查看更多>>摘要：We present numerical studies on a simple metamaterial absorber design operating at near-infrared frequencies. The absorber consists of a one-dimensional silicon strip array on a silicon substrate followed by a thin layer of gold with a thickness of 30 nm. Computer Simulation Technology Microwave Studio (CST Microwave Studio) based on finite integration technique was used for numerical simulations and to understand the mechanism of absorption in the system. Simulation results show that the absorber has an absorptance of around 0.99 with a full width at half-maximum (FWHM) of 18 nm. The absorption is caused by the simultaneous excitation of Fabry-Perot (FP) cavity resonance in the strip and between the consecutive strips, which leads to the confinement of electric fields in the strip and between the strips. In addition, we have also analyzed the sensing performance of the absorber in refractive index (RI) and found that it has high sensitivity and a large figure of merit (FOM). Therefore, the absorber can be exploited for high-performance RI sensor for sensing chemicals and biological samples, and even acidic samples due to its component's wise robustness.
查看更多>>摘要：The ability to distinguish and characterize differences in the optical properties of biological samples is crucial in various disease diagnosis applications. The present study investigates the feasibility for utilizing the Mueller matrix decomposition method based on a UV light Stokes polarimeter and a Mueller matrix imaging polarimetry technique based on a He-Ne laser diode to detect Hepatitis B virus (HBV) infection in human plasma samples. In the Mueller matrix decomposition method, the orientation angle of linear birefringence (a), phase retardance (fl), optical rotation angle of circular birefringence (y), orientation angle of linear dichroism (Oa), linear dichroism (D), and circular dichroism (R) are extracted for negative and positive human plasma HBV samples and the differences between them are analyzed. It is shown that statistically significant differences exist between the fl, y and R values of the negative and positive samples, respectively. Moreover, for both methods, the positive HBV samples show a greater degree of anisotropy than the negative samples. In general, the results confirm that both methods provide a feasible approach for distinguishing between negative and positive HBV samples and thus serve as potential tools for HBV detection and diagnosis.
查看更多>>摘要：Evolving from time stretching technique based on ultrashort optical pulse, wavelength-to-space-mapping imaging has become a common strategy for single-shot ultrafast imaging. In the technique, chirped broadband child pulses are generated and used to probe the transient scene typically, and the frames with temporal resolution up to picosecond scale can be achieved. Here we propose a single-shot ultrafast holographic microscopic system through a wide-spectrum pulse. A digital micromirror device (DMD)-based quasi-4f system and a dispersive medium are involved to generate chirped multi-wavelengths child pulses in sequence. A series of off-axis holograms are spatially dispersed and separated by a grating and captured simultaneously. The time-resolved three-dimensional (3D) profiles are retrieved using the reconstruction algorithm. In the paper, the temporal evolution of optical pulse and the mechanism of holographic imaging are detailed and numerically analyzed. A 10-frames holographic microscopic system with field of view (FOV) of 0.2 mm x 0.2 mm, frame rate of 6.8 x 1010 fps and exposure time of 5.4 ps is realized, where the interval and linewidth of the multi-wavelengths are 10 nm and 0.25 nm, respectively.
查看更多>>摘要：Deep learning technology has been used as a new approach for forward simulation and inverse design of nanophotonic structures. Deep learning technology greatly reduces the time of optical simulation and enables us to use back-propagation (BP) algorithm to optimize design parameters. But BP is very sensitive to the initial values and hard to converge to the optimal value for some initial values. In this research, we propose a hybrid optimization strategy that combined differential evolution (DE) with BP algorithm for the inverse design of multilayer nanofilms structures. The proposed method effectively utilizes the global parallel exploration capability of DE and the local exploitation capability of gradient descent based on BP. It can alleviate the sensitivity of the initial values for the BP algorithm and effectively compensate for the slower convergence properties of the DE. The results suggest that the hybrid DE-BP algorithm can greatly speed up the inverse design process of multilayer nanofilms and can search in a larger parameter space that even exceeds the parameter range of the training dataset that is used to train the forward prediction neural networks.
查看更多>>摘要：Reducing the dark current of InGaAs/InP avalanche photodiodes (APDs) is an important way to improve the performance of single-photon detection system. Therefore, the active region size of the APD is getting smaller and smaller to reduce the dark current, but that is based on sacrificing the quantum efficiency of the device. In this work, a metalens array is integrated with micro APD array, the metalens structure is proposed to converge light from tens of micrometers to several micrometers and form a focusing effect on the absorber layer to compensate for the loss of absorption efficiency due to the reduction in the size of the APD. The results show that the APD integrated with the metalens array structure behaves enhanced broadband absorption efficiency at optical-communication wavelengths. This design and proposed scheme offer the possibility of reducing the effective size of the APD to 2 mu m while improving broad-band optical response, owing to its light convergence capability.
查看更多>>摘要：Fourier ptychographic microscopy is a super-resolution technique, which could break through the Space-Band Product (SBP) limit of the system by employing varied-illumination and phase retrieval algorithm. A LED array is used to provide angularly varying illuminations, which is portable and cheap. However, the installation accuracy of the LED array is not sufficient, resulting in position misalignment errors. The misalignment errors not only cause the calculation error of the sub-apertures in the frequency domain, but also the artifacts in reconstruction images. Although some correction methods have been proposed, the correction ability of these methods cannot deal with the misalignment errors well. In this paper, we proposed a misalignment errors correction method. This method uses the Particle swarm optimization (PSO) algorithm to search the four misalignment parameters (delta x, delta y, theta, delta h) in space domain. It is termed as Space based correction (SBC) method. Compared with the state-of-art methods, the SBC method is more stable and accuracy.& nbsp;
查看更多>>摘要：In this paper, an all-optical microwave oscillator is proposed and experimentally demonstrated. Via cascaded stimulated Brillouin scattering effects, the second-order Stokes wave can be obtained. A microwave envelope can be generated by beating the continuous wave and the second-order Stokes wave. The functions of microwave envelope detection and feedback modulation are implemented by using cross-gain modulation of a semiconductor optical amplifier, further, the Vernier effect is used to improve the microwave signal. The second Brillouin-selective sideband amplification is employed to enhance oscillation frequency. In this reported scheme, the electrical microwave devices such as high-Q electrical bandpass filter and electro-optic modulator are not required in the microwave oscillation feedback loop. This all-optical microwave oscillator can shake off the electronic block. Meanwhile, the frequency of the generated microwave signal is twice the Stokes frequency shift of the stimulated Brillouin scattering. Furthermore, it can also result in phase noise reduction that only one laser source is used here. Finally, coupled cavities are used to suppress the harmonic presentation. The experimental results show that the all-optical microwave oscillator can generate a single-mode-microwave oscillation signal with a frequency of 21.66 GHz. The phase noise value at 10 kHz frequency offset is & nbsp; -90 dBc/Hz.
查看更多>>摘要：In this paper, the electric field enhancement of a two-dimensional symmetric gold array (2DSGA) fabricated by laser interference lithography (LIL), as a surface-enhanced Raman scattering (SERS) substrate, is thoroughly discussed and analyzed. The structure of 2DSGA is closely related to the exposure time and the thickness of the photoresist. 2DSGA, insensitive to the polarization of incident light, has a high enhancement factor (EF) with a lithography depth of 40 similar to 60 nm. The pattern fabricated by LIL will change and the EF will decrease when the theoretical lithography depth exceeds the photoresist thickness due to different exposure times. To obtain a high EF for 2DSGA, it is necessary to control the thickness of the photoresist and exposure time, which contributes to the actual preparation of SERS substrate.
查看更多>>摘要：An optical waveguide microcantilever sensor with a dual-output waveguide readout is developed to obtain a linear response for the deflection of cantilever. A finite element method is employed to characterize the optical waveguide microcantilever sensor. A systematic and detailed discussion has been presented to describe an optical waveguide cantilever sensor with a dual-output waveguide. One can see that most of the results are interesting, even very different from general opinions. The design is a tradeoff of the sensitivity, linearity and operation range. These will be helpful for an optimized design of the microcantilever sensor.
查看更多>>摘要：We theoretically investigate the propagation and non-reciprocal properties of cadmium selenide (CdSe) nanowire (NW), and achieve strongly field enhancement at communication wavelength of 1550 nm when combined with the hybrid nanostructure. By varying the parameters of the nanostructure, i.e., MgF2 and Ag substrates, together with grooves, relations between these properties and the parameters are illustrated in details. Particularly, with an optimal design, the propagation performance of the NW is highly improved. Moreover, by breaking the symmetry of the system, the non-reciprocal property without time modulations is obtained with high contrast employing the further optimal design. These novel results are significant to related applications such as photonic integrated circuit and optical communications.
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Elsevier