Researchers from Vienna University of Technology have proposed and simulated a method for all-optical address recognition that uses the semiconductor optical amplifier (SOA)-based Mach-Zehnder interferometer (MZI) as a faster and cheaper alternative to electrical systems.
At last month's Networking and Optical Communications Conference, the group revealed the configuration of the proposed all-optical header recognition system. It consists of an MZI equipped with an SOA at each interferometer arm.
A continuous wave (CW) light source is split into two coherent light beams. The two amplifiers, SOA1 and SOA2, then modulate the phases of the beams using incoming and local address signals, respectively. Crossgain modulation is also performed inside the SOAs.
The modulation of the two signals' phase and gain still varies with the power difference between incoming and local address peak power and their pulse widths.
A non-integrated device requires the insertion of a phase shifter into one arm to equalise the phase asymmetries of the MZI.
The device works by launching the incoming header into the first arm via coupler C2, while the local header is inserted into the second arm through coupler C3 in a counter-propagating manner relative to the CW beam direction. This eliminates the need for optical filters.
A group spokesman said: "A counter-propagating scheme was used to allow the address and the CW beam to be spaced relatively near in the frequency domain as it simplified the simulation. But for a practical set-up, a co-propagating scheme is even more favourable. The carrier density inside the SOA is changed even more due to the address signal."
The simulation results showed the method to be intrinsically unrestricted regarding the address size. But for higher bit rates and longer addresses, the power equalisation of the local and incoming signal, together with the synchronisation and detection capabilities of the deployed photodetector, need to be carefully controlled.