An electromagnetic wave attenuation superposition structure for thin-layer plasma

This work proposes a new plasma super-phase gradient metasurfaces(PS-PGMs)structure,owing to the limitations of the thin-layer plasma for electromagnetic wave attenuation.Based on the cross-shaped surface unit configuration,we have designed the X-band absorbing structure through the dispersion control method.By setting up the Drude dispersion model in the computer simulation technology,the designed phase gradient metasurfaces structure is superposed over the plasma,and the PS-PGMs structure is constructed.The electromagnetic scattering characteristics of the new structure have been simulated,and the reflectance measurement has been carried out to verify the absorbing effect.The results demonstrate that the attenuation effect of the new structure is superior to that of the pure plasma structure,which invokes an improved attenuation effect from the thin layer plasma,thus enhancing the feasibility of applying the plasma stealth technology to the local stealth of the strong scattering part of a combat aircraft.

Preparation and radar-absorbing properties of Al2O3/TiO2/Fe2O3/Yb2O3 composite powder

Al2O3/TiOe/FeeO3/Yb2O3 composite powder was synthesized via the sol-gel method. The structure, morphology, and ra- dar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes （100-200 rim） and the other is spherical A1203 particles （smaller than 80 rim）. Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 （at 15.68 GHz） in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increas- ing matching thickness. The effective absorption hand covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.

Ultra-compact variable optical attenuator based on slow light photonic crystal waveguide

An ultra-compact variable optical attenuator based on slow light photonic crystal waveguide with thermo- optic effect is demonstrated. Along with power consumption of as low as 30.7 roW, a variable attenuation range of 10 dB is experimentally achieved by shifting the transmission spectrum at about 4.6 nm. The length of the ProPosed device is only 20 μm.

Tunable and switchable dual-wavelength erbium-doped fiber laser based on in-line tapered fiber filters

A tunable and switchable dual-wavelength erbium-doped fiber laser(EDFL) based on all-fiber single-mode tapered fiber structure has been demonstrated. By adjusting the variable optical attenuator(VOA), the laser can be switched between the single-wavelength mode and the dual-wavelength mode. When the temperature applied on the tapered fiber structure varies, the pass-band varies and the wavelength of the output laser shifts correspondingly. When the temperature changes from 30 °C to 180 °C, the central wavelength of the EDFL generated by branch A shifts from 1 550.7 nm to 1 560.3 nm, while that of branch B shifts from 1 530.8 nm to 1 540.4 nm, indicating the wavelength interval is tunable. These advantages enable this laser to be a potential candidate for high-capacity wavelength division multiplexing systems and mechanical sensors.

Using OCT image to distinguish human acupoint from non-acupoint tissues after irradiation with laser in vivo:a pilot study

Using the optical coherence tomography（OCT） images,the optical attenuation coefficients（μ_t） of human Laogong acupoint and non-acupoint tissues are measured after empty irradiation and 808-nm 100-mW irradiation for 10 min in vivo non-invasively.The results show that there is no significant difference ofμ_t of Laogong acupoint and non-acupoint tissues after empty irradiation.However,there are significant differences ofμ_t between Laogong acupoint and non-acupoint tissues after laser irradiation at the power of 100 mW（statistical definition of probability p0.01）.The results of the pilot study indicate that the OCT could distinguish the acupoint from the surrounding tissues after irradiation with laser in vivo non-invasively.

Optical attenuator based on phase modulation of a spatial light modulator

In this Letter, we propose an optical attenuator based on the phase modulation of a spatial light modulator （SLM）. In this system, we use two polarized beam splitters （PBSs） to control the polarized light and one SLM to modulate the phase of the polarized light. In the initial state, the light beam is divided into p-light and s-light when it passes through the first PBS. When the light passes through the second PBS, s-light is reflected and p-light is detected by the CCD camera. By loading different grayscales on the SLM, p-light changes its polarized state to s-light. The light power can be attenuated during the loading process. Our experiment shows that the system can obtain a wide optical attenuation from 1-27.2 dB. When loading two grayscales, the SLM has a fast switching time of 25 ms under a low actuated voltage of 5.5 V. The response time of the optical attenuator depends on the switching time of the SLM. Therefore, the system can also have a fast response time. By using the method of spatial multiplexing and adding two mirrors in the system, it can also be extended into a 1 × 2 optical switch. The results verify its feasibility. The optical attenuator has wide applications in photonic signal processing and fiber-optic communication.

Performance analysis of quantum key distribution based on air-water channel

Considering the air-water interface and ocean water’s optical attenuation,the performance of quantum key distribution(QKD)based on air-water channel is studied.The effects of photons’various incident angles to air-water interface on quantum bit error rate(QBER)and the maximum secure transmission distance are analyzed.Taking the optical attenuation of ocean water into account,the performance bounds of QKD in different types of ocean water are discussed.The simulation results show that the maximum secure transmission distance of QKD gradually reduces as the incident angle from air to ocean water increases.In the clearest ocean water with the lowest attenuation,the maximum secure transmission distance of photons far exceeds the the working depth of underwater vehicles.In intermediate and murky ocean waters with higher attenuation,the secure transmission distance shortens,but the underwater vehicle can deploy other accessorial methods for QKD with perfect security.So the implementation of OKD between the satellite and the underwater vehicle is feasible.