ORC Seminar Series

"Time resolved motion of pulses in photonic crystal waveguides: a real space investigation "

Speaker: H. Gersen

Date: 4 February 2009

Time: 2pm

Venue: B53 Seminar Room

Abstract

H. Gersen1,*, T.J. Karle2, J. P. Korterik1, T.F. Krauss2, N.F. van Hulst1, L Kuipers1,3

1) Applied Optics group, MESA+ Research Institute, University of Twente, NL.

2) Photonic Band Gap Research Group, University of St. Andrews, UK.

3) Nanophotonics Group, FOM-institute for Atomic and Molecular Physics (AMOLF), NL.

*) Currently part of : Nano-physics and Soft Matter Group, University of Bristol, UK

Strong dispersion combined with distributed Bragg diffraction makes pulse propagation through a photonic crystal (PhC) an exciting research topic. To study the complex interplay between different mechanisms, local time-resolved measurements are crucial. However, peeking inside a photonic structure is far from trivial as conventional optical microscopy is limited by the diffraction limit. What occurs inside the device therefore remains mostly hidden. Recently, we demonstrated a non-invasive technique to “visualize” pulses as they propagate through an optical device with both temporal and spatial resolution. [1,2]

Figure 1 schematically depicts how we extended a heterodyne detection phase-sensitive PSTM, which allows the measurement of both the amplitude and phase of propagating light [3], to perform local time-resolved measurements. At a reference time determined by the position of an optical delay the position of a pulse is pinpointed. With this technique we have recently been able to observe time-resolved motion of an ultrashort pulse through a photonic crystal waveguide. Figure 2 shows an example for a fixed reference time in which a 120 femtosecond pulse has split in multiple pulses each with a different modal distribution. By repeating this measurement for different reference times the motion of each pulse can be followed through the waveguide in time, giving a direct measure for local group and phase velocities. At the same time the phase-sensitivity of our technique allows to directly measure the bandstructure for the first time, revealing multiple Brillouin zones due to zone folding.[4] At a specific optical frequency the existence of long-lived modes not propagating along the waveguide is found. During at least 3 ps, movement of this field is hardly discernible: its group velocity would be at most c/1000.[5] The huge trapping times without the use of a cavity reveal new perspectives for dispersion and time control within photonic crystals.

References

[1] M.L.M. Balistreri, H. Gersen, J.P. Korterik et al., Science 294 (5544), 1080 (2001).

[2] H. Gersen, J.P. Korterik, N.F. van Hulst, and L. Kuipers, Phys. Rev. E. 68, 026604-1 (2003).

[3] M.L.M. Balistreri, J.P. Korterik, L. Kuipers et al., Phys. Rev. Lett. 85, 294 (2000).

[4] H. Gersen, et. al., Phys. Rev. Lett. 94, 123901 (Apr. 2005)

[5] H. Gersen, et. al., Phys. Rev. Lett. 94, 073903 (Feb. 2005)

 



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