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Focal field modulation has attracted a lot of interest due to its potential in many applications such as optical tweezers or laser processing, and it has recently been facilitated by spatial light modulators (SLMs) owing to their dynamic modulation abilities. However, capabilities for manipulating focal fields are limited by the space-bandwidth product of SLMs. This difficulty can be alleviated by taking advantage of the high-speed modulation ability of digital micromirror devices (DMDs), i.e., trading time for space to achieve fine focus shaping. In this paper, we propose a new, to the best of our knowledge, technique for achieving four-dimensional focal field modulation, which allows for independent manipulation of the focal field’s parameters (including amplitude, phase, and polarization) in both the space and time domains. This technique combines a DMD and a vector field synthesis system based on a 4-f system. The high-speed modulation ability of DMDs enables versatile focus patterns to be fast switchable during the exposure time of the detector, forming multiple patterns in a single recording frame. By generating different kinds of focal spots and lines at different moments during the exposure time of the detector, we can finally get complete multifocal spots and lines. Our proposed method is effective at improving the flexibility and speed of the focal field modulation, which is beneficial to applications.

In order to optimize the design of underwater light screens, the transmission process of the light beam in water is analyzed with the Monte Carlo method. The trajectories and power attenuation of emitted photons, propagating in different types of water from the light source towards the receiver with different initial light powers and transmission distances, are simulated and calculated. The output power can then be obtained to calculate the transmission ratio quantitatively. According to the simulated data, by using the curving fitting method, the exact expression of transmission ratio is derived, which is in the same form as the Beer–Lambert–Bouguer law. Meanwhile, experiments are conducted in a light screen with a vertical line beam laser in clear water to verify the simulations. The experimental results are in agreement with the simulated results, and the differences between them are within ± 0.04 . The presented results give insight into the design of underwater laser screens.

With fractal amplitude masks of the Sierpinski carpet and Sierpinski triangle, we theoretically and experimentally present the diffraction properties and applications of spatially structured optical fields, including the vector optical field, vortex optical field, and vortex vector optical field. The diffraction patterns of the vector optical fields exhibit self-similarity, and the characteristics of the vector optical fields are maintained in every diffraction peak. The diffraction patterns of the vortex optical fields and vortex vector optical fields exhibit triangular lattice arrays, and the vortex topological charge can be determined by the number of peak spots in the triangular lattice array. We hope these diffraction properties with fractal amplitude masks can be applied not only in detecting topological charges of spatially structured optical fields, but also in generating flexibly controlled diffraction patterns and lattice arrays, which may be useful in optical machining, optical trapping, and information transmission.

We theoretically propose and experimentally generate the nondiffracting Bessel–Poincaré beams whose Stokes vortices radially accelerate during propagation. To this end, we design the Bessel beams whose intensity is specified to be uniformly distributed along the longitudinal direction. By superposing two such Bessel beams having different helical phases and mutually orthogonal polarizations, the synthesized vector beam is endowed with the polarization singularity that can rotate about the optical axis, while the total intensities maintain their profiles. Radially self-accelerating Stokes vortices in the resulting beam can be manipulated by adjusting the predefined parameters in the constituent beams.

A modified lateral shearing interferometry is proposed to measure the spatial coherence of partially coherent light beams. This interferometry based on a 4f system consists of a diffraction grating and a spatial light modulator (SLM). In this system, the diffraction grating splits the partially coherent wave into two copied waves, forming a shearing interferogram on the observation plane. The period of the composite blazing grating generated by the phase-modulated SLM is flexibly tuned for controlling the lateral displacement of the two copied waves. The complex degree of spatial coherence of the partially coherent field is obtained through measurements and Fourier analysis of the fringe pattern.

The scheme for generating vector optical fields should have not only high efficiency but also flexibility for satisfying the requirements of various applications. However, in general, high efficiency and flexibility are not compatible. Here we present and experimentally demonstrate a solution to directly, flexibly, and efficiently generate vector vortex optical fields (VVOFs) with a reflective phase-only liquid crystal spatial light modulator (LC-SLM) based on optical birefringence of liquid crystal molecules. To generate the VVOFs, this approach needs in principle only a half-wave plate, an LC-SLM, and a quarter-wave plate. This approach has some advantages, including a simple experimental setup, good flexibility, and high efficiency, making the approach very promising in some applications when higher power is need. This approach has a generation efficiency of 44.0%, which is much higher than the 1.1% of the common path interferometric approach.

We propose a method to generate a vectorial focal field with reconfigurable distributions for both the intensity and polarization state. The three-dimensional focal volume was configured by modulating the phase and polarization of the incident light. The incident light yielding the desired field was determined based on an iterative scheme involving vectorial diffraction calculations and fast Fourier transforms. Optical experiments on vectorial field shaping were performed to validate the feasibility of our method. This method may have applications in optical tweezers, such as for realizing the optical manipulation of particles via polarization modulation in addition to phase control.

Airy beams are attractive owing to their two intriguing properties--self-bending and nondiffraction--that are particularly helpful for optical manipulation of particles. We perform theoretical and experimental investigations into the focusing property of Airy beams and provide insight into the trapping ability of tightly focused Airy beams. Experiment on optical tweezers demonstrates that the focused Airy beams can create multiple traps for two-dimensional confining particles, and the stable traps exist in the vicinity of the main intensity lobes in the focused beams. The trapping pattern can be varied with changes in the cross section of the focused beam. The focused Airy beam offers a novel way of optically manipulating microparticles.

All-optical bistability was observed in thin-film waveguides made with acceptor-donor substituted azobenzene-doped poly(methyl methacrylate) polymer. Input-output curves with hysteresis characteristics were measured. The origin of the bistability was attributed to nonlinear coupling between a prism and a doped-polymer waveguide. An approximately theoretical analysis was introduced. Theoretical predictions were qualitatively consistent with experimental results.

We propose a method for realizing a polarization-selective diffractive optical element by using of a single twisted-nematic liquid-crystal display (TN-LCD). We have demonstrated that two orthogonal polarization-encoding channels can be formed using a single TN-LCD operated in some special conditions. Based on the two orthogonal encoding channels, two orthogonal polarized components of a field with any complex amplitude can be holographically encoded and reconstructed and, hence, different output images with different polarization states could be obtained, or a vector beam with spatially inhomogeneous polarization distributions, as well as the desired complex amplitude distributions, could be combined.

We propose a tri-arm (or Y-shaped) multipinhole (MP) interferometer for wavefront measurement based on a specially designed tri-arm MP plate. We demonstrate that the complex amplitude of a wavefront sampled by the tri-arm MP plate inserted between the object and the detector plane can be extracted directly from the Fourier transform of a far-field diffraction intensity pattern without the need for any iterative algorithm. A form of coherent diffractive imaging based on a rotatable tri-arm MP plate is also demonstrated, which provides a feasible approach for lensless diffractive imaging in real time.

Experimental and theoretical research on hybrid multiplexing for fiber-optic Fabry-Perot (F-P) sensors based on frequency-shifted interferometry is presented. Four F-P sensors multiplexed in a hybrid configuration were experimentally investigated. The location of each multiplexed sensor was retrieved by performing the fast Fourier transform, and the reflection spectrum of each sensor was also obtained in spite of the spectral overlap, which was consistent with the results measured by an optical spectrum analyzer. With theoretical modeling, the maximum sensor number of a two-channel hybrid multiplexing system reaches 26 with crosstalk of less than -50 dB and a maximum frequency-domain signal-to-noise ratio (SNR) of ∼25 dB, when the source power is 2 mW and the sensor separation is optimal, i.e., 40 m. And the sensor number is almost twice that multiplexed by a serial system under the same conditions. An SNR improvement of 3.9 dB can be achieved by using a Hamming window in a noise-free system compared with a Hanning window. In addition, we applied the experimental multiplexing system to a strain sensing test. The cavity lengths and cavity-length shifts of the four F-P sensors were demodulated, which was consistent with the actual situation. It provides a new feasible method to multiplex F-P sensors at large scale.

We have demonstrated stable self-starting passive mode locking in a diode-end-pumped Nd:Gd0.5-Y0.5VO4 laser by using an In0.25Ga0.75As absorber grown at low temperature (LT In0.25Ga0.75As absorber). An In0.25Ga0.75As single-quantum-well absorber, which was grown directly on the GaAs buffer by use of the metal-organic chemical-vapor deposition technique, acts simultaneously as a passive mode-locking device and as an output coupler. Continuous-wave mode-locked pulses were obtained at 1063.5 nm. We achieved a pulse duration of 2.6 ps and an average output power of 2.15 W at a repetition rate of 96.4 MHz.

A new algorithm for precise determination of the global phase shift between two interferograms is introduced. First we calculate the frame difference between the first and the second interferogram; the difference is multiplied by a properly chosen test phase factor, and then we implement a two-dimensional Fourier transform of the frame difference and calculate the energy of the first positive (or negative) diffraction order. An iterative approach is used for the test phase to ensure that the minimum energy is obtained, and then the correct phase shift value is found. This method is called the energy-minimum Fourier transform method, which is accurate and noise insensitive compared with the single-point Fourier transform method. Both the theoretical analysis and experimental results are given.

We propose a new computer-controlled phase-shifting method based on computer-generated holograms (CGHs) displayed on a spatial light modulator (SLM). In this method the accurate phase shifts required in phase-shifting digital holography or interferometry are induced by a suitable transformation of the encoding patterns of the CGH displayed on a SLM. Both the theoretical analysis and the experimental results demonstrate the feasibility of this approach. We also discuss possible applications of this method in the field of interferometric null testing of aspheres.

We demonstrate that high-resolution incoherent-to-coherent conversion can be carried out in an incoherent-to-coherent converter based on the photorefractive fanning effect. The output coherent image has the same direction as the incident coherent beam, and thus the resolution is not limited by the grating diffraction. We obtained a resolution as high as 90.5 line pairs/mm in this experiment. The transmittance of the coherent beam relative to the intensity of the incoherent beam was measured. We also theoretically estimated the resolving power with respect to the interaction length. The numerical results agree well with the experiments.

The low-power and broadband optical bistability in an acceptor-donor-substituted azobenzene-doped polymethyl methacrylate thin film, which relies on the excitation of surface plasmons with a cw laser of several tens of milliwatt power, is studied experimentally and theoretically. The observations on the characteristics of the bistability are essentially consistent with the theoretical predictions.