Optical system for collimating elliptical light beam and optical device using the same

An optical device for reading/writing to an optical disk, comprising:

• an optical system comprising:
• a light source, adapted for providing an elliptical light beam defining different diverging angles in different directions, wherein any cross-section of the elliptical light beam emitted from the light source defines a long axis and a short axis which are perpendicular to each other;
• a first lens, functioning as a diverging lens in directions corresponding to the short axis, for diverging the elliptical light beam and enlarging the short axis so as to narrow a difference between the long axis and the short axis and to narrow a difference between a diverging angle corresponding to the short axis and a diverging angle corresponding to the long axis, when the elliptical light beam passes therethrough, the light source and the first lens being arranged with no intervening lenses therebetween;
• a second lens, functioning as a converging lens in the directions corresponding to the short axis, for converging the elliptical light beam and adjusting the short axis in order to obtain a round light beam;
• and
• a third lens for converging the round light beam into a substantially parallel round light beam;
• wherein optical centers of the first lens, the second lens, and the third lens commonly define a common optical axis along which the elliptical light beam travels;
• a semi-reflective mirror, for allowing light beams from a first direction to pass therethrough and for reflecting light beams from a second direction, the second direction being substantially perpendicular to the first direction, the common optical axis being located along the second direction;
• an object lens for focusing parallel light beams to a point on an optical disk;
• a collimator arranged along the first direction for collimating light beams passing therethrough from the first direction;
• and
• an optoelectronic detector, for receiving the collimated light beams, detecting information from the collimated light beams, converting the information into electronic signals, and outputting the electronic signals.

An optical system for efficiently collimating elliptical light beams, comprising:

• a light source, adapted for providing an elliptical light beam defining different diverging angles in different directions, wherein any cross-section of the elliptical light beam emitted from the light source defines a long axis and a short axis which are perpendicular to each other;
• a first lens, functioning as a diverging lens in directions corresponding to the short axis, for diverging the elliptical light beam and enlarging the short axis so as to narrow a difference between the long axis and the short axis and to narrow a difference between a diverging angle corresponding to the short axis and a diverging angle corresponding to the long axis, when the elliptical light beam passes therethrough;
• and
• a second lens, functioning as a converging lens in the directions corresponding to the short axis, for converging the elliptical light beam and adjusting the short axis in order to obtain a round light beam;
• and
• a third lens for converging the round light beam into a substantially parallel round light beam;
• wherein the optical centers of the first lens and the second lens commonly define a common optical axis along which the elliptical light beams travels, the light source and the first lens are arranged with no intervening lenses therebetween, and an optical center of the third lens coincides with the common optical axis.