Wireless Optical Telecommunications

Chapter 11

Installation and System Engineering

“Innovation is an alliance between research, marketing, instinct, imagination, product and industrial courage”.

Antoine Riboud

(1918–2002)

11.1. Free-space optic system engineering and installation

11.1.1. Principle of operation

Basically, the principle of transmission of a free-space optic (FSO) is based on the transmission of a divergent beam in line of sight (LOS).

In Figure 11.1, the equipment is placed along the top of each building and they are pointed toward each other. The A equipment of the X site sends digital information to the Y site via a modulated optical beam, such as a laser diode. This beam is voluntarily slightly divergent to avoid problems of misalignment. Part of the wave front is collected on the receiving optics antenna and focused on the receiver diode (e.g. PIN diode) of the B equipment placed on the Y site. This operation is performed in the opposite direction, from Y to X (full-duplex).

Each device consists of several modules:

– For the transmission function:

- the connection interface: electrical or optical to send and receive digital data;

- the electrical/optical conversion module (case of optical interface);

- filtering and amplification of the electrical digital signal;

- the emission optical module containing the laser.

– For the receiving function:

- the receiver optical module containing the diode;

- filtering and amplification of the electrical digital signal;

- the electrical/optical conversion ...