Digital Optical HELP !

[~arronc]

I need to split a fibre optical digital signal between two sources.

I have tried to use a passive splitter, but the signal degrades so much I can no longer see the the clock, never mind the signal !

Does anyone have any experiance, or could reccomend a product ?

Cheers,

Arron

[test]

From a physics standpoint:
Optical fibres
Information can be transmitted by varying the intensity of light or infra-red radiation travelling through a transparent glass or plastic fibre. An analogue signal would be sent as a continuously variable light intensity but pulsed signals are more common. Serial rather than parallel data transfer keeps the number of fibres to a minimum.

Because a negative light intensity is not possible a sine wave must either modulate an otherwise constant light intensity (the carrier) or be converted to a digital signal and be transmitted as pulses of some sort.

Fibre optic waveguide action.
Light within an optical fibre striking the boundary between the fibre and the cladding of lower refractive index will be refracted only if the angle of incidence is less than the critical angle (see earlier). When the angle of incidence is greater than the critical angle for that boundary the light is totally internally reflected, and can be kept within the fibre by repeated total internal reflections. A fibre with a sharp change between the refractive index of the core fibre and the refractive index of the cladding is called a step index fibre.

Due to interference light cannot follow all the conceivable zigzag paths with the necessary internal reflection. The paths that are allowed are called the transmission modes of the fibre. In a thick fibre there will be a large number of modes.

Some light will travel directly parallel to the walls along the centre of the fibre (axial mode). Light of the highest order mode will be making the largest possible number of zigzags as it travels along the fibre and will be most steeply inclined to the fibre wall (hitting it at the critical angle).

Light travelling in a higher mode travels a greater distance than that in a low-order mode, and therefore will take a longer time to pass through a long fibre. Therefore, a pulse entering the fibre will come out as a pulse of longer duration and a different shape. Successive pulses may overlap at the end of the fibre. This can also cause distortion of analogue signals. Modal dispersion can be eliminated by using very thin fibres where only the axial mode exists (monomode fibres) or graded index fibres, where the light in the higher modes travels faster and therefore reaches the end of the fibre at the same time as the axial mode light.

The speed of light in the fibres is also affected by the frequency of the light, and therefore similar problems to those of modal dispersion can occur. The solution is to use filtered monochromatic light.

[~arronc]

OK : beleive me I know a lot about fibre, but the problem remain that I dont want to build my own repeater. The problem is not in the cable, but in the end coupling points.

[test]

try this link for product options:
http://optical-components.globalspec.com/ProductFinder/Optics_Optical_Components/Fiber_Optics

[~arronc]

Cheers for the link ;)

Perhaps I need to be more specific. I am looking for an active hub to fan out a single TOSLINK output to several synchronus TOSLINK inputs.

[test]

like this?
http://www1.dealtime.com/xKW-toslink_hubs/NS-1/GS.html

[~arronc]

Pretty close : but no. That allows switching between output, but does not allow splitting of the signal to simultaneous outputs.

Cheers for your help though : i think we're getting warm !

[test]

did u try 3COM?

how about this?
http://www.ramelectronics.net/html/audio_toslink_adapters.html

http://www.pacificcable.com/More_Pages/Toslink_Converter.html

maybe that is better

[~arronc]

No : not the right things ;)

[test]

ok .. nevermind .. i give up ... most of those kept the synchronus data line open to different sources even when switched so i dont know what u are trying to accomplish ... fiber optics isnt that complicated .. maybe u need to rethink what u want

then build it .. buy the parts u need and build it yourself ... geez

[~arronc]

Cheers : I do appreciate your help !

WHat i need to do is take a single toslink feed out the back of my mixer, and split the signal in two without degredation, and feed two active digital speakers, each with their own toslink input.

I have tryed an passive splitter, but it didnt work well enough. I could get someone i know to splice the feed into two cables with a fibre welder, but that doesnt sound much better.

[~spektron]

Hi arron,

if you have a RME card, you can use the on-chip digital mixer to reroute signals and "fan out" exactly the way you describe. The settings are done in software, which runs independently of your mixing software. The routing itself is just done in hardware, the software only changes the settings. You use up a buffer's latency, but that is really not that bad since everything will still be in sync. I don't know make cards with a toslink option, mine has adat (optical) and spdif (coax) connections. You'll want to do this especially since you must split the left and right channels!

[~arronc]

Hi there !

Yeah i have this facility on my soundcard (tascam PCI822) also, and am running ADAT to a digital mixer. My problem is then the mixers monitor out is a single toslink optical out, but I have two speakers. So i need to split the signial.

I still havent found a solution to this !

I agree if you had a card with 2 toslink outputs you could do what you are suggsting, but I dont know of one.

Cheers,

A

[~spektron]

Not sure about the Tascam, but the RME allows you to just reroute the digital signal back through the soundcard, bypassing any
software. As long as the tracks you use for routing don't collide with the ones you use to mix, the performance is *identical* to using a format converter box in that you only suffer single latency, not the usual double. And you can split apart the channels, which I think you need to do, regardless.

Anyway, I would be worried about the toslink format being interleaved, in that you'd be sending a garbled mess to both speakers if you could successfully split the cable. The ADAT seems interleaved with 8 channels on a single optical cable, you have to explicitly decode it to get anything useful. Anyway good luck with what you're trying to do!