3. 2×2 directional coupler

3.1 Description

In the previous paragraphs, we saw examples of the use of electro-optical components integrated into a lithium niobate crystal to modulate the optical signal in amplitude, phase, or both (I&Q). This section deals with the 2×2 directional coupler. This is a class of modulators that has been the subject of extensive research, particularly at the emergence of this technology, with a view to switching operations between waveguides. The idea is to be able to couple two parallel and adjacent optical waveguides in order to actively direct the light initially in one of the input waveguides to one or the other of the output waveguides.