Measurement of reflectivity of butt-joint active-passive interfaces in integrated extended cavity lasers

A method and measurement results are presented for the determination of the reflectivity of butt-joint active-passive interfaces in a series of extended cavity Fabry-Pe´rot lasers. The method is based on the analysis of subthreshold laser spectra. The small reflections at the two intracavity active-passive interfaces modify the mode structure of the laser. By fitting the calculated subthreshold mode structure to the recorded data, values of the reflectivities are extracted. An average value of 9.10-5 has been determined. The value of the reflectivity of those interfaces is relevant for photonic integrated circuits and particularly integrated mode-locked lasers

Self-switching in Mach-Zehnder interferometers with SOA phase shifters

A self-switching mechanism in Mach-Zehnder interferometers (MZIs) is described. The input light signal is distributed unequally over the interferometer arms using an multimode interference (MMI) coupler. In the arms, semiconductor optical amplifiers are placed as nonlinear phase shifters. Unequal intensities yield a nonlinear phase shift. The signals from the two arms are then recombined in an output MMI coupler. If an obtained nonlinear phase shift in the arms can compensate the coupler-induced phase difference between the arms, the signals are in phase at the output port. Choosing an appropriate output coupler, 2×1 and 2×2 devices can be obtained. The 2×2 and 2×1 MZIs can be used as pattern effect compensators and 2R-regenerators or low-loss combiner circuits, respectively. An active-passive integration technique is applied in order to realize the interferometric structures. Fabrication, simulation, and characterization of these devices are presented in this letter

Prevention of late-life Depression in Primary Care: Do we know where to begin?

OBJECTIVE: This study attempted to compare two models for selective (people at elevated risk) and indicated (those with subsyndromal depressive symptoms) prevention and to determine the optimal strategy for prevention of late-life depression. METHOD: Onset was assessed at 3 years with the Geriatric Mental State AGECAT in a randomly selected cohort of 1,940 nondepressed and nondemented older people in Amsterdam. Risk factors that can easily be identified in primary care were used. RESULTS: The association of risk factors with depression incidence was expressed in absolute and relative risk estimates, number needed to treat, and population-attributable fractions. Prevention models were identified with classification and regression tree analyses. In the indicated prevention model, subsyndromal symptoms of depression were associated with a risk of almost 40% of developing depression and a number needed to treat of 5.8, accounting for 24.6% of new cases. Adding more risk factors raised the absolute risk to 49.3%, with a lower number needed to treat but also lower attributable fraction values. In the selective prevention model, spousal death showed the highest risk, becoming even higher if the subjects also had a chronic illness. Overall, the attributable fraction values in the indicated model were higher, identifying more people at risk. CONCLUSIONS: Consideration of the costs and benefits of both models in the context of the availability of evidence-based preventative interventions indicated that prevention aimed at elderly people with depressive symptoms is preferred. The focus on treatment should be readdressed; a new approach is needed, with a stronger emphasis on prevention

Space-switching using wavelength conversion at 2.5 Gb/s and integrated phased array routing

Space switching of 2.5 Gb/s optical signals by lambda -conversion in a DBR laser and subsequent routing through a phased array wavelength demultiplexer is demonstrated. A novel component is presented that integrates 3 dB couplers and a phased array to form the passive part of a space switc

Elimination of ghost images in the response of PHASAR-demultiplexers

In this paper the occurrence of first-order modes in the performance of phased-array demultiplexers is investigated. It is found that they cause "ghost" images, which can be circumvented by optimising waveguide junction

A compact phased array based multi-wavelength laser

A phased-array-based multiwavelength laser with InGaAsP active layer has been fabricated in a simple ridge waveguide structure with nine channels spaced by 400 GHz around 1.55 mu m on an area of 3.5*3*2.5 mm/sup 2/. Simultaneous dual channel operation is demonstrate