Abstract
The potential of visible light communications based upon phosphor-converted white
resonant-cavity light-emitting diodes (RCLEDs) is investigated experimentally. To
fabricate a blue InGaN RCLED, a λ/4-thick
Ta<sub>2</sub>O<sub>5</sub>/SiO<sub>2</sub> distributed Bragg reflector, along with
a metallic Ag layer, were respectively coated onto the top and bottom of normal LEDs to
form an optical cavity. As evaluated from the emission spectrum of blue RCLEDs, the
discrepancy of the expected cavity length from the measurements suggests that cavity
oscillation may mostly occur in the GaN-based epistructures. In addition to the presence
of the optical cavity effect, the incorporation of a bottom reflector is useful to
increase the light extraction efficiency of the RCLEDs. As a result, these RCLEDs
exhibit improved operational characteristics over normal LEDs in terms of light output
power, external quantum efficiency, spectral purity, and directionality. With an
increase in injection current, the enhancement of the spontaneous emission rate is
responsible for the improved quality of eye patterns in blue RCLEDs operating at a
transmission rate of 100 Mbit/s and 175 mA . After encapsulating the blue RCLEDs with a
phosphor layer, we found that white RCLEDs have the capacity for free-space optical
communication with a data rate of 12 Mbit/s.
© 2012 IEEE
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