We propose to use SiO2 gratings on the InP membrane on silicon (IMOS) platform to form ultra-weak grating-based antennas for generation of ultra-narrow free-space optical beams. Such long gratings can produce narrow beam widths of below 0.1°. By using selective dry etching, both the grating shape and the etch depth have been precisely controlled, yielding a highly robust fabrication process. Initial results have shown a 0.088° FWHM of the emitted beam in the far-field for a 1-mm antenna length.
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