Indirect photonic transitions for light control in integrated photonics

• Applicant: Dr. Alexander Petrov
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 261759120

The goal of this research project is to let optical pulses strongly interact in silicon slow light waveguides with relativistically moving refractive index fronts. The right choice of a slow light waveguide and front velocity can allow a palette of inspiring physical experiments. Namely, the optical pulses can be shifted in frequency, stored for certain time, compressed and broadened. Apart from the listed effects the indirect quality of the photonic band transition causes it to be nonreciprocal in nature. Thus, physical phenomena such as optical isolation can be investigated as well. Apart from scientific interest the successful experimental realization of this proposal can lead to several new approaches for optical pulse manipulation in optical communication systems and other fields. The frequency shift in the direct transition is determined by just the refractive index step (namely the power that generates the free carriers) of the dynamic change. Such refractive index changes are usually in the order of 10-3 and thus lead to frequency changes of approximately 100 GHz for a signal at 1.5 µm wavelength. The indirect transition creates an additional way for frequency control via the choice of the front velocity. First of all, it is envisaged to demonstrate a non-reciprocal frequency shift using two counter propagating signals where the forward propagating signal experiences a different frequency shift as compared to the backward propagating signal. This concept can be used for optical isolation, which is a current scientific and technical topic of high interest. Also, by the right combination of the dispersion curve and the front velocity, very large frequency shifts can be obtained for small refractive index steps. Here we envisage frequency shifts of 1 THz and more.Tunable time delays are difficult to realise with direct transitions. Usually, the frequency of the signal is shifted but the group velocity stays the same. In case of an indirect transition in photonic crystal waveguides the choice of the front group velocity can allow transitions to states of any group velocity or even to a state of zero group velocity. Thus, we plan to demonstrate a tunable time delay by varying the front velocity.The indirect transition can be also used to compress or broaden optical pulses upon reflection from a moving photonic crystal front. There are several advantages of this approach. First of all, compression and broadening factors of the order of 1-10 can be realised. Almost 100% conversion efficiency can be achieved even with a small refractive index modulation. At the same time the center frequency stays the same in this transition, which is a very important advantage.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Manfred Eich