Lensless holographic imaging system using holographic optical element

Patent metadata

Field	Value
Publication number	US-2021294265-A1
Application number	US-202017078321-A
Country	US
Kind code	A1
Filing date	Oct 23, 2020
Priority date	Mar 18, 2020
Publication date	Sep 23, 2021
Grant date	—

Abstract

A lensless holographic imaging system having a holographic optical element includes: a coherent light source for outputting a first light beam and a second light beam, wherein the first light beam irradiates a first inspection plane to form first object-diffracted light; a light modulator for modulating the second light beam into reading light having a specific wavefront; a multiplexed holographic optical element, wherein the first object-diffracted light passes through the multiplexed holographic optical element, and the reading light is input into the multiplexed holographic optical element to generate a diffracted light beam as system reference light; and an image capture device for reading at least one interference signal generated by interference between the first object-diffracted light and the system reference light. The lensless holographic imaging system has a relatively small volume and relatively high diffraction efficiency.

First claim

1 . A lensless holographic imaging system having a holographic optical element, comprising:
a first partially coherent light source for outputting a first light beam and a second light beam partially coherent with respect to the first light beam, the first light beam being used to irradiate a first inspection plane of an object under inspection so as to form first object-diffracted light; a light modulator for receiving the second light beam and modulating the second light beam into at least one beam of reading light having a specific wavefront; a first multiplexed holographic optical element, the first object-diffracted light entering the first multiplexed holographic optical element through a first surface thereof, passing through the first multiplexed holographic optical element, and exiting the first multiplexed holographic optical element through a second surface thereof, the at least one beam of reading light being input into the first multiplexed holographic optical element to generate at least one diffracted light beam as at least one beam of first system reference light; and an image capture device adjacent to the second surface and configured to read at least one first interference signal generated by interference between the first object-diffracted light and the at least one beam of first system reference light.

2 . A lensless holographic imaging system having a holographic optical element, comprising:
a second partially coherent light source for outputting a second light beam; a light modulator for receiving the second light beam and modulating the second light beam into at least one beam of reading light having a specific wavefront; a second multiplexed holographic optical element irradiated with the at least one beam of reading light such that a portion of the at least one beam of reading light undergoes diffraction in the second multiplexed holographic optical element and exits the second multiplexed holographic optical element as at least one beam of second system reference light while another portion of the at least one beam of reading light exits the second multiplexed holographic optical element through a first surface thereof as second object-irradiating light, the second object-irradiating light being projected to and reflected by a second inspection plane of an object under inspection to form second object-diffracted light, the second object-diffracted light entering the second multiplexed holographic optical element through the first surface thereof, passing through the second multiplexed holographic optical element, and exiting the second multiplexed holographic optical element through a second surface thereof; and an image capture device located at the second surface and configured to read at least one second interference signal generated by interference between the second object-diffracted light and the at least one beam of second system reference light.

3 . The lensless holographic imaging system of claim 2 , further comprising a mirror provided on an outer side of a first inspection plane of the object under inspection, wherein the second object-irradiating light passes through the object under inspection, is projected to and reflected by the mirror, and then passes through the object under inspection again to form third object-diffracted light, and the third object-diffracted light enters the second multiplexed holographic optical element through the first surface thereof, passes through the second multiplexed holographic optical element, and exits the second multiplexed holographic optical element through the second surface thereof, in order for the image capture device to read at least one third interference signal generated by interference between the third object-diffracted light and the at least one beam of second system reference light.

4 . The lensless holographic imaging system of claim 3 , further comprising a transparent medium layer provided in a portion of a space between the second multiplexed holographic optical element and the mirror, wherein the second multiplexed holographic optical element is irradiated with the at least one beam of reading light such that a portion of the at least one beam of reading light undergoes diffraction in the second multiplexed holographic optical element and exits the second multiplexed holographic optical element as at least one beam of third system reference light while another portion of the at least one beam of reading light forms the second object-irradiating light, the third system reference light passes upward through the transparent medium layer, is reflected by the mirror, passes through the transparent medium layer again, and then passes through the second multiplexed holographic optical element, the second object-irradiating light exits the second multiplexed holographic optical element through the first surface thereof, passes through or does not pass through the transparent medium layer, is projected to and reflected by the mirror, and then passes through the object under inspection to form fourth object-diffracted light, and the fourth object-diffracted light passes through the second multiplexed holographic optical element and exits the second multiplexed holographic optical element through the second surface thereof, in order for the image capture device to read at least one fourth interference signal generated by interference between the fourth object-diffracted light and the third system reference light.

5 . The lensless holographic imaging system of claim 1 , wherein the partially coherent light source is a laser light source.

6 . The lensless holographic imaging system of claim 1 , wherein the light modulator is a rotatable mirror.

7 . The lensless holographic imaging system of claim 1 , wherein a said beam of first system reference light is a spherical wave originating from a point source, and the lensless holographic imaging system further comprises a first image reconstruction module for performing a first observation-depth-based digital image reconstruction process comprising the steps of:
inputting an observation depth, wherein the observation depth is a linear distance between the point source of a said beam of first system reference light and an inspection plane of a said object under inspection; reading a point source depth, wherein a linear distance between the point source of the first system reference light corresponding to the input observation depth and the image capture device is calculated and read as the point source depth; and performing first interference-signal- and observation-depth-based image reconstruction, wherein the first interference signal corresponding to the first system reference light corresponding to the input observation depth is converted into a first digital interference signal, the first digital interference signal corresponds to a first electric field, the first electric field is propagated to the read point source depth and is filtered at the read point source depth to remove a noise term while leaving a signal-term electric field, and the signal-term electric field is propagated to the input observation depth to generate a reconstructed image.

8 . The lensless holographic imaging system of claim 1 , wherein a said beam of first system reference light is a spherical wave originating from a point source, and the lensless holographic imaging system further comprises a first image reconstruction module for performing a first Fourier-transformation-based image reconstruction process comprising the steps of:
selecting an observation depth, wherein the observation depth is selected from a plurality of built-in observation depths, and each said observation depth is a linear distance between the point source of a said beam of first system ref

Assignees

• Univ Nat Central

Inventors

• Yu Yeh-Wei
• Sun Ching-Cherng

Classifications

• G03H2001/0033

  in hologrammetry for measuring or analysing · CPC title

• G03H1/0005

  Adaptation of holography to specific applications (holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042) · CPC title

• G03H1/12

  Spatial modulation, e.g. ghost imaging · CPC title

• G03H1/0443 Primary

  Digital holography, i.e. recording holograms with digital recording means (holobject computation G03H1/0866) · CPC title

• G03H1/0465

  Particular recording light; Beam shape or geometry (G03H1/06 takes precedence) · CPC title