JP2555128B2 - Hologram scanner - Google Patents

Description

The present invention relates to a hologram scanner that performs beam scanning by diffracting a beam by a hologram, and cuts disturbance light in the 0th order light direction that may enter from the outside to improve operation reliability of the hologram scanner. For this purpose, the hologram is provided with a reflection hologram that reflects and diffracts external incident light in the 0th-order light direction or a transmission hologram that diffracts external incident light at an angle equal to or greater than the critical angle.

[Industrial applications]

The present invention relates to a hologram scanner that scans a beam in a predetermined direction by diffracting the beam by a hologram.

Holographic scanners are widely used in laser scanners for bar code readers, laser scanners for printers, optical devices, and the like.

[Conventional technology]

The hologram is formed by using a hologram dry plate obtained by coating a transparent substrate (glass or acrylic substrate) with a photosensitizer, irradiating a plurality of laser beams on the hologram dry plate, and recording interference fringes on the photosensitizer.

First of all, the hologram scanner (hologram window) on which the present invention is based will be briefly described below.

The applicant of the present application has previously disclosed in Japanese Patent Application No. 61-239903 a hologram scanner (hologram window) 55 in which two strip holograms are laminated in a cross shape. In view of the fact that the conventional hologram scanner requires a space of about 100 mm between the hologram and the scanning pattern, which hinders the thinning of the apparatus, a transparent substrate is interposed between the two hologram scanners. The hologram scanner is thinned by stacking holograms and eliminating the space. The feature is that the light diffracted at the intersecting portion (center portion) of the two upper and lower stacked holograms is transmitted through the other hologram except for the Bragg angle condition.

That is, as shown in FIGS. 4 and 5, the hologram window has two strip-shaped first and second holograms 1 and 2 which intersect diagonally and are formed on the respective transparent substrates 11 and 12. . Both holograms 1 and 2 intersect at the center. The hologram window has a function of receiving laser scanning light emitted from a rotating mirror (not shown) or the like and diffracting the laser scanning light in a predetermined direction to form a desired scanning pattern. At that time, for the pattern near the center, beams corresponding to the upper and lower patterns are selected based on the following principle.

First, refer to FIG. 6 which shows a general characteristic curve of the diffraction efficiency and the transmittance of a hologram with respect to the incident angle. The diffraction efficiency shown by the solid line becomes maximum at a predetermined incident angle (Bragg angle) B, and the efficiency decreases as the angle deviates from the Bragg angle B. On the other hand, the transmittance shown by the broken line is opposite to the Bragg angle B
At the minimum, and becomes larger as it deviates from the Bragg angle B. Therefore, in FIGS. 4 and 5, if the Bragg angle of the central portion (intersection portion) of the upper second hologram 2 is aligned with the scanning beam (b), the scanning beam (diffracted by the lower first hologram 1 ( B) the incident angle is Bragg angle B
Most of them pass through the hologram 2 as shown in FIG. In this way, the holograms 1 and 2 formed above and below can generate intersecting scanning patterns without interfering with each other.

[Problems to be Solved by the Invention]

By the way, since the transmittance of the hologram in the 0th-order light direction cannot be completely set to 0% in practice, when such a hologram window is applied to a hologram scanner, strong ambient light is emitted from the 0th-order light direction. When incident, it may follow the same optical path as the signal light and enter the detector, and the signal may not be read.

Figures 7 and 8 show patterns of defects when applied to such a hologram scanner.

In Figs. 7 and 8, the signal scattered light 53 from the bar code 51 is
Is condensed and diffracted by the hologram window 55 shown in FIGS. This signal light passes through a mirror system (not shown) to form an image on the photodetector 61 by the condenser lens 57, where it is converted into an electric signal. However, when disturbance light enters from the 0th-order light direction of the hologram window 55 (Fig. 8), if the diffraction efficiency of the hologram window 55 is high and the transmittance in the 0th-order light direction is completely 0%, theoretically. The disturbance light does not enter the optical system. However, in reality, as described above, the transmittance in the 0th order light direction cannot be set to 0%, so that the disturbance light is a signal as shown in FIG. It enters the detector 61 along the same path as the diffracted light. As a result, when the ambient light is strong (for example, direct sunlight or direct light), the output (amplitude) of the detector 61 reaches a saturation level as shown in FIG. 8, and reading cannot be performed. There is.

Therefore, an object of the present invention is to improve the operational reliability of the scanner device by cutting off the disturbance incident light in the 0th order light direction in order to prevent the influence of such disturbance light.

[Means for solving the problem]

In order to achieve the above object, the hologram scanner according to the present invention is characterized in that a reflection hologram for reflecting and diffracting external incident light in the 0th order light direction in a predetermined direction is attached to the hologram. .

According to another solution of the present invention, a transmission hologram that diffracts at an angle equal to or greater than the critical angle is attached instead of the reflection hologram.

[Work]

The reflection type hologram reflects and diffracts disturbance light from the 0th order light direction and does not make it enter the optical system.

In addition, the transmission hologram diffracts incident light in the 0th order light direction to form a diffracted light having an angle equal to or greater than the critical angle, and this diffracted light is totally reflected by the substrate surface of the transmission hologram, and accordingly, 0
Ambient light in the next light direction does not enter the optical system.

〔Example〕

 Hereinafter, preferred embodiments of the present invention will be described.

According to the present invention, as shown in FIG. 1, the reflection hologram 40 is provided on the hologram window 55. The reflection hologram 40 is the second hologram 2 of the hologram window 55 (Figs. 4 and 5).
It may be directly adhered to the upper surface with an adhesive or the like, or may be installed at an appropriate interval.

The reflection hologram 40 diffracts and reflects the disturbance light in the 0th order light direction to prevent the disturbance light from entering the optical system. The reflection hologram 40 used here is preferably designed to match the Bragg angle with the incident angle of light from the 0th order light direction. As a result, most of the disturbance light 101 in the 0th order light direction is efficiently diffracted and reflected outward as indicated by 103. Since the disturbance light 101 in the 0th-order light direction and the signal scattered light 105 have different incident directions, the signal scattering light deviates from the Bragg angle condition in the incident direction (incident angle). Therefore, most of the signal scattered light is reflected. Type hologram
Passes through 40 and does not cause any inconvenience in signal detection function.

 2 and 3 show another embodiment of the present invention.

The second and third embodiments are characterized in that a transmission type total reflection hologram 45 is used instead of the reflection type hologram shown in FIG.

As shown in FIG. 3, the transmission type total reflection hologram 45 has a hologram (interference fringe) portion 49 formed on a transparent (glass) substrate 47, and disturbance incident light 101 from the 0th order light direction is reflected by the hologram portion 49. The diffracted light 107 becomes diffracted light 107 having an angle θ _{0 that is} equal to or greater than the critical angle of the substrate 47. This diffracted light 107 is totally reflected on the lower surface of the substrate as shown in FIG. 2, and escapes to the outside as totally reflected light 109. That is, it does not enter the optical system.

The black angle condition of the interference fringes 48 (enlarged portion in FIG. 3) of the hologram portion 49 is preferably that the signal scattered light 105 incident from the first-order diffracted light direction passes through the hologram portion 49 (that is, an angle other than the Bragg angle). Is set), and almost all of the disturbance incident light 101 from the 0th order light direction is diffracted (that is, the Bragg angle is set). By doing so, the transmission type total reflection hologram 45 can remove only the disturbance incident light in the 0th order light direction without disturbing the incidence of the signal light at all.

The transmission type total reflection hologram 45 is the first embodiment (Fig. 1).
The hologram window 55 (the second hologram of the hologram window) as in the case of
It may be directly adhered to the upper surface with an adhesive or the like, or may be installed at an appropriate interval (via an air layer).

FIG. 2 shows a case where the transmission hologram 45 is directly bonded onto the hologram window 55. In this way, the transmission hologram 45
If there is no air layer between the hologram window 55 and the hologram window 55, the diffracted light from the hologram 45 will be transmitted through the hologram window 55 as it is.
The lower surface of the substrate 12 of the hologram 2 (first and second holograms 1, 2
(When there is an air layer between the first and second holograms 1 and 2), or the lower surface of the substrate 11 of the first hologram 1 (when the first and second holograms 1 and 2 are in close contact).

Incidentally, in the first and second embodiments, even if the Bragg angle does not always satisfy the above condition, a part of the ambient light is surely cut, so that a certain effect can be expected.

Thus, the disturbance light from the 0th order light direction is reflected to the outside,
The problems of the prior art as described above are solved.

The present invention is not limited to the hologram window in which two holograms intersect as described above, but can be applied to all scanners using holograms.

〔The invention's effect〕

As described above, according to the present invention, by providing the reflection type hologram or the transmission type total reflection hologram, the disturbance light in the 0th order light direction is reflected to the outside and hardly enters the detector. The effect of preventing reading malfunction due to 0th-order light is surely improved.

[Brief description of drawings]

1 is an illustrative view showing one embodiment of a hologram scanner according to the present invention, FIG. 2 is an illustrative view showing a second embodiment of a hologram scanner according to the present invention, and FIG. 3 is shown in FIG. FIG. 4 is a diagram showing the basic principle of a transmission type total reflection hologram, FIG. 4 is a perspective view showing the basic structure of a hologram window to which the present invention can be applied, and FIG. 5 is a sectional view of the hologram window shown in FIG. FIG. 7 is a characteristic diagram of the diffraction efficiency and the transmittance of the hologram with respect to the incident angle, FIG. 7 is an illustrative view for explaining the scanner structure of the conventional hologram window, and FIG. 8 is the disturbance light in the conventional hologram window shown in FIG. Figure showing the influence of. 1,2 …… Hologram, 40 …… Reflective hologram, 45 …… Transmissive total reflection hologram, 55 …… Hologram window.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Murakawa 1015 Kamiodanaka, Nakahara-ku, Kawasaki, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Fumio Yamagishi 1015, Uedaka, Nakahara-ku, Kawasaki, Kanagawa Prefecture, Fujitsu Limited ( 72) Inventor Hiroyuki Ikeda 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (2)

(57) [Claims] 1. A hologram scanner for scanning a beam in a predetermined direction by diffracting a beam by a hologram,
A hologram scanner characterized in that a reflection hologram (40) for reflecting and diffracting external incident light in the 0th order light direction in a predetermined direction is additionally provided on the hologram (55). 2. A hologram scanner for scanning in a predetermined direction by diffracting a beam by a hologram,
A hologram scanner, characterized in that a transmission hologram (45) for diffracting external incident light in the 0th-order light direction to an angle equal to or greater than a critical angle is provided on the hologram (55).