During the past two decades there has been considerable research focused on the topic of "slow light", i.e. light whose group velocity is substantially smaller than the speed of light in vacuum. Such slow group velocity can be attained by exploiting extremely flat dispersion relation. The interest in slow light arises in part from the numerous applications that it enables, such as optical delay lines, optical filters, wavelength converters and optical rotation sensors, but also because of the fundamental physics it encapsulates. A convenient approach for the realization of such dispersion effects is by using specially designed coupled resonator optical waveguide (CROW) structures. Examples of slow light in such CROWs have been demonstrated with diverse optical platforms and unit-cells including Fabry-Perot etalons, ring resonators, photonic crystals and more.

One of the most fundamental mechanisms limiting the achievable delay in such structures is the inherent loss of the individual resonators - larger losses lead to high dissipation rates of the optical power which limit the possible delay. While it is possible to design high Q-factor structures, such cavities are difficult and expensive to fabricate, sensitive to environmental changes and difficult to couple, all of which make them difficult to use for real-life applications.

As an alternative it was suggested to use to active resonators, i.e. resonators with an active gain component in them. The logic behind this suggestion is that introducing gain into the system can balance the loss. In addition, the ability to independently control the gain coefficient of each resonator in the system provides a mean to control the effective refractive index of each component and leads to greater flexibility of the device. This in turn enables new and exciting applications which are unachievable using passive devices.

In our work we have focused on the use of an array of coupled vertical cavity surface emitting lasers (VCSELs) as candidates for use as such active CROWs. It has been shown that a chain of N coupled semiconductor lasers are described by a set of coupled non-linear differential equations.

Using these equations we have performed numerical simulations to better understand the behavior of laser arrays. Several applications were suggested for these arrays, such as tunable delay lines, all-optical RAM, all-optical routing and rate conversion. Additional simulations on two-dimensional arrays have uncovered several other application options such as dynamically tunable waveguides and couplers.

In this presentation we will discuss the theoretical background of using active CROWs for slow-light purposes and several of the suggested applications we have envisioned for them. Additionally, initial experiments were performed on VCSEL arrays and the results of these experiments will be presented and discussed.