Interview

Abstract

Dr Piotr Miluski of Politechnika Bialostocka, Poland, talks to us about the work behind the paper ‘Fluorescent polymeric optical fibre illuminator’, page 1550 Dr Piotr Miluski My field of interest is luminescent optical fibre applications. The well-known advantages of polymers, such as easy low-cost processing, have caused their uses in optical applications to continuously increase. A particular focus is functional luminescent materials, which can be produced by doping polymers using special compounds. Moreover, the energy conversion efficiency of organics may be significantly higher than in inorganic materials. This has caused widespread interest in the technology of organic light emitting diodes (OLEDs). The conversion of light energy can also be used in optoelectronic sensors or miniature light sources. The optical fibre illuminator is a specially constructed light source. Optical fibre technology guides light using total internal reflection; thanks to this, it is possible to guide light in flexible optical fibre structures over long distances. The light source can therefore be spatially separated from the illuminated area. Additionally, characteristics of optical fibres, such as spectral attenuation and directional emission, can be used in special illumination applications. The fibre optic illuminators are especially useful in all hard to access areas. This kind of technology is often used in endoscopy equipment and other demanding medical and microscopic applications owing to its high flexibility and small size. They also emit so-called “cold light”, meaning that infrared radiation is highly attenuated, and heat transfer is minimal. Using optical fibres assures galvanic isolation; this means they can be used during the inspection of industrial tanks and other technical equipment situated in explosive areas. Future areas of application are as spotlight sources in some specific lighting designs (e.g. within museums). Directly doping the polymer using two fluorescent dyes allows modification of the final luminescence spectrum, which in turn allows spectral properties to be determined during the polymer manufacturing process. In the presented paper, a combination of two dyes (Perylene and Rhodamine 6G) was used to obtain a continuous luminescence spectrum over a wide range of visible radiation. Transmitting the light through the cylindrical structure causes excitation radiation (in this case from a 405 nm laser diode) to interact with the dopants on a longer optical path. As a result of this, the spectrum shape is changed along the length of the luminescent tip through reabsorption effects. The concentration of dopants and the dimensions of fluorescent fibre can be used for spectrum shape optimisation. The significance of the presented design is the white light emission, which was obtained using the fluorescence of dyes incorporated directly into the polymeric fibre structure. This solution causes light to emit directly from the lateral optical fibre surface. In this case, the directional emissions characteristic is different compared to typical optical fibre illuminators, which emit according to the emission cone from the fibre tip. The fluorescence phenomenon causes diffused emission, which reduces glare and harsh shadows. This can be especially useful in medical observation. Typically in optical fibre illuminators, the emission spectrum is determined by the light source (e.g. halogen lamp). The idea of using fluorescence phenomenon for spectrum shape modification is already widely used in light emitting diode (LED) technology, where, thanks to the radiation conversion in phosphors, it is possible to obtain white light emission from single p-n junction LEDs. A similar technique is proposed here for optical fibre illuminators. The excitation radiation is guided within an optical fibre and the white light emission is obtained directly from the surface of the fluorescent tip. Moreover, the emission spectrum shape can be changed by shifts in the excitation wavelength. Our group's research field is based on new luminescent (inorganic and organic) materials for optical fibre technology. Our investigations are concerned with material science and new optical fibre constructions (e.g. energy transfer inside single and multicore optical fibres) for spectrum shape modification. These techniques are used for new radiation sources, such as supercontinuum generation, lasers, and optical amplifiers. Our latest investigations are focused on new optical fibre source fabrication for wide visible and infrared radiation emission spectrums. This technology is currently a high priority because of the possible medical and scientific applications.