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Liquid crystal (LC) adaptive optics systems (AOS) can potentially be used in ground-based large aperture telescopes, because of their high spatial resolution, low cost and compact size. However, their disadvantages, such as low energy efficiency and slow response speed, still hinder their application. In this paper, we demonstrate solutions to these problems. With newly synthesized fast nematic LC material and using an overdriving technique, the response time of a LC wavefront corrector was reduced to 0.75 ms. Under an open-loop control scheme, a novel optical system was designed to improve the energy efficiency of LC AOS. With those problems resolved, a LC AOS was built for a 1.23-m telescope. This system has a disturbance rejection bandwidth of 80 Hz, and could fully use the energy of 400–900 nm wavebands. Observation results showed that the diffraction limit resolution imaging of the telescope could be obtained after correction, which indicates that the LC AOS is ready to be used in ground-based telescopes for visible waveband imaging.

This study proposes a simple method of designing a high-speed liquid crystal variable retarder (LCVR) with reflection mode. First, a series of simple formulas is provided for analysing the effects ...

A set of liquid crystal adaptive optics system for visible light is installed for 2-meter telescope in Changchun, China. To get higher resolution images after adaptive optics, phase diversity (PD) is applied. Two liquid crystal spatial light modulators were used for two polarized states of light, and they were also used for two channel correction of focused image and diversity image. Observations about star HD 29139 were performed on March 23, 2018. The results of the star with the PD show that the full width half maximum was decreased from about 10 pixels to 4 pixels, corresponding to angular resolution improved from 0.5” to 0.2”. The peak intensity was improved by 66.7% after the PD. The root mean square of the wavefront estimated using the PD agrees with the Strehl ratio of observed image after adaptive optics. The observed results indicate that the PD technique can significantly improve the image resolution after liquid crystal adaptive optics.

Two-photon light-sheet microscopy (TP-LSM) system performance is greatly degraded by specimen-induced aberrations in illumination path, which limit the field of view, axial resolution and excitation efficiency of the system. Adaptive optics (AO) is an effective method for attenuating these effects. For the design and evaluation of an AO system, a comprehensive analysis of the effects of aberrations is needed. In this paper, a TP-LSM system is simulated, and new indexes based on integral intensity are introduced for the evaluation of an aberrated light-sheet. Then, the influences of each Zernike mode and random aberrations on the illumination path of the TP-LSM system are investigated with a numerical simulation method. Results show that high-order aberrations have little effect on the axial resolution and excitation efficiency of the system and only low-order components require correction. The random aberrations varied in strength with the depth of the specimens, so the number of corrected Zernike modes is variable. A general formula is generated for the estimation of the number of modes that should be detected and corrected under different aberrations and different numerical aperture of the objective. The results can provide important guidance in the design and evaluation of AO units for TP-LSM systems.

The performance of free-space laser communication (FSLC) is greatly decreased by horizontal atmospheric turbulence. Adaptive optics is used to overcome horizontal turbulence. This study investigated the effect of the 3 dB bandwidth of an adaptive optics system (AOS) on FSLC performance by using power-in-bucket (PIB) method, which considers the effect of receiving aperture and then, can accurately evaluate of the effect of system bandwidth on the communication performance. A 9 km horizontal maritime link experiment was performed through adaptive correction to validate the theoretical analysis. Results indicate that the effect of system bandwidth can be accurately evaluated using PIB method. This work provides a basis for designing and evaluating AOSs for FSLC.

The isoplanatic patch of the human eye is a key parameter for the adaptive optics system (AOS) designed for retinal imaging. The field of view (FOV) usually sets to the same size as the isoplanatic patch to obtain high resolution images. However, it has only been measured at a specific wavelength. Here we investigate the wavelength dependence of this important parameter. An optical setup is initially designed and established in a laboratory to measure the isoplanatic patch at various wavelengths (655 nm, 730 nm and 808 nm). We established the Navarro wide-angle eye model in Zemax software to further validate our results, which suggested high consistency between the two. The isoplanatic patch as a function of wavelength was obtained within the range of visible to near-infrared, which can be expressed as: θ =0.0028 λ − 0 . 74 . This work is beneficial for the AOS design for retinal imaging.

We present a weighted method of wavefront reconstruction for multiple laser guide stars (LGS) adaptive optics (AO) system. Unlike simple averaging method in the traditional ground layer adaptive optics (GLAO), the weighted method generates different weighting factors according to LGSs’ different positions for the reconstructed wavefront from different LGSs. And then the target aberration to correct could be obtained with summation of these wavefronts multiplied by their correspondent weighting factors. Wide-field simulations are presented and analyzed. Experiments in the lab are conducted to validate the method. The weighted method is better than the average method especially near the center area of FOV. At center of FOV, the SR is improved by about 0.2 compared to the average method and the SR decreases with enlargement of FOV. For the first time, the weighted wavefront reconstruction method effectively decreases the reconstruction error in multi-LGSs AO system. The simulation and experimental result show that weighted method is also promising to improve the imaging resolution of LGS adaptive optics systems in astronomical observations.

In recent years, there has been increasing interest in optoelectronic applications of transparent conductive oxide (TCO) thin-film-based materials and devices fabricated using patterning techniques. Meanwhile, femtosecond laser processing is a convenient method that further improves the performance of TCO-based functional devices and expands their application prospects. In this study, we proposed a simple and effective strategy to determine the fluences required for laser processing TCOs. We investigated the modification of an indium tin oxide (ITO) film induced by a femtosecond laser (45/150 fs, 800 nm) at different pulse fluences. The results reveal that the laser modification of ITO films is highly dependent on the irradiated pulse fluences. Several distinct types of final micro/nanostructures were observed and may be attributed to superficial amorphization, spallation ablation, stress-assisted delamination, boiling evaporation, and phase explosion. The final micro/nanostructures were studied in detail using optical microscopy, scanning electron microscopy, transmission electron microscopy and a surface profiler. At a lower fluence above the melting but below the ablation threshold, a laterally parabolic amorphous layer profiled with maximum thicknesses of several tens of nanometers was quantitatively attained. At a higher fluence, stress-assisted delamination and superheated liquid-induced micro-honeycomb structures emerged. Furthermore, the electron and lattice temperature evolutions were also obtained using a two-temperature model to prove the ablation mechanism and ascertain the micro/nanostructure formation principle. The predicted surface temperatures confirmed film amorphization without ablation below 0.23 J/cm2. These results reveal the interaction mechanism between femtosecond laser pulse and ITO film including the competition between the free electron heating of intraband transition and the multiphoton absorption of the interband transition, which promotes the potential applications for femtosecond laser processing TCO films and other wide-band-gap semiconductors such as photodetectors, solar cells, UV-light-emitting diodes, and flat-panel displays.

Free-space laser communication (FSLC) has attracted wide attention and developed rapidly due to its high bandwidth and strong capability to resist interception and interference. However, communication performance is severely affected by atmospheric turbulence. In this paper we consider the end face of the coupling fiber and adopted power-in-the-bucket (PIB) as the evaluation criterion instead of the traditionally used coupling efficiency. The relationship between FSLC performance (PIB) and adaptive optics parameters (corrected Zernike modes number) is derived for the first time. We simulated and conducted an 8.9 km horizontal FSLC experiment to analyze the effects of corrected modes on communication performance. The simulation and experiment results consistently show that, for turbulence of r0 = 7.51 cm, it is sufficient to correct the first 30 modes. The bit error rate (BER) and the PIB reached values of about 10−7 and 70%, respectively. For r0 = 4.43 cm correction of the first 22 modes, yielded BER and PIB values of around 10−5 and 55%, respectively. For r0 = 1.7 cm, no matter how many Zernike modes are corrected, the BER and PIB values are about 10−3 and 20% respectively. This experiment and its results provide an important reference for corrected modes on communication performance under different turbulence strengths.

There are more than eight large aperture telescopes (larger than eight meters) equipped with adaptive optics system in the world until now. Due to the limitations such as the difficulties of increasing actuator number of deformable mirror, most of them work in the infrared waveband. A novel two-step high-resolution optical imaging approach is proposed by applying phase diversity (PD) technique to the open-loop liquid crystal adaptive optics system (LC AOS) for visible light high-resolution adaptive imaging. Considering the traditional PD is not suitable for LC AOS, the novel PD strategy is proposed which can reduce the wavefront estimating error caused by non-modulated light generated by liquid crystal spatial light modulator (LC SLM) and make the residual distortions after open-loop correction to be smaller. Moreover, the LC SLM can introduce any aberration which realizes the free selection of phase diversity. The estimating errors are greatly reduced in both simulations and experiments. The resolution of the reconstructed image is greatly improved on both subjective visual effect and the highest discernible space resolution. Such technique can be widely used in large aperture telescopes for astronomical observations such as terrestrial planets, quasars and also can be used in other applications related to wavefront correction.

Electron multiplying charge-coupled-device (EMCCD) applied in Shack–Hartmann wavefront sensor (S–H WFS) makes the wavefront sensing more efficient for adaptive optics (AO). However when the brightness of the observed target changes in large ranges in a few minutes, a fixed electron multiplying (EM) gain may not be optimum. Thus an auto-gain-control (AGC) method based on the spots image of the S–H WFS is proposed. The designed control value is the average value of the maximum signals of all the light spots in a frame. It has been demonstrated in the experiments that the control value is sensitive to the change of the target brightness, and is stable in the presence of detecting noises and turbulence influence. The goal value for control is predetermined based on the linear relation of the signal with the EM gain and the number of photons collected in sub-apertures. The conditions of the self-protection of the EMCCD are also considered for the goal value. Simulations and experiments indicate that the proposed control method is efficient, and keeps the sensing in a high SNR which reaches the upper SNR limit when sensing with EMCCD. The self-protection of the EMCCD is avoided during the whole sensing process.

The interaction matrix significantly affects the correction accuracy of wavefront correctors. For diffractive liquid crystal wavefront correctors (LCWFCs), the diffraction wavefront error must be taken into account to improve the accuracy of the interaction matrix. In this paper, a tunable Zernike polynomial coefficient method is demonstrated that decreases the effect of the diffraction wavefront error on the interaction matrix. Moreover, to eliminate the effect of the random error, a least squares method is combined with the tunable coefficient method. Experimental results show that, with the combined method, the error of the interaction matrix is decreased by a factor of 2.5 compared to that when the least squares method is used alone. Furthermore, an open loop adaptive correction experiment was performed and a considerable improvement of the image resolution was obtained by the novel method. Therefore, this method is very useful for liquid crystal adaptive optics systems to acquire the high correction accuracy.

Open loop liquid crystal adaptive optics (LC AO) has overcome the disadvantage of low energy efficiency after years of research, and its use is very promising in ground-based large aperture telescopes for visible band imaging. However, the low system bandwidth of open loop LC AO still limits its application. In order to solve this problem, we bring the concept of proportional-derivative control (which is widely used in closed loop systems) into open loop LC AO in this paper. Experiment results verified that the system −3 dB rejection bandwidth could improve from 75 Hz to 112 Hz when tip-tilt aberration is introduced, and the mean relative contrast ratio of imaging results could improve 80% when high-order aberrations are introduced. The proposed control method has significant meaning in promoting the application of open loop LC AO in ground-based large aperture telescopes for visible imaging.

The adaptive optics system (AOS) has been used to eliminate the effect of atmospheric turbulence for free-space optical communications. The AOSs are designed based on the statistical average performance of the turbulence. In reality, the amplitude of turbulence changes drastically, and the AOS cannot always detect and correct the aberrations appropriately. To prevent the amplitude of turbulence from exceeding the designed range of the Shack–Hartmann wavefront sensor (SH WFS), the combination of the wavefront sensorless and SH WFS methods is proposed to extend the detection range. First, the control scheme is demonstrated, and the numerical simulation is performed. Then, the validation experiments are performed with static and dynamic turbulence. Results show that the proposed method is valid and that the effective communication time is greatly lengthened.

We propose a voltage-tunable hyperbolic dispersion metamaterial (HDM) consisting of silver nanowires and nematic liquid crystals (NLCs). The metamaterial shows a novel electro-optic effect, in which the dispersion relation switches between elliptic and hyperbolic dispersions at the visible waveband with an external electric field. HDM functionality is analysed in detail based on the effective medium theory. 5CB NLC is chosen for the simulation, and tunability is achieved between 454 and 475 nm. The effects of filling ratio on tunability are also analysed. Tunable bandwidth widens from 21 to 45 nm with decreased filling ratio from 0.27 to 0.09. Finally, the effects of birefringence (Δn) are considered. Tunable bandwidth widens from 21 to 63 nm as Δn changes from 0.2 to 0.6. These novel tunable performances of the HDM can be applied to optical devices and optical systems.

An experimental analysis was conducted to investigate the fitting error of diffractive liquid crystal wavefront correctors (LCWFCs). First, an experiment was performed to validate the theoretical equations presented in our previous work Cao et al., 2009 [9] . The results showed an apparent discrepancy between the theoretical and measured results for the fitting error. This difference was examined and the influence of nonlinearities and rounding errors generated by the LCWFC was analyzed and discussed. Finally, the fitting error formula of the LCWFC was modified to obtain a more effective tool for the design of LCWFCs for atmospheric turbulence correction. These results will be useful for researchers who design liquid crystal adaptive optics systems for large-aperture ground-based telescopes.

This Letter presents an optical design method based on the Seidel aberration theory for dynamic refocus systems. The function of a dynamic refocus system is to increase the amount of return photons when a pulsed laser travels over an extended height range. In this study, the dynamic refocus system is a short focal image system. The aberrations of the dynamic refocus system are calculated individually. Aplanatic lenses are used to eliminate the main spherical aberration. A field lens is used to change the stop position in order to eliminate comas and astigmatism. The effectiveness of the initial design results are confirmed, and the designed dynamic refocus objective with an aperture of F-number 0.98 and a focal length of 14.325 mm is achieved. The total motion of the dynamic refocus mirror is approximately 216 μm at heights that ranged from 8 to 18 km. The optimum result shows that the dynamic refocus system is an ideal optical image system at each conjugating height with 10 km sample thicknesses.

We have analyzed and discussed a flat-top Brewster filter that works in full conical mounting. Results reveal that flat-top reflection band can be formed by merging double peaks that corresponded to guided modes with different polarization states. Merging is achieved by adjusting the incident angle in the design. When the proposed single-layer waveguide grating structure is irradiated with transverse magnetic (TM) polarized plane wave at the Brewster angle, the filter has a highly efficient flat-top reflection spectral response with central wavelength of 547 nm, bandwidth of 15.5 nm (R > 90%), and sideband reflectance of

An eigenmode method is proposed to estimate the correction performance of atmospheric turbulence based on a deformable mirror (DM). On the basis of the eigenmode, a formula that describes the relationship among residual error, eigenmode N, and turbulence strength D/r0 (D, telescope aperture, r 0 , atmospheric coherence length) is derived. The eigenmode and the Zernike polynomial methods are compared, too. An experiment is conducted, and results validate the theoretical equations. Hence, the correction performance of atmospheric turbulence may be estimated with the eigenmode method. This result is helpful for conveniently designing and evaluating the adaptive optics system used for turbulence correction.

We demonstrate stopband modulation in a corrugated parallel plate waveguide (PPWG) in terahertz (THz) frequency. Different from the traditional approaches to achieve narrow band-pass filter, a method based on the junction of two stopbands is provided. Two stopbands can come closer through adjustment of plate distance and controlling the grooves depth, which generate a narrowband transmission region. It is found that plate distance can control the interval of two stopbands. On optimization of plate distance, the filter can achieve a range of zero-sideband, high transmissivity (T=99.8%), narrow linewidth (5.8 GHz), and high-quality factor (Q ≈ 220). Furthermore, we also present the designs of tunable filter and modulate performance when liquid crystal (LC) is used as waveguide material. So, an excellent tunable filtering characteristic has been achieved. Finally, this work provides a new possibility for the designing of narrow band-pass filter devices.

Atmospheric turbulence seriously affects the quality of free-space laser communication. The Strehl ratio (SR) is used to evaluate the effect of atmospheric turbulence on the receiving energy of free-space laser communication systems. However, the SR method does not consider the area of the laser-receiving end face. In this study, the power-in-the-bucket (PIB) method is demonstrated to accurately evaluate the effect of turbulence on the receiving energy. A theoretical equation is first obtained to calculate PIB. Simulated and experimental validations are then performed to verify the effectiveness of the theoretical equation. This work may provide effective guidance for the design and evaluation of free-space laser communication systems.

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.

Zonal method is widely used to reconstruct the wave-front. Up to now, the iterative algorithms have been used to reconstruct the arbitrary shape wave-front with high reconstruction accuracy. However, it has the shortcomings of long time consumption. To reduce the time delay, a shaped based method is proposed by adding the shape information into the geometry matrix. The simulated and experimental results indicate that the reconstruction accuracy of proposed method is similar to that of the iterative LS-based method, but the computation time of our method is 3 times less than that of the iteration method. Consequently, the high accuracy and low time consumption are simultaneously achieved with the proposed method.

In order to detect the aberration from a wide field of view (FOV) on the retina with adaptive optics, we present a multiple-object Shack–Hartmann wavefront sensor (MOSHWFS) design. The simulated results indicate that the wavefront from our MOSHWFS can be reconstructed for multiple objects, and the measurement error can be less than λ/7 with an MOSHWFS with an FOV of 6.7°, for maximum eye aberration. The experimental result with two objects indicates that the measurement error can be less than λ/14, with the root mean square of the reference wavefront as 0.798λ and 0.895λ, respectively.

In this paper, we propose a roll angle measurement method with a large range based on the photoelectronic autocollimator. According to the corresponding relationship between the rotation position of the measured shaft and the spot position on the circular trajectory, the roll angle is calculated quickly and conveniently using a simple algorithm. Only a mirror, a coupler and a fine shaft are contained in the measurement system besides the photoelectronic autocollimator. Aiming at the terrible measurement error induced by the axis wobbly error, two measurement schemes are proposed, which are linking the fine precision shaft to the measured shaft for reducing the axis wobbly error and using the segment measurement to enlarge the radius of the circular trajectory. The experimental results show that the measurement error is decreased by ±0.38°. The roll angle error of the mechanism is ±0.14°, and the measurement precision is about ±2′. The proposed method can be widely used in the engineering fields.

The average orientation of a liquid crystal (LC) director to the grating formation, morphology, and switching properties of a holographic polymer-dispersed liquid crystal (HPDLC) grating was systematically investigated in this study. The grating possessed high diffraction efficiency and low scattering with the LC director being parallel to the grating vector. The scanning electron microscope confirmed the well-defined morphology with the LC director being parallel to the grating vector. The grating was easily switched when the LC director was perpendicular to the grating vector. Moreover, polarization excitation was performed to investigate the polarization dependence behavior of the HPDLC-distributed feedback (DFB) laser. The results confirmed that the HPDLC grating is suitable as a laser oscillation when the LC director is parallel to the grating vector. Finally, the tuning range was obtained for the HPDLC DFB laser by applying an external electric field. The tunability, ease of fabrication, and mass production make the HPDLC DFB lasers suitable as smart laser sources for spectroscopy and communication.

Organic solid-state tri-wavelength lasing was demonstrated from dye-doped holographic polymer-dispersed liquid crystal (HPDLC) distributed feedback (DFB) laser with semiconducting polymer poly[-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and laser dye [4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran] (DCM) by a one-step holography technique, which centered at 605.5 nm, 611.9 nm, and 671.1 nm. The temperature-dependence tuning range for the tri-wavelength dye-doped HPDLC DFB laser was as high as 8 nm. The lasing emission from the 9th order HPDLC DFB laser with MEH-PPV as active medium was also investigated, which showed excellent s-polarization characterization. The diffraction order is 9th and 8th for the dual-wavelength lasing with DCM as the active medium. The results of this work provide a method for constructing the compact and cost-effective all solid-state smart laser systems, which may find application in scientific and applied research where multi-wavelength radiation is required.

In this paper, we present a heuristic method to simplify the liquid crystal adaptive optics system (LCAOS) into a single-input-single-output (SISO) system, then build the dynamic model of LCAOS based on subspace identification. Results show that the identified model could accurately describe the dynamical behavior of LCAOS (97% match), with extremely low complexity. The wonderful features of low complexity and high precision, make the identified model highly beneficial for model based controller design, system analysis and dynamical behavior simulation of liquid crystal adaptive optics systems.

To process real-time wavefront signal in our liquid crystal adaptive optics system (LCAOS), a real-time wavefront processor (RTWP) with graphics processing unit (GPU) accelerator is developed. A series of parallel acceleration algorithm is implemented to reconstruct wavefront, compute gray map and process lookup table (LUT). Especially, an algorithm by using symmetry of Zernike polynomial is designed to compute gray map and it provides a speedup of 3.16. Finally, the total computing time in our RTWP is 109 μs and temporal bandwidth in our LCAOS is 45 Hz; it is shown that our RTWP has the ability to real time process wavefront signal in our LCAOS.

Almost all the deformable mirror (DM) based adaptive optics systems (AOSs) used on large aperture telescopes work at the infrared waveband due to the limitation of the number of actuators. To extend the imaging waveband to the visible, we propose a DM and Liquid crystal wavefront corrector (DM/LCWFC) combination AOS. The LCWFC is used to correct the high frequency aberration corresponding to the visible waveband and the aberrations of the infrared are corrected by the DM. The calculated results show that, to a 10 m telescope, DM/LCWFC AOS which contains a 1538 actuators DM and a 404 × 404 pixels LCWFC is equivalent to a DM based AOS with 4057 actuators. It indicates that the DM/LCWFC AOS is possible to work from visible to infrared for larger aperture telescopes. The simulations and laboratory experiment are performed for a 2 m telescope. The experimental results show that, after correction, near diffraction limited resolution USAF target images are obtained at the wavebands of 0.7-0.9 μm, 0.9-1.5 μm and 1.5-1.7 μm respectively. Therefore, the DM/LCWFC AOS may be used to extend imaging waveband of larger aperture telescope to the visible. It is very appropriate for the observation of spatial objects and the scientific research in astronomy.

Self-aligned liquid crystals containing randomly dispersed nanoparticles are proposed to realise hyperbolic metamaterials at visible spectrum. Opposite signs for anisotropic permittivity tensors originated from the scattering of metallic nanoparticles in liquid crystals are achieved. Tunable effective wavelength properties are also demonstrated by choosing dielectric-metal core-shell nanoparticles.

The optimal cell gap of nematic liquid–crystal wavefront corrector (LCWFC) is proved theoretically by numerical computation of the Ericksen–Leslie equation based on finite differences and confirmed experimentally. The numerical results of optimizing cell gap overcome the constraints of many approximations e.g. the small angle approximation and agree much better with the experimental data than those of analytical solution. Therefore, this method supplies a useful tool to achieve the optimal cell gap of a nematic LCWFC with high precision. Together with high birefringence and low rotational viscosity liquid crystal (LC) material effect, a nematic LCWFC with response time of sub-millisecond can be achieved in the visible spectral region.

Ultrafast switchable wide angle negative refraction in a novel dual-frequency liquid crystal mixture is demonstrated experimentally. Laterally fluorinated isothiocyanato phenyl-tolane liquid crystal compound is doped into Merck MLC-2048 to acquire the high birefringence dual-frequency liquid crystal. The maximum negative refraction angle achieved is about 12° and the switching time is only 25 ms for a 40-μm cell which is two orders faster than switchable negative refraction achieved before in nematic liquid crystals. Such properties provide a feasible approach to design negative refraction devices based on liquid crystals.

Reverse hexagonal lyotropic liquid crystal template is proposed to achieve optical hyperbolic metamaterial composed of silver nanowire arrays. All angle negative refraction is obtained during the wide wavelength range from near-infrared to visible light. Hyperbolic metamaterial incorporated with gain dye molecules is calculated to show the possibility of eliminating energy losses and the transmittance can be enhanced in the selected wavelength range. 2013 Published by Elsevier B.V.

Negative refraction (NR) is a promising technique that provides an opportunity to manipulate beam behaviour. We have demonstrated experimentally the controllable NR with large refraction angle at visible wavelength in the novel high birefringence (Δn) liquid crystals. When the Δn of liquid crystal reaches 0.42, the NR angle and critical incident angle reach –14° and 23.2°, respectively, which are much larger than those achieved before by other liquid crystals. By applying the electric field, we control the switch from NR to positive.

Atmospheric turbulence deteriorates the image quality of astronomical objects and limits the spatial resolution of large aperture optical telescopes. Adaptive optics (AO) corrects the aberrations induced by atmospheric turbulence in real time, which concentrates the incident light and enables the telescope to achieve the diffraction-limited resolution on-axis or over an extended field-of-view (FoV). In this paper, we present the transfer function of our open-loop liquid crystal adaptive optics system. Based on the transfer function, we calculated the bandwidth of our nematic LC AO system: -3dB bandwidths are about 57.0 Hz and 82.4Hz for high order aberration and tilt-tip compensation control, respectively. Through further improvements on LC material, electronic interface port, shortened data processing time and optimized control, we will get a better LC AO system. 2013 IFAC.

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.

A novel liquid crystal wave front corrector (LCWFC) based open loop adaptive optics testbed for nonpolarized light was introduced in this paper. A polarizing beam splitter (PBS) was used behind the LCWFC to divide the reflected nonpolarized light into two orthogonal polarized lights with and without the modulation effect for high resolution imaging and aberration detection respectively. The alignment direction of LC molecules was parallel to the polarization direction of the light PBS reflected. This configuration was simple and easy for construction. It avoided the energy loss due to the use of polarizer for conventional LCWFC based closed loop adaptive optics system. Furthermore, it could be switched into closed loop configuration very easily, which was useful for quantitative system performance evaluation. The detailed construction and operation was reported in Section 2. In Section 3, this testbed was deployed at the coude focus of the 2.16 m telescope at the Xinglong Station of the Beijing Astronomical Observatory. The observation of star Arcturus was done. The Full Width Half Maximum (FWHM) resolution was improved from 2.12″ to 0.64″ successfully.

This paper reports 65° beam steering using a slanted holographic polymer dispersed liquid crystal (HPDLC) grating with the slanted angle at 16.6°. The HPDLC grating was fabricated using a convenient one-step holographic technique. The SEM image confirmed the slanted grating configuration. The grating showed anisotropic diffraction characterizations. The diffraction efficiency for the p-polarized light was as high as 80%. The Bragg angle deviation diffraction and the transmittance properties of the slanted HPDLC grating were investigated. The slanted HPDLC grating can be switched with an external electric field. The results in this work provide an optional method to fabricate a slanted grating configuration. The slanted HPDLC grating can be used in the field where polarized beam steering is required.

A method to improve the loop frequency of liquid crystal adaptive optics systems (LC AOSs) was investigated. Based on open-loop control, a concurrent control scheme was proposed and the correction frequency of the LC AOS was increased from 85 Hz to 212 Hz. A simulated correction analysis illustrates that the distortion rejection ability of our LC AOS was improved with −1.1 dB by using the concurrent control technique. A 500 m horizontal turbulence correction experiment was done to validate our considerations. Firstly, 500 m horizontal turbulence was measured and its Greenwood frequency and atmospheric coherence length is 31.5 Hz and 4–5 cm, respectively. Then, 500 m horizontal turbulence was corrected in real time by using consecutive and concurrent control methods. The corrected results indicate that the resolution and contrast of the image was significantly improved by the concurrent control method. These results show that the concurrent control method can be used for LC AOSs to improve the correction frequency.

The effect of twisted alignment on the phase modulation of a liquid crystal wave‐front corrector was investigated. First, the effect of twisted alignment is discussed in terms of the modulation principle of the liquid crystal molecule. Only partial incident light can be modulated because of the effect of the twisted alignment. Other unmodulated light will affect the correction accuracy and the resolution of the image. The blazed grating method is proposed to solve this problem. Adaptive correction was performed without the blazed grating method and the correction results are poor. A similar adaptive correction experiment was performed with the blazed grating method and a better correction result is obtained. The residual averaged wave‐front errors are PV = 0.101λ and RMS = 0.015λ and a resolvable image is obtained.

The liquid crystal spatial light modulator (LC SLM) is very suitable for wavefront correction and optical testing and can produce a wavefront with large phase change and high accuracy. The LC SLM is composed of thousands of pixels and the pixel size and shape have effects on the diffractive characteristics of the LC SLM. This paper investigates the pixel effect on the phase of the wavefront with the scalar diffractive theory. The results show that the maximum optical path difference modulation is 41 μm to produce the paraboloid wavefront with the peak to valley accuracy better than λ/10. Effects of the mismatch between the pixel and the period, and black matrix on the diffraction efficiency of the LC SLM are also analysed with the Fresnel phase lens model. The ability of the LC SLM is discussed for optical testing and wavefront correction based on the calculated results. It shows that the LC SLM can be used as a wavefront corrector and a compensator.

The durability of a liquid crystal (LC) modulator for use with a high power laser is measured at a wavelength of 808 nm. It is shown that the LC modulator can withstand a laser power density of 133 W cm−2. For a laser power density greater than 133 W cm−2 the phase transition is caused by the absorption of the material. In order to improve the durability, the absorption of glass, polyimide (PI), indium tin oxide and LC were measured. Results indicated that the phase transition of the nematic LC is mainly caused by the absorption of glass and PI. These results can be used for a LC modulator with nematic LC material, and it is important to use an LC modulator in optical systems with high power lasers.

We experimentally demonstrated a metamaterial composed of hexagonal arrays of silver nanowires that exhibits hyperbolic dispersion and negative refraction in the entire visual wavelength range. The nanowires with extremely small size of 10 nm diameter and 15 nm center-to-center distance were fabricated using the reverse hexagonal liquid crystalline phase template containing AgNO(3) solution. Through the experiments of angle dependent reflectance for s-polarization and p-polarization, the dielectric constants were measured in several wavelengths. Calculations and experiments both show hyperbolic dispersion relations from 370 nm to 750 nm which indicates the presence of all-angle negative refraction. For all the experimental wavelengths, the permittivities of the material are in good agreement with the theoretical calculations.

Temperature effect on the diffraction efficiency of the liquid crystal spatial light modulator is investigated. The birefringence of the liquid crystal as functions of the temperature is measured with and without the power supply. It is shown that the birefringence reduces while the temperature increases. And the change magnitude of the birefringence has an exponential decay relation with the applied voltage for different temperature intervals. The scalar diffractive theory is used to analyze this effect on the diffraction efficiency. It indicates that the diffraction efficiency decreases from 98.7% to 27.2% while the temperature increases from 10 to 90 °C for 16 quantified levels. At last, temperature effect on its applications in optical testing and wavefront correction is discussed. It indicates that it has almost no effect on optical testing, but has an important effect on wavefront correction. And two solutions are given to eliminate this effect.

We extended Berenger’s split-field perfectly matched layer (PML) absorbing boundary conditions (ABCs) to cylindrical coordinates for the use in body-of-revolution finite-difference time-domain (BOR FDTD) method that is suitable for the analysis of axially symmetric subwavelength diffractive optical elements (SWDOE). As application, we use our algorithm in the analysis of a multilevel microlens and its counterpart of binary SWDOE. Numerical results illustrate the efficiency of our PML ABCs.

This paper reports the ultra-broad 149.1 nm lasing emission from 573.2 to 722.3 nm using a simple [4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran] (DCM)-doped holographic polymer-dispersed liquid crystal (HPDLC) grating quasi-waveguide configuration by varying the grating period. The lasing emission beams show s-polarization property. The quasi-waveguide structure, which contained the cover glass, the DCM-doped HPDLC grating, the semiconducting polymer film poly[-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV), and the substrate were confirmed to decrease lasing threshold and broaden lasing wavelength. The operational lifetime of the device is 240 000 pulses, which corresponds to an overall laser duration of more than 6 h at a repetition rate of 10 Hz. In addition, the dual-wavelength lasing range from the 8th and 9th order is over 40 nm. The electrical tunability of the dual-wavelength lasing emission is over 1 nm. The experimental results facilitated the decreased lasing threshold and broadened lasing wavelength range of organic solid-state lasers.

Microscopy is an essential means for the Life Sciences research under the sub-micron scale. Because of the advantage in specific marking, dynamic indication, high contrast and non-destructive style, the biological fluorescence microscopy plays an important role in in-vivo imaging. When propagating in the non-transparent, non-homogeneous, anisotropic biological tissue, the excitation and emission light both will be distorted by refraction, scattering, absorption and other unknown effects and the point spread function (PSF) in each path will be consequently degraded. In order to improve the spatial resolution of fluorescence microscopy and increase the imaging depth, the adaptive optical technology has been employed in the microscope system to detect and correct the above aberrations in real-time. In this paper, aberrations in fluorescence microscope have been specified in different sources, both aberration sensing and correction methods have been introduced, and the characteristics of aberration correction in different imaging modes of fluorescence microscopy have been summarized. Then the latest applications of adaptive optics in different types of fluorescence microscopy have been discussed here and the further development trend is concluded.

Adaptive optics is used to compensate the atmospheric turbulence aberration for diffractive limit images, which makes the angular resolution of large aperture telescope not limited by the seeing or atmospheric coherence length. The continuous improvements of wavefront sensing, correctors and enlarged FOV for adaptive optics accelerate the development of astronomy. The main adaptive optics techniques include classical FOV and high resolution astronomical observation, extro-planet observation and solar observations and so on. And they have different technique requirements for adaptive optics. In the paper, we give some summarization and expectation of the advancement in the above three fields, especially in some new elemental techniques in detail, which will be helpful for our national adaptive optics development in large aperture telescopes.

The resolution of ground-based large aperture telescopes is decreased severely due to the effect of atmospheric turbulence. Adaptive optics systems (AOSs) have been widely used to overcome this, and low-order aberrations [tip–tilt (TT)] are corrected by a TT mirror. In the tip/tilt TT correction loop, the time delay affects the correction performance significantly and a predicted signal compensation method (PSCM) has been used to reduce its effect. However, the performance of the PSCM is reduced obviously due to the low identification accuracy of the TT AOS model. In this paper, a nonlinear least squares subspace identification (NLSSI) method is presented to obtain a high-precision model of the TT AOS. The system is identified with the subspace method first, and then the identified parameters are modified in the frequency domain. By using this method, a TT correction system is identified. Compared with the subspace identification method, the identification accuracies of the time domain and frequency response are increased 2 and 5 times, respectively, with the NLSSI method. Furthermore, with the NLSSI method, the −3 dB error rejection bandwidth is increased from 69 to 76 Hz. Finally, an adaptive correction experiment is performed on a 1.23 m telescope, and the astronomical observation results show that the correction accuracy is increased to 1.5 times with the NLSSI method. Moreover, the peak intensity of the image is improved by 11% with the NLSSI method. This work is very helpful to improve the TT correction accuracy of AOS, particularly for extreme adaptive optics and faint target observation.