This paper reports on the measurement system of the phase difference between s- and p-polarization components of the light passing through a guided-mode resonance (GMR) device using a digital micromirror device (DMD) gratings as a digital phase-shifting device. The phase of the non-zeroth order diffraction beams of the grating pattern displayed on the DMD can exhibit a phase change when the grating pattern is shifted. Two nearest different diffraction orders of p-polarized and s-polarized beams can be used as the reference and measurement beams, respectively, and are combined to implement the phase-shifting interferometry (PSI). The phase difference between the s- and the p-polarization components of the incident light passing through the GMR device can be obtained by applying the four-step phase-shift algorithm to the DMD-based PSI system. Experimental results show that this measurement system has a phase detection limit of 1° and was able to obtain the abrupt phase difference curve of the GMR device versus the incident angle.
In this study, we demonstrate a method to fabricate a guided-mode resonance (GMR) device on a flexible and transparent low-density polyethylene (LDPE) film and present the measurement results of this device as a pressure sensor. A simple thermal-nanoimprinting process was used to fabricate a grating structure on the LDPE film substrate. This very flexible film was attached to a glass plate using an adhesive and sacrificial layer for coating high-refractive-index titanic oxide on the grating surface to form the GMR device. The LDPE-GMR device was equipped with a gas chamber to act as a pressure sensor. When the pressure inside the chamber was increased, the grating period of the GMR sensor also increased, resulting in a shift in the resonance angle of the GMR device. Owing to the higher flexibility of the LDPE film, a better pressure detection sensitivity and resolution can be obtained. Using the transmitted-intensity detection approach, we show that the transmitted laser power changes proportionally with the pressure increase. The experimental results showed that the LDPE-GMR pressure sensor could achieve a sensitivity of 8.27 µW/mbar and a limit of detection of 0.012 mbar at a power meter noise of 0.1 µW.
A high-sensitivity phase-detection system is proposed for a reflection-type guided-mode resonance (GMR) sensor, which achieves the resonance condition by rotating the azimuth angle and utilizes an electro-optic (EO) heterodyne interferometer. By rotating the GMR sensor azimuthally, the direction of the reflected light can be maintained in reflection-type detection, and the optical system can be compactly constructed because the light-tracking rotation stage is not required. The phase-detection sensitivity can be enhanced in this common-path EO heterodyne interferometer by rotating the analyzer in front of the photodetector; therefore, this system can achieve both a high sensitivity and low limit of detection. Numerical and experimental results of the reflectivity and phase response curves versus the azimuth angle were compared. The proposed system was used to perform gas sensing, and its detection sensitivity and limit were 3.73 × 104 deg/RIU and 2.68 × 10−7 RIU, respectively.
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