JP4717087B2 - Optical deflection device - Google Patents

Description

  The present invention relates to an optical deflecting device, and more particularly to an optical deflecting device that deflects laser light.

  Today, the technique of optical deflection of laser light is applied in various fields. For example, an optical path difference correction for free space optical communication and a scanning system for laser radar can be cited as examples.

  Conventionally, a gimballed mirror is often used as an optical deflector for laser light or a pointing optical system. This method using a gimbal mirror is a direct and simple method because the direction of the laser beam is controlled by mechanically moving the mirror.

  Further, there is a prior art related to a liquid crystal prism in which a liquid crystal layer has a prism shape (see, for example, Patent Document 1 and Patent Document 2).

JP-A-6-194695 JP 7-92507 A

  However, in the above conventional method, since it is necessary to control a relatively large mirror with a large physical operation, it is necessary for a system that requires a light weight and a small size and an application that requires low power consumption. There was a problem that was not suitable.

  Further, in the liquid crystal prism having the liquid crystal layer in the prism shape, there is a problem that not only the manufacturing process is complicated, but also its control is difficult.

  The present invention has been made to solve the above-described problems (problems), and provides an optical deflecting device capable of achieving a high-quality and high-deflection angle with a simple structure suitable for miniaturization and weight reduction. With the goal.

  In order to solve the above problems, an optical deflection apparatus according to the present invention includes a liquid crystal optical phase modulation element that deflects and emits incident light using liquid crystal, and a driving unit that drives the liquid crystal optical phase modulation element. A light incident surface on which light emitted from the liquid crystal light phase modulation element is incident and a light emission surface from which light incident from the light incident surface is emitted are predetermined. The liquid crystal optical phase modulation element includes a first transparent substrate having a plurality of individual electrodes made of transparent conductors arranged in parallel stripes, and the transparent conductor. A second transparent substrate having a common electrode; and a liquid crystal layer sandwiched between the first transparent substrate and the second transparent substrate, and the driving means modulates the refractive index of the liquid crystal layer. Said to produce A predetermined voltage is applied to another electrode, and at least two of the liquid crystal optical phase modulation elements are arranged side by side, and light emitted from the previous liquid crystal optical phase modulation element is incident on the subsequent liquid crystal optical phase modulation element, and the wedge The mold prism is disposed on the emission side of the latter-stage liquid crystal optical phase modulation element, and has an incident surface on which light emitted from the latter-stage liquid crystal optical phase modulation element is incident, and light incident from the incident surface is emitted. And the direction of the individual electrodes of the preceding liquid crystal optical phase modulation element and the direction of the individual electrodes of the subsequent liquid crystal optical phase modulation element are substantially orthogonal, and The liquid crystal optical phase modulation element is arranged so that the alignment direction of the liquid crystal layer is substantially the same as the alignment direction of the liquid crystal layer of the subsequent liquid crystal optical phase modulation element.

  The optical deflecting device according to the present invention corresponds to each individual electrode group constituted by a predetermined number of the individual electrodes in the above invention, and is a collection connected in common to each individual electrode of the individual electrode group. An electrode and a pair of signal electrodes connected to both ends of the collector electrode are provided.

  According to the present invention, there is an effect that an optical deflecting device capable of achieving a high-definition and high-deflection angle that can have a simple structure suitable for reduction in size and weight can be obtained.

  Exemplary embodiments of an optical deflection apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings.

1-1. Configuration of Optical Deflection Device First, the configuration of an optical deflection device according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2 are schematic cross-sectional views showing the configuration of an optical deflecting device 100 in an embodiment of the present invention.

  As shown in FIG. 1, an optical deflecting device 100 according to the present invention includes a liquid crystal optical phase modulation element 101 and a wedge-shaped wedge prism 121 having an emission surface 161 inclined at a predetermined inclination angle γ. Further, a driving device 141 is connected to the liquid crystal optical phase modulation element 101.

Here, the exit surface 161 of the wedge prism 121 is in contact with the air layer. Therefore, a non-reflective coating is formed as necessary so as to prevent reflection at the interface between air and the substrate. As the non-reflective coating, for example, a coating made of a dielectric multilayer film of tantalum pentoxide (Ta ₂ O ₅ ) and silicon dioxide (SiO ₂ ) is used.

1-2. Arrangement of Liquid Crystal Optical Phase Modulation Element and Wedge Type Prism As shown in FIG. 1, the wedge type prism 121 is arranged in contact with the emission side of the liquid crystal optical phase modulation element 101. The liquid crystal optical phase modulation element 101 and the wedge prism 121 are fixed using an adhesive or the like. In addition, as shown in FIG. 2, the same effect as that of the present invention can be obtained even if the gaps 102 are arranged so as not to deviate from the deflection angle of the light emitted from the liquid crystal optical phase modulation element 101. By opening the interval 102, depending on the type of light, it is possible to avoid the problem that the heat generated by the passing light melts the adhesive or the like that fixes the liquid crystal optical phase modulation element 101 and the wedge prism 121. . In this case, since the exit surface 161 or the entrance surface 103 of the wedge-shaped prism 121 is in contact with the air layer, a non-reflective coating may be formed as necessary as in the above configuration.

2-1. Principle of Wedge Type Prism FIG. 3 is an explanatory diagram showing the principle of the optical deflection apparatus in the embodiment of the present invention. As shown in FIG. 3, the liquid crystal optical phase modulation element 101 performs an action of deflecting the incident light 151 by a predetermined angle ± θ. A P-polarized light 171 indicated by a double arrow schematically shows a direction of polarized light parallel to the cross-sectional view shown in FIG. In FIG. 3, the P-polarized light 171 with respect to the emission surface 161 of the wedge prism 121 is shown as the polarization state of the incident light 151. Note that S-polarized light may be used as the incident light 151. This can be dealt with by changing a part of the configuration of the liquid crystal optical phase modulation element 101. Details of using S-polarized light as incident light 151 will be described later.

  In FIG. 3, when θ is increased counterclockwise, the inclination angle γ is determined so that γ> θmax, where θmax is the maximum value of the variable range of θ. That is, by selecting the tilt angle γ to a predetermined value that satisfies γ> θmax, the deflection angle θmax can be expanded by the wedge prism 121 even if the deflection angle θmax of the liquid crystal optical phase modulation element 101 is small. It becomes.

In FIG. 3, when the liquid crystal light phase modulation element 101 deflects the incident light 151 by + θ, the first outgoing light 153 is emitted as an angle β ₁ as shown in Equation (1) according to Snell's law.

_ng · sin α ₁ = n ₀ · sin β ₁
Here, _ng is the refractive index of the wedge-type prism 121, and n ₀ is the refractive index of air.

Further, when the liquid crystal optical phase modulator 101 does not deflect the incident light 151, the second outgoing light 155, as the angle beta ₂ is emitted in accordance with Snell's law. In this case, from the definition of the inclination angle γ, the inclination angle γ and the angle α ₂ are equal. When the liquid crystal light phase modulation element 101 deflects the incident light 151 by −θ, the third emitted light 157 is emitted according to Snell's law as an angle β ₃ . Here, the relationship between the angle α which is the incident angle on the emission surface 161 and the deflection angle θ of the liquid crystal optical phase modulation element 101 is summarized as follows (1) to (3).

When θ = + θ, α = γ−θ (1)
When θ = 0, α = γ (2)
When θ = −θ, α = γ + θ (3)

When the angle β, which is the refraction angle, is π / 2 or more, the total reflection condition is satisfied, and the emitted light is lost. Here, as an example, when BK7 is used as the material of the wedge-type prism 121, the refractive index _ng is about 1.507, so that the critical angle α _c is calculated by using Equation (4),
sin α _c = n ₀ / _ng · sin (π / 2)
= 1 / 1.507 (4)
Therefore, α _c is about 0.726 radians (41.57 degrees).

Considering the critical angle α _c , the incident light 151 can be used more effectively if α ₃ is set smaller than α _c .
θmax <γ <α _c −θmax (5)
It is necessary to select the inclination angle γ so as to satisfy.

2-2. Relationship Between Incident Angle and Exit Angle Next, a graph showing the relationship between the incident angle α to the exit surface 161 of the wedge prism 121 and the exit angle β from the exit surface 161 will be described with reference to FIG. As shown in FIG. 4, it can be seen that the rate of change of the angle β rapidly increases when the angle α is in the vicinity of the critical angle α _c . In order to explain this in more detail, a graph showing the relationship between the angle α and the angle increase rate dβ / dα is shown in FIG. The angle increase rate dβ / dα was defined as the derivative of the angle β with respect to the angle α. Angle increase rate d.beta / d [alpha] Figures 5, it can be confirmed that grow rapidly in near the critical angle alpha _c. Therefore, the inclination angle γ of the wedge-type prism 121 in the configuration of FIG. 3 is more effective when the deflection angle θmax is smaller than the critical angle α _c but in a region close to the critical angle.

Here, when the angle α when the deflection angle θ is 0 is defined as the operating point angle α _a , as described above,
α _a = γ (6)
Therefore, the operating point angle α _a can be determined by the inclination angle γ.

Here, assuming that the maximum deflection angle θmax of the liquid crystal optical phase modulation element 101 is 1.5 degrees and the operating point angle α _a is 40 degrees as shown in FIG. 4, the input angle range from the graph of FIG. It can be seen that the output angle range (exit angle range) 303 is larger than the (incident angle range) 301. FIG. 6 shows a graph obtained by re-plotting the main parts of the input angle range 301 and the output angle range 303 shown in FIG.

  Here, the origin of the angle α is replaced with a variable as the input angle φ, the angle β at that time (φ = 0) is regarded as the origin, and the variable is set as the output angle Φ. FIG. 6 shows that the output angle range of the output angle Φ is about 17 degrees with respect to the input angle range of 3 degrees of the input angle φ, and the angle variable range can be expanded about three times.

3-1. Next, the structure of the liquid crystal optical phase modulation element 101 will be described with reference to FIG. FIG. 7 is a cross-sectional view showing the structure of the liquid crystal optical phase modulation element in the embodiment of the present invention. In FIG. 7, the nematic liquid crystal layer 501 shown as an example of the liquid crystal layer is formed on the composite electrode 211 of the first transparent substrate 201 of the liquid crystal optical phase modulation element 101 and on the common electrode 213 of the second transparent substrate 203. The formed alignment layer 217 is homogeneously aligned so that the tilt angle 209 of the director 207 of p-type (positive-type) liquid crystal molecules when no electric field is applied is 5 degrees or less. In the case of the liquid crystal optical phase modulation element 101 shown in FIG. 7, the incident linearly polarized light 511 has a component parallel to the cross-sectional view shown in FIG. The incident linearly polarized light 511 is P-polarized light when viewed from the exit surface 161 of the wedge prism 121.

Although not explicitly shown in FIG. 7, the first transparent substrate 201 and the second transparent substrate 203 are fixed via a spacer so that the nematic liquid crystal layer 501 maintains a predetermined constant thickness of several μm to several tens of μm. . Although not shown in FIG. 7, in order to prevent the composite electrode 211 and the common electrode 213 from being short-circuited, tantalum pentoxide (Ta ₂ O ₅ ) or carbon dioxide is formed on at least one of the composite electrode 211 and the common electrode 213. A transparent insulating film such as silicon (SiO ₂ ) may be formed. It is also desirable to improve the transmittance by making the transparent insulating film a multilayer film composed of a high refractive index film and a low refractive index film. The common electrode 213 formed on the second transparent substrate 203 may be a full-surface electrode made of a transparent conductive film. The structure of the composite electrode 211 will be described later.

  When using indium tin oxide (ITO) for the transparent conductive film forming the optical path portion of the composite electrode 211 and the common electrode 213, the film thickness should be 50 nm or less, and if the wavelength used is in the near infrared region, the transmittance should be In order to improve, it is desirable to use a film having a sheet resistance of several hundred Ω to about 1 kΩ with an increased oxygen concentration during film formation.

In addition to ITO, thin films such as indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), and zinc oxide (ZnO) can be used as the transparent conductive film. In this case as well, it is desirable to use a film with a film thickness of 50 nm or less and a sheet resistance of about several hundred Ω to 1 kΩ.

Necessary for preventing reflection at the interface between air and the substrate on the surface of the first transparent substrate 201 or the second transparent substrate 203 made of glass opposite to the nematic liquid crystal layer 501 in contact with the air layer. In response to this, an anti-reflection coat 215 is formed. As the non-reflective coating 215, for example, a coating made of a dielectric multilayer film of tantalum pentoxide (Ta ₂ O ₅ ) and silicon dioxide (SiO ₂ ) can be used.

  In addition, although the incident light 151 shown in FIG. 3 or the incident linearly polarized light 511 in FIG. 7 is shown as a representative configuration in the case of becoming the P polarized light 171 when viewed from the exit surface 161 of the wedge prism 121, FIG. 8 shows the structure of the liquid crystal optical phase modulation element 101 when it is S-polarized light as viewed from the exit surface 161 of the wedge-shaped prism 121 at the subsequent stage. The structure is the same as that shown in FIG. 7 except that the director 207 of the nematic liquid crystal layer 501 is parallel to the S-polarized light of the incident linearly polarized light 511.

3-2. Operation Principle of Liquid Crystal Optical Phase Modulation Element Next, the operation principle of the liquid crystal optical phase modulation element 101 will be described. FIG. 9 is a schematic diagram showing the basic principle of operation of the liquid crystal optical phase modulation element in the embodiment of the present invention. A p-type (positive-type) nematic that is oriented so that the major axis direction of the director 207 is parallel to the electric field direction when an external electric field is applied in a state where the director 207 is homogeneously oriented in a direction parallel to the xz plane. Consider that linearly polarized light 1110 oscillating in a direction parallel to the x-axis is incident on the liquid crystal optical phase modulation element 101 using liquid crystal in the z-axis direction. The incident wavefront 1113 before entering the liquid crystal optical phase modulation element 101 is a plane. When an in-plane distribution of the director 207 is controlled so that an electric field is applied to the liquid crystal optical phase modulation element 101 and a predetermined refractive index distribution is obtained, the incident wavefront 1113 is converted into a plane wave outgoing wavefront 1123 deflected by a predetermined angle θ. be able to.

This phenomenon will be described in more detail with reference to FIG. FIG. 10 is an explanatory diagram showing the operation principle of the liquid crystal optical phase modulation element in the embodiment of the present invention. In FIG. 10, the plane on the emission side of the nematic liquid crystal layer 501 of the liquid crystal optical phase modulation element 101 is the xy plane, and the liquid crystal is aligned so as to be parallel to the xz plane. At this time, the incident linearly polarized light 1201 enters the nematic liquid crystal layer 501 perpendicularly. In this nematic liquid crystal layer 501, the operating point is determined in advance so that the distribution 1211 of the extraordinary refractive index _ne (x), which is a function of the position x, linearly changes between a and b at the pitch P of the element grating. Keep it.

Further, although the thickness d of the nematic liquid crystal layer 501 is constant, the refractive index n _e (x) changes linearly with the pitch P, so that the incident linearly polarized light 1201 propagating in the nematic liquid crystal layer 501 is Depending on the retardation Δn (x) · d. Here, when n ₀ is an ordinary refractive index of liquid crystal,
_{Δn (x) = n e (} x) -n 0 (7)
It is.

When the incident linearly polarized light 1201 propagates in a nematic liquid crystal, that is, in a dielectric medium, the incident linearly polarized light 1201 propagates slowly when the retardation is large, and conversely propagates quickly when the retardation is small. Therefore, the output linearly polarized light 1203 emitted from the nematic liquid crystal layer 501 has a wavefront of tan θ = δΔn · d / P (8)
Will just lean.

Here, δΔn is a value obtained by calculating the difference between the retardations Δn (x) at point a and point b as in equation (9).
δΔn = Δn (a) −Δn (b) (9)

Thus, if the distribution 1211 of the extraordinary light refractive index _ne (x) in the nematic liquid crystal layer 501 of the optical deflecting device is linear, the wavefront of the outgoing linearly polarized light 1203 is also flat as in the case of the incident linearly polarized light 1201, and the result Thus, the outgoing linearly polarized light 1203 can be deflected by θ with respect to the incident linearly polarized light 1201.

Next, the conditions under which the extraordinary refractive index n _e (x) of the nematic liquid crystal layer 501 used in the present invention can be linearly approximated were considered. The incident linearly polarized light undergoes modulation determined by applied voltage-effective birefringence characteristics as shown in FIG. In FIG. 11, the horizontal axis represents the effective value of the voltage applied to the nematic liquid crystal layer 501 and the vertical axis represents the effective birefringence Δn of the liquid crystal molecules. The shape of the electro-optic response curve is determined by parameters such as the elastic constant of the liquid crystal to be used, the dielectric anisotropy characteristics, and the pretilt angle determined by the alignment film layer when no electric field is applied. This applied voltage-effective birefringence characteristic is that of a nematic liquid crystal material BL007 (trade name) manufactured by Merck.

  This characteristic is a theoretical curve obtained by assuming that Δnmax = 0.287 and the thickness of the liquid crystal layer is 20 μm. FIG. 11 shows the characteristics when the pretilt angles are 0.5 degree, 2 degrees, 5 degrees, and 10 degrees. When used as a liquid crystal optical phase modulation element 101 having a composite electrode 211a shown in FIG. 16 to be described later, it is necessary to use the vicinity of a linear region 1520 that can approximate a linear curve in order to obtain the operation of FIG. Accordingly, it can be understood that the pretilt angle of the nematic liquid crystal is preferably 5 degrees or less, more preferably 2 degrees or less in order to take a wide linear region 1520.

3-3. In the case where a plurality of liquid crystal light phase modulation elements are provided In the above description, the number of liquid crystal light phase modulation elements is one, but a plurality of liquid crystal light phase modulation elements may be provided. Here, three examples when two liquid crystal optical phase modulation elements are provided will be described.

3-3-1. Orientation direction of liquid crystal cell: parallel, individual electrode of liquid crystal cell: parallel FIG. 12 is a cross-sectional view showing two liquid crystal light phase modulation elements. In FIG. 12, a front-stage liquid crystal optical phase modulation element 101A (left in the drawing) and a rear-stage liquid crystal optical phase modulation element 101B (right in the drawing) are arranged side by side with respect to incident light. At this time, the alignment directions of the liquid crystal cells of the front-stage liquid crystal optical phase modulation element 101A and the rear-stage liquid crystal optical phase modulation element 101B are substantially parallel to each other. Similarly, the individual electrodes 211A and 211B of the liquid crystal cells are also substantially parallel. Therefore, two identical liquid crystal optical phase modulation elements are arranged in the same direction.

  With such a configuration, incident polarized light having a vibration plane parallel to the cross-sectional view of FIG. 12 is parallel to the cross-sectional view by the front-stage liquid crystal light phase modulation element 101A and the back-stage liquid crystal light phase modulation element 101B. It is deflected in the plane (in the xz plane). Therefore, the amount of phase modulation is twice that of a single liquid crystal optical phase modulation element, thereby realizing a large deflection. A larger deflection can be realized by increasing the number of liquid crystal optical phase modulation elements arranged side by side to 3 or more.

3-3-2. Liquid crystal cell orientation direction: orthogonal, liquid crystal cell individual electrode: parallel FIG. 13 is a cross-sectional view showing two liquid crystal light phase modulation elements. In FIG. 13, a front-stage liquid crystal optical phase modulation element 101A (left in the drawing) and a rear-stage liquid crystal optical phase modulation element 101B (right in the drawing) are arranged side by side with respect to incident light. At this time, the alignment directions of the liquid crystal cells of the front-stage liquid crystal optical phase modulation element 101A and the rear-stage liquid crystal optical phase modulation element 101B are substantially orthogonal to each other. Further, the individual electrodes 211A and 211B of the liquid crystal cells are substantially parallel.

  With such a configuration, incident polarized light having a vibration plane parallel to the cross-sectional view of FIG. 13 is modulated by the subsequent liquid crystal optical phase modulation element 101B and perpendicular to the cross-sectional view of FIG. Incident polarized light having an oscillating surface is modulated by the liquid crystal optical phase modulation element 101A in the previous stage. Therefore, it is possible to realize an optical polarization device that does not depend on incident polarized light and does not depend on incident polarized light. Further, the order of the liquid crystal light phase modulation element 101A at the front stage and the liquid crystal light phase modulation element 101B at the rear stage may be switched with respect to the incident linearly polarized light.

3-3-3. Orientation direction of liquid crystal cell: parallel, individual electrode of liquid crystal cell: orthogonal FIG. 14 is a cross-sectional view showing two liquid crystal optical phase modulation elements. FIG. 15 is a schematic diagram for explaining a configuration when the optical deflecting device according to the embodiment of the present invention is used as a two-dimensional optical deflecting device.

  In FIG. 14, a front-stage liquid crystal optical phase modulation element 101A (left in the drawing) and a rear-stage liquid crystal optical phase modulation element 101B (right in the drawing) are arranged side by side with respect to incident light. At this time, the alignment directions of the liquid crystal cells of the front-stage liquid crystal optical phase modulation element 101A and the rear-stage liquid crystal optical phase modulation element 101B are substantially parallel to each other. Further, the individual electrodes 211A and 211B of the liquid crystal cells are substantially vertical.

  As shown in FIG. 15, the optical deflecting device 100 of the present invention includes a front-stage liquid crystal light phase modulation element 101A, a rear-stage liquid crystal light phase modulation element 101B, and a triangular pyramid-shaped two-dimensional wedge-type prism 123. .

The two-dimensional wedge-type prism 123 is characterized by an xz plane tilt angle γ ₁ and a yz plane tilt angle (γ ₂ ). When coordinates are taken as shown in FIG.
tanγ ₁ = wz / wx (10)
tanγ ₂ = wz / wy (11)
It becomes.

  Here, consider that linearly polarized light 1110 that vibrates in a direction parallel to the x-axis is incident in the z-axis direction. In the liquid crystal optical phase modulation element 101B, the individual electrodes are set in advance so as to be parallel to the x-axis. The alignment direction of the liquid crystal is parallel to the xz plane. Further, the individual electrodes of the liquid crystal optical phase modulation element 101A are parallel to the y axis, and the alignment direction of the liquid crystal is parallel to the xz plane.

With such a configuration, the liquid crystal optical phase modulation element 101B performs an action of deflecting the traveling direction of the incident linearly polarized light 1110 by an angle θ _y in the yz plane, and the liquid crystal optical phase modulation element 101A includes the xz It acts to deflect the angle θ _{x in the} plane. Further, two-dimensional wedge prism 123, the angle theta _x expanded to determined by the tilt angle gamma _1, to enlarge the angle theta _y each independently as determined by the tilt angle gamma _2. With such a configuration, a two-dimensional light deflection apparatus can be realized. Further, the order of the liquid crystal light phase modulation element 101A in the front stage and the liquid crystal light phase modulation element 101B in the rear stage may be switched with respect to the incident linearly polarized light 1110.

4-1. Next, the structure of the first composite electrode 211a for forming the blazed diffraction grating of the liquid crystal optical phase modulation element 101 will be described in detail with reference to FIG. FIG. 16 is a plan view of a first composite electrode 211a having a first active region 671 with two diffraction grating regions of a first element grating 751 and a second element grating 761. FIG.

  In FIG. 16, the first element lattice 751 includes the first individual electrode 721 to the Nth individual electrode 730. The second element lattice 761 includes the (N + 1) th individual electrode 731 to the 2Nth individual electrode 740. In this first composite electrode 211a, N = 10 is set for convenience for ease of explanation. The first to second N individual electrodes 740 to 740 are formed of a transparent conductive film such as ITO having the above-described film thickness and resistance value.

  The first individual electrode 721 to the Nth individual electrode 730 are grouped into a plurality of groups (two groups in FIG. 16) outside the first active region 671, and the individual electrodes in each group are They are connected by a common collector electrode such as ITO, which is the same material as the individual electrodes. In FIG. 16, the first individual electrode 721 to the Nth individual electrode 730 are connected by the first collector electrode 701 outside the first active region 671, and the (N + 1) th individual electrode 731 to the second Nth individual electrode are connected. Similarly, 740 is connected by the second collector electrode 703.

  In addition, a first signal electrode 711 and a second signal electrode 713 made of a low-resistance metal material such as Mo or Ag alloy are connected to both ends of the first collector electrode 701, respectively, and the second collector electrode 703 is connected to the first collector electrode 703. The third signal electrode 715 and the fourth signal electrode 717 are connected to each other. In addition, the collector electrode is not only a film having a sheet resistance of several hundred to 1 kΩ, but may be configured to have a linear resistance in the long side direction of the electrode by further reducing the film thickness or reducing the electrode width. Good.

  In FIG. 16, for convenience, only two diffraction grating regions of the first element grating 751 and the second element grating 761 are shown. However, in the actual liquid crystal optical phase modulation element 101, the incident beam is incident on the first active region 671. It is necessary to form a predetermined number of element lattices according to the diameter. As a specific design example when the 850 nm band is used as incident light, it is assumed that light from a semiconductor laser is incident on the first active region 671 as parallel light by a collimator.

At this time, when the Gaussian beam diameter of the parallel light is set to 300 μm, the width L of the first active region 671 is set to 400 μm to 1.5 mm. In addition, the individual electrodes of each element grating preferably have a line and space of 2 μm or less in consideration of the wavelength of incident light, and when the pitch P _{0 of the} element grating is 30 μm to 100 μm, the width W of the first composite electrode 211a is About 800 μm to 2 mm is desirable. Therefore, when the pitch P ₀ is 30 μm, the number of element lattices is 27 to 67, and when the pitch P ₀ is 100 μm, the number of element lattices is 8 to 20.

  As apparent from the above description, in the liquid crystal optical phase modulation element 101 forming the blazed diffraction grating, even when one diffraction grating region is composed of N individual electrodes, it is connected to the control signal from the drive circuit. The number of signal electrodes is 2M with respect to the number of element lattices (M) by connecting to both ends of the collector electrodes 701 and 703. In particular, when the number of individual electrodes increases, there is an advantage that the number of signal electrodes can be greatly reduced.

4-2. Next, a method of driving the liquid crystal optical phase modulation element 101 having the first composite electrode 211a will be described. First, a part of the first element lattice 751 is taken out and described. FIG. 17 shows drive waveforms. A first drive waveform 1601 is applied to the first signal electrode 711, and a second drive waveform 1603 is applied to the second signal electrode 713. The first drive waveform 1601 and the second drive waveform 1603 have the same frequency and phase and differ only in voltage, and the second drive waveform 1603 has a larger voltage than the first drive waveform 1601.

In the period t1, the first drive waveform 1601 is + V ₁ [V], and the second drive waveform 1603 is + V ₂ [V]. Here, the common electrode 213 is set to 0 [V]. Therefore, since the potential is divided by the first collector electrode 701 formed of a linear resistance material such as a transparent conductive film, each individual electrode of the first element lattice 751 formed in the first active region 671 has a first electrode. The voltage applied to the first signal electrode 711 and the second signal electrode 713 is linearly divided depending on the arrangement position. Here, in the longitudinal direction of the individual electrode, the individual electrode is formed of a low resistance material as compared with the impedance of the nematic liquid crystal layer 501, so that the potential can be substantially the same. Furthermore, a period for applying a bias AC voltage to the common electrode 213 may be provided separately from the period 1 and the period 2 as necessary.

4-3. Next, the relationship between the potential gradient on the first collector electrode 701 in the first composite electrode 211a (FIG. 16) and the potential of each individual electrode will be described in detail. In the period t1 shown in FIG. 17, the potential distribution of the first collector electrode 701 that connects the first signal electrode 711 and the second signal electrode 713 is the first potential shown in FIG. A linear potential distribution indicated by a distribution 1801 is obtained. In the period t2 shown in FIG. 17, the potential distribution of the first collector electrode 701 is the potential distribution indicated by the second potential distribution 1803 in FIG.

Here, in FIG. 18, point a corresponds to the position of the individual electrode connected to the first signal electrode 711, and point b corresponds to the position of the individual electrode connected to the second signal electrode 713. . When the drive waveform shown in FIG. 17 is a rectangular wave with a 50% duty, the two first and second potential distributions 1801 and 1803 shown in FIG. 18 are alternately repeated in time. Therefore, the voltage applied to the nematic liquid crystal layer 501 through the common electrode 213 maintained at 0 [V] is changed to an alternating voltage at any individual electrode position, and no DC component is applied to the nematic liquid crystal layer 501. Since nematic liquid crystal has an effective value response, V ₁ [V] is always applied as an effective value to the first signal electrode 711 side, and a voltage of V ₂ [V] is applied to the second signal electrode 713. It can be considered that the potential applied and further divided by the first collector electrode 701 is applied to each individual electrode.

4-4. Next, the phase distribution generated in the collector electrode will be described. FIG. 19 is a graph showing the relationship between the voltage [Vrms] applied to the liquid crystal and the relative phase difference Δ when BL007 (trade name, manufactured by Merck Japan Ltd.) is used as the liquid crystal and the pretilt angle is set to 1 degree. . It can be seen that the characteristic curve 1711 has a linear approximation region 1701 in the vicinity of 1.4 to 1.8 [V]. It is assumed that the thickness d of the liquid crystal layer is 20 [μm] and the wavelength λ is 850 [nm].

The relative phase difference Δ is set such that the effective birefringence is Δn.
Δ = Δn · d / λ (12)
Define in.

  It can be seen from the linear approximation region 1701 of the relative phase difference Δ in FIG. 19 that at λ = 850 nm, the linear modulatable range 1705 can take two wavelengths or more, that is, about 4π in phase. As described above, if a linear approximation of the extraordinary refractive index can be performed by the pretilt angle, and a voltage within the operating voltage range 1703 operating in the linear approximation region 1701 within the range of the pretilt angle is applied, the first composite A phase distribution proportional to the position of the individual electrode can be realized in the first active region 671 of the electrode 211a.

4-5. Next, another method for realizing an arbitrary deflection angle with the liquid crystal optical phase modulation element 101 having the composite electrode 211a will be described.

4-5-1. Other driving methods (1)
FIG. 20 is a schematic diagram showing the phase distribution of the liquid crystal optical phase modulation element in the embodiment of the present invention. In this case, the pitch of the element lattice is P ₀ , and the maximum deflection angle θmax is
tan θmax = λ / P ₀ (13)
It is defined as

At this time, the maximum phase modulation amount for the phase modulation curve 2001 (the one-dot chain line) of θmax is one wavelength, that is, 2π at the distance P ₀ of the element grating. In the case of the first composite electrode 211a, since the positions of the first and second signal electrodes are determined in advance, it is impossible to reset by 2π at any electrode position in order to change the phase. is there. Therefore, in order to reset at a predetermined position, first consider a case where the angle θ _p slightly smaller than θmax is swung without generation of high-order light. At this time, in the phase modulation curve 2003 (solid line) of θ _p , it is necessary to reset between λ and 2λ. As described above, when the first composite electrode 211 is used, a driving method of resetting each element grating whose phase modulation amount falls within the range of λ to less than 2λ among the predetermined element gratings may be used.

4-5-2. Other driving methods (part 2)
Next, another driving method of the liquid crystal optical phase modulation element 101 having the first composite electrode 211a will be described. FIG. 21 is a diagram showing a waveform application period to signal electrode terminals arranged in one element lattice. In this driving method, one frame is divided into period 1 and period 2 for driving. Specifically, in order to prevent the deterioration of the nematic liquid crystal layer 501, an alternating voltage drive signal 2101 having an average value of 0 is applied to the first signal electrode 711, and the second signal electrode 713 is connected to the common electrode 213. A period 1 in which the potential is 0 [V] so as to be the same potential, and a drive signal 2101 having an alternating voltage is applied to the second signal electrode 713 so that the first signal electrode 711 has the same potential as the common electrode 213. This is a driving method in which periods 2 of 0 [V] are alternately provided.

  By using such a driving method, the liquid crystal potential distribution generated in the element lattice in one frame obtained by adding the period 1 and the period 2 takes a value close to the effective value of each period. The applied waveforms in the period 1 and the period 2 may be arbitrary. For example, two waveforms having different amplitudes can be applied. Further, a waveform whose effective value is controlled by pulse width modulation may be used. Furthermore, a bias AC voltage may be applied to the common electrode as necessary.

4-6. Other structure of composite electrode (1)
Next, another structure of the composite electrode for forming the blazed diffraction grating will be described in detail with reference to FIG. In addition to the structure of the first composite electrode 211a (FIG. 16) described above, the second composite electrode 211b has collector electrodes arranged on both ends of a group of individual electrodes outside the first active region 671. Adopt the configuration to do.

  In FIG. 22, the third collector electrode 801 is opposed to the first collector electrode 701 outside the first active region 671, and the second collector electrode 703 is opposed to the outside of the first active region 671. A fourth collector electrode 803 is disposed at a position where the second collector electrode 803 is located. Further, the third collector electrode 801 is connected to the fifth signal electrode 811 and the sixth signal electrode 813 made of a low resistance metal material such as Mo or Ag alloy, and the fourth collector electrode 803 is connected to the seventh signal electrode. 815 and the eighth signal electrode 817 are connected.

  In the structure of the second composite electrode 211b, the first signal electrode 711 and the fifth signal electrode 811, the second signal electrode 713 and the sixth signal electrode 813, the third signal electrode 715 and the seventh signal are included. The electrode 815 and the pair of the fourth signal electrode 717 and the eighth signal electrode 817 are driven by being short-circuited outside. In addition, the drive method demonstrated previously can be applied as it is to the drive method of the optical deflection | deviation apparatus using the 2nd composite electrode 211b.

  The structure of the second composite electrode 211b shown in FIG. 22 for forming the optical deflecting device is different from the impedance at the driving frequency of the nematic liquid crystal layer when the individual electrode is thin or long. This is particularly effective when the impedance of the signal becomes so large that it cannot be ignored.

4-7 Other structures of composite electrode (Part 2)
Next, the third composite electrode 211c having another configuration that is particularly effective in the case of an application requiring a high-speed response will be described. FIG. 23 is a plan view showing the relationship between the first active region 671 and the third composite electrode 211c for realizing a blazed diffraction grating. In FIG. 23, the third composite electrode 211c is formed of the Nth individual electrode 640, for convenience, N = 20 from the first individual electrode 621 formed of a transparent conductive film such as ITO constituting the composite electrode.

  In order to realize a blazed diffraction grating for performing light deflection in the first active region 671, it is necessary to apply a predetermined voltage to each of the individual electrodes 621 to 640 in the third composite electrode 211c. The voltage pattern applying means includes first to N-th individual electrodes 621 to 640 separately formed as shown in FIG. 23, and each individual electrode is independently driven by a driving circuit such as an IC. A stepwise potential difference is generated in the individual electrodes.

A method for realizing an arbitrary deflection angle using the liquid crystal optical phase modulation element 101 using the third composite electrode 211c will be described with reference to FIG. In the third composite electrode 211c, each individual electrode can independently apply an arbitrary voltage by a direct drive circuit. Therefore, an arbitrary deflection angle can be realized when the modifiable amount can be as small as 2π (one wavelength). For example, when a voltage that realizes the first phase modulation waveform 1901 in the first active region 671 is applied to each individual electrode, the deflection angle θ ₁ is
tan θ ₁ = λ / P ₁ (14)
Takes the value given by.

Here, λ represents a relative phase difference for one wavelength. In addition, the x-axis direction was a direction orthogonal to the individual electrode. By using this configuration, it is possible to bring the diffraction efficiency closer to 100% by resetting the phase by one wavelength at the pitch P ₁ where predetermined individual electrodes are bundled.

Next, when a voltage that realizes the second phase modulation waveform 1903 in the first active region 671 is applied to each individual electrode, the deflection angle θ ₂ is
tan θ ₂ = λ / P ₂ (15)
Takes the value given by. In this way, it is possible to easily realize an arbitrary deflection angle θ by changing the predetermined pitch P ₁ for resetting the phase.

  Furthermore, in the case of the liquid crystal optical phase modulation element 101 using the third composite electrode 211c, for example, not only the linear approximation region 1701 shown in FIG. 19 but also the entire characteristic curve 1711 can be used. Since it is known that the response speed from the application of an electric field to the application of no electric field in a liquid crystal cell is proportional to the square of the cell thickness, this is advantageous in reducing the thickness of the liquid crystal cell and achieving a high-speed response. This is because an arbitrary voltage can be applied to each individual electrode, so that the nonlinearity of the characteristic curve 1711 can be absorbed by weighting of the applied voltage.

  As is apparent from the above description, the optical deflection apparatus of the present invention has a simple structure, can be driven easily, and can be used for free space optical communication, laser radar, or an optical scanner capable of large-angle deflection. It is possible to realize a light and small-sized optical deflecting device that does not have a movable part.

  That is, in the present embodiment, in the optical deflecting device, the first transparent substrate 201 having a plurality of individual electrodes 721 to 740 made of transparent conductors arranged in parallel stripes and the common made of transparent conductors. By including a nematic liquid crystal layer 501 sandwiched between the second transparent substrate 203 having the electrode 213 and applying a predetermined voltage to each individual electrode 721 to 740 formed on the first transparent substrate 201, A wedge-shaped prism having a function of expanding the deflection angle of the light emitted from the liquid crystal light phase modulation element 101 on the light emission side of the liquid crystal light phase modulation element 101 configured to cause the refractive index modulation in the nematic liquid crystal layer 501. 121 is arranged. Further, in the present embodiment, a plurality of the liquid crystal optical phase modulation elements 101 may be configured.

  In this embodiment, a plurality of individual electrodes 721 to 740 are grouped into a plurality of groups, and the plurality of individual electrodes 721 to 740 in each group are connected by common collector electrodes 701 and 703. In addition, a pair of signal electrodes 711, 713, 715, and 717 are connected to both ends of the collector electrodes 701 and 703. In the present embodiment, drive waveforms having different voltages are applied to a pair of signal electrodes (for example, 711 and 713) arranged in at least one of the groups. Further, an alternating voltage is applied to one of a pair of signal electrodes (for example, 711, 713) arranged in at least one of the groups, the other is set to 0 [V], an alternating voltage is applied to the other, Periods in which one of them is 0 [V] may be alternately provided. The alternating voltage may be a pulse width modulated voltage. In this embodiment, a period in which an AC bias is applied to the nematic liquid crystal layer 501 from the common electrode 203 side may be provided.

  As described above, in the present embodiment, the liquid crystal light having a plurality of individual electrodes 211 made of a linear transparent conductive film and sandwiching the nematic liquid crystal layer 501 between the plurality of individual electrodes 721 to 740 and the common electrode 213. By adopting a configuration in which the wedge-shaped prism 121 that expands the deflection angle is disposed so as to be adjacent to the phase modulation element 101 and the liquid crystal optical phase modulation element 101, the liquid crystal optical phase modulation element 101 uses a wedge-type prism that is incident linearly polarized light. The incident angle incident on 121 is controlled. That is, the wedge-type prism 121 functions to increase the amount of deviation of the incident angle.

  Further, the liquid crystal optical phase modulation element 101 applies a predetermined voltage to the plurality of individual electrodes 721 to 740 formed on the first transparent substrate 201, thereby forming a spatial refractive index modulation region in the nematic liquid crystal layer 501. It induces and realizes a blazed diffraction grating. The plurality of individual electrodes 721 to 740 of the liquid crystal optical phase modulation element 101 are grouped into a plurality of groups, and the plurality of individual electrodes 721 to 740 in each group are shared by common collector electrodes 701 and 703. It is good also as a structure which reduces a drive electrode number significantly by setting it as the structure to bundle. In this case, a linear potential gradient is induced in the collector electrodes 701 and 703 by applying a predetermined potential difference to the pair of signal electrodes 711, 713, 715, and 717 provided on the collector electrodes 701 and 703. A predetermined potential is distributed to the electrodes 211 (721 to 740).

  As a driving method for inducing a predetermined potential difference in each individual electrode 211, for example, a method of applying driving waveforms of different voltages to the pair of signal electrodes 711 and 713 is employed. As another driving method, a period in which an alternating voltage is applied to the first signal electrode 711 of the pair of signal electrodes arranged in at least one of the groups and the second signal electrode 713 is set to 0 [V]; Then, a method is adopted in which an alternating voltage is applied to the second signal electrode 713 and the period in which the first signal electrode 711 is set to 0 [V] is alternately repeated.

  As described above, in the optical deflecting device of the present invention according to the present embodiment, a highly functional optical deflecting device can be realized with a simple configuration and a simple driving method.

It is a schematic cross section which shows the optical deflection apparatus in embodiment of this invention. It is a schematic cross section which shows the optical deflection apparatus in embodiment of this invention. It is explanatory drawing which shows the principle of the optical deflection apparatus in embodiment of this invention. It is a graph which shows the relationship between the incident angle and exit angle of the wedge-type prism in embodiment of this invention. It is a graph which shows the relationship between the incident angle and angle increase rate of the wedge-type prism in embodiment of this invention. It is a graph which shows the relationship between the incident angle and output angle of the optical deflection apparatus in embodiment of this invention. It is sectional drawing which shows the structure of the liquid crystal optical phase modulation element in embodiment of this invention. It is sectional drawing which shows another structure of the liquid crystal optical phase modulation element in embodiment of this invention. It is a schematic diagram which shows the basic principle of operation | movement of the liquid crystal optical phase modulation element in embodiment of this invention. It is explanatory drawing which shows the principle of operation of the liquid crystal optical phase modulation element in embodiment of this invention. It is a graph which shows the voltage-birefringence characteristic of the liquid crystal optical phase modulation element in embodiment of this invention. It is sectional drawing which shows the structure of the two liquid crystal optical phase modulation elements in embodiment of this invention. It is sectional drawing which shows another structure of the two liquid crystal optical phase modulation elements in embodiment of this invention. It is sectional drawing which shows another structure of the two liquid crystal optical phase modulation elements in embodiment of this invention. It is a schematic diagram which shows the basic composition of the two-dimensional optical deflection apparatus in embodiment of this invention. It is a top view which shows the structure of the composite electrode of the liquid crystal optical phase modulation element in embodiment of this invention. It is a schematic diagram explaining the drive waveform of the liquid crystal optical phase modulation element in the embodiment of the present invention. It is explanatory drawing which shows the electric potential distribution of the liquid crystal optical phase modulation element in embodiment of this invention. It is a graph which shows the voltage-relative phase difference characteristic of the liquid crystal optical phase modulation element in embodiment of this invention. It is a schematic diagram which shows phase distribution of the liquid crystal optical phase modulation element in embodiment of this invention. It is a schematic diagram which shows the drive waveform of the liquid crystal optical phase modulation element in embodiment of this invention. It is a schematic plan view which shows the structure of the composite electrode of the liquid crystal optical phase modulation element in embodiment of this invention. It is a schematic plan view which shows the structure of the composite electrode of the liquid crystal optical phase modulation element in embodiment of this invention. It is a schematic diagram which shows phase distribution of the liquid crystal optical phase modulation element in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Optical deflecting device 101 Liquid crystal optical phase modulation element 121 Wedge type prism 123 Two-dimensional wedge type prism 141 Driving device 151 Incident light 153 First outgoing light 155 Second outgoing light 157 Third outgoing light 161 Outgoing surface 171 P polarized light 201 First transparent substrate 203 Second transparent substrate 207 Director 209 Tilt angle 211 Composite electrode 213 Common electrode 301 Incident angle range 303 Output angle range 501 Nematic liquid crystal layer 511 Incident linearly polarized light 621. . . 640 Individual electrode 671 First active region 701 First collector electrode 703 Second collector electrode 711 First signal electrode 713 Second signal electrode 715 Third signal electrode 717 Fourth signal electrode 721. . . 740 Individual electrode 751 First element lattice 761 Second element lattice

Claims (2)

A liquid crystal light phase modulation element that deflects and emits incident light using liquid crystal; and
Driving means for driving the liquid crystal optical phase modulation element;
An incident surface that is disposed on an emission side of the liquid crystal optical phase modulation element and receives light emitted from the liquid crystal optical phase modulation element, and an emission surface from which light incident from the incident surface is emitted have a predetermined angle. A wedge-shaped prism having
With
The liquid crystal optical phase modulation element is
A first transparent substrate having a plurality of individual electrodes made of transparent conductors arranged in parallel stripes;
A second transparent substrate having a common electrode made of the transparent conductor;
A liquid crystal layer sandwiched between the first transparent substrate and the second transparent substrate;
With
The driving means applies a predetermined voltage to the individual electrodes so as to cause a refractive index modulation in the liquid crystal layer,
Arranging at least two liquid crystal optical phase modulation elements side by side;
The light emitted from the preceding liquid crystal light phase modulation element is incident on the latter liquid crystal light phase modulation element,
The wedge-type prism is disposed on the emission side of the latter-stage liquid crystal light phase modulation element, and has an incident surface on which light emitted from the latter-stage liquid crystal light phase modulation element is incident, and light incident from the incidence surface The exit surface to be emitted has a predetermined angle,
The direction of the individual electrodes of the liquid crystal optical phase modulation element at the front stage and the direction of the individual electrodes of the liquid crystal optical phase modulation element at the rear stage are substantially orthogonal, and the orientation direction of the liquid crystal layer of the liquid crystal optical phase modulation element at the front stage The optical deflecting device is arranged so that the alignment direction of the liquid crystal layer of the latter-stage liquid crystal optical phase modulation element is substantially the same. Corresponding to each individual electrode group composed of a predetermined number of the individual electrodes, a collector electrode commonly connected to each individual electrode of the individual electrode group,
A pair of signal electrodes connected to both ends of the collector electrode;
The optical deflection apparatus according to claim 1, further comprising:

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