Optical wireless power transfer (OWPT) can be a suitable candidate for long-distance wireless power transfer. We experimentally demonstrate the OWPT using a laser diode (LD) as the optical power transmitter and two candidates for the optical power receiver: a photodiode (PD) and a solar cell. Our results show a maximum electric-to-optic conversion efficiency of 72.7% for the LD at an optimum operating voltage. The maximum optic-to-electric conversion efficiencies of the solar cell and PD are 16.7% and 6.0% (including the receiving lens loss), respectively, with optimization of load resistance. Therefore, the total back-to-back transfer efficiency is 12.1% (DC-to-DC) with the solar cell receiver. Our results show a potential attenuation of 0.006 dB/m, implying a 3-dB distance of 500 m, if the laser beam divergence challenge can be addressed.
The relatively unsatisfactory performance of optical wireless communication (OWC) with respect to WiFi and millimeter-wave communications has formed a key issue preventing its commercialization. We experimentally demonstrate an OWC technology using a combination of positive real-valued orthogonal frequency-division multiplexing (OFDM) and optical beamforming (OB). Due to the intensity-modulation and direct-detection aspects of OWC systems, a positive real-valued OFDM signal can be suitably utilized to maximize the OWC data rate. Further, the OB technique, which can focus laser light on a desired target, can be utilized to increase the OWC data rate and transmission distance. Our experimental results show that the received optical signal power and electrical signal increase by up to 42 and 25 dB, respectively. Further, the data rate increases by a factor of 200 with OB over the conventional approach.
Solar cells are widely used in various applications. However, they are only used to harvest solar power. We propose and demonstrate a technique to use a solar cell as a simultaneous receiver of solar power and visible light communication (VLC) signals. First, we investigate the optic-to-electric conversion efficiency and the frequency response of a solar cell. Then, we demonstrate that a solar cell receiver can receive both solar power and VLC signals simultaneously. We also investigate the effect of solar power interference on the VLC performance. The results show that the VLC operation is successful even when the solar power is the maximum.
We propose and demonstrate a new wireless visible light communication (VLC) technology using optical beamforming to improve signal-to-noise ratio (SNR) and transmission distance. Optical beamforming is a technology that can focus light-emitting diode (LED) light on a desired target device. Our experimental results show that SNR can be improved by 12 dB and transmission distance can be almost doubled by using optical beamforming. We can also control the modulation depth of the optical beamforming if we want to use the LED light as illumination at the same time. We also propose an algorithm to direct the beam to the target device automatically.
We propose and demonstrate a wireless optical energy transmission using optical beamforming with a spatial light modulator. We demonstrate an optical beamforming technology to focus the light of an optical source on a desired target, which can be used in various applications. Our experiment shows a wireless energy transmission efficiency of 1.3% with a white light-emitting diode light source. Although the transmission efficiency is currently low in our experimental result, we expect that the transmission efficiency can be improved up to 30% with highly efficient devices. We also propose an algorithm based on the optical beamforming to detect the location of the target device automatically. The proposed wireless optical energy transmission has several advantages over the previous wireless energy transmission methods.
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