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Fiber Bragg Grating Fabrication
Published in Ricardo Oliveira, Lúcia Bilro, Rogério Nogueira, Polymer Optical Fiber Bragg Gratings, 2019
Ricardo Oliveira, Lúcia Bilro, Rogério Nogueira
As may be seen in Figure 2.6, the UV beam exiting from the HeCd laser (“A”) is reflected by three mirrors (“Bn”). The first reflection occurs at the mirror (“B1”), which is used to guide the beam upwards from the optical table. The second mirror (“B2”) is used to guide the beam parallel to the optical table, and the third one, (“B3”) is used to guide the beam downwards to the POF (“F”). Between the third mirror and the POF, there is a plano-convex cylindrical lens (“C”), that is used to focus the laser beam onto the core POF, increasing the power density in that region. The fiber is supported by a v-groove plate, placed on top of a 3D mechanical positioner (“H”). The latter is used to make a temporary free space coupling (“I”) between the cleaved/polished POF and the silica pigtail fiber (“K”), terminated with an FC/APC contact, required to prevent Fresnel reflections. Between the fibers, a drop of an index matching gel is normally introduced in order to lower the background noise. The fibers need to be close enough to prevent the formation of FP cavities that can deteriorate the visibility of the grating. To help the alignment process and to make sure that the light is propagated into the core of the POF, an objective (“E”) is normally placed at the far end of the POF and the near field image can be observed using a laser beam profiler (“D”). The pattern imprinted into the fiber is determined by the period of the phase mask (“G”) placed in close contact with the POF. The operation wavelength of the optical components shall suit the wavelength of the UV source, allowing to have high transmittance from the output laser to the fiber. The use of phase masks with operation wavelength other than the one of the laser source increases the intensity of the zeroth order, which is detrimental for the formation of the grating structure [43]. In such cases, the use of a modified Sagnac interferometer could be used, in order to block the zeroth-order and use only the ±1 orders [4].
Anomalous light scattering in photonic cholesteric liquid crystals
Published in Liquid Crystals, 2020
C. L. Folcia, J. Ortega, J. Etxebarria
We analysed the light polarisation of the main ring by measuring the intensity passing through a linear polariser that can be freely rotated. The analysis merely consisted in the measurement of the maximum and minimum detected intensities and their corresponding angular positions. The maximum intensity was observed when the polariser was oriented along the transverse direction , and the minimum was for the direction (see the scheme at the inset of Figure 2(b)). From measurements at different points of the ring and using various positions of the pumping beam spot on the sample, the relation resulted. Figure 2(c,d) show typical intensity profiles of a segment of the ring for and orientations of the polariser respectively as detected by a laser-beam profiler (Ophir – Spiricon, LLC).
Handheld pocket-size Fourier transform profilometry using projector-enabled smartphone
Published in The Imaging Science Journal, 2020
Joewono Widjaja, Sangchai Paichit, Jerasak Kamonboon, Jaroon Wongjaren
In the past few years, advancements in digital display and image array sensor technologies have triggered the evolution of smartphones. In conjunction with powerful information processing, smartphones have a profound impact not only on our everyday life but also on science and technology. Owing to the high pixel resolution of image sensors, there have been many studies devoted to the applications of smartphones to optical and holographic metrologies. For instance, laser beam profiler using smart phone has been recently reported by Hossain et al. [1]. Smartphones were developed for surface plasmon resonance-based chemical and liquid concentration sensors [2,3]. Digital holographic microscopies using cell phone have also been reported for imaging of micro-particles and biological samples [4,5].