  We introduce a concept that uses detuned arm cavities to increase the shot
noise limited sensitivity of LIGO without increasing the light power inside the
arm cavities. Numerical simulations show an increased sensitivity between 125
and 400 Hz, with a maximal improvement of about 80% around 225 Hz, while the
sensitivity above 400Hz is decreased. Furthermore our concept is found to give
a sensitivity similar to that of a conventional RSE configuration with a
Signal-Recycling mirror of moderate reflectivity. In the near future detuned
arm cavities might be a beneficial alternative to RSE, due the potentially less
hardware intensive implementation of the proposed concept.
