Two Fabry-Perot interferometers based on chemical etching in multimode graded index fibers are fabricated and their response to temperature and strain are compared. Chemical etching is applied in the graded index fiber end creating an air cavity. The interferometric cavity is formed when the graded index fiber with the air concavity is spliced to a single-mode fiber. The intrinsic sensors present high sensitivity to strain and low sensitivity to temperature. For the 62.5 μm core fiber, sensitivities of 6.99 pm/μe and, 0.95 pm/°C were obtained for strain and temperature, respectively. The sensor based in the 50 μm core fiber, on the other hand, presented sensitivities of 4.06 pm/μe and -0.84 pm/°C for strain and temperature, respectively.

Intrinsic Fabry–Pérot Cavity Sensor Based on Etched Multimode Graded Index Fiber for Strain and Temperature Measurement

Microlens-ended fibers could find great usefulness in future biomedical applications, particularly in endoscopic imaging applications. In this context, this paper focuses on microlens-attached specialty optical fibers such as imaging fiber that can be used for probe imaging applications. Stand-alone self-aligned polymer microlenses have been fabricated by microcompression molding. The fabrication parameters have been optimized for different materials, such as poly(methyl methacrylate) (PMMA), polycarbonate (PC Lexan 123R), Zeonor 1060R (ZNR), and Topas COC. A comparison study of the focusing and spatial resolution of the fabricated lenses is performed prior to employing them for fiber-optic fluorescence imaging applications.

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Design, fabrication, and characterization of thermoplastic microlenses for fiber-optic probe imaging

Optical fiber tips for biological applications: From light confinement, biosensing to bioparticles manipulation.

Fabry–Pérot cavities based on chemical etching for high temperature and strain measurement

A new class of all-fiber beam shaping devices has been realized by inverse etching the end face of single mode and multimode fibers to form a concave cone tip. Concave tip fiber can convert a Gaussian beam profile to a flat top beam profile with a uniform intensity distribution. A flat top beam with intensity variation of approx. 5% and flat top diameter to spot diameter ratio of 67% has been achieved. This device can also change the beam shape from a Gaussian to a donut by moving the observation plane. A flat top multimode fiber beam delivery is attractive for applications which require high power and uniform intensity distribution. In single mode fiber, concave tips could be used to reduce the beam spot size diameter, enabling efficient light coupling from a single mode fiber to an integrated optical waveguide.

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Laser beam shaping and mode conversion in optical fibers

Fabrication of polymer microlenses on single mode optical fibers for light coupling

Concave cone fabricated by a chemical etching process similar to the technique used to make fibre tips (convex cone) is presented. Typically, optical fibres are etched in a hydrofluoric (HF) solution with a thin layer of oil floating on top of the HF solution. The present investigation shows that concave cone etched fibre (CCEF) can be obtained by following the beginning of the etching process. Comprehensive measurements of the dependence of the width and height of the taper angle of the concave cone are plotted. The results of this investigation have led to an optimum approach for core fibre alignment that is suitable for use in connecting fibres for efficient coupling between single-mode fibres.

Chemical etching of concave cone fibre ends for core fibre alignment

This article presents a fibre-optic sensor that measures temperature and pressure. Its operating principle is based on the amplitude modulation caused by the variation in the radius of a concave micro-mirror crafted into the end of an SMF optical fibre. In fact, a micro-cavity engraved into the end of the fibre by selective chemical etching is filled with a PDMS (Polydimethylsiloxane)-type polymer. Due to surface tension, the polymer micro-drop takes on a hemispheric shape characterised by a certain radius. After polymerisation in an oven at 100 °C for one hour, the hemispheric micro-drop is coated with a thin layer of gold using the vacuum evaporation technique. Typically, concave micro-mirrors can be obtained with bend radii of between 10μm and 30μm. Under the action of a temperature gradient or a variation in pressure, the thickness of the PDMS changes and causes a variation in the bend radius of the micro-mirror. As a result, the light intensity guided by the optical fibre and reflected by the micro-mirror is modulated by the variation in its bend radius. In this configuration, the sensor has a thermo-sensitivity of – 0.08dB/°C with a resolution of 0.13 °C in a range of between 20 °C and 100 °C. It also has a pressure sensitivity of 0.11dB/bar between 10 and 20 bars. The measurements are taken by a reflectometer (OTDR). In addition, the experimental results have been validated by theoretical modelling. This sensor is relatively simple to make and can be used in a wide range of applications, in particular biomedical and industrial ones.

Fibre-optic temperature and pressure sensor based on a deformable concave micro-mirror

Shaped optical fiber tips have recently attracted a lot of interest for photonic jet light focusing due to their easy manipulation to scan a sample. However, lensed optical fibers are not new. This study analyzes how fiber tip parameters can be used to control focusing properties. Our study shows that the configurations to generate a photonic jet (PJ) can clearly be distinguished from more classical-lensed fibers focusing. PJ is a highly concentrated, propagative light beam, with a full width at half maximum (FWHM) that can be lower than the diffraction limit. According to the simulations, the PJs are obtained when light is coupled in the guide fundamental mode and when the base diameter of the microlens is close to the core diameter. For single mode fibers or fibers with a low number of modes, long tips with a relatively sharp shape achieve PJ with smaller widths. On the contrary, when the base diameter of the microlens is larger than the fiber core, the focus point tends to move away from the external surface of the fiber and has a larger width. In other words, the optical system (fiber/microlens) behaves in this case like a classical-lensed fiber with a larger focus spot size. The results of this study can be used as guidelines for the tailored fabrication of shaped optical fiber tips according to the targeted application.

Photonic Jet-Shaped Optical Fiber Tips versus Lensed Fibers

Several techniques of centring a microlens onto the fibre optic end face are studied. In most of them, microsphere lenses are centred with the aid of high-accuracy micro-positioners. This process is complicated with regard to the difficulty in manipulating microsphere lenses. In this paper, a simple and accurate self-centring method for mounting microsphere lenses using a concave cone etched fibre (Demagh et al 2006 Meas. Sci. Technol. 17 119–22) is described. This technique allows the centring of a wide variety of microlens radii, typically 7 µm to over 24 µm. The proposed process, however, is not affected by any spatial positioning control of microspheres. In over 85% of the attempts, the microsphere lenses were centred on the fibre axis to within 0.12 µm.

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Assia Guessoum

Papers

Fabrication of polymer microlenses on single mode optical fibers for light coupling

Chemical etching of concave cone fibre ends for core fibre alignment

Fibre-optic temperature and pressure sensor based on a deformable concave micro-mirror

Photonic Jet-Shaped Optical Fiber Tips versus Lensed Fibers

Self-centring technique for fibre optic microlens mounting using a concave cone-etched fibre