JPH01210922A - Hologram scanner - Google Patents

Abstract

PURPOSE:To prevent the read erroneous operation due to an incident 0th-order light by additionally providing a reflection hologram, which reflects and diffracts and external incident light of the direction of the 0th-order light in a prescribed direction, on a hologram. CONSTITUTION:In this hologram scanner, a reflection hologram 40 is provided on a hologram window 55. The reflection hologram 40 diffracts and reflects the diffused external light of the 0th-order light direction to prevent it from being made incident on the inside of an optical system. It is preferable that this reflection hologram is so designed that the Bragg angle is matched to the angle of incidence of light from the 0th-order light direction. As the result, almost all of diffused external light 101 of the 0th-order light direction is efficiently diffracted and reflected outward as shown by arrows 103. Since the diffused external light 101 of the 0th-order light direction and a signal scattered light 105 are different in direction of incidence, almost all of the signal scattered light is transmitted through the reflection hologram 40 and any trouble does not occur at all with respect to the signal detecting function, and the preventing effect of the read erroneous operation due to the incident 0th-order light is improved.

Description

[Detailed Description of the Invention] [Summary] Regarding a hologram scanner that performs beam scanning by diffraction of a beam by a hologram, the operational reliability of the hologram scanner is improved by cutting disturbance light in the direction of zero-order light that may be incident from the outside. For this purpose, the hologram is constructed by attaching a reflection type hologram that reflects and diffracts externally incident light in the direction of the zero-order light or a transmission type hologram that diffracts externally incident light to an angle equal to or greater than the critical angle.

[Industrial application field]

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

Hologram scanners are widely used in barcode league laser scanners, printer laser scanners, and optical equipment.

[Conventional technology]

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

First, the hologram scanner (hologram window) that formed the basis for developing the present invention will be briefly explained below.

The applicant of the present application previously disclosed in Japanese Patent Application No. 61-239903 a hologram scanner (hologram window) 55 which is formed by laminating two band-shaped holograms in a crosswise manner.

In view of the fact that conventional hologram scanners required a space of about 100 mm+ between the hologram l and the scanning pattern, which hindered the thinning of the device, a transparent substrate was interposed between the two. The hologram scanner is made thinner by stacking two holograms and eliminating the space between them. The feature is that the light diffracted at the intersection (center) of the holograms stacked in the upper and lower layers is transmitted through the other holograms with the Bragg angle condition removed.

In other words, as shown in Figure 4.5, the hologram window consists of two strip-shaped first and second strips that intersect diagonally. Second hologram 1, 2
are formed on respective transparent substrates 11 and 12. Both holograms 1.2 intersect in their central part.

The hologram window has a function of receiving laser scanning light emitted by a rotating mirror (not shown) or the like and diffracting it in a predetermined direction to form a desired scanning pattern. At this time, beams corresponding to the upper and lower patterns are selected for the pattern near the center based on the following principle.

First, reference is made to FIG. 6, which shows a general characteristic curve of diffraction efficiency and transmittance of a hologram versus incident angle. The diffraction efficiency shown by the solid line is maximum at a predetermined angle of incidence (Bragg angle) B, and the efficiency decreases as it deviates from the Bragg angle B. On the other hand, the transmittance shown by the broken line is minimum at the Bragg angle B, and increases as it deviates from the Bragg angle B. Therefore, in FIGS. 4 and 5, if the Bragg angle at the center (intersection) of the upper second hologram 2 is adjusted to the scanning beam (b), the scanning beam diffracted by the lower first hologram 1 ( Since the incident angle of the beam (a) is deviated from the Bragg angle B, most of the beam is transmitted through the hologram 2 as shown in FIG. Thus, the holograms 1.2 formed one above the other can generate an intersecting scanning pattern without interfering with each other.

[Problem to be solved by the invention]

By the way, the transmittance of the hologram in the direction of the 00th light cannot be completely reduced to 0% in practice, so when such a hologram window is applied to a hologram scanner, intense disturbance light may be incident from the direction of the 0th order light. Then, it may follow the same optical path as the signal light and enter the detector, making it impossible to read the signal.

Figures 7 and 8 show problems that occur when applied to such a hologram scanner.

In Fig. 7.8, signal scattered light 53 from the barcode 51 is focused by a hologram window 55 shown in Fig. 4.5.
It is diffracted. This signal light passes through a mirror system (not shown) and is imaged onto a photodetector 61 by a condenser lens 57, where it is converted into an electrical signal. However, the hologram window 55
When disturbance light enters from the 0th order light direction (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%, the disturbance light is theoretically optical. Although it does not enter the system, in reality, as mentioned above, the transmittance in the 0th order light direction cannot be made 0%, so the disturbance light is exactly the same as the signal diffracted light as shown in Figure 8. The light enters the detector 61 along this route. As a result, when the disturbance light is strong (for example, direct sunlight or direct light), the output (amplitude) of the detector 61 reaches the saturation level as shown in Figure 8, causing the problem that reading cannot be performed. There is.

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

[Means for Solving the Problems] In order to achieve the above object, the hologram scanner according to the present invention includes a reflection hologram that reflects and diffracts external incident light in the direction of the zero-order light in a predetermined direction on the hologram. The fact that it is attached is a structural feature.

According to another solution of the present invention, a transmission hologram that diffracts at an angle greater than the critical angle is provided in place of the reflection hologram.

[For production]

A reflection hologram reflects and diffracts the disturbance light from the direction of the zero-order light and does not allow it to enter the optical system.

In addition, the transmission hologram diffracts the incident light in the direction of the 0th-order light into a diffracted light having an angle greater than the critical angle, and this diffracted light is totally reflected on the substrate surface of the transmission hologram, so that it is reflected in the direction of the 0th-order light. Disturbing light does not enter the optical system.

〔Example〕

Preferred embodiments of the present invention will be described below.

According to the present invention, a reflection hologram 40 is provided above the hologram window 55, as shown in FIG.

The reflection hologram 40 may be directly adhered to the second hologram 2 (FIGS. 4 and 5) in the hologram window 55 with an adhesive or the like, or may be placed at an appropriate interval.

The reflection hologram 40 diffracts and reflects the disturbance light in the direction of the zero-order light to prevent it from entering the optical system. The reflection hologram 40 used here is preferably designed to match the Bragg angle to the incident angle of light from the zero-order light direction. As a result, the disturbance light 101 in the 00th order light direction is efficiently diffracted and reflected outward as shown by 103. Disturbance light 1 in the direction of 0th order light
Since the incident directions of the signal scattered light 105 and the signal scattered light 105 are different, the incident direction (incident angle) of the signal scattered light deviates from the Bragg angle condition. Therefore, most of the signal scattered light passes through the reflection hologram 40, This does not cause any inconvenience in terms of signal detection function.

Figure 2.3 shows another embodiment of the 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 on a transparent (glass) substrate 47.
, and the disturbance incident light 101 from the zero-order light direction
is diffracted by the hologram portion 49 and becomes diffracted light 107 having an angle θ0 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.

Preferably, the Bragg angle condition of the interference fringes 48 (enlarged portion in FIG. 3) of the hologram portion 49 is such that the signal scattered light 105 incident from the direction of the first-order diffracted light is transmitted through the hologram portion 49, that is, at an angle other than the Bragg angle. ), 0
It is determined to diffract almost all of the disturbance incident light 101 from the secondary light direction (that is, the Bragg angle). By doing this, the transmission type total reflection hologram 4
5 can remove only the disturbance incident light in the direction of the zero-order light without interfering with the incidence of the signal light at all.

The transmission type total reflection hologram 45 is the first embodiment (Fig. 1)
As in the case of , the hologram window 55 (second hologram) may be directly bonded with an adhesive or the like, or may be placed at an appropriate interval (via an air space).

FIG. 2 shows a case where a transmission hologram 45 is bonded directly onto a hologram window 55. In this way, when there is no air layer between the transmission type hologram 45 and the hologram window 55, the diffracted light 10-7 by the hologram 45
In that case, the lower surface of the substrate 12 (the first
．． (if an air layer exists between the second hologram 1.2), or the lower surface of the substrate 11 of the first hologram 1 (the first
, when the second hologram 1.2 is in close contact with the second hologram 1.2).

In addition, 1st. In the second embodiment, even if the /lag angle does not necessarily satisfy the above conditions, a certain effect can be expected because part of the disturbance light is reliably cut off.

In this way, the disturbance light from the direction of the zero-order light is reflected outward, and the problems of the prior art as described above are solved.

Note that the present invention is not limited to the above-described hologram window in which two holograms intersect, but is applicable to all scanners using holograms.

〔Effect of the invention〕

As described above (according to the present invention, by providing a reflection hologram or a transmission type total reflection hologram,
Since the disturbance light in the direction of the next light is reflected outward and hardly or never enters the detector, the effect of preventing reading errors caused by the incident zero-order light is reliably improved.

[Brief explanation of the drawing]

FIG. 1 is an illustrative diagram showing one embodiment of a hologram scanner according to the present invention, FIG. 2 is an illustrative diagram showing a second embodiment of a hologram scanner according to the present invention, and FIG. 3 is shown in FIG. FIG. 4 is a perspective view showing the basic structure of a hologram window to which the present invention can be applied; FIG. 5 is a cross-sectional view of the hologram window shown in FIG. 4; The figure is a characteristic diagram of the diffraction efficiency and transmittance of the hologram with respect to the incident angle, Figure 7 is an illustrative diagram explaining the scanner structure of a conventional hologram window, and Figure 8 is the disturbance light in the conventional hologram window shown in Figure 7. Illustrated diagram showing the influence of. 1.2...Hologram, 40...Reflection type hologram, 45...Transmission type total reflection hologram, 55...Hologram window.

Claims (1)

[Claims] 1. A hologram scanner that scans in a predetermined direction by diffracting a beam with a hologram, the hologram scanner (55) having a reflection device that reflects and diffracts external incident light in the zero-order direction onto the hologram (55) in a predetermined direction. A hologram scanner characterized in that a type hologram (40) is attached. 2. A hologram scanner that scans in a predetermined direction by diffracting a beam with a hologram, and a transmission hologram (45) that diffracts external incident light in the zero-order direction onto the hologram (55) to an angle equal to or greater than a critical angle. ) A hologram scanner characterized by being attached.