Tech Breakfast: Fibre Optic Cabling

Transcription

1 Tech Breakfast: Fibre Optic Cabling An on Twitter

2 Fibre optic cabling Applications within Film & TV Single mode vs. Multi mode fundamentally different. Tight buffered vs. loose tube cable Pre-made vs. spliced cable Connector types; LC, SC, ST, APC, MPO etc Future developments.

3 Applications within film & TV facilities Storage Area Networks Network switch uplinks (backbone / vertical segments / End-Of- Aisle topology) Synchronous broadcast signals MADI, SDi, HDMI KVM Long distance CWDM / DWDM (for December s Tech Breakfast!)

4 Single mode vs. multi mode cable Single mode cable ( OS1 / OS2 or 9µ/125µ ) is the original style of fibre optic cable developed by BT and Corning in the 1970s With a nine micron transmissive core the cable is able to contain the nm wavelengths efficiently. V = number of modes k 0 = wave number a = core s radius (9µ vs. 50µ) n 1 & n 2 = refractive indices

5 The cheap n cheerful young pretender Multi mode Whereas single-mode contains the light wave nearperfectly multi-mode cable relies on total internal reflection; the wavefront bounces down the fibre core as it hits the core/cladding interface. By clever use of interference modes many distinct waves can be launched down the cable and by using an interference detector laser-diode the modes can be recovered. All at 850nm typically. Limitations are length 500 1,500m typically Graded index fibre OM4 is the newest standard.

6 A bit of multi-mode history OM1 (lit. Optical Multimode type 1 ) ~ late 90s, obsolete 62.5µ core with 125µ cladding and VCSEL optimized glass OM2 ~ early 2000 s; largely unused! 50µ core with 125µ cladding and VCSEL optimized glass OM3 ~ 2007; still widespread. 50µ core with 125µ cladding and laser optimized glass OM4 ~ 2009; the current standard. 50µ core with 125µ cladding and laser optimized graded-index glass

7 Limitations of multi-mode optics Distance due to modal-dispersion Distances typically range from m (depending on application) and can be calculated using the bandwidth-loss product. 10Gbits -1 ; typical max data rate in Graded Index OM4 fibre uses a transmissive core that varies it s refractive-index across the diameter of the core so that the wavefront is better guided down the core.

8 Some multi-mode gotchas Encircled-flux refers to the effect of overfilling the fibre when launching with cheap optics. The cladding carries an interfering signal. At multi-mode your link budget is single-figure dbs at OM1 8dBs of loss is acceptable, at OM4 it should be sub 2dBs. If you mix & match 50µ and 62.5µ parts you loose ~2.5dBs at each junction.

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10 Live demo Wesley low-loss Cyrus shows cable splicing Pre-made patch cords are only really useful for local patching; 50m pre-mades are not good! Tight-buffered cable (used to make patch cords) has worse minimum-bend-radius vs. loose-tube cable. Tight-buffered cable is not easily repaired when damaged. Loose-tube cable spliced to pigtails is the better way.

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12 Cladding alignment vs. Core alignment splicing Any manufacturing tolerance issues in fibre show themselves in the position of the core within the cladding. Original machines used precisely milled v-grooves to give accurate cladding alignment Current gen machines (like the INNO IFS-15 Wes is using) use two cameras to accurately align the cores.

13 Poetry in fibrecabling.

14 Quick and cheap fibre infrastructure fault-finding 10 pocket laser pointer shows bad splices or damaged cores very quickly

15 Quick and cheap fibre infrastructure fault-finding cont. 100 fibre microscope shows contaminated connectors Cleetops is used to restore the condition.

16 The better technology single mode fibre. In many ways very similar to multi-mode technology, same connectors, style of patch panel, cable construction etc. Works in an entirely different way light is optimally constrained in a 9µ transmissive core so no need for total-internal-reflection with problems of modal dispersion etc. MUCH higher data rates and distances (80km without amplification) MUCH better signal-to-noise ratio; 28dBs with best optics. Wider application in video and data. Multiplexing is possible more of that in the next session.

17 Further reading

18 on Twitter