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Let´s suppose We have the following Optical Network Terminal :

enter image description here

According to datasheet, the receiver sensitivity is : -27 dBm

enter image description here

Now Let´s suppose We have the following fiber optical network :

enter image description here

As we see , the Optical Power Meter show us that we reach de limit (-27 dBm ).So I have several questions :

1 ) If we reach that limit (-27 dBm) : Does it affect the conectivity speed ?. For example If we pay conectivity of 300 Mbps this speed will down to 50 Mbps, or 30Mbps or 10Mbps ? Or just It cause intermitent conectivity ?

2 ) This second question is a little more elaborate :

If we have -27dBm so we have :

enter image description here

Does it means that our ONT can work until 2uW (microWatts )?

3 ) Why matter the -27 dBm ? Why just don´t elevate the energy (Watts) in the Optical Line terminal and we trade-off the losses and atenuation with more watts?

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2 Answers 2

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  1. Below -27 dBm, it stops working. That's the definition of "sensitivity". Of course, if you're at -26 dBm, your mutual information is not great, so you might experience lower data rate. How specifically that is implemented depends completely on the communication standard and the actual device.
  2. Yes. That is the definition of dBm. What's the question?
  3. Because you can't. This might simply be the maximum output power your transmitter can do, or the fiber is too nonlinear with higher powers, or this is a passively split multiuser medium where you can't just adjust parameters per user.
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  • \$\begingroup\$ 1) Thanks. I wanted to know if reach the limit of sensitivity affect the speed. \$\endgroup\$
    – NIN
    Commented Jul 25, 2021 at 3:56
  • \$\begingroup\$ Said that: it depends in the communication standard and the device. Actually reaching sensitivity would mean no communication is possible at all. Slightly above and some might still work, full speed might still work, whatever. \$\endgroup\$
    – mmmm
    Commented Jul 25, 2021 at 4:02
  • \$\begingroup\$ 1) Thanks. I wanted to know if reach the limit of sensitivity affect the speed. . . 2) So basically 27 dBm is the same that 2uW . 3 ) Sorry but it sound a litte trick. If this were a split multiuser even would be better for all the users, What do you try to say with : " the fiber is too linear with higuer powers " ? \$\endgroup\$
    – NIN
    Commented Jul 25, 2021 at 4:02
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    \$\begingroup\$ 3) nonlinear, not linear. There's no trick. "If you can't drive 900 km in 4 hours with your car, why don't you just drive faster?" Makes as much sense as "if it's not enough power, why not transmit more?" You just technically can't, usually. Also, more power in a nonlinear medium does not mean always better signal. You will need to read up on nonlinear optical channels if you're interested in the effects. \$\endgroup\$
    – mmmm
    Commented Jul 25, 2021 at 4:06
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enter image description here

Bit Error Rate and negotiated speed are both dependent on SNR above threshold. Your details are unknown, but it will have a similar response above threshold

There are implementation specific unknowns on dispersion, attenuation, phase jitter and crosstalk from EMI on the electrical side.

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  • \$\begingroup\$ Thanks tony, I'm not very clear what do you try to tell me. Could you explain me better please ? \$\endgroup\$
    – NIN
    Commented Jul 25, 2021 at 3:52
  • \$\begingroup\$ fiberoptics4sale.com/blogs/archive-posts/… \$\endgroup\$
    – D.A.S.
    Commented Jul 25, 2021 at 5:20

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