Investigations of highly efficient grating couplers for polymer slab and strip waveguides fabricated by electron-beam lithography are reported. A maximum input efficiency of 67% is achieved. The electron-beam direct-writing technique allows one to replicate the original gratings into polymer substrates by embossing. An all-polymeric optical chip with efficient grating couplers is demonstrated. Waveguide grating couplers with blazed profile and variable grating depth are investigated. Thus, the intensity distribution of the outcoupled light is matched to a Gaussian-like profile. A focusing blazed grating that couples the light with an efficiency of 42% into a polymer strip waveguide is reported. A curvature correction of the grating lines allows one to improve the focusing properties.
We report on the measurement of the electrooptic coefficient FJ| in proton exchanged LiNbO 3 waveguides. Using electrooptic prism (EOF) structures and waveguiding layer interferometers (WLI), we evaluated the electrooptic constants from the lateral Gaussian beam deflection and the measured phase shift, respectively, which are caused by external electric fields applied. For proton exchanged LiNbO 3 fabricated in 1 M% lithium enriched benzoic acid melt, we obtained a r 3 f value less than (2.0 + 0.3)· 10 ~6μιη/ν, significantly reduced in comparison with virgin LiNbO 3 . However, after strong annealing the electrooptic coefficient is almost re-established and arrives at (19.8 ± 1.5) · 10" 6 μπα/Υ.
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