JP2679990B2 - Semiconductor laser optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor laser optical device, and more specifically, to an astigmatic difference at the emission position of laser light obtained from a semiconductor laser on the optical axis of the laser light. The present invention relates to a semiconductor laser optical device that can be corrected by using the astigmatism characteristic generated by tilting the optical element disposed in the. [Background of the Invention] In recent years, with the improvement of laser technology, a semiconductor laser capable of obtaining stable high-power laser light has been developed and applied to various systems. For example, in the fields of printing and plate making, the image information carried on the document is electrically processed, the electrical signal is converted into an optical signal by the semiconductor laser, and the image is reproduced on the record carrier through the scanning optical system. Scanning and recording systems are widely used. By the way, since laser light obtained from a semiconductor laser is divergent light, a condensing optical system is required to record image information and the like using this semiconductor laser. Therefore, for example, as shown in FIGS. 1A and 1B, the laser light L emitted from the laser diode 2 which is a semiconductor laser is once converted into a parallel light flux by the collimator lens 4, and then the optical axis 8 by the condenser lens 6. Focused on top. Here, the laser diode 2 has a PN junction surface 10, and the laser light L
Is ejected from this joint surface 10 in the direction of arrow Z. In this case, the laser light L emitted from the joint surface 10 is parallel to the joint surface 10 (X-Z plane) and perpendicular to the joint surface 10 (Y-).
The positions of the injection points S and M are different from the Z plane),
It has a so-called astigmatic difference δ. Therefore, when the position of the emission point S is set to the focal position of the collimator lens 4, the laser light L _X is condensed by the collimator lens 4 and the condenser lens 6 at point a on the optical axis 8. On the other hand, the laser light L _Y emitted from the emission point M is focused on the point b which is farther from the laser diode 2 than the point a. As a result, for example, when placing the record carrier a point, the laser beam L _Y is not exactly focused on the record carrier, therefore, it has been pointed out a disadvantage that high-precision image can not be obtained. Therefore, in order to eliminate such an inconvenience, for example, if a cylindrical lens having a condensing characteristic only in the Y direction is interposed between the condensing lens 6 and the point b, the emission point M of the laser diode 2 can be obtained. It is possible to focus the laser beam L _Y emitted from the laser beam at the same point a as the laser beam L _X. However, in this case, the number of elements constituting the optical system increases and the cost becomes high, and the position adjustment work of the cylindrical lens or the like is required, which is a drawback. On the other hand, there is a technical idea disclosed in Japanese Patent Laid-Open No. 59-58414 that can correct the astigmatic difference δ of the laser diode 2 without increasing the number of elements of the optical system. In this prior art, as shown in FIG. 1c, the laser diode 2 is rotated by an angle θ in the YZ plane with respect to the optical axis 8 of the collimator lens 4. In this case, the laser light L _Y emitted from the emission point M of the laser diode 2 is focused on the point c equal to the laser light L _{X in the} arrow Z direction due to the astigmatism characteristic of the collimator lens 4. . However, in this case, as shown in FIG. 1C, the rays of the inclined portion are not accepted by the condenser lens 6, and so-called vignetting occurs. The amount of vignetting depends on the rotation angle θ of the laser diode 2 and the length of the optical system, for example, the collimator lens 4
And increases with the distance of the condenser lens 6. As a result,
It has been pointed out that disadvantages such as a decrease in the quantity of focused light at point c and an increase in the beam diameter. [Object of the Invention] The present invention has been made in order to overcome the above-mentioned inconvenience, and an optical system arranged on the optical axis of laser light obtained from a semiconductor laser is tilted at a predetermined angle with respect to the optical axis. By doing so, it is possible to accurately correct the astigmatic difference due to the emission position of the laser light in the semiconductor laser with an extremely simple configuration, and moreover, to efficiently focus the laser light at a desired point. It is an object of the present invention to provide a semiconductor laser optical device capable of performing the above. [Means for Achieving the Object] In order to achieve the above object, the present invention provides a condensing optical system for condensing a laser beam output from a semiconductor laser having an astigmatic difference, and the condensing optical system. In a semiconductor laser optical device having a scanning optical system for guiding and scanning the laser beam condensed by a scanning object, a lens constituting the condensing optical system is rotated so as to intersect the optical axis of the laser beam. A lens rotation mechanism that is rotatable about an axis is provided, and the lens rotation mechanism tilts the lens at a predetermined angle with respect to the optical axis to set the laser light of the scanning optical system. The feature is that the light is condensed on the optical axis. Embodiments Next, preferred embodiments of the semiconductor laser optical device according to the present invention will be given and described in detail below with reference to the accompanying drawings. In FIG. 2, reference numeral 20 indicates a scanning optical system of a laser printer to which the semiconductor laser optical device according to the present invention is applied. The scanning optical system 20 has a laser diode 2 which outputs a laser beam L, and a collimator lens 22, beam expanding lenses 24 and 26, on the optical axis of the laser beam L.
An optical system including a galvanometer mirror 28 and an fθ lens 30 is arranged. A drum 32 is arranged at the focal position of the fθ lens 30. Bonding surface 10 of laser diode 2 for emitting laser light L
Are set parallel to the XZ plane. In this case, as shown in FIGS. 3A and 3B, the laser light L is the laser light L _X emitted from the emission point S and the laser light L emitted from the emission point M.
L _Y and the exit point S is set at the focal position of the collimator lens 22. The collimator lens 22 collimates the laser light L and is held by the mechanism shown in FIGS. 2 and 3. That is, a pair of support members 36a and 36b are planted on the upper surface of the mount 34, and a holding ring 38 is mounted on the outer peripheral portion of the collimator lens 22. The upper ends of the support members 36a and 36b and the retaining ring 38 are supported by the support shafts 40a and 40b.
Connected by. In this case, the collimator lens 22 is pivotally supported about the X axis via the support shafts 40a and 40b. On the other hand, the laser light L made into a parallel light flux by the collimator lens 22 has its beam diameter adjusted by the beam expanding lenses 24 and 26 and enters the galvanometer mirror 28. The galvanometer mirror 28 is configured to swing at high speed in the direction of arrow A.
The laser beam L reflected by the laser beam f is a scanning lens.
It is irradiated onto the drum 32 via the lens 30. in this case,
The laser beam L is sub-scanned in the direction of arrow C on the drum 32 which rotates in the direction of arrow B by the swinging operation of the galvanometer mirror 28. The semiconductor laser optical device according to the present embodiment is basically configured as described above, and its operation and effect will be described next. First, the laser light L _X emitted from the emission point S of the laser diode 2 is turned by the angle ω around the X axis to be a parallel light flux by the set collimator lens 22, and then the light is expanded by the beam expander lens 24. It is focused on the point d on the axis 21 (see FIG. 3a). In this case, the collimator lens
The movement amount δ _{ZX of the} point d on the optical axis 21 due to the inclination of 22 is the broken line S _{X of} FIG. 4 with respect to the rotation angle ω of the collimator lens 22.
The sagittal curvature of field characteristic is represented by δ _ZX = α · S _X (1) Here, α is the vertical magnification of the optical system, and is defined by α = (f _ex / f _COLL ) ² (2) by the focal length f _COLL of the collimator lens 22 and the focal length f _ex of the beam expanding lens 24. It On the other hand, after the laser beam L _Y emitted from the emission point M of the laser diode 2 is converged into a parallel light flux by the collimator lens 22, it is focused on the point e on the optical axis 21 by the beam expanding lens 24 (FIG. 3 b)). In this case, the movement amount δ _ZY of the point e on the optical axis 21 due to the inclination of the collimator lens 22 is the fourth with respect to the rotation angle ω of the collimator lens 22.
Due to the meridional image curvature characteristic shown by the solid line M _Y in the figure, it is expressed by δ _ZY = α · M _Y (3) Therefore, the astigmatism α on the focal plane of the beam expanding lens 24 is such that the difference between the movement amount δ _{ZX of the} point d and the movement amount δ _{ZY of the} point e corresponds to the astigmatic difference δ of the laser diode 2.
If the turning angle ω of the collimator lens 22 is set so as to be equal to δ, that is, α · δ = δ _ZX −δ _ZY (4), the laser beams L _X and L _Y are collected. The light spots d and e can be matched. Here, (4) is easy to [delta] = represented S _X -M _Y ... (5), the value of ω relationship astigmatism of the collimator lens 22 (FIG. 4) than simply finding it is possible. Since the laser lights L _X and L _Y are focused on the optical axis 21, respectively,
Vignetting does not occur due to the optical system as in the prior art shown in FIG. C. Therefore, the amount of light at the condensing point of the laser light L may decrease, and the beam diameter at the condensing point may increase. Absent. Here, when the astigmatism characteristic of the optical element is opposite to S _X and M _Y as shown in FIG. 5, the turning direction of the optical element may be matched with the direction of the bonding surface of the semiconductor laser. That is,
In FIG. 3, by rotating the collimator lens 22 around the Y axis, the astigmatic difference δ of the laser diode 2 can be corrected. Next, the laser beam L adjusted to have a predetermined beam diameter by the beam expanding lens 26 is reflected by the galvanometer mirror 28 that rapidly oscillates in the direction of arrow A, and f
The recording material wound around the drum 32 is main-scanned in the direction of arrow C via the θ lens 30. In this case, the drum 32 is rotating at a constant speed in the direction of arrow B, so that image information is recorded on the recording material. As described above, according to the present invention, when the laser light obtained from the semiconductor laser is condensed using the optical system arranged on the optical axis of the laser light, the optical axis of the optical system is Is tilted according to the astigmatic difference caused by the laser beam emission position in the semiconductor laser. Therefore, the laser light can be accurately focused with an extremely simple configuration. In this case, since the principal ray of the laser light and the optical axis of the optical system coincide with each other and the laser light is condensed on the optical axis, vignetting of the laser light by the peripheral portion of the optical system does not occur,
It is possible to provide a semiconductor laser optical device that does not reduce the transmission efficiency of laser light at all. Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment. For example, even if a beam expanding lens is rotated as an optical element for correcting astigmatic difference. Needless to say, various improvements and design changes can be made without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are characteristic explanatory views of a semiconductor laser, FIG. 1C is an explanatory view of a conventional astigmatic difference correction method, and FIG. 2 is a semiconductor laser optical system according to the present invention. 3 is a schematic perspective view of a scanning optical system to which the apparatus is applied. FIGS. 3A and 3B are configuration explanatory views of a main part of a semiconductor laser optical apparatus according to the present invention. FIGS. It is a characteristic diagram. 2 ... Laser diode, 20 ... Scanning optical system 22 ... Collimator lens 24, 26 ... Beam expanding lens 28 ... Galvanometer mirror 30 ... f.theta. Lens, 32 ... Drum L ... Laser light

Claims (1)

(57) [Claims] A condensing optical system that condenses a laser beam output from a semiconductor laser having an astigmatic difference, and a scanning optical system that guides the laser beam condensed by the condensing optical system to a scanned object to perform scanning. In the semiconductor laser optical device having, a lens rotation mechanism is provided that allows a lens forming the condensing optical system to rotate about a rotation axis that intersects the optical axis of the laser light, A semiconductor laser optical device, wherein the laser light is condensed on the optical axis of the scanning optical system by setting the lens so as to be inclined at a predetermined angle with respect to the optical axis. 2. The device according to claim 1, wherein the tilt direction of the lens is set within a plane that includes the optical axis of the laser light and is orthogonal to the bonding surface of the semiconductor laser. 3. In the device according to claim 2, the lens is configured such that an emission point of a laser beam emitted in a direction parallel to a joint surface of a semiconductor laser and a laser beam emitted in a direction orthogonal to the joint surface. A semiconductor laser optical device, wherein the semiconductor laser optical device is set to be inclined by an angle corresponding to the distance from the emission point.