Optical device cover and optical component

Abstract

If a heat generating layer is arranged on the inner surface of the optical device cover in a coating manner, the number of layers of the coating is increased, and the transmittance is reduced. A cover according to the disclosed technology is an optical device cover that transmits light emitted from a light source to the outside, and is provided with a cover base material, a thin metal wire disposed on the light source side of the cover base material, and an anti-reflection layer embedded in and covering the thin metal wire. Namely, in the disclosed technology, the number of laminations of the inner surface coating layer is reduced by implementing a heat generation function and an anti-reflection function in one layer.

Description

Technical Field

[0001] The disclosed technology involves covers for optical devices such as LiDAR. Background Technology

[0002] LiDAR, short for Light Detection and Ranging, is a remote sensing technology that uses near-infrared, visible, and ultraviolet light to illuminate an object, captures the reflected light using light sensors, and determines the distance. In most cases, it involves illuminating an object with pulsed near-infrared laser light, measuring the time difference between its arrival and its bounce, and then determining the distance, position, and shape in three dimensions. For example, it is used in advanced autonomous driving systems.

[0003] Figure 1 This illustration schematically shows the use of LiDAR to determine workshop distances.

[0004] The LiDAR 103 is mounted on vehicle 101. The LiDAR 103 includes a light source 105 and an optical sensor 106. Illumination light passing through a near-infrared transparent cover 104 is irradiated onto vehicle 102, and the reflected light passes through the cover 104 again and is detected by the optical sensor 106.

[0005] Figure 2 This is a magnified view of a portion of the cover 104. The cover body 201 of the cover 104 is coated with an outer surface coating 202 and an inner surface coating 203. The outer surface coating 202 serves to prevent contamination and smoothly guide reflected light to the photosensor. The inner surface coating 203 serves to smoothly guide the irradiated light to the outside.

[0006] In addition, the thickness ratio is different from the actual thickness.

[0007] However, since LiDAR utilizes near-infrared lasers, light absorption and scattering caused by moisture become problematic. In particular, if snow adheres to the outer surface of the LiDAR cover or condensation forms on the inner surface, the snow and water droplets will obstruct the transmission of near-infrared laser light. Therefore, at low temperatures, a function to eliminate snow and condensation in the optical windows is required.

[0008] Figure 3 The housing for an optical device represents a prior art method for achieving snow melting and condensation elimination (Patent Document 1: International Publication WO2018 / 180421). Particular attention is paid to the inner surface coating.

[0009] The optical device housing of Patent Document 1 has a resistive heating element 301 (metal thin film or transparent conductive film) inside the light-transmitting component (cover body) 201. A moth-eye membrane 303 is fixed to the resistive heating element 301 via an adhesive layer 302. The moth-eye membrane 303 serves to prevent condensation and reflection. Summary of the Invention

[0010] If a heating layer is placed on the inner surface coating, there will be problems such as an increase in the number of coating layers and a decrease in transmittance.

[0011] To address the aforementioned problems, the disclosed technology involves an optical device cover that allows light emitted from a light source to pass through to the outside. It comprises a cover substrate, a fine metal wire disposed on the light source side of the cover substrate, and an anti-reflective layer embedded in and covering the fine metal wire. In other words, in the disclosed technology, the number of layers in the inner surface coating is reduced by achieving both heating and anti-reflective functions in a single layer.

[0012] According to publicly available technology, interface reflection is reduced and transmittance is increased by decreasing the number of stacked layers. Furthermore, by reducing the number of layers, manufacturing processes are also reduced, thus enabling the realization of low-cost optical device covers. Attached Figure Description

[0013] Figure 1 This is a diagram illustrating an example of applying LiDAR to workshop distance measurement.

[0014] Figure 2 This is a magnified view of a portion of the optical device cover.

[0015] Figure 3 This is a diagram illustrating the housing of an optical device in the prior art.

[0016] Figure 4 This is a diagram illustrating the structure of the inner surface coating involved in the disclosed technology.

[0017] Figure 5 It is a diagram illustrating the structure of a moth's eye.

[0018] Figure 6A This diagram illustrates an example of the formation steps of an outer coating that also serves as an anti-reflective film. It shows the process before the application of moth-eye ink.

[0019] Figure 6B This diagram illustrates the step of pressing a moth-eye embossing mold onto moth-eye ink during the formation of an outer coating that also serves as an anti-reflective film.

[0020] Figure 6C This diagram illustrates the step of irradiating moth-eye ink with UV light during the formation of an outer coating that also serves as an anti-reflective film.

[0021] Figure 6DThis diagram illustrates the step of removing the moth-eye embossed transfer mold during the formation of the outer coating antireflective film. Detailed Implementation

[0022] The embodiments of the disclosed technology will now be described in detail. Furthermore, structural parts with the same function will be labeled with the same reference numerals, and repeated descriptions will be omitted.

[0023] [First Implementation Method]

[0024] In publicly available technologies, the number of layers in the inner surface coating is reduced by achieving both heating and anti-reflective functions through a single layer. Figure 4 This is a diagram illustrating the structure of the inner surface coating involved in the disclosed technology.

[0025] The heater substrate 402 is bonded to the housing body 201 via an adhesive layer 401. Fine metal wires 404 (e.g., silver wires) are disposed on the heater substrate 402. The heater substrate 402 diffuses the Joule heat generated by the fine metal wires 404 and transfers it to the housing body 201.

[0026] The fine metal wire 404 is covered by an outer coating that also serves as an anti-reflective film 403. To prevent reflection, a moth-eye-shaped structure is provided on the light source side of the outer coating that also serves as an anti-reflective film 403.

[0027] Figure 5 This is a description of the moth-eye structure cited in reference 1. The moth-eye structure consists of regularly arranged bell-shaped protrusions, with the outermost surface (a) being roughly an air layer. The cross-sectional area of ​​the protrusions increases downwards. Due to this bell shape, the refractive index changes gradually, so light passing through the protrusions is not significantly reflected.

[0028] To achieve the same low reflectivity, the protrusion does not necessarily have to be bell-shaped; any structure where the cross-sectional area of ​​the protrusion increases downwards is acceptable. In this specification, such a structure is referred to as a moth-eye structure.

[0029] Reference 1: Uozu, [Development of a high-performance anti-reflective film that mimics the eyes of a moth], Journal of the Japan Intellectual Property Society, Vol.13, No.2, pp.43-49, 2016.

[0030] <Requirements for the Function of External Coating>

[0031] The outer coating, which also serves as an anti-reflective film, 403, requires high insulation, high moisture resistance, and low hygroscopicity. This is because if the metal wires come into contact with moisture, they will deteriorate due to oxidation and other factors. In addition, migration and precipitation caused by metal ionization can lead to poor insulation.

[0032] Therefore, regarding the moisture resistance of the cured film, the water absorption rate, defined by the weight reduction rate after immersing the cured moth-eye ink (described later) in water for 24 hours and then heating at 50°C for 60 minutes by thermogravimetric analysis, is preferably 2% or less, and more preferably 0.7% or less. Furthermore, the volume resistivity is preferably 10 Ω·cm. 12 Ω·cm or higher, more preferably 10 17 The volume resistivity of the resin is above Ω·cm. However, when the volume resistivity of the resin is high during moth-eye molding, the adhesion of foreign matter caused by the charge generated during demolding becomes a problem. As a countermeasure, it is preferable to perform antistatic treatment on the mold surface or to add an antistatic layer to the outermost layer of the moth-eye structure.

[0033] <Requirements for anti-reflective function>

[0034] In the fabrication of moth-eye structures for near-infrared applications, increasing the height-to-width ratio of the raised / lower-width shape is necessary to improve low-reflection performance. From the viewpoint of effective structural dimensions for low near-infrared reflection, the spacing and height of the moth-eye structure are preferably 200 nm or more, and from the viewpoint of structural formability, preferably 1000 nm or less. Based on the above, a spacing of approximately 200 nm to 1000 nm and a height of approximately 200 nm to 1000 nm are preferred. To reduce reflectivity at wide angles, a spacing of approximately 400 nm to 1000 nm and a height of approximately 700 nm to 1000 nm are more preferable. This achieves anti-reflection of near-infrared wavelengths from 800 nm to 1600 nm, or a portion of such wavelengths. Particularly in LiDAR applications, anti-reflection is achieved only in specific wavelength regions such as 910 nm ± 30 nm and 1550 nm ± 10 nm. Furthermore, the spacing of the moth-eye structure refers to the average interval between the apexes of the protrusions.

[0035] Figure 6 shows an example of the formation steps of the outer coating that also serves as an anti-reflective film 403.

[0036] Prepare heater substrate 402 with metal mesh pattern 404 printed on it. Figure 6A ).

[0037] Moth-eye ink 601 is applied to the heater substrate 402, and a moth-eye embossed transfer mold 602 is pressed onto the moth-eye ink 601. Figure 6B Additionally, moth-eye ink refers to a mixture of light-curing resins that are not exposed to light.

[0038] The moth-eye ink is cured by irradiating it with UV light while maintaining the shape of the moth eye. The moth-eye embossing mold 602 is, for example, a quartz mold, and UV light is irradiated from the mold side while the ink is being transmitted through the mold. Figure 6CThe moth-eye embossed transfer mold, for example, is a nickel mold or a silicon mold, which is subjected to UV irradiation from the substrate side of the heater without allowing UV light to pass through.

[0039] After the moth-eye ink has cured, remove the moth-eye embossed transfer mold 602 to complete the outer coating and anti-reflective film 403. Figure 6D Considering the demolding properties of the antireflective film that serves as both a mold and an outer coating, and the durability of the moth-eye structure during demolding, the indentation modulus of elasticity measured using a cured microhardness testing system (Fischer Scope HM2000) is preferably 5 Pa to 2000 MPa, and more preferably 500 Pa to 2000 MPa.

[0040] The outer coating antireflective film 403 needs to meet the above requirements. As a result of in-depth research, the inventors discovered the optimal composition of the mixed materials for forming the outer coating antireflective film 403. The details are as follows.

[0041] <First Group>

[0042] Table 1

[0043] Material Effect Principal component 1 imide backbone oligomers It imparts low moisture absorption and insulation properties. Principal component 2 acrylic oligomers It imparts flexibility to the cured film. Monofunctional monomer IBXA It imparts high hardness and low moisture absorption. Multifunctional monomers TMP-A It imparts high hardness (bridging properties). However, in order to keep it within the desired elastic modulus range, the number of functional groups was selected. solvent PGMA Adjust the ink viscosity to optimize the transferability of microstructures. Photopolymerization initiator Irg184 Impart UV curing properties

[0044] <Second Component>

[0045] Table 2

[0046] Material Effect Principal component 1 imide backbone oligomers It imparts low moisture absorption and insulation properties. Monofunctional monomer LA It imparts softness (aliphatic) and low hygroscopicity (aliphatic). Multifunctional monomers DPHA It imparts high hardness (crosslinking). Considering the balance with the softness of monofunctional monomers, a material with high crosslinking properties was selected. filler silicon dioxide It imparts high hardness and low refractive index, thereby improving the strength of the moth-eye structure. solvent PGME Adjust the ink viscosity to optimize the transferability of microstructures. Photopolymerization initiator Irg819 It imparts UV curing properties.

[0047] <Third Group>

[0048] Table 3

[0049] Material Effect Principal component 1 imide backbone oligomers It imparts low moisture absorption and insulation properties. Monofunctional monomer ISTA It imparts softness (aliphatic) and low hygroscopicity (aliphatic). Multifunctional monomers TMP-A It imparts high hardness (crosslinking). To converge to the desired elastic modulus, TMP-A with low crosslinking is selected. solvent MEK Adjust the ink viscosity to optimize the transferability of microstructures. Photopolymerization initiator Irg184 Impart UV curing properties

[0050] The above is a description of the first embodiment.

[0051] It should be noted that, as specific examples of monofunctional monomers, IBXA, LA, and ISTA are listed. However, when explaining the requirements of monofunctional monomers from the perspective of molecular structure, straight-chain, branched, or alicyclic acrylic monomers or methacrylic monomers with 8 or more carbon atoms in the side chain are effective in preventing the oxidation of metal wires.

[0052] In addition, TMP-A and DHPA are listed as multifunctional monomers. However, when describing the requirements of multifunctional monomers from the perspective of molecular properties, acrylic acid monomers or methacrylic acid monomers with more than three reactive groups with free radical properties are effective in improving the strength of moth-eye structures.

Claims

1. An optical device cover that allows light emitted from a light source to pass through to the outside, comprising: Cover substrate; Fine metal wires are disposed on the light source side of the cover substrate; An anti-reflective layer is embedded in and covers the metal wires.

2. The optical device cover as claimed in claim 1, characterized in that, The anti-reflective layer has a moth-eye-shaped structure facing the light source. The moth-eye structure allows light with wavelengths from 800 nm to 1600 nm, or a portion of that wavelength range, to pass through with low reflectivity.

3. The optical device cover as described in claim 2, characterized in that, The moth-eye-shaped structure has protrusions with a spacing of 200 nm to 1000 nm and a height of 200 nm to 1000 nm.

4. The optical device cover as claimed in claim 1, characterized in that, The anti-reflective layer is formed by photocuring a UV-curable resin and has a water absorption rate of less than 2%, defined as the weight loss rate after immersing the cured UV-curable resin in water for 24 hours and then heating it at 50°C for 60 minutes by thermogravimetric analysis, and a volume resistivity of 10. 12 Insulation properties above Ω·cm, and hardness with an elastic modulus of 5 Pa to 2000 MPa.

5. The optical device cover as claimed in claim 1, characterized in that, The antireflective layer is mainly composed of imide skeleton oligomers.

6. The optical device cover as claimed in claim 1, characterized in that, The anti-reflective layer is formed by photocuring a photocurable resin, which contains straight-chain, branched, or alicyclic acrylic monomers or methacrylic monomers with 8 or more carbon atoms in the side chains.

7. The optical device cover as claimed in claim 1, characterized in that, The anti-reflective layer is formed by photocuring a photocurable resin, which contains a polyfunctional acrylic monomer or methacrylic monomer with three or more reactive free radical groups.

8. The optical device cover as claimed in claim 2, wherein, The anti-reflective layer enhances the strength of the moth-eye structure through the use of fillers.

9. The optical device cover as claimed in claim 2, wherein, The refractive index of the antireflective layer is controlled by filler.

10. The optical device cover as claimed in claim 2, wherein, The anti-reflective layer is formed by curing a photopolymer compound using a photopolymerization initiator.

11. An optical component, comprising: A substrate configured with fine metal wires; and, An anti-reflective layer is embedded and covers the metal wires. The anti-reflective layer is formed by photocuring a photocurable resin and has a water absorption rate of less than 2%, defined by the weight reduction rate when the cured photocurable resin is immersed in water for 24 hours and then heated at 50°C for 60 minutes by thermogravimetric analysis.

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