Empowered Arcane Focus

You touch an arcane focus. Until the spell ends, this arcane focus becomes empowered with arcane magic. For the duration, creature using arcane focus to cast spells have  +2 bonus to spell attack rolls and to the saving throw DCs of your wizard spells

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the bonus increases to +3.