Informationen in deutsch Informations en français Информация на русском языке	Interesting to know about fiber optics The following summary about some of our standard products was designed to give you a short introduction about the possibilities and different types of applications with our fibre optic products. For the part of products, deliverable within one week we marked the prices. Please note, that the prices are without any obligation. The prices are marked without the value added tax. Please ask us too for our special offers and our customer specified products. What types of glass fibres are available and what are they used for? As a rule, quartz glass fibres are used in today's optical spectroscopy (UV/VIS and NIR). The fibres are drawn in special drawing towers from high-purity quartz glass pre-forms. These pre-forms consist of a core with a higher refractive index and a surrounding shell with a lower refractive index. For that reason, the drawn glass fibre forms a wave-guide making it possible to transmit light. This structure in the glass fibre remains intact during the drawing process. The cross section of individual fibres is usually in the range between 55 µm and 1000 µm. Our product range covers all fibres between 8 and 1000 µm. 1000 µm fibres require very large bending radii and are quite critical, as far as handling is concerned. Very small cross sections are frequently used in fibre bundles or specific fibre arrangements. Typical applications utilize individual quartz fibres between 100 µm and 600 µm core diameter. Fiber arrangements The so-called LOH fibre (low OH < 2 PPMS) only has very few OH groups. This type of fibre is required for NIR applications, since otherwise the attenuation will be too high even on short distances. HOH (high OH = 600 – 1000 PPMS) fibres correspondingly have more OH groups. The transmission capability of these fibres is significantly better in the UV range. Therefore, HOH fibres are predominantly used for UV/VIS applications. Typical attenuation of a HOH fibre (UV/VIS) Typical attenuation of a LOH fibre (NIR) How long can glass fibres be? Glass fibres of lengths up to several hundred meters are used in spectroscopy. This is particularly common in process applications in the NR spectroscopy, in order to transmit signals from external areas to the analyser or, for example, to retrieve signals from underwater applications. In case of UV applications, as of today there are still some limitations in the length of the glass fibres. The is primarily caused by the strongly increasing absorption and diffusion of the quartz glass fibres. To what extent can a glass fibre be bent? A rule of thumb says, that under short term loads, the bending radius of the fibres may not be less than 100 times, and in case of permanent installation, not less than 600 times the radius of the glass fibre. Summary optical Fibres The optical fibres made for spectroscopy are made of quartz glass. There are 3 different kinds of fibres. The using depends on the spectral region cause of the different wavelength depending transmission. For the UV/VIS-region there are fibres with an high concentration of OH (HOH). For the VIS/NIR-region fibres with low OH concentration are used. If you have very short wavelength (<215 nm) to transmit you have to use solarization resistant fibres (SHOH). For mechanical protection the fibres outer tube can be done out of metal. Custom made fibres (length, configuration) can be produced also. Please ask us for your customized optical fibres. Fiber with silicon sleeve Fiber with metall sleeve The Core For spectroscopic applications, generally, multi-mode step index silica fibres are used. These range in core thickness from 50 microns to 1 mm. The core is made out of pure silica. Other fibre cores with much higher absorption are made out of certain glass types or plastics. These are not offered in this catalogue. First a distinction is made between silica with high or low OH content. Silica fibres with high OH (600-1000 PPM) are used in the UV/VIS wavelength range because of the low absorption in the UV. They are referred to as UV/VIS fibres. For Deep-UV applications (below 230 nm) special solarization resistant fibres can be used. The water content causes strong absorption peaks in the NIR wavelength range. In order to get good fibres for the NIR range, the “water” is removed from the silica. This results in low OH fibres (<2 PPM) with low absorption in the NIR. They are referred to as VIS/NIR fibres. The Cladding In order to get the light guiding effect the core is cladded with a lower index of refraction material. For the highest quality fibres with the lowest absorption this is a fluorine doped silica, the so-called silica-silica or all-silica fibres with a numerical aperture (NA) of 0.22. The Buffers Without further protection fibres would easily break, because of small scratches or other irregularities on the surface. Therefore a next layer, the buffer, is added. This buffer also determines under what circumstances the fibre can be used. Temperature range, radiation, vacuum, chemical environment and bending are factors to be considered. Polyimide buffers offer a wide temperature range (-100 to 400°C) and superior solvent resistance. Also, this material is non-flammable. Drawbacks are sensitivity to micro bending and the difficulty to remove it. For extreme temperatures (-190 to 750°C) a gold buffer is used. Gold-coated fibres are virtually inert to all environments and make hermetically sealed high pressure feed through possible. (See: pressure feed through). The same is true for aluminium buffers for temperatures from -190 up to about 500°C. Low out gazing makes them also excellent for use in vacuum. Optical Fibre Numerical Aperture Numerical aperture is a relative measurement of how much light a fibre can gather. Numerical aperture is expressed as a result of Snell's law: NA = (N12 - N22) 1/2 = Nsinmax All our fibres have a numerical aperture of 0.22 which equals a whole acceptance angle of 24.8°. In case of needing other numerical apertures please contact us. Sketch of the numerical aperture Different types of fiberconnectors Terminations for our fibre assemblies include the price of SMA 905 connectors. FC and ST terminations, and 6.35-mm OD stainless steel ferrules are available for an additional charge. Bulkhead Bushing Assembly. The 21-01 SMA Bulkhead Bushing for example allows you to mount a fibre on a through-panel such as a chamber wall. Solarization-resistant Optical Fibres The UV radiation produced by some emission sources degrades the silica in a standard patch cord over time, resulting in increased absorption and invalid data. The degradation is called solarization. The active part of our solarization-resistant fibres consists of a silica core, surrounded by silica cladding. Then the fibre is coated in aluminium, which prevents the optical fibre from solarizing. The fibre pre-form (a high-grade silica rod used to make the fibre) is made in a hydrogen-rich environment that helps to heal the silicone/oxygen bonds broken down by UV radiation. Non solarization resistant 400µm UV-Fiber Solarization resistant 100um Fiber More about the Solarization effects you can read in our application forum. Fibres and Feed-through for your application in the Vacuum The FC-VFT vacuum feed-through are designed for use of fibre optics in vacuum chambers, such as for plasma monitoring. The vacuum feed-through consists of an M12 housing with Viton® O-ring and 2 SMA fibre optic interconnects to allow easily coupling to fibre optic cables and probes. The vacuum feed-through can be delivered for all fibre diameters, such as 50 µm, 100 µm, 200 µm, 400 µm and 600 µm, for UV/VIS as well as for VIS/NIR.