JPS58132719A - Optical scanning system having inclination correcting function using semicondutor laser - Google Patents

Abstract

PURPOSE:To make a titled system provided with an inclination correcting function, and also to shorten optical path length of the optical system, by placing a deflecting surface and a surface to be scanned, in conjugate relation, as to an image forming lens and a troidal lens, when a laser beam is deflected by a rotary polyhedral mirror. CONSTITUTION:A beam emitted from a semiconductor laser 1 is focused onto a deflecting surface 4 by a coupling lens 2. A cylindrical concave lens 3 has no refractive power on the surface in the sub-scanning direction, and there is no influence. The deflecting surface 4 is in conjugate relation geometrically to a surface to be scanned 7 as to an image forming lens 5 and a troidal lens 6, and it does not occur that a position of an image forming spot on the surface to be scanned 7 is influenced by inclination of the deflecting surface. In the main scanning direction, the beam emitted from the semiconductor laser 1 becomes an almost parallel luminous flux by the operation of the cylindrical concave lens 3, is made incident to the deflecting surface 4, and forms an image forming spot on the surface to be scanned 7 by th image forming lens 5 having an fTHETA characteristic. In this way, it is possible to form a spot of desired size on the surface to be scanned, by providing an inclination correcting function, and using a semiconductor laser having different light emitting size, in the orthogonal direction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to optical scanning using a semiconductor laser as a light source and directing a laser beam flJA using a rotating polygon.

In an optical travel device that uses a rotating polygonal mirror as an optical deflector, it is possible to prevent (b) each anti-reflective surface of the multifaceted mirror from tilting with respect to its (b) rotational axis due to manufacturing errors. This is the cause of the pitch unevenness of the scanning line, and the number of revolutions per rotation is
kU#I! , an attempt is made to eliminate this error by increasing the top It of Vi, resulting in a considerable increase in cost.

In this case, the so-called sub-scanning direction ICs parallel to the rotation axis of the rotating mirror? In this case, the so-called tilt correction l that puts the anti-II4 lens and the scanning plane in a geometrical military relationship is applied to the marriage lens system.
! 1! A powerful optical system was introduced. Such an optical system requires an optical system having different refractive powers in the scanning plane and in a plane perpendicular to the scanning plane.

Cylindrical lenses and toric tID in the II system
I have peace of mind knowing that I will be meeting with 14 other lenses. However, since cylindrical lenses generally produce a curvature in the direction of the needle, it is necessary to distribute power just before the scanning surface, which makes it impossible to prevent the optical system from increasing in size, and the introduction of a toric surface is However, no matter how many rows there were, manufacturing was difficult and costs were inevitably high.

A gas laser that emits a preliminary light beam is often used as a light source for such a conventionally known optical system having a tilt correction function. An optical f-device is required.

OJ function is used to control the oscillation in contact with the semiconductor laser.
No particular optical modulator is required, but the emission angle is large, and the emission angle and emission origin position of the emitted light are in the direction of the active layer.
It may be different depending on the direction of +&. Therefore, if a semiconductor laser having a coupling lens for collimating the emitted light is used as a light source, the light source device becomes large and the advantage of the semiconductor laser being small is lost.

On the other hand, it is known that even if semiconductor lasers with different emission origins are used, a sufficiently good spot can be obtained with the aid of a spherical lens, as long as the aperture and focal length are appropriately selected for purposes such as laser printers. (For example, JP-A-55-130
No. 512) The present invention includes a light source and 1. Using a semiconductor laser, the optical path length of the optical system is made as short as possible while having a tilt correction function, making the optical scanning I! compact and easy to manufacture! This will be explained in detail with reference to the drawings below 0, which is a book in which pupils are to be obtained.

FIG. 1 is a perspective view of the main parts showing the configuration of the scanning optical system of the present invention, in which the beam emitted from the semiconductor laser 1 is passed through a coupling lens 2K, a rotary pot (3), and a deflector 4 such as a mirror. It is focused on the deflection surface. The concave cylindrical lens 3 disposed between the coupling lens 2 and the lens 4 converts the condensed beam into a preliminary light beam within the scanning plane, and produces a linear spot on the deflection plane. −
The beam deflected and scanned by rotation in the direction of the arrow in the direction passes through a constellation lens 5 having a ratio of 10% and a toroidal lens 6, and forms a spot on the scanned direction 7.

If the effect of this scanning optics is applied to the so-called sub-scanning direction perpendicular to the scanning direction, the beam emitted from the semiconductor laser l is focused onto the deflection surface 4 by the coupling lens 2, as shown in 2nd rR<a). At this time, the concave cylindrical lens 3 has no refractive power within this plane, so there is no shadow IVi. The toroidal lens 6 has a geometrically optically conjugate relationship with the surface to be scanned 7, so that the position of the imaging spot on the surface to be scanned 7 is not affected by the tilting trap of the deflection surface. On the other hand, the spot on the tS metaplane is focused by the imaging lens 5, but an imaginary spot is generated on the laser side from the - direction (2), and this luminous flux Vi is focused by the toroidal lens 6 to
The beam spot is focused on the scanning direction 7 and formed into a beam spot of a predetermined size.

On the other hand, as shown in Fig. 2 (1b) K in the main scanning direction, the emitted beam from the semiconductor laser 1 is focused by the coupling lens 2 to form a crystalline spot near the deflection surface, as described above. However, due to the action of the concave cylindrical lens 3 disposed between the deflector and the deflector, the light becomes a substantially parallel light beam and enters the deflector 1114. The beam deflected and scanned by the polarization plane 4 is focused by the imaging lens 5 having a ratio of 10% to the scanned rti which is on the focal plane of the IfB irrigation lens.
Create an imaging spot on 7. This 1i! ! Within the scanning curve of the 6-piece toroidal lens, the lens is transposed in a direction that has no refractive power, so no lens action is exerted. However, if the toroidal lens 5 is an ordinary cylindrical lens, a large curvature of field will occur on the scanned surface in the main scanning direction. It requires length and also requires strong refractive power.

As described above, almost all the preliminary light beam is incident on the imaging lens 5, but the area of the light spot on the surface to be scanned is inversely proportional to the diameter of the incident beam.

In other words, the diameter of the beam spot due to the marriage lens is d
It is known that there is the following relationship, where φ is the diameter of the incident light beam, and λ is the focal length of the lens and the wavelength of the 1% beam light.

Therefore, in order to obtain a predetermined spot diameter d.

In a system where λ and f are given, it is necessary to change the beam width φ.

Methods for changing the light beam width in one direction, that is, in the transverse direction (2), include method 2 using a prism, method 3 using a beam compressor or beam expander using a cylindrical lens, and method 3 constricting the light beam with a slit. However, method 2 has a complicated optical system, and method 3 has the disadvantage that it is not possible to widen the beam width in addition to the loss of light quantity. FIG. 3 shows the 1gt requirement of the optical system when the beam is narrowed down to 411it using the prism 8.

An example of a sloped body in the above scanning optical system is as follows. ◎ Custom-made Gaussian beam focusing is shown by the following formula 〇 However, f
: Focal length of the lens ω1: Beam waist half of the 1-body chain f4 d, : Distance between the object-side beam waist and the object-side principal point of the lens ω2: The beam waist distance of the wife d2: The beam waist of the acid 11 and the S of the lens For one scanning direction VC shown in the spacing between side principal points in FIG.
A 4m long coupling lens is placed from the laser emitting surface, d, = 14.
If it is placed at the 6 dew position, the beam waist position d2 = 121.84- can be obtained from equation (3).

Similarly, from equation 12), ω2 is 9 μm, but since there is vignetting in the concatenation/z, the cage of ω2 is actually larger than the above. Here, proceed with the following calculations assuming 02218 μm ◎ A deflector is placed at the position d2 above, but in this case the distance between the light source and the deflector is shorter than in a conventional focusing system using a convex cylindrical lens. .

Next, if we use f = 271.3 lenses as fθ lenses and place them at the position of d = 93.58-, the object will be
) The heel fy est is the combined lens 2 yor heem waist, so its radius is (ll, = 1
8 p m, and from <z> r, 3> equation, d2=-1
An imaginary beam waist of 42.8 ω2 = 27 μm is obtained.

Next, the specifications of the toroidal lens are determined so that a beam spot of a desired size can be obtained near the focal plane of the fθ lens. If the beam spot size at point 1 on the scanned surface is ω2 = o, u 6■, then the given stripe f + ω, = 0.027, the conjugate motion by the toroidal lens is d2 + f. 142.8 1,271.3
■ = 414.2, Arnote, f = 89.37
wa, d, = 130.18■, d = 283.97■
get. Therefore, a toroidal lens with f = 89.37 cm may be placed at a position of 283°97 cm from the surface to be scanned.

In this arrangement, the toroidal lens is located closer to the deflector than the fθ lens, but in a three-element fθ lens like the one shown in @2, the principal point position protrudes from the lens toward the scanned surface. .

Lens arrangement as shown in the figure becomes possible.

On the other hand, in the main scanning direction shown in FIG. 2(b), the emission size of the semiconductor laser is smaller than that in the sub-scanning direction, ω, = α
At 5 μm, if you calculate under the same conditions as the sub-scanning direction,
For the coupling lens d2==121, 84 wm
ω2=511 m. [7], and due to the vignetting of the coupling lens, ω2 = 10 μmli degree.

The desired spot size on the scanned surface is ω2=α052
5■, then f = d2 = 271.3■ from the condition that the surface to be scanned coincides with the focal plane of the fθ lens, and from equation (3), d, = f must be satisfied. Also, from equation (2), ω, = 1.28■ is returned.

From the above results, the concave cylindrical lens Vi placed between the coupling lens and the coupling lens (al = 10 μ
m (d2= 1.28 wgx. Also,
As mentioned earlier, the position of ω is 93.58■ from the fθ lens.
The position of ω2 must be 271.3 cm from the fθ lens, so with respect to the concave cylindrical lens, d, +d2 = 271.3.
(J-93,58=177.72m. From now on
f=-51,678 d=-51,683 d2=-1
Obtain 2591 ■. Therefore, the lens with f=51.68 m may be placed at a distance of 51.68 mm from the deflector.

The traveling optical system of the present invention has a tilt correction function and
A spot of a desired size can be formed on the target surface by using semiconductor lasers with different emission sizes in orthogonal directions.

As shown in Fig. 3, when using Ike's optical system to shape the beam and obtain the desired beam spot, the free cover of the concave cylindrical lens and the appropriate negative focal length - A concave cylindrical lens with a focal point of 1
It may be placed near the opposite side.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the essential parts of one actual example of the scanning optical system of the present invention, FIG. 2 is an optical path diagram thereof, and FIG. 3 is a partial view of the optical arrangement of another embodiment. 1: Droplet conductor laser 2: Coupling lens 3: Concave cylindrical lens 4: (- direction! i 5: fθ lens 6:
Toroidal lens 7: Scanned surface 8 Nibrism Patent applicant Ajishiki Kaishi Ricoh No. 1

Claims (1)

[Claims] A scanning optical system having a semiconductor laser, a coupling lens for condensing a light beam from the semiconductor laser, a deflector for scanning the light beam, and a condensing lens for condensing the scanned light beam onto a scanned fith. In this case, the coupling lens is arranged so as to generate a beam waist near the deflection surface of the light beam from the semiconductor laser, and the light 'if' is the horizontal light flux given the scanning direction of the coupling lens and the deflector. A concave cylindrical/trical lens is disposed, and a toroidal lens is disposed between the concave lens and the toroidal lens. A scanning optical system that uses a semiconductor laser to perform a wear correction function.