  The Einstein Telescope (ET) is a proposed future gravitational wave detector.
Its design is original, using a triangular orientation of three detectors and a
xylophone configuration, splitting each detector into one high-frequency and
one low-frequency system. In other aspects the current design retains the
dual-recycled Michelson interferometer typical of current detectors, such as
Advanced LIGO. In this paper, we investigate the feasibility of replacing the
low-frequency part of the ET detectors with a Sagnac interferometer. We show
that a Sagnac interferometer, using realistic optical parameters based on the
ET design, could provide a similar level of radiation pressure noise
suppression without the need for a signal recycling mirror and the extensive
filter cavities. We consider the practical issues of a realistic,
power-recycled Sagnac, using linear arm cavities and polarizing optics. In
particular, we investigate the effects of nonperfect polarizing optics and
propose a new method for the generation of a local oscillator field similar to
the DC readout scheme of current detectors.
