glass fibre optic ST cable Question

ST and Single Mode are both AT&T products. Theta used single mode and called it LaserLinque. It is vastly superior to ST but very costly. It was (is?) an $800 option on a Theta transport or DAC plus $250 for the cable. Total cost $1850! My brother and I both have Theta front ends and he has the single mode hook up while I'm using Tara Decade balanced digital cables. We really can't do an empirical comparison as he has a Data II transport and a Gen IIIa Dac, while my rig is a Data Basic transport and a Gen Va balanced DAC. We have looked inside his stuff and the single mode units are little interface boxes that Theta has painted over. I'd sure like to know the source of the interface is as I'm sure they could be obtained for much less than Theta charges and my circuit boards are set up for them. 10 minutes with a soldering iron and... If you enter "single mode" on ebay, all sorts of stuff pops up and I wish I knew if any of it is what I need.

Toslink and ST are the two standards for digital audio fiber. My understanding is that the written standards specify the connector to be used, but are vague on the glass. Both SM and MM should work given the short distances involved. If you are lucky enough to have ST connections on your equipment then SM with well polished ST terminations should provide the best results.

I'll mention a few things here. I do not believe that single mode and multi mode fiber can be interchanged. Single mode is laser driven and multi mode is LED driven. Single mode is much smaller in diameter. Most of the "audio" fiber is terminated with "ST" connectors. Though I have seen some variations. I have compared AQ opti link pro 1 and 2 to a home brew multi mode fiber cable, a commercial fiber cable the Kimber Orchid and D60. The cheap home brew that my local network equipment supplier made for me was equal to them all and only cost $20. Find out what type of fiber your transport and dac require. They need to be the same. Since you have an IT back ground try to source a cable through a com wire supplier. Give the "cheap" commercial fiber patch cables a try before spending a couple 100 on a name brand. Fiber transmission was perfected long before it was used in the audio world. How much care is taken in the termination of the cable is what really matters.

Thanks for the replies. esp Mrderrick.
To clarify what I do know, and reiterate some of your replies, and can share:
ST is in fact just a connector - a bayonet connector.
And yes, SM and MM are not compatible. the "transceiver" - the thing that converts electrical signals to optical is made for one type of optical cable. both ends of the path must match!
and yes, SM and MM are different sizes and use different wavelengths.
I'm not sure if I agree about SM=laser MM=LED, but will defer to Mrderrick's statement. (regardless, never look into the end of an optical cable!!!).
I expect I just need to contact the manufacturers. I''m afraid they'll just say, use -our- cable.
But yes, I have lots of good IT fiber patch cords around and will play.

PS.. transceivers are made by people like IBM, ATT & Siemans. Its a very techy world, but IBM actually has all the specs of their solder-on transceivers online. I've forgotten all the variations of wavelengths, voltages etc.