Real-time coherence holography

We propose a simple implementation of off-axis coherence holography with a commercial projector combined with a Sagnac radial shearing interferometer. The projector functions as a device for display and incoherent illumination of a coherence hologram, which permits reconstruction of the hologram with a generic spatially-incoherent quasimonochromatic thermal light source. The Sagnac radial shearing interferometer, with its inherent stability of a common-path interferometer and controllable magnification introduced by variable shear, functions as a device for correlating optical fields to detect the 3-D coherence function that represents the object recorded in the coherence hologram. A set of phase-shifted Fourier transform holograms was displayed sequentially with the projector. The coherence function was detected by applying the phase-shift technique to the Sagnac radial shearing interferometer, and the object was reconstructed as the 3-D correlation map of the fields diffracted from the hologram. The technique can be applied for dispersion-free spatial coherence tomography and profilometry.

In this Letter, an all-fiber tunable mode converter for a mini-two-arm Mach-Zehnder interferometer (MTA-MZI) is proposed and realized for the first time to our knowledge. Employing an electric arc discharge technology, we couple a multi-mode fiber (MMF) and a single-mode fiber (SMF), resulting in an MZI characterized by centimeter-scale arms. The varied sensitivity of fiber modes to curvature makes the high-order modes of the MMF more prone to leakage when subjected to bending, leading to alterations in the output interference fringe pattern of the MZI. Through continuous monitoring of the interference fringes of the MZI, we effectively detect the mode properties within the MZI in real time. In addition, a verification experiment is conducted by introducing a peanut structure to excite further higher-order modes of light to enter the MZI in advance. Upon modifying the curvature of the MZI, these excited higher-order modes leak, causing the interference fringe pattern to revert to its initial state without a peanut structure. This experimental validation highlights the potential employment of the MTA-MZI as an all-fiber mode converter and paves the way for optical field mode conversion within an all-fiber framework.

We propose a novel optical instrument to simultaneously measure the phase variations of both orthogonal linear polarizations in a Mach–Zehnder interferometer. An integrated Ti-indiffused LiNbO3 Mach–Zehnder modulator is adopted for phase modulation and the optical homodyne scheme is used to measure the phase variations in the experimental setup. By using the multiplexed capabilities and flexible designs of a LABVIEW-based platform, the simultaneous measurements with real-time display of output interferomertic signals, spectrum results, and phase variations for both orthogonal polarizations, have been successfully demonstrated in this study. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:334–337, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25703

We propose a fast, new, position-independent reconstruction method, to our knowledge, for coherence holography using deep learning (DL) method, dubbed fast deep coherence holography (FDCH). Our trained network was developed to reconstruct the complex object field at the location corresponding to the position of the camera, which opens the ability to apply angular spectrum propagation to reconstruct the 3D object. Phase-shift coherence holography is a traditional analytical technique that also reconstructs the complex object, but it is subject to noise such as experimental noise, camera noise. In a previous work, deep coherence holography (DCH) was developed to predict a non-diffracted field from a noisy image, but it requires the camera to be inserted at the right position of the non-diffracted field, which increases the complexity and the cost of the experimental setup. In addition, while the analytical method one requires Nsin (Nsin>3) captured interferograms to reconstruct the complex field, and thenumber of the recorded images of the DCH is proportional to the number of sub-objects contained in the object, our new proposed DL method only needs two images at a random camera position. Hence, the total reconstruction time is reduced. Not only does the FDCH reconstruct the 3D object faster at any random position, but it also yields a better result than the above methods in terms of accuracy.

In this paper, we proposed a novel optical geometry for direct visualization of spatial coherence function. The full-field distribution of the coherence function from an incoherent circular aperture source is experimentally investigated. Meanwhile, the experiments of non-diffracting coherence function from an incoherent circular slit source have also been done. The experimental results show that the coherence function generated by an incoherent circular aperture source is in the form of Fresnel diffraction integral which diffracting during the propagation and the coherence function generated by an incoherent circular slit source is unaltered by propagating in free space.

Investigation of the spatial coherence function of wind loads on lattice frame structures

Method of generating a vortex array embedded in a partially coherent beam is proposed and experimentally demonstrated. The vortex array exists in the complex coherence function of a random field arising due to interference of three independent coherence functions with appropriate phase profiles. Existence of the vortex array is confirmed by presenting amplitude and phase distributions of the complex coherence function. The phase structure of the complex coherence function, embedded with a vortex array, is obtained by interfering it with an independent fourth coherence function known as a reference and applying the Fourier fringe analysis technique to the cross-covariance of the intensity of the resultant random field.

We propose a reconstruction method for coherence holography using deep neural networks. cGAN and U-NET models were developed to reconstruct 3D complex objects from recorded interferograms. Our proposed methods, dubbed deep coherence holography (DCH), predict the non-diffracted fields or the sub-objects included in the 3D object from the captured interferograms, yielding better reconstructed objects than the traditional analytical imaging methods in terms of accuracy, resolution, and time. The DCH needs one image per sub-object as opposed to N images for the traditional sin-fit algorithm, and hence the total reconstruction time is reduced by N×. Furthermore, with noisy interferograms the DCH amplitude mean square reconstruction error (MSE) is 5×104× and 104× and phase MSE is 102× and 3×103× better than Fourier fringe and sin-fit algorithms, respectively. The amplitude peak signal to noise ratio (PSNR) is 3× and 2× and phase PSNR is 5× and 3× better than Fourier fringe and sin-fit algorithms, respectively. The reconstruction resolution is the same as sin-fit but 2× better than the Fourier fringe analysis technique.

Copper was electrodeposited from 0.9 M aqueous solution for 8 s during a free‐fall experiment in a drop shaft. A horizontally oriented quasi two‐dimensional electrolytic cell, in which a 200 μm thick electrolyte layer was sandwiched between two sheets of slide glass, fell in the shaft. Electrolysis was conducted at constant current densities from 0.05 to , and the potential difference between electrodes was simultaneously monitored. A common‐path microscopic interferometer was installed in the capsule. The time variation of interference fringe pattern, corresponding to the concentration profile due to the ionic mass‐transfer rate accompanied with copper electrodeposition, was measured in situ around the periphery of a 1 mm diam circular cathode. The morphology of copper electrodeposited under microgravity conditions was compared with that obtained in a ground level experiment. The development of diffusion layer thickness measured by the interferometer increased with the square root of time during the 8 s experiment. The transient diffusion model combined with the migration effect reasonably explained the development of diffusion layer thickness. Calculated surface concentrations corresponded with the measured time variation of potential difference between electrodes. Under the gravitational field, the radius of annual interference fringe pattern developed at a rate much faster than that under microgravity, beginning 1 or 3 s after initiation of electrodeposition. Natural convection was evident in the ground level experiment, even using such a shallow electrolyte layer. Under microgravity, lower index planes preferentially grew to form a smaller number of larger grains, even though electrodeposition was conducted at only for 8 s.

Summary form only given. Interferometry is the basis of many high-precision measurements. The ultimate limit to the precision is due to quantum effects. This limit is most easily explored for a Mach-Zehnder interferometer The outputs of this device can be measured to yield an estimate /spl phi/ of the phase difference /spl phi/ between the two arms of the interferometer. It is well known that this can achieve the standard quantum limit for phase variance when an N-photon number state enters one input port. Several authors have proposed ways of reducing the phase variance to the Heisenberg limit. In this paper we show that there is a physical measurement scheme using photodetectors and feedback that is almost as good as the optimal measurement. The fundamental idea is that, in addition to the unknown phase we wish to measure, /spl phi/, in one arm of the interferometer, we introduce a known phase shift, /spl Phi/, into the other arm of the interferometer. After each photodetection we adjust this introduced phase shift in order to minimize the expected uncertainty of our best phase estimate /spl phi/ after the next photodetection. This feedback process is uniquely defined using Bayesian statistics, and can be solved exactly for moderate photon numbers.

Instantaneous phase-stepping interferometry based on a pixelated micro-polarizer array

Complex self-coherence function determination using geometric phase techniques

An extended difference of coherence test for comparing and combining several independent coherence estimates: theory and application to the study of motor units and physiological tremor

A two-step iterative algorithm is described for designing pupil functions for synthesis of bipolar point spread functions in a two-channel incoherent spatial filtering system. The first step uses the method of projections onto convex sets to determine an appropriate bias for the system pupil functions. This bias determines the complementary point spread functions and therefore the magnitude of the corresponding coherent spread functions. The phase of the coherent spread functions is obtained in the second step via iterative application of a magnitude constraint and a finite support constraint. With both magnitude and phase of the coherent spread functions established, the corresponding pupil functions are realized via Fourier transformation. Results are presented for a 2-D bandpass filter and compared with analytically obtained results. The comparison suggests that the iterative algorithm yields bias functions having less energy than bias functions determined by previously proposed analytic methods.

We investigate the possibility of interferometric optical field sensor with DMD forming a series of sampling interferometers in the pupil of an optical system. Our preliminary experiment validates the feasibility of our approach for the field reconstruction in the case of coherent field. We believe that this approach can be extended to sensing of speckle patterns and even incoherent fields, by analyzing not only the intensity and phase, but also the amplitude and the visibility of the interference patterns. Such analysis would yield the complete complex amplitude and/or coherence function, making the approach directly applicable to a wide range of inverse source problems in optics.