Femtosecond laser irradiation of polymethylmethacrylate for refractive index gratings

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Abstract
Polymethylmethacrylate (PMMA) or Perspex is an inexpensive polymer widely used for making the cores of communications grade polymer optical fibres (POFs) and as a substrate for polymer optoelectronic devices and integrated waveguides. Periodic refractive index structures have been written in undoped PMMA using multiple pulses of 40 fs duration from a 1 kHz Ti:sapphire femtosecond laser operating at the fundamental (800 nm). A refractive index change (Δn) of 5 ± 0.5 × 10−4 was observed before the onset of striations. Optimization of writing conditions for refractive index modification of POF fibres or bulk undoped PMMA will enable structures such as Bragg gratings, long-period gratings, mode couplers, microlens arrays, and zone plates to be written.