JPH0445412A - Optical scanning device - Google Patents

Abstract

PURPOSE:To correct the influence of variation in the wavelength of a semiconductor laser effectively over its entire range by providing plural correcting holograms which have correction effect in different wavelength ranges between a hologram and the focus position of a laser beam. CONSTITUTION:The laser light which is emitted by a semiconductor laser light source 6 is diffracted by a hologram disk 7 to make a scan along a specific scanning line on a scanned surface 9 through a hologram substrate 8 for correction. The hologram substrate 8 is constituted by arranging different striped holograms 8a, 8b, and 8c closely so that the holograms correct only laser beams with wavelengths bin determined ranges and also have the wavelength bands continuously. The boundary wavelengths of the holograms 8a, 8b, and 8c for correction are set to wavelengths where a mode hop (abrupt variation in wavelength with temperature) is caused to prevent a correcting function from not being obtained owing to the aligning of the laser beam on the border of the holograms for correction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical scanning device for linearly scanning a laser beam by deflecting it using a diffraction grating such as a hologram in, for example, a laser printer or a laser copying machine.

2. Description of the Related Art Optical scanning devices that scan a surface to be scanned by deflecting a laser beam have been known. As a type of such an optical scanning device, one using a semiconductor laser as a light source and a hologram disk as a deflection means has been proposed (for example, Japanese Patent Application No. 147544/1982 and Japanese Patent Application No. 55275/1983). Hereinafter, a conventional optical scanning device for a laser printer will be briefly explained with reference to FIG.

A laser beam emitted from a semiconductor laser light source 1 passes through a collimator lens 2, is diffracted by a first hologram 3 and a second hologram 4 as deflection means, and is imaged on a scanned surface 5 such as a photoreceptor drum. Ru. therefore,
By rotating the hologram 4, the laser beam spot on the surface to be scanned 5 can be scanned. The hologram 4 is composed of a plurality of 71 sets, and can be scanned by the number of facets in one rotation.

However, the wavelength of a semiconductor laser constantly changes depending on the ambient temperature and driving current, which can cause the linearity of the scanning line and laser beam diameter to deteriorate, to deviate up or down from a predetermined scanning line, or to change the scanning length. I do things.

A technique (first conventional example) has been proposed to solve this problem by controlling the temperature of the semiconductor laser. Note that since the semiconductor laser itself is extremely small and it is difficult to directly control its temperature, the temperature of the semiconductor laser is indirectly controlled by controlling the temperature of the holder that holds the semiconductor laser. Furthermore, a simple wavelength detection mechanism has been proposed to cope with changes in temperature characteristics over time by performing feedback control (Japanese Patent Application No. 89730/1982).

In addition, a technique (second conventional example) has been proposed in which a diffraction grating such as a hologram is provided in addition to the hologram disk to cancel out the effects of wavelength fluctuations of the semiconductor laser (Japanese Patent Application No. 1973-
No. 147544, Japanese Patent Application No. 57-55275).

Problems to be Solved by the Invention Now, the relationship between the temperature of a semiconductor laser and the wavelength of laser light is generally expressed by a stepped line, as shown in FIG.

This phenomenon of wavelength change in the step part is called a mode hop, and there is a wavelength change of about 0.5 nrn. Therefore, in the first conventional example, it is not possible to compensate for this instantaneous mode hop. Further, there was a problem in that it was difficult to respond to changes in ambient temperature.

Furthermore, in the second conventional example, although it is possible to correct the vertical deviation of the scanning line from a predetermined scanning line, it is not possible to compensate for the effects of wavelength fluctuations including other fluctuations such as the scanning length. The problem was that it was difficult.

Means for Solving the Problems In order to solve the above problems, the present invention provides a correction hologram that has a correction effect for different wavelength bands between the hologram and the focal position of the laser beam, and the wavelength bands are continuous. The configuration is such that a plurality of them are provided.

The linearity of the scanning line and the laser beam diameter may deteriorate due to wavelength fluctuations caused by temperature changes in the semiconductor laser, the scanning line may deviate vertically from a predetermined scanning line, or the scanning length may change. According to the above, by providing a correction hologram that can correct all effects due to wavelength fluctuations in a narrow range of about 3 nm or less, for example, wavelengths in a specific narrow range can be effectively corrected. If a larger wavelength variation occurs, it is corrected by another correction hologram that is installed close to the correction hologram and performs correction in a continuous wavelength range. Therefore, by providing a plurality of these correction holograms in succession, the influence of the wavelength fluctuation of the semiconductor laser can be effectively corrected over the entire range.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of the optical scanning device of this embodiment.

6 is a semiconductor laser light source, 7 is a hologram disk, 8 is a correction hologram substrate, and 9 is a surface to be scanned such as a photosensitive drum.

The laser beam emitted from the semiconductor laser light source 6 is diffracted by a hologram disk 7, and the wavefront of the laser beam is corrected by a correction hologram substrate 8 so that it scans along a predetermined scanning line on a surface to be scanned 9. .

Since the emission wavelength of the semiconductor laser light source 6 changes depending on the ambient temperature as shown in FIG. 2, the diffraction direction and focal position of the laser beam diffracted by the hologram disk 7 differ depending on the wavelength. In the vicinity of the scanned surface 9 where the laser beam of each wavelength is applied, a large change in the sub-scanning direction (direction perpendicular to the scanning line) appears, and the laser beam enters the correction hologram substrate 8 in that state.

The correction hologram substrate 8 has different strip-shaped holograms 8.
a, 8b, and 8c are arranged in close proximity to each other, each of which is arranged so as to correct only a laser beam having a wavelength in a predetermined band. Each rectangular correction hologram 8a, 8b
, 8c are each designed to be able to correct the laser beam within a range of 3 nm or less, and in the case of five holograms, these correction holograms have a correction function for wavelength fluctuations of about 15 nm in total.

In FIG. 2, the portion where the wavelength changes rapidly with respect to temperature is a phenomenon called mode hop, and laser beams with wavelengths between this period are not stably emitted. That is, each of the rectangular correction holograms 8a, 8b, 8c
By setting the boundary wavelength to the wavelength at which this mode hop occurs, the laser beam
.

8b, 8. It is possible to avoid the situation where the correction function cannot be obtained due to being located on the boundary of c.

When the correction holograms 8a, 8b, and 8c are constructed using holograms or are produced using computer generated holograms, the hologram disk 7 and the correction holograms 8a, 8b, and 8c are
It is necessary to find a configuration that does not exist in wavelengths only in a limited wavelength range, including the wavelength range, through optimal design. Correction holograms 8a, sb.

8c has a narrow correction wavelength range and is close to the scanned surface 9, so the incident area of the laser beam during one scan is large, so it is easier to design compared to conventional correction holograms, and correction is also a side effect. This can be done simultaneously for other than the deviation in the scanning direction.

As described above, according to this embodiment, the hologram disk 7
Correction holograms 8a, 8b, 8c that have correction effects for different wavelength bands between and the focal position of the laser beam
By providing a plurality of continuous wavelength bands, the linearity of the scanning line and the laser beam diameter may deteriorate due to wavelength fluctuations caused by temperature changes in the semiconductor laser 6, or the laser beam may deviate vertically from a predetermined scanning line. , it is also possible to correct phenomena such as changes in scanning length.

In the above embodiment, the correction hologram has a rectangular shape, but it goes without saying that it may have an arc shape or a cylindrical shape.

Effects of the Invention As described above, according to the present invention, the linearity of the scanning line and the laser beam diameter may deteriorate due to wavelength fluctuations caused by temperature changes in the semiconductor laser, the scanning line may deviate vertically from a predetermined scanning line, or the scanning It becomes possible to correct the sipping phenomenon where the length changes.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical scanning device according to an embodiment of the present invention, FIG. 2 is a diagram showing wavelength fluctuations of a semiconductor laser with respect to ambient temperature, and FIG. 3 is a configuration diagram of a conventional optical scanning device. 6...Laser light source, 7...Hologram disk, 8a, 8b, 8c...Correction hologram, 9...Scanned surface.

Claims (2)

[Claims] (1) In an optical scanning device using a laser light source and a hologram that scans a laser beam emitted from the laser light source along a predetermined scanning line, there is a difference in wavelength between the hologram and the focal position of the laser beam. An optical scanning device characterized in that a plurality of correction holograms having a correction effect on a band are provided so that the wavelength band is continuous. (2) The optical scanning device according to claim 1, wherein the correction hologram is formed on one substrate.