Dependence of output coupling efficiency on detuning in surface grating output couplers

The dependence of output coupling efficiency on the periodicity of a surface grating outcoupler was investigated. Horizontal cavity InGaAs/AlGaAs laser oscillators with two first-order surface gratings as feedback elements were integrated with detuned rectangular second-order gratings as surface output couplers by the use of electron-beam lithography and chemically assisted ion-beam etching. A high surface emission efficiency of more than 60% was achieved for grating periodicities detuned -2.5 nm to -15 nm and +2.5 nm from the resonance periodicity of 295 nm. For larger positive detuning, the surface emission efficiency is reduced because of the onset of secondorder diffraction into the substrate.