Slow light in photonic crystal waveguides Nikolay Primerov

Doctoral program in photonics “Photonic crystals” by Romuald Houdré Why do we need slow light? What is slow light? Possibilities to make a slow light Slow light in photonic crystals waveguides Conclusions Outline Nikolay Primerov

Doctoral program in photonics “Photonic crystals” by Romuald Houdré 1.Nonlinearities 2.Optical switching 3.Optical storage 4.Delay lines 5.Quantum optics T.F. Krauss, J. Phys. D: Appl. Phys. 40 (2007) Z. Zhu et al., Science, 318 (2007) F. Morichetti et al., Opt. Express, 16 (2008) Nikolay Primerov Why do we need slow light?

Doctoral program in photonics “Photonic crystals” by Romuald Houdré What is a slow light? Nikolay Primerov

Doctoral program in photonics “Photonic crystals” by Romuald Houdré = Pulse signal Nikolay Primerov What is a slow light?

Doctoral program in photonics “Photonic crystals” by Romuald Houdré The peak of the pulse propagates at the Group Velocity. Pulse signal Nikolay Primerov What is a slow light?

Doctoral program in photonics “Photonic crystals” by Romuald Houdré Thus, in a material and/or structure with large first order dispersion coefficient, V g can be drastically increased Nikolay Primerov Group index Group velocity What is a slow light?

Doctoral program in photonics “Photonic crystals” by Romuald Houdré Possibilities to make a slow light Stimulated Brillouin Scattering (SBS) Stimulated Raman Scattering (SRS) Electromagneticaly induced transparency (EIT) Coherent population oscillation (CPO) Coupled ring resonators Photonic crystals and others Nikolay Primerov

Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov Periodically structured medium Free space Medium with constant n k ω c= ω/k c/n= ω/k k ω π/a Band edge Band gap Slow light: Science and application / editors, J.B. Khurgin and R. Tucker, 388 p. Slow light in photonic crystal waveguides Slow down factor Maximum bandwidth

Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov Slow light in photonic crystal waveguides 1)Backscattering Standing wave  Slow mode optical mode is close to a resonance with the structure 2) Omnidirectional reflection No cut-off angle, mode at k≈0  slow modes of for k=0 standing wave T. F. Krauss, J. Phys. D: Appl. Phys. 40 (2007) The band edge is the most obvious place for the slow light

Slow light in photonic crystal waveguides But there are some problems: 1)Dispersion curve near the gand edge is typically parabolic  strong group velocity dispersion (GVD) 2)Band edge presents a cut off point  propagation mode turns to evanescence mode 3)Fabrication tolerance It’s not the best region for the slow light to operate Dispersion engineering Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov

J.Li, T.P. White, et al. Opt. Express, 16(9) (2008), Slow light in photonic crystal waveguides Section of constant group velocity over approximately 20% of Brillouin zone  low GVD N g = 30, 50, 80 Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov GVD handling

Slow light in photonic crystal waveguides Enhancement of the linear interaction Δφ=ΔkL=π Optical switching devices (for example, Mach-Zehnder configuration) Δk= Δnk 0 We have to distinguish between n mat and n eff Slow light regime Δk 1 > fast light regime Δk 2 T. F. Krauss, J. Phys. D: Appl. Phys. 40 (2007), D. M Beggs, et al., Opt. Lett., 33 (2008), Slow light regime yields a large Δk for a given Δn mat Slow light coupler 5 um length with Δn mat = 4×10^-3. Conventinal coupler 200 um long Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov

Problems to overcome 1)Signal distortion by GVD 2)Reflection losses due to modal mismatch between incident wave and guided wave 3)Losses due to disordering in the structure 4)Other loss sources 5)Tunability Solutions: 1. Chirping the waveguide properties, changing the waveguide width, changing the hole size and position of the photonic lattice close to the waveguide Many different effects involved. Need of transition region to build up to reduce the mode-matching problem Slow light operation away from the band-edge 5. ?? Conclusions Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov

Conclusions Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov Main Advantages: - Relatively large bandwidth from GHz up to few THz - Room temperature operation - Availability to tune the wavelength, slowdown factor and bandwidth with the structural design Main Disadvantages: - Tunability of the slowdown factor in given structure - Reflection and injection losses

Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov Thank you for attention!