Analysis, fabrication, and characterization of variable groove depth planar waveguide grating couplers are presented. A formula is derived to describe the grating groove depth variation necessary to produce an outcoupled beam of arbitrary profile. A variable depth grating for producing a Gaussian beam profile is fabricated on a waveguide by ion-beam etching through a scanning slit apparatus. A photoresist grating placed on the waveguide provides a mask to define the grating etched onto the waveguide. The near-field irradiance of the outcoupled beam is measured and shown to approach a Gaussian profile.

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We describe the modelling and fabrication of waveguide grating couplers with out-