Holographic imaging device and data processing method therefor

A data processing method used for a holographic imaging device, comprising the steps of:

• acquiring data of a plurality of object light holograms (IjOR, j=1, . . . , N), which are off-axis holograms of interference fringes between object lights (Oj, j=1, . . . , N) emitted from an object sequentially illuminated with illumination lights (Qj, j=1, . . . , N) and an off-axis spherical wave reference light (R) being off-axis with respect to the object lights (Oj, j=1, . . . , N), without passing the object lights (Oj, j=1, . . . , N) through a lens, wherein the illumination lights (Qj, j=1, . . . , N) are composed of parallel lights, including one vertical incident light, having mutually different incident directions (θj, j=1, . . . , N) to the object and the data is acquired for each of the incident directions;
• acquiring data of a reference light hologram (ILR), which is an off-axis hologram of interference fringes between an in-line spherical wave reference light (L) being in-line with the object lights (Oj, j=1, . . . , N) and the off-axis spherical wave reference light (R);
• generating object light wave holograms (gj(x,y), j=1, . . . , N), which represent light waves of the object lights (Oj, j=1, . . . , N) at a hologram plane (z=0) by using the data of the reference light hologram (ILR) and the respective object light holograms (IjOR, j=1, . . . , N);
• generating spatial frequency spectra (Gj(u,v), j=1, . . . , N) at the hologram plane (z=0) by Fourier-transforming each of the object light wave holograms (gj(x,y), j=1, . . . , N) and generating object light spatial frequency spectra (Hj(u,v), j=1, . . . , N)) at an object position (z=zm) by propagating each of the spatial frequency spectra (Gj(u,v), j=1, . . . , N) at the hologram plane (z=0) to the object position (z=zm)
• generating a synthetic object light spatial frequency spectrum (HT(u,v)), at the object position (z=zm), based on a fact that the illumination lights used to acquire the data of the object lights are parallel lights, enlarged so as to occupy a wider frequency space, by moving and arranging each of the object light spatial frequency spectra (Hj(u,v), j=1, . . . , N) at the object position (z=zm) in a two-dimensional space of a spatial frequency space (u,v) using a shift amount (ujs, vjs) derived based on calculation of a cross correlation function so that each of those object light spatial frequency spectra overlaps with another over an area in which changes of amplitude and phase are common to the mutually overlapped spectra, and by making the object light spatial frequency spectra (Hj(u,v), j=1, . . . , N) match mutually in the overlap area using fitting coefficients (aαβ, α≠β, α, β=1, . . . , N) obtained for adjusting mutual amplitude and phase of the object light spatial frequency spectra (Hj(u,v), j=1, . . . , N) having the overlap area mutually;
• and
• generating a synthetic object light wave hologram (hT(x,y)) used for reconstruction of the image of the object, by inverse-Fourier transforming the synthetic object light spatial frequency spectrum (HT(u,v)).

A holographic imaging device, comprising:

• a data acquisition unit for acquiring a hologram of an object light (O) emitted from an object illuminated with an illumination light (Q);
• and
• an image reconstruction unit for reconstructing an image of the object from the hologram acquired by the data acquiring unit, wherein
• the data acquisition unit comprises:
• an optical system for generating the illumination light (Q), an in-line spherical wave reference light (L) being in-line with the object light (O), and an off-axis spherical wave reference light (R) being off-axis with the object light (O), from a coherent light emitted from a light source, and for propagating those lights and the object light (O), and further for changing an incident direction of the illumination light (Q) to the object;
• a photo-detector for converting light intensity into an electric signal and outputting the electric signal;
• and
• a storing unit for acquiring and storing data of a plurality of object light holograms (IjOR, j=1, . . . , N), which are off-axis holograms of interference fringes between the off-axis spherical wave reference light (R) and the object lights (Oj, j=1, . . . , N) emitted from the object sequentially illuminated, respectively, with the illumination lights (Qj, j=1, . . . , N) generated by the optical system as parallel lights, including one vertical incident light, having mutually different incident directions (θj, j=1, . . . , N) to the object, and data of a reference light hologram (ILR), which is an off-axis hologram of interference fringes between the off-axis spherical wave reference light (R) and the in-line spherical wave reference light (L), using the photo-detector, wherein
• the image reconstruction unit comprises:
• a light wave generation unit for generating object light wave holograms (gj(x,y), j=1, . . . , N) at a hologram plane (z=0) defined at a light receiving surface of the photo-detector, which represent light waves of the object lights (Oj, j=1, . . . , N) for the respective incident directions (θj, j=1, . . . , N), by using the data of the reference light hologram (ILR) and the respective object light holograms (IjOR, j=1, . . . , N);
• a spectrum generation unit for generating spatial frequency spectra (Gj(u,v), j=1, . . . , N) at the hologram plane (z=0) by Fourier-transforming each of the object light wave holograms (gj(x,y), j=1, . . . , N) and generating object light spatial frequency spectra (Hj(u,v), j=1, . . . , N) at an object position (z=zm) by propagating each of the spatial frequency spectra (Gj(u,v), j=1, . . . , N) at the hologram plane (z=0) to the object position (z=zm);
• and
• a spectrum synthesis unit for generating a synthetic object light spatial frequency spectrum (HT(u,v)) enlarged so as to occupy a wider frequency space, by moving and arranging each of the object light spatial frequency spectra (Hj(u,v), j=1, . . . , N) in a two-dimensional space of a spatial frequency space (u,v) based on calculation of a cross correlation function so that each of those object light spatial frequency spectra overlaps with another over an area in which changes of amplitude and phase are common to the mutually overlapped spectra, and by making the object light spatial frequency spectra (Hj(u,v), j=1, . . . , N) match mutually in the overlap area using fitting coefficients (aαβ, α≠β, α, β=1, . . . , N) obtained for adjusting mutual amplitude and phase of the object light spatial frequency spectra (Hj(u,v), j=1, . . . , N) having the overlap area mutually, wherein
• a synthetic object light wave hologram (hT(x,y)) to be used for reconstruction of the image of the object is generated by inverse-Fourier transforming the synthetic object light spatial frequency spectrum (HT<u,v)) generated by the spectrum synthesis unit, wherein,
• the optical system comprises an angle change unit for changing the incident direction of the illumination light (Q) to the object, and the angle change unit comprises:
• a rotating plate having a circular center opening with a shutter and an eccentric opening provided at an eccentric position, for receiving a cone shape light diverging around an optical central axis going to the center of the photo-detector and for distributing a part of the diverging cone shape light as the illumination light (Q) by intermittently rotating around the central axis;
• a lens assembly having a plurality of lenses arranged around the central axis, for making each of the lights distributed by the rotating plate into a parallel light;
• and
• a deflection element assembly having a plurality of prisms or diffraction gratings, or a reflecting mirror assembly having a plurality of reflecting mirrors, for changing the direction of the parallel lights so that each of the parallel lights from the lens assembly passes through one point on the central axis by intersecting the central axis at the point at a predetermined angle.