InGaN LEDs fabricated with parallel-connected multi-pixel geometry for underwater optical communications

SU-8 planarized InGaN LED arrays are proposed for use as optical transmitters in underwater optical communications. In addition to alleviating current crowding effects, the parallel-connected design of the constituent pixels is useful to avoid LED failure. Experiments are conducted to investigate the impact of different numbers of emitting pixels on LED performance and system bandwidth of a data communication link passing through a water tank. Although a maximum light output power of 56.7 mW was obtained for LED arrays with all pixels available for light emission, LED arrays with 2 emitting pixels exhibit a high external quantum efficiency at a lower current (i.e., η_ext = 8.9% @ 9 mA). In addition, the maximum 3-dB modulation bandwidth of optical links in the water tank increased from 18 to 30.3 MHz with the use of LED arrays, but the number of emitting pixels is reduced from 16 to 2. Such improvement also reflects an increased data transmission rate of 200 Mbit/s through the use of a 2-emitting-pixel LED array. Finally, real-time transmission of digital TV signals over a moderate distance (∼100 cm)in tap water is shown to be feasible even when modifying the number of the emitting pixels within the LED arrays.