I'm a Physicist and have a good background into the Physics of optical systems, but I like to learn more indepth about the various formats used in optical communications such as ook, NRZ, RZ, PAM4, QPSK etc. Also Shannon's theory and other communications aspects. Can you suggest a book that covers these topics like modulation formats? I was hoping that there is a short descriptive book or video book etc.
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A lot of the work on optical modulation schemes is optimized for optical fibers, where nonlinearities of the material at high field strength causes distortions which increase with fiber length requiring occasional conversion back to electronic signals and regeneration as a new optical signal. The optimized modulation schemes allow longer distances between electronic regeneration (optical amplifiers are used in between). So it would be best to start by restricting your reading to introductions to Free-space optical communication – uhoh Apr 20 '23 at 23:07
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(what does "high field strength" mean? pushing hundreds of milliwatts of light through a several micron diameter fiber core results in high electric fields in a nearly but not quite perfect optical medium, resulting in several kinds of intermodulation distortions for example, which build up over tens of kilometers of fused silica class. This just doesn't happen in hundreds of millions of kilometers of interplanetary space because both the field strength and electron density are so incredibly low.) – uhoh Apr 20 '23 at 23:12
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potentially slightly helpful: Am I using Shannon-Hartley Theorem and thermal noise correctly here? When considering SNR, a very important point to understand for traditional free space optical communication and how it differs from radio is that radio receivers convert the electric field of the wave directly to a signal, whereas traditional photodetectors convert photons to electron-hole pairs and amplify the resulting photocurrent, which means radio wins over light for long distances. New technologies overcome that. – uhoh Apr 20 '23 at 23:16
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See Quantitatively, why will optical communication be better than X-band for deep-space communications? and especially see MarkAddler's "No, you don't need "at least some photons per data bit". 13 bits per photon has been demonstrated with laser communications" See also Receiver and transmitter in RF/optic satelite communciation: distance vs datarate – uhoh Apr 20 '23 at 23:21
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and Receiver and transmitter in RF/optic satellite communication: distance vs data rate v2 and Are direct conversion optical receivers being looked at for future deep-space communication? and How is the maximum data rate of the Psyche mission's Deep Space Optical Communications (DSOC) system expected to scale with distance? Basically, don't start from optical fiber communications texts - stick to free-space optical communications texts! – uhoh Apr 20 '23 at 23:22