Calibration method for frequency scanning interferometry distance measurement system using dispersive interferometry
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The long delay optical fiber is the length reference in the frequency scanning interferometry (FSI) distance measurement system, which is directly related to the stability of the system. This paper proposes a calibration method for the optical path difference (OPD) of long optical fiber. In this scheme, the optical frequency comb (OFC) is introduced into the measurement system, and the dispersive interferometry is used to complete the measurement of the OPD of the fiber. The light generated by the tunable laser and the light generated by OFC are led to the long optical fiber using a fiber coupler at the same time, which ensures the common path design of the calibration system and the measurement reference. The dispersive interferometry signal is detected by an optical spectrum analyzer. Experiments were designed to verify the repeatability of this calibration method. Experimental results show that using dispersion interferometry to calibrate the OPD of the fiber can achieve a relative accuracy lower than 10-7.Keywords:
Optical path length
Repeatability
Optical path
White light interferometry
SIGNAL (programming language)
Optical path length
Optical path
Tracking (education)
Phase difference
SIGNAL (programming language)
Path length
Accuracy and precision
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White light interferometry provides a precise method of determining the path difference in a remote sensing interferometer when it is compared with a locally controlled reference interferometer. Interference fringes will be detected when the path length of each interferometer is greater than the coherence length of the optical source and the relative path difference between them is less than the source's coherence length [1,2]. White light interferometric sensing systems have previously been employed to monitor a variety of external measurands such as; displacement [3], pressure [4], temperature [5] and refractive index [6]. In all these cases the change in the measurand induces a change in the path length of the sensing interferometer. This variation in path length is monitored at the reference interferometer and can be directly related to the measurand change.
White light interferometry
Optical path length
Interferometric visibility
Intensity interferometer
Path length
Optical path
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The purpose of recent developments of profilometry by using white light interferometry is to provide new tools for the analysis of rough samples which when studied by monochromatic phase-shifting interferometry, may cause phase calculation ambiguities. The usual way to perform depth measurements by white light interferometry is to analyze the coherence-limited interference fringes while the optical path difference is scanned. The method proposed here does not use optical path difference scanning. A spectroscopic device is used instead to separate the interference intensities associated to each spectral component of the light source. Phase variations due to wavelength change are proportional to the optical path difference and allows depth measurement to be performed without axial scanning. The profile of one line of the inspected sample is obtained from only one 2D interferogram. In this 2D interferogram one direction corresponds to the inspected direction of the surface while the other one is the chromatic axis which allows phase to change with wavelength. Experimental results show the ability of the proposed method to obtain the profile of 1D surface with nanometric resolution.
White light interferometry
Monochromatic color
Optical path length
Optical path
Phase difference
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A new method to deduce the optical path difference of a kind of ultra-rapid-scanning imaging spectrometer is provided.The process of the derivation is elaborated,and the ultimate formula is given.The formula of the optical path difference is recalculated by setting several related parameters.The curves of optical path difference are presented.They are given by changing one of those parameters with other parameters at fixed values.The contributions of the parameters is compared and discussed.The design of this kind of ultra-rapid-scanning imaging interferometer and the recovery of the interferogram to spectrogram should base on the optical path difference formula.
Optical path length
Optical path
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This study presents a novel absorption cell with a circular geometry that can be integrated into microfluidic devices for optical spectroscopy applications. The absorption cell is made of PDMS/SU8 and offers an optical path length that is 8.5 times its diameter, resulting in a significant increase in the sensitivity of the measurements. Overall, this design provides a reliable and efficient solution for optical spectroscopy in microfluidic systems, enabling the precise detection and analysis of small quantities of analytes.
Optical path length
Fluidics
Optical path
Path length
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The development of micro-nanomanufacturing technology leads to higher requirement for measurement technology, which gives birth to the ultra-precision measurement technology. As a kind of low coherence interferometry technology, spectral interferometry has been proposed. In this paper, the theory and system of white light spectral interferometry were described in detail, and the measurement principle of micro-structure was analyzed. The spectral interference signal was recorded and the phase information was retrieved from it by using five-step phase shifting algorithm, which includes the phase change on reflection from the stucture. So the optical path difference (OPD) can be obtained, which represents the height information. Three methods including slope method, single wavelength method and least square method were discussed based on the theory deduction and the experimental analysis. A step height standard was measured and the results show that this method has a good accuracy.
White light interferometry
Optical path length
Accuracy and precision
Nanomanufacturing
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Optical path length
Optical path
Path length
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An asymmetric polarization-maintaining single-mode fiber with one side-hole being incorporated into the fiber cladding has been investigated analytically in this work for potential pressure measurements. The material birefringence of the fiber is calculated using a thermo-elastic displacement potential method through the superposition of sectional displacement potentials. The results obtained are generic and are thus applicable to any one-hole fiber structures, should the hole diameter or position vary in the fiber cladding, or the fiber hole be empty or filled in with any material. This enables the analysis to be applied more widely in a range of optical fiber sensor applications.
Cladding (metalworking)
Mode volume
All-silica fiber
Plastic-clad silica fiber
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A flexible and detachable gas-absorption cell with variable optical path length was designed to obtain the optical path optimal length for gas detection based on ultraviolet differential optical absorption spectroscopy. A model of the gas-absorption cell structure was established based on Lambert-Beer law. This model demonstrates the effect of different optical path lengths on ammonia detection, and the optical path optimal length of the proposed system is 1.6 m. A gas detection system was developed with the proposed gas-absorption cell, and the feasibility and stability of the system were evaluated at different ammonia concentrations. Owing to the influence of light loss induced by spherical concave mirror reflection and ammonia absorption, the detection results for ammonia at a concentration of 17 ppm are more accurate when the optical path length is 1.6 m versus 0.8 and 2.4 m. The error is less than 0.6% that is consistent with the simulation results. When the optical path length is 1.6 m, the linearity between the detection and the standard values reaches 0.9993. The standard deviation of the detection results is less than 0.3 ppm, indicating good stability of the system. The minimum detection limit of 0.43 ppm per meter is achieved. Water has a slight influence on the results of ammonia concentration detection. When the relative humidity is 7.5%, the response time of the system is 120 s that becomes longer with the increase of relative humidity. This method can be used to detect other gases with high precision.
Optical path length
Optical path
Path length
Linearity
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A method for equalizing the path lengths of two arms of an optical fiber coupler is presented as a critical step towards construction of a high-resolution 3-D interferometric imaging system. Based on white-light interferometry (WLI), the technique combines absolute measurement capability with the ability to accurately measure near-zero path length differences. A controlled temperature increase in one arm of the coupler generates a shift in the WLI measurement, allowing the fibers to be polished to near-equal lengths. The technique is demonstrated to equalize the fiber lengths to better than 0.6 mum.
White light interferometry
Path length
Optical path length
Length measurement
Optical path
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