Optical Wedge Research Articles

Dispersion Compensation for PLCI Based on Fringe Peak Estimation and Polynomial Fitting

Polarized low-coherence interferometry (PLCI) is a promising technology to absolute displacement measurement and sensor demodulation. To avoid jump errors induced by dispersion and achieve a high response, a dispersion compensation method based on fringe peak position estimation and polynomial fitting is proposed to get rid of the dependence on the priori model and birefringence parameters, and make this method very robust. The nearly linear resolution between the envelope and ${m}$ -order PLCI fringe (PLCIF) centers are found and verified with both Gauss and non-Gauss profile broadband light sources. Then, the zero-order PLCIF is estimated and located to demodulate the measurement displacement. The demodulated results are significantly influenced by dispersion of the birefringence optical wedge and then polynomial fittings of sensing curve are conducted to raise the sensing accuracy. In comparison to the priori model and parameters based method, the proposed method can effectively avoid jump errors and has a higher accuracy than the directly envelope center method. Experimental results indicate that the measurement accuracy is higher than 19.5 nm which is enhanced by 6.88 times, the resolution is better than 2 nm, and its processing data rate can reach 35 kHz on an embedded system.

DIGITAL IMAGE QUALITY UNDER DIFFERENT LIGHT CONDITIONS RESEARCH

The article is devoted to the study of digital image quality at different levels of daylight. The quality of the digital image was evaluated by the resolution and contrast of the image in three spectral zones: blue, green and red. The test object for photographing was a white sheet of 594X841mm format with line targets, color scales and an image of an optical step wedge located on it. Line targets were located over the entire area of the sheet, which made it possible to study the image quality over all its area. Digital photography was performed by a NIKON SLR camera and was accompanied by measurements of illumination in the plane of the test object with the measurement of the height of the sun by theodolite. The resolution of the digital camera was measured during the day interval from 3:00 to 22:00. For each hour of shooting resolution was determined by 9 line targets, 8 of which were located on the perimeter of the sheet and one in the center. Spectral profiles on color scales were also obtained for each ur, and the value of contrast on the image of the optical wedge was determined. As a result of the study, an effective daily interval was determined to perform digital shooting from unmanned aircraft for the Moscow region (55°45′07″ W).

基于光楔的并行受激发射损耗荧光擦除图案产生方法

基于光楔的并行受激发射损耗荧光擦除图案产生方法

Small-sized all-round vision system with image blurring compensator for the infrared range of the spectrum based on multi-segment optical wedges

Small-sized all-round vision system with image blurring compensator for the infrared range of the spectrum based on multi-segment optical wedges

一种激光搜跟器的光学设计

In order to improve the search range and imaging resolution of the ground target by the laser tracker, a method of searching and tracking the target with a common aperture laser tracker under an airborne platform was presented and the optical system was designed. The laser tracker was fixed on the aircraft by strap down, its stability was improved. The R-C reflection telescopic system with common aperture was adopted to emit the laser and receive laser echoes, which reduced the overall size and improved the imaging resolution. The scanning search target was realized by double optical wedge component, and the search frequency was increased and the search field of view was enlarged. The relationship between the rotation angle of double optical wedge and the angle of outgoing optical deflection was given. The design results show that when the aperture of the system is φ300 mm and the focal length is 2 100 mm, the overall size is 685 mm, the search and scan field of view is ±5°, the imaging field is ±0.08°, the maximum size of the imaging spot speckle is 2.417 μm, and the MTF value of the system is greater than 0.4 at 50 lines per millimeter, which meets the imaging requirements. When the target distance is 3 km, the searchable range reaches 526 m, and the four-meter-sized target can be recognized with a imaging resolution of two seconds.

Curing of Epoxy Resin DER-331 by Hexakis(4-acetamidophenoxy)cyclotriphosphazene and Properties of the Prepared Composition.

The method of optical wedge revealed that the optimum temperature for compatibility of hexakis(4-acetamidophenoxy)cyclotriphosphazene (ACP) and DER-331 epoxy resin is in the range of 220–260 °C. The interdiffusion time of components at these temperatures is about 30 min. The TGA and differential scanning calorimetry (DSC) methods revealed the curing temperature of 280 °С for this composition. IR spectroscopy confirmed that the reaction between the resin and ACP is completed within 10 min. According to the DSC data, a glass transition temperature of 130 °С was estimated for the cured resin. Combustion test UL-94 demonstrated that the obtained material can be assigned to the fireproof category of V-0. Burning droplets were not formed during the burning. The coke formed during the combustion of samples possessed a dense and porous structure. The shape of pores is closed, while their size is in the range of 0.2–200 µm.

Switchable FoV infrared imaging system using micro-lens arrays

Infrared imaging provides invisible infrared pictures beyond that of normal human vision. However, common infrared imaging systems are incapable of capturing dynamical phenomena with high resolution and a wide field of view (FoV). The proposed modality purposefully selects the incident light with various instantaneous viewing angles and eventually combine them in different temporal sequences to form a larger FoV image, thus allowing one single cooled focal plane arrays to detect an area that appreciably exceeds what is possible with conventional counterparts. The primary principles of the 3.5 $\sim$∼ 5 $\mu$μm imaging system involve contracting and splitting the FoV with the optical wedges and switching the splitted FoV using the micro-lens arrays, which are realized with the secondary imaging structure. In this technique, the entire FoVs are enlarged from 15$^\mathrm{o}$o to 30$^\mathrm{o}$o both in 2-D and 3-D modality when the resolutions keep at 49 lp/mm. Proof-of-concept results demonstrate significantly our mid-infrared imaging modality performs high-quality images in the FoV of -15$^\mathrm{o}$o to 15$^\mathrm{o}$o. The present article has brought us a new class of wide FoV imaging configurations that permit the capture of moving objects in large area, which also preserves the high resolution.

Absolute Single Cavity Length Interrogation of Fiber-Optic Compound Fabry⁻Perot Pressure Sensors Through a White Light Non-Scanning Correlation Method.

A white light non-scanning correlation interrogation system was proposed and built to interrogate absolute length of the air cavity of fiber-optic compound Fabry–Perot pressure sensors for the extraction of pressure value. By carefully choosing thickness range and tilt angle of the optical wedge used for cavity length matching, correlation interferometric signal of the basal cavity can be naturally filtered out. Based on peak positioning by Fourier transform, bandpass filtering in frequency domain, inverse Fourier transform back to time domain, envelope fitting and zero fringe finding through a gravity center method, cavity length can be determined with an accuracy of 0.04%. The system was used for the interrogation of a fiber-optic compound Fabry–Perot pressure sensor under different pressures. For a pressure range of 0.1~2.9 Mpa, the linear relationship between the air cavity length and the gas pressure imposed was successfully extracted.

INTRACAVITY LARGE-SCALE HETEROGENEITY AND THEIR INFLUENCE ON RADIATION PARAMETERS OF POWERFUL LASERS

Large‑scale inhomogeneities occur in the optical resonator of a high‑power laser due to uneven redistribution of heat and errors in the alignment of the circuit. Such inhomogeneities can significantly affect the characteristics of laser radiation. The paper analyzes the effect of large‑scale phase inhomogeneities associated with the separation and thermal deformation of unstable resonator mirrors on the parameters of the laser radiation – the power and angular divergence. The numerical simulation of the unstable resonator in the di‑fractional approximation is carried out, on the basis of which the quantitative effect of phase aberrations such as optical wedge (separation) and spherical lens (thermodeformation) on the power and divergence of laser radiation depending on the main characteristics of the unstable resonator‑the Fresnel number and the magnification coefficient is determined. The results of experimental studies of the effect of separation on the radiation parameters of a 100‑kilowatt CO2 gas‑dynamic laser are presented. The results of the work should be taken into account in the structural‑parametric optimization of the resonator.

Double optical wedge optical axis pointing adjustment technology

Because the double-wedge system can accurately adjust the orientation of the optical axis, it has the advantages of simple and compact structure, fast adjustment speed, and large adjustment angle. In order to meet the needs of a certain product, optical axis adjustment trajectories of concentric circles and zigzags are realized. Based on the existing theories, this paper establishes the corresponding formula by establishing the relationship between the optical axis deflection angle and the bi-wedge rotation angle model, and combines the Matlab simulation, the fitting and the actual product testing, and designs the use of ARM and computer-controlled bi-optical wedges to adjust the orientation of the optical axis. The results show that the error of the optical axis pointing adjustment of the scheme is less than 0.5°, and the expected trajectory can be achieved to meet the requirements of actual products.

Design and simulation of MEMS-actuated adjustable optical wedge for laser beam scanners

This paper introduces both optical and mechanical design and simulation of large static deflection MOEMS actuator. The designed device is in the form of an adjustable optical wedge (AOW) laser scanner. The AOW is formed of 1.5-mm-diameter plano-convex lens separated by air gap from plano-concave fixed lens. The convex lens is actuated by staggered vertical comb drive and suspended by rectangular cross-section torsion beam. An optical analysis and simulation of air separated AOW as well as detailed design, analysis, and static simulation of comb -drive are introduced. The dynamic step response of the full system is also introduced. The analytical solution showed a good agreement with the simulation results. A general global minimum optimization algorithm is applied to the comb-drive design to minimize driving voltage. A maximum comb-drive mechanical deflection angle of 12 deg in each direction was obtained under DC actuation voltage of 32 V with a settling time of 90 ms, leading to 1-mm one-dimensional (1-D) steering of laser beam with continuous optical scan angle of 5 deg in each direction. This optimization process provided a design of larger deflection actuator with smaller driving voltage compared with other conventional devices. This enhancement could lead to better performance of MOEMS-based laser beam scanners for imaging and low-speed applications.

Optical Fiber Demodulation System with High Performance for Assessing Fretting Damage of Steam Generator Tubes.

In order to access the fretting damage of the steam generator tube (SGT), a fast fiber Fabry-Perot (F-P) non-scanning correlation demodulation system based on a super luminescent light emitting diode (SLED) was performed. By demodulating the light signal coming out from the F-P force sensor, the radial collision force between the SGT and the tube support plate (TSP) was interrogated. For higher demodulation accuracy, the effects of the center wavelength, bandwidth, and spectrum noise of SLED were discussed in detail. Specially, a piezoelectric ceramic transducer (PZT) modulation method was developed to get rid of the interference of mode coupling induced by different types of fiber optics in the demodulation system. The reflectivity of optical wedge and F-P sensor was optimized. Finally, the demodulation system worked well in a 1:1 steam generator test loop and successfully demodulated a force signal of 32 N with a collision time of 2 ms.

光楔式光纤法布里-珀罗传感器相关干涉信号特性分析

光楔式光纤法布里-珀罗传感器相关干涉信号特性分析

Flexible interferometry for optical aspheric and free form surfaces

A flexible interferometry is proposed to test concave optical aspheric and free-form surfaces. It employs a flexible aberration generator (FAG) consisting of a movable reflective sphere (MRS) and two counter-rotating optical wedges (CROW). The FAG is able to generate low-order Zernike aberrations to compensate the inherent aberrations of the test surface by the rotation of wedges in CROW and translation (or tilt) of the MRS. For some surfaces with mild departure, the FAG would result in a resolvable interferogram by the different aberrations compensation and the flexible test is thus achieved. The practical calibration for FAG is also reported. After calibration, experiment results showing the validity of the flexible test are presented by testing an ellipsoidal mirror and an off-axis paraboloidal mirror.

Transferring linear motion of an optical wedge to rotational frequency shift in an orbital angular momentum interferometer

We build a modified Mach-Zehnder (M-Z) interferometer with an embedded Dove prism in one arm to observe the interference between two conjugate orbital angular momentum (OAM) beams. By inserting and moving an optical wedge vertically in the other arm, we find that its linear motion can induce a rotational frequency shift equivalently, as a consequence of phase transfer from the path difference to the azimuthal difference between two OAM beams. The micron-scale movement of the wedge is driven by a compact motorized translation stage and is manifested by a significant rotation of the interference petal-like patterns. Our scheme offers an accurate method to measure the optical wedge angle with a simple method of digital image processing. This work may also find potential applications in the field of velocity sensing or temperature sensing.

A design of high optical efficiency wedge type light guide plate adopting twin inclined cylindrical surface

AbstractWe propose wedge type light guide plate (LGP) adopting twin inclined cylindrical surfaces (TICS) at the incident part of a LGP. It has higher optical efficiency than conventional wedge type LGP. In dimension of LGP which the thickness of incident part is 1.5 mm and that of luminance part is 0.7 mm, the optical efficiency of wedge type LGP adopting TICS is expected to be 96% in comparison with a normal flat LGP. In addition, there is an advantage to reduce the non‐uniformity of vicinity of light emitted diodes (LEDs) by TICS reflecting light laterally. However, it is necessary that the LED centers are aligned with the intersections of TICS. The misalignment of LED causes non‐uniformity of optical profile that is slightly larger than a normal LGP.

Validation of simultaneous reverse optimization reconstruction algorithm in a practical circular subaperture stitching interferometer

We demonstrate the validity of the simultaneous reverse optimization reconstruction (SROR) algorithm in circular subaperture stitching interferometry (CSSI), which is previously proposed for non-null aspheric annular subaperture stitching interferometry (ASSI). The merits of the modified SROR algorithm in CSSI, such as auto retrace error correction, no need of overlap and even permission of missed coverage, are analyzed in detail in simulations and experiments. Meanwhile, a practical CSSI system is proposed for this demonstration. An optical wedge is employed to deflect the incident beam for subaperture scanning by its rotation and shift instead of the six-axis motion-control system. Also the reference path can provide variable Zernike defocus for each subaperture test, which would decrease the fringe density. Experiments validating the SROR algorithm in this CSSI is implemented with cross validation by testing of paraboloidal mirror, flat mirror and astigmatism mirror. It is an indispensable supplement in SROR application in general subaperture stitching interferometry.

Extending the Alvarez-Lens Concept to Arbitrary Optical Devices: Tunable Gratings, Lenses, and Spiral Phase Plates

The Alvarez lenses consist of two parts with surface geometry designed to produce a change in refractive power with transversal translation between the upper and lower parts of the device. In this study, we present a new and straightforward approach to calculating the geometry of such devices and show that an Alvarez configuration can be found not only for lenses, but also for virtually any refractive device. Surface profiles required to realize an optical wedge, a blazed grating, a lens, and a spiral phase plate are presented. The performance of the devices is verified by numerical simulations and experimentally.

Lidar combined scanning unit

Subject of Research. The results of lidar combined scanning unit development for locating leaks of hydrocarbons are presented The unit enables to perform high-speed scanning of the investigated space in wide and narrow angle fields. Method. Scanning in a wide angular field is produced by one-line scanning path by means of the movable aluminum mirror with a frequency of 20Hz and amplitude of 20 degrees of swing. Narrowband scanning is performed along a spiral path by the deflector. The deflection of the beam is done by rotation of the optical wedges forming part of the deflector at an angle of ±50. The control function of the scanning node is performed by a specialized software product written in C# programming language. Main Results. This scanning unit allows scanning the investigated area at a distance of 50-100 m with spatial resolution at the level of 3 cm. The positioning accuracy of the laser beam in space is 15'. The developed scanning unit gives the possibility to browse the entire investigated area for the time not more than 1 ms at a rotation frequency of each wedge from 50 to 200 Hz. The problem of unambiguous definition of the beam geographical coordinates in space is solved at the software level according to the rotation angles of the mirrors and optical wedges. Lidar system coordinates are determined by means of GPS. Practical Relevance. Development results open the possibility for increasing the spatial resolution of scanning systems of a wide range of lidars and can provide high positioning accuracy of the laser beam in space.

Optical image encryption based on a joint Fresnel transform correlator with double optical wedges.

An optical cryptosystem based on the joint Fresnel transform correlator (JFTC) with double optical wedges is designed. The designed cryptosystem retains the two major advantages of JTC-based optical cryptosystems. First, the encrypted image is real-valued and therefore is easier to record and transmit. Second, the encryption process is simplified, since it doesn't require accurate alignment of optical elements or the generation of the complex conjugate of the key. Also, the designed optical cryptosystem can produce a decrypted image with higher quality than a JTC-based optical cryptosystem, because the original encrypted image is divided by the Fresnel transform power distribution of the key mask to generate the new encrypted image, which significantly reduces the noise during the decryption process. Simulation results showed that the correlation coefficient of the decrypted image and the original image can reach as large as 0.9819 after denoising and adequately selecting half-central interval a and encrypted image width w. Another improvement relative to JTC-based optical cryptosystems is that the attack resistibility gets enhanced due to the nonlinearity of the encryption process as well as the additional key parameter a, which enlarges the key space.