Modulation format conversion employing coherent optical superposition.

We propose and experimentally study the passive coherent optical addition of complex modulation format signals through the use of a delay line interferometer followed by a temporal gate to increase the encoded bits per symbol and consequently, the spectral efficiency of an incident signal. Modulation format conversion and packet compression are demonstrated as two possible application examples. A variety of modulation formats can be accommodated, whereas higher compression factors can be achieved through the use of a cascade of delay line interferometers.