SPLASH: Slow Photon Light Activated Switch

Project abstract

SPLASH project addresses the issues of optical switches, tuneable delay lines and optical buffering that is essential for realizing the vision of all-optical data processing. The CORECOM consortium will realize these functions by exploring optical slow light structures based on coupled ring resonators and photonic crystal waveguides.
The core demonstrators are:

• a) Broadband slow light. Photonic crystal waveguides that combine sizeable slowdown factors (10-20) with broad bandwidth (500 GHz) and efficient (>90%) optical coupling.
• b) Tuneable coupler. By exploiting slow light phenomena in photonic crystals, the coupler will be very compact (10's of µm), yet require only refractive index changes of order 10-3 for complete switching. Tuning will be thermo-optic, electro-optic and all-optical.
• c) Tuneable delay line. Tuneable ring resonators will be used to continuously control the delay properties of a system of coupled resonators.
• d) Switchable optical storage. By tuning/detuning the elements of a coupled resonator delay line, optical information will be stored.

Structures will be realized in silicon on insulator technology to achieve the maximum compactness and maximum number of stored bits/unit area. The proposed program is extremely timely, as the slow light opportunity needs to be seized now in order to be ready for exploitation on a 10-year horizon, when all-optical functionality will start to be implemented in systems and networks. The project kicked off in January 2007. In June 2007, at the end of the 6 month activity, three milestones was completed:

• Selection of a theoretical/numerical route for the 2D and 3D analysis of the impact of fabrication errors on losses at small group velocities and selection of W1-type waveguides for testing the impact of intentional geometrical fabrication errors.
• Decision on technology route (PMMA, ZEP520, HSQ) and optimum waveguide structure to achieve low loss waveguides with moderate bending radius.
• Directional coupler: passive slow light enhanced directional coupler with short coupling length (< 100μm).

Project results

Several relevant papers have been either recently submitted or published:

• J.P. Hugonin, P. Lalanne, T.P. White and T.F. Krauss, “Coupling into slow-mode photonic crystal waveguides”, submitted for publication.
• D.M. Beggs, T.P. White, L. O’Faolain and T.F. Krauss, “Ultracompact and low power optical switch based on silicon photonic crystals”, submitted for publication.
• A. Melloni, F. Morichetti, C. Canavesi, A. Breda, C. Ferrari, R. Costa and M. Martinelli, “2 bit continuously tunable slow wave delay line at 2.5 Gbit/s”, Postdeadline paper, ECIO 2007.
• R.J.P. Engelen, Y. Sugimoto, H. Gersen, N. Ikeda, K. Asakawa and L. Kuipers, “Ultrafast evolution of photonic eigenstates in k-space”, Nature Physics, 3, 401-404 (2007).
• L. O’Faolain, T. P. White, D. O’Brien, X. Yuan, M.D. Settle and T.F. Krauss, “Dependence of extrinsic loss on group velocity in photonic crystal waveguides”, submitted for publication.
• Melloni and F. Morichetti, “Direct Observation of Subluminal and Superluminal Velocity Swinging in Coupled Mode Optical Propagation”, Phys. Rev. Lett. 98, 173902 (2007).
• M. Gnan, D.S. Macintyre, M. Sorel, R. M. De La Rue and S. Thoms, “Enhanced stitching for the fabrication of photonic structures by electron beam lithography”, submitted for publication.