I'll offer a bit of frame challenge here...
The answer to "what is the difference between wired and wireless transmission?" is: there is no significant difference.
But that's not the question you're asking 😁 Your question actually is: what's the difference between wired/wireless transmission, and optical transmission.
- There is no big difference between wired and wireless transmission
In both cases, information is carried by electromagnetic fields that propagate as electromagnetic waves. Usually what matters to the receiver is the local electric field, for example a voltage on the gate of a FET, that will turn it ON or OFF.
If you use waveguides, for example wires or PCB traces, then you can make those EM waves go where you want. Then you can make a simplifying approximation that your cable is a lumped element which has stuff like "current" and "voltage" and "ground is zero volts". But if your cable gets long enough relative to the wavelength, then the approximation breaks down, you have to remember the signal actually propagates along your cable, which in this case is a transmission line, in other words a waveguide. Then, there is no concept of "current" or "voltage" in the whole cable, rather each point along the cable has local EM fields which wiggle around electrons, creating time-varying local currents in the conductors, which will all be different along the length of the cable.
Likewise, a transmitting antenna does not "create" electromagnetic waves from an "electric signal". The incoming electric signal is already an EM wave traveling along a waveguide (like a coax cable, but not necessarily). The antenna is also a waveguide that takes in the EM waves coming from the feed cable, and it is shaped just right to throw these EM waves into the air. It's basically an impedance transformer, which is the same as a lever or a funnel, but I digress. And a receiving antenna is also a waveguide, which has just the right shape to capture EM waves from the air and funnel them into another waveguide, like a cable or a PCB stripline.
Say you have a radio transmitter and a radio receiver.
If you move them close together until the antennas touch and make electrical contact, is it wired or wireless? The same physical phenomena are involved. Now if you disconnect the antennas (say they're mounted on SMA ports) and connect the ports together with a coax cable, pretty much nothing has changed except free wave propagation in the air was replaced with propagation inside a waveguide. The receiver will get a lot more power, but if it handles it, it'll work fine.
The difference is how the signals are encoded, and what frequencies are used. Different encodings and frequencies work best is you want your EM signal to propagate in different types of cable or in the air. For example simple logic levels aren't modulated on a carrier frequency, so they're really not suited to radio transmission.
If we take USART as an example for wired communication between two devices, the TX and RX lines are referred to a common signal(GND)
Well no. First, "GND" is not the same potential at the receiver and the transmitter. If your cable is long enough and/or some current flows into the "GND" wire then both ends of this wire will be at different potentials. There is no "GND".
This works because all receivers are differential. They care about voltage between two pins. Sometimes they are explicitly differential, for example a RS-485 receiver has "INPUT+" and "INPUT-" pins. Sometimes that's hidden, for example you have pins labeled "INPUT" and "GND", but what counts is the voltage between them. So if "GND" is at different potentials on both ends of your cable, the receiver won't care because it only knows about its local "GND" potential. It has no idea what "GND" means at the other end of the cable. As long as its "INPUT" pin is enough volts above its "GND" pin, that's a logic 1.
The notion of "voltage reference" is a convenient simplification to make human's job easier. But chips don't care. For example a FET has a gate. But what turns it on is the voltage between gate and source, so it has two input pins, one of which is low impedance (the source). And, since a 74HC logic inverter has two FETs in its input stage, it has three input pins: the one labeled "INPUT" connects to the gate of both input FETs, and the other two input pins are "VCC" and "GND" which connect to the sources of these FETs.
So, what your receiver cares about is voltage between two pins, ie electric field applied to the gate of the input FET, which determines if it turns ON or OFF.
When a "1" is transmitted, the transmitter launches an EM wave onto the wires, then this wave propagates, and its local voltage rides on top of what is locally labeled "GND". At the other end, the EM wave transfers its electric field into the receiving transistor, which turns on or off.
This happens at all frequencies. At low frequencies it is not noticeable, but it happens nonetheless.
- About optical...
DC, radio and light are all EM waves. The difference between wired/wireless and optical is the wave-particle duality.
Wired/wireless use the same physical mechanism, ie they receive EM waves as waves, using the EM fields, usually voltage.
Optical receives EM waves as particles, ie photons that kick an electron or molecule into an excited state. That is, photons trigger a mechanism that causes electrons to move, which then is current.