Search

A displacement detection method based on two-wavelength grating interferometry was presented.A measurement experiment was carried out by using an integrated grating sensor chip fabricated by silicon-glass bonding bulk process.The measurement setup consisted of a sensor chip,two lasers with wavelengths of 640 nm and 660 nm,two photodetectors and a data acquisition circuit.The sensor chip included moving parts with a reflective surface and a metal grating on the transparent substrate.In experiment,the laser beam illuminated the grating and the grating reflected the laser beam to form a diffraction pattern.As the intensity of the diffracted beams changed according to the displacement between movable structure and substrate,the displacement could be determined with an extended range than single wavelength and the absolute position could be obtained by measuring intensity signals of the two wavelengths respectively.Experimental results show that the initial gap between the moving part and the substrate is about 7.522 μm measured by proposed method and it can implement the displacement measurement in a range of 618 nm with a resolution of 0.2 nm.

A displacement measurement method for microcantilevers based on integrated dual gratings and a CCD image measurement system were presented.The displacement detection range was extended by using two gratings with a phase shift about π/2.The sensor chips were fabricated by surface sacrificial process.Grooves with the depth about 1/8 of the incident laser wavelength were etched on the glass substrate and two adjacent gratings patterned inside and outside of the groove and the reflective undersurface of a cantilever formed two phase sensitive integrated gratings,respectively.The integrated grating units formed an image on the CCD sensing surface through the 1st order diffraction light,and the gray value change of the light spot was related to the displacement change of the corresponding cantilever.Experimental results show that although the phase difference between the gratings deviates from π/2 caused by the depth errors of the etched grooves,the integrated dual gratings extend the range of displacement detection to multi periods.The insensitive areas at peaks and valleys for sinusoidal variation signal of interferometric displacement detection method are avoided by using alternately intensity signals from the two gratings.In the experiment,the measured displacement change of the cantilever is 650 nm.