers to recover the optical frequency variations with regard to injection current. The averaging of a reasonable number of samples gave sub-millimeter accuracy when the optimal current shape was used. The uncertainty in the average measurements are improved by roughly six times compared to the conventional triangular modulation. The reshaping also results in the range finding system being less sensitive to changes in ambient temperature

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

Laser range finding using the self-mixing effect in a vertical-cavity surface-emitting laser

In this paper we report on a laser range finding system built using the self-mixing effect in a Vertical-Cavity Surface-Emitting Laser (VCSEL). The distance to the target in these range finders is usually calculated by determining the time interval between the peaks in the resulting power fluctuations that are produced by the self-mixing effect. In this study we propose the use of a method that utilises the Fast Fourier Transform (FFT) that proves to have better performance than the traditional peak spacing methods used by other researchers. A range finding system has been built using a VCSEL and the FFT to measure a range of distances from 20cm to 1m with a maximum error of 1.5% and a resolution of 5mm. This is the first time to our knowledge that such a range finding system has been built with a VCSEL

A Critical Comparison of High-Speed VCSEL Characterisation Techniques

This paper critically compares, for the first time, common microwave and optical procedures used for the high-speed characterisation of vertical-cavity, surface-emitting lasers (VCSELs). The intrinsic small-signal modulation characteristics of a VCSEL are measured, and the related rate equation parameters are extracted. Observed trends show excellent agreement with theory. The modulation characteristics of the VCSEL are determined by examining three different responses: relative intensity noise, S21 response, and high-resolution optical spectra. The various experimental techniques yielded consistent results. The relative strengths and weaknesses of each measurement are investigated below

Minimising crosstalk in microchannel free-space optical interconnects with the presence of higher order modes

We investigate the combined effect of the diffraction-caused crosstalk noise (DCCN) and the stray-light crosstalk noise (SLCN) on the performance of FSOI system. A numerical simulator was employed in this study to investigate OI channel design. We determine that there exists an optimal focal length, which maximises the signal-to-noise ratio (SNR) by minimising the combined effects of DCCN and SLCN. For the fundamental mode., the optimal focal length is approximately 750 mu m; for both LG(01) and LG(10) modes, the optimal focal length occurs between f = 650 mu m and f = 700 mu m, depending on the interconnection distance and array pitch

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

Cultivation of Photosynthetic Bacteria Using Vertical-Cavity Surface-Emitting Lasers

We present for the first time experimental results demonstrating the cultivation of photosynthetic microorganisms using laser light. The demonstrated efficiency of the laser source opens the possibility of designing small-scale, energy efficient, compact photobioreactors

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