DEPENDENCE OF OUTPUT COUPLING EFFICIENCY ON DETUNING IN SURFACE GRATING OUTPUT COUPLERS

The dependence of output coupling efficiency on the periodicity of a s urface grating outcoupler was investigated. Horizontal cavity InGaAs/A lGaAs laser oscillators with two first-order surface gratings as feedb ack elements were integrated with detuned rectangular second-order gra tings as surface output couplers by the use of electron-beam lithograp hy and chemically assisted ion-beam etching. A high surface emission e fficiency of more than 60% was achieved for grating periodicities detu ned -2.5 nm to -15 nm and +2.5 nm from the resonance periodicity of 29 5 nm. For larger positive detuning, the surface emission efficiency is reduced because of the onset of second-order diffraction into the sub strate.