Hi, Is anyone here currently working on Power over Fibre (PoF) Power Over Fibre technology?

There is a very hard physical limit to the possible power densities. At a few kW per square mm, the glass core of the fibre softens and melts. This in effect destroys the waveguide nature of the fibre, so the only way that power handling can be increased is to expand the diameter of the region carrying the energy- which makes it very multimode. More or less standard multimode fibre with active optical core diameters of ~ 0.1mm might reliably manage 4 or 5 watts of optical power at most - while if that was directed in a single mode fibre, the core would be melted. Converting that back to electrical energy is not especially efficient either.  While the technology may be optimized a bit, I'm not aware of any changes to the underlying physics. There is also the optical hazard to consider - firing more than milliwatts into the human eye is irreversibly blinding. If you want more power, beyond a certain point, you need to run more fibres in parallel.

Mike.

I'm wondering what REN number it has for the 'final mile' of telephone lines to the home. Maybe rotary dials are coming back. (I'm still on rural ADSL)

Interesting area though.

Mohammad Junaid Khan said:

REN isn’t typically relevant

Partly that was a bit of clickbait, but also it is a level of loading that might be relevant for any time a PoF is provided to a 'modern' digital phone system that [currently] requires the home to have mains power to drive the receive electronics. The old REN level was for the Bell and other bits.

Strowger would be proud of his longevity [not buried yet - he was an undertaker !]

Even a REN of 1 needs half  a watt, ideally more like  one (4000 ohms, 25Hz,  at least 40V RMS but less than 80V at the customer terminals) will be beyond the power levels theoretically possible with the sort of fibres currently being installed in and to the typical UK house. The current customer end cables tend to be a varient of this stuff https://www.telenco.uk/documents/TELENCO_Dual%20sheath%20drop%20cable_LM050DS_1FO_0108.pdf

Note the 9um single mode core - and pretty much all the Openreach network uses something similar, as to the other providers.

 And that is combined/split 32 ways at the poles so that each customer gets rather less than 1/32 of the energy in the main cable. In current systems,  at the launch end we are looking at a laser optical power of perhaps 1mW to  a few mW ( 0dBm +/- a few) and after a few additional  losses about -25dBm at the receive end.  (1uW, -30dBm, is near the threshold for reporting a signal lost.)

You might just about manage something over that size of fibre,  with the UK ringing cadence,  if you were allowed to jack the power up to near fibre frying levels, and  to store the energy within the non-ring periods.

Oddly as a bit of an aside, I am helping my son build a thing for decoding the nos dialed on an analogue phone for a Scout challenge, based on an old 704 unit  He is finding the currents and voltages of the old 'POTS' phone system something of a surprise, being brought up in the world of 3,3V CMOS logic and so on. The transients of many tens of volts and the ringing voltage it generates have provided a valuable lesson in back EMF management and surge protection strategies. 

Mike 

That's a nice challenge - a POTS dialer.

There was a piece in Electronics Weekly a good few years back on how they did the Morse telephony in the WWI trenches and the "EMF management" of trying to keep them secure.

Interesting stuff.

Stealth comms 100 years ago, in the trenches of World [the power of web search!]