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Accurate measurement of the aperture area has always been the focus of optics and optical radiation measurement. The metrology institutes around the world have established absolute aperture area measurement facilities. In this paper, a measuring system of the aperture area based on optical flux comparison method is designed and implemented., which can transfer absolute values efficiently and accurately. The results show that the deviation between the area measured by optical flux comparison method and the area measured by effective area method is about 5×10-4 . The influences of the light source stability, irradiation field uniformity and aperture positioning difference on the measurement results are analyzed emphatically. The uncertainty of the measurement results is also evaluated, the relative expanded uncertainty is 9.9×10- 4 (k=2).

An LED-based integrating sphere light source (LED-ISLS) was designed and fabricated for radiance responsivity calibration of microscopes. The LED-ISLS was composed of a miniaturized integrating sphere, an LED chip, a thin circular aperture, and was successfully applied to calibrate the radiance responsivity of a home-built microscope system. Several issues remain to be discussed. Firstly, the area of the circular aperture, which served as an exit port, was measured by comparing the light flux through an area-certified standard aperture and the circular aperture. The measurement uncertainty was smaller than 0.2%. Secondly, the radiance uniformity on the exit port was discussed. Simulations and experiments were conducted to evaluate the effects of circular aperture edge thickness and integrating sphere internal material reflection parameters on the radiance uniformity. From the simulation it was found out that as the edge thickness increases, the radiance uniformity drops drastically; the Bidirectional Reflectance Distribution Function (BRDF) also has impact on the radiance uniformity of the LED-ISLS. By reducing the BRDF from 0.9 to 0.6, the radiance uniformity at the exit port was reduced by about 63%. The radiance uniformity was also evaluated experimentally by using a 1 mm small aperture to scan the different small areas of the exit port. The radiance non-uniformity across the exit port of the LED-ISLS was about 5% from the scanning results. This work further investigated the radiance non-uniformity of the LED-ISLS and offered ideas of technical optimization of the LED-ISLS for better radiance responsivity calibration performance.

The photon counting detectors have a wide range of applications in different areas, such as quantum communication, linear-optics quantum computing optical metrology and so on. In this work, a fiber-based 16-channel multiplexer with different time delays was designed based on a construction scheme of 1 (1×4) coupler = 4 (1×4) couplers = 16×optical fibers - 4 (4×1) couplers - 1 (4×1) coupler. The lengths (di, i =1, 2, ...16) of the optical fibers were manufactured to be 0 m, 8.0 m, ... 120.0 m, respectively, with a length difference (Δd) of 8 m. The time delay between the optical fibers (Δt) can then be calculated to be 38.8ns. A pulsed 850 nm laser with a repetition rate of 1 MHz and a pulse duration of 10 ns was adopted to test the time-multiplexing capability of the 16-channel fiber coupler. A 1-GHz Si photodetector and a 1-GHz oscilloscope were used to measure the overall insertion loss and relative power through the 16 different channels. The photoelectric pulse count of the pulsed light passing through the fiber bundle will be measured. According to the loss of optical fiber and the photon detection efficiency of detector, we can roughly the photon detection efficiency of the system. If the fiber bundle with 16 entrances instead of only one, the scheme would be used as a detector array, and for imaging. This is what we're going to do in the future.

Aperture is widely used in optical instruments, for which the area is of importance especially for instruments measuring radiometric or photometric quantities. To measure the radiometric area of the aperture, an optical method using a power stabilized laser to scan the aperture was proposed and investigated by many metrology institutes worldwide. The National Institute of Metrology (NIM) of China has built an apparatus to measure the radiometric area aperture by using the optical method. The scheme of experimental setup and related issues are discussed in this work. Uncertainties are analyzed for an aperture with nominal 6mm diameter. Approaches for further improvements are also discussed.

With high quantum efficiency, low capacitance, low dark current and wide bandwidth, InGaAs detectors has lots of applications in optical radiation measurement, optical communication and remote sensing. This paper using a spectral comparison facility based on supercontinuum white light source and double monochromator, in which a reference InGaAs trap detector is used for the relative spectral responsivity calibration of a planar InGaAs detector. Calibration of the same detectors using tungsten lamp as light source has also been done and shows a good consistency, which proves the feasibility of relative spectral responsivity calibration using supercontinuum white light sources.

A new comparator facility for spectral responsivity calibration of InGaAs photodiode based on cryogenic radiometer fundamental has been set up at the National Institute of Metrology of China (NIM). The comparator employed a stable supercontinuum light source, a prime-grating monochromator, a reliable 5-axis stage and some necessary optics as its main construction components. The supercontinuum source, monochromator and some beam path were also commonly utilized by the cryogenic radiometer, which was designed to minimize the deviations to the calibration procedure introduced by these components. The spectral responsivity of the InGaAs photodiode in the spectral range 900nm- 1600nm was determined. The repeatability obtained by this new comparator is one decade better than that of former InGaAs measurement facility. NIM has been better supported to finish the measurements of transfer detectors of key comparison of CCPR-K2.a.2016 by this new and accuracy comparator.

A spectrally tunable monochromatic integrating sphere photon source (ISPS) was built based on a laser driven plasma light source, a monochromator, an optical attenuator, and an integrating sphere. The wavelength of ISPS output photons can be tuned from 300 nm to 800 nm with a spectral bandwidth of 1 nm ~ 5 nm; the spectral optical radiant power into the integrating sphere can be adjusted over three decades through the optical attenuator; the diameters of the inner wall and the exit port of the integrating sphere are 100 mm and 50 mm, respectively. The spectral photon radiance of the ISPS can be measured by a photomultiplier-tube (PMT) based photon counter and two precision apertures. An integrating sphere was utilized in front of the PMT-based photon counter and the non-uniformity of the spectral optical radiant power responsivity was reduced to be ~0.5% over a 5-mm-diameter effective detection area. Two precision apertures were adopted to define the effective detection area and the solid angle extended for the field-of-view. The ISPS can be directly applied to calibrate the spectral photon radiance responsivity of a few-photon imaging system, which was demonstrated on a digital color camera and a focusing lens. The spectral photon radiance responsivity of a given imaging system can be effectively validated based on this ISPS apparatus.

It is important to measure the spectral transmission characteristics of materials when the spatial density of classical optical power (that is, the laser or attenuated light is a small spot, but the optical power hits a fixed position) is different from the spatial density of weak optical power. The most important scientific problem (research or experimental objective) is to distinguish the difference between the probability of photons passing through a sample with a specific absorption rate collectively and the probability of approaching a single photon passing through the same sample. We design an optical fiber system that can measure weak optical power. We use many methods to expand the linear measurement range so that it can measure its linearity in the power range of 1 fA-1 mA. In addition, the system can also verify the linearity of photon counter, starting from 0.1 pA block - essentially, when the detector is adjusted to 0.1 pA, the verification and evaluation of photon counting at the photomultiplier tube level is started. From the power measurement level of cryogenic radiometer to the photon counting level, the optical fiber measurement system covers 12 orders of magnitude, which also shows that the spectral transmittance and reflection ratio can cover a wide range, that is, it can be used to measure the characteristic materials with high transmittance.

Highly reflective diffuse boards or integrating spheres illuminated with lamps are routine laboratory equipment for 2D radiometric calibration. The traceability chain to validate the measurement results is from absolute cryogenic radiometer (spectral power and then spectral power responsivity) through filter radiometer (spectral radiance at single wavelength), standard blackbody radiation sources (spectral radiance over a wavelength range), and calibrated spectroradiometers (spectral radiance responsivity over a wavelength range), to the large area spectral radiance sources for large area optical sensors and imaging spectroradiometers. However, due to (1) the fairly long traceability chain, (2) the non-uniformity of lamp illuminated diffuse boards and integrating spheres, (3) the relatively low spectral power from the broadband source for high spectral resolution, and so on, the calibration uncertainties for spectral radiance and irradiance responsivity are above the level of a few per cents. In order to improve the calibration performance, tunable lasers have been widely adopted to generate a large, uniform radiometric calibration source. For instance, an integrating sphere can be illuminated with a wavelength tunable laser to form a good spectral radiance field. Though very high laser power is necessary if the exit port of the integrating sphere is large. An alternative way is to directly unify and expand the laser beam for a good spectral irradiance field. In this work, we built a large, uniform, spectrally tunable irradiance field based on a Ti-Sapphire laser. First, two double-convex lenses were employed as a beam expander; second, a rotary diffuser was placed at the common focal point of the two lenses; thirdly, the expanded optical beam was then delivered onto and through a micro lens array to form a highly uniform spectral irradiance field with a size of 30 mm by 30 mm. The non-uniformity was measured to be 0.24% over a 20 mm by 20 mm area. The total optical losses through the beam expansion and unification system would be significantly reduced compared with integrating sphere method. The traceability chain is from the absolute cryogenic radiometer (spectral power and then spectral power responsivity) and the effective radiometric aperture area to the photodetector with a precision aperture (spectral irradiance responsivity), and then to the large, uniform, laser-based spectrally tunable irradiance field (spectral irradiance) for the calibration large size optical sensors and imaging spectroradiometers. The traceability chain is short, the non-uniformity is low, and the signal-to-noise ratio is high, compared to that based on the lamp illuminated boards and integrating spheres. Furthermore, the laser-based spectral irradiance field can be easily converted to a large, uniform spectrally tunable radiance field by simply placing a large-size, highly reflective diffuse board in the irradiance field. The laser-based irradiance and radiance field would play an important role for radiometric calibrations with low uncertainties.

An absolute cryogenic radiometer (ACR) has been developed at the National Institute of Metrology of China. The system was built based on a mechanical cooling system, with a cavity receiver working at 5.2 K and a noise-equivalent power of ~2 nanowatts. The ACR cavity receiver was made from pure copper by electroplating, weighing only

The two-step method using Hypothesis-Generation two steps to early detect the low-small-slow target, is based on the theory of multi-source detection fusion. The Hypothesis-Generation of the target information is built by the data set of multi-sensor. Hypothesis-Union distinguishing of the target information is based on the method of multi-source decision fusion, is realized by distributed decision feature fusion based on Bias minimum risk rule. The experimental results verify the feasibility and effectiveness of the method.

In this paper, we propose a new algorithm integrating pure pixel identification into nonnegative matrix factorization (NMF) model to decompose the mixed pixels existing in hyperspectral imagery. The proposed algorithm employs traditional endmember identification algorithm to search for the pure pixel candidates, and then the principal component analysis is performed on the homogenous pixels which consist of the pure pixel candidates and its neighborhoods to identify the endmembers existing in the real scene. Finally, the known-endmember-based NMF unmixing algorithm is used to generate the other unknown endmembers. The proposed algorithm retains the advantages of both pure pixel identification method and NMF. Experimental results based on simulated and real data sets demonstrate the superiority of the proposed algorithm with respect to other state-of-the-art approaches.

Spectral mixture analysis (also called spectral unmixing) is one of the important and effective techniques to estimate abundance fractions of materials present in the hyperspectral imagery. Linear spectral mixture modeling is widely used in solving the spectral unmixing problems as its conciseness and clarity of physical meaning. This paper presents a novel algorithm to produce fully constrained (i.e. non-negative and sum to one constrained) abundance using the barycentric coordinates in the n-simplex. To impose non-negative constraint on the abundance, the proposed method use a serious of orthogonal projections to find the fully constrained solution, which takes into account the geometric structure of hyperspectral data set. The proposed algorithm is in line with the least squares criterion. The efficiency and effectiveness of the resulting unmixing algorithm is demonstrated using both synthetic and real hyperspectral images.

Various kinds of photo-detectors based on different materials have been successfully developed to expand the horizon of human eye. Spectral responsivity is the most important technical parameter for photo-detectors, which can mirror the converting ability of optical signal to electric current. Its measurement accuracy is critical for the development and research of photo-detecting field. In this paper, we will introduce the facility for photo-detector’s spectral responsivity calibration in the wavelength range of 300 nm to 1000 nm, built in National Institute of Metrology (NIM), China. Measurement uncertainty is analyzed at the wavelength 500 nm as an example. By adopting comparison method, choosing reference detectors with known standard value and traceable to SI units through upper level standards, we demonstrated a reliable measurement procedure for absolute spectral responsivity of photo-detectors.

A new scheme of adjustable full polarization imaging measurement system was presented in this paper in order to study the polarization properties of light. It realized the measurement and flexible switching of the linear, circular and elliptical polarization modes in the active and passive mode through the combination of a linear polarizer, 1/4 wave plate and angle adjusting device. A prototype of the adjustable full polarization imaging measurement system was developed and tested in the paper. The adjustable full polarization imaging system was mainly composed of a polarization transmitting unit, a polarization receiving unit and an imaging control unit. In the active mode, the polarization emission unit worked and emitted the active polarized light while in passive mode, the emission unit did not work, and the system got image via natural light. The entire system was integrated into an image sensor with compact structure and good consistency, which can be widely used in the laboratory and field polarization imaging measurement and quantitative analysis.

Cryogenic radiometer is the most accurate measurement setup for optical power measurement, underpinning the radiometry and photometry standards in many countries around the world. Typically cryogenic radiometers are designed for laser injection, and the measurement uncertainty at the laser wavelengths can reach 10-4. The National Institute of Metrology China has used the laser cryogenic radiometer to realize the absolute spectral responsivity of the detectors. In order to achieve spectral responsivity measurement ability in a wider spectral range, we establish the new spectral type cryogenic radiometer system using a supercontinuum white light source and a double monochromator, covering spectral range of 400 nm - 1100 nm. Establishment of the new cryogenic radiometer will greatly enhance the entire optical radiation measurement capablities, such as radiation illuminance and luminance measurement. A series of experiments have been undertaken, including measurement of noise level, heating equivalence, wavelength calibration, power stabilization, detector characteristics measurement, and different light source spectral radiation power measurement. The measurement uncertainties are analyzed and presented.

The quantum efficiency of photon counters can be measured with standard uncertainty below 1% level using correlated photon pairs generated through spontaneous parametric down-conversion process. Normally a laser in UV, blue or green wavelength range with sufficient photon energy is applied to produce energy and momentum conserved photon pairs in two channels with desired wavelengths for calibration. One channel is used as the heralding trigger, and the other is used for the calibration of the detector under test. A superconducting nanowire single photon detector with advantages such as high photon counting speed (

Optical fiber power is an important physical quantity for optical fiber communication measurement. Currently, the absolute optical fiber power is traceable to absolute radiometer, such as electrically calibrated radiometer, and cryogenic radiometer. For optical fiber power transfer, the primary standard of NIM is the cryogenic radiometer that has an uncertainty of 2 parts in 104. Because most cryogenic radiometers are designed to be used with collimated beams rather than divergent beams from an optical fiber; therefore transfer standards should be well designed for optical power measurement using the beam geometry correction. We designed a trap detector using for optical fiber power transfer. One can omit the beam geometry correction from an optical fiber using his design. We present a fiber power measurement using a planar detector compared with this trap detector, which are traceable to the primary standard (cryogenic radiometer). The difference between the comparison shows that the trap detector is suitable for absolute fiber power measurement, meanwhile optical fiber power transfer using planar detectors should be corrected when transferred from cryogenic radiometer.

Electrooptic sampling has been shown to be a very powerful technique for making time-domain measurements of fast electronic devices and circuits, such as oscilloscope. In this paper, we review the principles of electrooptic sampling technique for electronic waveform probing with applications to characterizing 100GHz photodetector pulse response.

In single-particle cryo electron microscopy, many electron microscope images each of a single instance of a biological particle such as a virus or a ribosome are measured and the 3-D electron scattering intensity of the particle is reconstructed by computation. Because each instance of the particle is imaged separately, it should be possible to characterize the heterogeneity of the different instances of the particle as well as a nominal reconstruction of the particle. In this paper, such an algorithm is described and demonstrated on the bacteriophage Hong Kong 97. The algorithm is a statistical maximum likelihood estimator computed by an expectation maximization algorithm implemented in Matlab software.

In an imaging system based on a coherent source of moderate power density, images can be blurred when a biased photorefractive crystal is applied at the focal point of the imaging lens. In the frequency domain of the original images, the intensity patterns are diffracted through the photorefractive crystal with varied bias voltage. The high intensity region, which is usually the center or low frequency region of the intensity patterns, is more readily focused or defocused, resulting in blurred images in perception. Such blurred images could not be simply recovered by defocusing methods, which can only indistinguishably focus or defocus the whole intensity patterns. However, the blurred images may be deblurred to certain extent for recovery if a second photorefractive crystal with bias voltage is employed at the focal point of a tandem imaging system. The mechanism of deblurring is similar to that of blurring: the blurred images are transferred through the frequency domain again using an imaging lens, where the second biased photorefractive crystal diffracts the intensity patterns to revert the sensitive region where previously gets focused or defocused. In this work, theoretical analyses are presented in detail to explain the blurring-deblurring mechanism using two biased photorefractive crystals and compatible experimental results are obtained and illustrated. Considering the blurring and deblurring function subgroups of the experiment setup can be potentially developed into encryption and decryption units compatible with far field propagation, the technology presented herein may be promising to find applications in secure laser-based free-space communication systems.

A comparison of different transfer standard optical fiber power detectors is present. Traceable to cryogenic radiometer, these planar, focus-planar and trap detectors have different characteristics during the optical fiber power values transfer because of the different input angles or fiber connectors. For different types of fibers and fiber connectors, a new trap detector is capable for the optical fiber power measurement, which has very little sensitivity for a variety of input conditions. Comparison of fiber power measurement using a planar and a trap detector is present by employing a three-lens method. A good agreement between the two types of detectors shows the feasibility of fiber power transfer using planar detectors.

High accuracy full field three dimensional (3D) deformation measurements have always been an essential problem for the manufacturing, instrument, and aerospace industry. 3D deformations, which can be translated further into 3D strain and stress, are the key parameter for design, manufacturing and quality control. Due to the fast development of the manufacturing industry, especially in the automobile and airs pace industry, rapid design and optimization concepts have already widely accepted. These concepts all require the support of rapid, high sensitive and accuracy 3D deformation measurement. Advanced optical methods are gaining widely acceptance for deformation and stain measurem ent by industry due to the advantages of non-contact, full-field and high measurement sensitivity. Of these methods, Electronic Speckle Pattern Interferometry (ESPI) is the most sensitive and accurate method for 3D deformation measurement in micro and sub micro-level. ESPI measures deformation by evaluating the phase difference of two recorded speckle interferograms under different loading conditions. Combined with a phase shift technique, ESPI systems can measure the 3D deformation with dozens of nanometer level sensitivity. Ca taloged by phase calculation me thods, ESPI systems can be divided into temporal phase shift ESPI systems and spatial phase shift ESPI system. This article provides a review and a comparison of temporal and spatial ph ase shift speckle pattern interferometry for 3D deformation measurement. After an overview of the fundamentals of ESPI theory, temporal phase-shift and spatial phase-shift techniques, 3D deformation measurements by the temporal phase-shift ESPI which is suited well for static measurement and by the spatial phase-shift ESPI which is pa rticularly useful for dynamic measurement will be discussed in detail. Basic theory, brief derivation and different optical layouts for the two systems will be presented. The potentials and limitations of the both ESPI systems will be demonstrated by examples of precise and simultaneous measurement of 3D deformations under either static or dynamic loadings. Keywords: 3D deformation measurement, tem poral phase-shift, spatial phase-shi ft, Speckle Pattern Interferometry

Degree of polarization (DOP) is an important physical quantity for describing the optical polarization effect and is widely applied in optical fiber communication, optical fiber gyro and the related technologies. Currently, the optical polarization degree tester for the purpose of communication uses mainly two kinds of measurement methods: Stokes vector method and extremum method. At present, there isn’t a standard to measure the accuracy and consistency of DOP parameter measurement by the devices listed above, affecting seriously the application of DOP parameter measurement in the fields of optical fiber gyro and optical fiber communication. So, it is urgent to table the accurate guarantees to trace the source of quantitative values of the DOP measuring devices and testers. In this paper, the polarization beam combination method is raised to research and manufacture the standard optical fiber light source device with the variable DOP, and an indicated error measurement has been conducted for a DOP meter. A kind of standard optical fiber light source device that uses a single light source to realize the variable DOP is put forward. It is used to provide the accurate and variable optical fiber polarization degree light with a scope of 0～100%. It is used to calibrate the DOP meters and widely applied in the field of national defense and optical communication fields. By using the standard optical power meter, DOP value by which the optical power meter calculates the optical signal can be measured, which will be used ultimately for calibration of the DOP meter. A measurement uncertainty of 0.5% is obtained using the polarization beam combination method.

In this paper, a kind of special optical fiber bonding high-temperature aging plan is raised. The armored optical fiber technology is applied to guarantee the long-term stability of the optical properties of the standard instrument itself. The temperature compensation encapsulation technology is adopted for optical fiber grating, that is, the wavelength will remain constant under the standard atmosphere pressure and chamber temperature. It becomes the optical fiber grating sensing wavelength standard instrument. The optical fiber grating standard instrument based upon this kind of new-type structure is tested, and the result has its word that the temperature shift of this optical fiber grating standard instrument after encapsulation is less than 0.5pm/℃. Coupled with the simple temperature control, the wavelength accuracy of the optical fiber grating standard instrument will be controlled below ±1pm and its long-term stability will be smaller than 2pm/℃. Differ from F-P standard instrument, this optical fiber grating standard instrument is one without mechanical device and is purely physical. So, it features more reliable performance and is applicable to mass production. The costs of this kind of optical fiber grating standard instrument is under control and will see an important application in the optical fiber grating sensing technology.

Mechanoluminescence (ML) materials have recently attracted considerab le attention due to their potential applications as an imaging sensor for detecting damages and measuring stress distributions in complex structures, which is difficult for conventional methods. SrAl 2 O 4 :Eu 2+ (SAOE) is a ML material with the best performance but it hydrolyzes rapidly under humid environment, which limits the scope of its applications especially in outdoor environm ents, e.g. structural health monitoring for buildings, bridges and tunnels. Thus ML materials with water resistance such as silicates and aluminosilicates have been developed, but the brightness of which is still much lower than SAOE. In this study, we report a novel method to improve the impact-induced ML in ML materials using the swift heavy ion (SHI) irradiation. The impact-induced ML intensity of CaSrAl 2 Si 2 O 8 :Eu 2+ was dramatically enhanced by about one order of magnitude using SHI irradiation. Furthermore, higher electronic stopping power and higher irradiation fluence were found to be more effective for improving the impact-induced ML. It is considered that the trap density suitable for the impact-induced ML was increased by the SHI irradiation, resulting in the impact-induced ML enhancement. The underlying mechanism was discussed, which is of great importance for developing new ML materials for structure health monitoring. Keywords: mechanoluminescence, structural health monitoring, swift heavy ion irradiation, impact, trap

Innovative mechanoluminescent (ML) particles emit light repeatedly in response to small stresses applied, such as deformation, friction, or impact. When dispersedly coated on a structure, each particle acts as a sensitive mechanical sensor, while the 2-dimentional emission pattern of the whole assembly reflects well the dynamical stress distribution inside the structure and mechanical information around crack and defect. Thus, we have applied the remarkable strong points of ML sensing technique to a bridge in use as a real social structure for the first time. For the first ML monitoring test at bridge, we selected a relatively old bridge (established in 1954, 3-span continuous T-type RC bridge, length 24.4 m, width: 7.89 m). The ML sheet type sensors were put around the central area (700×400 mm) of the main girder, and ML images originated from dynamic load application via general traffic vehicles had recorded by using lab-made CCD camera under roughly dark condition. As the result, we successfully detected intense ML patterns not only along visible crack but also at round soundless part on the girder at a glance with responding ML intensity reflecting the crack mouth opening displacement (CMOD) of visible crack and invisible progressing microcrack.

The phase perturbations due to propagation effects can destroy the high resolution imagery of Synthetic Aperture Imaging Ladar (SAIL). Some autofocus algorithms for Synthetic Aperture Radar (SAR) were developed and implemented. Phase Gradient Algorithm (PGA) is a well-known one for its robustness and wide application, and Phase Curvature Algorithm (PCA) as a similar algorithm expands its applied field to strip map mode. In this paper the autofocus algorithms utilized in optical frequency domain are proposed, including optical PGA and PCA respectively implemented in spotlight and strip map mode. Firstly, the mathematical flows of optical PGA and PCA in SAIL are derived. The simulations model of the airborne SAIL is established, and the compensation simulations of the synthetic aperture laser images corrupted by the random errors, linear phase errors and quadratic phase errors are executed. The compensation effect and the cycle index of the simulation are discussed. The simulation results show that both the two optical autofocus algorithms are effective while the optical PGA outperforms the optical PCA, which keeps consistency with the theory.

A demonstrator of synthetic aperture imaging ladar (SAIL) is constructed with the maximum aperture O300mm of antenna telescope. This demonstrator can be set with a rectangular aperture to produce a rectangular footprint suitable for scanning format with a high resolution and a wide strip. Particularly, the demonstrator is designed not only for the farfield application but also for the verifying and testing in the near-field in the laboratory space. And a 90 degree optical hybrid is used to mitigate the external phase errors caused by turbulence and vibration along line of sight direction and the internal phase errors caused by local fiber delay line. This paper gives the details of the systematic design, and the progresses of the experiment at a target distance around 130m.

The phase errors due to the nonlinear chirp of a tunable laser reduce the range resolution in Synthetic Aperture Imaging Ladar (SAIL). The analogue and digital image processing algorithms were developed, and all the image processing algorithms employed matched or nonmatched optical delay line. In this paper a theory of equiarm delay line to compensate the nonlinear chirp phase errors is proposed. This image processing algorithm includes three methods with different compensation precision and implementation difficulties, and promotes the application flexibility. Firstly, we derive the theory that the impact of the nonlinear chirp is suppressed with decreasing the delay time difference of the echo signal and the LO signal. Based on the theory, we propose three methods to establish the equiarm delay line: establishing matched target LO path, establishing reference path and dual coherent detections, establishing reference path and phase shifting calculation. Then the construction of the signal processing system and the mathematical flow of the algorithm are established. The simulations of the airborne synthetic aperture imaging ladar model approve that three methods suppress the phase errors of the nonlinear chirp to various extent, and improve the range resolution. The characteristics and the applicabilities of three methods are discussed finally.

We developed a novel technique for bolt tightening control by utilizing SrAl2O4:Eu (SAOE) paint film to detect axial force generated during bolt tightening. Conventionally, torque method is prevalently used for bolt tightening control. The major problem of this method which indirectly controls the axial force in bolted joints is that only a small proportion of the torque actually contributes to the bolt extension. It is the axial force due to such an extension that fastens the bolted joints. Therefore, it is urgently necessary to directly measure the axial force in order to realize a smart tightening control. Considering the extension of bolt during tightening can induce elastico-luminescence of SAOE if it is painted on the bolt or washer, we have painted SAOE/polymer film on the washer and consequently measured elastico-luminescence of SAOE film while tightening the bolt under various conditions. In the present work, we also demonstrated the correlation between the elastico-luminescence intensity and tightening conditions including tightening speed and strain as well as axial force.

Based on Fourier transform of heterodyne signal and linear fitting of phase time-evolution, a nonlinearity-induced phase error correction technique for synthetic aperture ladar is experimentally studied. The problem of beat frequency matching in the conventional method for nonlinearity-induced phase error correction in target channel by designing a reference channel and phase shift equations is practically analyzed, and its limitation on application under the condition of large time delay in target channel is verified. According to this problem, a new method of directly nonlinearity-induced phase error correction by linear fitting of phase time-evolution in target channel is proposed. In experiments, the rang resolution of 2 mm is gained at 1.5 μm wavelength, which is coincident well with theory. The results show that this technique can overcome the problem of beat frequency matching in two channels and is effective for practical applications with different time delay in target channel.

The phase errors due to the nonlinear chirp of tunable laser reduce the range resolution in synthetic aperture imaging ladar(SAIL). The compensating algorithms establishing matched and nonmatched reference paths were developed, and the phase errors were compensated in the whole echo pulse. In this paper a compensating algorithm by scan filtering is proposed. Compared to the compensation in the whole echo pulse, this compensating algorithm promotes precision and range resolution. Every echo pulse includes different echo components from all target points in footprint. The heterodyne signals of these different echoes are scan filtered from the heterodyne signal of one whole echo pulse in the spectrum. The phase errors of these heterodyne signals are measured by phase shifting algorithm in nonmatched reference path and compensated separately. Then the compensated signals are combined into whole heterodyne pulse and compressed in range. After all echo pulses are compressed in range the azimuth compensation and compression is followed. The mathematical flow of this algorithm is established. The simulation of the airborne SAIL model validates the feasibility, and the BW of range compression decreases obviously. The effects of width of the scan filter and nonlinear chirp are discussed. The conclusion of adequate width of the scan filter is given finally.

A fully 2-D synthetic aperture imaging ladar (SAIL) demonstrator is designed and being fabricated to experimentally investigate and theoretically analyze the beam diffraction properties, antenna function, imaging resolution and signal processing algorithm of SAIL. The design details of the multi-purpose SAIL demonstrator are given and, as the first phase, a laboratory-scaled SAIL system based on bulk optical elements has been built to verify the principle of design, which is similar in construction to the demonstrator but without the major antenna telescope. The system has the aperture diameter of about 1mm and the target distance of 3.2m.

Linear chirp laser signal is often employed as the transmitted signal of synthetic aperture laser radar (SAL). However, actual properties of frequency sweep of fiber laser always produces nonlinear terms such as quadratic and higher order terms. Existence of nonlinear terms of frequency produces phase errors during pulse time, leading to blurring of target in range direction and further reduces imaging resolution of range direction. It makes compensation of the nonlinear chirp from laser source a requirement. In this paper, we develop an algorithm of matched filtering in frequency spectrum to overcome the phase error from nonlinear chirp. The results of simulation show that the image in range direction can be well compressed. At the same time, we also analyze effects of signal compression in the range direction under different parameter situations such as reference channel length as well as ratio of nonlinear contribution.

Synthetic aperture imaging ladar (SAIL) used a series of pulses in which the optical frequency was swept linearly in time over a bandwidth greater than several gigahertz. The linearity of such broadly tunable sources is often poor which is leading to phase errors. Many methods are adopted to correct for quadratic and higher-order phase errors such as the reference channel or algorithm for unmatched channel of Aerospace and the reference interferometer of Naval Research Laboratory. If the real value of frequency swept quasi-linearly is measured another direct way to mitigate the waveform linearity problem can be developed. At first the frequency curve is measured with Fabry Perot fiber interferometer. Experiment and results are explained in detail in this paper. The quadratic and higher-order terms of frequency swept are calculated. They may be used to deduce the phase errors directly later. At the same time the wavefront is also measured by a Jamin shearing interferometer through the fringe analysis.

Full-field measurement of dynamic stress has been realized by coating the surface of the test object metal with a upgrade mechanoluminescence sensing film of SrAl2O4:Eu (SAOE). Mechanoluminescent materials are attractive smart materials that can emit light induced by mechanical deformation. The ML sensing film of SAOE has been developed to make possible to visualize dynamic stress. Consequently this visualization technique has been become a promising experimental technique to investigate full-field stress analysis. In this paper we report the applications of the SAO ML sensing film for full-field stress analysis in aluminum alloy 5052 samples. Using the SAOE ML sensing film, the stress concentration produced by a circular hole was observed with the naked eyes in real time and the two-dimensional stress distribution was quantitatively measured; the complex and dynamic Portevin-Le Chatelier (PLC) effect, known as instability during plastic deformation, has been visualized, and the propagating characteristics of PLC bands were precisely investigated.

Compared with direct detection, homodyne binary phase shift keying receivers can achieve the best sensitivity theoretically, and became the trend of the research and application in inter-satellite coherent laser communications. In coherent optical communication systems an optical hybrid is an essential component of the receiver. It demodulates the incoming signal by mixing it with the local oscillator. We present a design of a 2*6 optical hybrid. 4 output ports of the hybrid give the narrow mixed beams of the incoming signal and the local oscillator shifted by 90°for communication, and the others give the wide mixed beams with a shifted degree of 180°for position errors detection. CCD captures the interference pattern from the wide beams, and then the pattern is processed and analyzed by the computer. Target position information is obtained from characteristic parameter of the interference pattern. The position errors as the control signals of PAT (pointing, acquisition and tracking) subsystem drive the receiver telescope to keep tracking to the target. The application extends to coherent laser rang finder.

Due to the improved receiver sensitivity and wavelength selectivity, coherent detection became an attractive alternative to direct detection in inter-satellite laser communications. A novel method to coherent detection of position errors information is proposed. Coherent communication system generally consists of receive telescope, local oscillator, optical hybrid, photoelectric detector and optical phase lock loop (OPLL). Based on the system composing, this method adds CCD and computer as position error detector. CCD captures interference pattern while detection of transmission data from the transmitter laser. After processed and analyzed by computer, target position information is obtained from characteristic parameter of the interference pattern. The position errors as the control signal of PAT subsystem drive the receiver telescope to keep tracking to the target. Theoretical deviation and analysis is presented. The application extends to coherent laser rang finder, in which object distance and position information can be obtained simultaneously.

It is necessary, on the ground in a laboratory, to test the technical parameters and to verify the working performance for the optical pointing, acquisition and tracking (PAT) of an inter-satellite lasercom terminal. In this paper, we report a completed PAT test-bed for this aim. The test-bed works in a fully physical way and is an integration of a 2D optical scanner of two rotating prisms, a 2D fine beam deflector of two tilting optical wedges and a double-focus laser collimator, the overall aperture is about Φ440mm. The optical scanner is designed to scan the beam in the range of 30° with an accuracy of 100μrad and used to simulate the mutual movement between two satellites. The fine beam deflector has the maximum beam deviation of about 1mrad with a step of 0.5μrad and is used to measure the tracking error of a terminal. The collimator has the double focal lengths, respectively, of 1.5m and 10m, the former provides a wide view of field for the use in the acquisition process of the terminal and the latter a narrow view of field for the use in the tracking process. In this paper, the design and fabrication considerations of the PAT test-bed as well as the main specifications of the completed integrated test-bad are given.

Recent successful demonstrations of laser communications have demonstrated the feasibility of some of the key aspects of this technology. The demonstrations can not success without the full-up ground test and validation. So an integrate test-bed was build in build to test the technical parameters and to verify the working performance for the optical pointing, acquisition and tracking (PAT) of various inter-satellite lasercom terminals. In this paper, we detail the test technical scheme (TTS) and the corresponding experiments. The integrate test-bed is a high quality optical system that will measure the key characteristics of lasercom terminals, such as point error, tracking error, acquisition possibility etc.. The test-bed can operate over the relative wavelength range. Through quantitative tests, the terminal could be optimized base on the test results.

We developed an AFM-based new apparatus with a photomultiplier in order to measure the weak light emission from a single microparticle induced by applying a micro force and measured the emission intensity as a function of the applied micro force and speed. The emission intensity was approximately proportional to the speed of the applied micro- force and the square of the micro stress.

Inter-satellite laser communications attracted more and more attentions due to its excellent performances compared with the RF communications. But the test and verification of the communication terminals are very difficult because of the accuracy and aperture requirement. Large-aperture laser beam scanner was introduced to simulate the relative movement between satellites in the process of ground test for terminals. The scanner includes two same circular wedge prisms, which can scan an arbitrary position in a cone zone. The motivation of the assembly is to guarantee the accuracy of the scanner. Since the large-aperture and high-precision of the scanner, the assembly and test become a very troublesome problem. The test includes: (1) confirm the principal section of the wedge prisms; (2) test the optical quality of the wedge prisms; (3) confirm the scan range of the scanner; (5) test the scan accuracy of the scanner. The test results indicate the assembly process is reasonable. The scan range and accuracy can satisfy the requirement of the ground test of the inter-satellite laser communications terminals.