Development Of UV-NIR Full-Spectrum Tunable Light Source System Based On LEDs

LED-based spectrum-tunable light sources play an important role in the fields of multi-spectral imaging,calibration,biological lighting,detection,and solar simulator.This kind of tunable light source has great application prospects.However,the wave range of the existing spectrally tunable light source system is mostly distributed in the visible light band,rarely including the ultraviolet and infrared bands.The light output method is single,lacking in an appropriate feedback mechanism.And the lack of supports of remote control automation software contribute to great limitations.In this paper,the UV-NIR full-spectrum tunable light source system is developed with a series of ultraviolet-near infrared(UV-NIR)LEDs to address the deficiencies of the existing system.The specific work contents and innovations include:1.Build an UV-NIR full-spectrum tunable light source system based on LEDs,which cover the spectral range of 240nm-840nm.Among them,the current spectral tunable wave range is between 360 nm and 840nm.The system includes hardware circuit design part and software part.Design a 24-channel constant current source hardware circuit.Using 3 pieces of constant current source circuit board laminated design,each piece of constant current source circuit board contains 8 current output channels.The current of each channel can be independently programmed in the range of 0?1A.Use 16-bit high-precision low-noise DAC7734 chip to achieve 65535-level fine current adjustment.Aiming at heat generation problem for the constant current source circuit,methods to optimize the heat dissipation design and enhance the stability of the current output is proposed.MOS transistors which is used to provide power output employ a common radiator,and two axial fans are installed at both ends of the radiator in a convection manner to further enhance the cooling effect,suppress the temperature of the MOS transistors,reduce the temperature drift of the MOS transistors,and enhance the current output Stability.Each constant current channel drives a group of LEDs,and each group of LEDs does not interfere with others.2.Develop embedded softwares based on STM32,Linux and develop host computer software based on Delphi.24-channel constant current source is designed independently.Develop embedded software based on STM32 for constant current source and reserve custom protocol based on serial port protocol so that constant current source can be separated from the system as independent power supply instrument,which can be applied to the design of other large-scale instruments and has greater expansion.On one hand,the ARM server software is developed based on Samsung 4412 embedded Linux platform can drive 24 independent tunable constant current sources,relays and spectrometer hardware.On the other hand,it can be connected to the remote host computer software,and the data collected by the spectrometer can be processed and transmitted to the remote PC for further processing.The visual program based on Delphi is connected with the ARM server software under embedded Linux.The visual program transmits commands of the 24-channel constant current source and the spectrometer to the ARM server software.The real-time current value of each current channel,and the processed spectral parameters are visualized as data on the screen of the PC.The visual software can trigger the spectrum fitting procedure and automatically import the current value of each channel LED,and cooperate with the proposed spectrum regulation method to make the fitted output spectrum closer to the target spectrum.The coordination of multiple software systems enables remote control of the instrument and automated experiments,which is convenient for scientific researchers to carry out spectrum fitting experiments.3.The system supports dual light output mode with dual input and dual output fiber bundles.The two input ports of the fiber bundle receive the light emitted by the light source.One output of the fiber bundle is connected to the spectrometer for realtime measurement of the spectrum.When the other output is connected to an integrating sphere,the system can be used as a standard brightness source.And when it is connected to a collimating lens,the system can be used as a standard illuminance source,which can be flexibly switched.4.A serial port-based constant current source test software developed with QT is used to test the software and hardware system of 24 constant current sources.And the linear relationship between the digital quantity of 24 LEDs and the output current value is obtained by fitting.This relationship is programmed into the desktop visual software of the spectrum-tunable light source system,which makes the programmable constant current source more accurate.21 LEDs with different wavelengths are used to test the spectrally tunable light source system.The spectral distribution of each LED at 60 mA is obtained.And after normalizing it,the software fits the target spectrum to the existing LEDs.The current value of the corresponding channel is obtained and is used to drive LEDs.The real-time spectrum data is collected by the spectrometer to the desktop visualization software,and the functions of a complete set of software and hardware systems are verified.