Olsson's new deal has a summer get-out clause he signed earlier this season.
The 29-year-old said: "I don't like to speak about what is in my contract. It's confidential.
"But I made it clear that I am happy here when I signed for four years in September. I think that says it all.
"As I've said before, as a player you set goals with a team and as an individual and you always want to push higher in your career. I am no different to anyone else.
"I have dreams and ambitions to achieve - but I am very happy at the club and happy with what we have achieved this year and hopefully will achieve towards the end of the season."