Wavelength switching of semiconductor tunable lasers

Research Area: Integrated lasers and LEDs

Main Researcher: Bart Moeyersoon

To avoid the bottleneck associated with electronic packet switching and to have a more flexible and efficient usage of the very high bandwidth capacities delivered by WDM, it is expected that future network technologies will move towards optical packet/burst switching. One of the key requirements therefore is the availability of rapidly (order 10 ns) tunable transmitters. Some tunable semiconductor lasers allow such rapid, electronic tuning, but then one encounters problems on a larger timescale due to the thermally induced wavelength drift associated with the switching of the tuning currents.

Apart from modeling the wavelength switching dynamics of tunable lasers, we are also investigating different techniques that can be used to alleviate the thermally induced wavelength drift.
A first technique consists of precompensating the tuning currents using first order RC-networks, in order to compensate the different thermal time constants. This is a very simple, straightforward technique, but unfortunately it is difficult to optimise for different values of the current steps.
Therefore we developed a novel optical feedback loop that can be used to enhance the wavelength switching behaviour of tunable lasers. The scheme is pictured below and consists of an external feedback loop containing two powers splitters and a comb filter (a simple Fabry Perot etalon can be used) that is physically -and thus thermally- separated from the laser. The filter provides a stable frequency reference, independent of temperature changes in the laser sections. This technique works regardless of the value of the current step and numerically obtained results show that frequency drifts up to 15GHz can be suppressed. Currently work is in progress to implement this scheme in practice.

Other people involved:

• Bart Moeyersoon

PhD thesises