**7. Experimental Implementation**

This section investigates the simplicity of the proposed secure communication system in simulation and hardware implementation.

#### *7.1. Simulation Implementation*

The simulation results of the proposed secure communication system are presented here by Matlab 2017b programs and implemented in a computer with specification Core i3-2.00 GHz, Intel CPU, and 4 GB RAM. The decimal values of the secret key are selected as *x*<sup>0</sup> = 0.9382, *y*<sup>0</sup> = 0.3171, *α* = 4.6516, *s* = 0.5782, and *z* = 149936. Figure 14a–f depicts the simulation results of the proposed communication system. Empirical correctness of the system can be observed through the retrieved signal *Mr*(*s*), which is completely identical to the original signal *M*(*s*) that has been encrypted, and then sent through a free-space optical channel.

**Figure 14.** Simulation results: (**a**) the original signal; (**b**) the modulated output *Mb*(*k*); (**c**) the encrypted binary data *Me*(*k*); (**d**) the serial binary data; (**e**) the decrypted binary data; (**f**) the retrieved signal.
