JPH01238610A - Optical scanner - Google Patents

Abstract

PURPOSE:To obtain a high-speed optical scanner which executes parallel scanning by using plural light beams by projecting the respective light rays emitted from plural light emitting sources on the different parts of hologram lenses on a holographic laser scanner or projecting the same at different incident angles thereon. CONSTITUTION:The light rays oscillated from a laser array 1 disposed with two light emission points are collimated by a collimating lens 2 and are condensed by a lens 3. The condensed light scans a scanning surface 6 by the hologram lenses 5 of the holographic laser scanner 4. The spacing between the beams to project the hologram lenses changes in proportion to the spacing between the light emission points of the laser array 1 at this time. For example, the spacing between the light beams on the hologram lenses 5 is 500mum and the spacing thereof on the scanning surface 6 is 1mm when the light emission points are arrayed at 500mum spacing and the diverging beam of 1mm diameter is irradiated on the hologram lenses 5. The spacing between these light beams can be properly determined according to the conditions of use.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser scanner that scans laser light.

[Conventional technology]

As an optical scanning device, a Tisf-type optical scanning device has been proposed that uses a hologram in place of the conventional combination of a rotating polygon mirror and an f/θ lens. In this method, a plurality of holograms are arranged along the circumference of the disk, and by rotating the disk, as many scanning lines as there are holograms on the disk are scanned per rotation of the disk. When applying such an optical scanning device to a printer or facsimile,
It is necessary to scan linearly in proportion to the rotation of the disk. At this time, if the hologram has these functions,
No other optical system is required, simplifying the configuration.

[Problem to be solved by the invention]

However, if the number of holograms on the disk is increased to increase the printing speed, the scanning performance will deteriorate, and when used as a scanning device such as a printer or facsimile, the number of holograms is limited to 5 or 6. Ta. If we consider that the limit of the rotational speed of the motor is about 6000 rpm, the maximum number of scans per second is 600, and the printing speed per sheet of A4 size paper for a 360 dots/inch printer is:
It is 7 seconds. Furthermore, printing becomes slow in high-resolution printers, making it impractical.

An object of the present invention is to provide a high-speed optical scanning device that performs parallel scanning using a plurality of light beams.

[Means to solve the problem]

The optical scanning device of the present invention includes a holographic laser scanner in which a plurality of light emitting sources and a plurality of hologram lenses are arranged on a disk, and a holographic laser scanner in which each part emitted from each of the light emitting sources is arranged in a penal holographic laser scanner. The hologram lens is characterized by comprising an optical system that shapes the light emitted from each light emitting source so as to irradiate different parts of the hologram lens or to irradiate the light at different incident angles.

[Action/Principle]

In a holographic rape scanner, several holograms are arranged and fixed on the circumference of a disk, and light is scanned by rotating the holograms at high speed.

A hologram lens functions as a lens through diffraction. For example, in the case of a Fresnel zone plate, which is one of the hologram lenses, the relationship between its focal length f and phase distribution is φ(r)=πr/λf (1
). Here, λ represents the reproduction wavelength.

In equation (1), the position where the right side is an integral multiple of 2π indicates the position of the ring of the zone plate. A hologram lens having the phase distribution of formula (1) has no aberration when a plane wave is incident thereon, but when a spherical wave is incident therein in order to increase the scanning length, the aberration increases. Therefore, in a hologram scanner used in an optical system such as a laser printer, a phase distribution that minimizes aberrations is determined by ray tracing, and a hologram is manufactured using a computer-generated hologram method. By using this hologram method, it is possible to design an optimal hologram for any incident wavefront.

Therefore, in order to increase the printing speed of the printer, consider printing takes in parallel using multiple light sources. For example, consider a case where three light beams are used as shown in FIG. Light emitted from a laser array 101 in which light emitting points are arranged at intervals a is transmitted to a hologram lens 102.
The upper and lower spaced spots illuminate different parts of the hologram lens. At this time, if the phase distribution of the hologram lens is designed so that each light beam scans adjacent scanning lines 103, three times as many scanning lines can be generated at one time as when using a single light beam. be able to.

Each light beam incident on a different region of the hologram lens is deflected with a distance between each beam, so that it can scan on different scanning lines. Furthermore, when the incident angle of each party beam is changed, the deflection direction differs depending on the incident angle, so different scanning lines can be scanned.

If n light beams are used in this way, n scanning lines can be generated simultaneously, and n scanning lines can be scanned simultaneously, so printing can be performed at n times the speed of a single beam. can.

The phase distribution of the hologram can be obtained as shown in the following equation. As shown in Figure 3, the coordinate system is as follows: coordinates on the scanning plane are indicated by lowercase letters x, y, and coordinates on the hologram plane are indicated by uppercase letters X, y.
Represented by Y. Assume that the phase transfer function of the hologram lens is as follows.

A coefficient of 01.0 is used so that the light diffracted from the hologram having this phase transfer function has linear scanning properties and f/θ characteristics.
Determine the value of The direction cosine of the incident light is ('in+m1rl
+ nin ), then the direction cosine ('ou
t+”out + 'out) ii It is expressed by the following formula.

nout ”” (1”out no., 2) l/2
・・・・・・・・・ (5) On the other hand, linearity and f・θ
According to the characteristics, the desired direction cosine of the diffracted light (1out + M
ouj + Nou+) is expressed by the following formula.

Mo,, -2-gate...
・・・・・・・・・ (7) A "out-(1-Lout Mout")1'"
----(8) Here, A is expressed by the following formula, where h is the distance from the hologram to the scanning plane.

A-f(f-dθ-X+n)'Ytn""')""'・
(9) Since the direction cosine is a shift invariant with respect to coordinate transformation, the coordinate transformation between the coordinates (x, y) of the scanning plane and the coordinates (X, Y) of the hologram plane is as follows. It is sufficient to consider only the rotation θ.

X: X cos θ + Ys in θ −−・・−
= (10)y =-Xs inθ+Ycosθ
----(11) From equations (2) to (10), the following equation holds true.

If N beams are approximated by M rays, a total of NM equations will be obtained, so the coefficient 00 can be found by the least squares method. Based on equations (12) and (13), the coefficients are determined so that the following function is minimized.

f−dθ−X f(X, Y)−ΣΣ(←−” in k, 1−kl
A 2ΣΣ+ CI, X2"Y" )2+ ()"stop-
+4 A ” i n k , l−ΣΣJc ,, x 2 i
y h-1)2 ) ,...(14)+4 In order to obtain the minimum value of f(X, Y), equation (13) is partially differentiated.

ΣΣ1cH4X"-'Y')2X2iX"-'Y'1
” + (Y Ln k , l , , nk, l−ΣΣj
C,,X”A +4 Y”)2×jX'Y'-')・・・・・・・・・・・・
(15) According to equation (14), the optimal phase transfer function is obtained as a solution to the simultaneous -order equations expressed by the following equations.

〔Example〕

FIG. 1 is a perspective view showing an embodiment of the invention. Light emitted from a laser array 1 in which a plurality of light emitting points (two in this example) are arranged is collimated by a collimating lens 2, and then condensed by a lens 3.
A scanning surface 6 is scanned by a hologram lens 5 of a holographic laser scanner 4. At this time, the interval between the beams irradiating the hologram lens changes in proportion to the interval between the light emitting points of the laser array. For example, if the light emitting point is 500μ
When collimating the light beams from the laser array arranged at m intervals and irradiating the hologram lens with a diverging beam with a diameter of 111 m+, the light beam interval on the hologram lens was 500 μm and 1 mm on one scanning surface. This light beam interval can be appropriately determined depending on the usage conditions by changing the optical system, the phase distribution of the hologram lens, etc. In order to perform uniform linear scanning with this holographic laser scanner, the phase distribution of the hologram in the area where the lights from adjacent lasers overlap was optimized so that each scanning beam would satisfy the scanning performance.

〔Effect of the invention〕

As described in detail above, by using the optical scanning device of the present invention, a plurality of scanning lights can be generated simultaneously, and high-speed optical scanning can be realized.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 is a diagram showing the state of a beam on a hologram lens, and FIG. 3 is a diagram illustrating a method for determining the phase distribution of a hologram lens. It is a diagram. In the figure, 1,101-... laser array, 2...
Collimating lens, 3... Lens, 4... Holographic laser scanner, 5,102... Hologram lens, 6... Scanning surface. Agent Patent Attorney Shinji Uchihara 10- Leh + IU゛M3

Claims (1)

[Claims] a holographic laser scanner having a plurality of light emitting sources and a plurality of hologram lenses disposed on a disk;
The light emitted from each of the light emitting sources is shaped so that each light emitted from each of the light emitting sources illuminates a different part of the hologram lens disposed in the holographic laser scanner or irradiates at a different angle of incidence. An optical scanning device comprising an optical system.