JPH04113528A - Optical head device - Google Patents

Abstract

PURPOSE:To make light intensity distribution axially symmetric to the optical axis while reducing the loss of light quantity as much as possible with the small number of parts without deviating the optical axis by using optical filters for a beam shaping device so that the transmittivity is gradually decreased from the center to the outer periphery and the decreasing rates can be different from each other in two directions intersecting orthogonally with each other. CONSTITUTION:In respect to a light source 1 for which the light intensity distribution is different in two directions intersecting orthogonally with a face perpendicular to the optical axis, optical filters 5 with characteristics to gradually decrease the transmittivity from the center to the outer periphery and to make the decreasing rates different in two correspondent directions are disposed. In this case, since one direction having the light intensity distribution with wide spreading is made corresponding to one direction of the optical filter 5 having the larger decreasing rate of transmittivity for a beam emitted from the light source 1, the light intensity distribution after passing through the optical filter can be made coincident with the other direction having the light intensity distribution with narrower spreading. Thus, the obtained light beam can be made axially symmetric to the optical axis, and the optical axis is not deviated as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical head device including a beam shaping device that corrects the light intensity distribution from a light source in an axially symmetrical manner.

[Prior Art] Many semiconductor lasers are used as light sources for laser printers, laser facsimile machines, laser information recording and reproducing devices, and the like.

In a semiconductor laser, the divergence angle of emitted light differs between a horizontal transverse mode parallel to the junction surface and a vertical mode perpendicular to the junction surface. That is, the light intensity distributions in two orthogonal directions within a plane perpendicular to the optical axis are different, and each light intensity distribution exhibits a substantially Gaussian distribution.

When such a light beam is used in an optical scanning system, problems such as deterioration in image quality occur in image reading and crosstalk occur in signal reproduction from the information track.

Therefore, for a light source that is diffused light whose intensity distribution is not axially symmetrical with respect to the optical axis as described above, a beam shaping device that corrects the light intensity distribution to be axially symmetrical with respect to the optical axis has conventionally been used.

FIGS. 3 and 4 are diagrams showing an example of a conventional optical head device.

In FIG. 3, (1) is a light source such as a semiconductor laser whose light intensity distribution differs in two orthogonal directions in a plane perpendicular to the optical axis; (2) is a urimeter lens that shapes diffused light into parallel light; (3) is an optical prism. In the figure, the optical system of the optical head after the light source is shaped into a parallel beam is omitted.

In this optical head device, the divergence angle θ at the light source (1)
In the direction (θ1) where the divergence angle is large, the width of the light beam is reduced by the optical prism (3), and the width is shaped to be the same as the width of the light beam in the direction (θ2) where the divergence angle is small.

Therefore, after the light beam passes through the optical prism (3), it becomes parallel light whose light intensity distribution is symmetrical with respect to the optical axis. Therefore, the direction of the optical axis is different in the two directions where the divergence angle θ is different.

The optical head device shown in FIG. 4 corrects this deviation in the optical axis direction, and the optical prism (3) of the optical system shown in FIG.
A second optical prism (4) is inserted after the optical prism. By combining the first and second optical prisms (3) and (4), it is possible to equalize the width of the light beam in two directions and to make the directions of the optical axes in the two directions the same. can.

However, the deviation of the optical axis in two directions cannot be corrected.

As described above, when using light sources with different light intensity distributions in two orthogonal directions in a plane perpendicular to the optical axis, it is possible to try to correct the light intensity distribution so that it is axially symmetrical with respect to the optical axis. ,
Misalignment of the optical axis cannot be corrected.

On the other hand, proposals have been made to interpose optical filters with different light transmittances in different parts in the optical system to solve various problems caused by having different light intensity distributions in two directions without shifting the optical axis. .

JP-A-63-191119, JP-A-63-205
No. 828, etc., discloses that in the case where the diameter of parallel light is made constant by disposing an aperture in the optical path or by using the vignetting phenomenon of a collimator lens, the aperture,
Considering that side lobes occur in the light intensity distribution due to diffraction due to the edges of collimator lenses, etc., which can cause crosstalk and image quality deterioration, an optical filter whose light transmittance gradually decreases uniformly in the radial direction is installed in the optical path. The technology for distributing it has been disclosed.

The optical filter used here has a light transmittance that gradually decreases from the center to the periphery, so the so-called edge effect does not occur, but in order to eliminate the aforementioned sidelobes, it has transmission characteristics with an extremely steep Gaussian distribution. Since this is an optical filter, there is a large loss in the amount of light throughout the radiation direction.

[Problems to be Solved by the Invention] In the light beam shaping device using the optical prism shown in FIGS. 3 and 4, although it is possible to evenly correct the light intensity distribution in two different directions, There was a problem in that it was difficult to correct the deviation.

On the other hand, with the optical filter disclosed in JP-A-63-191119, etc., the light intensity distribution can be made uniform without causing any deviation of the optical axis, but since the purpose is to remove side lobes, the total light intensity is There was a problem in that the amount of light lost to the target was extremely large.

Purpose of the Invention This invention has been made to solve the above problems, and it is possible to change the light intensity distribution with respect to the optical axis by preventing the optical axis from shifting and by minimizing the loss of light quantity with a small number of parts. It is an object of the present invention to provide an optical head device that can be axially symmetrical.

[Means for Solving the Problems] The optical head device according to the present invention has a light transmittance that increases from the center to the outer periphery for light sources whose light intensity distributions differ in two orthogonal directions in a plane perpendicular to the optical axis. The present invention is characterized in that an optical filter is provided in which the rate of decrease gradually decreases, and the rate of decrease has different characteristics in two corresponding directions.

[Function] With this configuration, in the beam emitted from the light source, one direction (X direction) having a wide light intensity distribution corresponds to one direction of the optical filter in which the light transmittance decreases at a large rate. By doing so, the light intensity distribution after passing through the optical filter can be changed to another direction (X
direction).

Therefore, the obtained light beam is axially symmetrical with respect to the optical axis, and neither optical axis deviation nor diffraction occurs.

〔Example〕

FIG. 1 is a perspective view showing the main optical system portions of an optical head device according to an embodiment.

In the figure, (1) is a light source such as a semiconductor laser that has different light intensity distributions in two orthogonal directions in a plane perpendicular to the optical axis, θ1 is the divergence angle in the vertical direction (X direction), and θ2 is the horizontal direction ( (X direction), and has the relationship θ1>θ2. (2) is a collimator lens, (5) is an optical filter, and (6) is a light intensity distribution curve after output from the optical filter (5).

Figure 2 is a schematic diagram of the optical filter (5), which has light transmission characteristics as shown in the θ1 direction (X direction) and θ2 direction (X direction) of the light source (1). The rate of decrease in transmittance from the center to the periphery is large in the X direction, and small in the X direction.

Note that the transmittance at the center of the optical filter (5) is 1, that is, all light passes through the optical filter (5).

In this optical head device, the light source beam from the light source (1) has a so-called elliptical shape with different light intensity distributions in two different directions, that is, the X direction and the X direction. Although this light beam is turned into parallel light by the collimator lens (2), the light intensity distribution is still elliptical. Next, an optical filter (
5), the light intensity distribution in the X direction due to the large divergence angle θ1 is corrected to a predetermined light intensity distribution characteristic by the characteristics of the optical filter (5) having a large transmission reduction rate.

On the other hand, the light intensity distribution in the X direction due to the small divergence angle θ2 is corrected to a predetermined intensity distribution characteristic by the characteristic of the optical filter (5) having a small transmission reduction rate. At this time, the ratio of the major axis (X direction) and minor axis (X direction) in the elliptical light intensity distribution of the light source (1) is the same as that in the horizontal direction (X direction) and the vertical direction (X direction) in the optical filter (5). direction) is not set equal to the ratio of the transmittance reduction rate of the optical filter (5
) The light beam after exiting has an axially symmetrical intensity distribution with respect to the tip axis (
It is shaped into parallel light with a circular distribution).

Since this shaped beam is not affected by diffraction effects, it is a high-quality light beam that is close to a Gaussian beam.

Moreover, since the optical filter (5) ideally reduces the light transmittance only in either the X direction or the X direction, it is possible to minimize the loss of light quantity.

[Effects of the Invention] As explained above, this invention provides
Because we used an optical filter with characteristics in which the light transmittance gradually decreased and the rate of decrease was different in two directions,
It is possible to shape a light beam from a light source such as a semiconductor laser, which has a light intensity distribution that differs in direction, into a light beam that has an axially symmetrical light intensity distribution without causing any deviation of the optical axis.

Furthermore, optical loss can be minimized without unnecessarily increasing the number of parts.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the main optical system of an embodiment of the present invention, FIG. 2 is a characteristic diagram of an optical filter used in an embodiment of the present invention, and FIGS. FIG. 3 is an explanatory diagram of the main optical system of the optical head device. In the figure, (1) is a light source, (2) is a collimator lens, (3) and (4) are optical prisms, and (5) is an optical filter. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] A laser light source whose intensity distribution is different in two directions orthogonal to each other in a plane perpendicular to the optical axis, a collimator lens that converts the light emitted from the light source into parallel light, and a collimator lens that converts the intensity distribution of the parallel light to the orthogonal direction. an optical head device comprising a beam shaping device that corrects the beam so that the two directions are approximately equal, and the beam shaping device has a transmittance that gradually decreases from the center toward the outer periphery, and whose rate of decrease is An optical head device characterized in that the optical filters are different in the two orthogonal directions.