Optical Review最新文献

Electro-optic (EO) modulators are crucial components to generate high-speed photonic signals in the modern photonic communication system. Here we study the performance of a hybrid EO modulator employing a Si slot waveguide and a BaTiO₃ layer, where the EO effect of BaTiO₃ is stronger than that of widely used LiNbO(_3). We demonstrate that an appropriate design for the slot waveguide, the BaTiO(_3) layer, and doped Si connectors to metal contacts can achieve a low voltage-length product (V_pi L) of 0.16 V cm, a wide modulation bandwidth of 50 GHz, and a small propagation loss of (<1) dB/cm simultaneously. These values indicate efficient use of the proposed modulator in the photonic communication system.

This paper proposes a novel pixel shift-based dual-phase modulation method (PS-DPMM) designed to enhance the spatial resolution of complex amplitude modulations. Conventional techniques, including off-axis computer-generated holograms (CGH), double-phase holograms (DPH), and kinoforms, often encounter issues like low diffraction efficiency, limited spatial resolution, and high speckle noise. Although the dual-phase modulation method (DPMM), which employs two spatial light modulators (SLMs), achieves high diffraction efficiency, its spatial resolution is constrained by the intrinsic pixel size and resolution of the SLM. To overcome this limitation, we propose the PS-DPMM, an extension of the DPMM that introduces a 1/2-pixel shift between two SLMs. Although this sacrifices a portion of the modulation performance, it effectively improves the spatial resolution of complex amplitude modulation by nearly doubling. Through numerical simulations and experimental validation, we demonstrate that the PS-DPMM attains almost twice the spatial resolution of conventional methods while maintaining a relatively high-quality modulation. This approach provides a promising solution for advancing high-spatial-resolution SLM-based complex amplitude modulation with potential applications in holographic displays, fiber-optic systems, and other fields requiring high spatial resolution wavefront control.

Multiplication is a fundamental operation in computer systems but is often constrained by the carry-delay inherent to conventional addition methods. Ternary optical computing offers an efficient solution, leveraging its advantages such as large data capacity, reconfigurable processing, and MSD adder without carry-delay. This study introduces and develops a modified signed digit (MSD) multiplication routine. The proposed MSD multiplication algorithm is thoroughly analyzed, employing M-transformations to generate partial products and an optimization method designed to minimize processing time. The final product is computed using an MSD adder with four transformations: T, T', W, and W', to aggregate all partial products. Additionally, a pipelining strategy is introduced to further enhance performance. The routine’s construction steps are outlined, followed by extensive simulation experiments to validate its accuracy. The results demonstrate strong consistency and alignment with theoretical predictions. Finally, a comparative analysis with traditional electronic computers indicates superior performance of the proposed MSD multiplication routine.

In surveillance camera systems and other human-image analysis systems, it is important to measure human shapes with high resolution. However, the spatial resolution and image quality achievable through approaches based solely on optical design and image processing are fundamentally limited by hardware constraints and the inherent difficulty of the inverse problems involved. To overcome these limitations, we propose a super resolution imaging system for human silhouettes based on a jointly-optimized design involving coded illumination patterns and reconstruction networks. Our proposed method allows for the acquisition of human silhouette data with improved sampling resolution without modifying the camera hardware. We quantitatively demonstrated the effectiveness of our proposed method through simulations and also through optical experiments using a projector and a camera.

A simple-structured total internal reflection terahertz filter based on a microstructured optical fiber is proposed in this paper, consisting of two non-uniform thickness dielectric tubes symmetrically nested within an outer cladding. The investigation uses the finite element method and the simulation results show that the x-polarized fundamental mode (XPFM) is well confined within the fiber core, while the lowest-loss higher-order mode (LL-HOM) exhibits significant loss, and y-polarized fundamental mode (YPFM) exhibits even greater loss. Specifically, the loss difference between the XPFM and the LL-HOM is 15.39 dB/cm at 1 THz. After a 2 cm transmission length, the LL-HOM achieves an extinction ratio of 30 dB, while the insertion loss of the XPFM is only 0.67 dB. Furthermore, when the length of the filter is fixed at 4.1 cm, stable single-mode transmission of the XPFM is maintained over the frequency range from 0.755 THz to 1.075 THz, with the insertion loss of the XPFM remaining below 1.5 dB. The proposed filter demonstrates excellent fabrication tolerance and holds significant potential for applications in terahertz systems.

In this paper, a switchable multi-wavelength fiber laser mode locked by molybdenum disulfide (MoS₂) film wrapped microfiber is demonstrated. By tuning intra-cavity loss and linear birefringence, switchable single-, double-, and triple-wavelength conventional solitons (CSs) are formed. Additionally, quadruple-wavelength solitons with center wavelengths of 1528 nm, 1532 nm, 1552 nm, and 1562 nm are realized by precisely adjusting the polarization controller (PC) and pump power. Experimental results demonstrate that this compact and versatile multi-wavelength soliton laser has significant potential for various applications.

Underwater images often suffer from color shift and visual blur due to light absorption and scattering in the water medium. An adaptive image enhancement method is proposed for underwater image quality improvement. First, adaptive color compensation is proposed based on the color features of the image, and selectively apply the gray world assumption according to the degree of color unevenness. Second, we use the color correction result combined with a rough estimation of ambient light and medium transmission map to restore the brightness and contrast of the underwater image. Next, based on different ambient light estimation values, we obtain multiple restoration results with different local features. Finally, we introduce the well-known multi-scale fusion strategy, using gradient matrix as weight, to fuse multiple restoration results. Extensive experiments on natural and synthetic underwater image datasets show that our method is robust in underwater image enhancement to achieve color, high contrast, moderate brightness in various complex underwater environments. Moreover, its effectiveness is also verified in the applications of underwater image saliency detection and natural image enhancement.

The formation of thrombus in blood may be a cause of thrombosis which induces symptoms, such as myocardial infarction, cerebral infarction, and economy class syndrome. Recently, investigations on blood flows inside artificial blood vessel and artificial organ have been performed energetically for clinical application. Thus, in vitro monitoring of thrombogenesis in blood flow inside them is thought to be essential to optimize their function for stable blood perfusion in such as artificial dialysis system and blood transfusion system. In the present study, we propose a method for monitoring the size and dynamics of thrombus in artificial blood flow using speckle patterns obtained under the illumination of coherent light. We experimentally discuss the spatial and temporal variation information on speckle patterns in relation to the size and dynamics of thrombus, respectively, under illumination of a laser diode. The above information contributes to the quantification of degree of thrombogenesis. Experimental results show the feasibility of the present method for in vitro monitoring of the formation of thrombus in artificial blood flow.

Heat-assisted magnetic recording (HAMR) is a promising technology for improving the recording density of hard disk drives. A near-field transducer (NFT), which forms a small light spot on a recording medium, is necessary in HAMR. The authors’ group previously proposed a novel device, in which a metal nano-antenna acting as an NFT is attached to a semiconductor ring resonator acting as a light source via a dielectric spacer. In this study, the temperature rise including the recording medium using this device was analyzed through the combination of optical and thermal simulations. To reduce the temperature rise of the nano-antenna while heating the recording layer to the Curie temperature, the following two methods were used: first, the nano-antenna length and the spacer thickness were optimized. Second, a heat spreader, which surrounds the nano-antenna, was introduced. The nano-antenna was made of Au, and the spacer and heat spreader were made of SiO₂. When the peak temperature of the recording layer was 800 K, the temperature of the nano-antenna was 3350 K without the above methods, but it was significantly reduced to 400 K with the above methods. This is a sufficiently low value to keep the hardness of the nano-antenna. On the other hand, the thermal spot size in the recording layer was slightly increased from 62 × 64 nm² to 67 × 72 nm² by the above methods.

An aerial 3D image formed by the use of a 3D-shaped light source gives a greater sense of reality compared to the conventional aerial 2D image. In particular, an aerial image of hollow face evokes a kind of illusion that the direction of the face changes depending on the viewing direction. In this study, we investigate the viewing zone of an aerial 3D display that employs a 3D object as a light source in aerial imaging by retro-reflection (AIRR) optical system. The viewing zone is defined by the minimum observation distance and viewing angle where the entire width of the aerial 3D image is visible. The Formulae for the viewing zone are derived and confirmed experimentally. 3D objects in various shapes are used in the experiments. The aerial 3D image of each object was observed in the corresponding viewing zone. Hollow face illusion was evoked even under binocular observation. We have clarified the optical design of our proposed AIRR optical system for hollow face illusion.