We study the trade-off between energy harvesting and data communication for a two-meter wireless galliumarsenide vertical-cavity surface-emitting laser and photovoltaic link. The use of orthogonal frequency-division multiplexing with adaptive bit and power loading results in a peak data rate of 1041 Mb/s at a bit-error ratio (BER) of 2.2 × 10 −3 under short-circuit conditions. The receiver is shown to provide power harvesting with an efficiency of 41.7% under the irradiance of 0.3 W/cm 2 and simultaneous data communication with a rate of 784 Mb/s at a BER of 2.8 × 10 −3. The experimental system is envisioned to become a paradigm for next-generation wireless backhaul communications and Internet-of-Things applications.
This article demonstrates a fiber-based power-bylight system that is capable of delivering up to 6.2 W of continuous electrical power at common voltages of 3.3 and 5 V. This optical link includes bidirectional optical communication, for which the data stream from the base to the remote unit is realized by amplitude modulation of the laser beam over the same fiber. At the remote unit, a gallium arsenide-based photovoltaic (PV) laser power converter receives and converts the light. The data are demodulated with a dedicated electric circuit, while the power is forwarded to a dc-dc boost converter. The optical data uplink is realized over a separate optical fiber. In operation, a PV conversion efficiency of above 50% has been measured. For downlink data rates up to 115.2 kb/s, unperturbed signal integrities are demonstrated, at higher data rates, the signal integrity deteriorates. An assessment of power budget and power losses in the overall system is presented. Finally, a smart power management concept is introduced, which controls the laser output power with respect to changing electrical load, optimizes the operating point of the PV cell, and, thus, increases system efficiency for varying load operation. Thereby, it also minimizes laser and PV cell operating temperatures, and eventually prolongs the lifetime of the system.
Dual-junction GaAs laser power converters optimized for one monochromatic wavelength are presented, and their temperature dependence is experimentally evaluated. External quantum efficiency and irradiance-dependent currentvoltage measurements (10 to 104 W/cm 2 ) under monochromatic laser light (809 nm) have been undertaken to quantify temperature-and irradiance-dependent effects on the performance. The temperature dependence of the current matching of the two subcells, caused by the temperature-dependent absorbance, is quantified. Losses in performance due to variations in operating temperature for different power-by-light applications are calculated to be between 16.2% and 21.0%. Future potential enhancements in cell performance are discussed. For elevated temperatures, super-linear behavior of the spectral response with increasing irradiance is observed, which is attributed to effective luminescent coupling from the top to the bottom subcell as the device becomes more radiative limited. For low temperatures, where the bottom cell is overproducing, no dependence on irradiance is found, which shows the influence of photon transport losses to the substrate.
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