Optical device cover and optical component

Abstract

Adding a heat-generating layer to the inner coating of an optical device cover increases the number of coating layers, which reduces transmittance. [Solution] The cover according to the disclosed technology is a cover for an optical device that transmits light emitted from a light source to the outside, and comprises a cover substrate, a metal fine wire arranged on the light source side of the cover substrate, and an anti-reflective layer that embeds and covers the metal fine wire. In other words, the disclosed technology realizes both a heat-generating function and an anti-reflective function in a single layer, thereby reducing the number of layers of internal coating.

Description

Technical Field

[0001] The disclosed technology relates to covers for optical devices such as LiDAR.

Background Art

[0002] LiDAR is an abbreviation for Light Detection And Ranging, and refers to a remote sensing technology that irradiates an object with light using near-infrared light, visible light, or ultraviolet light, and measures the distance by capturing the reflected light with a photosensor. Most often, near-infrared laser light is pulsed and the time difference until it hits an object and bounces back is measured to measure distance, position, and shape in three dimensions. For example, it is used in highly automated driving systems.

[0003] Fig. 1 schematically shows how LiDAR measures the inter-vehicle distance. LiDAR 103 is mounted on vehicle 101. LiDAR 103 includes a light source 105 and a photosensor 106. The irradiation light that has passed through the cover 104 that is transparent to near-infrared light hits vehicle 102, and the reflected light passes through the cover 104 again and is detected by the photosensor 106.

[0004] Fig. 2 is a partially enlarged view of cover 104. The cover has a cover body 201 coated with an outer surface coating 202 and an inner surface coating 203. The outer surface coating 202 serves to prevent dirt and smoothly guide the reflected light to the photosensor. The inner surface coating 203 serves to smoothly guide the irradiation light to the outside. Note that the thickness ratio is different from the actual one.

[0005] By the way, since LiDAR uses a near-infrared laser, light absorption and scattering by moisture become problems. In particular, when snow adheres to the outer surface of the cover in front of the LiDAR or condensation occurs on the inner surface, the snow and water droplets inhibit the transmission of the near-infrared laser of the LiDAR. Therefore, a function to eliminate snow accumulation and condensation on the optical window is required at low temperatures. Figure 3 shows a case for an optical device according to a conventional technology (Patent Document 1) that aims to melt snow and eliminate condensation. Particular attention will be paid to the internal coating in this explanation.

[0006] The optical device case described in Patent Document 1 has a resistive heating element 301 (a thin metal film or a transparent conductive film) inside a light-transmitting member (cover body) 201. A moth-eye film 303 is fixed to the resistive heating element 301 via an adhesive layer 302. The moth-eye film 303 serves to prevent condensation and reflection. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International public access number WO2018 / 180421 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Adding a heat-generating layer to the internal coating presents a challenge: it increases the number of coating layers, leading to a decrease in transmittance. [Means for solving the problem]

[0009] To solve the above problems, the cover according to the disclosed technology is a cover for an optical device that transmits light emitted from a light source to the outside, and comprises a cover substrate, a metal fine wire arranged on the light source side of the cover substrate, and an anti-reflective layer that embeds and covers the metal fine wire. In other words, the disclosed technology realizes both a heat-generating function and an anti-reflective function in a single layer, thereby reducing the number of layers of internal coating. [Effects of the Invention]

[0010] According to the disclosed technology, reducing the number of layers reduces interfacial reflection and improves transmittance. Furthermore, reducing the number of layers also reduces the production process, enabling the creation of inexpensive optical device covers. [Brief explanation of the drawing]

[0011] [Figure 1] A diagram illustrating an example of applying LiDAR to measuring the distance between vehicles. [Figure 2] A close-up view of a portion of the optical device cover. [Figure 3] A diagram illustrating a case for an optical device based on conventional technology. [Figure 4] A diagram illustrating the configuration of the internal coating related to the disclosed technology. [Figure 5] A diagram illustrating the moth-eye structure. [Figure 6] A diagram illustrating an example of the procedure for forming an anti-reflective coating that also serves as an overcoat. [Modes for carrying out the invention]

[0012] The embodiments of the disclosed technology will be described in detail below. Components with the same function will be numbered identically, and redundant explanations will be omitted.

[0013] [First Embodiment] The disclosed technology achieves both heat-generating and anti-reflective functions in a single layer, reducing the number of layers required for the internal coating. Figure 4 shows the configuration of the internal coating related to the disclosed technology. The heater substrate 402 is bonded to the cover body 201 via an adhesive layer 401. A metal fine wire 404 (for example, a silver fine wire) is placed on the heater substrate 402. The Joule heat emitted by the metal fine wire 404 is diffused by the heater substrate 402 and transferred to the cover body 201. The thin metal wire 404 is covered with an overcoat-anti-reflective film 403. To prevent reflection, a moth-eye structure is provided on the light source side of the overcoat-anti-reflective film 403.

[0014] Figure 5 is an illustration of the moth-eye structure, taken from reference 1. The moth-eye structure consists of regularly arranged bell-shaped protrusions, with the outermost surface (a) being almost entirely air, and the cross-sectional area of ​​the protrusions increasing as you go downwards. Thanks to this bell shape, the refractive index changes smoothly, so light passing through the protrusions is not reflected significantly. To obtain the same low reflectance, the protrusions do not necessarily have to be bell-shaped, and any structure in which the cross-sectional area of the protrusions increases as it goes downward is acceptable. Such a structure will be referred to as a moth-eye type structure in this specification.

[0015] Reference 1: Gyokuzawa, "Development of High-performance Anti-reflection Films Imitating the Eyes of Moths", Journal of the Japan Intellectual Property Association, Vol. 13, No. 2, pp. 43-49, 2016.

[0016] <Requirements for the overcoat function> The overcoat and anti-reflection film 403 is required to have high insulation, high moisture resistance, and low hygroscopicity. This is because when the fine metal wires come into contact with moisture, they deteriorate due to oxidation and the like. Also, this is because insulation failure occurs due to migration in which the metal ionizes and moves and deposits. Therefore, the moisture resistance after film curing is preferably defined by the water absorption rate, which is the weight loss rate when the moth-eye ink (described later) after curing is immersed in water for 24 hours and then heated at 50°C for 60 minutes by thermogravimetry, and is 2% or less, and more preferably 0.7% or less. Also, the volume resistivity is preferably 10 12 Ω·cm or more, and more preferably 10 17 Ω·cm or more. However, when the volume resistivity of the resin is high in moth-eye molding, adhesion of foreign matter due to charging during mold release becomes a problem. As a countermeasure, it is preferable to perform an antistatic treatment on the mold surface or add an antistatic layer to the outermost layer of the moth-eye structure.

[0017] <Requirements for the anti-reflection function> In the case of moth-eye processing for near-infrared rays, in order to improve the low-reflection performance, it is necessary to increase the aspect ratio of the height / width of the uneven shape. The pitch and height of the moth-eye type structure are preferably 200 nm or more from the viewpoint of the structural size effective for reducing the reflection of near-infrared rays, and preferably 1000 nm or less from the viewpoint of the formability of the structure. From the above, a pitch of about 200 nm to 1000 nm and a height of about 200 nm to 1000 nm are desirable, and in order to reduce the reflectance at a wide angle, a pitch of about 400 nm to 1000 nm and a height of about 700 nm to 1000 nm are more desirable. Thereby, antireflection of near-infrared rays with wavelengths from 800 nm to 1600 nm or a part of the above wavelength range is achieved. Particularly in the Lidar application, antireflection is performed only in a partial wavelength range such as 910 nm ± 30 nm or 1550 nm ± 10 nm. Note that the pitch of the moth-eye type structure refers to the average interval of the apexes of the protrusions.

[0018] Fig. 6 shows an example of the formation procedure of the antireflection film 403 also used as an overcoat. Prepare a heater substrate printed with a metal mesh pattern (Fig. 6(a)). Apply moth-eye ink 601 onto the heater substrate and press a moth-eye uneven transfer mold 602 onto the moth-eye ink (Fig. 6(b)). Note that the moth-eye ink is a mixed material of a photocurable resin before light irradiation.

[0019] Irradiate the moth-eye ink with UV light to cure it while maintaining the moth-eye shape. When the moth-eye uneven transfer mold is, for example, a quartz mold and transmits UV light, UV irradiation is performed from the mold side (Fig. 6(c)). When the moth-eye uneven transfer mold is, for example, a nickel mold or a silicon mold and does not transmit UV light, UV irradiation is performed from the heater substrate side.

[0020] After the moth-eye ink has cured, the moth-eye relief transfer mold 602 is removed, and the overcoat / anti-reflective film 403 is completed (Figure 6(d)). Considering the release properties of the mold and the overcoat / anti-reflective film, and the durability of the moth-eye structure during demolding, the indentation modulus measured by the ultra-micro hardness testing system (Fischer Scope HM2000, manufactured by Fischer) after curing should be 5 Pa to 2000 MPa, and 500 Pa to 2000 MPa is even more desirable.

[0021] The overcoat-integrated anti-reflective coating 403 must meet the above requirements. Through diligent research, the inventors have discovered the optimal composition of the mixed materials for forming the overcoat-integrated anti-reflective coating 403. These are as follows:

[0022] <First composition> [Table 1]

[0023] <Second composition> [Table 2]

[0024] <Third composition> [Table 3]

[0025] The above is a description of the first embodiment. While IBXA, LA, and ISTA were given as specific examples of monofunctional monomers, the requirements for monofunctional monomers based on their molecular structure are that straight-chain, branched-chain, or alicyclic acrylic monomers or methacrylic monomers with eight or more carbon atoms in the side chain are effective in preventing oxidation of metal nanowires. Furthermore, while TMP-A and DHPA were mentioned as polyfunctional monomers, in terms of molecular properties, acrylic monomers or methacrylic monomers having three or more radical reactive groups are effective in improving the strength of the moth-eye structure. [Explanation of Symbols]

[0026] Vehicles 101, 102 103 LiDAR 104 Cover 105 Light source 106 Light Sensor 201 Cover body 202 Exterior coating 203 Internal coating 301 Resistive heating element 302 Adhesive layer 303 Moth-eye film 401 Adhesive layer 402 Heater base material 403 Overcoat and Anti-reflective coating 404 Fine metal wire 405 Moth-eye structure 601 Moth Eye Ink 602 Moth-eye relief transfer mold

Claims

1. A cover for an optical device that transmits light emitted from a light source to the outside, Cover base material and A thin metal wire is placed on the light source side of the cover substrate, The aforementioned metal wires are embedded and covered in an anti-reflective layer. An optical device cover equipped with [a specific feature / feature].

2. An optical device cover according to claim 1, The anti-reflective layer has a moth-eye structure facing the light source, The aforementioned moth-eye structure reduces the reflectance and transmits light with wavelengths from 800 nm to 1600 nm, or a portion of light in the aforementioned wavelength range. An optical device cover characterized by the following features.

3. The optical device cover according to claim 2, The aforementioned moth-eye structure has protrusions with a pitch of 200 nm to 1000 nm and a height of 200 nm to 1000 nm. An optical device cover characterized by the following features.

4. The optical device cover according to claim 1 The aforementioned anti-reflective layer is made by photocuring a photocurable resin, and its moisture resistance is defined as a water absorption rate of 2% or less, as determined by the weight loss 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, and its volume resistivity is 10% 12 It has insulating properties of Ω·cm or higher and a hardness with an elastic modulus ranging from 5 Pa to 2000 MPa. An optical device cover characterized by the following features.

5. An optical device cover according to claim 1, The anti-reflective layer mainly consists of an imide skeleton oligomer. An optical device cover characterized by the following features.

6. An optical device cover according to claim 1, The anti-reflective layer is obtained by photocuring a photocurable resin, and the photocurable resin contains a linear, branched, or alicyclic acrylic monomer or methacrylic monomer with 8 or more carbon atoms in its side chains. An optical device cover characterized by the following features.

7. An optical device cover according to claim 1, The anti-reflective layer is obtained by photocuring a photocurable resin, and the photocurable resin contains a polyfunctional acrylic monomer or methacrylic monomer having three or more radical reactive groups. An optical device cover characterized by the following features.

8. The optical device cover according to claim 2, The aforementioned anti-reflective layer improves the strength of the moth-eye structure with fillers. An optical device cover characterized by the following features.

9. The optical device cover according to claim 2, The refractive index of the anti-reflective layer was controlled by a filler. An optical device cover characterized by the following features.

10. The optical device cover according to claim 2, The anti-reflective layer was formed by curing a photopolymerized compound using a photopolymerization initiator. An optical device cover characterized by the following features.

11. A base material on which thin metal wires are arranged, The system comprises an anti-reflective layer that embeds and covers the aforementioned thin metal wires, The aforementioned anti-reflective layer is made by photocuring a photocurable resin, and after immersing the cured photocurable resin in water for 24 hours, it has moisture resistance defined by the weight loss rate when heated at 50°C for 60 minutes by thermogravimetric analysis, with a water absorption rate of 2% or less. Optical components.

Images