12 March 2013 Tapered nanowire waveguide layout for rapid optical loss measurement by 'cut-back' technique
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Abstract
Tantalum pentoxide (Ta2O5) is a promising material for both linear and nonlinear integrated optical device fabrication due to its high refractive index, low absorption over a wide wavelength range, high nonlinear refractive index, large value of chi 3 and high optical damage threshold. In particular Ta2O5 rib and ridge waveguides provide an interesting platform for solid state Laser applications. Waveguide surface roughness and sidewall slope profile can induce significant scattering loss reducing the efficiency of the device. Optimization of these parameters is key to obtain ultimate performance of the final device. In this paper, we present a method and photolithographic mask layout suitable to allow easy measurement of optical propagation loss for planar rib or ridge waveguides. The procedure is equivalent to the standard ‘cut- back’ method, but one that does not requiring devices to be cleaved and polished multiple times. The mask incorporates a set of narrow nano-wire waveguides coupled by tapered waveguide sections to wide input /output guides. The lengths of the central nano-wire section are determined precisely by the lithographic mask. The layout is designed to allow losses of each sub-component such as taper sections and input waveguides to be removed from the measurement, giving accurate measurement of loss in the central nanowire section of the guide. Optical loss measurements are presented for Ta2O5 nanowire rib waveguides. Loss was found to be dependent on lengths and widths of nanowire waveguide sections. Measured propagation losses for the rib waveguides are found to be just slightly higher than loss of a Ta2O5 slab waveguide as measured by a commercial Metricon system, validating the low loss nanowire waveguide fabrication processes.
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M. Firdaus A. Muttalib, M. Firdaus A. Muttalib, Ruiqi Y. Chen, Ruiqi Y. Chen, S. J. Pearce, S. J. Pearce, Martin D. B. Charlton, Martin D. B. Charlton, } "Tapered nanowire waveguide layout for rapid optical loss measurement by 'cut-back' technique", Proc. SPIE 8604, Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XII, 86040Z (12 March 2013); doi: 10.1117/12.2002472; https://doi.org/10.1117/12.2002472
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