ABSTRACT
We investigate a new configuration of a mode-locked fiber laser by using a nonlinear polarization rotation-based design to generate soliton pulses with low repetition rate. Unlike with previously reported configurations, we introduce a Faraday mirror after the first half of the cavity length to counteract the nonlinear polarization rotation effects. The total cavity length is 437 m including a 400-m long twisted SMF-28 fiber. The fiber was twisted to cancel the linear birefringence and to ensure that the polarization ellipticity is not altered as the pulse travels along the fiber. The strict control of polarization yields a stable relation between the polarization state of the pulses propagating in the cavity and the regimes of generation. Depending on the polarization state we observed three different emission regimes, the single soliton regime (SR), conventional noise-like pulses (NLP) and noise-like square-waveform pulse (NLSWP). In the SR, a 467.2 kHz train of solitons was obtained with pulse duration of 2.9 ps at 1558.7 nm.
ABSTRACT
A switchable and tunable multi-wavelength Tm-doped fiber laser is successfully demonstrated using a filter constructed with two tapered fiber elements in the cavity. The proposed system design uses a low-cost simple filter that allows stable dual, triple, quadruple, and quintuple-wavelength emission operation in the region around 1.9 µm. In the dual wavelength regime, the laser is capable of independently tuning each wavelength. For switching and tuning, a curvature is applied to the tapered fibers.
ABSTRACT
We report the dynamics of dissipative solitons in a ring cavity passively mode-locked fiber laser with a strict control of the polarization state. We study the relation between the polarization state of the pulses propagating in the cavity and the regimes of generation. We have found that at pulse ellipticities between 5° and 15°, the laser generates one bunch of pulses in the cavity, while at higher ellipticities the laser generates multiple bunches. At constant ellipticity we rotated the polarization azimuth and observed a regime transition from the generation of noise-like pulses (NLP) to that of soliton crystal. The NLP regime was found when the azimuth was rotated towards smaller low-power transmission through the polarizer. The number of solitons in the soliton crystal also depended on the azimuth in a straightforward way: the higher the initial transmission, the bigger the number of solitons.
ABSTRACT
Resumen OBJETIVO: cuantificar el número de ecografías durante la gestación y evaluar la calidad de los estudios del segundo y tercer trimestres en pacientes de bajo riesgo del área metropolitana de la Ciudad de México. MATERIALES Y MÉTODOS: estudio prospectivo, observacional y descriptivo de mujeres con control prenatal fuera de nuestra unidad que acudieron a la Clínica Perinatal de Embarazo de Alto riesgo, Hospital de la Mujer de la Ciudad de México, para la finalización del embarazo. Cuantificación de las ecografías tomadas durante la gestación, identificación del profesional encargado del estudio y evaluación de la calidad de los estudios del segundo y tercer trimestres mediante una lista de cotejo basada en guías internacionales; obtención del porcentaje de apego a las mismas. RESULTADOS: se estudiaron 199 pacientes a quienes se tomaron, en promedio, 3.7 ecografías; al 80% tres o más ultrasonidos. El análisis de las ecografías del segundo trimestre arrojó un promedio de 13.8 parámetros evaluados, con 43% de apego a las normas. En las ecografías del tercer trimestre, el promedio de parámetros evaluados fue de 10 con un porcentaje de apego de 66.7%. Los médicos ultrasonografistas fueron quienes realizaron el mayor número de estudios en ambos trimestres. CONCLUSIONES: la ecografía es un recurso accesible a la población del área metropolitana; sin embargo, debe insistirse en la calidad de los estudios.
Abstract OBJECTIVE: To quantify the number of ultrasound scans during pregnancy and evaluate the quality of ultrasound in the second and third trimester of gestation in the low risk obstetric population in the metropolitan area. MATERIAL AND METHODS: we conducted a prospective, observational and descriptive study in 199 women that arrived to the hospital for delivery without prenatal care in our unit, quantified the number of ultrasound scans performed during pregnancy, and evaluate the quality of the second and third trimester echographies with a check list based on international guidelines. The percentage of adherence was obtained and analyzed by the professional in health responsible of the study. RESULTS: The average scan per patient was 3.37, 80% had three or more. Analysis of ultrasound for the second trimester showed an average of 13.8 parameters evaluated with 43% of adherence to standards; in the ultrasounds of the third trimester, the evaluated parameters averaged 10 with a percentage of attachment of 66.7%. The largest number of studies was performed by sonographists. CONCLUSIONS: The ultrasound is a tool accessible to the population of the metropolitan area; however, it should be emphasized in the quality of studies.
