Wavelength selection for optical wireless communications systems

This paper explores one of the most important trade issues, the selection of the optical wavelength. Historically, most developers of such systems have employed wavelengths in the near-visible infrared spectral region (~780 nm to ~850 nm), principally because of the availability of efficient and reliable direct semiconductor diode-based sources at those wavelengths, and for the 780 nm devices, the cost advantages of utilizing the same wavelength as is used in CD recorders.While cost is obviously an important factor in the wavelength trade, one must also consider several additional constraints,most notably the need not to exceed eye-safe limits on transmitted intensities under conditions of high data-rate transmissions through heavy atmospheric attenuation (due to fog, for example). Other important trade criteria include overall performance,and the potential for system growth and scalability. When all of these factors are considered, it becomes clear that a more judicious approach is to employ wavelengths near 1550 nm, the same wavelength range used in commercial fiber-optic communications networks.