We propose and experimentally demonstrate an economical optical tweezers probe based on the fusion of several commercial optical fibers. By optimizing the structural parameters of the probe, non-contact active capture and manipulation of single or multiple biological particles were achieved. First, the probe structural parameter range was analyzed theoretically, and the theory was cross-verified by the finite element method. Second, the influence of the probe structure and length parameters on the laser focusing performance and particle capture ability was studied, and the optimal structural parameters of the probe in particle capture were determined. The measured capture distance exceeded 50 mu m, and the movement velocity of the particle during manipulation was measured. Finally, the capture performance before and after parameter optimization was compared with the dynamic effect of the particles, and the generation mechanism of multiple light traps and the mechanical properties of multi-particles during multi-particle capture were studied. The results indicate that this probe is expected to be used in biological or chemical micromanipulation research. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

In the current context of information explosion, securing the physical layer in the backbone networks of coherent optical communication is vitally important. In this letter, we experimentally validate a secure communication scheme for coherent optical communication systems based on electro-optic phase feedback encryption, thereby successfully transmitting a 40 Gb/s dual-polarization quadrature phase shift keying (DP-QPSK) signal over a distance of 180 km. By strategically incorporating a delay line interferometer and a dispersion component within the electro-optic feedback loop, it is possible to generate random phase scrambling at a moderate modulation depth. With the utilization of commercial hardware, the encryption of DP-QPSK signals can be seamlessly accomplished in a plug-and-play manner, removing the necessity for additional synchronization or key distribution systems. The proposed scheme paves a new way to protect the polarization-multiplexing signals and offers a promising approach for secure coherent optical communication system.

ABSTRACT We analyze the impact of the refractive index of optical fibers on the focusing properties of a miniaturized graded‐index (GRIN) fiber probe. The ABCD ray transfer matrix and characteristic parameters are employed to characterize the working distance, focusing spot size, and the depth of field effectively. The three‐dimensional (3‐D) function diagrams and two‐dimensional (2‐D) graphs are used to illustrate the impact of the no‐core fiber (NCF) refractive index and the center refractive index of GRIN fiber on the focusing properties. Numerical analysis results show that when the length of the NCF is 0.36 mm and the GRIN fiber is 0.1 mm, the variation of the refractive index of the NCF between 1.44 and 1.52 leads to the variation of the working distance in the range of 0.02 mm, while the focusing spot size varies in the range of 5 μm. A comparison of 12 probe samples reveals that a 0.02 difference in the center refractive index of GRIN fiber could result in a 0.16 mm variation in working distance and a variation in focusing spot size of over 3 μm. The experimental results indicate that alterations in the length of the fibers have a considerable effect on the focusing properties of the probe. In contrast, the range of variation in focusing properties with fiber refractive index is relatively limited.

A light and displacement-compensation-based iPPG algorithm is proposed in this paper for heart-rate measurement in complex detection conditions. Two compensation sub-algorithms, including light compensation and displacement compensation, are designed and integrated into the iPPG algorithm for more accurate heart-rate measurement. In the light-compensation sub-algorithm, the measurement deviation caused by the ambient light change is compensated by the mean filter-based light adjustment strategy. In the displacement-compensation sub-algorithm, the measurement deviation caused by the subject motion is compensated by the optical flow-based displacement calculation strategy. A series of heart-rate measurement experiments are conducted to verify the effectiveness of the proposed method. Compared with conventional iPPG, the average measurement accuracy increases by 3.8% under different detection distances and 5.0% under different light intensities.

Bandwidth is the core network resource. How to predict future traffic and adjust the network resource relocation early is an urgent problem to be solved. To this problem, a multi-time granularity GRU-BP neural network is proposed in this study for network traffic prediction. In the method, the network traffic data is fitted firstly by the cubic spline curve, and the fitted data is extracted according to different time granularities. Then, several GRU neural networks corresponding to specific time granularities are used for network traffic pre-prediction. Finally, the pre-prediction results of all the GRU neural networks are fed into the fully connected neural network. The fully connected neural network outputs the final network traffic prediction results. Comparison results show that the proposed method can improve the calculation accuracy by 9.0 % and reduce the calculation time by 28.6 %.

In order to obtain soft switching and simplify the controlling circuit of an interleaved two-switch Buck-Boost converter, two types of three-switch interleaved Buck-Boost converters are proposed in this paper. Firstly, this paper analyses the coupling process of the presented converters under a large coupling coefficient. Then, the operating principle of the two converters is given in detail. And it is concluded that the expended duty cycle and soft switching of most of power devices can be obtained and a sharing-current circuit is also not needed. This will deeply simplify the controlling circuit. Finally, the simulation and experimental results verify the analysis.

Psychological stress is a big threat to people's health. Early detection of psychological stress is important. The design of a stress recognition device based on the ECG (electrocardiograph) signal is presented in this paper. The device features intelligence, precision, portability, fast response, and low power consumption. In the design, the ECG signals are acquired by the AD8232 ECG module and processed by a low power consumption FPGA (Field Programmable Gated Array) development board PYNQ-Z2. Meanwhile, a modified Deep Forest model named Aw-Deep Forest (Adaptive Weight Deep Forest) is proposed. The Aw-Deep Forest has better performance than the Deep Forest model because it improves the fitting quality of the forests. By implementing the Aw-Deep Forest model on the FPGA, the device can assess people's state of psychological stress by analyzing the HRV (heart rate variability) parameters from ECG data. This paper mainly introduces the detailed process of ECG signal collecting, filtering, analog signal to digital signal conversion, HRV parameter analysis, and psychological stress recognition with Aw-Deep Forest. The final accuracy is 81.39%.

•Effective beam expansion range of no-core fiber length in an ultra-small Gradient-index fiber probe is proposed.•Verifying calculation method of effective beam expansion length of no-core fiber.•Analyzing the influence of no-core fiber on focusing performance of GRIN fiber probes.•Optimizing the structure of the ultra-small Gradient-index fiber probe.

Gradient-index(GRIN) fiber probe is an all-fiber ultra-small optical lens, which has broad application prospects in endoscopic image detection in small spatial tissues such as cardiovascular. However, its development lacks a systematic theoretical system. This paper discusses the key issues of the design, fabrication and performance testing methods of the probe. Based on the characteristics parameters of GRIN fiber probe, comparative analysis is conducted between the analytical method and numerical simulation methods. An integrated high precision optical fiber welding and cutting device is presented for the fabrication of ultra-small GRIN optical fiber probe. In addition, the method and device for detecting the focusing performance of ultra-small GRIN fiber probe are analyzed. As a result, a system method for design, fabrication and performance testing is provided for the research of GRIN fiber probes.

A high-precision test method based on infinity optical transformation system was investigated to detect the focusing performance of a small fiber lens. Consider the ultra-small gradient-index (GRIN) fiber probe as an example of the small fiber lens, its characters of focusing performances are analyzed. The infinity optical transformation system was employed to amplify and capture the exit beam from the probe in the non-contact mode. Then the curve fitting method is used to deal with the experimental data. The result shows that with the given small fiber lens the obtained working distance and waist diameter in the experiment system are 0.72 mm and 35 mu m, respectively, while the calculated working distance and waist diameter based on the theory are 0.75 mm and 33 mu m accordingly. The experimental results are in good agreement with the theoretical results. Therefore, the proposed test method based on infinity optical transformation system is applicable to detect the focusing performance of the small fiber lens.

The influence of transmission medium on the focusing performance of gradient-index (GRIN) fiber probe is analyzed for the development and performance evaluation of the ultra-small probe. ABCD matrix transformation is employed to derive the functional relationship between the focusing performance of GRIN fiber probe and the refractive index of transmission medium and present the curve graphs of working distance, spot size and depth of field on refractive index of transmission medium. Under the same parameters, the working distance and the depth of field of GRIN fiber probe increase with the increase of refractive index of transmission medium, but the spot size remains the same. The result shows that transmission medium has a certain influence on the working distance and the depth of field of GRIN fiber probe but has nothing to do with spot size.

The curve-fitting algorithm is adopted to measure the focusing constant of a gradient-index (GRIN) fiber lens, which is used to further design ultra-small GRIN fiber probes. Firstly, the refractive index profile of a GRIN fiber lens is acquired by using the Optical Fiber Refractive Index Profile tester. And the focusing constant of the GRIN fiber lens is obtained by means of the curve-fitting algorithm of quadratic polynomial. Secondly, the measured focusing constant is used to design ultra-small GRIN fiber probes with different focusing properties. Thirdly, according to the designed optical probe models, GRIN fiber probe samples have been fabricated and tested. Finally, comparative analysis is conducted between the theoretical focusing performance parameters and the experimentally measured values. The results show that, in the given condition, the fitted value of the focusing constant of GRIN fiber lens and the theoretical focusing performance parameters of GRIN fiber probes, respectively agree well with the nominal value provided by the manufacturer and the experimentally measured data. Therefore, the proposed methods of measuring the focusing constant of GRIN fiber lens and its application in designing GRIN fiber probes are validated and feasible to further developing ultra-small GRIN fiber probes requiring specific optical focusing performance. (C) 2016 Elsevier Ltd. All rights reserved.

提出了基于曲线拟合的光纤透镜聚焦常数的测试方法,用于超小自聚焦光纤探头研制过程中聚焦常数的直接测试.基于自聚焦光纤透镜模型及其折射率分布特征,研究了测量自聚焦光纤透镜聚焦常数的二次多项式拟合和线性化拟合算法.论述了聚焦常数对超小自聚焦光纤探针传光性能的影响.利用光纤端面折射率测试仪测试自聚焦光纤的折射率分布轮廓曲线,根据二次多项式拟合和线性化拟合算法分别求得聚焦常数和中心折射率.实验结果显示,利用二次多项式拟合算法和线性拟合算法求出的聚焦常数分别为5.587 mm-1和5.513 mm1,与厂家的标称值5.5 mm-1基本吻合,表明曲线拟合算法适用于对自聚焦光纤透镜聚焦常数的测量与分析.

Fabrication method and device of ultra-small gradient-index (GRIN) fiber probe were investigated in order to explore the development of ultra-small probes for optical coherence tomography (OCT) imaging. The beam-expanding effect of no-core fiber (NCF) and the focusing properties of the GRIN fiber lens were analyzed based on the model of GRIN fiber probe consisting of single-mode fiber (SMF), NCF and GRIN fiber lens. A stereo microscope based system was developed to fabricate the GRIN fiber probe. A fiber fusion splicer and an ultrasonic cleaver were used to weld and cut the fiber respectively. A confocal microscopy was used to measure the dimensions of probe components. The results show that the sizes of probe components developed are at the level of millimeter. Therefore, the proposed experimental system meets the fabrication requirements of an ultra-small self-focusing GRIN fiber probe. This shows that this fabrication device and method can be employed in the fabrication of ultrasmall self-focusing GRIN fiber probe and applied in the study of miniaturized optical probes and OCT systems.

A high-precision curve fitting method was investigated to evaluate the focusing performance of an ultra-small gradient-index (GRIN) fiber probe. Firstly, an overview of the GRIN fiber probe model is given. Secondly, according to the characteristics of Gaussian beam focusing through the GRIN fiber probe, the polynomial fitting method is proposed to evaluate the waist position and spot size of the focused beam. Finally, the evaluation method is analyzed for validation. The results show that, with the curve fitting method, the obtained working distance and waist diameter are 0.93 mm and 28.2 ��m, respectively. Under the same conditions, the experimentally measured working distance and waist diameter are 1 mm and 28 ��m, accordingly. The fitting results are in good agreement with the experiment data. Therefore, the proposed polynomial curve fitting method is applicable to evaluate the focusing performance of GRIN fiber probe.

In order to optimize ultra-small gradient-index (GRIN) fiber probes and provide a theoretical prediction for the fabrication of such probes with high performance, focusing performance of the GRIN fiber probe is further analyzed based on the optical characteristic parameters. According to the optical model of the GRIN fiber probe and its mathematical expressions of characteristic parameters, the three-dimensional (3-D) function diagram is used for analyzing the impact of the lengths of probe components on the characteristic parameters. Partial derivatives of the mathematical expressions of characteristics are derived to analyze the mutation of focusing performance caused by the different lengths of probe components. According to the analytical results, our predictions suggest that focusing performance could be reflected through the 3-D function diagram between the characteristic parameters and the continuous change of the lengths of probe components. In addition, mutation occurs in the focusing performance of the GRIN fiber probe when the length of probe components changes. The research results are of practical guiding significance for the fabrication of GRIN fiber probes requiring specific optical focusing performance. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)

A numerical method is investigated to design gradient-index (GRIN) fiber probes. The GRIN fiber probe is composed of a single mode fiber (SMF), a no-core fiber (NCF), and a GRIN fiber lens. The optical software GLAD is adopted to simulate the optical performance of the probe. The simulation results show that, given the length of the GRIN fiber lens 0.1mm and the length of the NCF 0.36mm, the working distance is 0.73mm and the focus spot size 33 mu m, which are well agreement with the experimental data. As a result, the proposed numerical method is validated to be effective to design such GRIN fiber probes.

Field-tracing based numerical simulation technique is investigated to design and analyze ultra-small self-focusing optical fiber probe. Firstly, the concept and principle of the field-tracing are described. Secondly, the method is discussed to implement the field-tracing technique in the physical optical software of VirtualLab. Finally, an ultra-small self-focusing optical fiber probe is simulated in the field-tracing based optical software of VirtualLab. In this paper, we find that under the conditions of a fiber spacer length of 0.36 mm and the self-focusing fiber lens lengths of 0.1 mm, 0.11 mm and 0.12 mm, the working distances of the probe are 0.75 mm, 0.63 mm and 0.51 mm, and the focus spot sizes are 32 μm, 24 μm and 19 μm respectively. The simulation results are in good agreement with the experimental data, showing that the field-tracing based numerical simulation technique is an effective tool for investigating ultra-small self-focusing optical fiber probe.

Field-tracing approach was proposed to model an ultra-small gradient-index (GRIN) fiber probe. Firstly, the optical model of the GRIN fiber probe was described that consists of a single-mode fiber (SMF), a no-core fiber (NCF), and a gradient-index fiber lens. Then, the term of the field-tracing was presented along with its application in the numerical modeling of the GRIN fiber probe. Finally, the commercial optical software, VirtualLab, was used to simulate the field-tracing model of the GRIN fiber probe, where the comparison analysis between the simulation results and published experimental data was performed. The simulation results show that with respect to the different lengths of NCF and GRIN fiber lens, the simulated working distances and focus spot sizes in VirtualLab all agree with the experimental data closely. Therefore, the proposed field-tracing approach is an effective tool for further optimal design of the GRIN fiber probe by using the software VirtualLab.

解析梯度折射率(GRIN)光纤探针的光学特征参数,用于光学相干层析技术(OCT)探头超小型化的研究.在概述由单模光纤、无芯光纤和GRIN光纤镜头构成的GRIN光纤探针模型的基础上,定义GRIN光纤探针的工作距离和聚焦光斑尺寸等光学特征参数,并用高斯光束复参数矩阵变换的方法推导探针光学特征参数的数学表达式,提出了探针光学特征参数的验证方法.结果显示,当无芯光纤和GRIN光纤镜头长度分别为0.48 mm和0.17 mm时,理论计算的工作距离和聚焦光斑尺寸分别为1.05 mm和28.2 μm;实验测得的工作距离和聚焦光斑尺寸分别为1.0 mm和28 μm.理论计算与实测结果吻合,验证了GRIN光纤探针光学特征参数及其解析方法的有效性.