Are fiber optic signals digital or analog?

Fiber optics is just a physical medium to carry signals just as a wire pair or a coax. A laser light is modulated by the signal to be transmitted. The signal itself is either analog (smoothly varying level such as a voice signal) or digital (level encoded into binary numbers). The signal to be transmitted determines whether it is analog or digital, and either analog or digital signals can be and in fact are carried by fiber optics.

I actually read this reply but needed some sleep; when I worked up, I was surprised to find more then 1 reply. If the experts here need to comment, then it is usually not a trivial question.

I think I now know the answer. Fiber optic signals could be analog or digital, at least theoretically. It is mainly intensity modulation. There is a reason why I don't know the answer; I believe some others too, like me, need to find out. I often get my doubts cleared with answers from Quora. This time, it seems the Quora experts were not too clear themselves; or rather they were not too aware of why some of us are not too sure if optical signals are analog or digital.

I am more of a physics students. Somehow, I do know that electrical signals could be transmitted in conducting circuit like telephony; we were shown a varying voltage waveform which could be seen in an oscilloscope - analog signals. Then RF radio signals too are analog when they are modulated "AM"; we may not know the details in-depth, but could sense the engineers could somehow imprint the voltage signals into the RF waves. The receiver end needs only to decode and produce an audio output just as with conducting wire circuits.

Then we study the basics of Maxwell's theory. Who would come across explanation about doing the double slit experiment with : "Let's produce a beam of monochromatic light of uniform intensity...then modulate its intensity...etc". Well, I have known about am/fm modulation in radio transmission but, somehow, I forgot that amplitude means intensity. Introduction to Maxwell's theory seldom touch on modulating light intensity unless it touches specifically on optic fiber communications.

Fiber optic lights are transmitted through internal reflections within the optical fiber. I now can have some idea how the light intensity(early stages use IR frequencies) could be modulated. It could be sending out light pulses, but with varying intensities. So instead of voltage/time variation, we now have intensity/time variations. Of course getting analog light signals maybe be more difficult. Most physics students probably think optical signals could more likely be digital 0/1 as with off/on in electrical signals.

Looking at this thread and asking, isn't fiber optics one connector and telegraph, (phone) two connectors, even if the second connector is the ground?

All signals are analog.

Some analog signals carry a digitally encoded message while others carry the information in a baseband signal (local telephone service) or some form of modulation be it amplitude (AM) or frequency modulation (FM) or one of a myriad other forms of modulation.

I think it is not correct to say "All signals are analog"; it is like saying all signals exist through change (Yi Ching - The Book Of Change) - the Red Indians wouldn't be able to send smoke signals if they only stand at attention

If I can measure the signal using an oscilloscope or a volt meter or an optical power meter, I will maintain that is analog. I can't measure encoding using using one of these devices unless the device has software to interpret the analog signals.

I know it's pedantic, but as an analog engineer, I have the occasion to counsel digital engineers on why their circuits are not working like they expected.

We live in an analog world, although quantum computing may change our view on that issue.

Unless you came from another world, I disagree with your assessment about signals not originally All analog, since We all are living in this analog world..

Which means that everything that transpires in real life are happening in a continuously changing fashion.. Similar to the way people think, the thoughts are formed continuously not in a discretely.

The smoke signals you cited are coded signals by the Indians just like the Morse code or the Semaphores..

The digital signals that you are more familiar with and now the norm, only came about when the A/D conversion techniques were perfected which I believe was sometime around the late 50's or early 60's only..

Fiber optic is just a medium for transmitting signals, be they digital or analog...

I've designed and built an analog fiber optic system. At that time the DC to 25 MHZ analog signal could not be digitized without prohibitive delays and resolution complications. We found that a DC bias was needed to be added at the transmitter LED to put the LED in a linear region. This DC bias was then removed at the receiver. A high-speed chopper circuit bounced the transmitter signal between bias + signal and bias. This allowed for a sample and hold circuit to provide the bias reference level in the receiver for subtraction. We even toyed with the idea of chopping in a bias plus reference level but found changes in gain were much less critical than diode thermal drift changing offsets.

Excellent for electrical isolation...

That was one of the reasons for implementing this design.

Calibration and amplification would be an issue with an analog light signal. No such issue would arise with a digital one.

Calibration and amplification would be an issue with an analog light signal.

That's true. If you want to stick with analog, you might modulate the light with a frequency modulated carrier. I recall using a precision tape recorder that used FM.

https://en.wikipedia.org/wiki/Frequency_modulation

First of all - The main difference between an analog and a digital signal is that an analog signal is a continuous time signal that changes over a time period and a sine wave represents it. While a digital signal is a discrete time signal that carries information in binary form and a square wave represents it.

Then - you can`t send light through coaxial cable, or electricity through fiber optic. Now i think you can answer yourself to your question!

i'm jumping in from the middle of the introductory part -- but you likely need to grasp the entire course

https://youtu.be/oIurmHsRFSc?t=1694

IMHO:

The entire universe may have a frequency which is higher than we can detect,faster than a Plank length wavelength.

In other words,the universe may be pixelated in such a fine format that we cannot measure it.

The universe could blink in and out of existence for millions of years and we would never know if it restarted where it left off.

How long does it take to blink your eyes?

What happened when your eyes were closed?

I realize this has strayed into the realm of philosophy,but it is something to think about..just don't think too hard.