Oxidation of AlInAs for current blocking in a photonic crystal laser

To make an electrically pumped photonic crystal membrane laser is a challenging task. One of the problems is how to avoid short circuiting between the p- and n-doped parts of the laser diode, when the membrane thickness is limited to 200-300nm. We propose to use the oxide of AlInAs to realize a current blocking function. In this way, based on submicron selective area re-growth, we aim for electrically injected photonic crystal lasers with high output power, small threshold currents and low power consumption. Here results are presented on the oxidation of AlInAs. The results show that it is feasible to use the oxide of AlInAs for current blocking in an InP-based membrane photonic crystal laser

Anxiety and depression in nursing home patients : Prevalence, risk indicators and consequences

Beekman, A.T.F. [Promotor]Eefsting, J.A. [Promotor]Pot, A.M. [Copromotor

Usability of an app-based clinical decision support system to monitor psychotropic drug prescribing appropriateness in dementia

BACKGROUND: Guidelines recommend reluctant psychotropic drug (PD) prescribing in nursing home residents with dementia and neuropsychiatric symptoms (NPS), as efficacy of PDs is limited, and side effects are common. Nevertheless, PDs are commonly prescribed to reduce NPS. A smartphone application that evaluates appropriateness of PD prescriptions and provides recommendations from the revised Dutch guideline on problem behaviour in dementia may promote guideline adherence and increase appropriate prescribing.OBJECTIVE: This study aimed to assess user experiences, barriers and facilitators of the Dutch 'Psychotropic Drug Tool' smartphone application (PDT) in the context of appropriate prescribing of PDs to nursing home residents with dementia and NPS.METHODS/DESIGN: The PDT was developed according to the recommendations of the Dutch guideline for treatment of NPS in people with dementia. Feedback provided during usability testing with two end-users was applied to improve the PDT before implementation in day-to-day practice. Sixty-three prescribers were asked to use the PDT at their own convenience for four months. User expectations and experiences were assessed at baseline and after four months with the System Usability Scale and the Assessment of Barriers and Facilitators for Implementation.RESULTS: Expected usability (M = 72.59; SD = 11.84) was similar to experienced usability after four months (M = 69.13; SD = 16.48). Appreciation of the PDTs user-friendliness (on average 6.7 out of 10) and design (7.3) were moderately positive, in contrast to the global rating of the PDT (5.7). Perceived barriers for PDT use were time consumption and lack of integration with existing electronic systems. Perceived facilitators were ease of use and attractive lay out. For broader implementation, physicians suggested a change in direction of the PDT: start assessment of appropriateness based on the list of NPS instead of PD as primary input.CONCLUSIONS: In this pragmatic prospective cohort study we found that the PDT was used by elderly care physicians, with mediocre user satisfaction. The PDT will be optimized based on user feedback regarding experienced usability, barriers and facilitators, after which broader implementation can be initialized. The Medical Ethics Review Board of the University Medical Center Groningen declared this is a non-WMO study (UMCG RR Number: 201800284).</p

Fabrication of short GaAs wet-etched mirror lasers and their complex spectral behaviour

A versatile fabrication technique for GaAs-AlGaAs wet-etched mirror lasers is presented. This technique works independently of the Al concentration in the cladding layers up to a value of 70%, and it requires four photolithography steps. Ridge waveguide lasers have been successfully processed using a double heterostructure (DHS) as well as graded index separate confinement heterostructures (GRINSCH) having different quantum-well (QW) active layers. This technique is used to fabricate short-cavity lasers in GRINSCH structures having GaAs multiple-quantum-well (MQW) or bulk active layers. Laser operation was obtained in a 29-µm-long device using a 5-QW structure. Short lasers with QW active layers show a complex spectral behavior. These lasers operate at higher current densities (~20 kA/cm2) and emit light at more than one wavelength. This implies that higher order transitions are involved which is not the case when using a bulk GaAs active layer. Besides the two peaks corresponding to the n=1 and n=2 transitions, we found an intermediate peak which corresponds presumably to the forbidden transition E1-HH

Characterization and modeling of gain spectra of single-layer InAs/InP(100) quantum dot amplifiers

In this contribution we present the small signal net modal gain measurement results of single-layer InAs/InP(100) quantum dot amplifiers in 1.6 to 1.8 µm wavelength range. The material shows sufficient optical gain to be used in the long-wavelength optical coherence tomography. The modal gain has been observed as a function of current density and temperature. An improved rate equation model has been applied to analyse the measurements. A good fit of the theory to the measurements was obtained with a temperature dependent carrier injection efficiency which is below 2%

Characterisation of monolithically integrated dual wavelength AWG-lasers for mm-wave generation

In this paper we present characterisation results of monolithically integrated InP based quantum well dual wavelength lasers in which an Array Waveguide Grating (AWG) is used as intra-cavity filter to allow lasing on two wavelengths within a common optical amplifier of the device. The devices require accurate control of the optical loss of each wavelength which is achieved through the use of Michelson interferometers (MIs) in the cavity. The results show that reasonably stable dual wavelength operation is possible with a side mode suppression ratio better than 20dB for each of the two wavelengths without fast active feedback control

Measurement and analysis of temperature-dependent optical modal gain in single-layer InAs/InP(100) quantum-dot amplifiers in the 1.6- to 1.8-µm wavelength range

In this paper, measurements and analysis of the small-signal net modal gain of single-layer InAs/InP(100) quantum-dot (QD) optical amplifiers are presented. The amplifiers use only a single layer of InAs QDs on top of a thin InAs quantum well. The devices have been fabricated using a layer stack that is compatible with active–passive integration scheme, which makes further integration possible. The measurement results show sufficient optical gain in the amplifiers and can thus be used in applications such as lasers for long-wavelength optical coherence tomography and gas detection. The temperature dependence of the modal gain is also characterized. An existing rate-equation model was adapted and has been applied to analyze the measured gain spectra. The current injection efficiency has been introduced in the model to obtain a good fit with the measurement. It is found that only a small portion ($sim$1.7%) of the injected carriers is actually captured by the QDs. The temperature dependence of several parameters describing the QDs is also discovered. The mechanisms causing the blue shift of peak gain as the current density increases and the temperature changes are analyzed and discussed in detail