ABSTRACT
In this Letter, we report an effective monolithic integration of a metal oxide semiconductor field effect (MOSFET) phototransistor (PT) and a light-emitting diode (LED) on a GaN-on-Si LED epitaxial (epi) wafer. Avoiding additional growth or Si diffusion, the PT was directly fabricated on the LED epi layer, providing a cost-effective and facile method. As a driver, the PT could modulate both peak value of the light intensity and output current of the integrated LED. As an ultraviolet (UV) detector, our PT showed sufficient responsivity. It was found that the gate-voltage-dependent photocurrent-response of the device had a shorter response time, and a higher responsivity was obtained at a higher gate-voltage bias. The device demonstrated a switching effect that the photoinduced current from the PT drove the LED when the UV lamp was turned on, whereas the photoinduced current stopped driving upon powering off the UV lamp. The experiment proved that the integrated device working as a UV detector exhibited a fast response time and a longstanding stability. We anticipate that such an approach could have potential applications for UV light detection and visible light communication (VLC).
ABSTRACT
The demand for on-chip multifunctional optoelectronic systems is increasing in today's Internet of Things era. III-nitride quantum well diodes (QWDs) can transmit and receive information through visible light and can be used as both light-emitting diodes (LEDs) and photodetectors (PDs). Spectral emission-detection overlap gives the III-nitride QWD an intriguing capability to detect and modulate light emitted by itself. In this paper, the coexistence of light emission and detection in a III-nitride QWD is experimentally demonstrated, and a wireless video communication system through light is established. When approximately biasing and illuminating at the same time, the III-nitride QWD can achieve light emission and detection simultaneously. This work provides a foundation for the development of multifunctional III-nitride QWDs and the realization of device-to-device data communication.
ABSTRACT
Underwater wireless optical communication (UWOC) is a promising means of realizing large capacity and high rate in aquatic media. In this paper, a photomultiplier tube (PMT)-based multiple-input multiple-output (MIMO) UWOC system is investigated. Photon counting is an effective technique used to detect very low-level light. A PMT with an excellent photon-counting mode is adopted, and the performance in terms of the bit error rate is discussed. The received optical power can be predicted based on the detected photocount in each symbol period, and the received photocount distribution may be simulated through MATLAB. Furthermore, the optical link model and energy per bit with on-off keying are evaluated for different water types at a 10 m optical link distance. This MIMO-UWOC system combines the advantages of PMTs and the MIMO scheme and has the potential to realize long-distance optical link transmission.
ABSTRACT
Underwater wireless optical communication (UWOC) is a promising technology that can be a candidate to improve the communication capacity and speed in aquatic media. The aim of this study is to examine the performance of a silicon photomultiplier (SiPM) array-based multiple-input multiple-output (MIMO) UWOC system. A SiPM is a modern solid-state photodetector with extremely high sensitivity up to the single-photon level or a photon-counting ability, which helps in detecting extremely weak light signals after long-distance underwater channel attenuation. We clarify the basic characteristics and photon-counting detection mode of a SiPM. In particular, the photocount of a SiPM is approximated by a Gaussian distribution, and theoretical analysis shows that only 13.3 photons need to be detected during "1" symbol period to achieve a bit error rate of 10-3 in an ambient light environment. Moreover, a SiPM also has a better analog mode detection ability than an avalanche photodiode (APD) and realizes 2 Mbps analog communication owing to its unique array structure and high photon detection efficiency. Furthermore, MIMO, i.e., spatial diversity, is applied as an effective method to relax the link alignment, improve the system performance, and alleviate the effect of optical turbulence. In our experiment, with a photon-counting 6×3 MIMO scheme, an energy per bit of 7.38×10-9 J/bit is achieved at a scintillation index of 4.66×10-3 in a 10 m water tank with 1 Mbps on-off-keying (OOK) modulation. To the best of our knowledge, this is the first study on a MIMO-UWOC system based on the photon-counting mode of a SiPM array. This UWOC system combines the advantages of SiPMs and the MIMO scheme and has the potential to realize long-distance UWOC under optical turbulence.
ABSTRACT
This study is screened for naphthalene degrading strains from a heavily polluted area with high naphthalene concentration in the rainwater for the effective removal of naphthalene from rainwater. Recently, naphthalene biodegradation has been achieved in water. However, the influences of organics and inorganics in the rainwater on the biodegradation of naphthalene remains unclear. The naphthalene degrading strain Klebsiella sp. (WJ-1) was identified from sewage sludge. The effects of temperature, pH, inoculum size, and rotation speed on the degradation ability of WJ-1 were studied. The results showed that the naphthalene degradation rates of WJ-1 in rainwater were higher than those in aqueous solution at different experimental conditions. The optimal conditions were 30 °C, 10% inoculum size, pH 7.0, and a rotation speed of 150 rpm. The substances in rainwater might be important co-metabolites of naphthalene degradation. Based on intermediate metabolites detected by gas chromatography-mass spectrometer (GC-MS), the naphthalene biodegradation pathway was identified, as being similar to the phthalic acid pathway. These results suggest WJ-1 as a good candidate for the efficient bioremediation of naphthalene from rainwater in heavily polluted areas.
