Dynamic Diffractive Optical Elements Research Articles

Vector Differential Interference Contrast Microscopy Based on a 3-in-1 Phase Mask through a Dynamic Diffractive Optical Element

Vector Differential Interference Contrast Microscopy Based on a 3-in-1 Phase Mask through a Dynamic Diffractive Optical Element

Programmable focused laser differential interferometer with a spatial light modulator as a dynamic diffractive optical element.

A spatial light modulator (SLM) is incorporated into a focused laser differential interferometer (FLDI) to generate a nonlinear array of beams, and this setup is used to measure the power spectral density of a Mach-1.5, underexpanded jet of air. The results are compared with measurements from a 1-point FLDI to assess the feasibility of using SLMs in FLDI to serve as dynamic diffractive elements for generating beam arrays of any shape. The spectra comparison illustrates that spatial light modulated-FLDI (SLM-FLDI) detects similar spectral profiles to that of 1-point FLDI, especially dominant frequencies in the jet. SLM-FLDI could provide a useful expansion of FLDI capabilities.

Electro-active metaobjective from metalenses-on-demand

Switchable metasurfaces can actively control the functionality of integrated metadevices with high efficiency and on ultra-small length scales. Such metadevices include active lenses, dynamic diffractive optical elements, or switchable holograms. Especially, for applications in emerging technologies such as AR (augmented reality) and VR (virtual reality) devices, sophisticated metaoptics with unique functionalities are crucially important. In particular, metaoptics which can be switched electrically on or off will allow to change the routing, focusing, or functionality in general of miniaturized optical components on demand. Here, we demonstrate metalenses-on-demand made from metallic polymer plasmonic nanoantennas which are electrically switchable at CMOS (complementary metal-oxide-semiconductor) compatible voltages of ±1 V. The nanoantennas exhibit plasmonic resonances which can be reversibly switched ON and OFF via the applied voltage, utilizing the optical metal-to-insulator transition of the metallic polymer. Ultimately, we realize an electro-active non-volatile multi-functional metaobjective composed of two metalenses, whose unique optical states can be set on demand. Overall, our work opens up the possibility for a new level of electro-optical elements for ultra-compact photonic integration.

Optimal trap velocity in a dynamic holographic optical trap using a nematic liquid crystal spatial light modulator

A dynamic holographic optical trap uses a dynamic diffractive optical element such as a liquid crystal spatial light modulator to realize one or more optical traps with independent controls. Such holographic optical traps provide a number of flexibilities and conveniences useful in various applications. One key requirement for such a trap is the ability to move the trapped microscopic object from one point to the other with the optimal velocity. In this paper we develop a nematic liquid crystal spatial light modulator based holographic optical trap and experimentally investigate the optimal velocity feasible for trapped beads of different sizes, in such a trap. Our results show that the achievable velocity of the trapped bead is a function of size of the bead, step size, interval between two steps and power carried by the laser beam. We observe that the refresh rate of a nematic liquid crystal spatial light modulator is sufficient to achieve an optimal velocity approaching the theoretical limit in the respective holographic trap for beads with radius larger than the wavelength of light.

Holographic Display System to Suppress Speckle Noise Based on Beam Shaping

In this paper, a holographic system to suppress the speckle noise is proposed. Two spatial light modulators (SLMs) are used in the system, one of which is used for beam shaping, and the other is used for reproducing the image. By calculating the effective viewing angle of the reconstructed image, the effective hologram and the effective region of the SLM are calculated accordingly. Then, the size of the diffractive optical element (DOE) is calculated accordingly. The dynamic DOEs and effective hologram are loaded on the effective regions of the two SLMs, respectively, while the wasted areas of the two SLMs are performed with zero-padded operations. When the laser passes through the first SLM, the light can be modulated by the effective DOEs. When the modulated beam illuminates the second SLM which is loaded with the effective hologram, the image is reconstructed with better quality and lower speckle noise. Moreover, the calculation time of the hologram is reduced. Experiments indicate the validity of the proposed system.

Spatial light modulator phase calibration based on spatial mode projection.

Spatial light modulators (SLMs), which are devices used to manipulate the phase of an incident wave front, are prolific in fields such as optical trapping, dynamic diffractive optical elements, and display technology. Of the many challenges inherent to using SLMs, one of the most ubiquitous is the calibration of the device's phase-shifting mechanism. In this paper, we present a new SLM calibration method based on spatial mode projection. We also implement a data processing technique to our data to generate accurate look-up tables from our calibration curves. We then evaluate the success of our method by propagating Laguerre-Gauss beams with computer-generated holograms. Our results show that the qualitative analysis of modes propagated using the SLM is a viable method of assessing performance. On the whole, we show that spatial mode projection provides clear performance improvements in the SLM's phase-modulating capabilities.

Invisible Visual Cryptography**Supported by the National Natural Science Foundation of China under Grant No 61575197, the K. C. Wong Education Foundation, the Fusion Foundation of Research and Education of Chinese Academy of Sciences, and the Youth Innovation Promotion Association of Chinese Academy of Sciences under Grant No 2017489.

We propose to realize visual cryptography in an indirect way with the help of diffractive optics, the pure-amplitude keys being substituted with the phase-only keys that are invisible for common-used intensity detectors, leading to the significantly enhanced security and improved usability for practice. Three typical realizations are provided by using static or dynamic diffractive optical elements, and the new concept of invisible visual cryptography (IVC) may be established. This concept is demonstrated by a compact opto-electronic system with only one spatial light modulator within time-delayed exposure, maintaining the fast speed of decryption and no requirement to the calculation of decryption in conventional visual cryptography. Further, IVC shows the immunity to noises and good information capacity, which is partly inherited from diffractive optics. IVC might suggest a new strategy for visual cryptography with the respective of diverse realizations, such as opto-electronic or even bio-chemical or other methods.

Measurement of characteristics and phase modulation accuracy increase of LC SLM "HoloEye PLUTO VIS"

Phase liquid crystal spatial light modulators (LC SLM) are actively integrated in various optical systems for dynamic diffractive optical elements imaging. To achieve the best performance, high stability and linearity of phase modulation is required. This article presents results of measurement of characteristics and phase modulation accuracy increase of state of the art LC SLM with HD resolution "HoloEye PLUTO VIS".

Diffractive generalized phase contrast for adaptive phase imaging and optical security

We analyze the properties of Generalized Phase Contrast (GPC) when the input phase modulation is implemented using diffractive gratings. In GPC applications for patterned illumination, the use of a dynamic diffractive optical element for encoding the GPC input phase allows for on-the-fly optimization of the input aperture parameters according to desired output characteristics. For wavefront sensing, the achieved aperture control opens a new degree of freedom for improving the accuracy of quantitative phase imaging. Diffractive GPC input modulation also fits well with grating-based optical security applications and can be used to create phase-based information channels for enhanced information security.

Design of an off-axis see-through display based on a dynamic phase correction approach

The design and the analysis of an off-axis (50°) diffractive imaging optical system is presented in this paper. A 10°x15° field of view is considered. The optical system is composed of two diffractive optical elements. A static diffractive optical element having a frozen phase transfer function is used to perform a virtual point in the considered field of view. A dynamic diffractive optical element having an adapted calculated phase transfer function is used to compensate for aberrations of the static element. Using a sequential creation of virtual image points and considering human eye characteristics, it is shown that a nine points virtual image can be obtained with current technology. Moreover, it is presented that aberrations can be compensated whatever the position of the virtual point in the 10°x15° field of view. Finally, using rigorous coupled wave analysis, it is shown that an average diffraction efficiency of 79% can be reached across the considered field of view with a standard deviation of nearly 5%.

Optical Eigenmodes; exploiting the quadratic nature of the light-matter interaction

For over a century diffraction theory has been thought to limit the resolution of focusing and imaging in the optical domain. The size of the smallest spot achievable is inversely proportional to the range of spatial wavevectors available. Here, we show that it is possible to locally beat the diffraction limit at the expense of efficiency. The method is based on the linearity of Maxwell's equations and that the interaction between light and its surroundings may be considered quadratic in nature with respect to the electromagnetic fields. We represent the intensity and spot size as a quadratic measure with associated eigenmodes. Using a dynamic diffractive optical element, we demonstrate optical focussing to an area 4 times smaller than the diffraction limit. The generic method may be applied to numerous physical phenomena relating to linear and measurable properties of the electromagnetic field that can be expressed in a quadratic form.

Speckle suppression in projection displays by using a motionless changing diffuser

Speckle suppression in projection displays with a laser light source can be achieved by imaging a changing diffuser with random phase cells onto the screen. Theoretical expressions for the speckle contrast in this method have been earlier obtained in the case when different realizations of the phase diffuser produced statistically independent patterns of the light field on the screen. In the present paper, these expressions are generalized in the case when different realizations of the phase diffuser produce partly correlated speckle patterns. The possible structure of a motionless changing diffuser is presented. It includes a dynamic diffractive optical element (DDOE) and a light homogenizer. The DDOE can be based on the electrically controlled spatial light modulator (SLM) with a deformable polymer layer. This type of SLM can handle high light power and, therefore, can be used in projection displays with powerful laser beams.

An SLM-based Shack–Hartmann wavefront sensor for aberration correction in opticaltweezers

Holographic optical tweezers allow the creation of multiple optical traps in 3Dconfigurations through the use of dynamic diffractive optical elements called spatial lightmodulators (SLMs). We show that, in addition to controlling traps, the SLM in aholographic tweezers system can be both the principal element of a wavefront sensor andthe corrective element in a closed-loop adaptive optics system. This means that aberrationsin such systems can be estimated and corrected without altering the experimental setup.Aberrations are estimated using the Shack–Hartmann method, where an array of spots isprojected into the sample plane and the distortion of this array is used to recoverthe aberration. The system can recover aberrations of up to ten wavelengthspeak–peak, and is sensitive to aberrations much smaller than a wavelength. Thespot pattern could also be analysed by eye, as a tool for aligning the system.

Application of dynamic diffractive optics for enhanced femtosecond laser based cell transfection

We demonstrate the advantages of a dynamic diffractive optical element, namely a spatial light modulator (SLM) for the controlled and enhanced optoinjection and phototransfection of mammalian cells with a femtosecond light source. The SLM provides full control over the lateral and axial positioning of the beam with sub-micron precision. Fast beam translation enables time-sequenced irradiation, which is shown to enhance the optoinjection efficiency and alleviate the problem of exact beam positioning on the cell membrane. We show that irradiation in three axial positions doubles the number of viably optoinjected cells when compared with a single dose. The presented system also enables untargeted raster scan irradiation which provides a higher throughput transfection of adherent cells at the rate of 1 cell per second. Additionally, fluorescent imaging is used to demonstrate cell selective two-step gene therapy.

Dynamic calibration for improving the speed of a parallel-aligned liquid-crystal-on-silicon display

The speed of most parallel-aligned liquid-crystal-on-silicon (LCoS) spatial light modulators (SLMs) is limited to the video rate of their drivers, which is a limitation for high-speed applications. However, the LCoS SLM presented here has a driver allowing a frequency range of up to 1011 Hz. Using the static phase modulation characterization and the static lookup table (LUT), the phase modulation characterization versus frequency shows that the SLM can operate at around 130 Hz or even higher for small phase changes and at 32 Hz for extreme phase changes. A dynamic calibration is carried out, and we propose a method allowing an increase of the frame rate while maintaining a maximum phase modulation of 2pi. Experimental results of dynamic diffractive optical elements displayed on the SLM at a frame rate of 205 Hz show that the dynamic LUT improves the reconstruction quality.

Fractional Talbot imaging set-up for high-efficiency real-time diffractive optics

An optical configuration based on the fractional Talbot effect is proposed to improve the diffraction efficiency of dynamic diffractive optical elements written on electronically addressed liquid crystal spatial light modulators with partially opaque pixels, or on any other spatial light modulator, where a part of the pixel area is inactive. Using diffractive cover plates, the high design efficiency of a ideal multilevel diffractive optical element can almost be achieved even if 3/4 of the pixel area is blocked by drive electronics; without such cover plates, the efficiency would be limited to 1/16 of the design efficiency.