Defect modes in optically induced photonic lattices in biased photovoltaic–photorefractive crystals

We show that defect modes in optically induced photonic lattices are possible in biased photovoltaic–photorefractive crystals. These defect modes exist in different bandgaps when the defect strength is changed. When the defect strength is positive, there is a defect-mode branch in each bandgap. When the defect strength is negative, there is a defect-mode branch in the first bandgap and are many defect-mode branches in higher bandgaps. For a given defect strength, the strongest confinement of the defect modes appears in the semi-infinite bandgap when the defect strength is positive and in the first bandgap when the defect strength is negative. On the other hand, these defect modes are those studied previously in optically induced photonic lattices in biased non-photovoltaic–photorefractive crystals when the bulk photovoltaic effect is negligible and predict those in optically induced photonic lattices in photovoltaic–photorefractive crystals when the external bias field is absent.

► Defect modes in biased photovoltaic–photorefractive crystals are possible.
► There is a defect-mode branch in each bandgap for a positive defect.
► There are many defect-mode branches in higher bandgaps for a negative defect.
► There is a defect-mode branch in the first bandgap for a negative defect.