  The effect of gravitational waves (GWs) has been observed indirectly, by
monitoring the change in the orbital frequency of neutron stars in a binary
system as they lose energy via gravitational radiation. However, GWs have not
yet been observed directly. The initial LIGO apparatus has not yet observed
GWs. The Advanced LIGO (AdLIGO) will use a combination of improved techniques
in order to increase the sensitivity. Along with power recycling and a higher
power laser source, the AdLIGO will employ signal recycling (SR). While SR
would increase sensitivity, it would also reduce the bandwidth significantly.
Previously, we and others have investigated, theoretically and experimentally,
the feasibility of using a White Light Cavity (WLC) to circumvent this
constraint. However, in the previous work, it was not clear how one would
incorporate the white light cavity effect. Here, we first develop a general
model for Michelson-Interferometer based GW detectors that can be easily
adapted to include the effects of incorporating a WLC into the design. We then
describe a concrete design of a WLC constructed as a compound mirror, to
replace the signal recycling mirror. This design is simple, robust, completely
non-invasive, and can be added to the AdLIGO system without changing any other
optical elements. We show a choice of parameters for which the signal
sensitivity as well as the bandwidth are enhanced significantly over what is
planned for the AdLIGO, covering the entire spectrum of interest for
gravitational waves.
