Hi there!
So I have a bit of a weird situation with my current set up, in that I have an Aquatica housing with LED flash trigger, and a YS-D1, and a YS-D2. As has been documented in various forum threads, the YS-D2 is not very sensitive, and so doesn't trigger from most LED flash triggers. That means that the solution I came up with is to trigger the YS-D1, and have the output of the D1 trigger the D2.
That means running a fiber optic from the housing to the left (D1) strobe, and another fiber optic from the left strobe ALL the way to the right (D2). This was not possible with the length of the arms and my usual fiber optic cables so I ordered a long Sea & Sea cable which cost over $80, and still was not long enough. So I am building my own.
For this after a few measurements I guesstimated that these parts would work:
25 feet of TosLink fiber optic (already tested with some Toslink to make sure it triggered): https://www.amazon.com/gp/product/B005LJQPE0/ref=oh_aui_detailpage_o03_s01?ie=UTF8&psc=1
Some rubber grommet thingys that would fit snugly in the Sea & Sea FO hole: https://www.amazon.com/gp/product/B00XBG5U82/ref=oh_aui_detailpage_o03_s01?ie=UTF8&psc=1
Some o-rings that would fit snugly over the grommets: https://www.amazon.com/gp/product/B01MTO0US6/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
So.. on to the build
Cut the fiber optic on a hard surface
Measure out the length by running it along the whole setup as if its being installed
Trim back the rubber from the outside of the fiber, exposing the still coated core
Trim the little ridge on the rubber grommet, so that the o-ring can fit in the groove
Place o-ring, this should now fit snugly in the FiberOptic hole
Trim the rubber on the fiber optic back to where when slide inside the grommet, it just peeks out the other end. The fit with this brand of fiber optic was nigh on perfect!
You should only need a bit of rubber cement to hold the fiber in place..
Thats pretty much it!! I now have over 2 foot of fiber optic for about $3! Pretty happy with the results. Obviously it doesn't have the coiling functionality of the branded fiber optic but I am going to be using some clips to hold it along the arms.
this from them for $25 or so. makes nicer cuts then doing it by hand.