Abstract

Optical bistability in semiconductors such as III–V compounds has long been under intense study, first, to understand the relationships between bistable phenomena and the mediating resonant intensity-dependent index of refraction n₂ and, second, to develop thin film nonlinear optical devices. Conjugated organic and polymer semiconductors and insulators are well known to exhibit unusually large nonresonant third-order nonlinear optical susceptibilities χ⁽³⁾ whose origin resides in highly correlated electronic excitations. We have succeeded for the first time, we believe, in designing ultrathin polymer dye films possessing large resonant n₂ values and in implementing wide-aperture Fabry-Perot polymer etalons for optical bistability studies. In addition to primary nonlinear optical properties, the design of the polymer dye etalons incorporated outstanding secondary material properties: (1) large saturable absorption with zero unsaturable background; (2) saturable absorption centered in the spectral range of operating laser diodes; (3) thin film formation; and (4) spin coatable films and high throughput fabrication. The polymer dye is composed of phthalocyanine oligomers which possess a quasi-2-D electronic structure and thereby exhibit an exceptionally large absorption (α of 1 × 10⁵ cm^–1 at 810 nm) that is easily saturable. Saturable absorption and optical bistability were studied in ultrathin films as a function of incident intensity, pulse duration (30 ps–1 s), and wavelength (800–900 nm).

© 1988 Optical Society of America