Abstract:
InGaN light-emitting diodes (LEDs) grown with an
asymmetric multiple quantum well (MQW) are proposed for use
in an optical link with an avalanche photodiode (APD) based
receiver. In contrast to the high photoresponse of red AlGaInP
LEDs in APDs, the proposed blue LEDs provide improved light
output and enhanced system bandwidth for directed line-of-sight
optical links passing through a 100-cm-long water tank. This improvement
is due to the nonuniform carrier distribution within
the InGaN MQWs being mitigated by using a thin GaN barrier
near the n-GaN to facilitate hole transport capacity. In addition,
bandwidth degradation resulting fromAPD module saturation can
also be avoided by using these blue LEDs, successfully establishing a
300 Mbit/s LED-based underwater data link. The proposed InGaN
LEDs (zero bias) under illumination exhibit a peak responsivity of
0.133 at λ = 370 nm, an ultraviolet (UV)-to-visible rejection ratio
of 4849 and a 3-dB cut-off frequency of 33.3 MHz. Using violet
UV laser diodes and the proposed LEDs respectively as the optical
transmitter and receiver, an underwater optical link (L= 100 cm)
with a data transmission rate of up to 130 Mbit/s and a bit error
rate of 4.2 × 10−9 is also demonstrated
