Hamidreza Habibiyan

The concept of performing mathematical operations with metasurfaces has been suggested by Silva et al (Science 343, 160 (2014)). However, their proposed structure in implementing any transfer function (corresponding to any mathematical operator) for various input signals faces limitations. To tackle this issue, in this study, four different scenarios are proposed on their metasurface-based structure to generalize in a way that can implement each spatial transfer function. To evaluate the performance of the presented scenarios, seven different transfer functions are simulated to encompass a wide range of mathematical operators in the spatial domain. The implementations are based on the Fourier approach. Simulation results based on the finite element method closely match the desired values. From the results of this study, it can be seen that the third and fourth scenarios provide better accuracy. For example, when the fifth transfer function is performed by the basic structure and the fourth scenario, the normalized root mean square error, decreases from the value of 0.235 to the value of 0.0348, respectively. Furthermore, a tunable structure is achievable using the third scenario to produce different operators on the same structure. The realization of these scenarios is possible by using nanostructure-based metasurfaces.

The optical implementation of mathematical spatial operators is a critical step toward achieving practical high-speed, low-energy analog optical processors. In recent years, it has been shown that using fractional derivatives in many engineering and science applications leads to more accurate results. In the case of optical spatial mathematical operators, the derivatives of the first and second orders have been investigated. But no research has been performed on fractional derivatives. On the other hand, in previous studies, each structure is dedicated to a single integer order derivative. This paper proposes a tunable structure made of graphene arrays on silica to implement fractional derivative orders smaller than two, as well as first and second orders. The approach used for derivatives implementation is based on the Fourier transform with two graded index lenses positioned at the structure's sides and three stacked periodic graphene-based transmit arrays in middle. The distance between the graded index lenses and the nearest graphene array is different for the derivatives of order smaller than one and between one and two. In fact, to implement all derivatives, we need two devices with the same structure having a slight difference in parameters. Simulation results based on the finite element method closely match the desired values. Given the tunability of the transmission coefficient of the proposed structure in the approximate amplitude range of [0,1] and phase range of [-180, 180], on top of the acceptable implementation of the derivative operator, this structure allows obtaining other spatial multi-purpose operators, which are a prelude to achieving analog optical processors and even improving the optical studies performed in image processing.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Early detection of circulating tumor cells (CTCs) in a patient's blood is essential to accurate prognosis and effective cancer treatment monitoring. The methods used to detect and separate CTCs should have a high recovery rate and ensure cells viability for post-processing operations, such as cell culture and genetic analysis. In this paper, a novel dielectrophoresis (DEP)-based microfluidic system is presented for separating MDA-MB-231 cancer cells from various subtypes of WBCs with the practical cell viability approach. Three configurations for the sidewall electrodes are investigated to evaluate the separation performance. The simulation results based on the finite-element method show that semi-circular electrodes have the best performance with a recovery rate of nearly 95% under the same operational and geometric conditions. In this configuration, the maximum applied electric field (1.11 × 10⁵ V/m) to separate MDA-MB-231 is lower than the threshold value for cell electroporation. Also, the Joule heating study in this configuration shows that the cells are not damaged in the fluid temperature gradient (equal to 1 K). We hope that such a complete and step-by-step design is suitable to achieve DEP-based applicable cell separation biochips.

Graphene has originally low absorption at telecommunication wavelengths. Therefore it is necessary to overcome this hurdle to use graphene as absorption media in many optoelectronic devices. In this paper, a narrow-bandwidth graphenebased total absorber is numerically and theoretically investigated.The proposed structure consists of a graphene sheet on a Si rectangular grating, which is placed on SiO2 spacer backed with the gold substrate. Due to the absence of plasmonic response of graphene in near infrared wavelengths, the method of critical coupling with guided mode resonance is employed to realize highly efficient absorption of light in the graphene sheet. The simulation results show that the maximum magnitude of absorption reaches near 100% (43-fold enhancement compared to isolated monolayer graphene absorption of 2.3%). Also, based on calculated results, the absorption of the proposed structure can be controlled by altering the geometrical parameters and chemical potential of graphene. In particular, the absorption spectrum is modulated by the external gate voltage. Moreover, we find that the operating wavelength is adjusted flexibly by incident source angle. As a result, the proposed absorber has high directivity and can act similar to an antenna. The control ability of total absorption in the proposed structure provides potential applications for the realization of ultra-compact and high-performance optoelectronic devices, such as sensors and narrow-band filters.