4. Conclusion

The two approaches to optically generating microwave signals, namely by amplitude modulation of the optical carrier or by beating two optical waves, were presented. The generation of frequency signals covering frequency ranges up to THz has revitalized applications in the sub-millimeter range. This approach makes it possible to directly generate microwave signals with high spectral purity. The second fundamental contribution is linked to the possibility of producing microwave oscillators with very high quality factors, very low phase noise and very high spectral purity (all these parameters being closely linked). The third is the ability to tune these microwave oscillators over extremely wide ranges.