Polar cap mesosphere wind observations: comparisons of simultaneous measurements with a Fabry-Perot interferometer and a field-widened Michelson interferometer

Polar cap mesospheric winds observed with a Fabry-Perot interferometer with a circle-to-line interferometer optical (FPI/CLIO) system have been compared with measurements from a field-widened Michelson interferometer optimized for E-region winds (ERWIN). Both instruments observed the Meinel OH emission emanating from the mesopause region (~86 km) at Resolute Bay, Canada (74.9 degrees N, 94.9 degrees W). This is the first time, to our knowledge, that winds measured simultaneously from a ground-based Fabry-Perot interferometer and a ground-based Michelson interferometer have been compared at the same location. The FPI/CLIO and ERWIN instruments both have a capability for high temporal resolution (less than 10 min for a full scan in the four cardinal directions and the zenith). Statistical comparisons of hourly mean winds for both instruments by scatterplots show excellent agreement, indicating that the two optical techniques provide equivalent observations of mesopause winds. Small deviations in the measured wind can be ascribed to the different zenith angles used by the two instruments. The combined measurements illustrate the dominance of the 12-h wave in the mesopause winds at Resolute Bay, with additional evidence for strong gravity wave activity with much shorter periods (tens of minutes). Future operations of the two instruments will focus on observation of complementary emissions, providing a unique passive optical capability for the determination of neutral winds in the geomagnetic polar cap at various altitudes near the mesopause.     

Assessment of a multibeam Fizeau wedge interferometer for Doppler wind lidar

The Fabry-Perot interferometer is the standard instrument for the direct detection Doppler lidar measurement of atmospheric wind speeds. The multibeam Fizeau wedge has some practical advantages over the Fabry-Perot, such as the linear fringe pattern, and is evaluated for this application. The optimal Fizeau must have a resolving power of 10(6) or more. As the multibeam Fizeau wedge is pushed to such high resolving power, the interference fringes of the device become complicated by asymmetry and secondary maxima. A simple condition for the interferometer plate reflectance, optical gap, and wedge angle reveals whether a set of parameters will yield simple, Airy-like fringes or complex Fizeau fringes. Tilting of the Fizeau wedge improves the fringe shape and permits an extension of the regime of Airy-like fringes to higher resolving power. Sufficient resolving power for the wind lidar application is shown to be possible with a large-gap, low-finesse multibeam Fizeau wedge. Liabilities of the multibeam Fizeau wedge in the wind lidar application include a smaller acceptance solid angle and calibration sensitivity to localized deviations of the plates from the ideal.     

激光干涉仪在纳米测量中的典型应用

激光干涉仪具有测量分辨力高、测量结果可溯源等优点,在纳米测量中的应用日益广泛。介绍纳米测量机和低膨胀材料线膨胀系数测量装置中应用的迈克尔逊型激光干涉仪以及在高准确度位移测量装置中应用的法布里-珀罗型激光干涉仪,并结合这些实例对激光干涉仪光学系统设计、测量环境控制、迈克尔逊干涉仪非线性误差补偿以及法布里-珀罗干涉仪量程扩展等方面的关键问题进行分析和总结。所述原则和方法对实现纳米级测量准确度具有重要意义,可为高准确度激光干涉仪的研制及其在纳米测量中的更广泛应用提供技术参考。     

Optical frequency-domain imaging microprofilometry with a frequency-tunable liquid-crystal Fabry-Perot etalon device

An optical frequency-domain interference microscope with a liquid-crystal Fabry-Perot interferometer as an optical frequency-scan device was developed for microscopic three-dimensional shape measurements. The proposed system can perform absolute measurement of the discontinuous surface profile of a microscopic object without use of mechanically moving components such as a piezoelectric transducer or a grating spectrometer. Experimental results are presented that demonstrate the validity of the principle.     

Surface profilometry with laser-diode optical feedback interferometer outside optical benches

A simple and robust interferometer with a laser diode subject to optical feedback from the interferometer is presented for surface testing of a spherical mirror. The fringe phase can be locked by the optical feedback within less than 0.2pi (peak-to-valley value) even when the interferometer is placed on a wooden table. The fringe locking is caused by the change of lasing wavelength that suppresses the net phase change to be much less than 2pi. The locked fringe pattern with spatial carriers can be analyzed by a fringe analyzer at a video rate, and the measurement results of the spherical mirror showed the same result as on an optical bench.     

Two-channel direct-detection Doppler lidar employing a charge-coupled device as a detector

A direct-detection Doppler lidar system is demonstrated that uses a CCD as a detector for the first time to our knowledge. The ability to use this linear device with the circular output from a Fabry-Perot etalon comes from use of a circle-to-line converter [Appl. Opt. 29, 1482 (1990)]. In addition to the gains in quantum efficiency obtained through use of this detector, the lidar system described in this paper also has the capability to measure winds from aerosol and molecular backscatter simultaneously in two separate channels by directing the light reflected from one channel into the other. Early measurements with this system are presented; it is shown that, although accurate aerosol wind measurements are easily obtained, molecular measurements require a carefully calibrated inverse model and special hardware to derive accurate wind measurements with this channel.     

Microelectromechanical system pressure sensor integrated onto optical fiber by anodic bonding

Optical microelectromechanical system pressure sensors based on the principle of Fabry-Perot interferometry have been developed and fabricated using the technique of silicon-to-silicon anodic bonding. The pressure sensor is then integrated onto an optical fiber by a novel technique of anodic bonding without use of any adhesives. In this anodic bonding technique we use ultrathin silicon of thickness 10 microm to bond the optical fiber to the sensor head. The ultrathin silicon plays the role of a stress-reducing layer, which helps the bonding of an optical fiber to silicon having conventional wafer thickness. The pressure-sensing membrane is formed by 8 microm thick ultrathin silicon acting as a membrane, thus eliminating the need for bulk silicon etching. The pressure sensor integrated onto an optical fiber is tested for static response, and experimental results indicate degradation in the fringe visibility of the Fabry-Perot interferometer. This effect was mainly due to divergent light rays from the fiber degrading the fringe visibility. This effect is demonstrated in brief by an analytical model.     

Design methodology for a Fabry-Perot interferometer used as a concentration sensor

We present the design methodology for a sensor that can nonintrusively monitor target gas concentration levels in a power plant exhaust flow. The measurement is based on radiative emission by rovibrational transitions that are well isolated from emission features of other constituents and requires both moderate spectral resolution (typically 1 nm or below) and relatively high optical throughput. A Fabry-Perot interferometer provides this capability, and its conceptual design is discussed at length. High-temperature radiative emission of nitric oxide in a background of water was used as a sample system for the design of a prototype Fabry-Perot interferometer. Predictions for the instrument are a minimum resolvable NO column density of 100 parts per million times meter based on a simple background subtraction scheme with a gas temperature of 800 K. Improved order sorting can dramatically lower this minimum. The prototype instrument was calibrated and tested with a laboratory simulator; results are presented and compared with predictions.     

Evaluation of the luminous flux intensity in a double-beam interferometer

Conclusion The luminance of the interference pattern in the plane of the photodetector slot can be determined by using the value of the luminous energy received through the input diaphragm for computing the attenuation of the luminous flux transmitted through the interferometer system. The half width of the utilized spectral line affects both a reduction in the fringe contrast with a rise in the interference-beam path-length difference and the total luminous intensity of the interference pattern. The photodetector slot which picks out a segment of the interference fringe produces definite conditions for modulating the luminous flux incident to the photomultiplier.Translated from Izmeritel'naya Tekhnika, No. 12, pp. 5–7, December, 1966.     

System model identification of a Fabry-Perot fiber optic sensingsystem

A Fabry-Perot fiber optic temperature sensing system is presented in this paper. It uses a Fabry-Perot interferometer (FPI) to transform the environmental temperature into modulated reflected light. This light is directed to a patented light cross-correlator that locates the position of the maximum interference fringe intensity, which is detected by a linear CCD array. Therefore, the actual observed data is the position of the CCD pixel detecting the maximum interference fringe intensity rather than the light intensity itself. Consequently, this sensing mechanism is tolerant to the loss of light power that may result from external effects. Based on an analysis of the entire sensing system, a theoretical dynamic model was developed, which shows that the system dynamic response depends on the heat transfer process in the sensor head and the signal processing in the signal conditioner. An experimental method was developed to validate the theoretical model. Two empirical dynamic models are also obtained from the experimental data. Comparing the theoretical model with the empirical models, the poles result from the heat transfer process in the sensor head     

Measuring the refractive indices of liquids with a capillary tube interferometer

A theoretical analysis of the fringe pattern produced by a capillary tube interferometer is presented, which is expected to be two-beam interference, and a computer program to simulate the interference fringe pattern is established. By comparing the simulated fringe pattern and the experimental fringe pattern, the refractive index of the liquid can be given when the two fringes coincide best. The results of this method are close to those of the Abbe refractometer.     

Interferometric sensor for detection of surface-bound bioreactions

An integrated optical interferometer for direct detection of affinity reactions is presented. A modern version of a Young's interferometer is built with a waveguide structure as beam splitter and as sensing element. Resistive waveguides were produced by plasma-enhanced chemical vapor deposition of silicon oxinitride. At the output of this device a fringe pattern is detected by a CCD line camera. The adsorption of molecules on top of the waveguides is observed with a detection limit of 750 fg/mm(2). The resolvable variation of effective refractive index is 9 x 10(-8).     

Two-spherical-wave ultraviolet interferometer for making an antireflective subwavelength periodic pattern on a curved surface

An ultraviolet two-spherical-wave interferometer was developed in order to make a subwavelength structured surface on a curved surface. The change in fringe period on the curved surface was significantly suppressed compared with the two-plane-wave interferometer. The optical setup method for suppressing the change in fringe period is described. The effect of the two-spherical-wave interferometer was investigated by numerical simulations. In an experimental demonstration for a concave spherical surface with 11.1 mm radius of curvature and 10 mm diameter, the change in period of the photoresist pattern was reduced to 12 nm for the target period of 250 nm.     

Image encryption based on a grating generated by a reflection intensity map

A virtual optical technique for image encryption and decryption is presented in this paper. The technique is carried out using optical operation and computational algorithms. In this technique, a grey-level image is captured by a charge-coupled device camera and encrypted using a linear grating superposed on the reflected intensity map of the object. The grating is generated as a fringe pattern by a computer algorithm. The reflected intensity map is determined using the grey level of the image. This reflected intensity map is included in the fringe pattern as an optical phase. It generates a grating, which is represented as a fringe pattern deformed according to the reflected intensity map. The decryption method is performed by a phase recovery method. The technique used here is a spatial synchronous method. This encryption and decryption technique has been used to encrypt real face images. To describe the accuracy of results obtained by this technique, the rms of error is calculated using decrypted and original data images. This encrypting technique is a virtual optical method because all the optical operations are performed by computer processes, and optical components are not required, which are advantages over optical methods, where some physical optical components are used. Simulated images are used in order to assess the technique. Finally, results on real images are presented.     

Simultaneous three-dimensional step-height measurement and high-resolution tomographic imaging with a spectral interferometric microscope

A noncontact, nonmechanical scanning, wide-field spectral interference microscope is developed for simultaneous measurement of three-dimensional step-height of discontinuous objects and tomographic imaging. A superluminescent diode (SLD) is used as a broadband light source and a liquid-crystal Fabry-Perot interferometer (LC-FPI) as a frequency-scanning device. By means of changing the injection current to the SLD, the spectral profile of the SLD is equalized, and a constant light input to the interferometer is achieved over the entire frequency-scan range. The Fourier-transform technique is used to determine both the amplitude and the phase of spectral fringe signals. Three-dimensional height distribution of a discontinuous object is obtained from the phase information, whereas optically sectioned images of the object are obtained either from the amplitude information alone or from the combination of both the amplitude and phase information. Experimental results with submicrometer resolution are presented for both step-height measurement and tomographic sectioning.     

Extension of distance measurement range in a sinusoidal wavelength-scanning interferometer using a liquid-crystal wavelength filter with double feedback control

The optical path difference (OPD) and amplitude of a sinusoidal wavelength scanning (SWS) are controlled with a double feedback control system in an interferometer, so that a ruler marking every wavelength and a ruler with scales smaller than a wavelength are generated. These two rulers enable us to measure an OPD longer than a wavelength. A liquid-crystal Fabry-Perot interferometer (LC-FPI) is adopted as a wavelength-scanning device, and double sinusoidal phase modulation is incorporated in the SWS interferometer. Because of a high resolution of the LC-FPI, the upper limit of the measurement range can be extended to 280 microm by the use of the phase lock where the amplitude of the SWS is doubled in the feedback control. The ruler marking every wavelength is generated between 80 microm and 280 microm, and distances are measured with a high accuracy of the order of a nanometer in real time.     

Analysis of mutually incoherent symmetrical illumination for electronic speckle pattern shearing interferometry

A speckle shearing interferometer has been designed using symmetrical mutually incoherent illumination, in an effort to provide measurements of in-plane strain. An analysis of the sensitivity to displacement and strain of this interferometer is presented, together with analysis of the optical phase extraction of the resultant fringe pattern. This interferometer is an improvement on previous designs as it provides information on the in-plane strain separated from components of the displacement. Experimental results provide qualitative data in the form of fringe patterns in support of the theoretical analysis.     

Resolving quadrature fringes in real time

In many interferometers, two fringe signals can be generated in quadrature. The relative phase of the two fringe signals depends on whether the optical path length is increasing or decreasing. A system is developed in which two quadrature fringe signals are digitized and analyzed in real time with a digital signal processor to yield a linear, high-resolution, wide-dynamic-range displacement transducer. The resolution in a simple Michelson interferometer with inexpensive components is 5 x 10(-13) m Hz(-1/2) at 2 Hz.     

Phase-demodulation error of a fiber-optic Fabry-Perot sensor with complex reflection coefficients

The influence of reflector losses attracts little discussion in standard treatments of the Fabry-Perot interferometer yet may be an important factor contributing to errors in phase-stepped demodulation of fiber optic Fabry-Perot (FFP) sensors. We describe a general transfer function for FFP sensors with complex reflection coefficients and estimate systematic phase errors that arise when the asymmetry of the reflected fringe system is neglected, as is common in the literature. The measured asymmetric response of higher-finesse metal-dielectric FFP constructions corroborates a model that predicts systematic phase errors of 0.06 rad in three-step demodulation of a low-finesse FFP sensor (R = 0.05) with internal reflector losses of 25%.     

Contrast enhancement of electronic speckle pattern interferometry addition fringes

The electronic speckle pattern interferometer in the double-pulse addition mode can be used to measure physical parameters in unstable environmental conditions. Owing to additive optical noise, however, the fringe patterns obtained have poor contrast. Some methods that use subtraction of addition double-pulsed fringe patterns improve fringe visibility but impose a limitation in measurement time ranges. To increase this range, to be limited by only the pulse separation, the contrast enhancement of double-pulsed addition-fringe patterns with a spatial filter based on local-standard-deviation measurements is investigated. Computer simulations and experimental results are presented.