Flexible opto-electronic AND/NAND logical gate circuit using lightwave interference and balanced photodetection

We report on an opto-electronic Boolean logical gate circuit for coherent optical signals, which is composed of an integrated-optic symmetric Mach-Zehnder interferometer and a balanced photodetector. The circuit flexibly operates as both AND and NAND gates by just changing the phase difference between the two lightwaves incident on the waveguide symmetric interferometer by π . As a preliminary investigation, we did not integrate the interferometer and the photodetector. We evaluated the gate circuit characteristics with the use of optical return to zero and on-off keying 40 Gbit/s signals in the 1.55 µm band. We confirmed that the gate circuit adequately operated for all the input bit patterns.