We propose and investigate a metallic Fresnel zone plate (FZP/MFZP) implemented on a silver-coated optical fiber facet for super-variable focusing of light, the focal point of which can be drastically relocated by varying the wavelength of the incident light. We numerically show that when its nominal focal length is set to 20 μm at 550 nm, its effective focal length can be tuned by ~13.7 μm for 300-nm change in the visible wavelength range. This tuning sensitivity is over 20 times higher than that of a conventional silica-based spherical lens. Even with such high tuning sensitivity with respect to the incident wavelength change, the effective beam radius at the focal point is preserved nearly unchanged, irrespective of the incident wavelength. Then, we fabricate the proposed device, exploiting electron- and focused-ion-beam processes, and experimentally verify its super-variable focusing functionality at typical red, green, and blue wavelengths in the visible wavelength range, which is in good agreement with the numerical prediction. Moreover, we propose a novel MFZP structure that primarily exploits the surface-plasmon-polariton-mediated, extra-ordinary transmission effect. For this we make all the openings of an MFZP, which are determined by the fundamental FZP design formula, be partitioned by multi-rings of all-sub-wavelength annular slits, so that the transmission of azimuthally polarized light is inherently prohibited, thereby leading to super-variable and selective focusing of radially polarized light. We design and fabricate a proof-of-principle structure implemented on a gold-coated fused-silica substrate, and verify its novel characteristics both numerically and experimentally, which are mutually in good agreement. We stress that both the MFZP structures proposed here will be very useful for micro-machining, optical trapping, and biomedical sensing, in particular, which invariably seek compact, high-precision, and flexible focusing schemes.
We propose a fiber-optic-plasmonic hybrid device that is based on a corrugation-assisted metal-coated angled fiber facet (CA-MCAFF) for wavelength-dependent off-axis directional beaming (WODB). The device breaks into two key structures: One is the MCAFF structure, which is a modified Kretschmann configuration implemented onto a fiber platform, thereby being able to generate a unidirectional surface plasmon with dramatically enhanced properties in terms of non-confined diffracted radiation loss and operational bandwidth. The other is the periodic corrugation structure put on the MCAFF, thereby enabling WODB functionality out of the whole structures. The corrugated metal surface out-couples the surface plasmon mode to free-space optical radiation into a direction that varies with the wavelength of the optical radiation with excellent linearity. We perform extensive numerical investigations based on the finite-element-method and analyze the out-coupling efficiency (OCEout) and spectral bandwidth (SBout) of the proposed device for various designs and conditions. We determine the seven structural parameters of the device via taking sequential optimization steps. We deduce two optimal conditions particularly for the fiber-facet angle, in terms of the averaged OCEout or the SBout in the whole visible wavelength range (400 - 700 nm), which eventually leads to OCEout = 30.4% and SBout = 230 nm or to OCEout = 24.5% and SBout = 245 nm, respectively. These results suggest substantial enhancements in both OCEout and SBout, in comparison with the performance properties of a typical nano-slit-based device having a similar type of WODB functionality. The proposed CA-MCAFF is a simple, compact and efficient WODB device that is fully compatible with the state-of-the-art optical fiber technology.
We introduce our design, simulation, and fabrication for cm-long waveguides and micro-ring resonators based on fully-etched thin-film lithium niobate on insulator (LNOI) incorporated with rare earth ions. We implant ytterbium ions (Yb3+) into the crystalline host and study their optical properties at 4 K temperature. We measure an intrinsic optical quality factor of higher than 2×106 after postimplantation annealing. We characterize the photoluminescence spectrum, lifetime, and absorption of Yb3+ ions. Incorporation of rare earth ions into LNOI as a crystalline and nonlinear photonic element may enable the development of multi-functional quantum photonic devices capable of generating, transducing, manipulating, and storing of quantum optical information.
We consider incubation of nanodiamonds (NDs) in endothelial culture cells as a way to measure their temperature with sub-Kelvin sensitivity. We discuss limitations of ND temperature sensing in living cells, how to overcome the limitations and potential applications of such measurements.
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