At present, ultraviolet light source has been widely used in medical sterilization, fluorescence spectroscopy, biological analysis/detection, water treatment, etc. The bactericidal properties of ultraviolet light source were discovered in the early 17th century, and the application of ultraviolet fluorescent tube technology began in the 1750s. The ultraviolet light sources used in these technologies are gas discharge lamps (such as low-pressure mercury lamps).
Advantages of UV LED communication
In terms of communication, the speed of ultraviolet light communication is far less than that of visible light communication, but ultraviolet light is used as invisible light. Communication has the unique advantages of low resolution, low eavesdropping rate and high confidentiality. 1 low resolution: ultraviolet light is invisible light, it is difficult for the naked eye to find the existence of ultraviolet light source; ultraviolet light propagates signals in all directions through atmospheric scattering, so it is difficult to determine the position of the ultraviolet light source from the scattered signal. 2 low eavesdropping rate: due to the strong absorption of atmospheric molecules and suspended particles, the intensity of the ultraviolet light signal is attenuated exponentially. This intensity attenuation is a function of distance. Therefore, the transmission power of the system can be adjusted according to the requirements of communication distance. Its radiated power in the non-communication area is minimized and difficult to intercept.
As a new type of military communication system, UV communication has the advantages of strong anti-interference ability, good confidentiality, non-line-of-sight communication and all-round communication, and has become the focus of research of military technicians at home and abroad. However, conventional ultraviolet light sources (low-pressure mercury lamps) have defects such as large volume, short life, low modulation rate, and fragility, which limit the development of ultraviolet light communication.
In order to solve the problem of ultraviolet light communication source, the Defense Advanced Research Projects Agency (DARPA) launched a project to develop a variable wavelength transistor ultraviolet light emitter in 2002, and successfully developed a day with a wavelength of 274 nm. Blind area ultraviolet light emitting diode (UVED). Compared with low-pressure mercury lamps, UV LEDs have the advantages of small size, long life, low-voltage power supply, and digital modulation.
The excellent properties of UV LEDs have made them useful in the field of UV communication as soon as they are available. In 2005, MIT used a 274nm UV LED manufactured by DARPA as a light source to develop a prototype of UV communication experiments, non-direct view communication, with a communication rate of 200b/s in the range of 100m; Ben Gurion University, Israel Other research institutes such as British Aerospace Systems Inc. and the University of California have also established ultraviolet light communication systems based on ultraviolet LEDs. However, the specific conditions and technical details of their research work are highly confidential.
In 2010, China's first 280nm deep-UV light-emitting diode (UV LED) production line was commercialized and mass-produced in Qingdao Jiesheng Electric Co., Ltd., and the 280nm deep-UV LED module produced by Qingdao Jiesheng Electric Co., Ltd. in 2011 was calibrated. More than 32mW, these research results have promoted the application of UV LEDs in the field of UV communication. In 2010, the modulation rate of the ultraviolet communication system set up by Chongqing University reached 7Mb/s. In 2010, the Space and Applied Research Center of the Chinese Academy of Sciences built an ultraviolet light image transmission experiment system using ultraviolet LED arrays.
UV LED modulation rate characteristics
The technical indicators announced by the UV communication system development unit are system-level parameters, such as data transmission rate, transmission distance and bit error rate; UV LED manufacturers only test the DC parameters of the manufactured products, such as working voltage/current. , peak wavelength and half width. The light source of the ultraviolet light communication system can only realize the data transmission when it is working in the modulation state. The modulation characteristics such as the modulation rate and modulation spectrum of the ultraviolet LED are studied, which will promote the application of the ultraviolet LED in the field of ultraviolet light communication.
(1) Principle of UV LED modulation rate test
The principle of UV LED modulation rate test is shown in the figure below. The experimental equipment is described as follows:
1 Function Generator: Agilent's 33250A is used to generate a standard square wave signal for driving UV LEDs.
2 UV LED: A single 280nm UV LED in T039 package produced by Qingdao Jiesheng Electric Co., Ltd., with output power >0.6mW.
3 Detector (Si): The PDA10A EC high-speed detector manufactured by THORLABS is suitable for the wavelength range of 200~1100nm and the response time is 1ns.
4 signal amplifier: The detector used in this experiment has signal filtering amplification effect. If the detector selects current output and has no amplification function, it needs to select the corresponding signal amplifier.
5 digital oscilloscope: Select the Tektronix DP07054 model storage oscilloscope with a bandwidth of 500MHz.
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