A technique for morphology control of self-assembled organic films based on laser ablation is presented. The
regioregular poly 3-hexylthiophene (RR-P3HT) films prepared by using drop casting method and spin coating method
are irradiated and ablated by the ultraviolet KrF excimer laser. Absorption spectra and XRD profiles of the films are
investigated. For spin coated films, Blue absorption spectral shift is observed; For drop cast films, Blue shift in the
absorption spectra, accompanied with the disappearance of the peak intensity of XRD profiles, are observed. The results
indicate that molecular structure has been changed due to photo-thermal effect and molecule cutting effect of laser
The photosensitivity of photosensitive fibers is studied experimentally and theoretically. In the experiment, the relationship between the diffractive index increment of photosensitive fibers and UV irradiating dose based on an unbalanced Mach-Zehnder Interferometer (MZI) is measured. The experimental results show that the photo-induced index's increment of photosensitive fibers is multi-decaying-exponentially proportional to the UV irradiating dose and the order of magnitude of the maximum value can reach 10-3. In order to explain the relationship, a new assumption is proposed, which can give a good explanation based on the "color center model" and the "Kramers-Kronig" principal.
We report a new method for writing the dual-wavelength Bragg fiber gratings. The method is based on the photosensitivity of Ge-doped optical fibers. Our double-exposure technique enables a good control over the grating's reflectivity and the separation of the two Bragg wavelengths. A grating with two equal transmission peak of 20.5dB is obtained by using this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, an optical add-drop multiplexer (OADM) that allows dropping two fixed wavelength channels is proposed.