The effect of Fabry-Perot interference on the packaging of SOI-based optoelectronic devices

During the packaging of optoelectrome device, a problem always met is the instability of output power. The main effect causing this problem, Fabry-Perot interference, is discussed in this paper. Both theoretical analysis and experimental test are carried out and in good agreement. As an example of avoiding the disadvantage of Fabry-Perot interference, the packaging process of Silicon-on-Insulator (SOI) based Variable Optical Attenuator(VOA) is shown at last.

High-speed electrooptical VOA integrated in silicon-on-insulator

In this paper, we present simulation results of an electrooptical variable optical attenuator (VOA) inte-grated in silicon-on-insulator waveguide. The device is functionally based on free carriers absorption toachieve attenuation. Beam propagation method (BPM) and two-dimensional semiconductor device simu-lation tool PISCES-Ⅱ were used to analyze the dc and transient characteristics of the device. The devicehas a response time (including rise time and fall time) less than 200 ns, much faster than the thermoopticand micro-electromechanical systems (MEMSs) based VOAs.

Coherent analysis of quantum optical sideband modes

We demonstrate a device that allows for the coherent analysis of a pair of optical frequency sidebands in an arbitrary basis. We show that our device is quantum noise limited, and hence applications for this scheme may be found in discrete and continuous variable optical quantum information experiments. (c) 2005 Optical Society of America.

Diffractive variable attenuator for femtosecond laser radiation control

We present a diffractive phase variable attenuator for femtosecond laser radiation control. It allows the control of beam power up to 0.75 10 ¹³ W/cm² without introducing serious distortions in spectra and beam shape while it operates in zero order diffraction. The attenuator can operate with wavelengths from DUV to IR. © 2009 Optical Society of America.

Regenerative amplifier with continuously variable pulse duration used in an optical parametric chirped-pulse amplification laser system for synchronous pumping

A Nd:glass regenerative amplifier has been set up to generate the pumping pulse with variable pulse width for an optical parametric chirped-pulse amplification (OPCPA) laser system. Each pulse of the pulse train from a cw self-mode-locking femtosecond Ti:sapphire oscillator is stretched to approximate to300 ps at 1062 nm to be split equally and injected into a nonlinear crystal and the Nd:glass regenerative amplifier, as the chirped signal pulse train and the seed pulse train of the pumping laser system, respectively. By adjusting the cavity length of the regenerative amplifier directly, the width of amplified pulse could be varied continuously from approximate to300 ps to approximate to3 ns. The chirped signal pulse for the OPCPA laser system and the seed pulse for the pumping laser system come from the same oscillator, so that the time jitter between the signal pulse and the pumping pulse in optical parametric amplification stages could be <10 ps. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Emittance estimation by an ion optical element with variable focusing strength and a viewing target

The emittance of an extracted ion beam can be estimated to first order by a series of three linear independent profile measurements. This estimation is restricted to the evaluation of an upper limit of the emittance value for a homogeneous, nonfilamented beam. The beam is assumed to be round, respectively elliptical, without any structure of the intensity distribution, no space charge has been assumed for the drifting beam, and the optics is assumed to be linear. Instead of using three different drift sections, a linear focusing element with three different focusing strengths can be used. Plotting the beam radius as function of focusing strength, three independent solutions can be used to calculate the Twiss parameters alpha, beta, and gamma and furthermore the emittance epsilon. Here we describe the measurements which have been performed with the SECRAL ion source at Institute of Modern Physics Lanzhou.

Variable dose rate application of herbicides using optical sensors

The aim of this study was to develop and evaluate a variable dose rate application of herbicides using an online electronic control based system with optical sensors for weed detection in forested areas. The proposed concept was to apply a basic dose on 100% of the area (aiming to control small weeds) and to apply a complementary patch-spraying dose only on areas with higher weed infestation. For that purpose, a conventional spray boom was adjusted to apply 40% of the herbicide dose on the full area and the optical sensors were used to control the application of the complementary dose (60%) only on areas with higher infestation. The results showed that the system performed adequately. Field applications presented herbicide savings around 20 to 30%, with a similar weed control performance as compared to the full dose application on 100% of the area.

Analytic optical design of linear Fresnel collectors with variable widths and shifts of mirrors

Linear Fresnel collectors still present a large margin to improve efficiency. Solar fields of this kind installed until current time, both prototypes and commercial plants, are designed with widths and shifts of mirrors that are constant across the solar field. However, the physical processes that limit the width of the mirrors depend on their relative locations to the receiver; the same applies to shading and blocking effects, that oblige to have a minimum shift between mirrors. In this work such phenomena are studied analytically in order to obtain a coherent design, able to improve the efficiency with no increase in cost. A ray tracing simulation along one year has been carried out for a given design, obtaining a moderate increase in radiation collecting efficiency in comparison to conventional designs. Moreover, this analytic theory can guide future designs aiming at fully optimizing linear Fresnel collectors' performance.

Development of optical ray tracing model of a standard parabolic trough collector

Parabolic trough concentrator collector is the most matured, proven and widespread technology for the exploitation of the solar energy on a large scale for middle temperature applications. The assessment of the opportunities and the possibilities of the collector system are relied on its optical performance. A reliable Monte Carlo ray tracing model of a parabolic trough collector is developed by using Zemax software. The optical performance of an ideal collector depends on the solar spectral distribution and the sunshape, and the spectral selectivity of the associated components. Therefore, each step of the model, including the spectral distribution of the solar energy, trough reflectance, glazing anti-reflection coating and the absorber selective coating is explained and verified. Radiation flux distribution around the receiver, and the optical efficiency are two basic aspects of optical simulation are calculated using the model, and verified with widely accepted analytical profile and measured values respectively. Reasonably very good agreement is obtained. Further investigations are carried out to analyse the characteristics of radiation distribution around the receiver tube at different insolation, envelop conditions, and selective coating on the receiver; and the impact of scattered light from the receiver surface on the efficiency. However, the model has the capability to analyse the optical performance at variable sunshape, tracking error, collector imperfections including absorber misalignment with focal line and de-focal effect of the absorber, different rim angles, and geometric concentrations. The current optical model can play a significant role in understanding the optical aspects of a trough collector, and can be employed to extract useful information on the optical performance. In the long run, this optical model will pave the way for the construction of low cost standalone photovoltaic and thermal hybrid collector in Australia for small scale domestic hot water and electricity production.

Remote sensing of leaf area index: enhanced retrieval from close-range and remotely sensed optical observations

A wide range of models used in agriculture, ecology, carbon cycling, climate and other related studies require information on the amount of leaf material present in a given environment to correctly represent radiation, heat, momentum, water, and various gas exchanges with the overlying atmosphere or the underlying soil. Leaf area index (LAI) thus often features as a critical land surface variable in parameterisations of global and regional climate models, e.g., radiation uptake, precipitation interception, energy conversion, gas exchange and momentum, as all areas are substantially determined by the vegetation surface. Optical wavelengths of remote sensing are the common electromagnetic regions used for LAI estimations and generally for vegetation studies. The main purpose of this dissertation was to enhance the determination of LAI using close-range remote sensing (hemispherical photography), airborne remote sensing (high resolution colour and colour infrared imagery), and satellite remote sensing (high resolution SPOT 5 HRG imagery) optical observations. The commonly used light extinction models are applied at all levels of optical observations. For the sake of comparative analysis, LAI was further determined using statistical relationships between spectral vegetation index (SVI) and ground based LAI. The study areas of this dissertation focus on two regions, one located in Taita Hills, South-East Kenya characterised by tropical cloud forest and exotic plantations, and the other in Gatineau Park, Southern Quebec, Canada dominated by temperate hardwood forest. The sampling procedure of sky map of gap fraction and size from hemispherical photographs was proven to be one of the most crucial steps in the accurate determination of LAI. LAI and clumping index estimates were significantly affected by the variation of the size of sky segments for given zenith angle ranges. On sloping ground, gap fraction and size distributions present strong upslope/downslope asymmetry of foliage elements, and thus the correction and the sensitivity analysis for both LAI and clumping index computations were demonstrated. Several SVIs can be used for LAI mapping using empirical regression analysis provided that the sensitivities of SVIs at varying ranges of LAI are large enough. Large scale LAI inversion algorithms were demonstrated and were proven to be a considerably efficient alternative approach for LAI mapping. LAI can be estimated nonparametrically from the information contained solely in the remotely sensed dataset given that the upper-end (saturated SVI) value is accurately determined. However, further study is still required to devise a methodology as well as instrumentation to retrieve on-ground green leaf area index . Subsequently, the large scale LAI inversion algorithms presented in this work can be precisely validated. Finally, based on literature review and this dissertation, potential future research prospects and directions were recommended.