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US-20260126565-A1 - HARDENED OPTICAL WINDOWS WITH ANTI-REFLECTIVE FILMS HAVING LOW VISIBLE REFLECTANCE AND TRANSMISSION FOR INFRARED SENSING SYSTEMS

US20260126565A1US 20260126565 A1US20260126565 A1US 20260126565A1US-20260126565-A1

Abstract

Described herein is a window ( 24 ) comprising first and second layered films ( 36.38 ). The window ( 24 ) exhibits a maximum hardness, measured at the first layered film ( 36 ) and by the Berkovich Indenter Hardness Test. of at least 8 GPa to facilitate durability and scratch resistance. The quantity, the thicknesses, number, and materials of alternating layers of the first and second layered films ( 36,38 ) are configured so that the window ( 24 ) has a relatively high transmittance (e.g., greater than 90%) and low reflectance (e.g., less than 5%) over a 50 nm wavelength range of interest centered at a wavelength between 850 nm and 950 nm, while still exhibiting a dark, opaque appearance when the window ( 24 ) is viewed from the first layered film ( 36 ).

Inventors

  • Casey James Gonta
  • Joshua Michael Jacobs
  • RUI LUO
  • Chuan Ni
  • Sang Ki Park

Assignees

  • CORNING INCORPORATED

Dates

Publication Date
20260507
Application Date
20231007

Claims (20)

  1. 1 . A window for a sensing system comprising: a substrate comprising a first surface and a second surface, the first surface and the second surface being primary surfaces of the substrate; a first layered film disposed on the first surface of the substrate, the first layered film comprising alternating layers of one or more higher refractive index materials and one or more lower refractive index materials, wherein refractive indices of the one or more higher refractive index materials of the first layered film are higher than refractive indices of the one or more lower refractive index materials of the first layered film; a second layered film disposed on the second surface of the substrate, the second layered film comprising alternating layers of one or more higher refractive index materials and one or more lower refractive index materials, wherein refractive indices of the one or more higher refractive index materials of the second layered film are higher than refractive indices of the one or more lower refractive index materials of the second layered film; and a maximum hardness, measured at the first layered film and by the Berkovich Indenter Hardness Test, of at least 8 GPa, wherein the quantity, the thicknesses, number, and materials of the alternating layers of the first and second layered films are configured so that the window has: an average percentage transmittance, calculated over a 50 nm wavelength range of interest centered at a wavelength between 850 nm and 950 nm, of greater than 90% for light incident on the first surface and the second surface at angles of incidence of less than or equal to 15°; an average reflectance, calculated over the 50 nm wavelength range of interest between 850 nm and 950 nm, of less than 4% for light incident on the first surface and the second surface at angles of less than or equal to 15°; and an average percentage transmission, calculated from 400 nm to 700 nm, of less than 5% for light incident on the first surface and the second surface at angles of incidence of less than or equal to 15°.
  2. 2 . The window of claim 1 , wherein the quantity, the thicknesses, number, and materials of the alternating layers of the first and second layered films are configured so that the window has an average P polarization transmittance and an average S polarization transmittance, calculated over the 50 nm wavelength range of interest, of greater than 85% for light incident on the first surface and the second surface at angles of incidence of less than or equal to 60°.
  3. 3 . (canceled)
  4. 4 . The window of claim 1 , wherein the quantity, the thicknesses, number, and materials of the alternating layers of the first and second layered films are configured so that the window has a CIELAB L* value for reflection of less than or equal to 37 for angles of incidence of less than or equal to 60° on the first layered film.
  5. 5 . (canceled)
  6. 6 . The window of claim 1 , wherein the quantity, the thicknesses, number, and materials of the alternating layers of the first and second layered films are configured so that the window has CIELAB a* and b* values for reflection of greater than or equal to −6.0 and less than or equal to 6.0 when viewed from a side of the first layered film.
  7. 7 . (canceled)
  8. 8 . The window of claim 1 , wherein: the refractive index of the substrate for electromagnetic radiation having a wavelength of 905 nm is from about 1.45 to about 1.55, the substrate is a glass substrate or a glass-ceramic substrate, the refractive index of the one or more higher refractive index materials is from about 1.7 to about 4.0, and wherein the refractive index of the one or more lower refractive index materials is from about 1.3 to about 1.6, and a difference in the refractive index of any of the one or more higher refractive index materials and any of the one or more lower refractive index materials is about 0.5 or greater.
  9. 9 . The window of claim 1 , wherein: one of the alternating layers of the first layered film that is farthest from the substrate forms a terminal surface material of the window, the terminal surface material of the window comprising the lower refractive index material, and the first layered firm comprises a scratch resistant layer formed of one of the one or more higher refractive index materials and having a thickness of greater than or equal to 1500 nm and less than or equal to 5000 nm.
  10. 10 . The window of claim 9 , wherein the scratch resistant layer is separated from the terminal surface by a plurality of the alternating layers of the one or more lower index materials and the one or more higher index materials of the first layered film, and wherein the scratch resistant layer is separated from the terminal surface by at least 1000 nm.
  11. 11 . (canceled)
  12. 12 . The window of claim 1 , wherein the one or more higher refractive index materials of the second layered film comprise silicon having an extinction coefficient of less than or equal to 0.01 over the 50 nm wavelength range of interest.
  13. 13 . (canceled)
  14. 14 . The window of claim 1 , wherein the second layered film comprises a layer of TCO material and two or more silicon layers, and wherein the two or more silicon layers are disposed between the layer of TCO material and the substrate.
  15. 15 . (canceled)
  16. 16 . The window of claim 14 , wherein the layer of TCO material comprises a thickness that is greater than or equal to 20 nm and less than or equal to 30 mm.
  17. 17 . The window of claim 16 , wherein the layer of TCO material is indium tin oxide and comprises an extinction coefficient that is less than or equal to 0.05 throughout the 50 nm wavelength range of interest.
  18. 18 . The window of claim 14 , wherein a silicon layer of the second layered film most proximate to the substrate comprises the smallest thickness of the two or more silicon layers.
  19. 19 . The window of claim 18 , wherein a combined thickness of the silicon layers contained in the second layered film is greater than or equal to 450 nm.
  20. 20 . The window of claim 12 , wherein a layer of the one or more higher refractive index materials in the second layered film is not silicon.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 63/414,128 filed on Oct. 7, 2022, and U.S. Provisional Application Ser. No. 63/525,029 filed on Jul. 5, 2023, the contents of which are relied upon and incorporated herein by reference in their entirety. FIELD OF THE DISCLOSURE The present disclosure relates to protective covers for sensor systems. Particularly, the present disclosure relates to protective covers including layered films so that the protective cover exhibits antireflective properties over a 50 nm wavelength of interest from 850 nm to 850 nm while exhibiting a dark, opaque appearance. BACKGROUND Light detection and ranging (“LIDAR”) systems include an electromagnetic radiation emitter and a sensor. The electromagnetic radiation emitter emits an electromagnetic radiation emitter beam, which may reflect off an object, and the sensor detects the reflected electromagnetic radiation emitter beam. The electromagnetic radiation emitter beams can be continuous wave, pulsed, frequency modulated, or otherwise distributed across a radial range to detect objects across a field of view. Information about the object can be deciphered from the properties of the detected reflected electromagnetic radiation emitter beam. Distance of the object from the electromagnetic radiation emitter beam can be determined from the time of flight from emission of the electromagnetic radiation emitter beam to detection of the reflected electromagnetic radiation emitter beam. If the object is moving, path and velocity of the object can be determined from shifts in radial position of the emitted electromagnetic radiation emitter beam being reflected and detected as a function of time, as well as from Doppler frequency measurements in some cases. LIDAR systems in automobiles, and other infrared sensing systems in exposed environments, such as aerospace or home security applications, need to be protected from the environment and various sources of damage, for example, with a covering lens or cover glass window. Vehicles are another potential application for LIDAR systems, with the LIDAR systems providing spatial mapping capability to enable assisted, semi-autonomous, or fully autonomous driving. In such applications, the electromagnetic radiation emitter and sensor are mounted on the roof of the vehicle or on a low forward portion of the vehicle. Electromagnetic radiation emitters emitting electromagnetic radiation having a wavelength outside the range of visible light, such as at 905 nm or 1550 nm are considered for vehicle LIDAR applications. To protect the electromagnetic radiation emitter and sensor from impact from rocks and other objects, a window is placed between the electromagnetic radiation emitter and sensor, and the external environment in the line of sight of the electromagnetic radiation emitter and sensor. A window is similarly placed between the electromagnetic radiation emitter/sensor and the external environment for other applications of the LIDAR system, such as aerospace and home security applications. However, there is a problem in that rocks and other objects impacting the window scratch and cause other types of damage to the window, which cause the window to scatter the emitted and reflected electromagnetic radiation emitter beams, thus impairing the effectiveness of the LIDAR system. SUMMARY The present disclosure solves that problem with a window that includes first and second layered films. The first layered film may face away from an electromagnetic radiation emitter/sensor when installed in a LIDAR system and include a scratch resistant layer embedded therein to provide damage resistance to the window. Thus, rocks and other objects impacting the window are less likely to cause defects to the window that scatter the emitted and reflected electromagnetic radiation from the LIDAR sensor, resulting in improved performance. In addition, the first and second layered films further include alternating layers of materials having different indices of refraction (including the material providing the hardness and scratch resistance), such that the number of alternating layers and their thicknesses can be configured so that the window has high transmissivity and low reflection in a desired wavelength range (e.g., over a 50 nm wavelength range about a center wavelength between 850 nm and 950 nm). The alternating layers of material may be further selected such that the window transmits and reflects relatively low amounts of radiation in the visible spectrum, thereby providing the window with aesthetically pleasing dark appearance while diminishing signal noise caused by visible light that may otherwise impinge on a detector of a LIDAR system. An aspect (1) of the present disclosure pertains to a window for a sensing system comprising: a substrate comprising a first surface and a second surface, the first surface and t