Zhu Lianqing

A 1.8-µm multiwavelength thulium-doped fiber laser based on a hybrid interference filter

ABSTRACT A 1.8-µm tunable multiwavelength thulium-doped fiber laser based on a hybrid filter is proposed. In the designed ring-cavity fiber laser, the filter consists of one Sagnac loop and one dual-pass Mach–Zehnder filter. In the experiment, the lasing threshold is 155 mW, and a continuously tunable and stable single-wavelength laser could be realized with a minimum tuning interval of 2.1 nm within a scope of 22.5 nm. When an 1858-nm laser is obtained, the peak power fluctuation is less than 0.83 dB within 20 minutes at room temperature. By adjusting the polarization controller, stable dual-wavelength lasers are simultaneously achieved, and the peak power shift is less than 1.24 dB within a scan time of 20 minutes at room temperature. By changing the polarization state, stable triple-wavelength lasing is obtained, and the power fluctuation is less than 1.95 nm. In the experiment, the 3-dB linewidth of the laser is less than 0.4 nm.

Multiple optical trapping based on high-order axially symmetric polarized beams

Multiple optical trapping with high-order axially symmetric polarized beams (ASPBs) is studied theoretically, and a scheme based on far-field optical trapping with ASPBs is first proposed. The focused fields and the corresponding gradient forces on Rayleigh dielectric particles are calculated for the scheme. The calculated results indicate that multiple ultra-small focused spots can be achieved, and multiple nanometer-sized particles with refractive index higher than the ambient can be trapped simultaneously near these focused spots, which are expected to enhance the capabilities of traditional optical trapping systems and provide a solution for massive multiple optical trapping of nanometer-sized particles.

Experimental verification on tightly focused radially polarized vortex beams

The theoretical and experimental results of tightly focused radially polarized vortex beams are demonstrated. An auto-focus technology is introduced into the measurement system in order to enhance the measurement precision, and the radially polarized vortex beams are generated by a liquid-crystal polarization converter and a vortex phase plate. The focused fields of radially polarized vortex beams with different topological charges at numerical apertures (NAs) of 0.65 and 0.85 are measured respectively, and the results indicate that the total intensity distribution at focus is dependent not only on the NA of the focusing objective lens and polarization pattern of the beam but also on the topological charge l of the beam. Some unique focusing properties of radially polarized vortex beams with fractional topological charges are presented based on numerical calculations. The experimental verification paves the way for some practical applications of radially polarized vortex beams, such as in optical trapping, near-field microscopy, and material processing.

Signal Tap-II Based Debugging Approach for the Data Acquisition System of Multi-joint Coordinate Measuring Machine

Data Acquisition System (DAS) is one of the key components of Multi-joint Coordinate Measuring Machine (MCMM) that affects the latters performance during practical usage. This article reports a SignalTap-II based debugging approach for the DAS of MCMM. Both the work principle and work process are illustrated. SignalTap-II online logic analyzer is employed to analyze and return real-time collected data to a personal computer (PC). Particular experimental results are provided in diagrams, indicating that the SignalTap-II based DAS debug approach is capable of monitoring the data acquisition process in real-time, reducing the time period for debug and verification, and shortening production cycle.)

Golf video tracking based on recognition with HOG and spatial–temporal vector

The hand and club movements contain golfer’s swing information, which can be obtained to provide good visualization to be shared on Internet and be summarized in golf studying. In this article, a hand and club tracking framework based on recognition with a complex descriptor combining histograms of oriented gradients and spatial–temporal vector is proposed to obtain their movement trajectories in golf video. After the hand and club are recognized in initial windows defined by the body region, a boosted classifier trained by the proposed descriptor is utilized for recognition and tracking in a searching window predicted by trajectory fitting with previous four object positions. Experiments show that the boosted classifier can have a precision and recall rate both better than 97%, and the hand and club tracking are basically correct in our testing videos.

Tight focusing of axially symmetric polarized vortex beams

Tight focusing of axially symmetric polarized vortex beams is studied numerically based on vector diffraction theory. The mathematical expressions for the focused fields are derived. Simulation results show that the focused fields and phase distributions at focus are largely influenced by both the polarization order and topological charge of the incident beams. Moreover, focal spots with flat-topped or tightly-focused patterns can be flexibly achieved by carefully choosing the polarization order and the topological charge, which confirms the potential of such beams in wide applications, such as optical tweezers, laser printing, lithography, and material processing.

Erbium-doped fiber ring laser sensor for high temperature measurements based on a regenerated fiber Bragg grating

ABSTRACT This article presents an erbium-doped fiber ring laser for high temperature measurement with high accuracy. The proposed laser sensor employs a regenerated fiber Bragg grating (RFBG) as a sensor element. Through thermal treatments, the RFBG with enhanced thermal resistance was obtained. The laser emission optical spectrum presents good performance with a high optical signal-to-noise ratio of 58dB. Experimental results demonstrate a wavelength sensitivity to the temperature is 15.5 pm/ºC with the temperature range from 300ºC to 900ºC, and the correlation coefficient is 0.999. The results prove it is able to provide potential applications in high temperature measurement.