These Limit Switches can detect micron displacements. They are available in solid-state models and models with contacts.
There are 2 products of High-precision Switches.
High-precision Switch
D5A
High-precision Switch for Detecting Micron-unit Displacement
High-precision Optical Switch
D5F
Optical System Achieves 1-μm Operating Position Repeatability in this 4-way Switch