JP2008304792A - Optical element and optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element composed of a liquid lens capable of eliminating a trouble caused by a rapid temperature rising, and to provide an optical scanner. <P>SOLUTION: The focal length of the liquid lens 14 is varied by deforming the shape of the boundary face S between an electrical conductive liquid 40 and an electrical insulating liquid 42 by the electrowetting phenomenon. Transparent plates 44 and 46 pinch and hold the electrical conductive liquid 40 and the electrical insulating liquid 42. Transparent plates 43 and 45 are arranged at predetermined intervals from the transparent plates 44 and 46. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical element and an optical scanning device including the optical element, and more particularly to an optical element including a liquid lens and an optical scanning device including the optical element.

  Among lenses used in an optical module having an autofocus function and an optical zoom, there is a so-called liquid lens. FIG. 9 is a cross-sectional structure diagram in a plane including the optical axis of the liquid lens 101. The liquid lens 101 is sealed in a container 104 so that the conductive liquid 102 and the insulating liquid 103 are in contact with each other without being mixed, and the conductive liquid 102 and the insulating liquid 103 constitute a lens. It is what. In the liquid lens 101, a voltage is applied to the conductive liquid 102, and the shape of the interface S between the conductive liquid 102 and the insulating liquid 103 can be changed by an electrowetting phenomenon. Thereby, the focus of the liquid lens 101 can be adjusted.

  Since the liquid lens 101 does not require a mechanism for moving the lens when adjusting the focus, it has been proposed in recent years to be used for various purposes. For example, Patent Documents 1 to 3 propose applying the liquid lens 101 to a collimator lens of an optical scanning device. These optical scanning devices are intended to realize higher-quality image formation by controlling the focal length of the liquid lens.

By the way, the optical scanning device is configured to have a highly sealed structure in order to prevent the beam from leaking to the outside. In addition, the optical scanning device is provided with a heat source such as a polygon mirror or a laser diode. Therefore, the inside of the optical scanning device tends to be in a high temperature state. In particular, when the optical scanning device is started up, the temperature in the optical scanning device rapidly increases. When the temperature in the optical scanning device rises rapidly, various problems occur in the liquid lens 14. Specifically, bubbles are generated in the conductive liquid 102 or the insulating liquid 103, or the volume of the conductive liquid 102 or the insulating liquid 103 is changed, and the shape of the interface S is distorted.
JP 2006-251343 A JP 2006-251513 A JP 2006-258838 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical element and an optical scanning device that can eliminate the inconvenience caused by a rapid temperature rise.

  According to a first aspect of the present invention, in the optical element that changes the focal length by changing the shape of the interface between the first liquid and the second liquid by an electrowetting phenomenon, the first liquid and the second liquid A first transparent plate and a second transparent plate sandwiching the liquid, and a third transparent plate arranged at a predetermined interval from the first transparent plate.

  According to the first invention, the third transparent plate is provided outside the first transparent plate and the second transparent plate sandwiching the first liquid and the second liquid, and the first liquid and the second liquid are provided. Two liquid containers have a double structure. Accordingly, the container has a heat insulating structure, and even if the temperature around the optical element is rapidly increased, the temperature of the first liquid and the second liquid is suppressed from rapidly increasing.

  1st invention WHEREIN: You may further provide the 4th transparent plate arrange | positioned at predetermined intervals with the said 2nd transparent plate.

  In the first invention, an air layer may exist between the first transparent plate and the third transparent plate.

  1st invention WHEREIN: The coating which reflects a heat ray may be given to the position corresponding to an optical axis on the main surface of the said 3rd transparent plate.

  According to the first aspect, the coating that reflects the heat rays is applied to the third transparent plate, so that the first liquid and the second liquid are more effectively prevented from being heated.

  The first invention can also be applied to an optical scanning device. Specifically, the first invention includes an optical element, an optical element, a light source that emits light to the optical element, and a deflecting unit that deflects the light that has passed through the optical element. It is characterized by this.

  According to a second aspect of the present invention, in the optical element that changes the focal length by deforming the shape of the interface between the first liquid and the second liquid by an electrowetting phenomenon, the first liquid and the second liquid And a cooling means for cooling the liquid.

  According to the second invention, since the cooling means is provided, it is possible to suppress the temperature of the first liquid and the second liquid from rising rapidly.

  In the second invention, the first liquid and the second liquid are sandwiched between a first transparent plate and a second transparent plate, and the cooling means includes the first transparent plate and the second transparent plate. On the side surface when the second transparent plate is the upper surface and the lower surface, a plurality of the transparent plates may be provided so as to sandwich the optical axis.

  According to the second invention, since the cooling means is provided so as to sandwich the optical axis, the cooling means sandwiches the first liquid and the second liquid. As a result, the first liquid and the second liquid can be cooled more effectively.

  The second invention can also be applied to an optical scanning device. Specifically, the second invention includes an optical element, an optical element, a light source that emits light to the optical element, and a deflecting unit that deflects the light that has passed through the optical element. It is characterized by this. In the second invention, the optical scanning device may further include a detecting unit for detecting a temperature, and a control unit for controlling the operation of the cooling unit based on the temperature detected by the detecting unit.

(First embodiment)
Hereinafter, the liquid lens according to the first embodiment of the present invention and the configuration of the optical scanning device including the liquid lens will be described with reference to the drawings. FIG. 1 is a top view of an optical scanning device 10 including a liquid lens 14 according to the first embodiment.

  As shown in FIG. 1, the optical scanning device 10 includes a laser diode 12, a collimator lens 13, a liquid lens 14, a cylindrical lens 18, a polygon mirror 20, scanning lenses 22, 24, a mirror 26, a light receiving element 28, a housing 29, and A control unit 30 is provided.

  The laser diode 12 serves as a light source that emits a beam. The beam emitted from the laser diode 12 is emitted light.

  The collimator lens 13 plays a role of condensing the beam emitted from the laser diode 12 so as to become parallel light. The liquid lens 14 serves to further collect the beam that has passed through the collimator lens 13 and has a function of changing the focal length of the beam. Details of the liquid lens 14 will be described later.

  The cylindrical lens 18 condenses the beam that has passed through the liquid lens 14 in the sub-scanning direction in the vicinity of the mirror surface of the polygon mirror 20.

  The polygon mirror 20 is rotated in the direction of the arrow by a motor (not shown), and serves as a deflecting unit that deflects the beam that has passed through the cylindrical lens 18 at a constant angular velocity in the main scanning direction. The scanning lenses 22 and 24 scan the beam deflected by the polygon mirror 20 at a constant speed and form an image of the beam on the photosensitive drum 32. The photosensitive drum 32 is rotationally driven at a predetermined speed. As a result, a two-dimensional electrostatic latent image is formed by the main scanning by the beam and the sub scanning by the rotation of the photosensitive drum 32.

  The mirror 26 plays a role of reflecting the beam deflected by the polygon mirror 20 and passing through the scanning lenses 22 and 24 toward the light receiving element 28. The light receiving element 28 receives the beam reflected by the mirror 26 and generates an electric signal indicating the beam diameter. The control unit 30 serves as a control unit that controls the focal length of the liquid lens 14 so that the beam diameter of the beam received by the light receiving element 28 is constant based on the electrical signal generated by the light receiving element 28. Fulfill. Thereby, even if the scanning lenses 22 and 24 are distorted by the influence of heat, the control unit 30 suppresses a change in the beam diameter of the beam irradiated to the photosensitive drum 32.

  As shown in FIG. 1, the housing 29 houses the laser diode 12, the collimator lens 13, the liquid lens 14, the cylindrical lens 18, the polygon mirror 20, the scanning lenses 22 and 24, the mirror 26, and the light receiving element 28.

  Next, the configuration of the liquid lens 14 will be described with reference to FIG. FIG. 2 is a cross-sectional structure diagram of a surface including the optical axis of the liquid lens 14. 2A is a cross-sectional structure diagram of the liquid lens 14 in a state where a voltage is applied, and FIG. 2B is a cross-sectional structure diagram of the liquid lens 14 in a state where no voltage is applied.

  As shown in FIG. 2, the liquid lens 14 includes a conductive liquid 40, an insulating liquid 42, transparent plates 43, 44, 45, 46, a first electrode 48, an insulating film 50, a second electrode 52, and side surfaces 53. including. The liquid lens 14 can change the focal length of the liquid lens 14 by changing the shape of the interface S between the conductive liquid 40 and the insulating liquid 42 by an electrowetting phenomenon. Specifically, when a voltage is applied, the interface S changes from the state shown in FIG. 2B to the state shown in FIG.

  The transparent plates 44 and 46 are made of transparent resin or glass, sandwich the conductive liquid 40 and the insulating liquid 42, and serve as the upper and lower surfaces of the container of the conductive liquid 40 and the insulating liquid 42. Fulfill. More specifically, the transparent plates 44 and 46 are arranged in parallel with each other leaving a predetermined gap, and the conductive liquid 40 and the insulating liquid 42 are sealed in the gap.

  The transparent plate 43 is arranged on the opposite side of the transparent plate 44 with a predetermined gap sp1 from the transparent plate 46. Further, the transparent plate 45 is arranged on the opposite side of the transparent plate 46 with a predetermined gap sp2 from the transparent plate 44. The gaps sp1 and sp2 are both air layers. Since the thermal conductivity of the air layer is smaller than that of the transparent plates 43, 44, 45, 46, the temperatures of the conductive liquid 40 and the insulating liquid 42 are moderate even if the temperature around the liquid lens 14 changes rapidly. To change. Thereby, even if the temperature around the liquid lens 14 rapidly increases, it is possible to prevent bubbles from being generated in the conductive liquid 40 and the insulating liquid 42 and the shape of the interface S from being distorted.

  Moreover, the coating for reflecting a heat ray is given to the area | region which is the outer surface of the transparent plates 43 and 45 and contains the position corresponding to an optical axis. Thereby, heating of the conductive liquid 40 and the insulating liquid 42 due to radiant heat generated from a heat source such as the laser diode 12 or the polygon mirror 20 is suppressed.

  The side surface 53 serves as a container for the conductive liquid 40 and the insulating liquid 42 together with the transparent plates 43, 44, 45, 46. The side surface 53 is a member corresponding to the side surface when the transparent plates 43, 44, 45, 46 are the upper surface and the lower surface, and is formed of a resin having a low thermal conductivity. Examples of the material used for the side surface 53 include engineering plastics. Particularly preferred engineering plastics for the side surface 53 include polyphenylene sulfide or polyether ether ketone. As described above, by applying a substance having a low thermal conductivity to the material of the side surface 53, a rapid temperature increase of the conductive liquid 40 and the insulating liquid 42 is suppressed.

  The conductive liquid 40 is an inorganic salt aqueous solution, an organic liquid, or the like that is conductive by itself, or a liquid made conductive by adding an ionic component. The insulating liquid 42 is a liquid that has a refractive index different from that of the conductive liquid 40 and is not mixed with the conductive liquid 40 such as silicone oil or paraffin oil. Therefore, the conductive liquid 40 and the insulating liquid 42 are separated from each other, and form an interface S. Thus, the conductive liquid 40 and the insulating liquid 42 constitute a lens. Note that the refractive index of the conductive liquid 40 is preferably smaller than the refractive index of the insulating liquid 42.

  The first electrode 48 is provided on the transparent plate 44 so as to be in contact with the conductive liquid 40. The second electrode 52 is provided between the transparent plate 46 and the first electrode 48. The insulating film 50 is formed so as to cover the second electrode 52. Specifically, the insulating film 50 is formed between the first electrode 48 and the second electrode 52 to insulate the first electrode 48 and the second electrode 52, and The second electrode 52 is formed on the inner peripheral surface of 52 so that the conductive liquid 40 and the insulating liquid 42 do not come into contact with each other. A voltage is applied between the first electrode 48 and the second electrode 52 when the liquid lens 14 is driven.

  The operation principle of the liquid lens 14 configured as described above will be described below with reference to FIG. FIG. 3 is an enlarged view of a portion C of the liquid lens 14 in FIG. 3A is an enlarged view of a portion C of the liquid lens 14 (corresponding to FIG. 2B) in a state where no voltage is applied, and FIG. 3B is a diagram in which voltage is applied. FIG. 3 is an enlarged view of a portion C of the liquid lens 14 (corresponding to FIG. 2A) in a state.

  First, the interfacial tension between the conductive liquid 40 and the insulating liquid 42 is set to an interfacial tension γ12, the interfacial tension between the insulating film 50 and the conductive liquid 40 is set to an interfacial tension γ31, and the insulating liquid 42 and the insulating film are set. The interfacial tension between 50 and 50 is defined as interfacial tension γ23. As shown in FIG. 3A, when no voltage is applied between the first electrode 48 and the second electrode 52, the interfacial tension γ12, the interfacial tension γ23, and the interfacial tension γ31 The interface S and the insulating film 50 form an angle θ1. At this time, the relationship of the formula (1) is established among the angle θ1, the interfacial tension γ12, the interfacial tension γ23, and the interfacial tension γ31 by Young's equation.

  Here, when a voltage is applied to the first electrode 48 and the second electrode 52, for example, as shown in FIG. 3B, positive charges are generated at the boundary between the insulating film 50 and the conductive liquid 40. appear. On the other hand, negative charges appear at the boundary between the insulating film 50 and the second electrode 52. As a result, a pressure drop due to the charge is generated between the insulating liquid 42 and the insulating film 50 in the same direction as the interfacial tension γ23. This pressure Π is expressed as in equation (2).

  Here, ε is the dielectric constant of the insulating film 50, ε0 is the vacuum dielectric constant, e is the thickness of the insulating film 50, and V is between the first electrode 48 and the second electrode 52. Voltage.

  Due to the occurrence of the pressure drop, the interface S and the insulating film 50 form an angle θ2 larger than the angle θ1. At this time, the interface S of the liquid lens 14 is curved as shown in FIG. This angle θ2 is expressed as in Expression (3).

  As described above, it can be seen that the angle formed between the interface S and the insulating film 50 is changed by changing the voltage applied between the first electrode 48 and the second electrode 52. Then, as the angle between the interface S and the insulating film 50 changes, the interface S is curved and the focal length is relatively short as shown in FIG. 2A when a voltage is applied. Become. Further, in the state where no voltage is applied, the interface S becomes flat as shown in FIG. 2B, and the focal length becomes relatively long. The control unit 30 shown in FIG. 1 controls the focal length of the liquid lens 14 by controlling the magnitude of this voltage.

  According to the liquid lens 14 according to the present embodiment, the container that stores the conductive liquid 40 and the insulating liquid 42 has a double structure. Rapid increase in temperature of the conductive liquid 40 and the insulating liquid 42 is suppressed. As a result, the generation of bubbles in the conductive liquid 40 and the insulating liquid 42 and the distortion of the shape of the interface S are suppressed.

  Further, since the liquid lens 14 is provided with a coating that reflects heat rays on the outer surfaces of the transparent plates 43 and 45, the conductive liquid 40 and the insulating liquid 40 are insulated by radiant heat generated from a heat source such as the laser diode 12 or the polygon mirror 20. The heating of the ionic liquid 42 is suppressed.

(Modification)
In addition, although the side surface 53 of the liquid lens 14 according to the present embodiment has a single structure, it may have a double structure like a side surface 53 ′ shown in FIG. FIG. 4 is a cross-sectional structure diagram of a surface including the optical axis of the liquid lens 14 according to the modification. By making the side surface 53 ′ have a double structure, a rapid increase in temperature of the conductive liquid 40 and the insulating liquid 42 is more effectively suppressed.

  Moreover, although the gaps sp1 and sp2 of the liquid lens 14 according to the present embodiment are air layers, they may be filled with a material having a thermal conductivity smaller than that of the transparent plates 43, 44, 45, and 46. This substance may be liquid, gas, or solid.

  In addition, the liquid lens 14 according to the present embodiment is applied to the optical scanning device 10, but may be applied to another device. The liquid lens 14 can be applied to, for example, an optical pickup device.

(Second Embodiment)
Hereinafter, a liquid lens according to a second embodiment and an optical scanning device including the liquid lens will be described with reference to the drawings. The optical scanning device 10 according to the present embodiment is shown in FIG. 1 as in the first embodiment. FIG. 5 is a cross-sectional structure diagram of a surface including the optical axis of the liquid lens 14 according to the present embodiment. FIG. 6 is an external perspective view of the liquid lens 14. In addition, in the liquid lens 14 which concerns on this embodiment, the same referential mark is attached | subjected about the same structure as the liquid lens 14 which concerns on 1st Embodiment.

  In the liquid lens 14 according to the present embodiment, as shown in FIGS. 5 and 6, instead of providing transparent plates 43 and 45 to insulate the liquid lens 14 according to the first embodiment, Peltier elements 64 a and 64 b are provided to cool the conductive liquid 40 and the insulating liquid 42. The other configuration of the liquid lens 14 according to the present embodiment is basically the same as the other configuration of the liquid lens 14 according to the first embodiment. Therefore, the following description focuses on the differences between the liquid lens 14 according to the present embodiment and the liquid lens 14 according to the first embodiment.

  In the liquid lens 14 according to the present embodiment, the side surface 63 is formed of a material having high thermal conductivity, such as aluminum. The side surface 63 is provided with Peltier elements 64a and 64b. The Peltier elements 64a and 64b are arranged so as to sandwich the optical axis and serve as cooling means. Details of the Peltier elements 64a and 64b will be described later.

  Further, as shown in FIG. 6, temperature sensors 65a and 65b are provided on the side surface 63 where the Peltier elements 64a and 64b are not provided. The temperature sensors 65 a and 65 b serve as detection means for detecting the temperature of the liquid lens 14. The Peltier elements 64a and 64b and the temperature sensors 65a and 65b are connected to the control unit 30 in FIG.

  The controller 30 serves as a control unit that controls the operation of the Peltier elements 64a and 64b based on the temperature information output from the temperature sensors 65a and 65b. Specifically, when the temperature sensors 65a and 65b detect a temperature equal to or higher than a predetermined temperature, a current is supplied to the Peltier elements 64a and 64b, and the heat of the liquid lens 14 is absorbed by the Peltier elements 64a and 64b. An example of the predetermined temperature is 25 ° C. ± 5 ° C.

  The Peltier elements 64a and 64b will be described below with reference to the drawings. FIG. 7 is a diagram showing a basic configuration of the Peltier element. In practice, a plurality of Peltier elements shown in FIG. 7 are connected in series.

  The Peltier element is an element that generates heat on one side and absorbs heat on the other side when an electric current flows. As shown in FIG. 7, the electrodes 70a and 70b, the P-type semiconductor 72, the N-type semiconductor 74, and the electrode 76. One end of the electrode 70 a is connected to the P-type semiconductor 72, and the other end of the electrode 70 a is connected to the positive electrode of the DC power supply 78. One end of the electrode 70 b is connected to the N-type semiconductor 74, and the other end of the electrode 70 b is connected to the negative electrode of the DC power supply 78. One end of the electrode 76 is connected to the P-type semiconductor 72, and the other end of the electrode 76 is connected to the N-type semiconductor 74.

  In the Peltier element configured as described above, when a current is passed from the P-type semiconductor 72 to the N-type semiconductor 74, the electrode 76 generates heat and the electrodes 70a and 70b generate heat. That is, heat moves from the electrode 76 to the electrodes 70a and 70b. Therefore, by disposing the Peltier element so that the electrode 76 is in contact with the side surface 63 of FIG. 5, the heat in the liquid lens 14 is released to the outside of the liquid lens 14. As a result, the temperature of the conductive liquid 40 and the insulating liquid 42 is suppressed from rising rapidly.

  In particular, when the Peltier elements 64a and 64b are arranged so as to sandwich the optical axis, the conductive liquid 40 and the insulating liquid 42 are positioned between the Peltier elements 64a and 64b. As a result, the conductive liquid 40 and the insulating liquid 42 can be cooled more effectively.

(Modification)
As shown in FIG. 8, Peltier elements 64a, 64b, 64c, and 64d may be provided on all side surfaces 63. FIG. 8 is an external perspective view of a liquid lens 14 according to a modification. In this case, the temperature sensors 65 a, 65 b, 65 c, and 65 d are preferably provided at the four corners of the transparent plate 44.

  In addition, the temperature sensors 65a, 65b, 65c, and 65d are attached to the liquid lens 14, but the attachment positions of the temperature sensors 65a, 65b, 65c, and 65d are not limited thereto. The temperature sensors 65a, 65b, 65c, and 65d may be provided around the liquid lens 14, and may be attached to the optical scanning device 10 side, for example.

  In addition, the liquid lens 14 according to the present embodiment is applied to the optical scanning device 10, but may be applied to another device. The liquid lens 14 can be applied to, for example, an optical pickup device.

  Further, in the liquid lens 14 according to the present embodiment, the container may have a double structure like the liquid lens 14 according to the first embodiment.

  Further, the beam deflected by the polygon mirror 20 passes through the scanning lenses 22 and 24 and then directly irradiates the photosensitive drum 32. However, the beam is sensitized after the traveling direction is changed by the mirror. The body drum 32 may be irradiated.

1 is a top view of an optical scanning device including a liquid lens according to a first embodiment. It is a cross-sectional structure figure in the surface containing the optical axis of the said liquid lens. FIG. 3 is an enlarged view of a portion C of the liquid lens in FIG. 2. It is a cross-sectional structure figure in the surface containing the optical axis of the liquid lens which concerns on a modification. It is a cross-sectional structure figure in the surface containing the optical axis of the liquid lens which concerns on 2nd Embodiment. It is an external appearance perspective view of the liquid lens. It is the figure which showed the basic composition of the Peltier device. It is an external appearance perspective view of the liquid lens which concerns on a modification. It is a cross-section figure of a liquid lens.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical scanning device 12 Laser diode 13 Collimator lens 14 Liquid lens 18 Cylindrical lens 20 Polygon mirror 22, 24 Scan lens 26 Mirror 28 Light receiving element 29 Housing | casing 30 Control part 32 Photosensitive drum 40 Conductive liquid 42 Insulating liquid 43,44 , 45, 46 Transparent plate 48 First electrode 50 Insulating film 52 Second electrode 53, 53 ', 63 Side surface 64a, 64b, 64c, 64d Peltier element 65a, 65b, 65c, 65d Temperature sensor S interface sp1, sp2 gap

Claims (9)

In the optical element that changes the focal length by deforming the shape of the interface between the first liquid and the second liquid by an electrowetting phenomenon,
A first transparent plate and a second transparent plate that sandwich the first liquid and the second liquid;
A third transparent plate disposed at a predetermined interval from the first transparent plate;
Providing
An optical element characterized by the above. A fourth transparent plate disposed at a predetermined interval from the second transparent plate,
To provide further,
The optical element according to claim 1. An air layer exists between the first transparent plate and the third transparent plate;
The optical element according to claim 1. On the main surface of the third transparent plate, at a position corresponding to the optical axis, a coating that reflects heat rays is applied,
The optical element according to any one of claims 1 to 3, wherein: An optical element according to any one of claims 1 to 4,
A light source that emits light to the optical element;
Deflecting means for deflecting light that has passed through the optical element;
Providing
An optical scanning device characterized by the above. In the optical element that changes the focal length by deforming the shape of the interface between the first liquid and the second liquid by an electrowetting phenomenon,
A cooling means for cooling the first liquid and the second liquid;
Preparing,
An optical element characterized by the above. The first liquid and the second liquid are sandwiched between a first transparent plate and a second transparent plate,
A plurality of the cooling means are provided so as to sandwich the optical axis on the side surface when the first transparent plate and the second transparent plate are the upper surface and the lower surface,
The optical element according to claim 6. An optical element according to claim 6 or 7,
A light source that emits light to the optical element;
Deflecting means for deflecting light that has passed through the optical element;
Providing
An optical scanning device characterized by the above. Detecting means for detecting temperature;
Control means for controlling the operation of the cooling means based on the temperature detected by the detecting means;
Further comprising,
The optical scanning device according to claim 8.

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