Flat optics for image differentiation

Patent metadata

Field	Value
Publication number	US-2021063717-A1
Application number	US-202017012189-A
Country	US
Kind code	A1
Filing date	Sep 4, 2020
Priority date	Sep 4, 2019
Publication date	Mar 4, 2021
Grant date	—

Abstract

A 2D spatial differentiator operates in transmission and comprises a Si nanorod photonic crystal that can transform an image, Ein, into its second-order derivative, Eout α ∇2 Ein, allowing for direct discrimination of the edges in the image. The use of a 2D photonic crystal allows for differentiation and edge detection in all directions with a numerical aperture (NA) up to 0.315 and an experimental resolution smaller than 4 μm. The nanophotonic differentiator is able to be directly integrated into an optical microscope and onto a camera sensor, demonstrating the ease with which it can be vertically integrated into existing imaging systems. Furthermore, integration with a metalens is demonstrated for realizing a compact and monolithic image-processing system. In all cases, the use of the nanophotonic differentiator allows for a significant reduction in size compared to traditional systems, opening new doors for optical analog image processing in applications involving computer vision.

First claim

What is claimed is:

1 . A flat photonic differentiator, comprising:
a substrate; a photonic crystal comprising a two-dimensional array of resonators positioned on the substrate, wherein each of the resonators has a first refractive index, a width, a height, and is centered in a unit cell of the substrate with a length; and a cladding layer with a second refractive index positioned on the substrate, wherein the resonators are embedded within the cladding layer, wherein the width, the height, the length, the first refractive index, and the second refractive index are configured to realize an optical transfer function in transmitted light through the photonic differentiator to produce a spatially differentiated image.

2 . The flat photonic differentiator of claim 1 , wherein the width, height, length, first refractive index, and second refractive index are related by

[

D
,
a
,
h

]

=

(

λ
0

n
avg

)

*

[

i
,
j
,
k

]

,

where D is the width, a is the length, h is the height, λ 0 is a free space wavelength of a working wavelength of the differentiator, n avg is an average of the first refractive index and the second refractive index, and i, j, and k are dimensional constants for the width, length, and height, respectively.

3 . The flat photonic differentiator of claim 2 , wherein [i, j, k]=[0.63, 1.35, 0.99], and wherein each of λ 0 , n avg , i, j, and k have a tolerance of +/−20%.

4 . The flat photonic differentiator of claim 2 , wherein the spatially differentiated image is a second-order derivative of an input image received by the photonic differentiator.

5 . The flat photonic differentiator of claim 2 , wherein the photonic crystal has a numerical aperture greater than 0.3.

6 . The flat photonic differentiator of claim 2 , wherein the photonic crystal does not perform polarization conversion for the transmitted light.

7 . The flat photonic differentiator or claim 2 , wherein the photonic crystal supports quasi-guided modes for p-polarized incident light.

8 . The flat photonic differentiator of claim 7 , wherein the photonic crystal reflects s-polarized incident light.

9 . The flat photonic differentiator of claim 2 , wherein the photonic crystal transmits a brightfield image of incident light with a wavelength more than a threshold difference than the working wavelength.

10 . The flat photonic differentiator of claim 2 , wherein the working wavelength is one or more wavelengths within a range of 100 nm of each other.

11 . The flat photonic differentiator of claim 1 , wherein the cladding layer is air.

12 . The flat photonic differentiator of claim 1 , wherein a cross-sectional shape of each of the resonators is selected from the group consisting of: a circle, a hexagon, a square, a triangle, and a regular polygon.

13 . An imaging system, comprising:
an illumination source configured to selectively transmit illumination light at a first wavelength; and a photonic differentiator positioned to receive light of a scene illuminated by the illumination light, wherein the photonic differentiator comprises:
a substrate;
a photonic crystal comprising a two-dimensional array of resonators positioned on the substrate, wherein each of the resonators has a first refractive index, a width, a height, and is centered in a unit cell of the substrate with a length; and
a cladding layer with a second refractive index positioned on the substrate, wherein the resonators are embedded within the cladding layer, wherein the width, height, length, first refractive index, second refractive index, and third refractive index are configured to realize an optical transfer function in transmitted light through the photonic differentiator to produce a spatially differentiated image of the scene when illuminated by illumination light at the first wavelength.

14 . The imaging system of claim 13 , further comprising:
an image sensor configured to capture the spatially differentiated image of the scene, wherein the photonic differentiator is positioned between the scene and the image sensor.

15 . The imaging system of claim 13 , further comprising:
an objective of a microscope, wherein the photonic differentiator is positioned between the scene and the objective.

16 . The imaging system of claim 13 , wherein the width, height, length, first refractive index, and second refractive index, are related by

[

D
,
a
,
h

]

=

(

λ
0

n
avg

)

*

[

i
,
j
,
k

]

,

where D is the width, a is the length, h is the height, λ 0 is a free space wavelength of a working wavelength of the differentiator, n avg is an average of the first refractive index and the second refractive index, and wherein the first wavelength is the working wavelength, and i, j, and k are dimensional constants for the width, length, and height, respectively.

17 . The imaging system of claim 16 , wherein the illumination source is configured to selectively transmit illumination light at either the first wavelength or a second wavelength, wherein the photonic crystal transmits a brightfield image of the scene when illuminated by the illumination light with the second wavelength.

18 . The imaging system of claim 17 , further comprising:
a controller configured to cause the illumination source to selectively transmit illumination light of the first wavelength to produce the spatially differentiated image and configured to cause the illumination source to selectively transmit illumination light of the second wavelength to produce the brightfield image.

19 . The imaging system of claim 16 ,

Assignees

• Univ Vanderbilt

Inventors

• Valentine Jason G
• Zhou You
• Zheng Hanyu

Classifications

• G02B1/005 Primary

  made of photonic crystals or photonic band gap materials (photonic band-gap structures or photonic lattices in integrated optics G02B6/1225; photonic band-gap structures or photonic lattices in optical fibres G02B6/02295) · CPC title

• H04N23/54

  Mounting of pick-up tubes, electronic image sensors, deviation or focusing coils · CPC title

• H04N23/55

  Optical parts specially adapted for electronic image sensors; Mounting thereof · CPC title

• H04N23/56

  provided with illuminating means · CPC title

• G02B3/0056

  arranged along two different directions in a plane, e.g. honeycomb arrangement of lenses (G02B3/0043 takes precedence; miniaturised objectives for electronic devices employing wafer level optics G02B13/0085) · CPC title