Resumen de Diffractive multifunctional plasmonic systems
In this Thesis we have investigated the modulation of the optical properties of photonic crystals sustaining plasmonic excitations. Such properties can be tuned or enhanced by incorporating functional materials in the crystals, including magnetic, ferroelectric or piezoelectric compounds, which add versatility to the control of light at the nanoscale. To probe the interplay between the optical properties and external magnetic and electric fields, we used grating couplers as the basic device structure for this analysis, with emphasis on the combined effects of diffraction and plasmonic resonances in the enhancement of magneto-optic responses. We started our work with magnetoplasmonic crystals grown on commercial digital disks (DVD, CD, Blu-ray), showing the potential of these platforms for the development of magnetoplasmonic devices.
We generalized the results found in these systems to magnetoplasmonic crystals with engineered optical responses, where the interplay between diffraction, plasmonics and magnetism paves the way to a versatile way to engineer the properties of photonic crystals that goes beyond the particular case of grating couplers. In particular, we have explored how, under some circumstances, light at off-normal incidence can excite unidirectional plasmonic propagating modes with particularly large magneto-optic responses. Finally, we close the Thesis with the study of ferroelectric magnetoplasmonic crystals, where the interplay between magnetization and ferroelectric polarization enables a way to modulate electrically the optical properties of grating couplers. In the following, a list is given of the most relevant outcomes described in this Thesis:
- Observation of unexpectedly large transverse magneto-optical Kerr effect at quasi-normal incidence, where, by geometry, the TMOKE amplitude tends to zero in magnetoplasmonics crystals. Interestingly, this observation was made in photonic crystals grown on top of commercial digital disks.
- Use of angle-resolved Fourier reflectance spectroscopy to analyze diffractive modes of light and plasmons, from which the interplay between magnetoplasmonic modes and diffraction has been revealed, associated with the amplification of the transverse magneto-optical Kerr effect at plasmonic resonances on the diffracted light.
- Geometrical conditions of grating couplers for the simultaneous maximization of reflectance and TMOKE, relevant for applications where signals are read out optically.
- Excitation of unidirectional forward- and backward- SPP propagating modes using grating couplers, with particularly large associated TMOKE responses.
- An advanced lithography design was developed and implemented, which allowed the optical access and in-situ ferroelectric and magnetic measurements. We used this methodology to analyze the effects of the ferroelectric polarization on the TMOKE response: under certain conditions, the sign of TMOKE can be reversed by electric fields.
