Qi Qiu

Multi-focus plasmonic lens design based on holography

Multi-focus plasmonic lens with metallic nanoslits of variant widths have great potential applications in optical interconnection, integrated optics and nanophotonics. But the design method with simulated annealing algorithm or Yang-Gu algorithm requires complex calculation and multi focuses are limited to be set on the same output plane. In this paper, we propose a design method based on holography. The desired light field distribution and the incident plane wave can be treated as object wave and reference wave, respectively. So the calculation is relative simple and multi focuses can be located in different output plane. Numerical simulation of multi-focus lens design is performed through finite-difference time-domain (FDTD) method and the result confirms the feasibility of our method.

High Precision Temperature Insensitive Strain Sensor Based on Fiber-Optic Delay

A fiber-optic delay based strain sensor with high precision and temperature insensitivity was reported, which works on detecting the delay induced by strain instead of spectrum. In order to analyze the working principle of this sensor, the elastic property of fiber-optic delay was theoretically researched and the elastic coefficient was measured as 3.78 ps/km·με. In this sensor, an extra reference path was introduced to simplify the measurement of delay and resist the cross-effect of environmental temperature. Utilizing an optical fiber stretcher driven by piezoelectric ceramics, the performance of this strain sensor was tested. The experimental results demonstrate that temperature fluctuations contribute little to the strain error and that the calculated strain sensitivity is as high as 4.75 με in the range of 350 με. As a result, this strain sensor is proved to be feasible and practical, which is appropriate for strain measurement in a simple and economical way. Furthermore, on basis of this sensor, the quasi-distributed measurement could be also easily realized by wavelength division multiplexing and wavelength addressing for long-distance structure health and security monitoring.

Nonmechanical Infrared Beam Steering Using Blue Addressed Quantum Dot Doped Liquid Crystal Grating

We present a scheme of nonmechanical laser beam steering using ZnS/InP quantum dots doping nematic liquid crystal as the optical recording film. Because of its internal electric field generated by blue laser-induced charge carrier distribution, liquid crystal molecules are reoriented to form a phase grating which make the incident angle steer to the angle as we desire. Being a nonmechanical programmable laser beam steering, the anisotropy of the relative permittivity tensor and blue laser-induced electric carriers play a significant effect in determining the reorientable liquid crystal molecule and reconfigurable phase modulation of the gratings, that determines the steering angle and steering efficiency.

A Heuristic Explanation for the Superluminal Behaviors of Evanescent Waves

Traditionally, the superluminal behaviors of evanescent waves have been studied by means of tunneling time theory. Seeing that evanescent waves are identical with near fields, to present a heuristic and straightforward explanation for the superluminal behaviors of evanescent waves, in this paper we study the superluminal behaviors of the near fields of an electric dipole antenna, and obtain the results in agreement with the phase time model of tunneling time theory.

Stochastic scanning method to shorten acquisition time using liquid crystal optical phased array

Abstract. Agile beam steering has been previously reported to be one of the unique properties of a liquid crystal optical phased array. We propose a stochastic scanning method using the property of agile beam steering to shorten acquisition time in building a free-space laser communication link. As a specific example, Gaussian stochastic scan enables higher acquisition probability and shorter acquisition time. In addition, there are two factors to influence the results: standard deviation of stochastic scanning angle and the width of the laser beam. Theoretical analysis is presented that the stochastic scanning method is a unique method to speed up the acquisition process in free-space laser communication.

Cascade-able optical fiber delay-based temperature sensor system

Abstract. A high-sensitivity temperature sensor based on optical fiber delay is proposed in this paper. The sensor system is designed and tested in a temperature range of 0°C to 100°C with increments of 5°C. The output delay difference is found to be linearly proportional to the temperature with an average fluctuation less than 0.1 ps. To achieve an overall low cost and practical detection, a simple detection system is developed to measure temperature, and a potential for high temperature sensitivity is shown by analyzing the system. As a result, this sensor system is proven to be feasible and practical, and temperature can be measured in a simple and economical way.

Agile Laser Beam Deflection With High Steering Precision and Angular Resolution Using Liquid Crystal Optical Phased Array

To improve the steering precision and angular resolution of liquid crystal optical phased array, in this paper, we proposed a modified periodic phase controlled method to realize a continuous scanning with a constant angular resolution of less than 20 μrad, meanwhile, its precision is less than 5 μrad (RMS). Also, another method we proposed is called sub-aperture coherence can realize even better angular resolution less than 5 μrad which is the limitation of our measurement instrument.

Design on serial optical digital-to-analog converter and its experiment

Optical techniques have the potential to overcome limitations of electronic digital-to-analog conversion (DAC). A serial optical DAC (ODAC) utilizing the dispersion property of fiber-optic is proposed and demonstrated. The structure of the proposed DAC is designed based on the concerning of dispersive summing and electro-optic bit selection, which is easier to be realized compared with the conventional serial optical DAC. An implementation is experimentally demonstrated at operating rate of 12.5 Gb/s. Tunable fiber-optic delay line (TFDL)-based phase matching is investigated. The technical issues to reach a higher performance of the proposed DAC are discussed, the designed schematic structure in this paper could be easily modified for realizing higher speed and higher resolution.

High-precision and long-range distance measurement independent of temperature based on two optoelectronic oscillators

A high-precision and temperature insensitive longrange distance measurement (DM) based on frequency detection is proposed and experimentally demonstrated. Two optoelectronic oscillators (OEOs) are grouped into a cross-referencing structure by Dense Wavelength Division Multiplexing (DWDM), which can greatly increase the measurement accuracy by reducing the influence of the environment such as temperature on the long fiber in the two OEOs. Because the long fiber is shared by the two OEOs, the frequency drifts caused by the long fiber are equal, then the surrounding disturbance for the measurement is overcome by mixing the oscillation frequency of the two OEOs. By measuring the intermediate frequency (IF) mixed by the two OEOs, the proposed DM acquires the frequency information converted by the distance information, which has taken advantage of the accumulative magnification in OEO and significantly improves the precision of the measured distance. In the experiment, the measurement error is ±20μm at an emulated distance of approximately 6km, and the measurement sensitivity is 17.867kHz/cm. The relative measurement precision in the proposed system is 10−9, which can be used to measure the displacement, refractive index change, temperature, etc.

Theoretical model and experimental verification on the PID tracking method using liquid crystal optical phased array

Liquid crystal optical phased array (LC-OPA) has been considered with great potential on the non-mechanical laser deflector because it is fabricated using photolithographic patterning technology which has been well advanced by the electronics and display industry. As a vital application of LC-OPA, free space laser communication has demonstrated its merits on communication bandwidth. Before data communication, ATP (acquisition, tracking and pointing) process costs relatively long time to result in a bottle-neck of free space laser communication. Meanwhile, dynamic real time accurate tracking is sensitive to keep a stable communication link. The electro-optic medium liquid crystal with low driving voltage can be used as the laser beam deflector. This paper presents a fast-track method using liquid crystal optical phased array as the beam deflector, CCD as a beacon light detector. PID (Proportion Integration Differentiation) loop algorithm is introduced as the controlling algorithm to generate the corresponding steering angle. To achieve the goal of fast and accurate tracking, theoretical analysis and experimental verification are demonstrated that PID closed-loop system can suppress the attitude random vibration. Meanwhile, theoretical analysis shows that tracking accuracy can be less than 6.5μrad, with a relative agreement with experimental results which is obtained after 10 adjustments that the tracking accuracy is less than12.6μrad.