LEDs can act also as a light sensor. I wonder if I could use one connection between neurons for bidirectional communication. I connected LEDs on both end of the optic fiber, and used length of the light instead of strength of the light as information. and it seems to work good!
In this test, I send some length of light from one Arduino in sequence from 2 pins. On receiving side, 2 pins are connected to LED-fiber optic. Every time they receive light, it sends out the same length of light back.
Arduino code used for receiver >> https://github.com/mikst/A.I.F.L./blob/master/arduino/LED_send_reciever_test/LED_send_reciever_test.ino