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Total-variation regularization is applied at each iteration of an iterative framework for optical diffraction tomography. Numerical and experimental tests are performed using various highly scattering objects, and significant improvement in reconstruction SNR are demonstrated.

Optical diffraction tomography (ODT) is a label-free and noninvasive technique for biological imaging. However, ODT is only applicable to weakly scattering objects. To extend ODT to the multiple-scattering regime, more advanced inversion algorithms have been developed, including optimization-based ODT (Opti-ODT) and iterative ODT (iODT). In this paper, we propose a combined strategy, namely, an iODT initialization for Opti-ODT, based on the observed complementarity of their individual advantages. This study numerically demonstrates that under this combined strategy, the reconstruction can accurately converge to a better local minimum, especially in the case of multiply scattering objects with large optical path differences.

Optical diffraction tomography (ODT) is used to reconstruct refractive-index distributions from multiple measurements in the object rotating configuration (ORC) or the illumination scanning configuration (ISC). Because of its fast data acquisition and stability, ISC-based ODT has been widely used for biological imaging. ODT typically fails to reconstruct multiply-scattering samples. The previously developed iterative ODT (iODT) was for the multiply-scattering objects in ORC, and could not be directly applied to ISC. To resolve this mismatch, we developed an ISC update and numerically demonstrated its accuracy. With the same prior knowledge, iODT-ISC outperforms conventional ODT in resolving the missing-angle problem.

Non-mode-selective (NMS) multiplexers (muxes) are highly desirable for coherent power combining to produce a high-power beam with a shaped profile (wavefront synthesis) from discrete, phase-locked emitters. We propose a design for a multi-plane light conversion (MPLC)-based NMS mux, which requires only a few phase masks for coherently combining hundreds of discrete input beams into an output beam consisting of hundreds of Hermite–Gaussian (HG) modes. The combination of HG modes as a base can further construct a beam with arbitrary wavefront. The low number of phase masks is attributed to the identical zero-crossing structure of the Hadamard-coded input arrays and of the output HG modes, enabling the practicality of such devices. An NMS mux supporting 256 HG modes is designed using only seven phase masks, and achieves an insertion loss of$-1.6\mathrm{dB}$, mode-dependent loss of 4.7 dB, and average total mode crosstalk of$-4.4\mathrm{dB}$. Additionally, this design, featuring equal power for all input beams, enables phase-only control in coherent power combining, resulting in significant simplifications and fast convergence compared with phase-and-amplitude control.

Conventional optical diffraction tomography (ODT) techniques fail in the presence of multiple scattering, and the problem becomes even more challenging when the medium is also lossy. Iterative ODT (iODT), which was shown recently to be more tolerant to multiple scattering than conventional ODT, is here augmented with an error-subtraction (ES) module. Numerical results demonstrate the accuracy and efficiency of iODT with ES for reconstructing multiply-scattering objects with complex refractive index.

We propose a Hermite–Gaussian (HG) mode-demulti-plexing hybrid (MDH) for coherent detection of mode-division multiplexed signals. The MDH, which performs multiple functionalities, including demultiplexing, local oscillator splitting, and optical 90-deg mixing, is realized based on the multi-plane light conversion technique. An isosceles right triangle output layout is employed to reduce the number of phase masks to fewer than the number of modes, significantly simplifying the construction of the MDH. A 10-Hermite–Gaussian (HG) mode MDH with only five phase masks is demonstrated by numerical simulation, achieving an insertion loss (IL) and mode dependent loss as low as$-<\#comment/>2.3$and 1.7 dB, respectively. The IL was further reduced to$-<\#comment/>1.5\mathrm{d}\mathrm{B}$through optimization of MDH parameters, such as the beam waists of the input HG modes and the output spots.