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Question Fibre HDMI supporting > 18gbps (4x 6gbps lasers or 12gbps lasers)

jfinnie

Distinguished Member
Came across this interesting post from CEDIA about fibre cables potentially able to operate above 18gbps:

HDMI Data Rates for 4K HDR

However, many AOC solutions already in the market today comprise 4x optical lanes — 3 are currently used for AV data, the 4th for being clock. If there's 4x 6Gbps lasers, then the cable could theoretically support the upcoming 24Gbps level of HDMI 2.1, as HDMI 2.1 will re-purpose the clock channel to a 4th AV data lane, and embed the clock. The good news is that the 24Gbps tier will be the most relevant for a long time yet, able to support up to 4K/60 4:4:4 with 12-bit Dolby Vision, all uncompressed. Brilliant!! Some AOC's are even using up to 12Gbps lasers per lane, which may prove to be fully compatible with the top tier of HDMI 2.1 at 48Gbps, unlocking further formats such as 8K up to 120fps. Please check with your vendor for details.
Does anyone know for easily available fibre cables in the market how they are configured and whether >18gbps support is likely?
 

ChuckMountain

Well-known Member
I suspect that individual cables already on the market will only work at up to 18Gbps. As the standards haven't fully flowed down yet then a manufacturer would be guessing at what to include and increasing their cost base.

If they can add another laser on a multi-mode then that might only necessitate a "head change"
 

jfinnie

Distinguished Member
I suspect that individual cables already on the market will only work at up to 18Gbps. As the standards haven't fully flowed down yet then a manufacturer would be guessing at what to include and increasing their cost base.

If they can add another laser on a multi-mode then that might only necessitate a "head change"
As above - mostly guess work at present.
The point made in the post is that some cables are purportedly already built in a way which might be compatible. I'm not talking about an eventual proper spec for fibre cables (please, HDMI.org, pull your finger out). Surely what is being said makes sense - if a cable was constructed with 4x6gbps lasers (instead of 3x6gbps lasers with a recovered clock) and the hardware starts signalling using the clock lane, there isn't any good reason for it not to work up to 24gpbs unless something unfortunate has been baked into one of the ends. What is very clear is that the 3 laser cable has zero chance of working above 18gbps.

So if there are common cables available with 3 lasers, and common cables available with 4 lasers, there has to be some advantage to thinking about the 4 laser cable? If the 4 laser cable were marginally more expensive, I'd consider that perhaps worth a couple of quid.

Re-terminating most of the HDMI fibre / hybrid leads isn't going to be workable from what I can see.

So does anyone know how particular cables in the market are configured?
 

ChuckMountain

Well-known Member
If the hardware had 4 different laser colours or 4 different optical paths and the firmware\hardware could support it then it might be feasible

So having a look at the cross section of the Ruipro on Joe's site



There are 4 optical fibres in the middle with presumably 4 same colour lasers driving them so a multi-core cable rather than multi-mode.

If the hardware supported a slightly different encoding and had 6Gbps lasers then with a suitable firmware update you might be able to get 24Gbps.

Whether that is feasible would be down to the manufacturers implementation of the head though...
 

jfinnie

Distinguished Member
There are 4 optical fibres in the middle with presumably 4 same colour lasers driving them so a multi-core cable rather than multi-mode.
Hopefully it's not a work of marketroid fiction... :)

Let's look at this from another angle - anyone know which cables have only 3x 6gbps lasers and so are definitely not going to be capable of any more than 18gbps?
 

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