Wenyang Sun

Volume holographic imaging in transmission geometry

We address the performance of transmission geometry volume holograms as depth-selective imaging elements. We consider two simple implementations using holograms recorded with spherical and plane beams. We derive the point-spread function (PSF) of these systems using volume diffraction theory and use the PSF to estimate depth resolution. Furthermore, we show that appropriately designed objective optics can significantly improve the depth resolution or the working distance of plane-wave reference holographic imaging systems. These results are confirmed experimentally and demonstrated for objects with millimeter axial features, imaged from the 5- to 50-cm range.

Rainbow volume holographic imaging.

We present a new form of volume holographic imaging with rainbow illumination. High depth resolution is obtained because each quasi-monochromatic band of the rainbow acts as a depth-selective confocal slit. The color slits work in parallel to achieve a wide field of view (FoV) and so the need to scan in one lateral dimension is eliminated. Our experiments demonstrated <250-micro m depth resolution over an approximately equal to 15 degree FoV at a 50-mm working distance.

Hyper-spectral imaging with volume holographic lenses

We present a hyper-spectral imaging system with volume holographic lenses. The Bragg selectivity of the volume holographic lenses enables the system to achieve high resolution in three spatial dimensions as well as the spectral dimension.

High-resolution volume holographic profilometry using the Viterbi algorithm

We use the Viterbi decoding algorithm to resolve depth features beyond the nominal resolution limit of a volume holographic profilometry system. The formulation treats the truncated point-spread function as an intersymbol interference and uses surface constraints and transition constraints to reduce the computational complexity. A factor-of-5 improvement in resolution was obtained in our experimental demonstration.

Volume holographic imaging

We overview the properties of volume holographic imaging properties and design framework for depth-selective and hyperspectral imaging. The Bragg selectivity and degeneracy properties of volume holograms are used for optical slicing and space-selective dispersion.

Maximum-likelihood surface reconstruction with Viterbi algorithm for volume holographic profilometry

We use maximum-likelihood (ML) estimation to clean up the depth-variant image blur in volume holographic profilometry and to reconstruct the surface with high accuracy. Viterbi algorithm is used in ML estimation to reduce computational complexity and bit error rate.

Super-resolving volume holographic profilometry

We address the use of transmission geometry volume holograms as depth-selective imaging elements in profilometry. We derive the point-spread function (PSF) of the volume holographic imaging system using volume diffraction theory and use the PSF to estimate depth resolution. Experimentally measured PSF and depth-selective images are presented to verify the theoretical predictions. Furthermore, we show that with prior knowledge of the object, depth resolution can be improved greatly with the method of inclined illumination. In more general cases, super resolution can also be achieved with digital post-processing methods such as Viterbi algorithm (VA). We show that computational complexity can be reduced with surface constraints. Resolution improvement by a factor of 5 was obtained in experimental demonstration.

Volume holographic imaging for surface metrology with long working distances

Volume holographic imaging (VHI) utilizes the Bragg selectivity of volume holograms to achieve 3D optical slicing. The depth resolution of VHI degrades quadratically with increasing object distance like most 3D imaging systems. We have devised an imaging scheme that takes advantage of the superior lateral resolution of VHI and a-priori surface information about the object to build a profilometer that can resolve 50 μm features at a working distance of ≈ 50 cm. We discuss the scheme and present experimental results of surface profiles of MEMS devices.

Resonant holographic optics

We analyze the image quality of resonant holographic imaging systems. We show that Gaussian apodization, implemented with a Hermite-Gaussian reference beams inside a confocal cavity greatly improves image quality.