A robust sinusoidal signal processing method for interferometers (original) (raw)
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Interference fringe detection system for distance measuring interferometer
Optics & Laser Technology, 2012
A novel photodetection system for a homodyne distance measuring interferometer by means of fringe counting method is presented. The system is based on applying compact size integrated photodetector operating with fringe pattern having fixed, finite period. 13-element integrated photodiode arranged in novel signal processing scheme receives interference fringes movement. Additional lens is used to adjust the fringe period to photoelements' distances. Due to the proposed configuration of the photoelement's signal processing and the applied lens the system has reduced sensitivity to interference fringe period errors caused by the angular misalignment of interfering beams. The theoretical analysis and experimental verification of the system metrological feasibilities are presented. Comparison of performance of examples of standard and novel detection systems is shown finally.
Precise interferometric length measurement using real-time fringe fitting
Optik, 2011
We created a simple device for the measurement of nanoscale displacements consisting in a Twyman-Green interferometer with one mirror having a slight offset in the horizontal plane with respect to the direction perpendicular to the incoming beam and one mobile mirror, a CCD array camera that captures frames of fringes (interferograms) generated by the interferometer and a software that acquires the interferograms captured by the camera and fits the fringes in order to determine the initial spatial phase of the series of fringes and, consequently, to monitor the movement of the mobile arm of the interferometer. Because the interferograms were acquired and analyzed sequentially, the algorithm could be parallelized easily on a multiprocessor/multicore platform. The device can work in real-time in which case the maximum speed of the mobile arm of the interferometer for which we can obtain unambiguous results is 30 /8/s, which is, assuming a He-Ne laser as the light source, almost 2.5 m/s. In real-time conditions, the precision and accuracy of the measurement are low. In stationary conditions, however, the precision was determined to be below 1 nm.
International Journal of Engineering Research and Technology (IJERT), 2018
https://www.ijert.org/design-fabrication-and-thrust-measurement-approaches-for-microthrusters https://www.ijert.org/research/design-fabrication-and-thrust-measurement-approaches-for-microthrusters-IJERTCONV6IS14020.pdf This paper presents a new electronic Vernier fringe counter for the wavelength measurement of a diode laser in a scanning interferometer. The system is intended to be a low cost alternative to commercial systems used for gauge block calibration. The counter stage and phase coincidence detector are made with a microcontroller and high-speed CMOS logic to achieve the required resolution. The microcontroller also can synchronize with other elements to make a fully automated measurement system. This electronic design improves the resolution of the electronic counters in the previous designs
Fringe-counting technique used to lock a suspended interferometer
Applied Optics, 1994
We implement a digital fringe-counting technique to measure in real time the relative mirror displacement of a suspended Michelson interferometer with modulated optical path length for oscillations much larger than the laser wavelength (). This provides the proper error signal for a servo mechanism that reduces the relative displacement within X/2. The implemented technique does not require extra optics or polarizers and thus can be used for interferometric gravitational wave detectors as a starting procedure to get the system locked.
Fast processing of optical fringe movement in displacement sensors without using an ADC
Photonic Sensors, 2013
An interferometer based optical sensor for displacement measurement is reported. This method requires quite simple signal processing as well as least electronic components. Referring to this technique, two photodiodes spatially shifted by 90 degrees were used. The output of photodiodes was converted into rectangular signals which were extracted in LabVIEW using the data acquisition card without using an analog to digital converters (ADC). We have also processed the signals in C++ after acquiring via parallel port. A Michelson interferometer configuration was used to produce linear fringes for the detection of displacements. The displacement less than 100 nm could be measured using this technique.
Optics Communications, 2017
A compact simplified algorithm for digital detection of the amplitude and phase of the interferometric signal delivered by a two-wave interferometer with sinusoidal phase modulation is presented. The algorithm consists of simple mathematical combinations of four frames obtained by integration by a camera of the time-varying intensity in an interference pattern during the four successive quarters of the modulation period. The algorithm is invariant by circular permutation of the four image frames. Any set of four consecutive frames can be used for the calculations, which simplifies the practical implementation of the method. A numerical simulation has been carried out to evaluate the efficiency of the algorithm for fringe envelope extraction in low-coherence interferometry. A theoretical analysis of the effect of noise in phase map calculation is conducted. A comparison with the conventional sinusoidal phase-shifting algorithm is made.
Detection of Self-Mixing Interferometric Fringes of a Laser Sensor Using Matched Filter
2017
Self-Mixing (SM) is a promising technique for sensing vibration, distance, velocity etc. To retrieve accurate metric measurements from an acquired SM signal, it is necessary to correctly detect all interferometric fringes. Traditionally, SM fringes are detected by a derivative based threshold (DBT) scheme. However, such a scheme gives correct results only for SM signals with high signal-to-noise ratio (SNR) and moderate optical feedback regime. So, in this paper, a better fringe detection method, based on Matched Filter (MF), is proposed which has provided correct SM fringe detection even in case of low SNR and weak optical feedback regime. The proposed approach has resulted in fringe detection accuracy of 100% for a low SNR SM signal belonging to the weak feedback regime.
Applied Optics, 2003
Interferometry associated with an external cavity laser of long coherence length and broad wavelength tuning range shows promising features for use in measurement of absolute distance. As far as we know, the processing of the interferometric signals has until now been performed by Fourier analysis or fringe counting. Here we report on the use of an autoregressive model to determine fringe pattern frequencies. This concept was applied to an interferometric device fed by a continuously tunable external-cavity laser diode operating at a central wavelength near 1.5 microm. A standard uncertainty of 4 x 10(-5) without averaging at a distance of 4.7 m was obtained.
Fringe analysis in scanning frequency interferometry for absolute distance measurement
Fringe 2005
A novel technique to measure absolute distances is presented. It is based on a Michelson interferometer where two tuneable lasers are superposed to create a synthetic wavelength. Relative and absolute interferometry theories are merged together. Its experimental realization allows absolute distance measurements with subfringe resolution. Preliminary results are presented in this work.
Novel micro interferometer for length measurements
Journal of Non-Crystalline Solids, 2004
A novel micro interferometer for length and displacement measurements based on sampling an optical standing wave was developed. The interference of two laser beams propagating in opposite direction results in a sinusoidal light intensity profile, which can be detected by thin transparent photodiodes. Two detectors positioned on the optical axis of a standing wave allow bi-directional fringe counting. The operation principle of a setup consisting of a phase sensitive transparent detector based on two integrated nip-diodes of amorphous silicon and its alloys will be discussed. Lissajous figures close to a perfect circle are recorded to demonstrate the operation principle of the new device.