Optical unit for use in laser beam printer or the like.

摘要

In an optical unit (2) incorporated in a laser beam printer, a laser beam generated by a laser diode (l2) is converted by a group of conversion lenses (l0) into a laser beam having a predetermined-size cross section. The laser beam is directed toward a photosensitive body (90) by a scanner unit (50), so as to scan the photosensitive body. A focusing lens (72) allows the rotating angle of the reflecting faces of the scanner unit to correspond to a desirable point on the surface of the photosensitive body (90). In other words, the rotating angle is made to correspond to the distance between the optical axis center determined with respect to a main scanning direction and a point to which the laser beam is irradiated for scanning. The conversion lenses (l0) include at least one aspheric glass lens (l4). The conversion lenses further includes a pair of plastic lenses (l6, l8) which have substantially the same power and opposite polarities with respect to either the main scanning direction or a sub-scanning direction. Among the lenses (l4, l6, l8) mentioned above, that lens (l6) which is located closest to the glass lens (l4) is integral with the laser diode (l2). The focusing lens (72) is formed of a material having substantially equivalent characteristics to those of the paired plastic lenses.