Influence of several grating sensor parameters on the modulation depth of moiré signals under incoherent illumination

Theoretical expressions for the modulation depth of moiré signals under incoherent illumination are derived. Consequently, the modulation depth of a moiré signal is related to the following factors: the geometric shape and the size of the light source; the diffraction effect of the grating, which relates to the number of lines in the grating; the line and the space ratio; the grating pair gap; the geometric shape and the size of the receiving window; etc. In addition, the influence of the grating pair on the period and the inclination of moiré fringes under noncollimated illumination are discussed, and the changes in the moiré signal modulation depth under noncollimated illumination with that under collimated illumination are made. Finally, some experimental results are given to verify the theoretical expressions. This research is useful for the actual design of grating sensors.