Is optical fiber an analog channel?

Now all the people who write books are not worthy of the preface. . . .

The signal in optical fiber or wireless is a baseband digital signal modulated into a high-frequency carrier by modulation (that is, a voltage signal of 0 10 1). For example, the carrier frequency in wireless is from several hundred MHz to several GHz, and the carrier frequency in light is about 194THz (corresponding to the optical wavelength 1550nm).

So the so-called analog signal in the first sentence should refer to the modulation signal. All long-distance communication systems (wireless communication and wired communication) are the same, and you can regard them as "analog". Only short-distance transmission (such as between chips on a circuit board) is directly transmitted by digital signal of 0 10 1.

The second sentence should refer to the coding mode of the signal. For example, a direct transmission of audio is a continuous voltage signal (imagine the waveform of heartbeat), which is analog. The purpose of digital is to sample this voltage signal first, turn it into a string of 0 10 1, and then spread it (for example, drinking 0V is 0, 1 is 5V), so it is "digital" after quantization and coding.

I hope it helps you. Now he's really a book writer. . . . .

From the modulation point of view, the signal in optical fiber is analog (all long-distance communication is analog), because if it is directly transmitted by digital signal, the loss is too great. The so-called modulation is actually to move the baseband digital signal to a certain frequency band of high frequency, so that the loss is relatively small when propagating.

From the coding point of view, the signal is digital (there is basically no analog coding now)

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Well, there's nothing I can do to insist on treating ignorance as fearless. It's really a bull's head and a horse's mouth