“Eyes are the windows of the soul”
The emitted optical radiation of the emission module of an optical device is a very significant parameter in the calculation of the optical link budget. This radiation is characterized by the emitted power, its aperture (or field of view — FOV), and the emission wavelength. For reasons of safety, precautions or limitations can be considered according to the values of these three parameters. This is what will be developed in the first part of this chapter. The second part will approach the safety aspect of the communication, the third part evokes the power consumption, and, finally, the last part relates to the legislation.
Human beings, among others, can see wavelengths ranging from 400 nm (blue) to 700 nm (red), this is probably due to the evolution of the species, because this range corresponds to the peak of the solar spectrum (see Figure 3.12). Nevertheless, some tissues of the human eye can also interact with other ranges of the spectrum of optical radiation and are thus likely to be damaged under particular conditions.
In the near infrared (from 700 nm to 1,400 nm), radiations can be particularly dangerous for the retina of the eye (Figure 7.1), not only because of the process of concentration of the optical beam by the eye, but especially because of the absence of the palpebral reflex (blinking of the eyelid), ...