Timing jitter reduction in semiconductor lasers induced by optical injection.

We present an experimental study of the effect of continuous-wave optical injection (OI) from a vertical-cavity surface-emitting laser (VCSEL) on the timing jitter of a gain-switched discrete-mode semiconductor laser (DML). Timing jitter was analyzed over a wide range of temperatures of the DML, which allowed tuning the detuning between the lasers emissions, and it was compared with the inter-pulse timing jitter. We have found that there is a range of detunings in which OI diminishes the jitter by 70% with respect to the jitter of the solitary DML. However, within this region, there are some detunings for which OI significantly increases the jitter.

Random polarization switching in gain-switched VCSELs for quantum random number generation.

In this paper, we report an experimental and theoretical study of the random excitation of the linearly polarized modes of a gain-switched VCSEL characterized by having polarization switching under continuous wave operation. We show that equal probability of excitation of both linearly polarized modes can be achieved by adjusting the modulation conditions and the sampling time. Our VCSEL is such that the bistable region associated to the polarization switching is very narrow, indicating that the random process of excitation of the polarizations works independently of the existence of those bistable regions. A characterization of the random polarization switching is performed by analyzing the dependence of the probability of excitation, autocorrelation, and histograms of both polarized signals on the modulation conditions and sampling times. We finally present preliminar results on random number generation using the analyzed system.

Phase diffusion in gain-switched semiconductor lasers for quantum random number generation.

In this paper, we report a theoretical and experimental study of the phase diffusion in a gain-switched single-mode semiconductor laser. Our modelling includes nonlinear dependencies of the carrier recombination rate and the semiconductor material gain on the carrier number. Also a comparison with the results obtained with linear models is performed. We focus on the below threshold operation, that is, the regime where most of the phase diffusion occurs in quantum random number generators based on the above mentioned system. Using the extracted parameters for our laser and simple analytical expressions for the laser linewidth, we show that logarithmic material gain and cubic carrier recombination dependence on the carrier number must be considered for a good agreement between experiments and theory. In this way we show that consideration of these nonlinearities is essential for obtaining a good quantitative description of the phase diffusion when using rate equations modelling.

Polarization dynamics induced by parallel optical injection in a single-mode VCSEL.

We report an experimental study of the polarization nonlinear dynamics in a 1550 nm single-mode vertical-cavity surface-emitting laser (VCSEL) subject to parallel optical injection. Experimentally measured stability maps identifying regions of different nonlinear dynamics for various values of bias current are reported. We show that VCSELs with more than a 35 dB polarization mode suppression ratio can have rich nonlinear dynamics in both linear polarizations, including periodic and chaotic behaviors appearing simultaneously in both polarization modes.

Polarization switching and injection locking in vertical-cavity surface-emitting lasers subject to parallel optical injection.

Polarization switching in a long-wavelength vertical-cavity surface-emitting laser (VCSEL) under parallel optical injection is analyzed in a theoretical and experimental way. For the first time, to our knowledge, we report experimentally a state in which injection locking of the parallel polarization and excitation of the free-running orthogonal polarization of the VCSEL are simultaneously obtained. We obtain very simple analytical expressions that describe both linear polarizations. We show that the power of both linear polarizations depend linearly on the injected power in such a way that the total power emitted by the VCSEL is constant. We perform a linear stability analysis of this solution to characterize the region of parameters in which it can be observed. Our measurements qualitatively confirm the previous theoretical predictions.

Investigation of elliptically polarized injection locked states in VCSELs subject to orthogonal optical injection.

We demonstrate experimentally the existence of the elliptically polarized injection-locked (EPIL) state. This state is observed when a single-transverse mode VCSEL is subject to orthogonal optical injection. The spectral feature of the EPIL state is verified and the power of each polarization is measured. The regime of the EPIL state is identified in the parameter plane of frequency detuning and injection power for different bias currents. As current decreases the frequency detuning range for the EPIL to exist is narrower and shifts toward the negative frequency detuning. Periodic dynamics of the VCSEL is found in the neighborhood of the EPIL regime.

Integrating gender and rights into sexuality education: field reports on using It's All One.

International policy agreements, along with emerging evidence about factors influencing programme effectiveness, have led to calls for a shift in sexuality education toward an approach that places gender norms and human rights at its heart. Little documentation exists, however, about the degree to which this shift is actually taking place on the ground or what it entails. Field experiences in using new curriculum tools, such as It's All One, offer one lens onto these questions. To gain a sense of practitioners' experience with this tool, a two-part exercise was conducted. First, responses from an on-line survey of It's All One users were synthesized. Additionally, five programmes were selected for documentation, including two school-based programmes (Nigeria, China), two reaching extremely vulnerable youth (Haiti, Guatemala), and one reaching adolescents from a polygamous Mormon community (United States). Findings suggest the shift to an empowerment approach is indeed taking place in diverse geographic and programmatic contexts, and that It's All One has strengthened the ways their programmes address gender, foster young people's critical thinking skills and use interactive teaching methods. A common challenge across many programmes is strengthening teacher capacity. Recommendations for further implementation and research are presented.

Two-frequency injection on a multimode vertical-cavity surface-emitting laser.

We have studied experimentally effects of two-frequency optical injection on a multimode vertical-cavity surface-emitting laser (VCSEL). The injected signal comes from another VCSEL. Polarization switching (PS) with and without frequency locking occurs for relatively small frequency detuning. Outside the regime of polarization switching, the VCSEL demonstrates two types of instabilities. The instability regions and boundaries of PS of each transverse mode are mapped in the parameter plane of frequency detuning versus injected power.

Nonlinear dynamics induced by parallel and orthogonal optical injection in 1550 nm Vertical-Cavity Surface-Emitting Lasers (VCSELs).

We report a first experimental study of the nonlinear dynamics appearing in a 1550 nm single-mode VCSEL subject to parallel and to orthogonal optical injection. For the first time to our knowledge we report experimentally measured stability maps identifying the boundaries between regions of different nonlinear dynamics for both cases of polarized injection. A rich variety of nonlinear behaviours, including periodic (limit cycle, period doubling) and chaotic dynamics have been experimentally observed.

Stigma among key populations living with HIV in the Dominican Republic: experiences of people of Haitian descent, MSM, and female sex workers.

OBJECTIVE(S): To describe stigma among seropositive MSM, female sex workers (FSWs), and Haitian-descent individuals in the Dominican Republic, and to assess whether stigma is associated with HIV treatment outcomes. DESIGN: Cross-sectional survey using Stigma Index 2.0. METHODS: People living with HIV (PLHIV) interviewed seropositive adult MSM, FSWs, Haitian-descent persons, and other PLHIV who did not identify with these communities about experiences of social exclusion, harassment, stigma in healthcare settings, and internalized stigma. Bivariate analyses were conducted to compare experiences between FSWs and other women; MSM and other men; and Haitian-descent participants and non-Haitian PLHIV. Within each community, separate multivariate logistic regression analyses were conducted to examine the association between stigma experiences with viral suppression and with missed antiretroviral doses. RESULTS: The 891 participants consisted of 154 MSM, 216 FSWs, 90 Haitian-descent persons, and 447 who did not identify with any of these three communities. Compared with other women, FSWs reported significantly higher levels of harassment due to their HIV status, and those of Haitian descent reported significantly lower levels of social exclusion compared with non-Haitian PLHIV. In adjusted analyses, MSM who experienced more stigma in HIV-specific services had a significantly lower odds of knowing they had undetectable viral load (adjusted odds ratio 0.37, P < 0.05). Higher internalized stigma scores were significantly associated with missing an antiretroviral treatment dose among FSWs (adjusted odds ratio 1.26, P < 0.05). CONCLUSION: For FSWs and MSM, efforts to mitigate HIV-related stigma are necessary to improve treatment adherence and viral suppression. For Haitian-descent PLHIV, interventions must address not only their HIV-specific needs, but also the broader social and legal barriers to care.

Power and wavelength polarization bistability with very wide hysteresis cycles in a 1550 nm-VCSEL subject to orthogonal optical injection.

We have measured optical power and wavelength polarization bistability in a 1550 nm-Vertical Cavity Surface-Emitting Laser (VCSEL) subject to orthogonally-polarized optical injection into the orthogonal polarization of the fundamental transverse mode. Optical bistability with very wide hysteresis cycles, up to four times wider than previously reported results has been measured for both the optical power and wavelength domain. We also report the experimental observation of three different shapes of polarization bistability, anticlockwise, clockwise and X-Shape bistability, all of them with wide hysteresis cycles. This rich variety of behaviour at the important wavelength of 1550 nm offers promise for the use of VCSELs for all-optical signal processing and optical switching/routing applications.

Child Marriages and Unions in Latin America: Understanding the Roles of Agency and Social Norms.

PURPOSE: Child marriages and unions can infringe upon adolescent and youth sexual and reproductive health (AYSRH). Interventions increasingly promote strategies to transform social norms or foster the agency of adolescent girls. Recent empirical studies call for further understanding of how social norms and agency interact in ways that influence these practices, especially in contexts where girls' agency is central. METHODS: A secondary cross-case analysis of three qualitative studies (in Brazil, Guatemala, Honduras) was conducted to inform the investigation of how norms and agency may relate in sustaining or mitigating child marriage. RESULTS: Social norms dictating how girls/young women and how men should act indirectly led to child marriages and unions. The data showed that (1) social norms regulated girls' acceptable actions and contributed to their exercise of "oppositional" agency; (2) social norms promoted girls' "accommodating" agency; and (3) girls exercised "transformative" agency to resist harmful social norms. CONCLUSIONS: Research should advance frameworks to conceptualize how social norms interact with agency in nuanced and context-specific ways. Practitioners should encourage equitable decision-making; offer confidential, adolescent-friendly AYSRH services; and address the social norms of parents, men and boys, and community members.

1/f noise in the intensity fluctuations of vertical-cavity surface-emitting lasers subject to parallel optical injection.

A first analysis of fluctuations of the light intensity of vertical-cavity surface-emitting lasers operating in a bistable regime reveals the presence of 1/f noise. In this regime the intensity fluctuates between two recently characterized states with residence times {τ_{1}} and {τ_{2}}. We identify three distinct processes. One of them presents a coherence enhancement phenomenon, and in the other two the distribution of residence times in one of the states follows either a power law P(τ_{1})∼τ_{1}^{-2} or P(τ_{2})∼τ_{2}^{-2}, and this is the cause of the 1/f shape in the spectral density of the intensity. The process at the coherence enhancement zone shows 1/f fluctuations in the light intensity and also in the time residence process. It is shown that the origin of these fluctuations is due to a power-law distribution in the time separation between pulses observed in the time residence series.

Attractor hopping between polarization dynamical states in a vertical-cavity surface-emitting laser subject to parallel optical injection.

We present experimental and theoretical results of noise-induced attractor hopping between dynamical states found in a single transverse mode vertical-cavity surface-emitting laser (VCSEL) subject to parallel optical injection. These transitions involve dynamical states with different polarizations of the light emitted by the VCSEL. We report an experimental map identifying, in the injected power-frequency detuning plane, regions where attractor hopping between two, or even three, different states occur. The transition between these behaviors is characterized by using residence time distributions. We find multistability regions that are characterized by heavy-tailed residence time distributions. These distributions are characterized by a -1.83±0.17 power law. Between these regions we find coherence enhancement of noise-induced attractor hopping in which transitions between states occur regularly. Simulation results show that frequency detuning variations and spontaneous emission noise play a role in causing switching between attractors. We also find attractor hopping between chaotic states with different polarization properties. In this case, simulation results show that spontaneous emission noise inherent to the VCSEL is enough to induce this hopping.

[Iatrogenic ureteral injury]. / Trauma de uréter yatrógeno.

OBJECTIVES: To determine the most frequent causes of ureteral injury, and the way to correct severe damage of the ureter. METHODS: We reviewed the medical records of 25 patients who suffered ureteral injuries during abdominal or pelvic surgery in a five-year period; endoscopic injuries were excluded. RESULTS: The most common presentation included pain, urinary incontinence and fever. Hysterectomy was the most frequent operation causing ureteral injuries. The diagnosis was made by intravenous urography and ultrasound. Ureteral reimplantation using a Boari's flap, without other complications, was the preferred treatment due to ureteral damage. Right side and distal third of the ureter where the most frequently affected sites. CONCLUSIONS: In cases of iatrogenic injuries of the distal third of the ureter with severe lesions, ureteral reimplantation with a Boari's flap may be the option.

Trauma de uréter yatrógeno / Iatrogenic ureteral injuries

OBJETIVO: Determinar las causas más frecuentes del trauma de uréter, y la manera de corregir el daño severo del uréter. MÉTODOS: Se revisó las historias de 25 pacientes que sufrieron trauma de uréter en el transcurso de cirugía de abdomen o pelvis en un periodo de 5 años, se excluyeron los traumas endoscópicos. RESULTADOS: La presentación más frecuente fue dolor, incontinencia de orina y fiebre. La histerectomía fue la causa más frecuente del trauma ureteral. El diagnóstico se efectuó mediante la U.I.V y ecografía renal. Por el daño del uréter el tratamiento más practicado fue el reimplante uteral tipo Boari, sin mayores complicaciones.El lado y sitio más afectado fueron el derecho y el tercio distal del uréter. CONCLUSIONES: En los casos de trauma yatrógeno de uréter del 1/3 distal con lesiones graves el reimplante ureteral tipo Boari puede ser la alternativa (AU)