Ultraviolet (UV) light plays an important role in air/water/surface sterilization now. Maintaining a certain light intensity is often required to attain the targeted effect. In this paper, on-chip power monitoring of a UV-A light-emitting diode (LED) via sapphire substrate is reported. A p–i–n photodiode loop that surrounds the UV-A LED was designed and fabricated to monitor the output power by detecting the scattered light of the LED propagating through the sapphire substrate. No particular waveguide structure or processing parameter control was needed. The monitoring responsivities per unit of surface-emitting power obtained were approximately 21 and 25 mA/W at photodiode biases of 0 and 3 V, respectively. When combined with a transimpedance amplifier, a monitoring responsivity of 1.87 V/mW at zero bias was measured, and a different monitoring responsivity could be customized by adjusting the gain of the transimpedance amplifier. The operation principle of this device might be applicable to UV-B or UV-C LEDs.

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Constant light power operation of an ultraviolet (UV) LED based on portable low-cost instrumentation and a monolithically integrated monitoring photodiode (MPD) has been reported for the first time. UV light irradiation has become one of the essential measures for disinfection and sterilization. Monitoring and maintaining a specified light power level is important to meet the criteria of sterilization. We built a module composed of a monolithically integrated UV LED and MPD, a transimpedance amplifier, an Arduino Uno card, a digital-to-analog converter and a Bluetooth transceiver. An Android App that we wrote remotely controlled the UV LED module via Bluetooth. The Arduino Uno card was programmed to receive demands from the smartphone, sent a driving voltage to the LED and returned the present MPD voltage to the smartphone. A feedback loop was used to adjust the LED voltage for maintaining a constant light output. We successfully demonstrated the functioning of remote control of the App, and the resultant UV LED measured power remained the same as the setting power. This setup can also be applied to visible or white LEDs for controlling/maintaining mixed light’s chromaticity coordinates or color temperature. With such controlling and internet capability, custom profiling and maintenance of precision lighting remotely would be possible.

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