Probe beam intensities more than an order of magnitude larger than pump beam intensities do not erase photorefractive gratings during nondegenerate four‐wave mixing in photorefractive GaAs/AlGaAs quantum wells. The pump and probe laser wavelengths are absorbed in spatially separated regions of the multilayer structure. The photoconductivity of a probe beam around 840 nm is confined to the GaAs quantum wells and cannot easily erase the trapped space‐charge gratings in the AlGaAs barriers written by an above‐band‐gap HeNe laser at 633 nm. This allows a weak visible control beam to modulate a strong infrared signal beam.