Ok guys;
I just finish my test using fiber optics to send data from a PC to an Ardiuno. I use the Ardiuno code and the Processing code from this tread --> http://arduino.cc/forum/index.php/topic,76586.0.html I just change the pins numbers of the LCD display inline with my DIY LCD shield.
Here the experiment :
I use a USB - TTL breakout box, connect the +5, gnd and tx. The Tx line was connected to a simple transistor circuit controling the part MFOE71. The transistor is a 2N3904 and the limiting resitor is 68 ohms. I test the circuit and to "see" the IR at the fiber optic, I use my cell phone camera to "see" the IR.
Connect the USB cable, add this line in the void draw() ---> myport.write("this is a test"); for continious loop to test my receiver circuit. My receiver circuit is simply the example circuit from the datasheet for the part MFOD72. Instead of the 74LS132, I use a 74LS14. I even try the combo --> +5 - 220 k resistor --- opto-receiver - gnd. <-- That did not work. I was "force" to use the datasheet example. I try again, I got a nice waveform on my scope. I connect the Ardiuno / LCD shield, conect the output of the NOT gat to the RX of the Ardiuno ( pin 0 ) and ... Not working..Humm..I look again at the chip... "I forgot a gnd !! " Connect the gnd to the chip and ...Work just fine... 
Here some pictures of my setup.
Still need to find the fiber cable...
