Enhancing daytime detection of objects with the use of a system incorporating dual diffractive elements with corresponding diffraction efficiencies and bandwidths

Patent metadata

Field	Value
Publication number	US-10976478-B2
Application number	US-201916295189-A
Country	US
Kind code	B2
Filing date	Mar 7, 2019
Priority date	Mar 12, 2018
Publication date	Apr 13, 2021
Grant date	Apr 13, 2021

Abstract

An optical imaging system employing a device containing a sequence of first (pre-dispersor) and second (main) volume holograms configured to operate as a sequence of optical diffractive elements possessing different blazing curves. A pre-cursor hologram has a thickness smaller than the thickness of the following, disperser hologram, and a comparatively broad spectral selectivity as compared to that of the main hologram, allowing the pre-cursor to diffract light in transmission within a very large range of the angles of incidence. The use of the combination of the pre-cursor and the main holograms not only implements selective imaging of the chosen target object at every angle at which various portions of the object are seen at the optical system, but also facilitates the spectroscopic measurements of such object.

First claim

What is claimed is:

1. An optical imaging system comprising:
a first optical diffractive element having a first spectral characteristic,
wherein the first spectral characteristic has a first portion representing a first diffraction efficiency of the first optical diffractive element as a function of wavelength of light for a chosen first angle of incidence of the light onto the first optical diffractive element, the first spectral characteristic having a first bandwidth,

a second optical diffractive element having a second spectral characteristic and disposed to receive a first light wavefront diffracted at the first optical diffractive element and to form second light wavefront as a result of diffraction of the first light wavefront at the second optical diffractive element,
wherein the second spectral characteristic has a second portion representing a second diffraction efficiency of the second optical diffractive optical element as a function of the wavelength of light for a chosen second angle of incidence of the first light wavefront onto the second optical diffractive element, the second spectral characteristic having a second bandwidth,
wherein the second bandwidth is narrower that the first bandwidth, and

an optical detector positioned to receive light from the second wavefront and produce an output signal representing distribution of irradiance of the second wavefront across the optical detector.

2. The optical imaging system according to claim 1 , further comprising
a combination of at least a first optical element and a second optical element, each of the at least the first optical element and the second optical element dimensioned to change a degree of divergence of light incident thereon,
wherein the first optical element from the combination is disposed to transmit the light incident thereon towards the first optical diffractive element, and
wherein the second optical element from the combination is disposed to receive the second wavefront and to relay it to the optical detector.

3. The optical imaging system according to claim 2 , wherein the combination of the at least the first optical element and the second optical element is configured as a telescope.

4. The optical imaging system according to claim 3 , wherein the at least the first optical element and the second optical element are not disposed co-axially with one another.

5. The optical imaging system according to claim 1 , wherein at least one of the first and second optical diffractive elements is configured as a holographic layer carrying a hologram therein.

6. The optical imaging system according to claim 1 , wherein the first optical diffractive element is configured as a first holographic diffraction grating having a first thickness, wherein the second optical diffractive element is configured as a second holographic diffraction grating having a second thickness, and wherein the first thickness is smaller than the second thickness.

7. The optical imaging system according to claim 1 , wherein the first optical diffractive element and the second optical diffractive element are separated from one another by a substantially zero distance.

8. The optical imaging system according to claim 1 , wherein a ratio of the first bandwidth to the second bandwidth is at least 10.

9. The optical imaging system according to claim 1 , wherein the second spectral characteristic further includes a third portion representing a third diffraction efficiency of the second optical diffractive optical element as a function of the wavelength of light for a chosen third angle of incidence of light onto the second optical diffractive element, the third portion having a third bandwidth,
wherein the third bandwidth is narrower that the first bandwidth.

10. The optical imaging system according to claim 9 , wherein the first bandwidth is greater than a sum of i) the second bandwidth, ii) the third bandwidth, and iii) a spectral separation between a central wavelength of the second bandwidth and a central wavelength of the third bandwidth.

11. The optical imaging system according to claim 9 , wherein an absolute value of a difference between the chosen second angle of incidence and the chosen third angle of incidence is a value within a range between zero degrees and twelve degrees.

12. The optical imaging system according to claim 1 , wherein the first optical diffractive element contains a diffraction grating characterized by a first spatial frequency, the second optical diffractive element contains a diffraction grating characterized by a second spatial frequency, and wherein the first spatial frequency is substantially equal to the second spatial frequency.

13. The optical imaging system according to claim 1 , wherein the first optical diffractive element includes a holographic layer containing a hologram with a refractive index modulation of at least 0.1.

Assignees

• Univ Arizona

Inventors

• Blanche Pierre Alexandre
• Pearce Eric C

Classifications

• G01J3/1838

  Holographic gratings · CPC title

• G02B27/4277

  being separated by an air space · CPC title

• G01J3/18

  using diffraction elements, e.g. grating (gratings per se G02B) · CPC title

• G02B5/18

  Diffraction gratings {(holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44)} · CPC title

• G02B27/4244

  in wavelength selecting devices (spectrometry G01J) · CPC title