A displacement sensor comprising at least one pair of co-planar photonic
crystal waveguide (PCWG) sections aligned along or parallel to a common
axis and separated by a gap, one PCWG section of a pair operative to
perform a displacement relative to the other section of the pair. In some
embodiments, the sensor is linear, comprising two PCWG sections seperated
by a gap that forms a cross PCWG, the displacement sensing performed
preferrably differentially between two edges of the cross PCWG. In other
embodiments, the sensor includes Mach Zehnder Interferometer (MZI)
configurations with gaps between fixed and moving PCWG sections.
Displacement induced changes in the gap widths are reflected in changes
in an output parameter of the MZI.