Xu Huanyu

Bio: Xu Huanyu is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Wavefront & Adaptive optics. The author has an hindex of 5, co-authored 36 publications receiving 134 citations.

Performance analysis of an adaptive optics system for free-space optics communication through atmospheric turbulence.

Abstract: The performance of free-space optics communication (FSOC) is greatly degraded by atmospheric turbulence. Adaptive optics (AO) is an effective method for attenuating the influence. In this paper, the influence of the spatial and temporal characteristics of turbulence on the performance of AO in a FSOC system is investigated. Based on the Greenwood frequency (GF) and the ratio of receiver aperture diameter to atmospheric coherent length (D/r 0 ), the relationship between FSOC performance (CE) and AO parameters (corrected Zernike modes number and bandwidth) is derived for the first time. Then, simulations and experiments are conducted to analyze the influence of AO parameters on FSOC performance under different GF and D/r 0 . The simulation and experimental results show that, for common turbulence conditions, the number of corrected Zernike modes can be fixed at 35 and the bandwidth of the AO system should be larger than the GF. Measurements of the bit error rate (BER) for moderate turbulence conditions (D/r 0 = 10, f G = 60 Hz) show that when the bandwidth is two times that of GF, the average BER is decreased by two orders of magnitude compared with f G /f 3dB = 1. These results and conclusions can provide important guidance in the design of an AO system for FSOC.

Electrooptical properties of new type fluorinated phenyl-tolane isothiocyanate liquid crystal compounds

Abstract: A series of 4ʹ-(4-alkyl-phenyl)-2ʹ,6ʹ-difluorotolane isothiocyanate liquid crystal (LC) compounds were synthesised, and their phase transitions and electrooptical properties were investigated. These compounds exhibit high birefringence, about 0.47–0.52. As the number of carbon atoms in the alkyl chains increases, these LC compounds can exhibit smectic phases. When these LCs were mixed into the commercial LCs, the birefringence values of LC mixtures become higher than pure commercial LCs, and the visco-elastic coefficients of five LC mixtures are very close to each other at every test temperature. The results of response properties indicate that the compounds with a tri-fluorine substitution and n-propyl end group possess better response performance than the others. These LC compounds are particularly attractive for achieving fast response times in LC optic devices.

Time delay compensation method for tip–tilt control in adaptive optics system

Abstract: The time delay engendered by wavefront sampling and data processing inevitability exists in almost all the wavefront sensor (WFS) based adaptive optics (AO) systems. Also, when WFS is used for tip-tilt aberration detection, the time delay significantly reduces the tip-tilt correction performance of the AO system. In this paper, we focus on researching time delay in a tip-tilt (TT) control system and introduce a predicted signal compensation method (PSCM) to compensate the time delay by modifying the WFS detected signals. Based on a precise model of a TT dynamic control system, the detection delay of TT corrections included in a WFS detected signal can be compensated. Experiments are conducted in the lab: the pure integrator (I), proportional and integral (PI) wavefront TT controllers, and these controllers with PSCM are compared to test the efficiency of the PSCM for TT corrections. For the PI controller, the rejection bandwidth increases from 52 to 62 Hz by using PCSM; meanwhile, the open-loop phase margin increases from 45 to 60 deg. In addition, astronomical observation results are also given based on the PI wavefront TT controller. The PSCM improves the Strehl ratio by a factor of 1.3. The new method is proven to improve the AO system closed-loop performance not only for increasing the closed-loop rejection bandwidth but also in favor of the error attenuation at low frequency. Furthermore, the method does not introduce more noise to the system.

Rotation shaft rotation angle measuring method restraining shafting dip angle rotation error

Abstract: The invention belongs to the field of optical measurement, and relates to a rotation shaft rotation angle measuring method restraining shafting dip angle rotation error. The measuring principle system of the invention is shown in figure 1. A rotation shaft (2) with an optical wedge (5) is placed between an auto-collimator (1) and a mirror (3). Due to refraction of the optical wedge (5), a reflected light beam, which is generated after the light beam emitted by the auto-collimator (1) passes through the mirror (3) and is reflected back, forms a deflection angle Beta with the outgoing light beam, returns to the auto-collimator (1) and converges into a light spot image; when the rotation shaft (2) and the optical wedge (5) rotate as a whole, the reflected light beam rotates about the axis of the rotation shaft (2), and the light spot image in the auto-collimator (1) moves along a circular trajectory; and a computer (4) records the coordinates of the center of mass of the light spot image on the circumference, fits out the coordinates of the center of the trajectory circle, specifies the start point A and the end point B on the circumference, and works out the corresponding center-of-circle opening angle based on the coordinate values of A and B, wherein the angle is the rotation angle of the rotation shaft (2) from A to B needing to be measured. In the invention, the shafting dip angle rotation error has almost no effect on the measurement accuracy of rotation angle.

Analysis and reduction of errors caused by Poisson noise for phase diversity technique.

Abstract: An effective method for reducing the sensitivity of phase diversity (PD) technique to Poisson noise is proposed. The denoising algorithm based on blocking-matching and 3D filtering is first introduced in the wavefront sensing field as a preprocessing stage. Then, the PD technique is applied to the denoised images. Results of the numerical simulations and experiments demonstrate that our approach is better than the traditional PD technique in terms of both the root-mean-square error (RMSE) of phase estimates and the structural similarity index metrics (SSIM). The RMSEs of phase estimates on synthetic data are decreased by approximately 40% across noise levels within the range of 58.7-18.8 dB in terms of peak signal-to-noise ratio (PSNR). Meanwhile, the overall decline range of SSIM is significantly decreased from 49% to 9%. The experiment and simulation results are in good agreement. The approach may be widely used in various domains, such as the measurements of intrinsic aberrations in optical systems and compensations for atmospheric turbulence.

Mutational drivers of cancer cell migration and invasion.

Abstract: Genomic instability and mutations underlie the hallmarks of cancer-genetic alterations determine cancer cell fate by affecting cell proliferation, apoptosis and immune response, and increasing data show that mutations are involved in metastasis, a crucial event in cancer progression and a life-threatening problem in cancer patients. Invasion is the first step in the metastatic cascade, when tumour cells acquire the ability to move, penetrate into the surrounding tissue and enter lymphatic and blood vessels in order to disseminate. A role for genetic alterations in invasion is not universally accepted, with sceptics arguing that cellular motility is related only to external factors such as hypoxia, chemoattractants and the rigidity of the extracellular matrix. However, increasing evidence shows that mutations might trigger and accelerate the migration and invasion of different types of cancer cells. In this review, we summarise data from published literature on the effect of chromosomal instability and genetic mutations on cancer cell migration and invasion.

Performance analysis of an adaptive optics system for free-space optics communication through atmospheric turbulence.

Abstract: The performance of free-space optics communication (FSOC) is greatly degraded by atmospheric turbulence. Adaptive optics (AO) is an effective method for attenuating the influence. In this paper, the influence of the spatial and temporal characteristics of turbulence on the performance of AO in a FSOC system is investigated. Based on the Greenwood frequency (GF) and the ratio of receiver aperture diameter to atmospheric coherent length (D/r 0 ), the relationship between FSOC performance (CE) and AO parameters (corrected Zernike modes number and bandwidth) is derived for the first time. Then, simulations and experiments are conducted to analyze the influence of AO parameters on FSOC performance under different GF and D/r 0 . The simulation and experimental results show that, for common turbulence conditions, the number of corrected Zernike modes can be fixed at 35 and the bandwidth of the AO system should be larger than the GF. Measurements of the bit error rate (BER) for moderate turbulence conditions (D/r 0 = 10, f G = 60 Hz) show that when the bandwidth is two times that of GF, the average BER is decreased by two orders of magnitude compared with f G /f 3dB = 1. These results and conclusions can provide important guidance in the design of an AO system for FSOC.

Lateral substituent effects on UV stability of high-birefringence liquid crystals with the diaryl-diacetylene core: DFT/TD-DFT study

Abstract: To study the effect of the lateral substituents on the UV stability of high birefringence liquid crystals (LCs), computational chemistry was used to examine a series of high birefringence LCs based on a diphenyl-diacetylene (DPDA) central core, thiophene segments as elongated π-conjugated units and four electron-withdrawing groups (-F, -CF3, -OCF3, -CN) as lateral substituents. In the present study, geometry optimisations have been performed using the DFT/B3LYP/6-311G (d, p) method. Out of a series of functional and basis sets examined, the functional ωB97X-D and basis set 6-31G (d, p) are most successful in predicting charge transfer absorption. The theoretical study indicates that the enhancement of UV stability is related with the types, numbers and positions of the lateral substituents. The calculated results indicate that the electron-withdrawing groups can shorten triple bond length, decrease energy gap value and increase the absorption maxima of the high-Δn LCs, which is beneficial for good...

Photodynamic therapy, priming and optical imaging: Potential co-conspirators in treatment design and optimization — a Thomas Dougherty Award for Excellence in PDT paper

Abstract: Photodynamic therapy is a photochemistry-based approach, approved for the treatment of several malignant and non-malignant pathologies. It relies on the use of a non-toxic, light activatable chemic...

Design of new super-high birefringent isothiocyanato bistolanes – synthesis and properties

Abstract: We report the synthesis of new laterally ethyl-substituted high birefringent phenylethynyltolane liquid crystals with alkylsulphanyl chain and isothiocyanate terminal group. The thermal and optical properties such as birefringence are measured and discussed based on their molecular structures. The compounds exhibit birefringence (Δn) in the range of 0.63–0.75 and are expected to be excellent components of high birefringent nematic mixtures for various applications.