Design Of Photodetector Array For Visible Light Communication And Its Application In Encrypted-information Transmission

The surge in internet user traffic has led to the depletion of radio frequencies.It is necessary to develop a new(e.g.,visible light)communication technology to transmit data with the growing requirement of ubiquitous data transfer.Low-light,long-distance communications and other applications need large-enough output signal of the photodetectors.Generally,increasing active area of the photodetector or connecting photodetectors in parallel can increase the output current,but the response speed is reduced.How to balance the responsivity and response speed of the photodetectors has become an important research problem in the field of photoelectric detection.In addition,optical encryption communication systems usually involve encryption chips and software encryption algorithms as encryption modules.The use of encryption modules is so difficult.Also,the use of encryption modules increases the complexity of the communication system.Therefore,it is necessary to develop the simple and effective way of encryption.The main contents of this paper are as follows:(1)A set of visible light communication(VLC)system was built.The commercial light sources and photoelectric conversion devices were compared.The LED driving circuit and the transimpedance amplifier circuit were designed and fabricated.The visible light communication system could stably transmitted analog and digital audio signals in real time.Also,it had good anti-jamming performance to environment lighting.The construction of visible light communication system and the realization of audio information transmission lay a foundation for the optimization of photoelectric conversion components and the expansion of multifunctional applications.(2)Based on the design principle of traveling wave photodetector array,the inductors were connected to the negative electrodes of the adjacent photodetectors.Then,the capacitance of multiple photodetectors was not added directly.Also,the response speed of the receiver could be controlled.The simulation results showed that the response speed of the photodetector array was not obviously lower than that of the single photodetector.Experimental results showed that the response time of the single perovskite photodetector was 0.84 μs,the response time of the as-designed perovskite photodetector array using four perovskite photodetectors was 0.91 μs,and the response time for the case with parallel connection was 3.50 μs.Under the fixed illumination,the output current of the perovskite photodetector array was 69.87 mA,while the output current of the single perovskite photodetector was only 18.30 mA.The results showed that the as-designed photodetector array had the comparable response speed and greatly improved output current relative to the single photodetector.(3)A dual-light-source communication system was constructed to realize the encrypted information transmission based on the perovskite photodetectors with polarity conversion and multi-band detection characteristics.A single bipolar perovskite photodetector was used to receive two kinds of optical signals simultaneously.A 540 nm light source was used as the interference light source.An 850 nm light source was used as the effective information transmission carrier.Then,the electrical signal output was decoupled to eliminate interference signal,and finally the original effective information was restored accurately.However,the signal from two light sources was not decoupled by a unipolar silicon detector.It demonstrated that the dual-light source communication system based on the bipolar perovskite photodetector could realize the transmission of encrypted information with a relatively simple setup.In this thesis,we first built a visible light communication system which can transmit audio signal in real time.Then,the perovskite photodetectors made by our research group were used for array design.The output current of the array can be increased greatly,along with the response speed not being obviously decreased.Finally,the encrypted information transmission was realized based on the bipolar perovskite photodetector.This article provides a new route for the performance improvement and the application expansion of the visible light communication system in the view of detector array design and functionalization.