Gravitational waves detectors; are they all similar? Are the gravitational waves detectors all working on the same 
principle/effect?
 A: The fundamental effect of gravitational waves exploited by all detectors is the same: one tries to detect minute oscillatory changes in distances between different parts of the device. These changes are of the order of 1 part in 1020 or smaller, so detecting them is a real challenge.
Different types of detectors do differ significantly when it comes to the techniques they employ to measure these minute changes. Interferometers look out for relative changes in phase of two light beams travelling in perpendicular directions. Weber bars exploit resonance to magnify vibrations caused by gravitational waves of a given frequency. Pulsar timing arrays compare timing of pulsar signals coming from different directions looking out for small differences caused by tiny expansion and contraction of space through which the signals propagate. High frequency detectors examine microwaves circulating in a loop looking out for polarization changes caused by spacetime contraction and expansion in different directions. See this wikipedia article for details.
Depending on how good given detector's isolation from unwanted influences is, it may require substantial effort to extract gravitational wave signature from data collected by these detectors. For example, LIGO phase loops lose lock every time a freight train passes by. The Einstein@Home project allows volunteers to donate the computing power of their home computers to this effort.
