JPH07261205A - Optical scanner - Google Patents

Abstract

PURPOSE:To intercept diffracted light other than scanning light and to improve performance as to an optical scanner using a light deflector. CONSTITUTION:This optical scanner is constituted of the light deflector 11, a driving circuit 12, a light source 13, a polarizer 14 and a convex lens for condensing light 15. S polarized light emitted from the light source 13 is made a focused light beam by the convex lens 15 and made incident on the light deflector 11 to generate the diffracted light on an exiting side. By arranging the polarizing direction of the polarizer 14 orthogonally to the polarizing direction of the incident light, the zero order light and even number order diffracted light are intercepted by the polarizer 14, and only -1st order diffracted light and fist order diffracted light are transmitted through the polarizer 14. The fist diffracted light or the -1st diffracted light is used for the scanning light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device.

[0002]

As is well known, a bar code reader, a laser printer and the like in a POS system are equipped with an optical scanning device. For example, in a bar code reader, an optical scanning device is used to deflect a light beam and scan the bar code.

The conventional optical scanning device is generally of the type that performs optical scanning by mechanically rotating a polygon mirror or a galvano mirror.

[0004]

As described above, the optical scanning device having the mechanically movable portion has poor controllability and causes a response delay, and the optical axis is displaced due to mechanical vibration. was there.

The present invention has been made in view of the above-mentioned problems of the prior art. It has no mechanically movable parts, can be electrically controlled, has good controllability, and requires no scanning light. It is an object of the present invention to provide a high-performance optical scanning device that can block various kinds of light.

[0006]

The present invention adopts the following means in order to solve the above problems.

<Summary of the Invention> The optical scanning device of the present invention comprises:
(A) a light source (13), (b) an optical deflector (11),
(C) A drive circuit (12) and (d) a polarizer (14) are provided. The outline of the components of the present invention and the points thereof will be briefly described.

[Light Source] The light emitted from the light source (13) is preferably S-polarized or P-polarized linearly polarized light. When the light emitted from the light source (13) is non-linearly polarized light, a polarizer is arranged between the light source (13) and the light deflector (11) so that only the linearly polarized light component is generated by the light deflector (11). ).

[Optical Deflector] The optical deflector (11) connects the liquid crystal (5) which produces parallel stripes when a voltage is applied to the transparent electrode (2).
2) Inserted between them. In the optical deflector (11), the pitch of the parallel stripes changes according to the magnitude of the applied voltage, and the parallel stripes function as a diffraction grating. When light is incident on the light deflector (11), diffracted light is generated on the emission side. When any of the diffracted light is used as the scanning light, the incident light is deflected by the optical deflector (11) to become the scanning light.

[Drive Circuit] The drive circuit (12) is a circuit for applying a voltage whose magnitude changes with time between the transparent electrodes (2, 2) of the optical deflector (11). The applied voltage can be a DC voltage or an AC voltage.

[Polarizer] The polarizer (14) is an optical deflector (1
It is arranged on the emission side of 1). The polarizer (14) acts to block diffracted light other than scanning light.

For example, as scanning light, + 1st order or -1
When the next diffracted light is used, it is arranged so that the polarization direction of the polarizer (14) and the polarization direction of the light incident on the optical deflector (11) are orthogonal to each other. In this way, the zero-order light (transmitted light) and the even-order diffracted light are blocked by the polarizer (14).

When + 2nd-order or -2nd-order diffracted light is used as the scanning light, the polarization direction of the polarizer (14) and the polarization direction of the light incident on the optical deflector (11) should be parallel. Distribute. In this way, the odd-order diffracted light is blocked by the polarizer.

<Additional Constituent Elements of the Present Invention> The present invention is composed of the above-mentioned basic constituent elements, but is also realized by adding the following constitutions.

[Condensing Optical Element] A condensing optical element (1) for condensing light on the incident side or the exit side of the light deflector (11).
5) is provided. A convex lens can be illustrated as the condensing optical element (15).

[Incident Angle] The incident angle of the incident light on the optical deflector (11) is the Bragg angle of the diffracted light used as the scanning light.

[Combination of Each Component] The above-mentioned additional components can be appropriately combined. For example,
The incident angle of the incident light on the optical deflector (11) may be set to the Bragg angle, and the condensing optical element (15) may be provided on the incident side or the emitting side of the optical deflector (11).

<Raw Material of the Present Invention> As a typical example of the liquid crystal (5) used in the optical deflector (11), there may be mentioned Chemical formula 1, but the invention is not limited to this.

[0019]

[Chemical 1]

<Applicability of the Present Invention> The present invention is applicable to an optical scanning device incorporated in a bar code reader, a laser printer, or the like.

[0021]

[Action]

<Operation of the present invention> The transparent electrode (2, 2) of the optical deflector (11)
When a voltage is applied to 2), parallel stripes are generated on the liquid crystal (5), and these parallel stripes function as a diffraction grating. When the magnitude of this applied voltage is changed with time, the diffraction angle changes.
The light can be scanned.

The light emitted from the light source (13) is incident on the optical deflector (11) to generate diffracted light on the emission side of the optical deflector (11). The polarizer (14) arranged on the exit side of the optical deflector (11) almost blocks diffracted light other than the diffracted light used as the scanning light.

<Operation when Additional Components are Added>
When the condensing optical element (15) is added, when the light from the light source (13) is a focused light beam, the condensing optical element (15)
Compared with the case without the
Has the effect of approaching. When the light from the light source (13) is a divergent ray or a parallel ray, the condensing optical element (15) has a function of condensing the light from the light source (13) to form an image.

The incident angle of the incident light on the optical deflector (11) is
When the Bragg angle of the diffracted light used as the scanning light is set, the diffraction efficiency is maximized, the intensity of the diffracted light used as the scanning light is maximized, and the intensities of other diffracted lights can be sufficiently reduced. Target.

[0025]

【Example】

[V. G. M Phenomenon] Before describing the optical scanning device of the present invention, V. G. The M phenomenon and the optical deflector utilizing this phenomenon will be described.

It has been reported that when a certain kind of nematic liquid crystal molecule is sandwiched between transparent electrodes and a DC or AC voltage is applied, parallel stripes with a pitch of several μm appear when the voltage exceeds a certain threshold value. (B.H.Soff
er et, al. Opt. Eng. 22, 6, 198
3). This phenomenon is G. M (Variable Gr
It is called an asking mode). The parallel stripes are caused by the distribution of the secondary alignment in the liquid crystal, and the pitch of the parallel stripes (that is, the spatial frequency) changes depending on the magnitude of the applied voltage.

Many liquid crystals in which the VGM phenomenon occurs have a dielectric constant difference Δε <0. V. G. A typical example of a liquid crystal in which the M phenomenon occurs is shown in Chemical formula 2. It is commercially available as N-4 from Merck and is available.

[0028]

[Chemical 2]

Since the fringes act as a diffraction grating, the diffraction angle can be changed by changing the applied voltage.
It is known that the pitch of the parallel stripes becomes narrower in proportion to the increase of the applied voltage and the diffraction angle becomes larger.

FIG. 3 shows this V. G. It is a basic block diagram of the optical deflector using M phenomenon. In the optical deflector 1, a pair of transparent glass plates 4 and 4 provided with a transparent electrode 2 and an alignment film 3 on one surface are arranged to face each other, and a V. GM
A liquid crystal in which a phenomenon occurs (for example, Merck N-4)
5 is inserted, and a drive circuit 6 is connected to the transparent electrodes 2 and 2 so that an AC voltage or a DC voltage can be applied.

FIG. 4 shows an example of the voltage waveform of the applied voltage, and FIG. 4A shows the case of an AC voltage.
(B) is a case of a DC voltage. Although the AC signal is given as a pulse in this figure, the present invention is not limited to this.
For example, an AC signal whose voltage value continuously increases and decreases may be used.

[Principle of Optical Scanning Device] Next, the principle of the optical scanning device using the optical deflector 1 will be described with reference to the drawings of FIGS.

When the light emitted from the light source 7 enters the optical deflector 1, as shown in FIGS. 5 and 6, the transmitted light (0th order light) and the ± 1st, ± 2nd, ... Light appears (in the figure, high-order diffracted light of the third order or higher is omitted because its intensity is very small). Of these diffracted lights, the diffracted light with the highest intensity is used as the scanning light. Usually, the + 1st order diffracted light is often used as the scanning light.

Here, it is reported that when the incident light is linearly polarized, the polarization directions of the odd-order diffracted light and the 0-th order light and the even-order diffracted light are orthogonal to each other (B.H. Soffe).
ret, al. Opt. Eng. 22, 6, 198
3). That is, if the incident light is S-polarized light, the 0th-order light and the even-order diffracted light are S-polarized light, and the odd-order diffracted light is P-polarized light.

Then, when the magnitude of the voltage applied to the optical deflector 1 is temporally changed by the drive circuit 6, the light is scanned on one straight line as shown in FIG. by the way,
As described above, the diffracted light other than that used as the scanning light also exists on the emission side of the optical deflector. The presence of such diffracted light may impose restrictions on the configuration of the device or adversely affect the performance.

For example, when used for a bar code reader, if there is no difference in the diffraction angle of each diffracted light, it is scanning light +
The barcode is irradiated with light other than the primary light, and the reflected light is incident on the photodetector, resulting in poor reading accuracy.

Therefore, it is the optical scanning device of the present invention that can block the diffracted light which is an obstacle other than the scanning light. An embodiment of an optical scanning device according to the present invention will be described below with reference to the drawings of FIGS. 1 and 2. It should be noted that this embodiment is an aspect of an optical scanning device incorporated in a bar code reader.

[Embodiment 1] FIG. 1 is a block diagram of an optical scanning device in a first embodiment. The optical scanning device 10 includes an optical deflector 11, a drive circuit 12, a light source 13, a polarizer 14, and
It is composed of a convex lens 15 (optical element for condensing light).

The optical deflector 11 is the same as the optical deflector 1 described above, and when a voltage is applied, parallel stripes functioning as a diffraction grating appear, and the pitch of the parallel stripes changes according to the magnitude of the applied voltage. However, the diffraction angle changes.

The drive circuit 12 is a circuit for applying a voltage whose magnitude changes periodically between the transparent electrodes of the optical deflector 11, and by changing the magnitude of the voltage with time,
It is possible to scan the light by changing the deflection angle of the light deflector 11. The scanning speed of the scanning light is determined by the wave number of the voltage applied to the optical deflector 1.

The light source 13 emits S-polarized laser light. The convex lens 15 is arranged between the light source 13 and the light deflector 11. The light emitted from the light source 13 is a convex lens 1
5 becomes a focused light beam, and after passing through the optical deflector 11,
It is designed to focus and form an image.

The polarizer 14 is arranged on the exit side of the optical deflector 11, and the polarization direction of the polarizer 14 is orthogonal to the polarization direction of incident light. Therefore, in this optical scanning device 1, as shown in FIG.
The secondary light (transmitted light) and the even-order diffracted light are blocked, and only the + 1st-order diffracted light and the −1st-order diffracted light are transmitted through the polarizer 14. When the + 1st-order diffracted light is used as the scanning light, the -1st-order diffracted light is unnecessary, but since the angle difference between the + 1st-order diffracted light and the -1st-order diffracted light is large, the existence of the -1st-order diffracted light causes a problem.
Practically few.

[Second Embodiment] FIG. 2 is a block diagram of an optical scanning device according to a second embodiment. The optical scanning device of the second embodiment differs from that of the first embodiment in that when the parallel stripes of the optical deflector 11 have a predetermined spatial frequency (for example, the maximum spatial frequency), the optical deflector is deflected. Angle of incidence of incident light on 11
Is set at the Bragg angle of the + 1st order diffracted light.

When the incident angle θ is set in this way, +1
The diffraction efficiency of the second-order diffracted light is maximized, and the intensity of diffracted light other than the + 1st-order diffracted light can be sufficiently reduced. Therefore, the intensity of the minus first-order diffracted light that can be transmitted through the polarizer 14 can be minimized, and the performance can be further improved as compared with the first embodiment.

Since the other structure is the same as that of the first embodiment, the same reference numerals are given to the same mode parts and the description thereof will be omitted.

[0046]

As described above, according to the present invention,
By disposing the polarizer on the emission side of the optical deflector, it is possible to block extra diffracted light other than the scanning light. Therefore, the optical scanning device is hardly affected by diffracted light other than the scanning light, and the performance of the optical scanning device can be improved.
It is possible to achieve simplification of the device and expansion of design freedom.

In particular, it is more effective if the incident angle of the incident light on the optical deflector is the Bragg angle of the diffracted light used as the scanning light. When the condensing optical element is added, when the light from the light source is a convergent light beam, the image forming point of the light can be brought closer to the optical deflector as compared with the case where the condensing optical element is not provided. There is an effect that can be made small. Further, when the light from the light source is a divergent ray or a parallel ray, there is an effect of condensing the light from the light source and forming an image.

[Brief description of drawings]

FIG. 1 is a principle diagram of a first embodiment of an optical scanning device of the present invention.

FIG. 2 is a principle view of a second embodiment of the optical scanning device of the present invention.

FIG. 3 is a basic configuration diagram of an optical deflector used in the optical scanning device of the present invention.

FIG. 4 is a diagram showing an example of a voltage waveform applied to an optical deflector.

FIG. 5 is a principle view of an optical scanning device having no polarizer.

FIG. 6 is a principle view of an optical scanning device having no polarizer.

FIG. 7 is a principle diagram of an optical scanning device having no polarizer.

[Explanation of symbols]

 10 Optical Scanning Device 11 Optical Deflector 12 Drive Circuit 13 Light Source 14 Polarizer 15 Convex Lens (Optical Element for Condensing)

Claims (5)

[Claims] 1. A liquid crystal (5) is inserted between (a) a light source (13) and (b) a transparent electrode (2, 2) arranged to face each other, and a voltage is applied between the transparent electrodes (2, 2). Is applied, parallel fringes functioning as a diffraction grating are generated in the liquid crystal (5), and the optical deflector (11) changes the pitch of the parallel fringes according to the magnitude of the applied voltage. A drive circuit (1) for applying a time-varying voltage to the optical deflector (11)
2) and (d) a polarizer (14) arranged on the emission side of the optical deflector (11), the optical scanning device (10). 2. The optical scanning device (10) according to claim 1, further comprising a condensing optical element (15) for condensing light on an incident side or an emitting side of the optical deflector (11). An optical scanning device (10) characterized by the above. 3. The optical scanning device (10) according to claim 1 or 2, wherein the polarization direction of the polarizer (14) and the polarization direction of the incident light to the optical deflector (11) are orthogonal to each other. Optical scanning device (1
0). 4. The optical scanning device (10) according to claim 1 or 2, wherein the polarization direction of the polarizer (14) and the polarization direction of incident light to the optical deflector (11) are parallel to each other. Optical scanning device (1
0). 5. The optical scanning device (10) according to claim 1 or 2, wherein the incident angle of the incident light on the optical polarizer (11) is set to the Bragg angle of the diffracted light used as the scanning light. A characteristic optical scanning device (10).