A helicity-dependent computational ghost image generated by a metasurface hologram offers a promising optical encryption scheme.

Ultrahigh-Q chiroptical resonance metasurfaces based on merging bound states in the continuum (BICs) are investigated and numerically demonstrated. The destruction of C₂ symmetry results in the leakage of BICs into quasi-BICs, and a chiral quasi-BIC is obtained by oblique incidence or continuous destruction of the mirror symmetry of the structure. Due to the significant topological properties of merging BICs, the Q factor (over 2 × 10⁵) of the chiral resonance peak obtained is much higher than that of the previous work. Moreover, the proposed structure is easy to fabricate because no additional out-of-plane asymmetry is introduced. The proposed scheme is of importance in chiral biosensing applications.

We demonstrate theoretically and experimentally a high extinction ratio and compact size TE-pass polarizer made by a D-shaped fiber coated with a double graphene/PMMA stack. The light propagating in the core of the fiber can be efficiently coupled into the graphene sheet thanks to the giant enhancement of the modal evanescent field associated with the high refractive index graphene/PMMA cladding. The strong interaction between the light and graphene produces a large attenuation difference between modes with orthogonal polarizations, resulting in an improved extinction ratio and a reduced insertion loss due to the device compactness. A double graphene/PMMA stack coated polarizer with an extinction ratio of up to 36 dB and an insertion loss of 5 dB has been achieved when the device length is only 2.5 mm. The double graphene/PMMA stack has proved to be significantly better than single graphene/PMMA stack and bilayer graphene/PMMA structures, providing a polarizer with maximum extinction ratio of 44 dB for a length of 4 mm. The achieved results indicate that the proposed high extinction ratio polarizer is a promising candidate for novel in-fiber graphene-based devices.

Fiber Bragg gratings (FBGs) in a hollow eccentric fiber (HEF) have been proposed and demonstrated experimentally. The single-core and two-core HEF FBGs have been inscribed successfully using KrF excimer laser (248 nm), respectively. The temperature and axial strain sensing properties of the two samples have been measured. The experimental results indicate that the temperature and axial strain sensitivities of the two samples are similar, but they are smaller than that of conventional SMF-FBGs. Furthermore, the bending characteristics of the two-core HEF-FBG strongly depend on the bending direction due to the asymmetry of the fiber. Therefore, the proposed two-core HEF-FBGs facilitate temperature-compensated vector-bending sensing by measuring the difference between peak shifts of the two gratings. In addition, the two-core HEF-FBG can be a promising candidate for achieving two-channel filter since the signal crosstalk between the two cores can be largely eliminated by the central air hole.

We demonstrate theoretically and experimentally a novel in-fiber Mach-Zehnder interferometer (MZI) with piecewise interference spectrum. The interferometer is constructed by splicing a short section of single eccentric hole-assisted dual-core fiber (SEHADCF) to two single mode fibers (SMFs) with a lateral-offset. Due to the offset splicing and the small distance between cores, different core modes in two cores of the SEHADCF can be excited to form interference at the different wavelength ranges. The discontinuous region of the interference spectrum can be employed as a mark to identify the order of the interference valley. The in-fiber MZI is experimentally investigated as a refractive index sensor, the sensitivity of 353.9 nm/RIU is obtained in the RI range of 1.335 ~1.395. The in-fiber MZI with a high sensitivity has a great potential in biological and chemical applications. Especially, due to the ability to identify the order of interference valleys by the discontinuous region, the proposed in-fiber MZI can improve the reliability of fiber sensors in remote monitoring applications.

Long period fiber gratings (LPGs) in a two-core hollow eccentric fiber (TCHF) have been demonstrated experimentally. Two LPGs have been fabricated into the respective core of the TCHF by a high frequency CO₂ laser. The coupling characteristics in the TCHF-LPG have been studied using the coupling mode theory (CMT). The resonant peak is mainly caused by the coupling between the core mode LP₀₁ and cladding mode LP₈₁. The experimental results agree well with the simulation results. Furthermore, the sensing properties of the TCHF-LPG have been investigated with respect to bending, temperature and axial strain. Compared with the LPG in the single mode fiber (SMF), the experimental results indicate that the sensitivity of the TCHF-LPGs to bending curvature is low and even very small at some bending directions. In addition, TCHF-LPGs are insensitive to the axial strain while sensitive to the temperature. Therefore, the proposed TCHF-LPGs can efficiently sense the changing temperature that is independent of the strain. Moreover, the TCHF-LPGs can also be applied to two-channel filters without signal crosstalk between two cores.