SYNOPSISAn investigation was made of the optical and waveguiding properties of thin films fabricated from solutions of chitosan-acetic acid (chitosan/HAc) and chitosan/HAc doped with rareearth metal ions (Er+++ or Nd+++). For all three films, the refractive indices were approximately 1.5 and there was nearly no absorption in the range of 300 to 2700 nm. The optical loss in a waveguides was less than 0.5 dB/cm. Morphological observations disclosed that all the films possessed a dense and homogeneous amorphous structure with smooth surfaces. Extrinsic scattering, especially the scattering caused by surface impurities, was the dominating factor affecting the optical loss value. It is also interesting to note that for all the films, doped with rare-earth metal ions or not, the morphological characteristics were alike and the optical properties were similar. Doping rare-earth metal ions into chitosan thin films did not seriously influence optical waveguiding. This paper reports, we believe, the first study of chitosan films for optical applications. The experimental results demonstrate that chitosan and its derivatives are potential candidates for optical materials. 0

The dependence of electrooptic (EO) coefficient on electronic properties of the host polymer and specific chromophore-host interactions were examined. The r 33 of 10 wt % Disperse Red 1 (DR1)-and 4-(dicyanomethylene)-2-methyl-6-(p-(dimethylamino)stryryl)-4H-pyran (DCM)-doped poly(2-vinyl pyridine) films (6.4 and 5.8 pm/V, respectively) was up to 70% larger than comparable poly(methyl methacyrlate)-doped films (3.7 and 3.9 pm/V, respectively) and as much as a factor of 12 larger than comparable polystyrene-doped films (0.5 and 0.4 pm/V, respectively). The variation in EO coefficient was addressed by quantifying the effects of resonance enhancement, local field factors, field responsivity of the host, and specific guest-host interactions. Resonance enhancement and local field effects account for 20-25% of this variation. In contrast, the largest variations in r 33 were associated with specific chromophore-host and chromophore-choromphore interactions. These influence the molecular miscibility and thus alter the effective chromophore concentration and therefore the EO coefficient. An ultimate EO coefficient of 15 pm/V for a 25 wt % DR1-P2VP system was obtained in which specific secondary interactions (hydrogen bonding) occur between chromophore and host. Additionally, synergy between chromophore and a field responsive host (P2VP) may facilitate chromophore orientation and subsequent stability. These results demonstrate the potential associated with modification of guest-host interactions in chromophore-doped polymer films for the development of highly nonlinear, stable EO materials.

A new form of planar index-guided laser diode is demonstrated with a relatively thick (∼0.4 μm) native oxide employed to define the lateral optical waveguide (transverse to the laser stripe). Oxidation of high-gap AlxGa1−xAs in a ‘‘wet’’ ambient results in the transformation of most of the upper confining layer to a lower-index current-blocking native oxide outside of the active stripe. Planar quantum well heterostructure (QWH) AlxGa1−xAs-GaAs laser diodes fabricated by this process exhibit both optical and current confinement. Continuous 300 K threshold currents as low as 10 mA (uncoated facets) and kink-free single-longitudinal-mode operation are demonstrated for ∼2-μm-wide active region devices.