RESUMO
We present the inscription of narrow-linewidth fiber Bragg gratings (FBGs) into different types of multicore fibers (MCFs) using ultrashort laser pulses and the phase mask technique, which can act as notch filters. Such filters are required, e.g., to suppress light emitted by hydroxyl in the Earth's upper atmosphere, which disturbs ground-based observation of extraterrestrial objects in the near infrared. However, the inscription into a commercially available seven-core fiber showed a quite large core-to-core deviation of the resonance wavelength of up to 0.45 nm. Two options are presented to overcome this: first, we present the photo-treatment of the FBGs to tune the resonance wavelength, which allows for sufficient resonance shifts. Second, adapted MCFs containing 12 cores, arranged on a circle, are fabricated. For this, two different fabrication procedures were investigated, namely, the mechanical drilling of the preform for a rod-in-tube version as well as a stack-and-draw approach. Both adapted MCFs yielded significant improvements with core-to-core wavelength variations of the FBGs of only about 0.18 nm and 0.11 nm, respectively, sufficient to fulfill the requirements for astronomical filter applications as discussed above.
RESUMO
We present an innovative concept of a semi-aperiodic phase mask design that enables the realization of multi-notch fiber Bragg gratings (FBG). This design utilizes the overlap and interference of near-infrared ultrashort laser pulses diffracted by short sequenced phase mask sections, which not only allows for a highly stable and reproducible inscription of a large number of wavelength filters but also paves the way towards full aperiodic phase masks. The semi-aperiodic FBG inscribed by this phase mask enables versatile notch filters showing multiple non-equidistant resonances. Those filters target applications, for instance in ground-based telescopes, where a large number of hydroxyl emission lines emitted in the upper atmosphere at near-infrared wavelengths restrict the observation of faint extraterrestrial objects.
RESUMO
PIP: Immigration patterns in the US in the last 50 years have defied the conventional wisdom that most international migrants are young, working-age males. Since 1930 more than 1/2 of all immgrants to the US have been women, and 2/3 have been women or children. Data show that the persistently large number of marriages of foreign-born or native-born US residents to alien women, coupled with increasing government regulation of immigration and a strong policy bias against the seperation of spouces and children, has resulted in the preponederance of women and children in immigration since 1930. The shift in the sex and age distribution of immgrants in the US in 1930 can also be attributed to the effectiveness of the 1924 quota laws in drastically reducing the enormous influx of immigrants from southern and eastern Europe, when the remaing flow was dominated by wives and children. Traditional sex role behavior has played a significant role in determining both the level and patterns of immigration to the US--while large inflows of economically motivated males induced 2nd flows of women and children before 1930, the 1940s saw the flow of foreign-born wives and children of US servicemen in the wake of Korean and Vietnam wars. An analysis of the Immigration and Naturalization Service data tapes for the 3.6 million fiscal 1972-79 arriving immigrants shows that almost 1/4 are children under 15. Except in this age group, females outnumber males in all other age groups. While immigrants are predictably younger than the US born population regardless of sex, immigrant women are more likely to be married than men, and both are more likely to be married than their US born peers. Immigrant women are substantially less likely to report labor market experience than immigrant men. Unlike US workers, immigrants tend to cluster at the top or bottom of the occupational scale, regardless of sex. Immigrant women are also clustered in the sterotypical female dominated occupations.^ieng