optical decision circuit based on feedback between a laser diode and an SOA

Research Area: III-V Semiconductor Photonic ICs

Main Researcher: Wouter D'Oosterlinck

With the current trend towards all-optical networks all the funcions need to be performed in the optical domain. Among these functions are optical decision functions and as a part of that all-optical regenerators. Several solutions have been proposed to come to an optical decision circuit or regenerator, also in this research group (see above). Most of them are based on the non-linear effects of a SOA in or near saturation. To take advantage of those non-linear effects usually interferometric schemes are used. Since the rely on the phase difference between two different paths of the interferometer they are quite dependent on environmental changes but still offer the big advantage of the possibility to integrate them on a single chip.
In this research topic a new type of optical decision circuit, that depends on the optical feedback between an SOA and a laser diode is examined.

for a low input signal the laser can still inject a lot of power into the SOA resulting in a situation where the injected laser power determines the carrier distribution in the SOA. When the input power rises the power coming from the SOA and injected into the laser also rises, resulting in a (initially) slightly lower output power of the laser. When the feedback between the rising output power of the SOA and the consequently decreasing laser output power reaches a threshold value the output power of the SOA drops significantly causing a flip in the carrier distribution in the SOA. This causes a steep step in the output power of the decision circuit.
By adjusting the currents of the SOA and laser in such a way that the SOA is always saturated (either by the input signal or the laser signal) and that the output saturation power of the SOA after propagation trough the coupler makes the laser to work just above threshold. In this case a very steep decision function can be obtained while maintaining the possibility for high-speed operation.

Other people involved:

• Sam Verspurten

PhD thesises