Optical switching element

Abstract

To provide an optical switching element that can scan a wide range freely and increase the light propagation efficiency.SOLUTION: An optical switching element includes: a light source unit 3 configured by a stack of one or more first substrates 1 and one or more second substrates 2 including liquid crystal cell layers 11 and 21 including liquid crystal elements and diffraction layers 12 and 22 provided on an emission side of the liquid crystal cell layers 11 and 21 and including a polarizing diffraction lattice that diffracts in accordance with polarized light, the light source unit delivering a light beam to the liquid crystal cell layers 11 and 21 of the substrates 1 and 2 at the lowermost layers; and a voltage application unit 5 that can apply freely voltage to the liquid crystal cell layers 11 and 21 on the substrates 1 and 2. The diffraction layer 12 on the first substrate 1 and the diffraction layer 22 on the second substrate 2 are disposed so that their diffraction directions are different.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light beam steering device for controlling the exit position of an emitted light beam. [Background technology]

[0002] Various devices combining liquid crystal elements and polarizing diffraction gratings have been proposed. Among them, applications to optical switching elements capable of freely controlling the emission position of a light beam are being considered, with the assumption that they will be applied to LIDAR for automobiles and robots (see, for example, Patent Documents 1 to 4).

[0003] According to the technology disclosed in Patent Document 1, a laminate consisting of multiple transparent electrodes and multiple transparent spacers is provided with electrodes arranged alternately as positive and negative electrodes within the liquid crystal, so that the direction in which voltage is applied to the electrodes can be parallel to the transparent electrodes.

[0004] The technology disclosed in Patent Document 2 is characterized in that silicon wedges, which are inclined members, are attached to the front and back of the liquid crystal panel so as to be point symmetrical, and an angle is generated in the light beam L incident on the liquid crystal substrate. This allows the light beam L to be obliquely irradiated onto the director, generating retardation.

[0005] According to the technology disclosed in Patent Document 3, a photo-alignment layer covering a liquid crystal material is made of a photosensitive polymer that is physically changed by exposure to two interfering light beams with opposite rotation directions of circularly polarized light. This can be applied to a reconfigurable optical add / drop multiplexer for optical transmission network equipment, allowing dynamic increase / decrease in communication capacity.

[0006] According to the technology disclosed in Patent Document 4, a high-speed switch can be realized by constructing an optical deflection element with a layered structure consisting of liquid crystal, a phase panel that controls the phase (polarization) of light, and a polarizing grating plate that exhibits birefringence depending on the phase (polarization) of light. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] WO2022 / 181781 publication [Patent Document 2] JP 2020-106616 A [Patent Document 3] Special Publication No. 2015-505995 [Patent Document 4] WO2018 / 110431 publication Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, there has been an increasing need for optical switching elements that can freely scan a particularly wide range. In addition, there has been an increasing social demand for optical switching elements that can improve the light propagation efficiency. Therefore, in addition to the techniques disclosed in the above Patent Documents 1 to 4, there is a demand for proposals for optical switching element techniques that can meet these demands.

[0009] Therefore, the present invention has been devised in consideration of the above-mentioned problems, and its object is to provide an optical switching element that can freely scan a wide range and also improve the light propagation efficiency. [Means for solving the problem]

[0010] The optical switching element of the first invention is constructed by stacking one or more first substrates and one or more second substrates having a liquid crystal cell layer made of a liquid crystal element and a diffraction layer made of a polarization diffraction grating that diffracts light in response to polarization and is provided on the exit side of the liquid crystal cell layer, and is characterized in that the element is provided with a light incidence means for injecting a light beam into the liquid crystal cell layer of the lowermost substrate and a voltage application means that allows a voltage to be applied freely to the liquid crystal cell layer of each of the substrates, and the diffraction layer of the first substrate and the diffraction layer of the second substrate are arranged so that their diffraction directions are different from each other.

[0011] An optical switching element according to a second aspect of the present invention is characterized in that, in the first aspect, the diffractive layer on the first substrate and the diffractive layer on the second substrate are arranged so that their diffraction directions are perpendicular to each other.

[0012] The optical switching element of the third invention is characterized in that, in the first invention, the polarization of the light beam incident by the light incident means is changed in accordance with a voltage applied to the liquid crystal cell layer, and the diffraction direction in the diffraction layer is changed in accordance with the changed polarization of the light beam, sequentially performed from the bottommost substrate to the topmost substrate, thereby controlling the emission position of the light beam emitted from the diffraction layer of the topmost substrate.

[0013] The optical switching element according to a fourth aspect of the present invention is the optical switching element according to the first aspect of the present invention, characterized in that the liquid crystal cell layer is made of a liquid crystal element selected from the group consisting of smectic liquid crystal, nematic liquid crystal, and ferroelectric liquid crystal.

[0014] An optical switching element according to a fifth aspect of the present invention is characterized in that, in the fourth aspect, the liquid crystal cell layer is made of a liquid crystal element of smectic liquid crystal further laminated with a retardation plate. Effect of the Invention

[0015] The optical switching element having the above-mentioned configuration changes the polarization of the incident light beam in response to the voltage applied to the liquid crystal cell layer, and changes the diffraction direction in the diffraction layer in response to the changed polarization of the light beam, sequentially from the bottom substrate to the top substrate, thereby controlling the emission position of the light beam emitted from the diffraction layer of the top substrate. This makes it possible to freely scan the emission position of the light two-dimensionally over a wide range, thereby improving the light propagation efficiency. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of an optical switching element to which the present invention is applied. [Diagram 2] FIG. 2 is a perspective view showing the detailed configuration of the first substrate and the second substrate. [Diagram 3] FIG. 3 is a diagram for explaining the operation of the optical switching element to which the present invention is applied. [Figure 4] FIG. 4 is a plan view of the switching element viewed from the emission side. [Diagram 5] FIG. 5 is a plan view of switching elements viewed from the emission side in a case where five first substrates are stacked and five second substrates are stacked thereon. [Figure 6] FIG. 6 is a diagram showing an example in which the number of first substrates and the number of second substrates are not the same. [Figure 7] FIG. 7 is a diagram showing a configuration in which first substrates and second substrates are alternately stacked in a staggered manner. [Figure 8] FIG. 8 is a diagram showing an example in which a retardation plate is laminated when a smectic liquid crystal is used as the liquid crystal cell layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an optical switching element to which the present invention is applied will be described in detail with reference to the drawings.

[0018] 1 shows a cross-sectional configuration of an optical switching element 10 to which the present invention is applied. The optical switching element 10 is configured by stacking one or more first substrates 1 and one or more second substrates 2. The optical switching element 10 also includes a light source unit 3, a polarizing element 4, a voltage application unit 5, and a control unit 6.

[0019] 1, five first substrates 1a-1e are stacked from the bottom side of the optical switching element 10, and five second substrates 2a-2e are stacked on top of the topmost first substrate 1e. The stacked substrates 1 and 2 are stacked so that they are in surface contact with each other with no gaps between them.

[0020] The light source unit 3 is composed of a semiconductor laser or the like that emits a light beam. The semiconductor laser used in the light source unit 3 is a light-emitting element that utilizes recombination light emission of a semiconductor, and emits laser light of a predetermined wavelength. The light beam emitted by this semiconductor laser is a mixture of various polarized components, such as an S-polarized component and a P-polarized component. The light beam emitted from the light source unit 3 is supplied to a polarizing element 4. Note that a collimator lens (not shown) may be separately disposed on the emission end side of the light source unit 3 to make the emitted light beam into a parallel light.

[0021] The polarizing element 4 transmits, for example, a circularly polarized component among various polarized components in the light beam emitted from the light source unit 3 and guides it to the substrates 1 and 2, while reflecting other polarized components.

[0022] FIG. 2 is a perspective view showing the detailed configuration of the first substrate 1 and the second substrate 2. The first substrate 1 and the second substrate 2 each include a liquid crystal cell layer 11, 21 and a diffraction layer 12, 22 provided on the exit side of the liquid crystal cell layer 11, 21. Transparent electrodes 14a, 14b are formed on the entrance side and exit side of the liquid crystal cell layer 11, respectively, and transparent electrodes 24a, 24b are formed on the entrance side and exit side of the liquid crystal cell layer 21, respectively. The voltage application unit 5 described above is connected to these transparent electrodes 14, 24, and as a result, the polarization state of the light beam passing through can be changed by applying a voltage to the liquid crystal cell layers 11, 21 sandwiched between the transparent electrodes 14, 24. Glass layers 13a, 13b may be attached to the entrance side of the transparent electrode 14a and the exit side of the transparent electrode 14b, respectively. Similarly, glass layers 23a and 23b may be attached to the incident side of the transparent electrode 24a and the exit side of the transparent electrode 24b, respectively.

[0023] The liquid crystal cell layers 11 and 21 are made of liquid crystal elements, examples of which include smectic liquid crystal, nematic liquid crystal, and ferroelectric liquid crystal, but are not limited thereto, and any other known liquid crystal elements may be used.

[0024] Smectic liquid crystal is a liquid crystal that is composed of rod-shaped molecules, maintains directional regularity and height-directional regularity in the molecular arrangement, and has a layer structure (one-dimensional periodic structure). In the present invention, a liquid crystal cell made of SSD (smectic single domain) may be used as the smectic liquid crystal.

[0025] Nematic liquid crystals are liquid crystals whose constituent molecules have an orientation order but no three-dimensional position order. In nematic liquid crystals, the long axes of the rod-shaped molecules are oriented in a certain direction, but unlike smectic liquid crystals, they do not form layers and there is no regularity in the position of the center of gravity of the molecules. For example, TN (Twisted Nematic), VA (Vertical Alignment), IPS (In Plane Switching), etc. may be used as nematic liquid crystals.

[0026] Ferroelectric liquid crystals (FLCs) have spontaneous polarization and ferroelectricity, which is different from other liquid crystals. This allows ferroelectric liquid crystals to respond quickly to electric fields, unlike other liquid crystals, which have induced polarization due to an external electric field.

[0027] The diffraction layers 12 and 22 are made of a polarization grating (PG) that diffracts light according to the light. The polarization grating is configured by utilizing the anisotropy of liquid crystal molecules, and can realize a large diffraction angle with high efficiency. Here, the polarization grating in the diffraction layer 12 and the polarization grating in the diffraction layer 22 are set so that the axial angles of the birefringence axes are different from each other. This allows the diffraction layer 12 in the first substrate 1 and the diffraction layer 22 in the second substrate 2 to be arranged so that their diffraction directions are different from each other.

[0028] In the example of FIG. 1, the first substrates 1a-1e, which are stacked in five stages, are each designed to have a diffraction layer 12 that can diffract light in the x direction. In contrast, the second substrates 2a-2e, which are stacked in five stages on the emission side of the first substrates 1a-1e, are each designed to have a diffraction layer 22 that can diffract light in the y direction (the depth direction of the paper in the figure). That is, the diffraction layers 12, 22 are designed so that the diffraction directions of the first substrate 1 and the second substrate 2 are orthogonal to each other. This makes it possible to perform two-dimensional, planar switching control of the light beam incident from the light source unit 3, as described later.

[0029] The voltage application units 5-1, 5-2, ..., 5-n are provided for each liquid crystal cell layer 11 on each of the first substrates 1a to 1e and each liquid crystal cell layer 21 on each of the second substrates 2a to 2e. The voltage application units 5-1, 5-2, ..., 5-n are configured as so-called liquid crystal driving units for independently and freely applying voltages to each of the liquid crystal cell layers 11 on each of the first substrates 1a to 1e and the second substrates 2a to 2e. Each of the liquid crystal cell layers 11, 21 can change the polarization state of the light beam incident from the light source unit 3 and emit it based on the voltage applied by the voltage application units 5-1, 5-2, ..., 5-n.

[0030] The control unit 6 is configured as a so-called central control unit that controls the voltages applied to the voltage application units 5-1, 5-2, ..., 5-n. By controlling the voltages applied to the liquid crystal elements in the liquid crystal cell layers 11, 21 from the voltage application units 5-1, 5-2, ..., 5-n through the control unit 6, the polarization state of the light beam emitted from each of the liquid crystal cell layers 11, 21 can be adjusted. The control unit 6 may be connected to an electronic device such as a personal computer, a smartphone, a tablet terminal, a wearable terminal, or the like, or may be configured as such an electronic device itself. The voltages applied to the liquid crystal elements in each of the liquid crystal cell layers 11, 21 may be controlled based on a program previously acquired in these electronic devices.

[0031] The optical switching element 10 to which the present invention is applied may further include a light detection unit 7 that detects the light beam emitted from the diffraction layers 12, 22 of the uppermost substrates 1, 2. This light detection unit 7 is composed of, for example, a light receiving element, a screen for projecting visible light, etc. The detection position of the light beam emitted from the diffraction layers 12, 22 can be specified via this light detection unit 7. However, the configuration of this light detection unit 7 is not essential and may be omitted.

[0032] Next, the operation of the optical switching element 10 to which the present invention is applied will be described. For simplicity, the optical switching element 10 will be described by taking as an example a case in which a first substrate 1a consisting of one layer and a second substrate 2a consisting of one layer are laminated as shown in Fig. 3. Note that in Fig. 3, the first substrate 1a and the second substrate 2a are actually laminated in surface contact with each other, but for the purpose of explanation, they are shown in a state in which they are separated from each other.

[0033] First, a light beam is incident on the first substrate 1 by the light source unit 3. The light beam incident from the light source unit 3 may have, for example, a controlled wavelength and may be controlled in advance to have a circular polarization direction or a linear polarization direction at 0° with respect to the x direction.

[0034] Such a light beam is incident on the lower first substrate 1a from the incident side. The light beam passes through the glass layer 23a of this first substrate 1a and enters the liquid crystal cell layer 11.

[0035] As described above, the voltage applied to the liquid crystal cell layer 11 is controlled via the voltage application unit 5-1. Therefore, by controlling the voltage applied to the liquid crystal cell layer 11 on which the light beam is incident, the polarization state of the light beam itself can be adjusted. The light beam with the adjusted polarization state passes through the glass layer 23b and then enters the diffraction layer 12.

[0036] The light beam incident on the diffraction layer 12 is diffracted in accordance with the axial angle of the birefringence axis of the polarization diffraction grating designed in advance in the diffraction layer 12. For example, the diffraction layer 12 on the first substrate 1a is designed to be diffracted in the x direction, so that the diffraction direction of the incident light beam can be diffracted in the x direction. The polarization state of the light beam has already been adjusted in the liquid crystal cell layer 11 below it via the voltage application unit 5-1. Therefore, the light beam is diffracted in the x direction in the diffraction layer 12 in accordance with the adjusted polarization state. In this way, the diffraction in the x direction in the diffraction layer 12 can be controlled by adjusting the polarization state of the light beam via the voltage application unit 5-1.

[0037] The light beam emitted from the diffraction layer 12 of the first substrate 1a is incident on the incident side of the second substrate 2a in surface contact with the first substrate 1a. The light beam passes through the glass layer 23a of the second substrate 2a and enters the liquid crystal cell layer 21.

[0038] As described above, the voltage applied to the liquid crystal cell layer 21 is controlled via the voltage application unit 5-6. Therefore, by controlling the voltage applied to the liquid crystal cell layer 21 on which the light beam is incident, the polarization state of the light beam itself can be adjusted. The light beam with the adjusted polarization state passes through the glass layer 23b and then enters the diffraction layer 22.

[0039] The light beam incident on the diffraction layer 22 is diffracted in accordance with the axial angle of the birefringence axis of the polarization diffraction grating designed in advance in the diffraction layer 22. For example, the diffraction layer 22 in the second substrate 2a is designed to be diffracted in the y direction, so that the diffraction direction of the incident light beam can be diffracted in the y direction. The polarization state of the light beam has already been adjusted in the liquid crystal cell layer 21 below it via the voltage application unit 5-6. Therefore, the light beam is diffracted in the y direction in the diffraction layer 22 in accordance with the adjusted polarization state. In this way, the diffraction in the y direction in the diffraction layer 22 can be controlled by adjusting the polarization state of the light beam via the voltage application unit 5-6. The light beam whose diffraction direction has been controlled in this way via the diffraction layer 22 is emitted from the second substrate 2a.

[0040] That is, the light beam emitted from the second substrate 2a has its diffraction direction controlled in the x direction through the diffraction layer 12 as described above, and its diffraction direction controlled in the y direction through the diffraction layer 22. FIG. 4 is a plan view of the optical switching element 10 as viewed from the emission side. The emission position of the light beam emitted from the second substrate 2a on the emission side is two-dimensionally controlled in the y direction in addition to the x direction. When the voltage is switched in two stages, ON / OFF, through the voltage application unit 5-1 on the first substrate 1a, the diffraction direction in the x direction through the diffraction layer 12 is adjusted in two stages through the ON / OFF of the voltage. Similarly, when the voltage is switched in two stages, ON / OFF, through the voltage application unit 5-6 on the second substrate 2a, the diffraction direction in the y direction through the diffraction layer 22 is adjusted in two stages through the ON / OFF of the voltage. As a result, the emission position of the light beam emitted from the second substrate 2a on the emission side can be selected from a total of four positions, two stages in the x direction and two stages in the y direction. Selection of the four emission positions can be achieved by applying a voltage via the voltage application unit 5. Such two-dimensional adjustment of the emission position can be achieved by setting the polarization diffraction grating in the diffraction layer 12 and the polarization diffraction grating in the diffraction layer 22 so that the axial angles of the birefringence axes are different from each other.

[0041] In this way, the optical switching element 10 to which the present invention is applied changes the polarization of the incident light beam according to the voltage applied to the liquid crystal cell layers 11 and 21, and changes the diffraction direction in the diffraction layers 12 and 22 according to the polarization of the changed light beam, sequentially from the bottom substrate 1 and 2 to the top substrate 1 and 2, thereby controlling the emission position of the light beam emitted from the diffraction layer of the top substrate 1 and 2. This allows the emission position of the light to be freely scanned two-dimensionally over a wide range. In addition, the light propagation efficiency can be improved by coating each surface of the glass layer 23a and the glass layer 23b with an anti-reflection film, or by applying matching oil or the like so that air does not get between the glass layers 23a and the glass layer 23b. In this case, in addition to applying matching oil to the glass layers 23a and the glass layers 23b, for example, a transparent optical adhesive may be used to bond them together.

[0042] In the above-mentioned embodiment, for convenience of explanation, the case where the first substrate 1a consisting of one layer and the second substrate 2a consisting of one layer are stacked is taken as an example, but the present invention is not limited thereto. As shown in FIG. 1, the first substrates 1a to 1e are stacked in five stages from the bottom, and the second substrates 2a to 2e are stacked in five stages on the top layer of the first substrate 1e, so that the incident light beam can be freely diffracted in the x and y directions by the applied voltage via the voltage application unit 5. As a result, as shown in FIG. 5, the emission position of the light beam can be further widened, and the selectable emission positions can be further increased two-dimensionally. When the emission position can be controlled in two stages through each substrate 1 and 2, when the first substrates 1a to 1e and the second substrates 2a to 2e are configured to have a total of 10 layers as shown in FIG. 5, the emission position can be controlled in two stages. 10 That is, the output position of the light beam can be adjusted over two positions depending on the number of layers n of the substrates 1 and 2 to be stacked. n It can be adjusted in places.

[0043] In addition, the substrates 1 and 2 have been described using an example in which the bottom layer is the first substrate 1 and the top layer is the second substrate 2, but this is not limited to this, and both the bottom layer and the top layer may be assigned to either the first substrate 1 or the second substrate 2.

[0044] The number of first substrates 1 and second substrates 2 is not necessarily limited to the same number. Fig. 6(a) shows a configuration with three layers of first substrates 1a to 1c and four layers of second substrates 2a to 2d, but the output position of the light beam can be freely controlled over 128 positions (8 x 16) as shown in Fig. 6(b). When the number of layers is N, N It can emit light to the street. In the case of a four-layer structure, 4 =Light can be projected onto 16 different points.

[0045] In the above-mentioned embodiment, the first substrate 1 is continuously laminated from the lower layer on the incident side, and the second substrate 2 is continuously laminated on the upper layer, but the present invention is not limited to this. Fig. 7 shows a form in which the first substrate 1 and the second substrate 2 are alternately laminated in a staggered manner, and in this case, it is also possible to adjust the emission position of the light beam two-dimensionally. In addition, the present invention is not limited to the case in which the first substrate 1 and the second substrate 2 are completely alternately laminated, and it is of course possible to include a portion in which only the first substrate 1 and only the second substrate 2 are continuously laminated.

[0046] In the above-mentioned embodiment, the first substrate 1 and the second substrate 2 having the diffraction layer 22 whose birefringence axis has a different axial angle from the diffraction layer 12 of the first substrate 1 are used as an example, but the present invention is not limited to this. The present invention may also be configured to include another substrate in which a diffraction layer having a diffraction direction different from that of the diffraction layer 12 of the first substrate 1 and the diffraction layer 22 of the second substrate 2 is laminated on a liquid crystal cell layer.

[0047] 8 shows an example in which a retardation plate 29 is laminated when smectic liquid crystal (SSD) is used as the liquid crystal cell layers 11 and 21. For example, a wave plate (such as a quarter wave plate) may be used as the retardation plate 29. This retardation plate 29 may be provided on the entrance side or exit side of the liquid crystal cell layers 11 and 21. Furthermore, this retardation plate 29 may be configured to sandwich the liquid crystal cell layers 11 and 21 from the entrance side and the exit side. By providing such a retardation plate 29, it is possible to improve the response performance and efficiency when the diffraction angle is made larger. [Explanation of symbols]

[0048] 1 First board 2 Second board 3 Light source section 4 Polarizing elements 5. Voltage application section 6. Control Unit 7 Light detection section 10 Optical switching element 11, 21 Liquid crystal cell layer 12, 22 Diffraction layer 13, 23 Glass layer 14, 24 Transparent electrode 29 Retardation plate

Claims

1. a light incidence means configured by laminating one or more first substrates and one or more second substrates, the first substrate having a liquid crystal cell layer made of liquid crystal elements and a diffraction layer made of a polarization diffraction grating that diffracts light in response to polarized light and provided on the exit side of the liquid crystal cell layer, for irradiating a light beam onto the liquid crystal cell layer of the substrate located at the bottom; An optical switching element comprising: a voltage application means capable of freely applying a voltage to each of the liquid crystal cell layers on each of the substrates; and a diffraction layer on the first substrate and a diffraction layer on the second substrate arranged so that their diffraction directions are different from each other.

2. 2. The optical switching element according to claim 1, wherein the diffractive layer on the first substrate and the diffractive layer on the second substrate are disposed so that their diffraction directions are perpendicular to each other.

3. The optical switching element according to claim 1, characterized in that the polarization of the light beam incident by the light incident means is changed in accordance with the voltage applied to the liquid crystal cell layer, and the diffraction direction in the diffraction layer is changed in accordance with the changed polarization of the light beam, which is carried out sequentially from the bottommost substrate to the topmost substrate, thereby controlling the emission position of the light beam emitted from the diffraction layer of the topmost substrate.

4. 2. The optical switching element according to claim 1, wherein said liquid crystal cell layer is made of any one of a smectic liquid crystal, a nematic liquid crystal, and a ferroelectric liquid crystal.

5. 5. The optical switching element according to claim 4, wherein the liquid crystal cell layer is made of a liquid crystal element of smectic liquid crystal further laminated with a retardation plate.

Images