We demonstrate a simple, robust, and highly sensitive temperature sensor based on the resonant excitation of whispering gallery modes in a coated single-mode fiber (SMF) loop that was created by ...means of bending a standard coated SMF into a loop with a radius of 5 mm. Clear interference fringes were observed in the transmission spectrum of the coated-SMF loop. The resonant wavelength exhibits a linear temperature response at the temperature range from -60° to 10 °C, and a quadratic temperature response at the temperature range from 10° to 140 °C. Moreover, the coated-SMF loop exhibits an ultrahigh sensitivity of up to -5.22 nm/°C at 120 °C, and the sensitivity (i.e., -4.01 nm/°C at 80 °C) is two orders of magnitude higher than that of an uncoated-SMF loop (i.e., 0.04 nm/°C at 80 °C). Hence, such a coated-SMF loop could be used to develop a temperature sensor with a large measurement range from -60° to 140 °C.
This paper investigates a moiré-based mark for high-precision wafer bonding alignment. During alignment, the mark is combined with digital grating, which has the benefits of high precision and small ...size. A digital grating is superimposed on the mark to generate moiré fringes. By performing a phase calculation on the moiré fringe images corresponding to the upper and lower wafers, the relative offset of the upper and lower wafers can be accurately calculated. These moiré fringes are exceptionally stable, thereby enhancing the alignment stability. In this study, through practical experiments, we tested the rationality and practicability of the mark.
In this paper, a practical modeling and robust controller optimization strategy is presented for an ultraprecision positioning stage with position-dependent dynamics to achieve ultraprecision ...positioning accuracy. A linear-fractional-transformation structured uncertainty modeling procedure is proposed to describe the varying dynamics of the stage. The modeling process involves the global curve fitting of frequency response functions and dimensionality reduction for the uncertainty structure so that the uncertainty set could be minimized. Then, a robust loop-shaping controller optimization method is presented to improve the control performances. The optimization objective includes the control bandwidth and the disturbance rejection ability, and μ analysis is employed as a nonconservative robust condition with respect to the structured uncertainty. A genetic algorithm is then utilized to determine the optimal parameters of the controller. Comparative experiments on a developed ultraprecision positioning stage are finally conducted, and the results validate that significant improvements on rising time, settling time, and positioning accuracy have been achieved.
The disk electrodynamic suspension device (DEDSD) features stable suspension capability, simple structure, low cost, and no mechanical rotation. For analysis and design optimization of the DEDSD, an ...accurate whole space harmonic force model utilizing magnetic vector potential (MVP) is developed in this paper. The DEDSD is unfolded along the circumference direction and equivalent into a special linear induction motor (LIM). Then, a 2-D MVP method for the equivalent LIM is derived where the longitudinal discrete distribution of coils is represented by longitudinal space harmonics. The 2-D MVP method is further expanded to a 3-D MVP method where new boundary conditions are derived and the transverse edge effect is represented by transverse space harmonics. Consequently, a whole space harmonic force model of the DEDSD is obtained from the 3-D MVP method. Characteristics of the whole space harmonics are analyzed and proper orders are chosen. Finally, the proposed model is verified by experiments on a prototype.
We demonstrate a high-sensitivity gas pressure sensor by use of an in-fiber Fabry-Pérot interferometer (FPI) based on hollow-core photonic bandgap fiber (HC-PBF) with a side-opened channel. The FPI ...was constructed by splicing a thin piece of HC-PBF between two stander single-mode fibers. Then, a side-opened channel was drilled through the hollow core of the HC-PBF by use of a femtosecond laser. Such an FPI with a side-opened channel greatly enhanced the gas pressure sensitivity up to 4.24 nm/MPa, which is two orders of magnitude higher than that of FPI with an enclosed cavity. In addition, the effects of cavity length on the gas pressure sensing performance were also studied. A shorter cavity gives rise to broader measurement range while offering larger detection limit, and vice versa. The structure size is tens of micrometers, which makes it possible to develop an ultracompact high-sensitivity gas pressure sensor.
An all-fiber twin-core fiber (TCF) fan-out device is proposed and experimentally demonstrated. The device is capable of simultaneously accessing optical signals from both cores for a variety of TCF ...types. The device was fabricated via bi-tapering of a fiber bundle consisting of two parallel large-core multimode fibers, each of which was tapered-spliced with single mode fibers. A commercial fiber fusion splicer was used in the device fabrication process for both tapering and splicing. A series of experiments were conducted in which two different TCF types, featuring different inter-core distances, were connected to test the functionality of the proposed device. The results demonstrate successful accessing of optical signals from the two TCF cores with a low crosstalk of -38.6 dB. The proposed all-fiber TCF fan-out device could be further developed for applications in novel fiber sensors or advanced optical communication systems.
We demonstrated a novel intensity-modulated strain sensor based on a fiber in-line Mach-Zehnder interferometer with a large fringe visibility of up to 17 dB, which was fabricated by splicing a ...section of thin core fiber between two sections of single mode fibers with one misalignment-spliced joint. Such a strain sensor exhibited an ultrahigh sensitivity of -0.023 dBm/με within a measurement range of 500 με, which is about one order of magnitude higher than that reported in references. Displacement and stress distributions at the misalignment spliced joint were simulated by use of finite element method. In addition, the proposed strain sensor has an advantage of compact size of ~10 mm.
We propose and demonstrate a symmetric step-apodized distributed feedback (DFB) fiber laser, which has an improved efficiency and a narrow linewidth. This special DFB laser cavity is based on a ...unique symmetric step-apodized π-phase-shifted fiber Bragg grating (FBG) directly inscribed in a heavily erbium-doped fiber. The symmetric step-apodized phase-shifted grating is equivalent to a weak uniform phase-shifted FBG embedded in a pair of strong FBGs, and this design could increase the effective cavity length of a DFB fiber laser. Moreover, the symmetric step-apodized DFB laser cavity proposed in this work has a phase shift located in the cavity center. It could simplify the design process significantly due to the symmetry in the laser cavity. Experimental results show that the slope efficiency of a symmetric step-apodized DFB fiber laser could be increased to 1.06%, which is significantly higher than that of a uniform DFB fiber laser (i.e., 0.45%) under the same cavity length and pump conditions. In addition, the proposed DFB fiber laser exhibits a high stability. The fluctuations in lasing wavelength and output power were less than 12 pm (corresponding to a frequency shift of 1.49 GHz) and 0.13 dB within 24 h, respectively. Moreover, the full-width at half-maximum linewidth of the symmetric step-apodized DFB fiber laser was ∼2.6 kHz, measured by the delayed self-heterodyne method with a 50-km fiber delayed line. As such, the proposed symmetric step-apodized DFB fiber laser could potentially be used as high-performance light source for fiber-optic sensors or coherent optical communication systems.
A novel, highly efficient terahertz fully polarized transmission line is designed by two-dimensional tellurium photonic crystals consisting of square lattice rod arrays with a complete photonic ...bandgap. The TE and TM photonic bandgaps of the tellurium photonic crystals, which are computed by plane wave expansion, happen to coincide, and the complete photonic bandgap covers from 2.894 to 3.025 THz. The function of the designed waveguide is simulated by the finite element method, and the transmission characteristics are optimized by accurately adjusting its structural parameters. The transmission efficiency of the waveguide for TE mode achieves a peak value of −0.34 dB at a central frequency of 2.950 THz and keeps above −3 dB from 2.82 THz to 3.02 THz, obtaining a broad relative bandwidth of about 6.84 percent. The operating bandwidth of the tellurium photonic crystals’ waveguide for TM mode is narrower than that of TE mode, whose relative bandwidth is about 4.39 percent or around 2.936 THz above −5 dB. The designed terahertz photonic crystals’ waveguide can transmit both TE and TM waves, and not only can it be used as a high-efficiency transmission line, but it also provides a promising approach for implementing fully polarized THz devices for future 6G communication systems.
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