JPH0533372B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an optical scanning device.

(Prior technology) As an optical scanning device, a conventional rotating polygon mirror and θ
A disk-type optical scanning device using a hologram instead of a combination of lenses has been proposed.
In this method, a plurality of holograms are arranged along the circumference of the disk, and by rotating the disk, scanning lines corresponding to the number of holograms on the disk are scanned per rotation of the disk. At this time, generally
As the disk rotates, the scan line curves. Optical scanning devices used in laser printers and laser fax machines require straight-line scanning, and if the scanning line is curved, image quality will be degraded.

Conventionally, this has been corrected by setting special conditions for the off-axis angle of the hologram lens. Further information on this method can be found, for example, in the article ``Holographic disk scanners capable of linear scanning'' in the journal Applied Optics, 1983, pages 2132-2136.
for bow-free scanning). As shown in FIG. 4, the center of the holographic scanner 31 is the origin 0, the radius is R, and the amount of rotation of the laser beam irradiation position Q with respect to the x-axis is θ _R.
On the other hand, the hologram lens that makes up Scanyana is
It consists of a zone plate 32 having its center at c(x _c,p ). If the radius of the zone plate is γ and the angle that CQ makes with the x-axis is θ _r , then γ=√ ² _c ² −2 _{c R} …(1) θr=cos ⁻¹ (γ ² +x _c ² −R ² /2rx _c ) …(2). If we introduce a coordinate system x'-y' that rotates with the holographic scanner 31, the scanning position of the beam will be x' = lcos (θ _R + θr) y' = lsin (θ _R + θr) ... (3a) (3b) It is. Here, l is the distance between the disk and the scanning surface, and is expressed as tanθ _o , where the diffraction angle is θ _o .
The scanning line can be made straight by selecting the off-axis angle θ = x _c - R/ (4) as shown in equation (4) so that x' remains constant as y' changes. I can do it. In the above paper, conditions (4) were optimized, with a scanning length of 40 cm and a distance from the holographic scanner to the scanning plane of 80 cm.
Achieved linear scanning within 100μm. However, in this method, the off-axis angle is a special condition, so it is not possible to make the scanning line a straight line under arbitrary conditions.

(Objective of the Invention) An object of the present invention is to provide an optical scanning device that can easily straighten any scanning line by eliminating the above-mentioned drawbacks.

(Means for Solving the Problems) The present invention provides a wavelength tunable light source, an optical system for shaping the beam shape of monochromatic light emitted from the light source, and a tunable light source guided by the optical system. A holographic scanner, in which a holographic lens irradiated with the beam is placed on a disk, detects the curvature of the scanning line of the scanning light emitted from the holographic scanner, and adjusts the wavelength so that the scanning line becomes a straight line. The optical scanning device is equipped with a control means for changing the wavelength of the variable light source.

(Principle of Operation) In a holographic laser beam scanning device such as a holographic scanner, several holograms are arranged and fixed on the circumference of a disk and are rotated at high speed to scan a laser beam. At this time, the scanning beam is curved as the holographic scanner rotates.

Holograms reproduce images using diffraction.
When a hologram with spatial frequency ν (lattice spacing α) is irradiated with light of wavelength λ, the diffraction angle of the +1st order diffracted light is θ=sin ^-1 (λ/α)=sin ^-1 (νλ) …(5) It is expressed as Therefore, by changing the wavelength λ of the light that illuminates the hologram, the diffraction angle θ can be changed. For example, 1000 spatial frequencies/
When a hologram with a diameter of
changes up to. If the distance from the disk to the scanning plane is 150 mm, the beam position can be changed by 11 mm on the scanning plane.

The oscillation wavelength of a semiconductor laser generally changes depending on the injection current. In particular, cleavage-coupled resonator semiconductor lasers ( ^C3 lasers) have a variable wavelength width of 150
It is suitable for this application because it can perform GHz modulation in Å and the oscillation output does not change due to injection current. For example, the magazine ``Applied Physics Letter'' has written about this semiconductor laser.
Letfer), 1983, pages 650-652, ``High-speed direct single-frequency modulation of cleavage-coupled cavity semiconductor lasers with a large tunable wavelength range''.
direct single−frequency modulation with
large tuning rate and frequency excursion
incleaved−coupled−cavity semiconductor
It is described in detail under the title ``Laser''. This semiconductor laser splits a conventional semiconductor laser into two,
One is used as a laser and the other as a modulator. The mode spacing of the oscillation wavelengths of the two semiconductor lasers is slightly shifted. If the injection current of the laser is kept constant and the mode is changed by changing the injection current of the modulator, the laser oscillates when the two modes match. Therefore, a discontinuous wavelength change corresponding to the mode difference between the laser and the modulator is possible. In the above paper, the wavelength change with respect to the injection current10
Å/mA, variable wavelength width 150 Å, oscillation wavelength 1.3 μm,
Achieved switching time of 1nsec. By using this, the position of the scanning beam can be detected and the information fed back to adjust the injection current, change the oscillation wavelength, and change the diffraction angle.
Curved scan lines can be straightened.

(Example) FIG. 1 shows a first example of the present invention. Light emitted from a semiconductor laser 1, which is a wavelength tunable light source, is collimated by a collimating lens 2, converged by a cylindrical lens 3, and scanned on a scanning surface 6 by a hologram lens 5 of a holographic scanner 4. do. In this embodiment, a collimating lens 2 and a cylindrical lens 3 form an optical system. A beam splitter 7 is placed between the hologram lens 5 and the scanning surface 6 to take out a part of the scanning beam. The extracted beam is focused in the scanning direction by a cylindrical lens 8 onto a one-dimensionally arrayed photodetector 9 . By imaging the light in the scanning direction,
The deviation in the sub-scanning direction is imaged in accordance with the arrangement direction of the photodetectors 9. The differential output from the photodetector is processed by an arithmetic circuit 10, such as a microcomputer with a GP-IB interface, to calculate the wavelength value for the amount of deviation using the relationship between the oscillation wavelength and the diffraction angle shown in equation (5). Calculate. Furthermore, using the relationship between the injection current and the oscillation wavelength, the current of the power source 11 having an interface such as GP-IB is changed. A flowchart at this time is shown in FIG. In this embodiment, in addition to scanning line curvature correction, it is also possible to correct jitter and inclination. In this embodiment, the control means includes a beam splitter 7, a cylindrical lens 8, a photodetector 9,
It consists of an arithmetic circuit 10 and a power supply 11.

FIG. 2 shows a second embodiment of the invention. In this embodiment, information on the curvature of the scanning line is input into the memory in advance, and as the disk rotates, the data in the memory is read and the voltage of the power supply 24 is controlled. That is, the control means includes a position detector 21 for detecting the rotational position of the holographic scanner, a memory 23, an arithmetic circuit 22, and a power source 24. The light oscillated from the semiconductor laser 1 is. Collimating lens 2
After being collimated at , it is converged by a converging lens 3 and scanned on a scanning surface 6 by a hologram lens 5 of a holographic scanner 4 . Scanning line curvature information is calculated or experimentally analyzed in advance and stored in the memory 23. The rotational position of the holographic scanner 4 is detected by a position detector 21 such as a photocoupler, for example. The curvature information of the corresponding hologram lens is accessed from the memory 23 to the arithmetic circuit 22, and the voltage of the power supply 24 is changed. FIG. 3 shows an example of information stored in the memory 23 regarding the current value and the position of the hologram.

If you use a hologram with an off-axis angle of 20 degrees, a disk rotation speed of 6000 rpm, and a distance of 150 mm from the hologram to the scanning surface, the scanning line will have a difference of 5 mm between the scanning edge and the center. Draw an arc. At this time, we were able to make the scanning line straight by changing the current in a 2KHz sine wave shape as shown in Figure 3.

(Effects of the Invention) As described above in detail, according to the present invention, an optical scanning device that can easily perform linear scanning on an arbitrary scanning line can be obtained by changing the wavelength of the light source.

[Brief explanation of drawings]

FIG. 1 shows a first embodiment of the invention, and FIG. 2 shows a first embodiment of the invention.
Embodiment 2 of the present invention, FIG. 3 is an example of data stored in the memory of the second embodiment, FIG. 4 is a schematic diagram of scanning line curvature correction in the conventional example, and FIG.
The figure is a diagram showing the flow of the correction procedure in the first embodiment. In the figure: 1... Semiconductor laser, 2... Collimating lens, 3... Cylindrical lens, 4... Holographic scanner, 5... Hologram lens, 6... Scanning surface, 7... Beam splitter, 8... Cylindrical lens, 9...One-dimensional array photodetector, 10... Arithmetic circuit, 11... Power supply, 21... Position detector, 22...
...Arithmetic circuit, 23...Memory, 24...Power supply, 3
1... Hologram disk, 32... Zone plate.

Claims (1)

[Claims] 1. A holographic scanner in which a wavelength tunable light source, an optical system that shapes the beam shape of monochromatic light emitted from this light source, and a hologram lens that is irradiated with the beam guided by this optical system are arranged on a disk. , detect the curvature of the scanning line of the scanning light emitted from the holographic scanner,
An optical scanning device comprising: control means for changing the wavelength of the variable wavelength light source so that a scanning line becomes a straight line.