JPS59216164A - Light source device - Google Patents

Abstract

PURPOSE:To eliminate the influence of wavelength variation of a semiconductor laser excellently by a simple method by providing a variable stop which controls the quantity of light from the semiconductor laser to a photosensitive drum according to the sensitivity characteristics of the photosensitive drum to wave- length. CONSTITUTION:A light source part 30 consists of a semiconductor chip 20, distributed index lens 21, and variable aperture stop 22. Then, reference wavelength and the aperture diameter of the variable aperture stop 22 are predetermined according to the wavelength sensitivity characteristics of the photosensitive drum 34 to control the quantity of light. For example, when the photosensitive body decreases in sensitivity as the wavelength becomes longer, the aperture diameter of the variable stop 22 is increased for long wavelength to increase the quantity of light. Thus, the influence of wavelength variation of the semiconductor laser to the wavelength sensitivity characteristics of the photosensitive characteristics is eliminated excellently by the simple means.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light source device suitable for laser beam printers and the like.

In recent years, with the development of lasers, more and more lasers have been used for various purposes.

FIG. 1 is a diagram schematically showing an embodiment of a recording apparatus having a laser in a light source section.

In FIG. 1, reference numeral 1 denotes a light source section consisting of a laser and a collimator optical system that converts the beam from the laser into a predetermined beam diameter, 2 a deflector, 6 a beam scanning lens, and 4 a photosensitive drum. Recently, semiconductor lasers have been widely used as light sources, taking advantage of their ability to self-modulate and the ability to miniaturize 6D devices.

However, compared to gas lasers such as He--Ne lasers or solid-state lasers, the oscillation wavelength of semiconductor lasers is wider (varies) depending on the individual chips.

However, as shown in Figure 2, the wavelength dependence of the sensitivity of the photosensitive drum exhibits rapid attenuation on the long wavelength side, and especially when the wavelength of the semiconductor laser shifts to the long wavelength side, the amount of light tends to be insufficient. It becomes very difficult to obtain good image quality. As a countermeasure, it may be possible to increase the light emitting output of the laser, but this is not desirable from the perspective of life expectancy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light source device that can improve the above-mentioned drawbacks even when a semiconductor laser is used as a light-receiving medium whose sensitivity changes with respect to wavelength.

The light source device according to the present invention aims to achieve the above object by controlling the amount of light emitted by the semiconductor laser.

That is, depending on the wavelength of the semiconductor laser, the aperture diameter of the diaphragm interposed between the light section and the light-receiving medium is changed to adjust the amount of light that reaches the light-receiving medium. In short, the standard wavelength and the aperture diameter of the variable diaphragm are determined in advance according to the wavelength sensitivity characteristics of the light-receiving medium, and the light amount is controlled accordingly. In this method, when the actual wavelength shifts to the long wavelength side, the aperture diameter of the variable diaphragm is widened to increase the amount of light.The present invention will be described in detail below.

FIG. 3 is a diagram showing an embodiment of the light source device according to the present invention,
10 is a semiconductor laser chip, 11 is a collimator lens,
12 is a diaphragm whose aperture diameter is variable. This diaphragm 12 is a variable diaphragm so that its aperture diameter can be set according to the wavelength of the semiconductor laser 10 and the wavelength sensitivity characteristics of the light-receiving medium. The light beam from the semiconductor laser 10 is converted into a parallel light beam by a collimator lens 11, and a part of the parallel light beam is blocked by an aperture 12 depending on the wavelength of the laser beam and the wavelength sensitivity characteristics of the light-receiving medium. Ru.

FIG. 4 is a diagram showing another embodiment of the light source device according to the present invention. In FIG. 4, 20 is a semiconductor laser chip;
1 is a gradient index lens, and 22 is a variable aperture. In the gradient index lens 21, in order to correct aberrations, an end surface 21a on the incident side of the light beam is a flat surface, and an end surface 22a on the exit side of the light beam is a spherical surface with a convex surface facing the aperture stop υ21b. The refractive index distribution n (r) at a distance r from the central axis to the periphery of the gradient index lens is rl''(r)=n2(o) (1-(gr)'+h4
(gr)'+ha(gr)') 67g expressed in (I) is a parameter representing the strength of the distribution on the paraxial axis. h4. ht is a coefficient. Now, n (0)=
1.552, gro = 0.248, ro
'= 1.587, b+-0,9, 116-10,
Using a material of 0, the distance between the vertices on both sides is ^1'z = 2
．． 425, a good wavefront could be obtained when the radius of curvature it of the end surface 21b on the emission side of the light beam satisfies -4,0≦R≦-2,2.0.fist (2). Note that the value of R is shown as a negative value in relation to the position of the center of curvature. R of this gradient index lens 21 is -4,0, I is also -2,3, ■--
A longitudinal aberration diagram (corresponding to the spherical aberration diagram of the 11I ordinary lens) in the case of 2.2 is shown in FIG. In addition, the vertical axis is lens 2
1 represents the height of incidence of a luminous flux incident on 1. As can be seen from FIG. 5, if l'L falls within equation (2), good imaging performance is achieved.

Next, in the present invention, the wavelength sensitivity characteristic of the light-receiving medium is
As shown in Figure 2, the longer the wavelength, the worse the sensitivity (
In such a case, we will discuss how fluctuations in the beam spot diameter on the surface of the light-receiving medium can be kept small. It is widely known that the intensity of laser light has a deep distribution, but if we define the intensity of the center intensity EXP (-2) as the luminous flux and the spot diameter, then the imaging spora)
D is D=K fist F 豐λ
−・・・・ It is given by (6).

Here, if the wavelength shifts to the long wavelength side, D
increases. However, since the sensitivity of the light-receiving medium decreases,
The aperture diameter of the variable aperture is widened, but if the focal length of the imaging lens is f1 and the aperture diameter is a, then (6)
Since F in the equation is given by F-f/a, the value of F is obviously small.

Furthermore, widening the aperture diameter a means that the EX of the laser beam
P(-2) The ratio a/b of the aperture diameter a to the luminous flux diameter becomes thick (becomes), and therefore the constant iK of equation (6) also becomes small.

(Mj, HUZAWA: LASERFOCUS SE
P, P82 (1980)) In the end, in equation (6), the product of KXF and λ on the right-hand side have the effect of canceling out their variations, so the change in spot diameter due to variation in aperture diameter is sufficiently small as shown in the above two equations. In the description, the purpose of correcting variations in oscillation wavelength due to manufacturing errors of semiconductor lasers has been described, but the present invention can also be used to correct variations in oscillation wavelength due to temperature changes of semi-integrated lasers during use. You can. In this case, if a means for monitoring the oscillation wavelength of the semiconductor laser is provided, and the diaphragm is opened and closed based on the output signal from this monitor, even if the oscillation wavelength changes, the diaphragm can be opened and closed automatically. It is possible to correct the amount of light reaching the light receiving medium.

FIG. 6 is a diagram illustrating an embodiment of a recording apparatus having a rotating polygon mirror surface tilt correction device u-th to which the optical adjustment device u according to the present invention is applied. In FIG. 6, 60 indicates an optical general section according to the present invention, and the internal components are as shown in FIG.
The semiconductor laser chip 20 is composed of a plane end face on the incident side of the laser beam, a gradient index lens 21 whose exit end face is concave toward the laser chip side, and a variable aperture diaphragm 22.

62 is a rotating polygon mirror, and 61 is a rotating polygon mirror 62.
A cylindrical lens 66 is a spherical lens that has power only in a cross section perpendicular to the main scanning plane formed by the deflected beam and forms a linear image of the light beam from the light source section 60 near the deflection reflecting surface of the rotating polygon mirror 62. This is an anamorphic beam scanning sub-lens system consisting of a single lens 33a and a single lens 35b having a toric surface, and the deflection reflection surface and the photosensitive dome 64 are in an optically conjugate relationship in the cross section perpendicular to the main scanning direction. By doing so, the tilt of the deflector 620 surface is corrected.

In the above explanation, for the sake of simplicity, the lens in the optical focal point has a collimating function, but according to the spirit of the present invention, the luminous flux emitted from the variable aperture is not limited to parallel light. Divergent light or convergent light may be used.Furthermore, a variable aperture may be placed between the laser chip and the light source lens.

As described above, the photodetection device according to the present invention can satisfactorily eliminate the influence of the wavelength change of the semiconductor laser on the wavelength sensitivity characteristics of the light-receiving medium using simple means.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional recording device, FIG. 2 is a diagram showing a sensitivity characteristic line in an example of a light-receiving medium whose sensitivity is wavelength dependent, and FIGS. The figure shows an embodiment of a recording device to which the light source device of the present invention is applied. 10.20... Semiconductor laser, 11... Collimator lens, 12, 22... Variable aperture, 21
−・・・Gradient index lens. (nm'4 diagram (X70-')

Claims (2)

[Claims] (1) A light source device comprising a semiconductor laser and a variable diaphragm that controls the amount of light that reaches a light receiving medium of the semiconductor laser in accordance with the wavelength sensitivity characteristics of the light receiving medium. (2) A semiconductor laser, a deflection device that deflects a light beam from the semiconductor laser to scan the photosensitive drum, and controls the amount of light of the semiconductor laser that reaches the photosensitive drum according to the wavelength sensitivity characteristics of the photosensitive drum. A recording device characterized by being equipped with a variable aperture.