For the accurate cavity-length demodulation of fiber-optic Fabry–Perot (FP) sensors, a combined correlation method based on the fundamental cross-correlation and a higher-order one is proposed, simulated, and experimentally verified. By extending the reflection spectrum eightfold through continuous frequency-doubling three times, cross-correlation using both the original and eightfold spectra, and determination of the main peak of the fundamental cross-correlation coefficient function with the assistance of the eighth-order cross-correlation coefficient, the cavity-length demodulation resolution for fiber-optic FP sensors can be significantly improved even when the spectral bandwidth of the source is limited or the cavity length is relatively short. A cavity length resolution better than 1.8 nm is achieved for an FP sensor with a cavity length of ∼162 μm. The proposed demodulation method can effectively reduce the bandwidth requirement of the light source for the cavity-length extraction of fiber-optic FP sensors, particularly those with relatively short cavity lengths.
To realize precise absolute distance measurement, an all-fiber beat-frequency laser heterodyne distance measurement system based on a fiber-optic interferometric structure was proposed and demonstrated. An acousto-optic frequency shifter is introduced into one arm of a fiber-optic Mach–Zenhder interferormeter to generate the beat-frequency laser beams in two fiber-optic paths. By a ternary sinusoidal curve fitting method to extract the initial phases of the two beat-frequency laser signals and their phase difference, a distance measurement precision of several tens micrometers can be realized in a distance range of several meters. Experiments showed a maximum relative error of 0.0548% and a resolution of 83.333 μm in a distance range of 0 to 600 mm.
Quality of exposures in step and scan lithographic equipment highly depends on the synchronization of wafer and reticle stage. In order to increase the synchronization between the two stages, a high precision synchronization control method for scanning movement of reticle and wafer stage based on phase compensation of tracking error with the same frequency is presented. This method is quite different from the traditional ones, which just focus on designing the synchronization control systems of wafer and reticle stage. In this paper, with the analysis of relationship between MA, MSD and correlation of tracking errors, the estimation of tracking error and the phase compensation with same frequency, the performance of synchronization control for reticle and wafer stage is improved notably. Compared with the traditional ones, this method has advantage of higher precision, lower cost and greater portability.
In this work, a new type of optical fiber pressure sensor based on Frequency Modulated Continuous Wave (FMCW) laser interference technology was designed and produced. The sensor consists of a diaphragm-type Fabry-Perot (F-P) cavity structure, which is made of 316L stainless steel with excellent elastic properties. The deformation of the diaphragm occurs under the gas pressure, which causes the length of the F-P cavity to change. The FMCW laser interference technique was employed to demodulate the change of cavity length. The experimental results show that the linearity of pressure and cavity length can reach 0.99993 whin the range of 0~600 kPa, and also verify that the pressure sensor has good repeatability and stability.
To eliminate the serious detrimental effects caused by frequency drifts of acousto-optic frequency shifters (AOFSs) in conventional all-fiber-optic heterodyne Doppler measurement systems, a differential all-fiber-optic heterodyne configuration is proposed. By delicate arrangement of the fiber-optic path and using only one AOFS, zero drift, which commonly occurs in conventional systems, is eliminated. Based on the proposed configuration, a differential all-fiber-optic heterodyne Doppler measurement system has been built. Using a piezoelectric ceramic oscillator as the moving object, it has been verified that the proposed system is able to eliminate zero drift, and the displacement and velocity measurement accuracies reach 0.775 μm and 0.009 mm / s, respectively. It has been shown that the differential all-fiber-optic heterodyne Doppler measurement system can achieve good performance in both displacement and velocity measurements, even in a harsh environment with drastic temperature variation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.