  This paper experimentally demonstrates that the AC impedance spectrum of the
LED as a photodetector heavily depends on the received optical power, which may
cause the impedance mismatch between the LED and the post trans-impedance
amplifier. The optical power dependent impedance of the LED is well fitted by a
modified dispersive carrier transport model for inorganic semiconductors. The
bandwidth of the LED-LED visible light communication link is further shown to
decrease with the optical power received by the LED. This leads to a trade-off
between link bandwidth and SNR, and consequently affects the choice of the
proper dada modulation scheme.
