Norwich boss Bryan Gunn told the club's official website: "Alan brings power and having watched him myself over the last two years and in games against Norwich City he's a very awkward customer to play against.
"He's got tenacity, he chases lost causes and he provides a goal threat.
"With the seven games we have got left he's very keen to come here and do well. He could have signed for another Championship club who were interested in him, which shows that he is committed to coming and playing for us."