Photoinscription of channel waveguides and grating couplers in azobenzene polymer thin films

Poly(methyl methacrylate) slab waveguide materials were prepared, incorporating covalently attached azobenzene side groups. Birefringence was rapidly photoinduced in the films with linearly polarized light from an Ar+ laser to define stable channel waveguides, and the irradiated regions were shown to be suitable for multimode guiding of light at 633 nm. This single-step photoinscription process gives a controlled refractive index variation up to 0.012 for step or graded index channels, and can be rapidly modulated or completely erased with irradiation from a circularly polarized Ar+ laser beam. Written waveguides are stable indefinitely. Coupling in and out of the waveguides can be achieved with diffraction gratings photoinscribed in the polymer film using interfering beams from the same Ar+ laser. These high efficiency volume and surface diffraction gratings are stable over time and light exposure at the guiding wavelength. The grating spacing can be controlled by the geometry of the interference pattern, and hence can be optimized for high efficiency in-coupling and out-coupling at any required angle. Gratings with fringe spacings from 350 nm to 2000 nm were photoinscribed, and shown to couple light in and out of birefringent channel waveguides photoinscribed in the same material. The reversibility of the channels allows the guides to be photoaddressed for switching and mode filtering.