How do you guys solve the rotary slip ring issue with fiber optic on the reel? Slip rings for fiber optic are insanely expensive. Another question, is it possible to have such fiber optic tether easily detachable from the ROV without having to use penetrator which would have to be un-screwed every time, and seals replaced after some time? It is possible to make some kind of easily plug-able connector at the bulkhead for fiber?
Hi @laukejas, welcome to the forum 
This comment from another thread is likely relevant:
Iām not aware of any available options for this, but itās also not an area Iām experienced in, so itās possible thereās something I donāt know about. In general, many things are possible in theory but may not be readily available and affordable, and may not be robust enough to be a good idea.
From a theoretical standpoint the primary requirements of such a connector would be:
- keeps water out when connected (dry mate-able)
- this is likely feasible, but would probably require some form of locking sleeve, and a seal that gets replaced from time to time
- ideally it would also keep water out when disconnected / if the tether gets cut (wet mate-able)
- if thereās a marine epoxy that bonds well enough to the fiber this could work, in which case a replaceable seal may not be required
- provides a sufficiently good optical connection
- as Etienne described above, the low requirements of a general ROV use-case compared to the optimal capacity of the fiber itself mean that this could be ok (using the āfastā termination method, since the other methods form more permanent connections)
- the connector would likely need some form of locating and/or clamping feature(s), for repeatable alignment and contact between the fibers
- this could be quite challenging to do robustly, in a way that ensures good contact between the fibers while also avoiding damaging them
- some form of protection and/or regular checks and maintenance to ensure the fibers do not get damaged while they are disconnected, and to prevent/remove any particulate matter (e.g. dust, salt, etc) that could block the light path
- maintenance for this could be challenging to avoid damaging the fibers
Hi @laukejas
There are connectors for underwater fibres in the workclass segment.
For example: OptoLink
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Hi, @EliotBR, and thatnk you for the info! Regarding that bailing reel, that would be a very nice solution indeed. Sad that the guy in that topic you linked to, got robbed before he could take any pictures. I am still not sure how it would work. I mean, I know I could bail the tether manually by wrapping it around the reel, but I wonder if there is any way to automate it without going crazy technical so the tether could be wound with a crank or something. Is there anyone else who has done this? A few pics for reference would help a lot.
I looked into the connector that @Boko linked to - the fact that they donāt advertise the price, says a lot 
I need to make some research and maybe some experiments to see if I can build such a connector myself - I have a 3D printer and access to a metal lathe. Although I am still not sure how that would such connector integrate into the end cap. I build my end caps myself, and since the rest of my electrical setup is with copper, I usually just embed copper rods in plastic end cap with epoxy, soldering wires to the ends of the rods. Embedding a fiber optic connector into the end cap would be very difficult, and risky (if the embedded part of fiber breaks, the whole end cap is ruined). I wonder if I could simply embed a glass/acrylic āwindowā into the end cap, with fully removable connectors on each side, so that the fiber light could shine through that window? If aligned well enough, that should work, right?
Also, what happens if water gets inside the fiber optic cable? Does that ruin it completely, or just worsens the signal? I donāt think that could be avoided with DIY fabrication means.
Hi, @laukejas, My setup has the fiber media converter inside a waterproof box (red) mounted in the middle of the reel. A gigabit slipring with some extra conductors for the high voltage power to the vehicle and low voltage to power the media converter. Iāve run this for years with no issues. The subsea side has a 2" BlueRobotics WTE with the media converter inside it, and two BlueTrail Engineering cables connecting gigabit LAN, and HV power to the vehicle power supply. Sorry the photos are pretty rough.
MacArtney has told me they are working on a hybrid fiber connector for this use. Will keep my eye out for that.
Cheers,
Ken
Iām not particularly familiar with different fishing reel mechanisms, but I searched online for how the mentioned mechanism works and found this description and this video to be the most immediately informative results that I came across, and this page shows some pictures of internals.
A further search along the lines of āspinning reel mechanism internalsā may prove fruitful if youāre after additional information (there may be some useful diagrams in an image search) - less specific searches tend to yield results centred around what to consider when buying or operating a fishing reel.
Thanks for sharing! Your subsea converter side is larger than my entire ROV But it makes sense. Complicated, but avoids slip rings.
Thank you for sharing these links. The mechanism seems extremely complicated, I am not sure how it could be made on a large scale, especially the part that ensures the tether is wound uniformly along the width of the reel. I wrote to Daryll (from the first link you gave), perhaps he will share his solution.
Hi Etienne,
Can you please share the steps of converting the Fathom-X to fiber optic? here is my email ssaravin@gmail.com
Hi, i tried replacing the Fathom X with ethernet to fibre converter. But there is no communication received at the topside. Can you some input on what are the possible causes?
hi matt, i would like to see some post or pictures of your fiber setup, also what BiDi module did you use for your tether? i appreciate your knowledge feel free to email me. mccully.cris@gmail.com TIA !