be due to recombination defect reactions [Lang74, Kime78]. This annealing process is thought to occur as a result of defect motion in response to locally deposited vibrational energy resulting from a non-radiative electronic transition through the defect in a depletion region. Zhao et al. have performed detailed annealing measurements on MQW lasers to characterize the post irradiation annealing of the optical power as a function of forward bias [Zhao 98]. They observed that the degradation in optical power was less at lower proton fluxes as a result of in-situ forward biased annealing during irradiation. This would indicate that tests at laboratory dose rates may over-estimate the degradation that would be observed on-orbit. However, unlike the complete recovery observed for gamma-irradiated GaAs lasers [Barn70], the lasers exposed to protons have only exhibited a partial optical power recovery [Mind76, Paxt97, IV-91 Zhao98]. Since various LEDs and laser diodes exhibit different degrees of forward biased annealing, this effect should be characterized for the devices of interest to a specific program. Significant long term annealing at room temperature has not been observed in unbiased devices [e.g., Barr95], as expected. As discussed in section 2.3.2, care is required in the choice of a damage function for the purpose of performing on-orbit predictions, since the energy dependence of the GaAs NIEL calculation at higher proton energies appears to diverge with recent measurements on GaAs LEDs [Barr95] and MQW lasers [Zhao97]. Depending on the particular proton environment and degree of device shielding, the predicted displacement damage dose can vary by factors of 2-3, (and possibly more) depending on whether the calculation is based on the energy dependence of the calculated NIEL or that of the measured damage factors. 3.3.5 Optocouplers Optocouplers are hybrid modules comprised of an LED optical source, a coupling medium, and a detector that is sometimes followed by an amplifier stage. They provide the basic func