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In this paper, a photonic crystal fiber (PCF) sensor based on the surface plasmon resonance (SPR) effect for refractive index (RI) detection is proposed. We design a D-shaped polished PCF structure consisting of air holes arranged in a hexagonal lattice. The silver film is coated on the middle channel of the polished surface of the PCF. The finite element method is used to analyze the propagation characteristics of the proposed D-shaped SPR-PCF sensor. Simulation results show that the proposed D-shaped SPR-PCF sensor has a maximum wavelength sensitivity of 30,000 nm/RIU, an average wavelength sensitivity of 6785.71 nm/RIU, and a maximum resolution of 3.33×10−6RIU in the RI range of 1.22–1.36. Owing to the high wavelength sensitivity in the considered RI range, the proposed D-shaped SPR-PCF sensor is suitable for applications in water contamination detection, liquid concentration measurement, food safety monitoring, etc.

Real-time dense view synthesis based on three-dimensional (3D) reconstruction of real scenes is still a challenge for 3D light-field display. It’s time-consuming to reconstruct an entire model, and then the target views are synthesized afterward based on volume rendering. To address this issue, Light-field Visual Hull (LVH) is presented with free-viewpoint texture mapping for 3D light-field display, which can directly produce synthetic images with the 3D reconstruction of real scenes in real-time based on forty free-viewpoint RGB cameras. An end-to-end subpixel calculation procedure of the synthetic image is demonstrated, which defines a rendering ray for each subpixel based on light-field image coding. In the ray propagation process, only the essential spatial point of the target model is located for the corresponding subpixel by projecting the frontmost point of the ray to all the free-viewpoints, and the color of each subpixel is identified in one pass. A dynamic free-viewpoint texture mapping method is proposed to solve the correct graphic texture considering the free-viewpoint cameras. To improve the efficiency, only the visible 3D position and texture that contributes to the synthetic image are calculated based on backward ray tracing rather than computing the entire 3D model and generating all elemental images. In addition, an incremental calibration method by dividing camera groups is proposed to satisfy the accuracy. Experimental results show the validity of our method. All the rendered views are analyzed for justifying the texture mapping method, and the PSNR is improved by an average of 11.88dB. Finally, LVH can achieve a natural and smooth viewing effect at 4K resolution and the frame rate of 25 ∼ 30fps with a large viewing angle.

In this paper, an ultra-short polarization beam splitter (PBS) based on a rhombic structure dual-core photonic crystal fiber (RS-DC-PCF) with a central hole filled nematic liquid crystal (NLC) is proposed. For the RS-DC-PCF, the air holes of different sizes are arranged in a rhombic lattice, and the NLC (E7) is introduced to enhance the birefringence. The full vector–finite element method is used to investigate the coupling and propagation characteristics of the PBS. Moreover, the effects of different structure parameters on the coupling lengths ( C L x , C L y ) and coupling length ratio in the x -polarization and y -polarization directions and the preparation tolerances of different air hole diameters are investigated. And the effects of the temperature and molecule angle of the NLC (E7) on the extinction ratio (ER) are also analyzed. The simulation results show that the ultra-short splitting length of the optimized RS-DC-PCF PBS is 58 µm, the ER is higher than 20 dB in the wavelength range of 1.306 to 1.641 µm, and the bandwidth is up to 335 nm, covering most of the O + E + S + C + L communication bands.

Due to the limited pixel pitch of the spatial light modulator (SLM), the field of view (FOV) is insufficient to meet binocular observation needs. Here, an optimized controlling light method of a binocular holographic three-dimensional (3D) display system based on the holographic optical element (HOE) is proposed. The synthetic phase-only hologram uploaded onto the SLM is generated with the layer-based angular spectrum diffraction theory, and two different reference waves are introduced to separate the left view and the right view of the 3D scene. The HOE with directional controlling light parameters is employed to guide binocular information into the left-eye and the right-eye viewing zones simultaneously. Optical experiments verify that the proposed system can achieve binocular holographic augmented reality 3D effect successfully with real physical depth, which can eliminate the accommodation-vergence conflict and visual fatigue problem. For each perspective, the FOV is 8.7° when the focal length of the HOE is 10 cm. The width of the viewing zone is 2.3 cm when the viewing distance is 25 cm.

An ethanol and gold wires-filled single-polarization hollow-core negative curvature fiber is proposed for temperature sensing. The average sensitivity and R2 can reach 3.03 nm/ and 0.999 in the temperature range of 20 to 70, respectively.

In this paper, we propose a polarization-insensitive AlGaAs waveguide. For both quasi-TE and quasi-TM modes, the coherent supercontinuums, which span more than 1.95 octaves at −40 dB level, can be generated at mid-infrared spectral region.

An ultra-short and broadband dual-core photonic crystal fiber polarization beam splitter with a gold film based on surface plasmon resonance effect is proposed. The splitter length and bandwidth are 194 μm and 243 nm, respectively.

With hollow-core negative curvature fiber, a refractive index (RI) sensor based on surface plasmon resonance effect is proposed. The average sensitivity can be up to -7024 nm/RIU in the RI range from 1.29 to 1.39.

In this paper, a novel X-shaped dual-core photonic crystal fiber polarization beam splitter (X-DC-PCF PBS) with an air hole filled gold rod based on G e 20 S b 15 S e 65 glass is proposed. According to the DC mode coupling theory and surface plasmon resonance effect, the mode coupling phenomena of the x polarization (X-pol) and y polarization (Y-pol) odd and even modes are analyzed, respectively. The variation laws of coupling lengths of the X-pol and Y-pol and the coupling length ratio with different structural parameters at wavelength 1.55 µm are investigated. When the shortest polarization splitting length ( L P S ) is 230 µm, there is only the X-pol and Y-pol light in the cores A and B, respectively. By considering the variation of the extinction ratio and insertion loss (IL) with wavelength, the final polarization splitting bandwidth (PSB) is 358 nm (1.367–1.725 µm), and the maximum ILs of the X-pol and Y-pol in the whole PSB are 0.04 and 0.8 dB, respectively. The proposed X-DC-PCF PBS has ultra-wide PSB, short L P S , and ultra-low IL, so it will play an important role in the development of optical integration technology and the construction of an all-fiber loop platform.

A nematic liquid crystal-filled dual-core photonic crystal fiber single-polarization wavelength splitter is proposed. The length of the splitter is 2.38 mm, and the crosstalk between the wavelengths 1.31 and 1.55 μm can achieve -68.18 dB.

An ultra-broadband silicon dual-core photonic crystal fiber polarization beam splitter at mid-infrared spectral region based on surface plasmon resonance is proposed. The bandwidths of the cores A and B are 730 and 580 nm, respectively. © 2020 The Author(s).

A method for adjusting the differential order of a silicon-based waveguide grating differentiator by inputting light, which is through two-photon absorption and free carrier absorption effects, is proposed. The simulation results are demonstrated.

We design a dual-core photonic crystal fiber (PCF) polarization beam splitter (PBS) based on surface plasmons resonance effect. The maximum extinction ratio of the PBS can be up to -160.56 dB at wavelength 1.55 μm.

We propose and demonstrate a directional bend sensing based on Mach-Zehnder interferometer in a high birefringence dual-core photonic crystal fiber. Its curvature sensitivity is up to 4.24 nm/m–1 within the curvature range of 2.19-3.99 m–1.

Three-Dimensional (3D) light-field display plays a vital role in realizing 3D display. However, the real-time high quality 3D light-field display is difficult, because super high-resolution 3D light field images are hard to be achieved in real-time. Although extensive research has been carried out on fast 3D light-field image generation, no single study exists to satisfy real-time 3D image generation and display with super high-resolution such as 7680×4320. To fulfill real-time 3D light-field display with super high-resolution, a two-stage 3D image generation method based on path tracing and image super-resolution (SR) is proposed, which takes less time to render 3D images than previous methods. In the first stage, path tracing is used to generate low-resolution 3D images with sparse views based on Monte-Carlo integration. In the second stage, a lite SR algorithm based on a generative adversarial network (GAN) is presented to up-sample the low-resolution 3D images to high-resolution 3D images of dense views with photo-realistic image quality. To implement the second stage efficiently and effectively, the elemental images (EIs) are super-resolved individually for better image quality and geometry accuracy, and a foreground selection scheme based on ray casting is developed to improve the rendering performance. Finally, the output EIs from CNN are used to recompose the high-resolution 3D images. Experimental results demonstrate that real-time 3D light-field display over 30fps at 8K resolution can be realized, while the structural similarity (SSIM) can be over 0.90. It is hoped that the proposed method will contribute to the field of real-time 3D light-field display.

In this paper, a simple structure dual-core photonic crystal fiber (SS-DC-PCF) polarization beam splitter (PBS) based on the surface plasmon resonance (SPR) effect and symmetric dual-core coupling mode theory is proposed. For the proposed SS-DC-PCF-1 PBS, the coupling lengths (CLs) and coupling length ratio (CLR) are analyzed, and the variations of the normalized output powers with the propagation length are investigated for the chosen wavelengths 1.434, 1.451, and 1.469 µm. The extinction ratio in cores A and B are compared at the three splitting lengths (SLs) 170, 173, and 176 µm. When the optimal SL is 176 µm, the splitting bandwidth (SB) is 255 nm (1.437–1.692 µm), and the insertion loss (IL) is less than 0.043 dB. The regulations of the CLs and CLR with the change of the structure parameters are analyzed. For the proposed SS-DC-PCF-2 PBS, the optimal SL is 232 µm, the SB is 201 nm (1.249–1.450 µm), and the IL is less than 0.042 dB. Finally, it is demonstrated that the total SB of the proposed SS-DC-PCF-1 PBS and SS-DC-PCF-2 PBS is 443 nm (1.249–1.692 µm), which can cover theO+E+S+C+L+Uband, even if the gold film thickness changes by±1nm. The proposed SS-DC-PCF PBS has excellent performances, such as ultrashort SL, ultrawide SB, ultralow IL, and good error-tolerance rate. It will have important applications in all-fiber optical systems.

Three-dimensional (3D) light-field display has achieved a great improvement. However, the collection of dense viewpoints in the real 3D scene is still a bottleneck. Virtual views can be generated by unsupervised networks, but the quality of different views is inconsistent because networks are separately trained on each posed view. Here, a virtual view synthesis method for the 3D light-field display based on scene tower blending is presented, which can synthesize high quality virtual views with correct occlusions by blending all tower results, and dense viewpoints on 3D light-field display can be provided with smooth motion parallax. Posed views are combinatorially input into diverse unsupervised CNNs to predict respective input-view towers, and towers of the same viewpoint are fused together. All posed-view towers are blended as a scene color tower and a scene selection tower, so that 3D scene distributions at different depth planes can be accurately estimated. Blended scene towers are soft-projected to synthesize virtual views with correct occlusions. A denoising network is used to improve the image quality of final synthetic views. Experimental results demonstrate the validity of the proposed method, which shows outstanding performances under various disparities. PSNR of the virtual views are about 30 dB and SSIM is above 0.91. We believe that our view synthesis method will be helpful for future applications of the 3D light-field display.

Time-multiplexed light-field displays (TMLFDs) can provide natural and realistic three-dimensional (3D) performance with a wide 120° viewing angle, which provides broad potential applications in 3D electronic sand table (EST) technology. However, current TMLFDs suffer from severe crosstalk, which can lead to image aliasing and the distortion of the depth information. In this paper, the mechanisms underlying the emergence of crosstalk in TMLFD systems are identified and analyzed. The results indicate that the specific structure of the slanted lenticular lens array (LLA) and the non-uniformity of the emergent light distribution in the lens elements are the two main factors responsible for the crosstalk. In order to produce clear depth perception and improve the image quality, a novel ladder-type LCD sub-pixel arrangement and a compound lens with three aspheric surfaces are proposed and introduced into a TMLFD to respectively reduce the two types of crosstalk. Crosstalk simulation experiments demonstrate the validity of the proposed methods. Structural similarity (SSIM) simulation experiments and light-field reconstruction experiments also indicate that aliasing is effectively reduced and the depth quality is significantly improved over the entire viewing range. In addition, a tabletop 3D EST based on the proposed TMLFD is presented. The proposed approaches to crosstalk reduction are also compatible with other lenticular lens-based 3D displays.

A novel optical reverse mapping (ORM) method and an ORM criterion are proposed to evaluate the relevance between the directional backlight (DB) 3D light-field display system aberration and the crosstalk. Based on the ORM criterion, the space-division-multiplexed catadioptric integrated backlight (SCIB) and symmetrical triplet-compound lenticular array (triplet LA) are designed. The SCIB is composed of hybrid Fresnel integrated backlight unit (hybrid Fresnel unit) and space-division-multiplexed microprism unit (microprism unit). The hybrid Fresnel unit is used to provide the directional light, and the divergence angle is 2.4-degrees. The average uniformity of 83.02% is achieved. The microprism unit is used to modulate the directional light distribution into three predetermined directions to establish a 90-degree viewing area. Combined with SCIB, the triplet LA is used to suppress the aberrations and reduce the crosstalk. In the experiment, a DB 3D light-field display system based on SCIB and triplet LA is set up. The displayed light-field 3D image can be observed in a 90-degree viewing angle. Compared to the conventional DB 3D display system, the light-field 3D image is aberration-suppressed, and the SSIM values are improved from 0.8462 to 0.9618. Meanwhile, the crosstalk measurement results show that the average crosstalk is 3.49%. The minimum crosstalk is 2.31% and the maximum crosstalk is 4.52%. The crosstalk values in 90-degree are lower than 5%.

Three-dimensional (3D) light field displays require samples of image data captured from a large number of regularly spaced camera images to produce a 3D image. Generally, it is inefficient to generate these images sequentially because a large number of rendering operations are repeated in different viewpoints. The current 3D image generation algorithm with traditional single viewpoint computer graphics techniques is not sufficiently well suited to the task of generating images for the light field displays. A highly parallel multi-view polygon rasterization (PMR) algorithm for 3D multi-view image generation is presented. Based on the coherence of the triangular rasterization calculation among different viewpoints, the related rasterization algorithms including primitive setup, plane function, and barycentric coordinate interpolation in the screen space are derived. To verify the proposed algorithm, a hierarchical soft rendering pipeline with GPU is designed and implemented. Several groups of images of 3D objects are used to verify the performance of the PMR method, and the correct 3D light field image can be achieved in real time.

A novel catadioptric retroreflector floating device (CRA) used in the 3D floating light-field system is proposed. The floating light-field image constructed by the CRA is aberration-suppressed. The luminance and the contrast of the image are substantially improved in a 90-degree viewing angle. The CRA is constituted of the designed catadioptric retroreflector (CR). The CR consists of three lenses, the first and the second lens is to refract the light, and the rear surface of the third lens is coated with reflective coating in order to reflect the incident light. The CRA is processable and the fabrication process using UV embossing is also described. A spectrophotometer is utilized to measure the retroreflective efficiency of the CRA. The average retroreflective efficiency of the CRA is 80.1%. A beam quality analyzer is utilized to measure the beam spot quality of the CRA, and the image quality can satisfy the requirements of human eye observation. In the experiment, compared to the floating light-field image constructed by the micro-beads type retroreflector floating device (MRA), the image quality of the floating light-field image constructed by the CRA is significantly enhanced. In the quantitative computer simulation, the PSNR values of the images are increased from 23.0185 to 32.1958.

In this paper, a novel silicon dual-core photonic crystal fiber (Si-DC-PCF) polarization beam splitter (PBS) based on the surface plasmon resonance effect is proposed. The mode-coupling characteristics between the X - and Y -polarized even and odd modes and surface plasmon polariton mode are analyzed by using the finite-element method and coupled-mode theory. The influences of the structure parameters of the Si-DC-PCF on the coupling length and coupling length ratio are investigated. The normalized output power of the X - and Y -polarized modes in cores A and B and the corresponding extinction ratio are also discussed. By optimizing the structure parameters of the Si-DC-PCF, the PBS length of 192 µm and bandwidth of 830 and 730 nm in cores A and B are achieved. It is believed that the proposed Si-DC-PCF PBS can find important applications in mid-infrared laser and sensing systems.