Optical system for optical disc drive

A head of an optical data recording/reproducing device, comprising:

• a laser source that emits a laser beam;
• a deflector on which said laser beam emitted by said laser source is incident;
• a relay optical system that includes a relay lens group and an imaging lens group;
• an objective lens system, said laser beam emitted by said laser source being incident on said objective lens system through said deflector and said relay optical system, a vicinity of a deflecting plane of said deflector and a principal plane position of said objective lens system having a substantially conjugate relationship;
• a beam splitter provided substantially at a focal point of said laser beam between said relay lens group and said imaging lens group, said beam splitter dividing said laser beam passed through said relay lens group into a first beam and a second beam;
• a one-dimensional optical position detector that detects said second beam;
• and
• a controller that determines a direction and amount of rotation of said deflecting plane of said deflector in accordance with said second beam received by said optical position detector.