A particular photonic crystal fiber (PCF) designed with all circle air holes is proposed. Its characteristics are studied by full-vector finite element method (FEM) with anisotropic perfectly matched layer (PML). The simulation results indicated that the proposed PCF can realize high birefringence (up to 10⁻²), high nonlinearity (50W⁻¹·km⁻¹ and 68W⁻¹·km⁻¹ in X and Y polarizations respectively) and low confinement loss (less than 10⁻³dB/km at 1.55um wavelength).

Magnetic continuum robots offer flexibility and controllability, making them promising for minimally invasive surgery (MIS). However, the clinical application of these robots is relatively limited due to the difficulty of integrating miniaturized triaxial force sensors and their single functionality. This paper proposes a multifunctional magnetic catheter robot with magnetic actuation steering and triaxial force-sensing capabilities. The robot features 3 channels at its tip that integrate multi-segmented magnets, a novel triaxial force sensor, and various functional instruments. The sensor is calibrated, demonstrating high sensitivity and accuracy. The steering characterization of the robot confirms that the catheter tip exhibits effective flexibility and force sensing. Palpation experiments involving various hard lumps are performed on porcine kidney, with results verifying that the robot can reliably detect abnormal hard lumps within tissues. Additionally, palpation experiments in bronchial phantom demonstrate the robot’s imaging and palpation capabilities for lung nodules with an integrated endoscope. Further, the robot, equipped with biopsy forceps, successfully performs palpation and biopsy functions on simulated stomach polyps, demonstrating its capability for effective tissue manipulation. By leveraging force-sensing capabilities and integrating multifunctional instruments, the robot shows potential for expanded applications in MIS, paving the way for important advancements in clinical procedures.

A photonic crystal fiber (PCF) with high relative sensitivity was designed and investigated for the detection of chemical analytes in the terahertz (THz) regime. To ease the complexity, an extremely simple cladding employing four struts is adopted, which forms a rectangular shaped core area for filling with analytes. Results of enormous simulations indicate that a minimum 87.8% relative chemical sensitivity with low confinement and effective material absorption losses can be obtained for any kind of analyte, e.g., HCN (1.26), water (1.33), ethanol (1.35), KCN (1.41), or cocaine (1.50), whose refractive index falls in the range of 1.2 to 1.5. Besides, the PCF can also achieve high birefringence (∼0.01), low and flat dispersion, a large effective modal area, and a large numerical aperture within the investigated frequency range from 0.5 to 1.5 THz. We believe that the proposed PCF can be applied to chemical sensing of liquid and THz systems requiring wide-band polarization-maintaining transmission and low attenuation.

Light trapping within waveguides is a key practice of modern optics, both scientifically and technologically. Photonic crystal fibers traditionally rely on total internal reflection (index-guiding fibers) or a photonic bandgap (photonic-bandgap fibers) to achieve field confinement. Here, we report the discovery of a new light trapping within fibers by the so-called Dirac point of photonic band structures. Our analysis reveals that the Dirac point can establish suppression of radiation losses and consequently a novel guided mode for propagation in photonic crystal fibers. What is known as the Dirac point is a conical singularity of a photonic band structure where wave motion obeys the famous Dirac equation. We find the unexpected phenomenon of wave localization at this point beyond photonic bandgaps. This guiding relies on the Dirac point rather than total internal reflection or photonic bandgaps, thus providing a sort of advancement in conceptual understanding over the traditional fiber guiding. The result presented here demonstrates the discovery of a new type of photonic crystal fibers, with unique characteristics that could lead to new applications in fiber sensors and lasers. The Dirac equation is a special symbol of relativistic quantum mechanics. Because of the similarity between band structures of a solid and a photonic crystal, the discovery of the Dirac-point-induced wave trapping in photonic crystals could provide novel insights into many relativistic quantum effects of the transport phenomena of photons, phonons, and electrons.

A photonic crystal fiber (PCF) based on high resistivity silicon (HRS) is reported that exhibits high birefringence, low loss, and flat dispersion characteristics across a wide bandwidth in the THz regime. Except for the center region, which remains the background dielectric, its core is occupied by a set of rectangular air slots. The material and configuration lead to high birefringence and low loss. The simulation results, which include the material losses, indicate that a birefringence value of 0.82 and a total loss of 0.011 cm$^{-1}$, including the effective material loss (EML) and confinement (CL) losses, are achieved at 1.0 THz. These values are a factor of 10 times higher and 4 times lower respectively, than many recent designs. The numerical analyses also demonstrate that the reported PCF can be scaled to any desired portion of the THz regime, while maintaining a similar birefringence, simply by changing the lattice constant. This “scalable” characteristic is shown to be applicable to other PCF designs. It could facilitate a novel way of testing THz fibers, i.e., it suggests that one only needs to test the preform to validate the performance of the fiber at higher frequencies. This outcome would significantly reduce the design complexity and the costs of PCF testing.

—A novel photonic crystal fiber (PCF) design that yields very high birefringence is proposed and analyzed. Its significantly enhanced birefringence is achieved by filling selected air holes in the cladding with an epsilon-near-zero (ENZ) material. Extensive simulation results of this asymmetric material distribution in the lower THz range demonstrate that the reported PCF has a birefringence above 0.1 and a loss below 0.01 cm⁻¹ over a wide band of frequencies. Moreover, it exhibits near zero dispersion at 0.75 THz for both the X- and Y-polarization modes and a birefringence equal to 0.28. This THz PCF is then scaled successfully to optical frequencies. While the high birefringence is maintained, this optical PCF has a very high loss in its Y-polarization mode and, consequently, yields single-polarization single-mode (SPSM) propagation, exhibiting near zero dispersion at the optical telecom wavelength of 1.55 μm. The ideal ENZ materials used for these conceptual models are replaced with realistic ones for both the THz and optical PCF designs. With the currently available ENZ materials, the realistic PCFs still have a high birefringence, but with higher losses compared to the idealized results. Future developments of ENZ materials that achieve lower loss properties will mitigate this issue in any frequency band of high interest.