Caulker held talks with Dens Park boss Neil McCann before finalising the move.
“Then the phone call came in from Neil to come up here. I met with him last night and he blew me away.
“He said: ‘Here’s your chance to come and play’. It’s a chance I want to take.
“It’s great just to get a sweat on during training. It’s been a great first day and I’m just getting used to the cold weather.”
Caulker admitted earlier this year that he has suffered with drinking and gambling addictions, and that they became so serious that he even contemplated suicide.
He started his career at Spurs and had loan spells at Yeovil, Bristol City and Brendan Rodgers’ Swansea, where he helped the club to an 11th-place finish in the Premier League.
Having returned to White Hart Lne, he won his first and only England cap to date under Roy Hodgson in the 4-2 friendly defeat away to Sweden in November 2012, a game in which he also scored.
Cardiff signed Caulker in a club-record £8million deal in July 2013, but following the Welsh club’s relegation from the top flight, he moved to QPR and had subsequent loan spells at Southampton and Liverpool.
He had made four appearances for the Loftus Road side this season, but has not played since September’s 1-1 draw with Barnsley.