JPH0229614A - Laser printer device - Google Patents

Abstract

PURPOSE:To make transmissivity identical in an optical system when it employs two laser beams by inserting a phase plate into the optical path of laser beams polarized in their orthogonal directions and converting them into circularly polarized light. CONSTITUTION:Lenses 3 and 4 make parallel the laser beams from two semiconductor lasers 1 and 2, respectively. Linearly polarized semiconductor laser beams 5 and 6 in their orthogonal directions are synthesized in the same direction through a polarizing prism 7 which passes through linearly polarized light in one direction and reflects linearly polarized light orthogonal to the former light. After the two laser beams are synthesized, their polarized directions are orthogonal to each other. By inserting a lambda/4 plate 8 between a polarizing prism 7 and a rotary polygon mirror 9, the directions of the two laser beams are reversed in circular polarization, that is, clockwise and counterclockwise. By putting the circularly polarized beams into a scanning optical system, their reflectances and transmissivities are different even if the rotating direction of a vector is reversed, and after the two laser beams pass by, the entire transmissivity is constant without difference.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a laser printer device that uses two laser beams, and an object of the present invention is to eliminate variations in light utilization efficiency.

[Conventional technology]

In order to increase the speed and resolution of laser printers, attempts have been made to use multiple laser beams to prevent the number of rotations of the rotating polygon mirror from increasing due to the increase in speed and resolution. Applied Obtake XVo Q 2
6. &13 (1987) p2554 (Applied
0ptics Vo Q 26, NCkl 3
(1987) p. 2554, two orthogonally polarized semiconductor laser beams LD are used as shown in FIG.
Using LDa, two laser beams are emitted by a polarizing prism pp.

Attempts have been made to simultaneously scan in parallel using the same rotating polygon mirror so that the images are combined in the same direction.

This combines two laser beams with mutually orthogonal polarization so that the laser beams go in the same direction using a polarizing beam prism that passes through the negative polarization direction and reflects the other polarized light. The idea is to introduce the two laser beams into a scanning optical system consisting of an angle and angle theta lens, and simultaneously scan the two laser beams in parallel using a single rotating polygon mirror.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, the polarization states of the two combined laser beams are also orthogonal to each other.

However, these laser beams then enter a scanning optical system consisting of a rotating polygon mirror and a scanning lens called an Fθ lens. In particular, the angle of incidence on a rotating polygon mirror changes greatly between the start and end of scanning for one surface. On the other hand, it is well known that when the polarization of light is different, and when the incident angle is other than normal incidence, a difference occurs in the reflectance.

FIG. 3 shows the reflectance when lights of different polarizations are incident in mutually orthogonal directions.

Of course, the transmittances also differ.An object of the present invention is to make the transmittances of the two laser beams the same even when the two laser beams pass through the scanning optical system.

[Means to solve the problem]

The above purpose is to insert a λ/4 plate or a phase plate having an equivalent effect into the optical path of two combined laser beams polarized in directions orthogonal to each other, and to change the polarization states of each laser beam from each other. This is achieved by converting the light into circularly polarized light with the opposite direction of rotation.

By using these two converted circularly polarized lights, the transmittance of the optical system can be made constant when two laser lights are used.

[Effect]

The λ/4 plate is inserted into the optical path until the two laser beams are combined by a polarizing prism and then entered into a scanning optical system consisting of a rotating polygon mirror and an Fθ lens.

The polarization state of each laser beam becomes circularly polarized light in opposite directions. If we put this circularly polarized light into a scanning optical system.

1 reflectance even if the direction of rotation of the vector is opposite.

There is a difference in transmittance, and even if two laser beams pass through, there is no difference in the overall transmittance of each, and the transmittance can be kept constant.

〔Example〕

FIG. 1 shows an embodiment of the present invention. Laser beams from two semiconductor lasers 1 and 2 are collimated by lenses 3 and 4, respectively.

Two semiconductor laser beams 5 and 6 linearly polarized orthogonally to each other
are combined in the same direction through a polarizing prism 7 which passes linearly polarized light in one direction and reflects linearly polarized light perpendicular to it. At this time, the polarization directions of the two laser beams after being combined are also orthogonal to each other.

A λ/4 plate 8 is inserted between the polarizing prism 7 and the rotating polygon mirror 9. Then, what are the polarization directions of the two laser beams?

The light becomes circularly polarized in opposite directions, counterclockwise and clockwise.

Therefore, two circularly polarized laser beams enter the scanning optical system composed of the Fe lens 10.

If the light is circularly polarized, there will be no difference in reflectance or transmittance when it passes through the optical system even if the direction of rotation of the circularly polarized light is reversed.

In other words, even if two laser beams pass through the scanning optical system,
As long as the output power of the laser beams is made equal, there will be no variation in intensity between the two laser beams after passing through the scanning optical system.

〔Effect of the invention〕

According to the present invention, when performing laser scanning using two laser beams polarized in orthogonal directions, by using a wave plate to make both beams circularly polarized, the efficiency of light utilization is increased. Since there is no difference between the laser beams, it is possible to perform good optical scanning without uneven printing results.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing a conventional example, and Fig. 3 is a diagram of reflectance due to polarized light.

Claims (1)

[Claims] In a laser printer device in which one or two laser beams linearly polarized in orthogonal directions are scanned in parallel at the same time by a rotating polygon mirror and narrowed down by a scanning lens, the two laser beams are applied to the rotating polygon mirror and the scanning lens. A laser printer device characterized in that when the laser beam is incident, the polarization of the laser beam is converted into a circularly polarized state by inserting a wavelength plate into the optical path of the laser beam.