JPH0445410A - optical scanning device - Google Patents

Abstract

PURPOSE:To correct even abrupt wavelength variation in scanning by detecting variation in the wavelength of a laser beam by using a diffraction grating for wavelength detection. CONSTITUTION:The light emitted by a laser light source 6 is split by a half- mirror 7 and one beam is made incident on the diffraction grating 10 for wavelength detection; and a wavelength detector 12 detects a shift in the position of the laser beam due to variation in the diffraction angle of the diffraction grating 10 to detect the variation in the wavelength due to the temperature variation of the semiconductor laser and the variation of a driving current at all times, thereby compensating a phenomenon such as deterioration in the linearity of scanning lines and the diameter of the laser beam due to the wavelength variation, an upward/downward deviation from a specific scanning line, and the variation in the scanning length. The diffraction grating 18 for wavelength detection is installed behind a hologram 16, the light of 0th order of the hologram 16 is utilized to eliminate the need for an optical element dedicated to the separation of the laser beam into beams for scanning and wavelength detection, and the wavelength detection is performed at all times without deteriorating the light intensity of the scanning laser beam.

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.

Prior Art As a type of optical scanning device that deflects a laser beam to scan a surface to be scanned, one has been proposed that uses a semiconductor laser as a light source and a hologram disk as a deflection means (for example, Japanese Patent Application No. 147544/1983). No., patent application No. 57-5527
No. 5). Hereinafter, the basic configuration of an 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. Further, the hologram 4 is composed of a plurality of facets, 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 drive current, which can cause the linearity of the scanning line and laser beam diameter to deteriorate, to deviate vertically from a predetermined scanning line, or to change the scanning length. I do things.

Conventional examples have been proposed to solve such problems by controlling the temperature of the semiconductor laser. Also,
A simple wavelength detection mechanism for responding to changes in temperature characteristics over time by performing feedback control has also been proposed (Japanese Patent Application No. 59-89730).

Problem to be Solved by the Invention However, the laser beam detection mechanism in an optical scanning device can only detect once per scan, even in position detection and wavelength detection, so it is necessary to compensate for fluctuations that occur during scanning. I couldn't.

Further, the relationship between the temperature of the semiconductor laser and the wavelength of the 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 nm. Therefore, the one-scan, one-detection method cannot compensate for this instantaneous mode hop.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an optical scanning device that can constantly detect wavelengths.

Means for Solving the Problems In order to achieve the above object, the present invention splits a laser beam emitted from a laser light source, makes one part incident on a diffraction grating for wavelength detection, and generates a laser beam by changing the diffraction angle. The configuration is such that wavelength fluctuations are detected by detecting changes in the position of the beam.

By dividing the working laser beam and using it, the beam for wavelength detection can be extracted without affecting the scanning beam.
Inject it into a diffraction grating for wavelength detection. Here, the wavefront of the beam is corrected so that it is imaged on the detection means. The position of the laser spot on the detection means varies depending on the wavelength due to the diffraction grating designed so that the diffraction angle varies greatly depending on the wavelength variation. This positional change allows wavelength changes to be detected at all times.

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

FIG. 1 shows a schematic configuration of an optical scanning device according to a first embodiment of the present invention.

6 is a semiconductor laser light source, 7 is a half mirror as a laser beam splitting means, 8 is a hologram, 9 is a scanned surface such as a photosensitive drum, 10 is a diffraction grating for wavelength detection, 1 is a reflection mirror, and 12 is a wavelength detector. be.

A laser beam emitted from the semiconductor laser light source 6 is split by a half mirror 7 into a laser beam 13 for scanning and a laser beam 14 for wavelength detection. A scanning laser beam 13 enters the hologram 8, is diffracted, and reaches the scanned surface 9.

A laser beam 14 for wavelength detection is a diffraction grating 1 for wavelength detection.
The wavefront of the diffracted light is corrected so that it is incident on the wavelength detector 12 and focused on the wavelength detector 12. The wavelength detection diffraction grating 10 is set so that the diffraction angle changes greatly depending on the wavelength fluctuation of the laser beam, and the wavelength fluctuation can be detected on the detector 12 as a positional change of the laser beam spot.

As described above, according to this embodiment, the light emitted from the laser light source 6 is divided by the half mirror 7, and one of the parts is made incident on the diffraction grating 10 for wavelength detection, and the change in the diffraction angle in the diffraction grating 10 is By detecting changes in the position of the laser beam with the wavelength detector 12, it is possible to constantly detect wavelength fluctuations caused by changes in the temperature of the semiconductor laser or changes in the driving current. It is possible to correct phenomena such as deterioration of the diameter, vertical deviation from a predetermined scanning line, or change in scanning length even during scanning.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a configuration diagram of the optical scanning device in the embodiment.

In the figure, 15 is a semiconductor laser light source, 16 is a hologram, and 17 is a surface to be scanned. The difference from the configuration of the first embodiment is that the wavelength detection diffraction grating 18 is located behind the hologram 16, and the 0th order light (non-diffracted light) of the hologram 16 is
is made so that it is incident.

Although the laser beam incident on the hologram 16 is designed to be diffracted and reach the scanned surface 17, in reality, a portion of the laser beam is transmitted through the hologram 16 or reflected without being diffracted. Of these, a laser beam (zero-order light) that passes through the hologram 16 is used. The zero-order light is made incident on the wavelength detection diffraction grating 18, and the wavefront is corrected so that it is imaged on the detector 19.

The wavelength detection diffraction grating 18 is set so that the diffraction angle changes greatly depending on the wavelength fluctuation of the laser beam, and the wavelength fluctuation can be detected on the detector 19 as a positional change of the laser beam spot.

As described above, the wavelength detection diffraction grating 18 is attached to the hologram 1.
6 and uses the zero-order light of the hologram 16, there is no need for a dedicated optical element to separate the laser beam into scanning and wavelength detection. Wavelength detection can be performed at all times without deterioration compared to the above configuration.

In the first and second embodiments, one wavelength detection diffraction grating is used, but it goes without saying that two or more diffraction gratings may be used.

Effects of the Invention As described above, according to the present invention, it is possible to constantly detect variations in the wavelength of a laser beam, so it is possible to correct even sudden wavelength variations during scanning.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical scanning device according to a first embodiment of the present invention, FIG. 2 is a configuration diagram showing an optical scanning device according to a second embodiment of the present invention, and FIG. 3 is a configuration diagram showing a conventional optical scanning device. FIG. 4, a block diagram of the apparatus, is a diagram showing wavelength change characteristics of a semiconductor laser light source. 6.15... Laser light source, 7... Half mirror 8, 16... Hologram, 10.18
...Diffraction grating for wavelength detection, 12.19...
··Detector.

Claims (2)

[Claims] (1) In an optical scanning device using a laser light source and a diffraction grating that scans the laser beam emitted from the laser light source along a predetermined scanning line, a laser beam that splits the laser beam emitted from the laser light source a dividing means;
A wavelength detection diffraction grating into which the divided wavelength detection laser beam is incident, and a detection means for detecting wavelength fluctuation by detecting a change in the position of the laser beam due to a change in the diffraction angle in the wavelength detection diffraction grating. An optical scanning device comprising: (2) The optical scanning device according to claim 1, wherein the laser beam incident on the wavelength detection diffraction grating is 0th order diffracted light of the diffraction grating.