Optically addressed liquid crystal cell and its transmissive high damage threshold spatial light modulator

Abstract

An optical addressing liquid crystal cell and its transmissive high damage threshold spatial light modulator, comprising an optical addressing liquid crystal cell, a patterned photosensitive light generating unit and a dichroic mirror, the optical addressing liquid crystal cell comprising a first transparent conductive substrate, a voltage dividing medium, a photoconductive crystal layer, a first liquid crystal alignment layer, a liquid crystal layer, a second liquid crystal alignment layer, a second transparent conductive substrate, a liquid crystal spacer and an alternating voltage source, the photosensitive light generating unit comprising a photosensitive light collimating output light source, a polarization cube, an electrically addressing spatial light modulator and an imaging lens. By making the photoconductive crystal surface in the optical addressing liquid crystal cell not in direct contact with the conductive film layer or the conductive gas, the difficulty of device processing and preparation is reduced, the need for a high-stable voltage driving source of ten thousand volts is avoided, and the device can work under a conventional alternating voltage driving. Not only can the optical addressing spatial light modulator work in a transmissive mode, but also the high damage threshold characteristic of the device is realized.

Description

Technical Field

[0001] This invention belongs to the field of liquid crystal devices, specifically relating to an optically addressed liquid crystal cell and its transmissive high damage threshold spatial light modulator. Background Technology

[0002] Liquid crystal spatial light modulators (SLPs), as active optical field control devices, can achieve real-time and flexible control of the amplitude, phase, or polarization state of laser beams. As a programmable and remotely controllable device, it enables intelligent and programmable control of laser beams by connecting to relevant control units, thus finding important applications in inertial confinement fusion, laser processing, and laser additive manufacturing. In the field of inertial confinement fusion, large laser facilities such as the US NIF facility, the French LMJ facility, and the Shenguang series of facilities in China use SLPs to achieve beam homogenization to improve the facility's operating throughput, shield damage points to extend the lifespan of large-diameter components, and thus reduce the facility's operating and maintenance costs. In the fields of laser processing and additive manufacturing, SLPs flexibly adjust the beam pattern to improve processing and manufacturing efficiency.

[0003] Liquid crystal spatial light modulators are currently mainly divided into two categories: optically addressed and electrically addressed. Compared with electrically addressed spatial light modulators, optically addressed spatial light modulators have advantages such as high transmittance, high fill factor, and simple processing technology. They can effectively avoid problems such as the black gate effect and achieve high-fidelity light field modulation without any additional distortion.

[0004] In practical applications, the continuous increase in laser energy places increasingly higher demands on the damage threshold of liquid crystal spatial light modulators. The bottleneck in the damage threshold of spatial light modulators lies primarily in the conductive film layer. Our research group has previously proposed using gallium nitride (GaN) material for the transparent conductive layer and has applied for patents for both reflective and transmissive structures. Patent document CN113126373B, through the design of a reflective structure, avoids the irradiation of the conductive film on the photoconductive crystal side by the modulated laser, utilizing the higher laser damage threshold of GaN material to improve the overall laser damage threshold of the optically addressed liquid crystal spatial light modulator. However, reflective devices place high demands on the residual reflectivity coating and flatness processing precision of the liquid crystal window substrate, easily leading to problems such as large spectral distortion and large wavefront distortion. Patent document CN114594633A discloses a high laser damage threshold transmissive optically addressed liquid crystal spatial light modulator for 1053nm linearly polarized light beam shaping. It uses gallium nitride (GaN) as the transparent conductive layer and zinc oxide (ZO) film as the photoconductive material. Compared to existing liquid crystal spatial light modulators using liquid crystal cells, it achieves a higher damage threshold for high-energy lasers. Compared to reflective high-damage spatial light modulators, it avoids the black gate effect and simplifies the structure. However, it requires processing a ZO film on GaN, involving both the photoconductive ZO film processing and the high-density bonding of ZO and GaN materials, which presents certain processing difficulties given current domestic and international technology levels. Our research group's patent application, "Transmissive High Damage Threshold Optically Addressable Spatial Light Modulator" (CN116736584A), is based on the concept of plasma electrodes in existing technology and combines it with the device structure of optically addressed spatial light modulators. By rationally designing the relative positions of the photoconductive crystal, the photoconductive crystal serves as both the liquid crystal alignment layer and the substrate layer of the plasma electrode (discharge gas). This not only enables optically addressed spatial light modulators to operate in transmission mode, but also achieves high damage threshold characteristics for the device. However, the plasma electrode requires a high voltage drive of over 10,000 volts, while the liquid crystal layer typically only requires a stable AC voltage drive of less than 5 volts. Commonly used liquid crystal devices usually only require a drive voltage of tens of volts. Therefore, there are extremely high requirements for the output stability of the 10,000-volt high-voltage drive, which still presents certain processing difficulties given the current domestic and international technological level. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an optically addressed liquid crystal cell and its transmissive high-damage-threshold spatial light modulator. Existing optically addressed spatial light modulators typically employ a two-layer voltage divider structure in their circuit architecture. This invention, however, designs a three-layer voltage divider circuit structure, adding a voltage divider medium that contacts the photoconductive crystal. This fills the space between the transparent conductive substrate and the photoconductive crystal with the voltage divider medium, thereby arranging the voltage divider medium, photoconductive crystal, and liquid crystal layer in series in the electrical structure. This design avoids direct contact between the photoconductive crystal surface and the conductive film layer or conductive gas, reducing the difficulty of device fabrication and manufacturing, and eliminating the need for a high-stability, 10,000-volt driving source, allowing the device to operate under conventional AC voltage.

[0006] The technical solution of the present invention is as follows:

[0007] A light-addressable liquid crystal cell includes a first transparent conductive substrate, a voltage-dividing medium, a photoconductive crystal layer, a first liquid crystal alignment layer, a liquid crystal layer, a second liquid crystal alignment layer, a second transparent conductive substrate, liquid crystal spacers, and an AC voltage source. The AC voltage source is connected between the first transparent conductive substrate and the second transparent conductive substrate. The voltage-dividing medium is characterized by being disposed between the first transparent conductive substrate and the photoconductive crystal layer. The first transparent conductive substrate serves two purposes: firstly, to provide a supporting substrate for the voltage-dividing medium; and secondly, to create a uniform surface voltage distribution on the side of the voltage-dividing medium closest to the first transparent conductive substrate. The voltage-dividing medium prevents direct contact between the photoconductive crystal layer and a conductive film layer or a conductive gas, thus forming a series structure between the voltage-dividing medium, the photoconductive crystal layer, and the liquid crystal layer. This allows the voltage generated by the AC voltage source to be applied to the photoconductive crystal layer and the liquid crystal layer even without conductive material on the side of the photoconductive crystal layer.

[0008] The resistivity ρ1 of the voltage dividing medium and the resistivity ρ2 of the liquid crystal layer satisfy the following relationship:

[0009] 1 / 10ρ2≤ρ1≤10ρ2

[0010] The thickness d1 of the voltage dividing medium and the thickness d2 of the liquid crystal layer satisfy the following relationship:

[0011] 1 / 10d2≤d1≤10d2

[0012] The first transparent conductive substrate and the second transparent conductive substrate are any one of the following materials: a sapphire substrate coated with a gallium nitride thin film layer; a gallium nitride crystal; a gallium oxide crystal; a sapphire, quartz, or K9 substrate coated with an indium tin oxide film layer.

[0013] The optical guide crystal layer has a thickness >0.5mm and has no absorption or very little absorption in the modulated laser band; when the optical guide crystal layer is irradiated by a light beam with a wavelength in the range of 350nm-500nm, the material conductivity decreases as the intensity of the irradiated light increases.

[0014] The transmissive high damage threshold spatial light modulator employing the above-mentioned optically addressed liquid crystal cell further includes a patterned photosensitive light generating unit and a dichroic mirror. The patterned photosensitive light emitted by the patterned photosensitive light generating unit is reflected by the dichroic mirror and then transmitted sequentially through the first transparent conductive substrate and the voltage dividing medium before being imaged onto the photoconductive crystal layer.

[0015] Furthermore, the photosensitive light generation unit includes a photosensitive collimated output light source, a polarization cube, an electrically addressed spatial light modulator, and an imaging lens. The collimated light emitted by the photosensitive collimated output light source is sequentially transmitted through the polarization cube, reflected by the electrically addressed spatial light modulator, reflected by the polarization cube, and transmitted through the imaging lens before being output.

[0016] Furthermore, the electrically addressed spatial light modulator is a reflective amplitude-type electrically addressed spatial light modulator.

[0017] Furthermore, the dichroic mirror has a reflectivity of >95% for the output light of the patterned photosensitive light generation unit at 45 degrees and a transmittance of >95% for the modulated laser wavelength band incident at 45 degrees.

[0018] Compared with the prior art, the advantages and features of the present invention are as follows:

[0019] This invention adds a voltage-dividing medium in contact with the photoconductive crystal, filling the space between the transparent conductive substrate and the photoconductive crystal with the voltage-dividing medium. The equivalent circuit exhibits a three-layer voltage-dividing structure, further enabling the voltage-dividing medium, photoconductive crystal, and liquid crystal layer to be distributed in series. By rationally designing the total voltage applied to the optically addressed device, the voltage division of the liquid crystal layer under different photosensitive light intensities can be kept within a normal range, allowing the device to operate in amplitude or phase modulation modes. This invention not only enables the optically addressed spatial light modulator to operate in transmission mode but also achieves a high damage threshold characteristic for the device.

[0020] Compared with patent CN114594633A, this invention avoids the processing of conductive films such as zinc oxide on the surface of the photoconductor crystal, which greatly reduces the difficulty of device processing and fabrication. Compared with patent CN116736584A, this invention avoids direct contact between the surface of the photoconductor crystal and the conductive gas, avoids the need for a high-stability voltage driving source of 10,000 volts, and enables the device to operate under conventional AC voltage driving. Attached Figure Description

[0021] Figure 1This is a schematic diagram of the structure of the optically addressed liquid crystal cell and its transmissive high damage threshold spatial light modulator of the present invention;

[0022] Figure 2 This is a schematic diagram of an embodiment of the optically addressed liquid crystal cell 1 in this invention;

[0023] Figure 3 This is a schematic diagram of an embodiment of the patterned photosensitive light generating unit 2 in this invention;

[0024] Figure 4 This is a measured effect diagram of the spatial shaping of a 1053nm wavelength beam demonstrated in this invention;

[0025] In the figure, 1-optically addressed liquid crystal unit, 1a-first transparent conductive substrate, 1b-voltage divider medium, 1c-photoconductive crystal layer, 1d-first liquid crystal alignment layer, 1e-liquid crystal layer, 1f-second liquid crystal alignment layer, 1g-second transparent conductive substrate, 1h-liquid crystal spacer, 1i-AC voltage source, 2-patterned photosensitive light generation unit, 2a-photosensitive light collimation output light source, 2b-polarization cube, 2c-electrically addressed spatial light modulator, 2d-imaging lens, 3-dichroic mirror. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0027] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of the optically addressed liquid crystal cell and its transmissive high damage threshold spatial light modulator of the present invention. As can be seen from the figure, the optically addressed liquid crystal cell and its transmissive high damage threshold spatial light modulator of the present invention include an optically addressed liquid crystal cell 1, a patterned photosensitive light generating unit 2, and a dichroic mirror 3.

[0028] Figure 2 This is a schematic diagram of an embodiment of the optically addressed liquid crystal cell 1 of the present invention. As shown in the figure, the optically addressed liquid crystal cell 1 includes a first transparent conductive substrate 1a, a voltage dividing medium 1b, a photoconductive crystal layer 1c, a first liquid crystal alignment layer 1d, a liquid crystal layer 1e, a second liquid crystal alignment layer 1f, a second transparent conductive substrate 1g, a liquid crystal spacer 1h, and an AC voltage source 1i. The AC voltage source 1i is connected between the first transparent conductive substrate 1a and the second transparent conductive substrate 1g. The voltage dividing medium 1b, the photoconductive crystal layer 1c, the first liquid crystal alignment layer 1d, the liquid crystal layer 1e, and the second liquid crystal alignment layer 1f are arranged sequentially between the first transparent conductive substrate 1a and the second transparent conductive substrate 1g.

[0029] The first transparent conductive substrate 1a and the second transparent conductive substrate 1g can be any of the following materials:

[0030] (1) A sapphire substrate coated with a gallium nitride (n-type doped) silicon thin film, wherein the gallium nitride carrier concentration is 1×10⁻⁶. 18 cm -3 ~1×10 19 cm -3 The thickness of the gallium nitride thin film is 5 μm, and the thickness of the sapphire substrate is 0.3 mm to 0.5 mm.

[0031] (2) A sapphire substrate coated with a magnesium gallium nitride (p-type doped) thin film layer, wherein the magnesium gallium nitride carrier concentration is 1×10⁻⁶. 18 cm -3 ~1×10 19 cm -3 The thickness of the gallium nitride thin film is 5 μm, and the thickness of the sapphire substrate is 0.3 mm to 0.5 mm.

[0032] (3) Silicon-doped gallium nitride crystal with a thickness of 1 mm to 3 mm.

[0033] (4) Magnesium-doped gallium nitride crystal with a thickness of 1 mm to 3 mm.

[0034] (5) A sapphire substrate coated with an indium tin oxide film, wherein the thickness of the indium tin oxide film is 10nm-100nm and the thickness of the sapphire substrate is 1mm-3mm.

[0035] (6) A quartz substrate coated with an indium tin oxide film, wherein the thickness of the indium tin oxide film is 10nm-100nm and the thickness of the quartz substrate is 1mm-3mm.

[0036] (7) A K9 substrate coated with an indium tin oxide film, wherein the thickness of the indium tin oxide film is 10nm-100nm and the thickness of the K9 substrate is 1mm-3mm.

[0037] The pressure dividing medium 1b can be air, and its thickness can be controlled by liquid crystal spacer silicon spheres and other materials with micron-level thickness; it can also be quartz or K9 glass sheets with a thickness within 100 micrometers.

[0038] The thickness d of the liquid crystal layer 1e is controlled by the liquid crystal spacer 1h. When the optically addressed spatial light modulator is amplitude-type, the liquid crystal layer 1e operates in twisted nematic mode, and its liquid crystal layer thickness d and liquid crystal birefringence Δn satisfy the following: When the optically addressed spatial optical modulator is phase-type and phase modulation capability is required... When the liquid crystal layer 1e operates in nematic mode, its thickness d and birefringence Δn satisfy the following: The optical guide crystal layer 1c can be a 1mm thick bismuth silicate single crystal or bismuth germanate single crystal, and is treated with double-sided anti-reflection.

[0039] The first liquid crystal alignment layer 1d can be made of polyimide or SD1 material.

[0040] The second liquid crystal alignment layer 1f can be made of polyimide or SD1 material.

[0041] The effective voltage value V of the AC voltage source 1i RMS The voltage range is 10V-200V, the frequency range is 50Hz-1000Hz, and both the voltage amplitude and frequency are adjustable.

[0042] Figure 3 This is a schematic diagram of an embodiment of the patterned photosensitive light generation unit 2 in this invention. As shown in the figure, the patterned photosensitive light generation unit 2 includes a photosensitive collimated output light source 2a, a polarization cube 2b, an electrically addressed spatial light modulator 2c, and an imaging lens 2d. The collimated light emitted from the photosensitive collimated output light source 2a is transmitted through the polarization cube 2b, reflected by the electrically addressed spatial light modulator 2c, reflected again by the polarization cube 2b, and transmitted through the imaging lens 2c before being output as patterned photosensitive light. In this embodiment, the photosensitive collimated output light source 2a includes a blue LED and a collimating lens assembly. The center wavelength of the output light can be set around 460nm, and the output spot size is less than Φ20mm. The polarization cube 2b is a polarization beam splitter cube, model PBS251, from Thorlabs. The electrically addressed spatial light modulator 2c is a reflective amplitude-type electrically addressed spatial light modulator, which can be an LCOS-type spatial light modulator manufactured by companies such as Hamamatsu (Japan), BNS (USA), or UPOLABS (China).

[0043] The patterned photosensitive light emitted by the patterned photosensitive light generating unit 2 is sequentially reflected by the dichroic mirror 3, transmitted through the first transparent conductive substrate 1a and the voltage dividing medium 1b, and then imaged onto the photoconductive crystal layer 1c. The voltage dividing medium 1b fills the space between the first transparent conductive substrate 1a and the photoconductive crystal layer 1c.

[0044] The dichroic mirror 3 has a reflectivity of over 99% for beams incident at 45 degrees in the 460nm band.

[0045] Figure 4This is a measured effect diagram demonstrating the spatial shaping of a 1053nm wavelength beam according to one of the above embodiments. In this embodiment, the optically addressed liquid crystal unit 1 has the following structure: the first transparent conductive substrate 1a is a K9 substrate coated with an indium tin oxide film layer, the thickness of the indium tin oxide film layer is 50nm, and the thickness of the K9 substrate is 3mm; the voltage dividing medium 1b is air with a thickness of 5µm, and the thickness is controlled by adding liquid crystal spacer silicon spheres at the edges; the photoconductive crystal layer 1c is a 1mm thick bismuth silicate single crystal, and is treated with double-sided anti-reflection; the first liquid crystal alignment layer 1d and the second liquid crystal alignment layer 1f are both polyimide materials; the thickness of the liquid crystal layer 1e is 5µm, and the liquid crystal spacer 1h is a silicon sphere material with a diameter of 5µm; the effective voltage value V of the AC voltage source 1i is... RMS Set to 42V and frequency to 800Hz.

Claims

1. A light-addressable liquid crystal cell, comprising a first transparent conductive substrate (1a), a voltage divider medium (1b), a photoconductive crystal layer (1c), a first liquid crystal alignment layer (1d), a liquid crystal layer (1e), a second liquid crystal alignment layer (1f), a second transparent conductive substrate (1g), liquid crystal spacers (1h), and an AC voltage source (1i), wherein the AC voltage source (1i) is connected between the first transparent conductive substrate (1a) and the second transparent conductive substrate (1g), characterized in that, A voltage divider medium (1b) is disposed between the first transparent conductive substrate (1a) and the photoconductive crystal layer (1c). The first transparent conductive substrate (1a) serves to provide a supporting substrate for the voltage divider medium (1b) and to form a uniform surface voltage distribution on the side of the voltage divider medium (1b) close to the first transparent conductive substrate (1a). The voltage divider medium (1b) is used to avoid direct contact between the photoconductive crystal layer (1c) and the conductive film layer or conductive gas, so that the voltage divider medium (1b), the photoconductive crystal layer (1c), and the liquid crystal layer (1e) form a series structure. Thus, even without conductive material on the side of the photoconductive crystal layer (1c), the voltage generated by the AC voltage source (1i) can be applied to the photoconductive crystal layer (1c) and the liquid crystal layer (1e).

2. The optically addressed liquid crystal unit according to claim 1, characterized in that, The resistivity ρ1 of the voltage divider medium (1b) and the resistivity ρ2 of the liquid crystal layer (1e) satisfy the following relationship: 1 / 10ρ2≤ρ1≤10ρ 2。 3. The optically addressed liquid crystal unit according to claim 1, characterized in that, The thickness d1 of the voltage dividing medium (1b) and the thickness d2 of the liquid crystal layer (1e) satisfy the following relationship: 1 / 10d2≤d1≤10d 2。 4. The optically addressed liquid crystal unit according to claim 1, characterized in that, The first transparent conductive substrate (1a) and the second transparent conductive substrate (1g) are any one of the following materials: a sapphire substrate coated with a gallium nitride thin film layer; a gallium nitride crystal; a gallium oxide crystal; a sapphire, quartz, or K9 substrate coated with an indium tin oxide film layer.

5. The optically addressed liquid crystal unit according to claim 1, characterized in that, The optical guide crystal layer (1c) has a thickness >0.5mm and has no absorption or very little absorption in the modulated laser band; when the optical guide crystal layer (1c) is irradiated by a light beam with a wavelength in the range of 350nm-500nm, the material conductivity decreases as the intensity of the irradiated light increases.

6. A transmissive high-damage-threshold spatial light modulator employing any one of the optically addressed liquid crystal cells according to claims 1-5, characterized in that, It also includes a patterned photosensitive light generating unit (2) and a dichroic mirror (3). The patterned photosensitive light emitted by the patterned photosensitive light generating unit (2) is reflected by the dichroic mirror (3) and then transmitted through the first transparent conductive substrate (1a) and the voltage dividing medium (1b) in sequence before being imaged onto the photoconductive crystal layer (1c).

7. The transmissive high-damage-threshold spatial light modulator according to claim 6, characterized in that, The photosensitive light generation unit (2) includes a photosensitive collimated output light source (2a), a polarization cube (2b), an electrically addressed spatial light modulator (2c), and an imaging lens (2d). The collimated light emitted by the photosensitive collimated output light source (2a) is transmitted through the polarization cube (2b), reflected by the electrically addressed spatial light modulator (2c), reflected by the polarization cube (2b), and transmitted through the imaging lens (2d) before being output.

8. The transmissive high-damage-threshold spatial light modulator according to claim 7, characterized in that, The electrically addressed spatial light modulator (2c) is a reflective amplitude-type electrically addressed spatial light modulator.

9. The transmissive high-damage-threshold spatial light modulator according to claim 6, characterized in that, The dichroic mirror (3) has a reflectivity of >95% for the output light of the patterned photosensitive light generating unit (2) at 45 degrees and a transmittance of >95% for the modulated laser band incident at 45 degrees.

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