Delay–bandwidth product and storage density in slow-light optical buffers

Introduction: Optical delay line buffers will be key components in future optical communications and information processing systems [1–4]. Recent research results on slow light include experimental demonstration of light speed reduction to 17 m=s in atomic vapour cells using electromagnetically-induced transparency (EIT) [1], a slowdown factor of more than 31 000 using population oscillations (PO) in pumped quantum well material [3], and simulations of slow light in tuned photonic crystals [4]. This Letter reports a theoretical comparison of the capabilities and limitations of slow-light buffers based on a number of technology approaches including EIT, PO and photonic crystal filters. We derive an expression for the delay–bandwidth product of slow-light buffers, which highlights the inherent trade-off between bandwidth and delay. The density of data storage in slow-light buffers is ultimately limited to one bit of data per unit wavelength of device length.