Effects of Proton Irradiation on InGaAs/AlGaAs Multiple Quantum Well Modulators (Preprint)

Abstract : Recently large area multiple quantum well (MQW) optical modulators have been coupled to cornercube optical retro-reflectors to allow free-space optical communications using a lightweight, low-power device. A pointing/tracking system and laser are required only on one end of the link. Such a system is attractive for ground-to-space links or space-to-space communication between a satellite and a microsat. An important question for these potential space-borne systems is the radiation tolerance of the MQW modulator, which is the principle active component. To investigate this subject, we irradiated three 0.5 cm diameter InGaAs/AlGaAs modulators using a sequence of bombardments of 1 MeV protons. One of the devices was irradiated while under a normal operating reverse bias voltage of 15 V; the other devices were unbiased. After each exposure the electronic, optical and modulation characteristics of the modulators were evaluated. No degradation was observed until a cumulative fluence of 1x10(exp 14) protons/sq cm, equivalent to an ionizing radiation dose of approximately 200 Mrad(Si).