JP5388711B2 - Liquid crystal optical element - Google Patents

Description

  The present invention relates to a liquid crystal optical element, and more particularly to a liquid crystal optical element capable of deflecting an incident beam.

  A beam deflector may be used to adjust the position or the like of the beam spot. As the beam deflector, there is a reflection mirror and the like. However, in order to finely adjust the position of the reflection mirror, there is a problem that it is necessary to provide a mechanical reflection mirror operating means.

  Therefore, a beam deflector using liquid crystal has been proposed. For example, in a liquid crystal optical element in which a liquid crystal layer is sandwiched between a grid-like transparent electrode disposed on a first transparent substrate and a counter common electrode disposed on a second transparent substrate, a predetermined interval is provided between the electrodes. It is known that a liquid crystal optical element is used as a beam deflector by applying the above voltage (for example, Patent Document 1).

  However, in a liquid crystal optical element using a grid-like transparent electrode, noise light is generated by the action of a gap provided between the gratings, and a predetermined proportion of beams incident on the liquid crystal optical element. However, there was a problem that it was not actually deflected.

Japanese Patent Laying-Open No. 2005-292349 (FIG. 2)

Accordingly, an object of the present invention is to provide a liquid crystal optical element aimed at solving the above problems.
Another object of the present invention is to provide a liquid crystal optical element that is set so as to increase the proportion of incident beams that contribute to deflection as much as possible.

  In order to solve the above problems, a liquid crystal optical element according to the present invention includes a first transparent substrate, a second transparent substrate, a liquid crystal layer sandwiched between the first and second transparent substrates, and an incident light on the liquid crystal layer. A belt-like electrode pattern for applying a voltage for generating a predetermined refractive index distribution that deflects the beam, and the belt-like electrode pattern has a plurality of belt-like electrodes arranged at intervals S and pitches P, P is set to be within a range of 10 × S to 500 μm.

  In the liquid crystal optical element according to the present invention, the strip electrode pattern has a plurality of strip electrodes arranged at intervals S and pitches P, and the pitch P is set to be in the range of 20 × S to 300 μm. It is preferable that

  Since the liquid crystal optical element according to the present invention is transmissive, the liquid crystal optical element is not fogged like a reflecting mirror and can be electrically controlled, so that it does not require a driving mechanism or the like, and functions as an inexpensive and reliable optical deflector. Became possible.

  Further, the liquid crystal optical element according to the present invention is configured to comprehensively reduce noise light due to quantization error due to the diffraction grating property of the strip electrode pattern and noise light due to leakage light between the strip electrodes of the strip electrode pattern. Therefore, the ratio of the beam contributing to the deflection can be increased.

It is a figure which shows the schematic sectional drawing of the liquid crystal optical element which concerns on this invention. 2 is a diagram illustrating a configuration of a transparent electrode 12. FIG. It is a figure which shows the relationship between a strip electrode, an applied voltage, and an effective refractive index. It is a figure for demonstrating the beam deflection function of a liquid crystal optical element. It is a figure for demonstrating the noise light which arises by a quantization error. It is a figure which shows the relationship between the ratio and the pitch of noise light in case the space | interval S of a strip | belt-shaped electrode is 3 micrometers. It is a figure which shows the relationship between the ratio and the pitch of noise light in case the space | interval S of a strip | belt-shaped electrode is 4 micrometers. It is a figure which shows the relationship between the ratio and the pitch of noise light in case the space | interval S of a strip | belt-shaped electrode is 5 micrometers. It is a figure which shows the relationship between the ratio and the pitch of noise light in case the space | interval S of a strip | belt-shaped electrode is 6 micrometers. It is a figure which shows the usage example which utilized the liquid crystal optical element 10 which concerns on this invention for the electrophotographic type laser printer.

  The liquid crystal optical element according to the present invention will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a schematic cross-sectional view of a liquid crystal optical element according to the present invention.

  In the liquid crystal optical element 10, the transparent electrode 12 and the first alignment film 12 are formed on the first transparent substrate 11, and the transparent counter electrode 16 and the second alignment film that are solid electrodes are formed on the second transparent substrate 17. 15 is formed. The liquid crystal layer 14 is sealed and sealed between the first transparent substrate 11 and the second transparent substrate 17 and the seal member 18. It should be noted that each element shown in FIG. 1 is exaggerated for convenience of explanation, and is different from an actual thickness ratio. Further, by applying a predetermined voltage from the voltage supply means between the transparent electrode 12 and the transparent counter electrode 16, the liquid crystal optical element 10 acts as a beam deflector, and the incident beam (A) has a deflection angle. It is emitted as a beam (A ′) deflected by θ. The principle of deflection will be described later.

  The first transparent substrate 11 and the second transparent substrate 17 are flexible and are formed of polycarbonate resin having a thickness of 100 μm. However, the first transparent substrate 11 and the second transparent substrate 17 may be a transparent glass substrate, a modified acrylic resin, a polymethacrylic resin, a polyether sulfone resin, a polyethylene terephthalate resin, a norboltene resin, etc., and the thickness is 50 μm. It can be set to ˜250 μm.

  The thickness (cell gap) of the liquid crystal layer 14 in the liquid crystal optical element 10 was 6 μm. Moreover, the liquid crystal layer was formed of parallel alignment liquid crystals. It is also possible to use vertically aligned liquid crystal.

  FIG. 2 is a diagram illustrating a configuration of the transparent electrode 12.

  The transparent electrode 12 is configured to include an electrode pattern including a plurality of sprite-like strip electrodes 20 to 27 and a connection electrode 30 that connects each strip-like electrode (sprite electrode). The strip electrodes 21 to 27 have a width W and a length L, for example, and are formed of low-resistance ITO, and the strip electrodes 21 to 27 are arranged at intervals S and pitches P (= W + S). . The connection electrode 30 is made of high-resistance ITO and connects the strip electrodes with a width R (3 μm). In FIG. 2, eight strip electrodes are shown, but the transparent electrode 12 as a whole has a length and a length L (for example, 1 to 3 mm) at least as large as the beam diameter. The number of strip electrodes (for example, 200 to 600) is included.

  FIG. 3 is a diagram showing the relationship between the strip electrode, the applied voltage, and the effective refractive index.

  FIG. 3A is a diagram showing a cross section of a part of the strip electrode on the first transparent substrate 11. As shown in FIG. 2, the strip electrodes are connected to each other by connection electrodes 30. Actually, a predetermined AC voltage is applied from the power source 40 between the strip electrode located at the rightmost end of the transparent electrode 12 and the strip electrode located at the leftmost end. In FIG. 3, for convenience, it is assumed that the voltage V <b> 1 is applied to the strip electrode 20 and the voltage V <b> 2 is applied to the strip electrode 27 from the power source 40. The reason why the AC voltage is applied is that if a DC voltage component is applied to the liquid crystal for a long time, problems such as burn-in and decomposition of the liquid crystal occur.

  FIG. 3B shows the effective voltage applied between each strip electrode and the transparent counter electrode 16. Since the high-resistance connection electrodes have the same width R, the strip electrodes are equivalent to being connected to each other by resistors having the same resistance value. Further, since each strip electrode is made of low-resistance ITO, there is no potential difference in each strip electrode. Therefore, in the case of FIG. 3A, the strip electrodes 20 to 27 are resistance-divided by the connection electrode 30, and stepwise effective potentials of potentials V1 to V2 are applied as shown in FIG. 3B. It becomes a state.

  FIG. 3C shows the effective refractive index N by each strip electrode. By applying an effective voltage as shown in FIG. 3B to each strip electrode, N1 to N2 as shown in FIG. 3C are applied to the incident beam passing through the corresponding liquid crystal layer. A stepwise effective refractive index is exhibited. Therefore, the liquid crystal optical element 10 has an effective refractive index distribution as shown by the dotted line 50.

  The incident beam to the liquid crystal optical element 10 is modulated by the optical path length (effective refractive index × cell gap). However, since the cell gap is constant in the liquid crystal optical element 10, the optical path length and the effective refractive index are proportional. Therefore, the optical path length distribution and the effective refractive index distribution are similar.

  In the gap S (dead space) between the strip electrodes, the effective voltage actually applied is 0 V, but the effective refractive index does not drop as in the region 52 of FIG. This occurs because the gap between the strip electrodes is very narrow (for example, 3 μm), and the response speed to the change in the applied voltage of the liquid crystal is slow.

  FIG. 4 is a diagram for explaining the beam deflection function of the liquid crystal optical element.

When the beam A is incident on the liquid crystal optical element 10, a phase delay corresponding to the refractive index distribution 50 shown in FIG. 3C is generated. Thus, the exit angle of the exit beam A ′ is deflected by the angle θ. That is, it can be expressed as θ = tan θ ⁻¹ (δ / D). Here, D is the effective diameter (μm) of the incident beam, and δ is the optical path length difference (μm) between the left end and the right end of the effective diameter D.

  Further, it can be understood from FIG. 4 that the deflection angle θ of the incident beam can be adjusted by adjusting the angle θ of the refractive index distribution 50 of the liquid crystal optical element 10. Since the angle θ of the refractive index distribution 50 can be changed by adjusting the effective voltage applied to the strip electrode pattern of the transparent electrode 12 of the liquid crystal optical element 10, it is applied from the power source 40 to the liquid crystal optical element. By controlling the voltage, it becomes possible to easily adjust the deflection angle θ of the incident beam without using moving parts.

  Hereinafter, generation of noise light in the liquid crystal optical element will be described.

  There are two main causes for the generation of noise light in the liquid crystal optical element. The first is noise light due to leakage light that passes through the gap S (dead space) between the strip electrodes. Secondly, as shown in FIG. 3C, the effective refractive index distribution 50 is not completely smooth and a quantization error remains, but it is noise light due to diffracted light generated by the remaining quantization error.

  First, consider the noise light generated by the leaked light passing through the gap S (dead space) between the strip electrodes. As described in FIG. 3C, the refractive index similar to the desired refractive index distribution 50 cannot be obtained in the gap S between the strip electrodes (see the region 51 in FIG. 3C). Therefore, light (leakage light) that passes through the dead space becomes a noise light component. However, in order to apply a stepwise effective voltage to a plurality of strip electrodes, it is necessary to form a gap for insulation between the strip electrodes. For example, when a strip electrode pattern is formed on the transparent electrode 12 by using the sputtering method, it is necessary to provide a gap S of at least 1 μm, for example, 3 μm, in order to prevent an insulation failure.

  Since the ratio of dead space is S / P × 100 (where P is the arrangement pitch of the strip electrodes), in order to suppress the generation of noise light due to the incident beam passing through the gap S (dead space) between the strip electrodes. Therefore, it is only necessary to form the strip electrodes so as to increase the pitch P of the strip electrodes as much as possible.

  FIG. 5 is a diagram for explaining noise light caused by diffracted light generated due to a quantization error.

  Next, noise light due to diffracted light generated due to quantization error will be considered using FIG. As shown in FIG. 3C, the refractive index distribution 50 is actually formed by a plurality of stepped (quantized) refractive indexes. For example, in the region 53 of FIG. As shown, the portion of the refractive index distribution 50 that protrudes from the upper part of the figure remains as a quantization error. FIG. 5 shows a situation in which the remaining quantization error forms a refractive index distribution component 60 like a sawtooth grating.

  The refractive index distribution component 60 such as a sawtooth grating is formed corresponding to the pitch P of the strip electrode pattern, and the refractive index distribution component 60 such as a sawtooth grating is a diffraction grating with respect to the incident beam A. Works. Therefore, a part of the beam incident on the liquid crystal optical element 10 becomes a diffracted light A ″ or A ″ by a diffraction grating formed by the refractive index distribution component 60 as shown in FIG.

  The diffracted light is considered to increase in proportion to the height H of the refractive index distribution component 60 such as a sawtooth grating. In order to reduce the height H, the quantization error should be made as small as possible, in other words, the strip electrode should be formed as finely as possible. That is, it is only necessary to form the strip electrodes so as to make the pitch P of the strip electrodes as small as possible.

  As described above, in order to suppress noise light due to leakage light, it is necessary to increase the pitch P of the strip electrode pattern, and in order to suppress noise light due to quantization error, the pitch P of the strip electrode pattern is decreased. There is a need. Therefore, by optimizing the pitch P of the strip electrode pattern, it is necessary to cause the liquid crystal optical element 10 to function as a deflector while suppressing the generation of noise light.

  FIG. 6 is a diagram showing the relationship between the ratio of the noise light and the pitch when the interval S between the strip electrodes is 3 μm.

  In FIG. 6, the strip electrode pattern of the strip electrodes having the length L (3 mm) arranged at the interval S (3 μm) in the transparent electrode 12 of the liquid crystal optical element 10 is varied so that the pitch P is 10 μm to 500 μm. The ratio (%) of noise light in the case is measured and shown. The wavelength of the incident beam was 650 nm, the incident beam diameter was 2 mm, the cell gap of the liquid crystal layer 14 was 6 μm, the optical path length difference δ was π, and the beam deflection angle θ was 0.16 milliradian.

  The ratio of noise light was determined by measuring the light quantity E of the incident beam and the light quantity E ′ of the deflected beam at the adjusted beam deflection angle θ, and calculating the ratio of the noise light by (EE−E ′) / E × 100. A laser power meter was used for measuring the beam light quantity. Also, experience shows that if the ratio of noise light is 10% or less, it is sufficiently suitable for practical use, and if the ratio of noise light is 5% or less, it will function as a very good beam deflector. It is done.

  From FIG. 6, it can be considered that if the pitch of the strip electrode pattern is in the range of 30 μm to 500 μm, the ratio of noise light is 10% or less, which is sufficiently suitable for practical use. If the pitch is in the range of 45 μm to 300 μm, It is thought that it functions as a good beam deflector.

  FIG. 7 is a diagram showing the relationship between the ratio of the noise light and the pitch when the interval S between the strip electrodes is 4 μm.

  FIG. 7 shows the noise when the transparent electrode 12 of the liquid crystal optical element 10 is formed by changing the strip electrode pattern of strip electrodes having a length of L3 mm arranged at an interval S (4 μm) so that the pitch P is 10 μm to 500 μm. The percentage of light (%) is measured and shown. The wavelength of the incident beam was 650 nm, the incident beam diameter was 2 mm, the cell gap of the liquid crystal layer 14 was 6 μm, the optical path length difference δ was π, and the beam deflection angle θ was 0.16 milliradian.

  From FIG. 7, it can be considered that if the pitch of the strip electrode pattern is in the range of 40 μm to 500 μm, the ratio of noise light is 10% or less, which is sufficiently suitable for practical use. If the pitch is in the range of 80 μm to 300 μm, It is thought that it functions as a good beam deflector.

  FIG. 8 is a diagram showing the relationship between the ratio of the noise light and the pitch when the interval S between the strip electrodes is 5 μm.

  FIG. 8 shows noise when the transparent electrode 12 of the liquid crystal optical element 10 is formed by changing the strip electrode pattern of strip electrodes having a length of L3 mm arranged at an interval S (5 μm) so that the pitch P is 10 μm to 500 μm. The percentage of light (%) is measured and shown. The wavelength of the incident beam was 650 nm, the incident beam diameter was 2 mm, the cell gap of the liquid crystal layer 14 was 6 μm, the optical path length difference δ was π, and the beam deflection angle θ was 0.16 milliradian.

  From FIG. 8, it is considered that if the pitch of the strip electrode pattern is in the range of 50 μm to 500 μm, the ratio of the noise light is 10% or less, which is sufficiently suitable for practical use. If the pitch is in the range of 100 μm to 300 μm, It is thought that it functions as a good beam deflector.

  FIG. 9 is a diagram showing the relationship between the ratio of the noise light and the pitch when the interval S between the strip electrodes is 6 μm.

  FIG. 9 shows the noise when the transparent electrode 12 of the liquid crystal optical element 10 is formed by changing the strip electrode pattern of strip electrodes having a length of L3 mm arranged at an interval S (6 μm) so that the pitch P is 10 μm to 500 μm. The percentage of light (%) is measured and shown. The wavelength of the incident beam was 650 nm, the incident beam diameter was 2 mm, the cell gap of the liquid crystal layer 14 was 6 μm, the optical path length difference δ was π, and the beam deflection angle θ was 0.16 milliradian.

  From FIG. 9, it can be considered that if the pitch of the strip electrode pattern is in the range of 60 μm to 500 μm, the ratio of noise light is 10% or less, which is sufficiently suitable for practical use. If the pitch is in the range of 120 μm to 300 μm, It is thought that it functions as a good beam deflector.

  6 to 9, the liquid crystal optical element 10 has a ratio of noise light that is considered to be sufficiently suitable for practical use if the pitch P is in the range of 10 × S μm to 500 μm, where S is the distance between the strip electrodes. Thus, if the interval between the strip electrodes is S, it can be used as an optical deflector having a very good ratio of noise light if the pitch P is in the range of 20 × S μm to 500 μm. The lower limit of the pitch P is a function of the interval S because the values of the pitch P and the interval S are approximate, and the upper limit of the pitch P is not a function of the interval S. This is probably because the value is much larger.

  FIG. 10 is a diagram showing an application example in which the liquid crystal optical element 10 according to the present invention is used in an electrophotographic laser printer 100.

  In the laser printer 100 shown in FIG. 10, the laser beam output from the light source 120 is converted into substantially parallel light by the collimator lens 121, passes through the liquid crystal optical element 10 and the Fresnel lens 122, and enters the reflection surface of the polygon mirror 123. To do. The laser beam reflected from the reflecting surface of the polygon mirror 123 passes through the first scanning lens 124 and the second scanning lens 125 in order to scan the photosensitive drum 126 in the direction of the arrow 140 at a constant speed. The photosensitive drum is exposed. A laser beam exposes the photosensitive drum 127 charged by a configuration (not shown) to form a latent image, and a toner is attached to the latent image by a developing device (not shown) to form a toner image. The image is transferred to a copy sheet by a transfer device, fixed, and output.

  Here, in order to accurately form the latent image, it is necessary to accurately align the exposure start position on the photosensitive drum 126. Therefore, the liquid crystal optical element 10 according to the present invention deflects the laser beam, finely adjusts the position of incidence on the reflecting surface of the polygon mirror 123, and sets the exposure start position on the photosensitive drum to, for example, beam spots 130 to 132. It is possible to make fine adjustments such as which one to use.

  In fine adjustment, the laser beam reflected from the polygon mirror 123 is reflected by the detection mirror 127 and received by the light receiving element 128, and detection timing and detection deviation are detected and output to the control unit 110. The control unit 110 determines the deflection angle θ in the liquid crystal optical element 10 according to the received detection timing and detection deviation, and a voltage is applied so that an effective refractive index distribution corresponding to the generated deflection angle θ is generated in the liquid crystal layer 14. Control.

  As described above, the liquid crystal optical element 10 according to the present invention can be used to adjust the position of the laser beam in the laser printer 100 as shown in FIG.

DESCRIPTION OF SYMBOLS 10 Liquid crystal optical element 12 Transparent electrode 14 Liquid crystal layer 16 Transparent counter electrode 20-27 Strip electrode 30 Connection electrode 40 Power supply 50 Effective refractive index distribution

Claims (1)

First and second transparent substrates;
A liquid crystal layer sandwiched between the first and second transparent substrates;
A strip-shaped electrode pattern that applies a voltage that generates a predetermined refractive index distribution that deflects an incident beam to the liquid crystal layer, and
The strip electrode pattern has a plurality of strip electrodes arranged at intervals S and pitches P, and the pitch P is set to be in a range of 20 × S to 300 μm .
A liquid crystal optical element characterized by the above.

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