Liam O'Faolain

Slow-light Enhanced Nonlinear Optics in Silicon Photonic Crystal Waveguides

We present a summary of our recent experiments showing how various nonlinear phenomena are enhanced due to slow light in silicon photonic crystal waveguides. These nonlinear processes include self-phase modulation (SPM), two-photon absorption (TPA), free-carrier related effects, and third-harmonic generation, the last effect being associated with the emission of green visible light, an unexpected phenomenon in silicon. These demonstrations exploit photonic crystal waveguides engineered to support slow modes with a range of group velocities as low as c/50 and, more crucially, with significantly reduced dispersion. We discuss the potential of slow light in photonic crystals for realizing compact nonlinear devices operating at low powers. In particular, we consider the application of SPM to all-optical regeneration, and experimentally investigate an original approach, where enhanced TPA and free-carrier absorption are used for partial regeneration of a high-bit rate data stream (10 Gb/s).

Controllable low-loss slow light in photonic crystals

The key figures of merit for integrated optical components include the device footprint and operating energy consumption, both being major contributors to the purchase and operating cost, respectively. Slow light in silicon photonic crystal (PhC) devices has the potential to significantly reduce both, through enhanced light matter interactions, for both linear and non-linear optics applications. However, for all applications a precise control over the slow-down factor and reduced optical losses are paramount. In this paper, we present our work on various low-loss slow light systems based on PhC technology. We discuss the ability to control the group index and propagation loss of a PhC waveguide through appropriate device design - dispersion and loss engineered waveguides. This control, providing us with a free choice of group index ranging from 5 to 100, has already led to a range of non-linear optical applications, such as third harmonic generation, four-wave mixing and photon pair generation. We extend this approach to kagome lattice based PhCs and show that group indices exceeding 100 000 are possible in photonic crystal based geometries. We further discuss the post-fabrication control over slow light in PhC waveguides. Here both permanent, passive control is possible - through post-processing of the PhC devices - and adaptable, active control, through electro-optic or thermo-optic tuning. We apply the latter to a coupled cavity geometry that displays a transmission peak analogous to electromagnetically induced transparency and show a tuneable delay of 300ps with a delay loss of approximately 15dB/ns.

Understanding the rich physics of light propagation in slow photonic crystal waveguides

We study propagation losses in slow light photonic crystal waveguides and show that dispersion engineering can reduce the loss. We develop an improved understanding of why and how this occurs and develop an new approach to modeling these devices that provides new design insights.

ADVANCES IN SLOW AND FAST LIGHT III

We study propagation losses in slow light photonic crystal waveguides and show that dispersion engineering can reduce the loss. We develop an improved understanding of why and how this occurs and develop an new approach to modeling these devices that provides new design insights.

Ultracompact Switches and Modulators Based on Slow Light in Photonic Crystals

Photonic crystal slow light waveguides enable modulators with high speed and large bandwidth. Group indices of 30-40 are achieved with low loss and we demonstrate modulators of <100 µm length with switching times of 3ps.

Slow light enhanced nonlinear effects in silicon photonic crystal waveguides

We demonstrate how nonlinear optical phenomena are enhanced by slow light in dispersion engineered silicon photonic crystal waveguides, and how this can be applied to perform all-optical signal processing at 640Gbit/s.

Systematic Design of Broadband Slow Light Photonic Crystal Waveguides

We present a systematic design approach for broadband slow light photonic crystal waveguides. Precise control of group velocities between c/30 and c/90 is possible while maintaining an almost constant group index-bandwidth product.

Low Loss and Slow Light Photonic Crystal Waveguides in SOI

Photonic crystal waveguides have evolved from an academic curiosity to an area where practical applications are beginning to appear feasible. Waveguides consisting of a single line of missing holes (W1) have become the benchmark to assess fabrication quality, and losses of order 10 dB/cm and below are now possible. We discuss fabrication aspects of such waveguides, made both by e-beam and by deep UV lithography, and highlight some of the key requirements for low loss operation. While these results are very encouraging, true functionality arises from the exploitation of dispersive effects, especially operation in the slow wave regime. Novel designs enabling non-dispersive slow wave operation with considerable bandwidth are discussed