Side Polished Fiber:A Versatile Platform for Compact Fiber Devices and Sensors

Side polished fiber(SPF)has a controllable average roughness and length of the side-polishing region,which becomes a versatile platform for integrating multiple materials to interact with the evanescent field to fabricate all-fiber devices and sensors.It has been widely used in couplers,filters,polarizers,optical attenuators,photodetectors,modulators,and sensors for temperature,humidity,strain,biological molecules,chemical gas,and vector magnetic monitoring.In this article,an overview of the development history,fabrication techniques,fiber types,transmission characteristics,and varied recent applications of SPFs are reviewed.Firstly,the fabrication techniques of SPFs are reviewed,including the V-groove assisted polishing technique and wheel polishing technique.Then,the different types of SPFs and their characteristics are discussed.Finally,various applications of SPFs are discussed and concluded theoretically and experimentally,including their principles and structures.When designing the device,the residual thickness and polishing lengths of the SPF need to be appropriately selected in order to obtain the best performance.Developing all-fiber devices and sensors is aimed at practical usability under harsh environments and allows to avoid the high coupling loss between optical fibers and on-chip integrated devices.

High-sensitivity and fast-response fiber optic temperature sensor using an anti-resonant reflecting optical waveguide mechanism

Temperature sensing is essential for human health monitoring.High-sensitivity(>1 nm∕℃)fiber sensors always require long interference paths and temperature-sensitive materials,leading to a long sensor and thus slow response(6–14 s).To date,it is still challenging for a fiber optic temperature sensor to have an ultrafast(~ms)response simultaneously with high sensitivity.Here,a side-polished single-mode/hollow/single-mode fiber(SPSHSF)structure is proposed to meet the challenge by using the length-independent sensitivity of an anti-resonant reflecting optical waveguide mechanism.With a polydimethylsiloxane filled sub-nanoliter volume cavity in the SP-SHSF,the SP-SHSF exhibits a high temperature sensitivity of 4.223 nm/℃ with a compact length of 1.6 mm,allowing an ultrafast response(16 ms)and fast recovery time(176 ms).The figure of merit(FOM),defined as the absolute ratio of sensitivity to response time,is proposed to assess the comprehensive performance of the sensor.The FOM of the proposed sensor reaches up to 263.94(nm/℃)∕s,which is more than two to three orders of magnitude higher than those of other temperature fiber optic sensors reported previously.Additionally,a threemonth cycle test shows that the sensor is highly robust,with excellent reversibility and accuracy,allowing it to be incorporated with a wearable face mask for detecting temperature changes during human breathing.The high FOM and high stability of the proposed sensing fiber structure provide an excellent opportunity to develop both ultrafast and highly sensitive fiber optic sensors for wearable respiratory monitoring and contactless in vitro detection.

Photonic cavity enhanced high-performance surface plasmon resonance biosensor

Herein we propose a novel strategy to enhance surface plasmon resonance(SPR)by introducing a photonic cavity into a total-internal-reflection architecture.The photonic cavity,which is comprised of a highly reflective photonic crystal(PC),defect layers,and a gold(Au)film,enables Fabry–Perot(FP)resonances in the defect layers and therefore narrows the SPR resonance width in the metallic surface as well as increases the electric field intensity and penetration depth in the evanescent region.The fabricated sensor exhibits a 5.7-fold increase in the figure of merit and a higher linear coefficient as compared with the conventional Au-SPR sensor.The demonstrated PC/FP cavity/metal structure presents a new design philosophy for SPR performance enhancement.

High-performance fiber-integrated multifunctional graphene-optoelectronic device with photoelectric detection and optic-phase modulation

In graphene-based optoelectronic devices,the ultraweak interaction between a light and monolayer graphene leads to low optical absorption and low responsivity for the photodetectors and relative high half-wave voltage for the phase modulator.Here,an integration of the monolayer graphene onto the side-polished optical fiber is demonstrated,which is capable of providing a cost-effective strategy to enhance the light–graphene interaction,allowing us to obtain a highly efficient optical absorption in graphene and achieve multifunctions:photodetection and optical phase modulation.As a photodetector,the device has ultrahigh responsivity(1.5×10^(7) A/W)and high external quantum efficiency(>1.2×10^(9)%).Additionally,the polybutadiene/polymethyl methacrylate(PMMA)film on the graphene can render the device an optical phase modulator through the large thermo-optic effect of the PMMA.As a phase modulator,the device has a relatively low half-wave voltage of 3 V with a 16 dB extinction ratio in Mach–Zehnder interferometer configuration.

Optimized weak measurement of orbital angular momentum-induced beam shifts in optical reflection

Tiny but universal beam shifts occur when a polarized light beam is reflected upon a planar interface.Although the beam shifts of Gaussian beams have been measured by the weak measurement technique, the weak measurement for orbital angular momentum(OAM)-induced spatial shifts of vortex beams is still missing.Here, by elaborately choosing the preselection and postselection states, the tiny OAM-induced Goos–H?nchen and Imbert–Fedorov shifts are amplified at an air–prism interface. The maximum shifts along directions both parallel and perpendicular to the incident plane are theoretically predicted and experimentally verified with optimal preselection and postselection states. These maximum shifts can be used to determine the OAM of vortex beams.

Distance-controllable and direction-steerable opto-conveyor for targeting delivery

Opto-conveyors have attracted widespread interest in various fields because of their non-invasive and non-contact delivery of micro/nanoparticles.However,the flexible control of the delivery distance and the dynamic steering of the delivery direction,although very desirable in all-optical manipulation,have not yet been achieved by optoconveyors.Here,using a simple and cost-effective scheme of an elliptically focused laser beam obliquely irradiated on a substrate,a direction-steerable and distance-controllable opto-conveyor for the targeting delivery of microparticles is implemented.Theoretically,in the proposed scheme of the opto-conveyor,the transverse and longitudinal resultant forces of the optical gradient force and the optical scattering force result in the transverse confinement and the longitudinal transportation of microparticles,respectively.In this study,it is experimentally shown that the proposed opto-conveyor is capable of realizing the targeting delivery for microparticles.Additionally,the delivery distance of microparticles can be flexibly and precisely controlled by simply adjusting the irradiation time.By simply rotating the cylindrical lens,the proposed opto-conveyor is capable of steering the delivery direction flexibly within a large range of azimuthal angles,from-75°to 75°.This study also successfully demonstrated the real-time dynamic steering of the delivery direction from-45°to 45°with the dynamical rotation of the cylindrical lens.Owing to its simplicity,flexibility,and controllability,the proposed method is capable of creating new opportunities in bioassays as well as in drug delivery.