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We experimentally demonstrate the performance of 16-ary orbital angular momentum shift keying (OAM-SK) decoders based on convolutional neural networks (CNNs) in an underwater optical wireless communication (UOWC) system. We verify the decoding accuracy of the OAM-SK system in a 1-m tank filled with flowing salty water. The oceanic turbulence is emulated by the random phase screen method by a spatial light modulator (SLM). The results show that the decoders are robust to short-distance water fluctuations induced by the water flow, with an accuracy of more than 99% in clean water. In turbid water, the decoders require input images with a greater number of pixels and can reach an accuracy of more than 99% with a pixel number of 64 × 64. The decoders are tolerant to weak turbulence, with accuracies greater than 96.78% and 99.75% for input pixel numbers of 32 × 32 and 64 × 64 in 20-m temperature-induced channels with an equivalent temperature structure parameter of C n 2 = 1 0 − 15 K 2 ⋅ m − 2 ∕ 3 . As the strength of the oceanic turbulence increases, the accuracy decreases to lower than 85.5%. In both turbid channels and turbulent channels, large OAM modes are more likely to be incorrectly recognized. Increasing the pixel number of the input images or decreasing the order of the coding format can improve the decoding accuracy under moderate-to-strong turbulence conditions. This work will be beneficial for the design of UOWC systems.

We consider two-parameter real-valued parabolic diffraction-free beams. An analytical expression for the complex amplitude of the beam is obtained using the superposition of the Bessel functions. Symmetry properties of beams are analyzed and numerically demonstrated for different cases. The variety of the formed pictures increases significantly in comparison with earlier regarded parabolic beams. Particularly interesting properties exhibit beams with half-integer indices, they have symmetry properties different from the symmetry of beams with integer indices. For an arbitrary fractional index, the beams have a more complex distribution and do not have any symmetry. This fact facilitates the solution of the inverse problem when it is necessary to form similar structures, since just small changes in two parameters of the analytical expression are needed. This is much simpler than the implementation of iterative procedures, which, as a rule, provide essentially non-smooth solutions that are complex in optical implementation. Experimental generation of the fractional two-parameter parabolic beams is implemented for the first time by a spatial light modulator using phase coding of the calculated complex amplitudes. The different types of experimentally generated parabolic beams are in a good agreement with the modeling results.

The results of the laboratory experiments are presented for synthesis of the I m -Bessel correlated beams by a Spatial Light Modulator (SLM) and a Digital Micromirror Device (DMD) as well as for their interactions with atmospheric turbulence simulated by either an SLM or a mixed-air turbulent chamber. The synthesis procedure of these beams relies on the incoherent superposition of their coherent modes being Laguerre-Gaussian (LG) functions having a variable radial mode and a fixed azimuthal mode carrying the Orbital Angular Momentum (OAM). As a result of such construction the correlation functions of these random beams have separable phase carrying the OAM with the index inherited from the coherent modes. The coherence states of these beams are controlled by the distribution of weights of the coherent modes in superposition, varying from perfectly coherent to nearly incoherent. We explore the effects of the cycling rates of the SLM and the DMD used for source synthesis on the average intensity and the scintillation index of the generated beams having different OAM indices and coherence states after propagation in atmospheric turbulence. Our analysis indicates that for fairly incoherent beams with sufficiently large OAM index and high cycling rates the atmospheric turbulence can be efficiently mitigated.

An optical multiple images encryption method based on θ modulation and computer generated hologram is proposed. After modulated by double random phases in Fresnel transform and θ modulation system, the images are superimposed together and encoded into a binary real value CGH. The decryption is achieved in optical spatial filtering and Fresnel transform system with spatial light modulator. Multiple images can be encrypted at once in the proposed method which has high efficiency. Except the random phase, the diffraction distance and wavelength can be used as keys to improve the security. The numerical simulation and experimental results verify the validity of proposed method in this paper.

An improved single-random-phase holographic encryption (SRPHE) is proposed by using double-phase method and demonstrated by a spatial light modulator (SLM). Different from the conventional SRPHE using Fresnel diffraction and the bidirectional error diffusion method, the proposed SRPHE employees the angular spectrum diffraction and double-phase method to generate a phase-only hologram, and the phase-only hologram is encrypted into ciphertext by multiplying a single random phase mask. When the ciphertext is modulated by the conjugate of the random phase mask and loaded to a SLM, the decrypted image can be achieved successfully. The improved SRPHE has two advantages of better quality of the decrypted image, and lower time-cost of hologram generation, which is compared with the conventional SRPHE. Numerical simulations and optical reconstruction results have been carried out to verify the validity of the proposed SRPHE.

Successive images of a scene are captured and then further processed to achieve the moving object tracking. However, due to modulation rate limitations of the spatial light modulator in single-pixel imaging (SPI) system, the imaging frame rate cannot meet the high-resolution and real-time requirements for object tracking. In this paper, we demonstrate a fast object tracking technique based on SPI with an ultra-low sampling rate that is independent of imaging. We construct modulation information that satisfies the projection conditions and can transform 2D images into 1D projection curves. The 1D projection curves, which provide the location information of the moving object, can be obtained with high resolution in real-time, and then the tracking of the moving object is realized. A background subtraction technique for tracking moving objects that removes static components from a scene is also proposed. The proposed technique is verified by computational simulations and laboratory experiments. In the laboratory experiments, we demonstrate that the proposed method can be used to track moving objects with less than 0.2% of the measurements established by the Nyquist criterion, and it presents 256 × 256 pixels at ∼ 177 fps. The reported technique accelerates the tracking speed of SPI and provides an efficient strategy for remote sensing and biomedical applications.

In this paper, a speckle noise suppression method employing time multiplexing in holographic display is proposed. The recorded object is separated into object point groups by pixel separation. For each object point group, some phase-only subcomputer-generated holograms (sub-CGHs) with independent initial random phases are generated. In the reconstruction process, a spatial light modulator (SLM) is used to load the sub-CGHs. The reconstructed image is generated through time multiplexing technology. Meanwhile, the speckle noise of the reconstructed image is reduced effectively by averaging the speckle noise and separating the adjacent image points in space. Compared with the pixel separation method, both simulation and optical experiments are carried out to confirm that the proposed method suppresses the speckle noise effectively with less computation burden.

Large three-dimensional (3D) scene reconstruction is a challenge for current colour holographic displays. In this study, we develop a compact display system to reconstruct a large 3D scene using a 21-inch liquid crystal display (LCD) panel that serves as a spatial light modulator (SLM). We utilise a Fresnel lens instead of a conventional lens to reduce the complexity of the system. A spatial multiplexing colour filter attached to the SLM is used to simplify the structure of the colour display. Additionally, an independent block holographic algorithm is developed to record accurate depth information. Numerical simulations and optical experiments are performed to verify the proposed system. The optically reconstructed 3D colour scene is 480 mm × 300 mm × 500 mm in size. Therefore, the proposed display system represents development toward a commercial product for its low device requirements.

Holographic laser beam shaping using a spatial light modulator can provide flexible adaptation of the intensity profile. However, speckle noise exists in the shaped beams, which reduces the beam quality seriously. In this paper, a new method is proposed to implement noise reduced flat-top beam shaping. The Gerchberg–Saxton (GS) algorithm with special spherical initial phase profile is adopted to calculate the phase-only hologram. When the spherical phase distribution is properly selected, the speckle free flat-top beam with high diffraction efficiency and low root-mean-square error can be obtained. Both simulations and experiments are performed to verify the feasibility of the proposed method. The comparison with the conventional GS algorithm using a random initial phase distribution is also carried out.

The scarcity of RF spectrum at lower frequencies has recently been addressed by millimeter wave transmission in fiber-wireless and radio-over-free-space optics networks for more flexible frequency spectrum allocation. This work focuses on parallel transmission of four independent radio OFDM based channels, each carrying 20Gbps data, by optical millimeter mode division multiplexing of spiral-phased Laguerre–Gaussian modes and Hermite–Gaussian modes using a spatial light modulator to realize 80 Gbps–160 GHz data over 50 km free-space link. The performance of proposed system is evaluated under the influence varying levels of fog.

Tailoring electromagnetic waves has a wide range of applications, such as optical trapping, focus engineering, imaging, laser cutting, and optical communication. To do so, the spatial distribution of at least one of the four degrees of freedom of electromagnetic waves, amplitude, phase, polarization ratio, and retardance, must be modified. Arbitrary vectorial optical fields (VOF) can be engineered by spatially modulating all four degrees of freedom simultaneously. However, existing dynamic vectorial optical field generators (VOF-Gens) require intensive alignment and many optical elements in order to achieve high efficiency. Here, we design a dynamic VOF-Gen that can generate arbitrary VOFs using only five optical elements. Experimentally, we demonstrated an efficiency of 72%, the highest ever demonstrated.

The strong need in life science and medicine research has prompted the development of wide-field, high-resolution and real-time microscopic imaging based on camera array. For large-scale sub-image stitching on the order of billion pixels, it is highly challenging to calibrate the camera array with low-overlapping fields of view (FOVs). To address the challenge, we propose a camera array calibration method to obtain the complete camera model and global mapping coordinates. The method utilizes spatiotemporal structured light encoding provided by a spatial light modulator to establish the correspondence between the physical coordinates of the keypoints in the object plane and their pixel coordinates in the sub-image plane. This achieves fast and accurate calibration of a camera-array-based microscopic system without the requirement of sub-FOV overlap. A series of experiments, including reprojection evaluation and global image stitching on the resolution chart and biological specimen slice, verified the effectiveness of the proposed approach. The method supports calibration of global geometric position with 0.2-pixel accuracy and has a broad potential for application to general camera array-based imaging systems.

In this paper, a projection-type dual-view holographic three-dimensional (3D) display consisting of a single spatial light modulator (SLM) and a grating light-guide plate is proposed and implemented. A synthetic phase-only hologram of two different 3D objects is calculated by the layer-based Fresnel diffraction method and uploaded onto the SLM for 3D reconstruction. A grating with special design and fabrication is used as the light-guide plate to re-direct the two reconstructed 3D images into the two separated viewing zones simultaneously. Optical experiments demonstrate that the proposed system can realize the function of dual-view holographic 3D display, and it can present 3D images to the human eye with sufficient depth cues, which enables the observers free of the accommodation-vergence conflict and visual fatigue problem. Furthermore, the proposed dual-view holographic 3D display system is applied to the see-through display for augmented reality (AR) applications, and the performance of this system is also tested in the experiments and the results show that the system can provide the dual-view AR 3D sensation successfully.

We propose an optical encryption method allowing the parallel encryption and hierarchical retrieval for multi-channel images based on a joint Fresnel transform correlator. In our designed scheme, the linear phase shift operation for the phase masks is utilized to achieve the aim of ensuring that the center of the complex amplitude distributions from the same group can overlap with each other in Fresnel domain, and the phase retrieval algorithm for designing the phase masks is used to avoid the cross talk between multi-channel images. The optimized phase masks can be flexibly reconfigured on the spatial light modulator without increasing the additional optical hardware and system complexity. Our designed scheme can encrypt multi-channel images simultaneously into a single cipher-text, which can also be used to recover arbitrary original images with corresponding keys. Thus, this method can achieve the aim of the hierarchical retrieval of encrypted images from a single cipher-text. Moreover, because the encryption process does not require any transformative lenses and accurate alignment of optical elements, the encryption scheme is easy to be optically implemented. Furthermore, compared with the previous JTC-based cryptosystems, the Fresnel diffraction distance and the position of the key masks in our proposed scheme can both be utilized as the additional encryption keys, which can enhance the security effectively. The theoretical analysis and numeric simulation results both validate the feasibility and effectiveness of the designed scheme.

We demonstrate a 2-channel orbital angular momentum (OAM) multiplexed free space optical communication (FSO) link using perfect optical vortex (POV) beams. POV beams are able to be transmitted coaxially over than 1m with the assistance of a microscope objective and normal lens. 16QAM-OFDM signals are used to measure the performance, which is also compared with the FSO link based on Laguerre–Gaussian (LG) vortex beams multiplexing in the same experimental environment. The results show that, the FSO link employing POVs multiplexing can bring a better performance to the system, which can always obtain a lower BER under the same received power; The using of POVs as carriers greatly reduces the systems’ sensitivity to the change of OAM topological charge numbers; And the constant diameter of POVs is also improve the versatility of the optical devices of different channels in the system.

We present a common path interference setup for detection of surface depth differences of the order of 200 nm, using a vortex and a Gaussian beam generated with a spatial light modulator. The phase of a vortex with a topological charge +1 and the phase of a lens are encoded next to each other onto the spatial light modulator. Both beams are incident onto a surface with a step feature; the Gaussian beam is incident onto a flat mirrored surface, while the vortex beam scans through the step. Upon interaction with the testing surface, both beams are superposed and their interference pattern is captured, collecting a set of images as a result of the scanning process. A phase detection algorithm is applied to these images and by tracking the vertical positions of the phase singularity along the scanning, the depth variations are estimated. The proposed set up is able to detect a 179 nm step feature, working with light at a wavelength of 830 nm and using a vortex with a diameter of 177 μ m.

Since the measurement of spatial coherence requires multiple sampling to acquire the complex coherence factor of a wavefield, it is convenient to accomplish such dynamic work by a non-redundant multi-slit through a programmable device such as spatial light modulator (SLM). In this study, we examined the influence of SLM-like pixelated structure, parameterized by whose fill factor, on both intensity distribution (first-order statistics) and complex coherence factor (second-order statistics). Based on the generalized Van Cittert–Zernike theorem that as the source satisfied the quasi-homogeneous condition, the coherence factor of the wavefield was irrelevant to the pixelated sampling structure. The inference was validated by a SLM-based experiment from a pseudothermal light source. We expected this work to be useful for future dynamic coherence measurement.

Microscopy has been widely used to obtain three-dimensional images of a biological sample. However, it requires a scanning in axial direction and considerable time to acquire multiple depths information of a volumetric sample. In this paper, we demonstrate a method for single-shot multi-plane imaging based on programmable multiplexed grating patterns with no mechanical moving parts by using a digital micro-mirror device (DMD). The multiplexed grating pattern displayed on DMD, in a Fourier plane, splits light into separated beam paths and are able to compensate aberrations from the proposed system. In addition, resolution can be improved using an aberration-corrected multiplexed gratings pattern. We present and characterize the design, implementation, and experimentally demonstrate the proposed system’s ability through simultaneous multiple planes imaging of the biological samples.

It is reported a method which may simplify the optical setups used to achieve super-resolution through the amplitude multiplication of two waves. For this end we decompose a super-resolving pupil into two complex masks and with the aid of a Spatial Light Modulator (LCoS) we obtain two intensity images that are subtracted. With this proposal, the traditional experimental optical setups are considerably simplified, with the additional benefit that different masks can be utilized without needing to perform the setup alignment each time.

We present a new pseudo color imaging scheme named pseudo color ghost coding imaging based on ghost imaging but with multiwavelength source modulated by a spatial light modulator. Compared with conventional pseudo color imaging where there is no nondegenerate wavelength spatial correlations resulting in extra monochromatic images, the degenerate wavelength and nondegenerate wavelength spatial correlations between the idle beam and signal beam can be obtained simultaneously. This scheme can obtain more colorful image with higher quality than that in conventional pseudo color coding techniques. More importantly, a significant advantage of the scheme compared to the conventional pseudo color coding imaging techniques is the image with different colors can be obtained without changing the light source and spatial filter.

In this paper, we propose a high-dimensional free-space optical communication scheme using orbital angular momentum (OAM) coding. In the scheme, the transmitter encodes N -bits information by using a spatial light modulator to convert a Gaussian beam to a superposition mode of N OAM modes and a Gaussian mode; The receiver decodes the information through an OAM mode analyser which consists of a MZ interferometer with a rotating Dove prism, a photoelectric detector and a computer carrying out the fast Fourier transform. The scheme could realize a high-dimensional free-space optical communication, and decodes the information much fast and accurately. We have verified the feasibility of the scheme by exploiting 8 ( 4 ) OAM modes and a Gaussian mode to implement a 256 -ary ( 16 -ary) coding free-space optical communication to transmit a 256 -gray-scale ( 16 -gray-scale) picture. The results show that a zero bit error rate performance has been achieved.

Two-index Bessel beams (TIBBs) was introduced by Ornigotti and Aiello (2014) theoretically. In this paper, we propose a simple experimental scheme for generation of two-index Bessel–Gauss beams (TIBGBs), as an extension of the TIBBs. The scheme is based on manipulating the amplitude and phase in the Fourier plane with the use of a spatial light modulator and a spiral phase plate. Furthermore, we experimentally report the generation of the several examples of the TIBGBs based on the proposed optical system. The focusing properties of the TIBGB with indices p = 1 and l = 2 passing through a single lens are investigated both theoretically and experimentally. The experimental results agree well with theoretical predictions.

It remains a tough task for designing a microscopy system to approach the diffraction limit over a wide field of view due to its restricted space bandwidth product (SBP). Fourier ptychographic microscopy (FPM) has been developed to broaden the SBP of a conventional microscope platform without major hardware modifications. In this paper, we propose a novel FPM system based on the phase-coded speckle illumination, termed PSI-FPM, which employs a laser source with a speckle illumination control optical system. A phase-only spatial light modulator (SLM) with a condenser lens is utilized in the PSI-FPM system to project the phase-coded speckle illumination patterns onto the sample. The convolution between the sample spectrum and the illumination spectrum in the Fourier domain extend the numerical aperture of the objective that acts as a low-pass filter with cut-off frequency. The SLM is introduced in the PSI-FPM system to produce the specific illumination patterns so that the number of the captured images used for reconstruction are greatly reduced. In addition, the generated pattern is scanned to different directions without mechanical movement, which improves the robustness of the system. The PSI-FPM system is validated against simulations and experiments, and as a result reconstructs high-resolution images once the phase retrieval algorithm is employed. We envision that the PSI-FPM system will be suitable for many other speckle imaging applications.

The complex modulation is applied to indirectly generate a focusing flattop beam, which can modulate the amplitude and phase in the optical pupil combining with the phase retrieval theory. The simulation results show that this algorithm has good uniformity. However, the alignment errors of various components in the actual optical system have an impact on the beam uniformity, especially after the implementation of SLM (Spatial Light Modulator) error calibration, the beam uniformity still hardly meets the requirements. In this paper, the error source of the complex modulation beam shaping system is theoretically analyzed, while the Mixed Region Amplitude Freedom (MRAF) method is selected as a comparative reference in this research. It is found that the defocus aberration in the SLM illumination is the main aberration which has a special grid-facula, and the error source is proved through the actual experiment. Finally, then the correction is carried out, the complex modulation has better uniformity than MRAF.

In this paper, a wide-spectrum orbital angular momentum (OAM) based free space communication system is experimentally demonstrated. The wide-spectrum laser can be generated using narrow-linewidth pulses to pump nonlinear fiber and the OAM beam can be generated with spatial light modulator (SLM). In the experiment, a controllable atmospheric turbulence simulation device was used to ensure a unified test environment. The results show that with the combination of wide-spectrum laser and OAM beam, the received sensitivity can achieve a 4.23 dB gain compared with narrow-linewidth Gaussian beam-based communication system in weak atmospheric turbulence environment.