Development of LED Intelligent Lighting System for Visible Light Communications

White light-emitting diodes (LEDs) is considered as the next-generation of mainstream lighting technology due to their unique features including energy saving, short response time, and long-term reliability, etc. Recently, other interesting application based upon visible LEDs (white LEDs in particular) is focus on the realization of an intelligent lighting system, in which LEDs provide lighting and can also be used as an optical transmitter. In this project, we seek to design and fabricate a thin-film (substrate-free) InGaN resonant-cavity light-emitting diode (Thin-film InGaN RCLED) due to light sources with an increased light output and an enhanced modulation speed are necessary for such systems. By placing a yellow phosphor layer array from the blue LED (known as remote phosphor coating), white LEDs can be easily created by mixing two complementary colors (i.e., blue and yellow light). As a result of optical cavity effect, RCLEDs can exhibit highly directional emission; therefore, they are useful in visible light communications with a directed line-of-sight path between the transmitter and the receiver. This will alleviate the issues associated with multipath induced intersymbol interference (ISI). Experimentally, RCLED array along with PIN array will be used in line of sight visible light communication system to service as a transmitter/receiver, respectively. Besides, they will combine with an optical lens to increase angular coverage and achieving angle-diversity detection. Further improvement of the data transmission rate could be achieved by the incorporation of an advanced modulation scheme or by using a modified receiver. The program schedule is organized as: 1. In the first year: we shall focus on epitaxial growth of InGaN/GaN multiple quantum wells (MQWs) with an asymmetric barrier layer, simultaneously, inserting an electron emitter layer (EEL) between the n-type layer and the MQW so that the energetic carriers (electron) come from the n-GaN will be decelerated before they enter the MQW region. In addition, the EEL was also used to control the piezoelectric field and indium content in the InGaN MQWs. Otherwise, thin-film InGaN RCLEDs (chip size ~ 1 mm2, Po ＞ 400 mW & Vf ＜ 3.5 V @ at 350 mA, f3dB ＞ 100 MHz) will be fabricated by using electrodeposition and laser lift-off technologies and then a yellow remote phosphor layer was used for down-conversion of blue to white light (luminous output ＞ 100 lumens, luminous efficiency ＞ 100 lm/W, Wattage = 1 W, semi-angle at half power ＜ 50o). 2. In the second year: we will demonstrate that Energy Star LED luminaires fabricated with the thin-film RCLED array (cascade designs) and the YAG:Ce+3 phosphor (remote phosphor coating) are suitable for use in visible light communication system. To improve the performance of optical wireless links, an angle-diversity receiver with an optical lens and a PIN array was designed to collect the optical signals. Further improving the signal to noise ratio of the receiver could be achieved by using a clock and data recovery (CDR) circuit. Finally, we anticipate that the data transmission rate could be larger than 250 Mbit/s as an advanced modulation scheme (e. g., Quadrature Amplitude Modulation) was introduced.

Project ID:PB10207-1900
External Project ID:NSC102-2221-E182-058