Organic waveguide laser by a surface-relief holographic grating formed by photoisomerization

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Diffraction gratings have been important elements in integrated optics for many applications such as spectral filtering, optical feedback, and coupling light into and out of optical waveguides. Recently, several re-searchers have reported that a light-induced surface relief hologram can be formed on azo-benzene containing polymers by trans-cis photoisomerization in a one step process at room temperature. This method involves exposing the polymer to a simple two- beam interference pattern, and can allow quick fabrication of large area gratings having small periods, with good control over the grating parameters.In this research, we present a laser oscillation of a poly-mer waveguide with distributed feedback based on a light-induced surface relief hologram.The polymer thin-film fabricated by spin-coating technique was composed of azo-benzene containing polymer Poly-Orange-Tom-1 film. Its thickness was approximately 1 μm. Distributed-feedback gratings (DFB gratings) based on surface relie … More f hologram were formed by the interferential irradiation system.A diode-pumped, continuous-wave Nd:YAG green laser used for a recording light source was collimated, and passed through the film. Its intensity on the film was 100mW/cm^2. The polarization of the recording laser was perpendicular to the grating vector of the relief hologram. The film and the tuning mirror were fixed on the rotational mount. And the grating period formed on the film was controlled by varying a rotational angle of the mount. The holographic recording was typically conducted for 2000s at any grating periods. After 2000s, the diffraction efficiency almost reached up to the maximum level. And then, a height of the relief gratings was 〜25 nm with a period of 370 nm. A height of the relief gratings was 〜60 nm with a period of 550 nm.In order to fabricate the waveguide laser, a laser dye (DCM) doped PVK film was over-coated onto the azo-benzene polymer film with DFB gratings by the spin-coating technique. This device was pumped by a mode-locked Q-switched di-ode-pumped Nd:YAG green laser (λ=532 nm) with a pulse duration of 20ps at a repetition rate of 10 Hz. The device with the grating period of 370nm lased at 630nm, and then, the lasing threshold was 20mJ/cm^2. Less