A study of nonlinear optical polymers for use in ultrafast electro -optic sampling measurements.

Abstract

Recently, electro-optic sampling (EOS), which utilizes a combination of ultrafast laser technology and the Pockels effect, has been refined into a fiber-based system that benefits from an enhanced positioning ability and measurement flexibility. EOS would still be improved further with an increase in field sensitivity and a decrease in capacitive loading (invasiveness) for near-field and integrated circuit measurements of ultrahigh bandwidth devices. Electro-optic polymers, with higher electro-optic coefficients and lower dielectric permittivities would address these two issues. This dissertation focuses on a theoretical and experimental study of the potential viability of electro-optic polymers as Electro-Optic Sampling probe materials. Finite element method simulations of EOS probe materials were performed to study the effect of the material's dielectric permittivity on performance. These simulations found that the sensitivity of an EOS probe material increases while its invasiveness decreases as its dielectric permittivity is decreased. Simulations of polymer EOS probes suggest that they would be ideal. Numerical analysis of the polymer's index ellipsoid was completed in order to study a polymer probe's potential for cross-polarization suppression capability. These results showed that an electro-optic polymer could be capable of isolating tangential electric field components, but not normal field components. A variety of electro-optic polymers were poled and tested as EOS field sensors. Poly(gamma-benzyl-L-glutamate) (PBLG) was poled using the Solution Evaporation Electric-field Poling method, producing a film with an electro-optic coefficient (<italic>r</italic>₃₃) of 1.62 pm/V. This is believed to be the highest reported value for a poled PBLG film to date greater than that for PBLG poled by thermal poling techniques by a factor of over 30. A fiber-mounted polymer EOS electric field sensor was constructed and tested using a contact electric-field poled film of copoly(Disperse Red 1-Methyl Methacrylate). This was the first-ever fiber-mounted polymer EOS sensor, and the first external polymer EOS sensor to be used with its poling electrodes removed. The final experiment consisted of the testing of another fiber-mounted polymer EOS sensor using a 120-mum-thick polymer consisting of a novel guest/host system. This probe was tested by successfully performing EOS measurements on a silicon microstrip operating at frequencies up to 15 GHz.