Fiber optic tethers - fiber converters


#1

Hi i am currently in my final year of college an as such I must undertake a final year project. my project will be changing the setup of the video ray so that it can be controlled using a fiber optic cable. my problem lies with my understanding of fiber optics more specifically with the converters. I am finding it very hard to find any information on how they work other then electric in light out. I was hoping that someone might be able to give me more information on the workings of the converters. I have not yet decided on which type of fiber to use as it will come down to cost at a later stage. But any general information on how they work in terms of taking in the electric signal, converting it to light and the opposite would be greatly appreciated!


#2

Hi David,

That sounds like an ambitious project- good luck!

Here's a link to a page that I learned a lot from. It's great because it starts with an overview of what the basic modes and characteristics are, then dives right into how each part of the system actually works.

Also, Beau is a guy here on the forums who actually made his own fiberoptic transceiver cape for an OpenROV (awesome, right?!) . Here's a link to his post about it.

I should note that what makes fiber really desirable for small ROVs is that by using two different wavelengths for TX and RX, its possible to both transmit and receive along the same strand which can be extremely thin and light, and can be paid out from the ROV much like a spider spinning a web. The equipment to communicate this way is less common then what you would generally be able to find off the shelf, but it might be worth looking into (OpenROV could certainly use an open-source design for something like this). If you want to see such a system being used, watch James Cameron's documentary "Ghosts of the Abyss". That documentary was a big inspiration for me.

Eric


#3

Hi Eric,

ha ah ya but for the sake of my degree it must be done!

thanks very much thats a very useful page! thats a great help!

David


#4

A couple of comments:

1) The Nereus fiber is spooled at both ends and the twisting is balanced as it unspools from both ends. Also the fiber is not recovered at the end of the dive, but lost in the water. For a hobbyist this may be expensive and my be rough on swimming pool filters.

2) If your fiber is short (a few hundred meters) and you can time division multiplex (alternate packets sent down and up the fiber) you can put a transmitting LED at each end of the fiber and use those LEDs as receivers as well. Something like this should do the job but you will have to roll your own interface board. http://www.digikey.com/product-detail/en/HFBR-1414TZ/516-2039-ND/1990437