The meaning of analog video on PON

Can somebody explain me the meaning of analog video on Passive Optical Network?. I am not able to get as to how the RF overlay is being used in the fibre optics.
Thanks
-Sidd

As well as you can modulate the light with on/off modulation (digital), it can also be modulated with an analog RF carrier signal. Key issue here is the linearity of the modulation and demodulation.

Dear Radiohead,
My doubt on the issue is that making light ON & OFF is one thing but can we really modulate light in the fashion as we do RF carrier....I mean changing Amplitude, Phase and frequency. Does a light at 1550 nM wavelength can be modulated....
And if it is so why we reuire only ON OFF type of optic transmission, why not the conventional RF type modulated wave transmission.
Please enlighten....
-Sidd

Well, I know for sure it's possible to do AM modulation of the generated light. Just by changing the current bias of your laser diode, the output power changes accordingly. But as stated before, a laser diode inherently is non-linear, so your modulation quality will be mediocre. An alternative is operating the laser in CW and modulating the output with an optical modulator.

PM modulation is might be possible but I do not know how it can be done and certainly not in an economical way. So we're stuck to AM. ON/OFF keying is just a special case of this.