Storage-bit-rate product in slow-light optical buffers

Introduction: All-optical storage and signal processing are of intense interest for numerous applications, ranging from true-time delay for antenna remoting to all-optical convolution functions, all-optical signal regeneration, all-optical wavelength conversion, and all-optical buffers. The ability to control the optical group velocity over a wide range with high resolution is critical to enable such novel functionalities, particularly optical buffering. Recently, ultraslow light devices with variable group velocities have been suggested as a promising candidate for all-optical buffers [1–3]. Buffering is accomplished by slowing the signal, as opposed to routing the signal onto a long distance loop to produce delay [4]. For a practical buffer, the most critical attributes are the storage density and how the storage varies as the signal bandwidth increases. Recently, we analysed this problem analytically by considering a device with a spectral hole in its absorption spectra created by, for example, electromagneticallyinduced transparency (EIT) [5]. Similar delay-bandwidth analyses are published for coherent population oscillation and other physical mechanisms [6, 7]. In this Letter, we numerically simulate the bit error rate (BER) performance for pseudorandom signals propagating through an EITbased ultraslow light device, as discussed in [1, 2]. The group velocity of the signal beam in such a device is adjustable by changing the intensity of a control laser. We calculated the power penalty introduced by the optical buffer in an optical link against increased bit rate and storage.