On September 21st, 2015, Carlos Belmonte Palmero successfully defended his PhD thesis entitled "Semiconductor lasers for random bit generation, wavelength tuning and circularly polarized light emission" in a public session.In his PhD research, Carlos showed that semiconductor lasers can efficiently be used for generating sequences of random bits at high-speed, but also that, combined with the properties of liquid crystal, they can be extremely versatile devices.
First, Carlos focused on a semiconductor laser-based quantum random number generator. He clearlyshowed the limits of the current scheme which relies on the random choice of single photon at a beam-splitter and requires post-processing operations to obtain good randomness.
Carlos introduced new scheme based on the parity of the single photon detection and achieved 10-times improvement of the bit generation rate.
Next, he combined surface-emitting laser diodes with liquid crystals to bring their versatility to a new level. Thus he demonstrated polarization control - forcing the laser to emit circularly polarized light emission -, and wavelength tuning properties by adding a liquid crystal overlay or an intra-cavity liquid crystal layer to the laser structure.