R. Zanoni

Third order nonlinear integrated optics

The authors review progress in the application of nonlinear optical phenomena to integrated optics. Essentially all integrated optics devices such as directional couplers, Mach-Zehnder interferometers, prism couplers, etc., can be used for all-optical signal processing when at least one of the waveguiding media exhibits an intensity-dependent refractive index. Experimental and theoretical results on the operating characteristics and figures of merit of such devices, as well as a new class of phenomena based on large nonlinear changes in waveguide properties will be summarized. Also discussed are measurement techniques for evaluating waveguide nonlinearities. Progress in the implementation of other nonlinear third order interactions, such as degenerate four-wave mixing and nonlinear spectroscopy, will also be reviewed. >

Fabrication of integrated optical structures in polydiacetylene films by irreversible photoinduced bleaching

Spin‐coated and solution‐cast films of poly[5,7‐dodecadiyn‐1,12‐diol‐bis(n‐butoxycarbonyl‐methyl‐urethane)], or briefly, poly‐4BCMU, irreversibly bleach when irradiated by light tuned within the absorption band of the polymer sample. Characteristic bleaching times have been measured at several wavelengths. The refractive index of poly‐4BCMU has been measured at 1.064 μm for various photobleaching energies. Refractive index changes as large as −0.08 have been measured, and the decrease in refractive index has been used to define waveguide channels and gratings.

Organic films in non-linear integrated optics structures

Abstract Organic films with specifically engineered optical properties hold considerable promise for applications in integrated optics. Light can be propagated for up to centimeter distances in waveguides to interact with organic films of thicknesses 1–5000 nm which are either deposited onto the waveguide or form the guiding medium, depending on the application. The potential advantage of using organic materials is that the molecules can be optimized for their optical response, e.g. second- and/or third-order optical non-linearities for efficient modulation, harmonic generation, all-optical signal processing etc. The basic concepts of integrated optics, non-linear guided wave interactions, material requirements for various applications and progress to date are reviewed.

Bistability and switching in nonlinear prism coupling

We demonstrate that when a nonlinear coupler is operated in the switching regime, small amounts of either nonlocality in the optically induced refractive index change or of longitudinal feedback can lead to optical bistability. Outside the switching regime, there is a threshold for the amount of nonlocality or feedback required for bistability. The diverse predictions of previous theoretical formulations are therefore reconciled.

The cubic susceptibility dispersion of poly (4-BCMU) thin films: third harmonic generation and two-photon-absorption measurements

Abstract The near infrared dispersion of the third order nonlinear optical susceptibility, χ (3) , of poly [5, 7-dodecadiyn-1, 12-diol-bis (n- butoxycarbonyl-methyl-urethane)], poly (4-BCMU), is investigated by third-harmonic-generation and two-photon-absorption. A four level model gives a good fit to the measured dispersions in the range of 0.770 μm to 1.904μm. The coupling between the first 1 B u state and the two 1 A g states, located above and below it, control the dispersion of χ (3) in the linear transparency region of poly (4-BCMU).

Measurement of nonlinear refractive index and transmission in polydiacetylene waveguides at 1.319 μm

Nonlinear optical measurements in strip‐loaded channel waveguides of poly(4‐BCMU) at 1.319 μm are reported. Using a pulse‐modulated interferometry method, the intensity‐dependent refractive index is found to have an electronic contribution, n2=(4.8±2.7)×10−8 cm2/MW, and an estimated thermal contribution, n2=−(7.9±4.5)×10−11 cm2/MW, for 60 pS laser pulses at 76 MHz. The two‐photon absorption coefficient β is less than 0.25 cm/GW. Figures‐of‐merit suggest that poly(4‐BCMU) has properties desirable for all‐optical devices, but that fabrication losses and thermal effects due to absorption will limit device performance.

Nonlinear optical processes in a polymer waveguide: Grating coupler measurements of electronic and thermal nonlinearities

We report here the first clear demonstration of intensity‐dependent phase shift due to electronic nonlinearity in a nonlinear polymer waveguide in which propagation distances over 5 cm have been achieved with total attenuation of ∼1.2 cm−1 . Intensity‐dependent coupling angle, intensity‐dependent coupling efficiency, and limiter action behavior have been observed in the polyamic acid waveguide using grating excitation with 400 fs, 80 ps, and 10 ns pulses. A nonlinear grating coupler analysis identifies the subpicosecond and picosecond processes with electronic nonlinearity, but the dominant effect in the nanosecond experiment is due to thermal nonlinearity derived from weak absorptions. The magnitude and sign of n2 of electronic nonlinearity are measured.

Elastic constants of Cu/Nb superlattices

Abstract Brillouin scattering has been performed on Cu/Nb metal superlattices with a multipass tandem interferometer. Behavior similar to that reported by Kueny et al. [Phys. Rev. Lett., 48, 166 (1982)] has been observed for the Rayleigh wave dispersion with bilayer periodicity. Multiple guided acoustic waves have been observed and their dispersion measured in order to obtain the variation in the c44 and c33 elastic constants with bilayer thickness.

Nonlinear Organic Materials in Integrated Optics Structures

Nonlinear organic materials, in conjunction with integrated optics structures, can potentially be used to perform a variety of all-optical operations on subpicosecond time scales. A number of potential devices are described and the material properties necessary to implement them are summarized. Progress in our laboratory toward these goals is detailed.

Brillouin scattering from Love waves in Cu/Nb metallic superlattices

Love waves have been observed for the first time by Brillouin scattering. The c12 constant of the metallic superlattice Cu/Nb has been measured.