Slow light in a semiconductor waveguide at gigahertz frequencies

Abstract

We experimentally demonstrate slow-down of light by a factor of three in a 100 microm long semiconductor waveguide at room temperature and at a record-high frequency of 16.7 GHz. It is shown that the group velocity can be controlled all-optically as well as through an applied bias voltage. A semi-analytical model based on the effect of coherent population oscillations and taking into account propagation effects is derived and is shown to well account for the experimental results. It is shown that the carrier lifetime limits the maximum achievable delay. Based on the general model we analyze fundamental limitations in the application of light slowdown due to coherent population oscillations.

Theory of Optical-Filtering Enhanced Slow and Fast Light Effects in Semiconductor Optical Waveguides

“…In the practically important case where the input optical signal is a double-sideband signal generated by sinusoidal modulation of a laser beam, it can be shown that the refractive index dynamics plays no role in the observed phase shift [5]. The change in group velocity is in this case only controlled by the gain or absorption dynamics.…”

“…This effect relies on the beating between two externally injected laser beams, or a single intensity-modulated laser beam with sidebands, which leads to oscillations of the electron density in the medium, which in turn alter the effective index seen by the optical signal. In general, the effect can therefore be described as a wave mixing phenomenon, where interactions between the frequency components are mediated by the complex susceptibility, which in semiconductor structures has contributions from various carrier dynamical processes [5], [6]. It has by now been experimentally demonstrated that light-speed control can be realized by CPO effects in a number of different semiconductor structures, i.e., bulk, quantum well (QW) or QD semiconductor optical amplifiers (SOAs) [6]- [10], electro absorbers (EAs) [5], and integrated SOA-EA pairs [11], [12].…”

“…However, the maximum phase shift and bandwidth will be limited by different effects [14]. In both SOAs and EAs, the carrier lifetime sets an important limit [5], [6]. For absorbing media, the residual loss further limits the achievable delay [6].…”

Tunable true-time delay of a microwave photonic signal realized by cross gain modulation in a semiconductor waveguide

“…In particular, slow light in active semiconductor waveguides can provide very fast tuning speed, compact size, and low power consumption. [10][11][12][13] Though microwave phase shifts beyond 360 have been experimentally demonstrated, 13 fundamental limitations 11,14 make it difficult to achieve true time delays over a broad bandwidth, e.g., several tens of GHz, by using slow light effects.…”

“…Hence, in the low-frequency range, the obtained time delay will be the same for the co-and counter-propagating configurations and is dominated by dynamical gain saturation effects. 14 …”