Effects of proton irradiation on InGaAs/AlGaAs multiple quantum well modulators [for free-space optical communication]

Recently large area multiple quantum well (MQW) optical modulators have been coupled to corner-cube 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 spaceborne systems is the radiation tolerance of 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 1×10¹⁴ protons/cm², equivalent to an ionizing radiation dose of approximately 200 Mrad(Si)