  We present a comparative experimental study of three silicon photonic echelle
grating demultiplexers that are integrated with a Mach-Zehnder interferometer
(MZI) launch structure. By appropriate choice of the MZI configuration, the
temperature induced shift of the demultiplexer channel wavelengths can be
suppressed (athermal) or enhanced (super-thermal), or be controlled by an
on-chip micro-heater. The latter two configurations allow the channel
wavelengths to be actively tuned using lower power than possible by temperature
tuning a conventional echelle demultiplexer. In the athermal configuration, the
measured channel spectral shift is reduced to less than 10 pm/C, compared to
the 83 pm/C shift for an unmodified echelle device. In super-thermal operation
an enhanced channel temperature tuning rate of 170 pm/C is achieved. Finally,
by modulating the MZI phase with an on-chip heater, the demultiplexer channels
can be actively tuned to correct for ambient temperature fluctuations up to 20
C, using a drive current of less than 20 mA.
