Laser Emitters

Earlier this month I was asked to assist a customer with a 32 link, DTX Series system. The customer failed to understand what transparent point-to-point transmission actually means and I will be addressing this in my next posting.

What I do want to talk about is safety precautions that need to be taken when working with fibre optic transmission equipment that use Laser Emitters. Both our Fibre Pro and DTX Series use laser emitters. These Lasers provide stimulated emission, i.e. they are on all the time.

The Fibre Pro and DTX Series products emit intense infrared light at 1310nm and 1550nm which is invisible to the human eye. This radiation can permanently damage the retina of the human eye. The diagram below shows the visible and invisible light spectrum.

All Fibre Pro and DTX Series products are packaged in antistatic bags that are sealed with a cautionary notice. Please read the notice before tearing the seal. The notice is there for your safety.

Please take the following precautions:

1. Never look into the source or the fibre cable.
2. Never power-up the source useless the fibre optic cable is connected to it.
3. Always keep the protector cap on the source if no fibre optic cable is connected.
4. Be cautious!!!

Fibre Pro


DTX Series

www.BFRDigital.co.za

Calculating - Fibre Optic Power Budget

Calculating the Optical Power Budget for a fibre optic cable link is really simple. Firstly, we need to start with some known facts. The losses quoted below are the norm but you can obtain the cable and connector losses from your local cable manufacturer for a more accurate calculation.

Let’s look at the following example:

1. Calculate the Cable Loss
Cable loss = Cable Distance x Cable Loss per km
Cable loss = 2km x -2.5dB/km
Cable loss = -5dB

2. Calculate the Connector Loss
Connector Loss = Connector Quantity x Connector Loss
Connector Loss = 2 x -0.5dB
Connector Loss = -1dB

3. Calculate the Splice Loss
Splice Loss = Splice Quantity x Loss per Splice
Splice Loss = 2 x -0.2dB
Splice Loss = -0.4dB

4. Calculate the Total Link Losses
Total Link Losses = Cable Loss + Connector Loss + Splice Loss
Total Link Losses = -5dB + -1dB + -0.4dB
Total Link Losses = -6.4dB

We have now successfully completed the first part of the calculation and we have established that the total loss on this fibre optic link is -6.4dB. The second part of the calculation is even simpler because most manufacturers of fibre optic transmission equipment quote the Optical Power Budget in their spec sheets. For example the Optical Power Budget for the Fibre Lite Range of products is -12dB. Alternatively, we can calculate the Optical Power Budget:

Transmitter Output Power (LVTXD-010-SMM Fibre Lite) = -14dBm (quoted by the manufacturer)
Receiver Sensitivity (LVRXD-010-SMM Fibre Lite) = -26dBm (quoted by the manufacturer)

Optical Power Budget = Output Power - Receiver Sensitivity
Optical Power Budget = -14dBm - (-26dBm)
Optical Power Budget = 12dB

Power Margin = Optical Power Budget – Total Link Losses
Power Margin = 12dB + (-6.4dB)
Power Margin = 5.6dB

It is good practice to allow for a Power Margin of 3 dB. This allows for cable degradation and should you ever have the misfortune of having the cable damaged or cut you still have enough Budget to re-splice the cable.


www.BFRDigital.co.za

Fibre Lite

We at BFR Digital have just completed our Fibre Lite product range. This range of products caters for the transmission of CCTV video signals and unidirectional data signals over multimode fibre optic cable. Fibre Lite offers an optical budget of 12dB; which means a maximum cable distance of 2.5km and a system safety margin (excess power margin) of 3dB.

This product range is the first in its class to feature Digitally Controlled AGC; this feature automatically adjusts the AGC to compensate for optical cable degradation and other insertion losses. Each video receiving channel has it own dedicate processor that continuously samples and adjusts the AGC.

In true BFR Digital fashion the Fibre Lite range is designed to be robust and easy to use; for this reason the Fibre Lite range is offered with a 2 year warranty. We achieve this robustness and reliability by over engineering our products.

www.BFRDigital.co.za