Experimental study on fabrication of optical waveguides in Er3+-doped phosphate glass by ultrashort pulse laser
Ultrashort pulse laser provides an efficient way to fabricate integrated photonic devices by modulating the refractive index of optical materials with nonlinear absorption to form three-dimensional optical waveguides.Er3+-doped phosphate glass,due to its excellent characteristics and emission spectrum in the communication band near 1.55 μm,has become a research hotspot in integrated optical active gain materials.In the experi-ment,the Ti:sapphire femtosecond laser amplification system with the output pulse laser parameters of repetition frequency of 1 kHz,center wavelength of 800 nm and pulse width of 120 fs was used as the inscribed light source.The impact of processing parameters on waveguide formation,waveguide morphology and optical proper-ties were systematically studied.The experimental results show that under the transverse writing condition with slit shaping assisted short focus microscope objective,with a fixed pulse energy of 1.8 μJ,the optical waveguide can be formed in the scan speed range of 10 μm/s-160 μm/s.With a fixed scan speed of 40 μm/s,the writing pulse energy window of the optical waveguide is 1.6 μJ-2.0 μJ.The waveguide cross-section is symmetrical and the refractive index is obviously modified,within the depth range of 125 μm-200 μm from the surface.The near-field intensity measurement results show that the near-field intensity distribution of the prepared waveguide is symmetrical,and the light guiding characteristics are maintained well.The refractive index modifi-cation distribution in the waveguide region is simulated based on the finite difference method,and the results show that the maximum refractive index modification value is Δn =6.6×10-4.The results of cut-back meas-urement show that the lowest waveguide propagation loss is only 0.91 dB/cm.
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