SENSOR FOR HYPERSPECTRAL IMAGING BASED ON A METASURFACE-INTEGRATED LIGHT DETECTOR ARRAY

Abstract

A spectroscopic microscope device, comprising at least one array of metasurfaces, and at least one CCD array integrated with the array of metasurfaces. The metasurfaces in the array are configured to separately direct LCP an RCP components of light incident on the metasurface to separate pixels in the CCD array.

Claims

1. A spectroscopic microscope device, comprising: a. at least one array of metasurfaces; and b. at least one CCD array integrated with the array of metasurfaces, wherein each metasurface of the metasurface array is configured to direct LCP components of light incident on the metasurface to a first pixel in the CCD array and RCP components of light indicent on the meta surface to a second pixel in the CCD array.

2. The device of claim 1, wherein the array of metasurfaces is sub-millimeter in thickness.

3. The device of claim 1, wherein the device is configured to build spectrally resolved images for colorimetry.

4. The device of claim 1, wherein the device is configured to build spectrally resolved images for Raman spectroscopy.

5. The device of claim 1, wherein the device is configured to build spectrally resolved images for Circular Dischroism spectroscopy.

6. The device according to claim 1, wherein an array of metasurfaces is integrated with a CCD array to build a spectrally resolved microscope image.

7. The device according to claim 1, wherein the metasurface array is fabricated on top of a CCD array.

8. The device according to claim 1, wherein the metasurface is adjustable to work within a plurality of wavelengths including ultraviolet, visible, and infrared.

9. The device according to claim 1, wherein the device is configured to generate spectroscopically resolved images from samples observed under microscopes.

10. The device according to claim 1, wherein the device configured to perform biological sensing in vitro and in vivo.

11. The device according to claim 1, wherein the device is configured to perform DNA structural analysis.

12. The device according to claim 1, wherein the device is configured to perform stereochemical applications.

13. The device according to claim 1, wherein the device is configured to perform crystallography.

14. The device according to claim 1, wherein the device is configured to perform live monitoring of biological molecules in naturally behaving subjects.

15. The device according to claim 1, wherein an array of said devices are used to build a sensor network.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein:

[0013] FIG. 1 shows a diagram of a Circular Dichroism CCD (CD-CCD) array according to one embodiment, using transmissive metasurface arrays.

[0014] FIG. 2 shows an image of a fabricated reflective Circular Dichroism metasurface, imaged using field emission scanning electron microscope (FE SEM) according to one embodiment.

[0015] FIG. 3A shows a schematic of an optical arrangement used to confirm that the metasurface scatters different wavelengths of different polarizations at different angles according to one embodiment.

[0016] FIG. 3B shows the spectrum of collected light for LCP and RCP incident beams as a function of scattering angle.

[0017] FIG. 4 shows a basic schematic of a microscope with a CCD camera with Circular Dischroism metasurface according to one embodiment.

[0018] FIG. 5 shows the tube lens focusing on-axis and off-axis light components onto separate metasurfaces within the metasurface array according to one embodiment.

DETAILED DESCRIPTION

[0019] The presently disclosed CD CCD array may be submillimeter in dimensions. FIG. 1 shows a diagram of a Circular Dichroism CCD (CD-CCD) array 10 according to one embodiment, using transmissive metasurface arrays 15. A layer of metal 11 is deposited on top of the structures and holes 13 (which are in the range of 100-400 m wide) are exposed to ensure light reflected from a specimen passes through the metasurface 14. Each pixel 18 of the CCD array is in the range of 0.5-1 mm in width (although they could also 0.25-1.5 mm in width) and two such pixels 18 are aligned with a metasurface array. One pixel 19 collects the LCP light, while the other pixel 20 collects RCP light, allowing for simultaneous collection. The size of the metasurface array and the thickness of the polymer layer is dictated by the angle spread of the wavelengths, to ensure all signals are captured by the CCD array.

[0020] The array 10 can be attached to any standard microscope to capture real-time CD microscopy images. Incident light beams 12 are reflected from a sample of interest, which is normally incident on the transmission metasurface 15. The LCP and RCP components are then scattered as shown (beams 16), with different wavelengths scattered in different angles, and thereby spatially separating LCP and RCP components of different wavelengths. With this metasurface, LCP and RCP components can be detected by different pixels 18 on the CCD array, allowing for simultaneous measurement and fast construction of CD images.

[0021] The LCP and RCP components are scattered by the metasurface such that they can be detected by separate CCD pixels (e.g., pixels 18 and 19). The distance between the metasurface 15 and the CCD array is dictated by the CCD pixel size and the spatial spread of wavelengths. In order to have all wavelengths of both LCP and RCP fully collected by 2 adjacent CCD pixels 18 and 19, the distance between the metasurface and CCD array should be on order of a few micrometers. This is achieved by spin-coating a transparent dielectric polymer 20 on top of the CCD array and fabricating the metasurface on top of this polymer layer 20.

[0022] For the device of FIG. 1, the metasurface functions in transmission. FIG. 3A shows a schematic of an optical arrangement 30 used to confirm that the metasurface 31 scatters different wavelengths of different polarizations at different angles according to one embodiment. A tunable monochromatic source 32, a polarizer 34 and a retarder 36 are provided as shown to generate circularly polarized light for different wavelengths. Scattered light is collected as a function of scattering angle using a detector 38 and analyzer 40 on a rotating arm, for example. FIG. 3B shows the associated spectrum of collected light for LCP and RCP incident beams as a function of scattering angle.

[0023] The metasurface of FIG. 3A can be configured for transmission by changing the materials used, depending on the needs of the application. The structure comprises a repeating pattern (e.g., a period of 4 structures in the illustrated example shown in FIG. 2). Within each period, the major axes of the antennas are oriented at different angles, to span a full 180 degree orientation. In one embodiment, the antennas are oriented at 0, 45, 90 and 135. The structure in FIG. 3A includes a back reflecting metal layer 46 covered by a dielectric spacer layer 48. On top is the metasurface structure comprising metallic nano-antennas 44. For the transmission metasurface, there will be no back reflecting plate 46. The metallic nanoantennas 44 will have a sandwich structure with bottom metal layer, dielectric spacer layer, and top metal layer. This structure may be fabricated using electron beam lithography or photolithography using standard photoresists. After the pattern is made, metal and dielectric layers can be deposited, followed by lift-off to leave sandwich-structure nanoantennas. The metal layers may be formed using any metal (gold, silver, copper, aluminum, titanium nitride, zirconium nitride . . . etc.). The thickness of the bottom and top metal layers can vary from tens to hundreds of nanometers, and can be deposited using chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques. The dielectric spacer layer 48 is in the range of a few tens of nanometers in thickness and can also be deposited using any of the chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques.

[0024] As an example, a reflecting metasurface, shown in FIG. 2 was fabricated with a bottom gold layer 50 nm thick, covered by a 50 nm alumina spacer layer. The top most layer was an array of 30 nm thick rectangular gold antennas. The antennas were 230 nm280 nm, with a separation of 450 nm. The materials were deposited using electron beam evaporation, and the antenna array was patterned using electron beam lithography.

[0025] The fabricated metasurface functions in the near-infrared region, and was tested using the optical arrangement as shown in FIG. 3A. The setup consists of a monochromatic source, a polarizer and a retarder to generate circularly polarized light for different wavelengths. The light is incident on the metasurface at normal incidence. The light scattered from the metasurface is collected using a detector mounted on a rotating arm, which allows for collection as a function of reflected angle. FIG. 3B shows that the LCP light is reflected to the right, while the RCP light is reflected to the left. Also, different wavelengths between 1.2 m and 1.7 m are scatted at different angles, ranging from 40 to 70. As shown, the metasurface efficiently spatially separates LCP and RCP light of different wavelengths.

[0026] The incident light beam need not be generated from a laser source. Any non-coherent lamp source, or light-emitting diode (LED) or Xenon lamp with equal components of LCP and RCP can be used with the presently disclosed device.

[0027] In order to have proper collection of LCP and RCP components of light using the CCD array, the metasurface patterns should be properly located with respect to the CCD pixels. To do this, the CCD array will be used as a substrate for fabrication and metasurfaces will be aligned with pixel array. First, a polymer layer is spin coated on top of the CCD array. The thickness of this layer depends on CCD pixel size. The thicker the polymer layer, the larger the separation between different wavelengths at the CCD array. So the polymer layer must be thick enough to achieve sufficient spatial separation, but thin enough to ensure all wavelengths are collected by single CCD pixel. Then a thick (hundreds of nanometers) metal layer will be deposited. A layer photo resist will be spin coated on top of CCD array. Photolithography or electron beam lithography will be used to expose patches for metasurface arrays. Arrays will be situated on top of the polymer layer at the center of two adjacent CCD pixels, as seen in FIG. 1. Exposed metal will be etched using reactive ion etching. This is to ensure that all light collected by CCD array passes through the metasurface arrays. A second layer of photo resist will be spin coated on top of remaining metal. Photolithography or electron beam lithography is used to pattern the metasurface arrays. Metal and dielectric layers will be deposited for metasurface array, followed by lift off.

[0028] After integrating the metasurface with the CCD array, the array can be built into a standard microscope setup as shown in FIG. 4. An LED, or other non-coherent light source 50, is provided to generate non-coherent white light. A dichroic mirror 52 reflects the light down to the specimen 54 through an objective 56. The reflected light is taken up through a tube lens 58, focusing the light onto the individual metasurfaces 60. The metasurface then spatially separates LCP and RCP light of different wavelengths onto the CCD camera pixels 62.

[0029] As discussed above, a non-coherent light source 50 generates white light that is focused onto the specimen 54 using an objective 56. The reflected light is sent back up the microscope column and is focused by a tube lens 58 onto the circular dichroism metasurface array. To ensure that the reflected light impinges on the metasurface with minimal divergence angle, the metasurface should be within one Rayleigh length away from the focus of the tube lens. The tube lens 56 focuses light from on-axis and off-axis rays onto different areas of the metasurface array, and the CCD array, as shown in FIG. 5. Each individual metasurface 60 in the array may have dimensions varying from 10 um to 1 mm, depending on the required spatial resolution. For example, with a tube lens with 200 mm focal length and with 20 mm aperture diameter, the divergence angle at the focus will be only 0.12 radians, or 0.0021, with a Rayleigh length of 280 um and waist size of 7 um at the focus. The distance between the metasurface array and CCD array can vary between 50 um and 1 mm depending on the size of the metasurface arrays. For the metasurface provided as an example here which separates wavelengths 1.2-1.7 um over a range of 40-70, a distance of 55 um is needed between the metasurface array and CCD array to ensure that all spectral components are separate spatially to be collected by individual CCD pixels. This distance of 55 um is within the Rayleigh length for a 200 mm tube lens, ensuring that the beam divergence angle is quite small, and so all spectral components can be collected without any distortions.

[0030] FIG. 5 shows the tube lens 58 focusing on-axis and off-axis light components onto separate metasurfaces 60 within the metasurface array. Each metasurface then spatially separates the LCP and RCP components as shown, which are collected by the CCD array.