Feiliang Chen

A high-performance blue filter for a white-led-based visible light communication system

A high-performance blue filter was demonstrated and employed to increase the modulation bandwidth and dramatically reduce the bit error rate of a white-LED-based VLC system. It has a very wide stopband (500-1050 nm), high transmittance passband (average 97.5 percent in the blue signal range of 430-485 nm), and a sharp and precise cutoff edge. Not only can the blue filter completely remove the slow phosphorescent component from modulated signals, but it can also effectively reject ambient solar radiation. Meanwhile, the blue light signals of the LED can almost be retained. This results in a high SNR and improves the performance of a VLC system, including increased modulation bandwidth and reduced BER. The BER can be dramatically reduced from 3.6 × 10-2 to 1.7 × 10-4 at 50 MHz bandwidth, and from 2.6 × 10-2 to 1.9 × 10-5 at a distance of 30 cm compared to a VLC system without our blue filter. More importantly, the stop band covers the whole response range of the receiver except for the blue signal band, which strongly increases the ability of a VLC system used in the sun or outdoors.

Tuning phase transition temperature of VO2 thin films by annealing atmosphere

A simple new way to tune the optical phase transition temperature of VO2 films was proposed by only controlling the pressure of oxygen during the annealing process. Vanadium films were deposited on glass by a large-scale magnetron sputtering coating system and then annealed in appropriate oxygen atmosphere to form the VO2 films. The infrared transmission change (at 2400 nm) is as high as 58% for the VO2 thin film on the glass substrate, which is very good for tuning infrared radiation and energy saving as smart windows. The phase transition temperature of the films can be easily tuned from an intrinsic temperature to 44.7 °C and 40.2 °C on glass and sapphire by annealing oxygen pressure, respectively. The mechanism is: V3+ ions form in the film when under anaerobic conditions, which can interrupt the V4+ chain and reduce the phase transition temperature. The existence of V3+ ions has been observed by x-ray photoelectron spectroscopy (XPS) experiments as proof.

Control of optical properties of TiN x O y films and application for high performance solar selective absorbing coatings

TiNxOy films with controllable optical properties have been fabricated by reactive mid-frequency magnetron sputtering from titanium nitride target. The optical and electrical properties were studied as a function of the reactive gas flow and were correlated with the film stoichiometry. The results showed that the behavior of TiNxOy films can be adjusted from metallic to dielectric by increasing oxygen content, which is of great significance to their extensive applications. Owing to the accurate control of optical properties, a TiNxOy based solar selective absorbing coating has been designed and prepared with the aid of TiO2/Si3N4/SiO2 antireflection layers. Its solar absorbance is as high as 97.5% and thermal emissivity is 4.3% with total thickness of 230 nm. The solar absorbance can maintain above 90% for a broad incident angle range from 0° to 65°.

High performance colored selective absorbers for architecturally integrated solar applications

Architecturally integrated solar thermal technologies such as solar water heaters and solar thermoelectric generators (STEGs) rely on spectrally selective solar absorbers. These solar absorbers need to have simultaneous high solar absorptivity (α) and low thermal emissivity (e), which always makes them look dark blue or black and so blocks architectural integrated solar applications. A colorful appearance should be taken into account for integration into architectural applications. Herein, colored absorbers with a TiNxOy absorbing layer and a TiO2/Si3N4/SiO2 dielectric stack are elaborately designed and can be fabricated with only two targets, Ti and Si, by using reactive magnetron sputtering. Both the theoretical and experimental results show that the color can be tuned a huge amount, while keeping solar absorptivity higher than 95% and thermal emissivity lower than 5%. The highest absorptivity and energy efficiency (α/e) values are 97.6% and 27.2, respectively. These materials can also be fabricated onto thermoelectric generators to demonstrate the conversion of solar energy into electricity. The open circuit voltage dramatically increases from 171 mV to 523 mV (3.1 times) when using the absorbers. Additionally, the colored solar absorbers can be deposited onto most types of substrate, even flexible substrates. They can simultaneously satisfy the aesthetic requirements and excellent energy performance required for architecturally integrated solar thermal and thermoelectric applications, as well as applications in other fields.

Colorful solar selective absorber integrated with different colored units.

Solar selective absorbers are the core part for solar thermal technologies such as solar water heaters, concentrated solar power, solar thermoelectric generators and solar thermophotovoltaics. Colorful solar selective absorber can provide new freedom and flexibility beyond energy performance, which will lead to wider utilization of solar technologies. In this work, we present a monolithic integration of colored solar absorber array with different colors on a single substrate based on a multilayered structure of Cu/TiN(x)O(y)/TiO(2)/Si(3)N(4)/SiO(2). A colored solar absorber array with 16 color units is demonstrated experimentally by using combinatorial deposition technique via changing the thickness of SiO(2) layer. The solar absorptivity and thermal emissivity of all the color units is higher than 92% and lower than 5.5%, respectively. The colored solar selective absorber array can have colorful appearance and designable patterns while keeping high energy performance at the same time. It is a new candidate for a number of solar applications, especially for architecture integration and military camouflage.

Simulation of superconducting single photon detector coupled with metal-insulator-metal circular grating

Metal-insulator-metal (MIM) circular grating structure has been introduced to couple with superconducting nanowire single-photon detector (SNSPD) to enhance its response. According to our numerical simulation results, the coupling efficiency at 1.55μm can be enhanced by MIM circular grating and improving the response of SNSPD obviously. About 19.5 times of enhancement in response can be obtained with proper structure parameters.

Colored solar-thermal absorbing coatings with high absorptance

Its difficult to obtain different color appearance and keep high absorptance simultaneously. We introduce TiO2/Si3N4/SiO2 films into TiNxOy based solar-thermal absorbing coatings to tune the color appearance in a large range, while keeping the absorptance higher than 95%.