- #1
Aziza
- 190
- 1
In our lab we are to measure speed of light by making a light signal travel through optical fiber. At one end there is the transmitter, which will output the light signal into the fiber, and it will also "modulate" the signal. According to my lab manual, "The reason that the signal is made to modulate is because that gives us a reference point for observing the time delay between signals because the delay will show up as a phase shift between the two modulations. It would be very hard to observe the time delay between two constant dc signals"
I have absolutely no clue what that entire sentence means at all...
From what I understand of the rest of the manual, I know that this "modulated signal" will appear on an oscilloscope. Also at the other end of the fiber there will be connected a receiver, which will display the signal coming in from the fiber on the oscilloscope. So there should be two signals: a modulated signal and the actual light signal (i think..actually, does modulation somehow change the actual light signal? or does it just output its own signal?) but the sentence I quoted above speaks of two modulated signals, not one...but there shouldn't be three signals total...I am very confused and can't find a simple explanation anywhere...
I have absolutely no clue what that entire sentence means at all...
From what I understand of the rest of the manual, I know that this "modulated signal" will appear on an oscilloscope. Also at the other end of the fiber there will be connected a receiver, which will display the signal coming in from the fiber on the oscilloscope. So there should be two signals: a modulated signal and the actual light signal (i think..actually, does modulation somehow change the actual light signal? or does it just output its own signal?) but the sentence I quoted above speaks of two modulated signals, not one...but there shouldn't be three signals total...I am very confused and can't find a simple explanation anywhere...