Spectral target-detecting system using sine-wave modulation

Target detection is one of the key technology of precision chemical application.Previously the digital coding modulation technique was commonly used to emit and receive the optical signal in the target detection systems previously in China.It was difficult to adjust the output power,and the anti-interference ability was weak in these systems.In order to resolve these problems,the target detection method based on analog sine-wave modulation was studied.The spectral detecting system was set up in the aspects ...     

Extension of the distributed point source method for ultrasonic field modeling

The distributed point source method (DPSM) was recently proposed for ultrasonic field modeling and other applications. This method uses distributed point sources, placed slightly behind transducer surface, to model the ultrasound field. The acoustic strength of each point source is obtained through matrix inversion that requires the number of target points on the transducer surface to be equal to the number of point sources. In this work, DPSM was extended and further developed to overcome the limitations of the original method and provide a solid mathematical explanation of the physical principle behind the method. With the extension, the acoustic strength of the point sources was calculated as the solution to the least squares minimization problem instead of using direct matrix inversion. As numerical examples, the ultrasound fields of circular and rectangular transducers were calculated using the extended and original DPSMs which were then systematically compared with the results calculated using the theoretical solution and the exact spatial impulse response method. The numerical results showed the extended method can model ultrasonic fields accurately without the scaling step required by the original method. The extended method has potential applications in ultrasonic field modeling, tissue characterization, nondestructive testing, and ultrasound system optimization.     

Concentration scheme for partially entangled photon states via entanglement reflector and no Bell-state analysis

We propose a protocol to concentrate partially entangled states of photons using entanglement reflector, which consists of a single electron spin confined in a charged quantum dot inside a single-sided microcavity. The outstanding advantage of the proposed scheme is its experimental simplicity and feasibility since it only needs to perform a single local measurement on electronic spins rather than a joint Bell-state measurement on photons. We then extend this scheme to concentrate N-photon Greenberger-Horne-Zeilinger state. Finally, we analyze the influence of various imperfections on the scheme.     

Conversion efficiency enhanced photovoltaic device with nanohole arrays in antireflection coating layer

In this paper, the authors introduce an enhanced photovoltaic device with nanohole arrays only in its antireflection coating. These nanoholes can improve light trapping efficiency as well as photoelectric conversion efficiency of the device. The authors analyze the light absorption of the devices with nanohole arrays by Finite-Difference Time Domain method and calculate the photoelectric conversion efficiency. The results show that the nanohole arrays can improve the light trapping more efficiently than the Si₃N₄ antireflection coating, especially, in 400-600 nm spectral range. Nanohole arrays with different characteristic parameters were fabricated in the antireflection coating layer of a Φ200 μm Si detector by using focused-ion beam system. With the optimized nanohole arrays, the enhancements factor of the experimental sample's photoelectric conversion efficiency is ~ 16% within the 400-600 nm spectral range and ~ 10% within the 400-1100 nm spectral range.     

Preparation of well-aligned carbon nanotubes by pyrolysis of phenolic resin in anodic alumina pores

Well-aligned carbon nanotubes (CNTs) of high quality were synthesized by pyrolysis of phenolic resin at 800 °C in anodic alumina oxide (AAO) pores under argon protection. The innocuous source materials and safe operational conditions permit this method to synthesize well-aligned CNTs in large-scale and low cost. The formation mechanism of the synthesized CNTs is also proposed in this work by a series of visual sketches and is proved with obvious evidence. Firstly, phenolic resin nanotubes form in the template pores through the evaporation of solvent. Heat treatment then transfers these tubes into CNTs.     

Long period grating cascaded to photonic crystal fiber modal interferometer for simultaneous measurement of temperature and refractive index

We propose and demonstrate a novel and simple dual-parameter measurement scheme based on a cascaded optical fiber device of long-period grating (LPG) and photonic crystal fiber (PCF) modal interferometer. The temperature and refractive index (RI) can be measured simultaneously by monitoring the spectral characteristics of the device. The implemented sensor shows distinctive spectral sensitivities of -30.82 nm/RIU (refractive index unit) and 47.4 pm/°C by the LPG, and 171.96 nm/RIU and 10.4 pm/°C by the PCF modal interferometer. The simultaneous measurement of the temperature and external RI is experimentally demonstrated by the sensor. The temperature shift and RI shift calculated by the sensor matrix agree well with the actual temperature and RI change in the experiment.     

Beam focusing from double subwavelength metallic slits filled with nonlinear material surrounded by dielectric surface gratings

Based on the radiation properties of surface plasmon polaritons (SPPs) can be controlled by adjusting the refractive indexes of dielectric materials in the metallic slits, a novel plasmonic focusing structure formed by two subwavelength metal apertures filled with Kerr nonlinear material surrounded by surface dielectric gratings is proposed and demonstrated numerically. Directions of radiation fields are determined by the phase difference of the surface waves at the exit interface and resonance property of each surface grating. Numerical simulations using two-dimensional (2D) Finite-Difference Time-Domain (FDTD) method verify that the deflection angle and focal length can be controlled easily by changing the intensity of incident light, dynamically tunable on-axis and off-axis focusing effects can be achieved.