Search

The performance of new three-section master oscillator power amplifiers emitting at around 1.5 ?m has been analyzed in regard with their application as laser sources for a differential absorption lidar. The devices incorporate a modulation section that can be separately driven thus allowing the required random modulation of the laser emission. The bent design of this section together with the tilting of the output facet ensures a stable single-mode emission in the entire range of driving conditions. At the required modulation frequency (12.5 MHz) a square wave emission profile with high optical modulation amplitude and 22 dB extinction ratio is obtained.

ispartof: Tijdschrift voor Bedrijfs- en Verzekeringsgeneeskunde vol:23 issue:1 pages:9-11 status: published

Direct optical modulation of a 1.55 ?m three-section Master Oscillator Power Amplifier has been demonstrated. The temporal response, the optical spectra and the optical modulation amplitude have been analyzed as a function of the frequency and the modulating amplitude. For low modulation amplitude, no spectral broadening was observed up to 1.5 GHz. However, at 12.5 MHz an optical broadening of ~ 4 pm was observed for high modulation amplitudes. At this frequency an extinction ratio of 42 dB has been achieved. The modulation amplitude degrades for frequency values higher than 30 MHz. The device performance under modulation at 12.5 MHz is interesting for its application as laser source for CO2 detection by differential absorption LIDAR operating in the Continuous Wave Random Modulation mode.

We theoretically investigate a dynamical regime, experimentally observed in monolithically integrated master oscillator power amplifiers emitting at 1.5 7 μm, consisting in large emission wavelength jumps of the device from the Bragg wavelength to that of the gain peak. Our analysis is based on numerical simulations by means of a travelling wave model that incorporates spatial effects such as spatial hole burning and coupled-cavity effects. Thermal effects are included by considering the optical response of the quantum well active medium within the quasi-equilibrium approximation at finite temperature, with a phenomenological description of the redshift of the gain peak and the changes in the background material refractive index by means of self- and cross-heating coefficients for both sections. We find that whereas the thermally-induced index changes are the responsible of the modal jumps between consecutive modes, the carrier-induced refractive index changes are the responsible of the jumps occurring between the Bragg wavelength and the gain peak.

High power (> 0.5 W) single-mode frequency laser at 1.55 μm are nowadays key components for a large number of applications such as lidar systems, telemetry or free-space communications. For this level of power, the most suitable and available sources are solid-state lasers and fiber lasers. Semiconductor devices, which are more compact and more efficient, have still to demonstrate very high power operation to be a credible competitor. In order to obtain these levels of power with semiconductor devices, the more suitable device seems to be the Master Oscillator Power Amplifier (MOPA). Single-mode emission is generated by a Distributed Feedback laser (DFB) and the signal is then amplified with a Power Amplifier (PA). To avoid complex optical coupling and to simplify the packaging, it is possible to integrate on the same chip the laser and the amplifier. The main challenges are the fabrication of the multi-section device (at least 2 sections: one for the laser and one for the amplifier) and the reduction of the reflections. Indeed the facet and the internal reflections can create multiple cavities behavior and disturb the laser single-mode emission. In this contribution, we report the realization of a 3-section monolithic MOPA on InP.

We present two different photonic integrated circuits aimed to generate electrical signals within the microwave and millimeter wave range with two different techniques. The first approach uses the heterodyne technique, implementing a monolithic dual wavelength source by integrating on a single chip two distributed feedback (DFB) lasers together with the high speed photodiode. The second approach, using mode locked lasers, describes a novel device structure based on multimode interference reflectors (MIR).

Nowadays the interest in high power semiconductor devices is growing for applications such as telemetry, lidar system or free space communications. Indeed semiconductor devices can be an alternative to solid state lasers because they are more compact and less power consuming. These characteristics are very important for constrained and/or low power supply environment such as airplanes or satellites. Lots of work has been done in the 800-1200 nm range for integrated and free space Master Oscillator Power Amplifier (MOPA) [1]-[3]. At 1.5 ?m, the only commercially available MOPA is from QPC [4]: the fibred output power is about 700 mW and the optical linewidth is 500 kHz. In this paper, we first report on the simulations we have done to determine the appropriate vertical structure and architecture for a good MOPA at 1.58 ?m (section II). Then we describe the fabrication of the devices (section III). Finally we report on the optical and electrical measurements we have done for various devices (section IV).

The TNO review Essential interventions on Workers’ Health by Primary Health Care shows those interventions in primary, secondary and tertiary prevention are necessary and feasible but not yet satisfactorily evidence-based. Necessary, because primary or community health care covers about 80% of the world population, and can reach many of the 80 to 90% of the workers worldwide without any occupational health care at all, who nevertheless are the backbone of national economies. WHO is exploring such a strategy that can only succeed when PHC is well trained, equipped, supported and motivated to do this job – which mostly is not yet reality. Feasible, because our study, assigned by WHO, reports about a variety of primary health care activities for workers’ health in different regions in the world, varying form small-scale initiatives improving daily practice during office hours to large-scale programs involving thousands of professionals and millions of workers. Structured large-scale programs involving primary and community health care started only recently in e.g. Thailand, China, the UK and Indonesia, demonstrating the pioneering phase we are in. In other countries, many small-scale activities and interventions are noted, aiming to improve activities within existing primary health care practices aimed to improve workers’ health. We found reports underlining the need to develop good policies leading to programmatic conditions needed to implement structural essential interventions successfully. Investments are needed in four connected areas: policies, infrastructure, tools and education. In several initiatives we recognized the vital support role by experts of various disciplines in occupational health and safety. Not yet satisfactorily evidence-based because the level of evidence supporting especially the quality of concrete interventions - including the effect on working conditions and on the ality of enterprise policy, and on health, safety and work ability of the workers, is mostly not high. The level of evidence is many times low and sometimes even very low. Accordingly we strongly recommend developing and funding large research and development programs to support projects and programs with existing knowledge and experiences, and to deliver more scientifically sound evaluation studies to support adequate evidence-based policies Unexplored territory Because this is quite unexplored territory, we had to start with our own conceptual analysis of the domains, relations and interactions between primary or community and occupational health care, before we could describe essential interventions on three levels of prevention. Then we had to choose for the relatively new scoping review method as an adequate method different from the systematic review approach, related to a well explored territory. This method resulted in about 800 literature hits. We first selected 200 publications, later on reduced to few dozens described in Chapter 4 as our scientific building blocks. Our main conclusions regarding the three intervention levels are: Primary prevention activities – including workplace visits - can be part of PHC interventions on workers’ health in situations where the community has a dominant industry or where agriculture is dominant and when expert support is available. Serious limitations in PHC interventions can be found in more complex activities where experts are needed such as for most risk assessments and advises regarding more complicated improvements of working conditions. Education and training in prevention and health promotion can be executed by primary health care professionals. Secondary prevention in PHC may include periodic general health examinations to detect work-related health problems and occupational diseases. Screening tests as part of a workers’ health surveillance program such as for pesticide poisoning or exposure, can be performed by PHC under the condition of guidance by experts. Tools and education are available for primary health care to detect occupational diseases in daily practice. We did not find well-designed studies showing that better tools and education result in a better detection, individual therapy or support, screening or notification of occupational diseases. Tertiary prevention may include first aid services and emergency treatment by primary health care and consultations of working patients regarding their health and work ability. In several countries the attitude and communication skills of GPs regarding work have to improve. New tools can lead to more GP knowledge on the risks for long-term sickness absence and to better advices toward patients with a chronic disease and problems at work. Employment advisors and GPs with extra training in occupational medicine obtained good results while working within primary health care.

High brightness semiconductor lasers are potential transmitters for future space lidar systems. In the framework of the European Project BRITESPACE, we propose an all-semiconductor laser source for an Integrated Path Differential Absorption lidar system for column-averaged measurements of atmospheric CO2 in future satellite missions. The complete system architecture has to be adapted to the particular emission properties of these devices using a Random Modulated Continuous Wave approach. We present the initial experimental results of the InGaAsP/InP monolithic Master Oscillator Power Amplifiers, providing the ON and OFF wavelengths close to the selected absorption line around 1572 nm.

In de periode van 2007 tot en met 2013 is een grootschalig onderzoeksprogramma uitgevoerd op het terrein van de preventieve bedrijfsgezondheidszorg (BGZ), gefinancierd door Instituut GAK met cofinanciering door universiteiten, TNO en diverse andere partners.

In het kader van de bezuinigingen is een wetsvoorstel ingediend dat de meervoudige behandeling van rechtszaken moet beperken. In dit artikel wordt een experiment beschreven dat is gebaseerd op de aanname dat rechterlijke besluitvorming niet wezenlijk afwijkt van andere besluitvormingsprocessen. Naar die processen is het nodige onderzoek gedaan en daaraan kunnen verwachtingen omtrent (de kwaliteit van) rechterlijke besluitvorming worden ontleend. Het experiment concentreert zich op de vraag of er aantoonbare verschillen in uitkomst zijn tussen enkelvoudige en meervoudige besluitvorming waar het gaat om het maken van fouten. Hoewel er ook onder de betrokken professionals en in de literatuur enige steun is voor het ook in hoger beroep enkelvoudig behandelen van zaken met een geringe complexiteit, manen de uitkomsten van dit experiment tot voorzichtigheid. Op www.njb.nl is, onder Actuele documenten (week 6), een uitgebreide (Engelstalige) methodologische verantwoording te vinden van het onderzoek waarop dit artikel is gebaseerd.

In criminal cases judges evaluate and combine probabilistic evidence to reach verdicts. Unavoidably, errors are made, resulting in unwarranted conviction or acquittal of defendants. This paper addresses the questions (1) whether hearing cases by teams of three persons leads to less error than hearing cases alone; (2) whether deliberation leads to better decisions than mechanical aggregation of individual opinions; and (3) whether participating in deliberations improves future individual decisions. We find that having more than one judge consider cases reduces error effectively. This does not mean that it is necessary to deliberate about all cases. In simple cases many errors can be avoided by mechanical aggregation of independent opinions, and deliberation has no added value. In difficult cases discussion leads to less error. The advantage of deliberation goes beyond the case at hand: although we provide no feedback about the quality of verdicts, it improves individual decisions in subsequent cases.

Het wetsvoorstel 'verhoging griffierechten' heeft al menig pen in beweging gebracht. De auteurs van dit artikel schreven er in november 2010 al over in dit blad. Zij waarschuwden toen dat de voornemens van de regering voor dit wetsvoorstel de aanblik van de rechtspleging in ons land radicaal zouden kunnen veranderen en dat de plannen nog allerminst doordacht waren. Daarmee zwengelden zij een discussie aan die al maar verhitter raakte en die de gemoederen nu nog steeds bezighoudt. Juist nu ook weer, want de Tweede Kamer buigt zich momenteel over het wetsvoorstel. De minister heeft zijn plannen naar aanleiding van de kritieken aangepast. Maar wat te vinden van dit wetsvoorstel? Wordt de toegang tot de rechter voldoende gewaarborgd? En hebben de auteurs hun meningen bijgesteld?

International audience; In a semi-conductor optical amplifier (SOA) or a laser, the behavior of the device can be effected the temperature elevation due to high current injection level in the chip and a limited efficiency. For example, the optical output power of a laser or the optical gain in a SOA is reduced when the temperature of the junction increases. This latter can be controlled or monitored thanks to a thermo-electronic cooler (or a Peltier element) and a thermistor. In this paper, we calculate the thermal dissipation in semiconductor Optical Amplifier and laser. We investigate the effect of the material composition, the number of wells, the type of structure (Buried or Ridge), on the thermal resistance of the component and try to extract some rules towards minimization of temperature elevation. The influence of heat repartition inside the wells has been evaluated as well as the use of thick asymmetric cladding layer in the structure. In the latter case, optimization of layer composition and waveguide dimension has been performed.

National audience