In this paper the effect of antireflective coating (ARC) on the emitting facet on the light power output of edge emitting diode is reported.In high speed GaAs/GaAlAs DH-LEDs with sputtered A1

2

O

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as AR coating on the front emitting facet

a remarkable increase in light power output has been achieved. The fabricated LEDs have two types of structure:normal edge emitter and edge emitter with optical waveguide structure.A conventional rf sputtering equipment with the source power of 3kW at 13.5 MC was used in preparing the A1

2

O

3

AR coating (refractive index 1.65~1.7). A high purity A1

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O

3

disk was employed as a target.Before sputtering the high-purity Ar gas was further purified by passing it through molecular sieve 5A and hot Ti coils.The light power output of a normal edge emitter as a function of current density is plotted in Fig.3.At a driving current density of 4kA/cm

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the light power increases from 370nW for the uncoated LED to 495uW for the same diode coated with~1890Å A1

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O

3

.This corresponds to a light-power increase of~34%.