Is fiber optic Digital or analog? optical signal is digital or analog?

what kind of signal Fiber generate? I mean traditional phone system is analog, but Ethernet is digital, but what about Fiber Optic? please keep it simple.

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    – Ron Maupin
    Commented Jan 3, 2021 at 21:30

9 Answers 9


Due to the way that fiber lasers work, common digital encoding on fiber is <20% is a 0 and >80% is a 1 so the beam is never "off" it just varies between low and high power. Turning the laser OFF is much more of an event than varying its power level, so this method is faster.

The transmitted data is put through various encodings before going on the fiber which ensure things like an equal number of 1's and 0's and never having a very long string of 1s or 0s in a row - the received data is decoded from that format before being passed on, and for Ethernet anyway the actual "raw" data speed in the line is greater than the "nominal" speed to permit carrying decoded data at the nominal speed.

At 10 GB, the encoding schemes have been altered to make them less of a burden - rather than using 10 raw bits to carry 8 data bits as is done at 1 gigabit, 66 raw bits carry 64 data bits.


All signals are analog, wether if it's electricity (copper), light (fiber) or radio (wifi), signals/waves can have any arbitrary value. However, in the computer world they carry digital information (either 1 or 0) and they are processed digitally, transforming the analog information into digital information. How this transformation done depends on the encoding. Check the Wikipedia article about the Manchester code for more information.



the answer of this question is depend of how we under stand data transmission across fiber optic ??
lets say we have a group of 0's and 1's represent the data need to be transferred from end to end . simply across the fiber optic ,transmitting such data is by turning laser light on for interval to represent 1 and turn it off for interval to represent 0 , this behave of sending data is DIGITAL the next figure show basic transmit and receive based on this concept enter image description here


There are many differences between analog and digital, but one of the primary distinctions that will easily answer your question is that analog signals make use of sine waves while digital signals make use of square waves.

Since fiber optic data transmissions in networking use square waves, it is a digital signal.

However, you can also transmit a analog signal over fiber optic, such as a video. It is not the medium that determines the type of signal, but the devices on each end.

  • Love to know what someone didn't like about this answer. Yes, I could have made it much more technical, but the OP requested that the answer would "please keep it simple."
    – YLearn
    Commented Sep 20, 2015 at 18:07
  • I guess this is one of those cases where we will have to disagree. Yes, it is very simplistic, but it is still true. A square wave is formed based on changes in amplitude, frequency, phase, or a combination of the same. Without getting into the differences of types of square waves and exactly how they are used, digital signals are all square waves, even if you are using fixed voltage ranges. It doesn't actually mean you are producing a "square wave" in that sense. Conversely analog signals also all encode data onto a sine wave in some manner.
    – YLearn
    Commented Sep 20, 2015 at 20:09
  • 1
    you should take up analog circuits as a hobby; it would help disabuse you of your misunderstandings Commented Sep 21, 2015 at 0:12
  • Im getting quiet confused right now need to sit and read all these stuff through! thanks Commented Sep 24, 2015 at 6:58
  • @YLearn The square-vs-sine distinction may be usable in many areas but it doesn't work out everywhere. Various digital modulation schemes use sine carrier waves (PSK, DMT, ...). Even fiber optic communication uses a sine wave (light) that is most often amplitude modulated - of course it all depends on the point of view. Additionally, analog signals are not necessarily sine in nature. Of course, you can interpret any wave as a sum of sines (refer to FFT)...
    – Zac67
    Commented Aug 20, 2018 at 12:39

The transmission medium is completely irrelevant when deciding whether a signal will be digital or analog. Basically, Computers talk to each other in digital transmission(0s and 1s) and analog transmission is used for things like phone calls, radios, etc. Whether a signal is analog or digital depends on our requirement.

I think you're associating frequency modulation(FM) with analog transmission. What you need to understand is that optical fibers are capable of carrying analog signals as well as digital signals using amplitude modulation(AM). Technology for frequency modulation(FM) through optical fibers does not exist.


In layman’s terms, in a Fibre optic system, two electronic circuits are linked with an optic fibre . The optic fibre is only a transport medium. During communication of the two electronic circuits, the transmitter will convert the electrical signal into light/optical signal so that it can travel in the optic fibre, on arrival to the receiving end, the detector in the receiver will convert the optical signal back into the electrical signal. From this analogy, l turn to believe that the optic fibre is a physical conductor that transport both digital and analogue signals in the form of light.


While there are already great answers here, surprisingly none has gone to the core of the question.

The short answer: it's both, depending on what you're looking at. A fiber optics designer will look at the actual signal in an analog way, while a switch designer and anyone "higher up" will see it as digital.

The longer answer: in its core, analog means that you express information in a value (voltage, frequency) that is proportional to the information (or its logarithm etc.). Digital means that you quantize the information (measure a voltage level, assign logical values etc.) and transmit the numerical value instead of the actual analog value.

This is most apparent in audio applications. On analog magnetic tape, sound is recorded as a magnetic fluctuation that is analog to the acoustic amplitude or pressure. On analog cable the acoustic amplitude is expressed as a voltage level.

On digital CD, the acoustic amplitudes have been measured (sampled) and the numerical values are stored on the disc (PCM). These numerical values are also transmitted over digital audio connections (S/PDIF, TOSLINK, HDMI).

That said, the network signal on optical fiber (or copper cable) expresses digital values, so it's (mostly) digital.

The most commonly used optical Ethernet PHYs use simple line codes like 8b/10b and 64b/66b that may be purely digital as well. This has changed somewhat with high-speed lanes (50+ Gbit/s) that have begun to use more analog-ish encoding methods like pulse-amplitude modulation (PAM) - but still, the underlying transport method is digital.


I understand your confusion, you'll need a blackboard or animation explanation to clear it, I cannot put it in words.

  1. The Optical signal is not relevant in this area of discussion, Optical fibres are called optical because they use an optical property of light( internal reflection ) to transmit a signal or a long continuous signal(data)

  2. Data in the computers or any digital device is stored in digital format ( 10011011101) (highs and lows) (On s and Off s)..

    The goal is to transfer the sequence in the exact order, this can be done by taking an analog radio signal at a standard frequency and wavelength etc and tune it according to the sequence , example: when digit is 1 set the frequency to high and when 0 a different frequency (usually low ) this should be done at a fixed clock rate, another way is to tune the amplitude of the radio signal etc..

Here though the sequence of digits are transfered the signal is originally analog but changed at the clock speed according the digital data.


Here is a layman's answer to a presumably layman's question:

Information in a fiber optic system can be transmitted analog (signal varies continuously) or digital (signal exists at discrete levels representing zeros and ones). Most fiber optic transmissions used by telecommunications/cable operators are digital.

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