Unification of Irreversibility and Energy Diagram Theory

[Image: see text] A simultaneous emission-detection phenomenon occurs when a quantum well (QW) diode is biased with a forward voltage and illuminated with a shorter-wavelength light beam. The diode is able to detect and modulate light emitted by itself due to its spectral emission-detection overlap. Here, two identical QW diode units separately function as a transmitter and a receiver to establish a wireless light communication system. In association with energy diagram theory, we explain the irreversibility between light emission and light excitation in the QW diode, which may help us deeply understand various expressions in nature.