JPH03177808A - Optical scanner - Google Patents

Abstract

PURPOSE:To remove the discontinuity of a recording image due to variation in the wavelength of a semiconductor laser by using a scanning optical system which has its magnification chromatic aberration (one factor of lateral aberration) compensated in the main scanning direction (optical scanning direction). CONSTITUTION:An expression I holds, where (f) is the focal length of a scanning lens in its main scanning plane, deltalambda the wavelength variation width of a light source, lambdac the wavelength of a C line, lambdaF the wavelength of an F line, PSId1 the reciprocal of the focal length of each single lens constituting the scanning lens to a (d) line, upsilond1 the Abbe number of each lens constituting the scanning lens to the (d) line, alpha the angle of scanning by a deflector, and (d) the main- scanning directional diameter of the spot of luminous flux image at a specific position through the scanning lens. Consequently, the chromatic aberration of magnification is compensated to improve the discontinuity of a scanning recording image due to a shift in scanning position with the wavelength of the semiconductor laser and deterioration in resoluting off the optical axis due to the oscillation wavelength width of a multimode oscillation semiconductor laser, thereby improving the quality of the scanning recording image.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an optical scanning device used in a laser beam printer, a laser beam copying machine, etc. that has an electrophotographic process and is required to output high-definition images, that is, The present invention relates to an optical scanning device that exposes and scans an image carrier or the like with a light beam from a semiconductor laser or the like.

[Prior Art] Conventionally, optical scanning devices that optically scan and write images on image carriers using semiconductor laser elements in laser beam printers and laser beam copying devices suffer from self-heating of the semiconductor laser and changes in ambient temperature. As a result, the output mode of the semiconductor laser changes and the wavelength of the laser beam changes, which causes changes in the focus (beam waist position) on the image carrier, which is the scanned surface, and chromatic aberration in the magnification of the optical scanning position optical system. There is a phenomenon in which scanning position fluctuations occur in the optical scanning direction. As a countermeasure to this problem, the semiconductor laser element itself was placed at a constant temperature and the environment was controlled.

For example, by thermally adhering a Bertier element to a semiconductor laser element and controlling the temperature of the laser element by heating and cooling, or by providing a heater to adjust the temperature of the laser element at a higher temperature than the outside temperature, the semiconductor laser This prevents fluctuations in the focus and optical scanning position caused by wavelength fluctuations due to changes in the output mode of the element, and prevents the quality of the optical scanning image from deteriorating.

On the other hand, as the demand for oscillation wavelengths of semiconductor lasers is becoming shorter, it is necessary to use gain guide type (gain waveguide type) multimode oscillation semiconductor lasers with a wide wavelength band width (half width). 2~3n
There are situations in which it is necessary to use an element with a shorter wavelength as a substitute for an element with a shorter wavelength.

[Problems to be Solved by the Invention] However, in the conventional example of placing a laser element under a constant temperature, a Vertier element, a heater, a temperature control means, etc. must be used to adjust the temperature of the semiconductor laser element. This results in an expensive optical scanning device.

In addition, in this conventional example, some percent of the intensity of the light emitted from the semiconductor laser element is reflected by an optical member such as a collimator lens, and the self-oscillation light that returns to the semiconductor laser element itself causes an output mode change. It was difficult to deal with the phenomenon. As a countermeasure for this phenomenon, the anti-reflection coating of optical components such as the collimator lens mentioned above is made up of a multilayer film to minimize the reflectance, thereby suppressing the return light. There is a method of blocking reflected light from the optical member by installing it in the optical path between the optical members, but in any case, it is inevitable that the product will be expensive.

Furthermore, it is possible to correct longitudinal chromatic aberration through the entire optical scanning optical system to prevent the scanning image plane from shifting due to wavelength fluctuations of the semiconductor laser; however, this method does not prevent the scanning image plane from shifting. Although it is possible to do so, the chromatic aberration of magnification is not corrected, so if the wavelength of the semiconductor laser changes due to mode jumps due to changes in ambient temperature, the length of the optical scan will change (distortion changes will also occur at the same time). Therefore, the further away from the optical axis of the optical scanning lens, the more the light irradiation position deviates from the ideal position. In extreme cases, mode hops occur instantaneously, so the wavelength changes not continuously but discretely.
This also results in the scanned image being recorded in an interrupted state.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical scanning device that can scan and record high-quality images by eliminating discontinuities in recorded images caused by wavelength fluctuations of a semiconductor laser.

[Means for Solving the Problems] In the present invention, which is a distant relative of the above object, a laser beam emitted from a laser oscillator is deflected by an optical deflector such as a single-sided or multi-sided reflective mirror, and the laser beam is deflected onto an irradiated object or an image carrier. In an optical scanning device that scans light upward, the main scanning direction (light scanning direction)
A scanning optical system is used that corrects lateral chromatic aberration (a cause of lateral aberration).

[Example] FIG. 1 is an optical path diagram of an embodiment of the optical scanning device of the present invention.

The center of FIG. 1 shows the configuration in the main scanning plane formed over time by the scanned light beam, and the main scanning plane is a plane parallel to the plane of the paper. Parallel to this, the periphery of Figure 1 shows the configuration in the sub-scanning direction, which is perpendicular to the main scanning plane (i.e., the direction perpendicular to the optical scanning direction of the two axes perpendicular to the optical axis). .

In FIG. 1, a light beam emitted from a semiconductor laser diode 1, which is a light source that is modulated and driven according to an image signal, is converted into a parallel light beam by collimator lenses 3a, 3b, 3c, and 3d, and an aperture member 10 adjusts the beam outer diameter. is determined.

Then, this beam is transmitted through the cylindrical lenses 4a and 4.
In b, the light is focused only in the sub-scanning direction and enters the reflecting surface of the rotating polygon mirror 6, which is an optical deflector, as a linear beam, and after being deflected there, the f/θ characteristic is reflected in the optical scanning direction. Anamorphic lenses 7a and 7b are configured as a conjugate imaging system in the sub-scanning direction.

An image is formed on the irradiated object surface 9 by 7C. At this time, by uniformly rotating the rotating polygon mirror 6 in the direction of the arrow in FIG.
This focused beam on the irradiated object surface 9 is optically scanned in a linear manner.

In the configuration shown in FIG. 1, reference numerals 2, 5.8 are cover glasses for dustproofing, and anamorphic lenses 7a to 7c have conjugate points on the reflective surface of the rotating polygon mirror 6 and the irradiated object surface 9 in the sub-scanning direction. ing. Therefore, even if the rotating polygon mirror 6 causes precession as it rotates, or even if the adjacent surfaces are tilted due to the accuracy of the reflective surface processing of the rotating polygon mirror 6 itself,
The same scanning line is scanned on the surface 9 of the irradiated object. It has a so-called tilt correction function.

For example, as a semiconductor laser diode that is a light source,
In a semiconductor laser diode with a wavelength of 675 nm, there is a wavelength fluctuation of about ±5 nm in a temperature range of 8° C. to 42° C.

In addition to the above, in the embodiment of the present invention, even if the laser emission mode changes due to environmental temperature changes (including self-heating) of the semiconductor laser 1 and the oscillation wavelength fluctuates discretely (Figs. 5 and 7), (Refer to) In order to ensure continuity of optical scanning, optical scanning and condensation is required when using a multi-mode oscillation type laser with a wide wavelength band width such as a gain guide type semiconductor laser (see Figure 6). In order to eliminate blur caused by spot chromatic aberration, the axial chromatic aberration is naturally corrected in the entire optical system from the light source to the irradiated object surface, and the anamorphic lenses 7a to 7C are corrected by light deflection by the rotating polygon mirror 6. The chromatic aberration of magnification is suppressed to an optical scanning position variation of ±13 μm when the laser wavelength varies ±5 nm.

That is, regarding longitudinal chromatic aberration, a variation of ±5 nm in wavelength is corrected to within ±50 gm (see Figures 2 and 3), and when this amount corresponds to lateral aberration, it is corrected to within ±2.5 μm. In other words, if the spot diameter does not change within the laser beam waist, but outside the beam waist, the spot diameter of optical scanning is 30 μm, the laser wavelength fluctuation of ±5 nm causes a maximum of 30 ± 2.5 μm.
This means that only a slight variation in spot diameter occurs.

Regarding chromatic aberration of magnification, the mode hop of a semiconductor laser causes a wavelength fluctuation of about 1 nm when the wavelength is about 670 nm (see Figure 7). If a wavelength fluctuation of lnm occurs at an arbitrary time, the optical scanning position fluctuation will be approximately 2.5 μm at maximum (
4v1315) It has been corrected to the extent that it moves (see Figure 4).

This amount of movement of about 2.5 μm means that the optical scanning beam spot diameter of this embodiment (measured as the width of the intensity that is 1/e2 of the peak light intensity) is approximately 30 μm in the scanning direction (in the sub-scanning direction). (approximately 65 μm), the discrete and discontinuous fluctuation of the scanning position is less than 1/10 of the spot diameter in the main scanning direction. If this degree of variation exists, it cannot be recognized by the human eye as a recorded image on the irradiated object 9, so no deterioration in image quality is observed and optical scanning of a high-quality image becomes possible.

The above means that for a wavelength width of 5 nm, it is sufficient that the discrete and discontinuous fluctuation of the scanning position is about % or less of the spot diameter in the main scanning direction.

On the other hand, when using a multimode oscillation laser, the wavelength bandwidth differs depending on the number of modes of the laser (see Figure 6), but according to this example, the wavelength band width differs depending on the number of modes of the laser. Since the difference in spot diameter between positions can be reduced, it is possible to eliminate the problem of an optically scanned image having good resolution near the optical axis, but the resolution worsening toward the end of the optically scanning area. Therefore, a multimode semiconductor laser device may be used as the laser oscillator.

The optical parameters of the above examples are detailed in Table 1 below. The symbols are as shown in FIG.

Table 1 Example (in Fig. 1), scraping scanning direction 1 of aperture 1o
3.2 mm, sub-scanning direction 10.5 mm, laser wavelength used 675 ± 5 nm, θ = 53° (mm) di 2 d 2 1 d, 48.512 d4 2.73 d, 4.19 da 1.52 dy o , 61 da3.14 d, 27.71 (adjustment) dl. 4 dl125 (adjustment) d I2 6 di3 4 dl4107.7 (adjustment) dis 14,59 dia ot dia l1I dz.

dz+ 12 zs dz4 S.S. zs zt 29, 28 0 24.11 4,83 4, 72 20, 06 2, 28 18.13 286, 81 0 Main scanning direction (mm) 0 0 166.67 -44.438 O Sub-scanning direction (mm) 0 0 166.67 -44.438 0 6 7 8 9 rh.

r++ rhz rhs z 15 I6 17 rha I9 20 rt+ zz 23 Main scanning direction (mm) 35.753 39.996 -49.716 0 151.41 0° O 0 0° o.

-80,298 0 -1136,15 -102,9 0 -148,41 0 0 Sub-scanning direction (mm) 35.753 39.996 -49.716 0 151.41 38.912 -42.648 0 0 0 0 0° 0 0 -90. 473 -28. 685 0 o.

nd υdn+
1. 51633 64. In2
1. 51633 64. 1n
3 1. 72825 28. 5n
a1. 6031 1 60.
7na 1. 51633 6
4. In8 1. 5 1 633
64. 1n? 1. 72825
28. 5ns 1, 5 1
633 64. 1n9 1
, 62004 36. 3n10
1, 603 1 1 60.
7rl+t, 622.99
58. 2rlB 1. 51633
64. The length of one beam scanned is ±150 mm from the optical axis center, and the rotating polygon mirror 6 has a circumscribed circle diameter of φ73 mm.
The spot diameter in the main scanning direction of the light beam focused on a predetermined position via the facepiece, scanning lenses (7a to 7c) is 30 μm, and the focal length of the scanning lens (7a to 7c) in the main scanning direction is f=28.
6.5 mm, and if the maximum deflection angle from the optical axis of the scanning lens shown in Fig. 1 is the scanning angle α of the deflector, then the scanning angle α of the deflector = 30″ Here, the beam from the laser light source is deflected by the deflector. A conditional expression for correcting lateral chromatic aberration in the main scanning direction (light scanning direction) in an optical scanning device that deflects and forms an image at a predetermined position via a scanning lens having an fθ characteristic of the deflected light beam will be described.

ψ is the power of a single lens.

Temple ψ" One ψC (ψ, -ψC) is the difference in power between the F line and the C line.

ψ＾ given Σψ1 ψ is the power of the entire scanning lens system, and ψ1 is the power of each single lens constituting the scanning lens.

Therefore, the power fluctuation of the scanning lens when the wavelength changes is becomes.

a is a correction constant of 0.2.

δ is the wavelength fluctuation width (nm) due to temperature change of the light source.

λ. is the wavelength of the C line, which is 656.27 nm.

The wavelength of F-line is 486.13 nm.

ψ1. υ61 is the reciprocal of the focal length of each single lens constituting the scanning lens, and the Abbe number of each single lens. If the scanning lens is composed of two single lenses, i=1
．． 2. When the scanning lens is composed of three single lenses, i=1.2.3.

Therefore, The focal length of the scanning lens when the wavelength changes The fluctuation is becomes.

f is the focal length of the scanning lens in the main scanning direction.

Therefore, the amount of displacement of the irradiation position (chromatic aberration of magnification) when scanned to the maximum from the optical axis of the scanning lens is the maximum deflection angle from the optical axis of the scanning lens, where α is the scanning angle [radian] by the deflector. .

Therefore, the light beam from the laser light source is deflected by a deflector,
In an optical scanning device that images the deflected light beam at a predetermined position via a scanning lens having an fθ characteristic, lateral chromatic aberration in the main scanning direction (light scanning direction) is caused by It is preferable that the spot diameter is corrected to within 1/2 of the spot diameter in the scanning direction, so... (1) d is the spot diameter in the main scanning direction, and the spot imaged at a predetermined position through the scanning lens is This is the required spot diameter in the main scanning direction.

Further, the above-described equation (1) assumes that a light beam parallel to the main scanning direction, that is, a light beam parallel to the main scanning plane enters the scanning lens.

Furthermore, the above-mentioned equation (1) considers the case where a scanning lens having fθ characteristics is used as the scanning lens. ftanθ
If a scanning lens having a characteristic is used, α in the above-mentioned equation (1) may be replaced with janα.

FIG. 8 is an optical path diagram of another embodiment of the optical scanning device of the present invention. The center of FIG. 8 shows the configuration in the main scanning plane formed over time by the scanned light beam. The main scanning plane is a plane parallel to the plane of the paper. In parallel, the area around FIG. 8 shows the configuration in the sub-scanning direction, which is perpendicular to the main scanning plane (i.e., the direction perpendicular to the optical scanning direction of the two axes orthogonal to the optical axis). .

In FIG. 8, a light flux emitted from a semiconductor laser diode 31, which is a light source that is modulated and driven according to an image signal, is transmitted through collimator lenses 32a, 32b, 32c, and 3.
2d is converted into a parallel light beam, and the beam outer diameter is determined by the aperture member 40. Then, this beam is focused by the cylindrical lenses 33a and 33b only in the sub-scanning direction onto the reflective surface of the rotating polygon mirror 35, which is an optical deflector, and becomes a linear luminous flux, and after being deflected there. The light is focused on the irradiated object surface 38 by anamorphic lenses 36a and 36b, which have f/θ characteristics in the optical scanning direction and are configured as a conjugate imaging system in the sub-scanning direction. At this time, by uniformly rotating the polygon mirror 35 in the direction of the arrow in FIG. 8, the focused beam on the surface of the irradiated object 38 is linearly scanned.

In the configuration shown in FIG. 8, 34 and 37 are cover glasses for dustproofing, and anamorphic lenses 36a and 36b have conjugate points on the reflective surface of the rotating polygon mirror 35 and the irradiated object surface 38 in the sub-scanning direction. . For this reason, the rotating polygon mirror 3
5 causes precession as it rotates, and even if adjacent surfaces are tilted due to the accuracy of the reflective surface processing of the rotating polygon mirror 35 itself, the same scanning line is scanned on the irradiated object surface 38. It looks like this. It has a so-called tilt correction function.

The parameters of the above embodiments are detailed in Table 2 below. The symbols are as shown in FIG.

Table 2 Example 2 (in FIG. 8), the aperture 40 was 11.0 mm in the rear scanning direction, 7.2 mm in the sub-scanning direction, and the laser wavelength used was 675 nm±5 nm.

53″ θ = (mm) ds+ 29. 168 ct,, 2.58 ds, 1.32 ds4 1.04 d3s 4.12 dse 4.11 dst 12.00 (Fl adjustment) dsa 3.00 dsa 12.00 (adjustment) d4゜　　　　4. 00 d4.　　　　　3.00 d42 74.18 (adjustment) d, 3 17.21 d, 4 34.72 d4a　　　　　to, o.

d4e 2.00 d □, 18.22 48 411 d.

sl SZ S.S. 21.

61.

18゜320゜2゜50゜ 2 8 6 0 rs+ si 33 sa 3s 36 r3? 311 39 40 41 Main scanning direction (mm) 83.906 -21.826 -41.862 15.253 30.467 -16.997 0 101.8 0°0 O Sub-scanning direction (mm) 83.906 -21 .826 -41.862 15.253 30.467 -16.997 0 101.8 30.034 -30.034 0°42 r43 44 r<a 4a 47 4a 49 Main scanning direction (mm) 0 0ri -101 ,41 -110,47 -147,43 -41,694 0 CI) -218,74 n! + 32 33 34 311 3a 37 sa nd 1, 51633 1, 72825 1. 60311 1, 51633 1, 51633 1, 74077 1, 51633 1, 62299 υ d 64, 1 28° 5 60, 7 64, 1 64, 1 27, 8 64, 1 58, 2 nd vdnse
1. 6031 1 60. 7n4
o 1. 51633 64.
The length of one light scan is ±150 mm from the center of the optical axis.The rotating polygon mirror 35 has an octahedron with a circumscribed circle diameter of 82 mm.The main scanning of the light beam is focused on a predetermined position via the scanning lens (36a, 36b). Direction spot diameter 45gm, scanning lens (3
6a, 36b) focal length in the main scanning direction f = 343.5
If the maximum deflection angle from the optical axis of the scanning lens shown in Fig. 8 is the scanning angle α of the deflector, then the scanning angle α of the deflector is 24.75° or more, which satisfies the condition of equation (1). Since lateral chromatic aberration in the main scanning direction (optical scanning direction) can be corrected by using a scanning lens, it is possible to correct discontinuities in scanned recorded images due to variations in scanning position due to wavelength variations in semiconductor lasers, or oscillations in multimode oscillation semiconductor lasers. Off-axis resolution deterioration due to wavelength width is improved, and the quality of scanned recorded images is improved. Moreover, since a temperature control device for the semiconductor laser can be omitted, it is possible to reduce the cost.

[Effects of the Invention] As explained above, according to the present invention, in an optical scanning optical system using a semiconductor laser, chromatic aberration of magnification is corrected, so that chromatic aberration due to fluctuations in scanning position due to wavelength fluctuations of the semiconductor laser is corrected. This improves the quality of the scan-recorded image by improving off-axis resolution deterioration caused by discontinuity in the scan-recorded image or the oscillation wavelength width of the multi-mode oscillation semiconductor laser. Moreover, since a temperature control device for the semiconductor laser can be omitted, it is possible to reduce the cost.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is an aberration diagram showing the amount of beam waist field curvature in the scanning direction of the embodiment, and FIG.
The figures are an aberration diagram showing the amount of beam waist field curvature in the sub-scanning direction of the example, Figure 4 is an aberration diagram showing the lateral chromatic aberration of the example, Figure 5 is a diagram showing the wavelength characteristics of a single mode semiconductor laser, FIG. 6 is a diagram showing the wavelength characteristics of a multimode semiconductor laser, FIG. 7 is a diagram showing the temperature dependence of the oscillation wavelength of the semiconductor laser, and FIG. 8 is a diagram showing the configuration of another embodiment of the present invention. 1...Semiconductor laser 2.5.8...Cover glass 38-3c...Collimator lenses 4a, 4b...Cylindrical lens 6...Rotating polygon mirror 78-7c...Anamorphic lens 9...・ Irradiated object 10...Irradiation Yuchi 2 Figure scanning bee L7 hiss) -i Qing surface A et al oil amount (J = Ayuchi) 3rd
Diagram A
(Voluntary) Indication of the case of December 20, 2015, Hirasoko No. 318084 Name of the invention: Person who corrects optical scanning device Relationship to the incident

Claims (1)

[Claims] (1) In an optical scanning device in which a light beam from a light source is deflected by a deflector, and the light beam deflected by the deflector is imaged at a predetermined position by a scanning lens having an fθ characteristic, the scanning lens includes a light beam in the main scanning plane. A parallel beam of light is incident on the scanning lens, the focal length in the main scanning plane of the scanning lens is f, the wavelength variation width of the light source is δ_λ, and the wavelength of the C line is λ_C, F
The wavelength of the line is λ_F, the reciprocal of the focal length of each single lens constituting the scanning lens is ψ_1, the Atsube number of each single lens constituting the scanning lens is υ_d_1, the scanning angle by the deflector is α, the scanning lens Let d be the spot diameter in the main scanning direction of the light beam focused on a predetermined position via ▲
An optical scanning device characterized by having mathematical formulas, chemical formulas, tables, etc.▼.