Excited diode allow flow opposite direction, possible?
Yes, an LED will conduct in reverse if excited by an optical signal (of the right wavelength). This is basically just using an LED as a photodiode. Any reference on photodiodes will explain the underlying physics.

In fact, pretty much any diode will have this behavior. However, silicon diodes are typically packaged in opaque encapsulents to avoid the photoelectric effect producing significant reverse conduction. Also, photodiodes designed as photodiodes will be optimized to maximize the effect, while LEDs will not be.