JPH09179146A - Beam deflecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the linearity of stripe and to suppress the spread of deflected beam. SOLUTION: This deflecting device has structure sandwiching liquid crystal 20, for which the anisotropy of dielectric constant is negative, between transparent electrodes 12 on facing transparent substrates 10 and generates parallel stripe-shaped patterns having the close/tight distribution of spatial defraction factor through an electric field, and incident light is deflected and emitted. In this case, this device is driven by impressing the AC current of low frequency between the transparent electrodes 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light deflection device that deflects incident light and emits it.

[0002]

2. Description of the Related Art Conventionally, a light deflecting means such as a galvanometer mirror having a mechanically movable portion has been used for performing light deflection. However, such an optical deflecting unit having a mechanically movable portion is not preferable because vibrations are generated from the movable portion as a vibration source.

Further, since it has a movable part, it is electrically high speed,
It was also difficult to control with high accuracy. Therefore, an optical deflection device using a liquid crystal display having no mechanically movable part has been proposed. The principle of this optical deflection device is as follows.

Dielectric constant difference (Δ
It has been reported that when a DC electric field is applied to a nematic liquid crystal with a negative ε), parallel stripe patterns appear when the voltage exceeds a certain threshold (W. Greubelet, al, App.Phys.Lett.19,7,1971).

This phenomenon is caused by VGM (Variable Grating Mod).
e). This fringe is caused by the distribution of the secondary alignment in the liquid crystal, and the fringe spacing (spatial frequency) changes as the voltage changes. Black and white stripes with a spatial frequency proportional to the applied voltage are generated.

FIG. 1 shows a VGM having the above-described principle.
9 shows a change in spatial frequency with respect to an applied voltage of a liquid crystal device. By applying a DC voltage exceeding the threshold voltage Vmin, black and white stripes having a spatial frequency proportional to the applied voltage are generated.

FIG. 2 shows the appearance of stripes when a DC voltage is applied to the VGM liquid crystal device. A pair of transparent electrodes 2 and 4 is connected to a DC power source 6, and when a DC voltage is applied from the power source 6, stripes 5 parallel to the initial alignment direction (rubbing direction) of the liquid crystal are generated.

FIG. 3 shows an example of the structure of the VGM liquid crystal device. The VGM liquid crystal device 8 includes transparent electrodes 12a, 12 made of ITO or the like on a pair of transparent substrates 10a, 10b made of glass or the like.
b are formed respectively.

An alignment film 14 of polyimide or the like for aligning liquid crystal molecules is formed on each transparent electrode 12a, 12b, and the alignment film 14 is subjected to a rubbing process.

These transparent electrodes 12a, 12b are opposed to each other with a gap 16 (2 to 6 μm) interposed with a spacer 16 interposed therebetween, and the liquid crystal 20 is filled in the gap and sealed with a sealant 18. . Since the alignment film 14 is rubbed, the liquid crystal 20 filled in the gap has the major axis of liquid crystal molecules initially aligned along the rubbing direction.

A lead wire 24 is joined to the pair of transparent electrodes 12a and 12b with a silver paste 22. When the lead wire 24 is connected to a DC power source (not shown) and a voltage equal to or higher than the threshold voltage is applied between the pair of transparent electrodes 12a and 12b, stripes parallel to the initial alignment direction of the liquid crystal as shown in FIG. Occur.

[0012]

However, it has been experimentally confirmed that when the VGM liquid crystal device is driven by direct current, the linearity of the stripes generated for some reason is not good. The presence of foreign matter in the liquid crystal further disturbs the linearity of these stripes.
Light diffracted by fringes with poor linearity is scattered,
There is a problem that it becomes wider than the beam diameter of the incident light.

The present invention has been made in view of the above points, and an object thereof is to provide an optical deflection device capable of suppressing the spread of the beam diameter of a deflected beam.

[0014]

According to the present invention, a liquid crystal having a negative dielectric anisotropy is sandwiched between transparent electrodes on opposing transparent substrates, and a spatial refractive index is generated by an electric field. An optical deflection device for generating a parallel striped pattern having a coarse and dense distribution of, deflecting incident light, and outputting the deflected light.
There is provided an optical deflection device characterized in that a low-frequency AC voltage is applied between the transparent electrodes for driving.

Preferably, the applied low frequency frequency is in the range of about 20 Hz to about 200 Hz. By changing the frequency of the applied voltage within this range, the spatial frequency can be controlled, and as a result, the deflection angle can be controlled.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A VGM liquid crystal device having a gap between transparent electrodes 12a and 12b of 2 μm as shown in FIG. 3 was prepared. Then, the pair of lead wires 24 was connected to an AC power source, and a low-frequency AC voltage was applied between the transparent electrodes 12a and 12b. The AC waveform used for driving is a sine wave. The alignment film of this embodiment is formed of polyimide, and the liquid crystal is an ester nematic liquid crystal.

FIG. 4 shows the change in spatial frequency with respect to the applied voltage when the AC voltage is changed from 20 Hz to 200 Hz. For reference, the change in spatial frequency when a DC voltage is applied is indicated by ●.

When a DC voltage is applied, a voltage of 15V
Stripes (spatial frequency) are generated from the vicinity, and the number of stripes linearly increases up to 60V, and the number of stripes is about 1,100 at an applied voltage of 60V.

In low frequency AC driving, an applied voltage of about 30V
Stripes occur between ~ 80V. When AC 200 Hz is applied, the threshold voltage becomes about 40V. AC 500
When a voltage of Hz was applied, no stripes were observed.

Therefore, by applying an AC voltage having a frequency of about 20 Hz to about 200 Hz to the transparent electrode, it is possible to generate a parallel striped pattern having a spatially uneven distribution of the refractive index, and the straight line of this strip. It was confirmed that it was good.

FIG. 5 shows a change in spatial frequency when the drive frequency is changed with an applied voltage of 60V. Drive frequency 20
When changed within the range of Hz to 200 Hz, the spatial frequency changes in the region of about 850 to about 1,150 lines. This change can be represented by a quadratic function of frequency. By changing the drive frequency, the spatial frequency changes, and the deflection angle of the laser beam can be controlled.

In the optical deflection device used in this embodiment,
If the spatial frequency of the stripe is y and the drive frequency is x, then x and y
Can be expressed as y = −0.006x ² + 3.009x + 807.684.

Next, the spread and intensity distribution of the beam when the light beam is deflected using the optical deflection device of this embodiment will be described with reference to FIGS. 6 to 9. FIG. 6 shows an outline of the beam intensity distribution measuring device used in the experiment.

The laser beam emitted from the He-Ne laser 28 is incident on the optical deflection device 8, and the screen 30 is arranged at a position 100 mm from the optical deflection device 8.
The beam projected on the screen 30 is photographed by the CCD camera 32.

7 to 9 show the beam spot projected on the screen 30 and its intensity distribution. In each figure, the upper part shows the beam spot and the lower part shows the intensity distribution.

FIG. 7 shows the intensity distribution when no voltage is applied to the device. At this time, the laser beam goes straight without being deflected. FIG. 8 shows a beam spot and its intensity distribution when a DC voltage is applied so that the deflection angle (diffraction angle) of the first-order diffracted light is about 40 °.

(A) shows a beam spot in the main scanning direction (in this case, the vertical direction) and its intensity distribution, and (B).
Indicates a beam spot in the sub-scanning direction (lateral direction) and its intensity distribution. As is clear from this figure, it is observed that the beam spread is particularly remarkable in the sub-scanning direction.

FIG. 9 shows a beam spot and its intensity distribution when an AC voltage of 50 Hz is applied to the optical deflecting device. (A) shows the beam spot in the main scanning direction, and (B) shows the beam spot in the sub scanning direction and its intensity. The distribution is shown.

As is clear from this figure, the spread of the beam is considerably suppressed when the AC voltage is driven as compared with the case of applying the DC voltage shown in FIG. This indicates that the AC drive has improved the linearity of the stripes.

The same measurement was performed by changing the frequency within the range of 20 Hz to 200 Hz, and it was confirmed that the spread of the beam spot was considerably improved as compared with the case of DC drive.

[0031]

According to the present invention, it is possible to suppress the spread of the deflected beam, which is a problem in DC driving, by driving the optical deflecting device with a low-frequency alternating current. Furthermore, by changing the frequency with a constant voltage,
The spatial frequency can be changed, and as a result, the beam deflection angle can be arbitrarily changed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in spatial frequency with respect to an applied voltage.

FIG. 2 is a diagram showing the appearance of stripes during DC driving.

FIG. 3 is a cross-sectional view of a typical VGM liquid crystal device.

FIG. 4 is a diagram showing a change in spatial frequency with respect to an applied voltage when the frequency is changed.

FIG. 5 is a diagram showing a change in spatial frequency when a drive frequency is changed with an applied voltage of 60V.

FIG. 6 is a view showing a beam intensity distribution measuring device used in an experiment.

FIG. 7 is a diagram showing a beam intensity distribution when a voltage is not applied.

FIG. 8 is a diagram showing a beam intensity distribution when a DC voltage is applied.

FIG. 9 is a diagram showing a beam intensity distribution when an AC voltage of 50 Hz is applied.

[Explanation of symbols]

 8 VGM liquid crystal device 10a, 10b transparent substrate 12a, 12b transparent electrode 14 alignment film 20 liquid crystal 28 He-Ne laser 30 screen 32 CCD camera

Claims (5)

[Claims] 1. A parallel striped structure having a structure in which a liquid crystal having a negative anisotropy of dielectric constant is sandwiched between transparent electrodes on opposing transparent substrates, and having a spatially uneven distribution of refractive index due to an electric field. An optical deflection device that generates a pattern, deflects incident light, and emits the light, wherein the device is driven by applying a low-frequency AC voltage between the transparent electrodes. 2. The low frequency is about 20 Hz to about 200 Hz.
The light deflection device according to claim 1, wherein 3. The optical deflection device according to claim 2, wherein the deflection angle is controlled by changing the frequency of the AC voltage within the range. 4. An alignment film made of polyimide formed on the transparent electrode is further provided.
3. The optical deflection device according to any one of 3 above. 5. The optical deflection device according to claim 1, wherein the liquid crystal is an ester-based nematic liquid crystal.