After assembling connectors and straighting the cable, the fibre is “longer” and adopts a serpent shape inside the tube creating a high focal ratio degradation. In this case the fibre “shrinks” with respect to the tube. The reason is to avoid the differential length between the fibre and the tube when rolled. Next, bring the first folded tube to the ends, etc. For rough lapping (reducing the excess of glue, for example), we use very fine sandpaper (P240 or higher, grain 10m), do not roll up the jacket in a wheel but fold it in halves: the tube lies straight on the floor, take a tube end bring together the tube ends. After experience in polishing, we found that we need basically 2 abrasive sheets, the 3 and 0.3 μm. Jacket/Tube: the stainless steel tubing is more expensive than the plastic one but it offers the highest protection against accidents, forced loops and light pollution.If the fit between connector and tube is too loose you may need to use some crimping tool. The rear part (boot type or tubing) has to fit in the protective tube. Remember that the standard ferrule diameter is 125 µm, therefore you can accommodate fibres with buffer/jackets of up to 125 µm diamter, or with cladding of up t0 125 µm if the jacket is removed (see Polymicro document here on how to remove the jacket). Connector: Check carefully both, the diameter of the fibre including the buffer/jacket and the inner diameter of the connector ferrule.1 meter longer than required in order to operate it with some comfort. We advice to buy fibres protected with polyimide jacket because you can leave it into the connector making it more robust against strenghts. Fibre: Best optical fibres for linking telescopes to spectrographs are multimode step index fibre with high UV transmission.Miscellanea: scissors, alcohol (propanol, isopropanol or methanol), acetone, water, microscope, optical tissue.Polishing Sheets 3 µm and 0.3 µm from AMP Netconnect or Thorlabs.Polishing Bushing (Disc) with SMA from Thorlabs.Sapphire-tipped Scribe Tool from AMP Netconnect or Diamond Scribe from Thorlabs.Adhesive: Epoxy two components, transparent, 2 minutes curing, from UHU profi-shop.Connectors: SMA-905 connectors from Kientec Systems model 504-R-Z-127-A3-3, ferrule type: zirconia, ferrule ID 127 µm.Tube: Square-locked stainless steel tube from Kientec Systems model SLP-40N (internal diameter 4 mm) with PVC sheath.Other characteristics at Polymicro Technologies. Fibre: Silica Optical Fiber Polymicro, Step Index, Numerical Aperture 0.22, Core 50 µm, Clad 70 µm, Buffer 90 µm.The User Guidelines from Polymicro contain salso very useful information about the handling of fibres. It is basically the same process we use for linking telescopes to spectrographs were we take special care to reduce the focal ratio degradation. The document describes the assembly process fot their SMA connectors types 906 and 905 for data and telecommunications applications. In particular, we have prepared a 10m, 50μm core fibre with SMA connectors and protected with a square-locked stainless steel tube.Ī very descriptive document is the instructions sheet 408-9863 distributed by Tyco Electronics: OPTIMATE FSMA Fiber Optic Connector Types 905 and 906 in PDF format. In this post we want to show through pictures and drawings the process of assembling a bare fibre into a protective jacket and ended with commercial connectors for spectroscopy purposes.
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