Collimator filter

Patent metadata

Field	Value
Publication number	US-2021004557-A1
Application number	US-201916976712-A
Country	US
Kind code	A1
Filing date	Mar 8, 2019
Priority date	Mar 9, 2018
Publication date	Jan 7, 2021
Grant date	—

Abstract

A collimator filter (10) comprises an entry surface (11) to receive incident light (Li, Li′) at different angles of incidence (θi, θi′) and an exit surface (12) to allow output light (Lo) to exit from the collimator filter (10). A filter structure between the entry surface (11) and the exit surface (12) transmits only parts of the incident light (Li) having angles of incidence (θi) below a threshold angle (θmax). The filter structure comprises a patterned array of carbon nanotubes (1), wherein the nanotubes (1) are aligned extending in a principal transmission direction (Z) between the entry surface (11) and the exit surface (12). The nanotubes (1) are arranged to form a two dimensional pattern (P) transverse to the principal transmission direction (Z). Open areas of the pattern (P) without nanotubes (1) form micro-apertures (A) between the nanotubes (1) for transmitting the output light (Lo) through the filter structure.

First claim

1 . A collimator filter comprising:
an entry surface for receiving incident light at different angles of incidence with respect to a principal transmission direction of the collimator filter; an exit surface at an opposite side of the collimator filter with respect to the entry surface for allowing output light to exit from the collimator filter; and a filter structure between the entry surface and the exit surface for transmitting at least part of the incident light having angles of incidence below a threshold angle with respect to the principal transmission direction as the output light, and blocking the incident light having angles of incidence above the threshold angle from passing the filter structure; wherein the filter structure comprises a patterned array of carbon nanotubes, wherein the carbon nanotubes of the patterned array are aligned extending in the principal transmission direction between the entry surface and the exit surface, wherein the carbon nanotubes are arranged to form a two dimensional pattern transverse to the principal transmission direction for absorbing the incident light hitting the carbon nanotubes, wherein open areas of the two-dimensional pattern without the carbon nanotubes form micro-apertures between the carbon nanotubes that enable transmitting of the output light through the filter structure.

2 . The collimator filter according to claim 1 , wherein the filter structure is encased in a transparent solid matrix to fixate the carbon nanotubes.

3 . The collimator filter according to claim 2 , wherein the micro-apertures are at least partially filled by a material of the transparent solid matrix.

4 . The collimator filter according to claim 2 , wherein the transparent matrix forms an optically flat cover layer to cover the entry surface.

5 . The collimator filter according to claim 1 , wherein the micro-apertures have a cross-section diameter between one and ten micrometer, wherein the micro-apertures have an aperture height that is at least fifty times the aperture diameter.

6 . The collimator filter according to claim 1 , wherein the filter structure is formed as a sheet having a thickness of less than half a millimeter.

7 . The collimator filter according to claim 1 , wherein the carbon nanotubes form a pattern of interconnected walls wherein ones of the micro-apertures are each surrounded by respective parts of the walls, wherein the walls have a thickness between half a micrometer and two micrometer, wherein the wall thickness is less than the aperture diameter, by at least a factor three, wherein a total surface area of the filter structure covered by the micro-apertures is at least forty percent.

8 . The collimator filter according to claim 1 , wherein the carbon nanotubes form a pattern of interconnected walls enclosing the micro-apertures, wherein a top of the walls is covered by a reflective layer and the micro-apertures are free of the reflective layer to allow the nanotubes to absorb light at angles of incidence above the threshold angle impinging the walls inside the micro-apertures.

9 . The collimator filter according to claim 1 , wherein the carbon nanotubes are arranged in walls to form a pattern of cells arranged in a hexagonal pattern, wherein the micro-apertures formed inside respective cells are circular.

10 . An image detector comprising:
a photodetector comprising an array of light sensitive detector pixels for detecting light to form an image of a nearby object; a transparent cover plate with a thickness; and a collimator filter comprising:
an entry surface for receiving incident light at different angles of incidence with respect to a principal transmission direction of the collimator filter;
an exit surface at an opposite side of the collimator filter with respect to the entry surface for allowing output light to exit from the collimator filter; and
a filter structure between the entry surface and the exit surface for transmitting at least part of the incident light having angles of incidence below a threshold angle with respect to the principal transmission direction as the output light, and blocking the incident light having angles of incidence above the threshold angle from passing the filter structure;
wherein the filter structure comprises a patterned array of carbon nanotubes,
wherein the carbon nanotubes of the patterned array are aligned extending in the principal transmission direction between the entry surface and the exit surface,
wherein the carbon nanotubes are arranged to form a two dimensional pattern transverse to the principal transmission direction for absorbing the incident light hitting the carbon nanotubes,
wherein open areas of the pattern without carbon nanotubes form micro-apertures between the carbon nanotubes that enable transmitting of the output light through the filter structure, and
wherein the collimator filter is disposed between the transparent cover plate and the photodetector for only passing part of the incident light from the object which is received at or near a normal direction of the entry surface of the collimator filter to improve image resolution of the imaged object on the detector pixels.

11 . The image detector according to claim 10 , wherein each of the detector pixels is covered by a plurality of micro-apertures.

12 . The image detector according to claim 10 configured as a fingerprint detector and further comprising:
image processing circuitry to:
receive, from the image detector, an image of a fingerprint of a finger pressed against the transparent cover plate as the object to be imaged, and
process the image to recognize the fingerprint by comparing to a reference fingerprint.

13 . A display device comprising:
a fingerprint detector, for detecting a finger pressed against a display screen of the display device; display pixels configured to emit light to display an image on the display screen; a photodetector comprising an array of light sensitive detector pixels for detecting light to form an image of a nearby object; a transparent cover plate with a thickness; and a collimator filter comprising:
an entry surface for receiving incident light at different angles of incidence with respect to a principal transmission direction of the collimator filter;
an exit surface at an opposite side of the collimator filter with respect to the entry surface for allowing output light to exit from the collimator filter; and
a filter structure between the entry surface and the exit surface for transmitting at least part of the incident light having angles of incidence below a threshold angle with respect to the principal transmission direction as the output light, and blocking the incident light having angles of incidence above the threshold angle from passing the filter structure;
wherein the filter structure comprises a patterned array of carbon nanotubes,
wherein the carbon nanotubes of the patterned array are aligned extending in the principal transmission direction between the entry surface and the exit surface,
wherein the carbon nanotubes are arranged to form a two dimensional pattern transverse to the principal transmission direction for absorbing the incident light hitting the carbon nanotubes,
wherein open areas of the pattern without carbon nanotubes form micro-apertures between the carbon nanotubes that enable transmitting of the output light through the filter structure,
wherein the collimator filter is disposed between the transparent cover plate and the photodetector for only passing part of the incident light from the object which is received at or near a normal direction of an entry surface of the collim

Assignees

• TNO

Inventors

• Tordera Salvador Daniel
• Gelinck Gerwin Hermanus
• Unnikrishnan Sandeep
• Akkerman Hylke Broer
• Peeters Bart
• Van Breemen Albert Jos Jan Marie

Classifications

• B29D11/00788

  Producing optical films · CPC title

• B29D11/00634

  Production of filters · CPC title

• G06V40/1324

  by using geometrical optics, e.g. using prisms (G06V40/1312 takes precedence) · CPC title

• G06V40/1318 Primary

  using electro-optical elements or layers, e.g. electroluminescent sensing · CPC title

• G02B5/20 Primary

  Filters (polarising elements G02B5/30) · CPC title