Photopolymerization process is present in the optical fiber technology since its beginning. Organic coatings preventing degradation of an optical fiber was the most important implementation of this process which ensured its practical industry application in telecommunication. However, this process can be implemented to design specialty transducers related to both optical and chemical sensors, as well. Simple optical transducer can be a microtip being an extinction of the optical fiber core as a polymer microelement. A chemical transducer can be a thin polymer layer manufactured on the tapered part of optical fiber. The second type of transducer can be applied to chromatography measurements as a solid phase microextraction fiber. In the paper, technology of the tapered optical fiber and photopolymer sensing layer formations were described. In the first step a standard heat and pull technique was used to taper an optical fiber which, then, was cleaved in two symmetric pieces. Light was launched to such a single element and output optical power from tapered part of the fiber was measured to optimize the photopolymerization process. Placing this element in a photopolymerizable monomer mixture and using a specially selected holder allow for manufacturing a polymer sorption layer applicable as a solid phase microextraction fiber. Extended description of technology of this chemical transducer type and preliminary experimental results displaying its feasibility were presented.
Presented article shows the effect of using ZnS:Mn nanoparticles in the solution of higher alkanes on the light wave propagation in a biconical, adiabatic optical fiber taper. The used mixture of alkanes with nanoparticles forms a special cladding surrounding a fiber taper. Described studies show change of beam intensity depending on mixture temperature and its state of aggregation. Tests were carried out in a wide spectral range from the visible up to infrared wavelengths. The taper was made of a standard single-mode telecom fiber, pulled out to a length of 20.0 ± 0.5 mm and the diameter of the taper waist is 14.0 ± 0.2 μm. Such taper causes the beam to leak out of a waist structure and allows to add an external beam-controlling cladding material. The built-in sensor containing nanoparticles operates on the on-off principle. Nanoparticles added to the alkanes cause increase of hysteresis in a heating and cooling process. Such mixture makes also a significant shift of temperature characteristic in a heating process in which mixture change their physical state with a simultaneous slight shifting of the characteristics during cooling. Depending on the source used, weakening or amplification of the signal was obtained after switching to the liquid state.
The main aim of this paper is to present a geometry shaping of a polymer microtip manufactured on the end of different multi-mode optical fibers by using UV radiation. Used fabrication process is based on a photopolymerization where the microtip grows on one end of the optical fiber when light is launched to its other end. Two different types of the photopolymerizable mixtures and two typical multi-mode optical fibers with different core sizes and refractive index profiles were used for tested microtips. In order to assess their geometries scanning electron microscopy images were used. These images have showed that the influence on the microtip geometry has optical power and spectral characteristics of the UV light. The sensor’s transducer properties were evaluated on the basis of backscatter measurements when a refractive index of a surrounded medium of the microtip changes. Dynamic ranges of tested optical fibers with selected microtips have reached 25-28 dB for the gradient-index multi-mode optical fiber while for the step-index one were around 14 dB. Future research will be focused on increase of dynamic range for the sensor’s application and will be tested as micro-lens.