Polarization-maintaining few mode fiber composed of a central circular-hole and an elliptical-ring core

We propose a novel waveguide design of polarization-maintaining few mode fiber(PM-FMF) supporting ≥10non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core,a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δn_(eff) between the adjacent guided modes could be kept larger than 1.32 × 10^(-4) over the whole C +L band. The proposed fiber structure can flexibly tailored to support an even larger number of modes in PM-FMF(14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.

Flexible microbubble-based Fabry-Pérot cavity for sensitive ultrasound detection and wide-view photoacoustic imaging

Interaction of acoustic waves and microbubbles occurs in numerous biomedical applications including ultrasound imaging,drug delivery,lithotripsy treatment,and cell manipulation,wherein the acoustically driven microbub-blcs routincly act as active microscale oscillators or actuators.In contrast,microbubbles were utilized here as passive reccivers to detect broadband ultrasound waves in aqueous environments.The microbubble was photo-thermally generated on a microstructured optical fiber(MOF)tip,forming a flexible Fabry-Perot cavity whose gas-water interface was sensitive to ultrasound waves.The MOF severed as both a low-loss waveguide and a compact light condenser,allowing high-efficiency generation and stabilization of ultrasmall microbubbles.Integrated with all-fiber interferometry,a 10 um diameter microbubble exhibited a low noise-cquivalcnt pressur elevei of^3.4 mPa/Hz^1/2 and a broad bandwidth of^0.8 MHz,capable of detecting weak ultrasounds emittedfrom red blood cells irradiated by pulsed laser light.With advantages of high sensitivity,compact size,and low cost,the microbubble-based ultrasound sensor has great potential in biomedical imaging and sensing applications.

Acousto-Optics Tunable Filter Based on a Hollow Optical Fiber for Broadband Polarization Switch Application

A novel acousto-optic tunable filter (AOTF) using a hollow optical fiber (HOF) is proposed. Its broadband rejection over 100nm was observed and high polarization dependence as a polarization switch is discussed.

Irreversible denaturation of DNA:a method to precisely control the optical and thermo-optic properties of DNA thin solid films

The denaturation of double-stranded deoxyribonucleic acid(ds-DNA) has been well known to break nucleobase bonds, resulting in single-stranded deoxyribonucleic acid(ss-DNA) in solutions, which can recombine to form ds-DNA in a reversible manner. We developed an efficient process to irreversibly maintain various DNA denaturation levels in thin solid films in order to investigate the impacts of the denaturation on the optical properties of DNA films. By adding NaOH in an aqueous solution of salmon testis DNA, we flexibly controlled the level of denaturation in the solution, which was then spin-coated on Si and silica substrates to irreversibly bind ss-DNAs in a thin solid film. The denaturation of DNA in thin solid films was experimentally confirmed by ultravioletvisible and Fourier transform infrared spectroscopic investigations, whose level could be controlled by the NaOH content in the aqueous solution precursor. By this irreversible denaturation process, we developed a new method to flexibly vary the refractive index of DNA thin solid films in a wide range of Δn > 0.02 in the visible to nearinfrared range. Thermo-optic coefficients dn/d T of the films were also experimentally measured in the temperature range from 40℃ to 90℃ to confirm the significant impacts of denaturation. Detailed thin film processes and optical characterizations are discussed.

Quantitative in situ measurement of optical force along a strand of cleaved silica optical fiber induced by the light guided therewithin

We propose an optomechanical system to quantify the net force on a strand of cleaved silica optical fiber in situ as the laser light is being guided through it.Four strands of the fiber were bonded to both sides of a macroscopic oscillator,whose movements were accurately monitored by a Michelson interferometer.The laser light was propagating with variable optical powers and frequency modulations.Experimentally,we discovered that the driving force for the oscillator consisted of not only the optical force of the light exiting from the cleaved facets but also the tension along the fiber induced by the light guided therewithin.The net driving force was determined only by the optical power,refractive index of the fiber,and the speed of light,which pinpoints its fundamental origin.

Laser-driven self-exfoliation of graphene oxide layers on a fiber facet for Q switching of an Er-doped fiber laser at the longest wavelength

A new method to make an all-fiber nonlinear optic device for laser pulse generation is developed by depositing multi-layer graphene oxide(GO)selectively onto the core of the cleaved fiber facet by combining the electrical arc discharge and the laser-driven self-exfoliation.Using the GO colloid droplet with sub-nanoliter volume,we obtained a GO bulk layer deposited on a fiber facet of the order of milliseconds by using an electric arc.The prepared fiber facet was then included in an Er-doped fiber laser(EDFL)cavity and we obtained a few layers of GO having nonlinear optic two-dimensional(2D)characteristics selectively on the fiber core by the laser-driven self-exfoliation.The 2D GO layers on the fiber core served as a stable and efficient saturable absorber enabling robust pulse train generation atλ
1600.5 nm,the longest Q-switched laser wavelength in EDFLs.Pulse characteristics were analyzed as we varied the pump power atλ
980 nm from 105.2 mW to 193.6 mW,to obtain the maximum repetition rate of 17.8 kHz and the maximum output power of 2.3 mW with the minimum pulse duration of 7.8μs.The proposed method could be further applied to other novel inorganic 2D materials opening a window to explore their novel nonlinear optic laser applications.

Nanoliter liquid refractive index sensing using a silica V-groove fiber interferometer

A unique all-fiber interferometric sensor was proposed and successfully demonstrated efficient low-refractiveindex liquid sensing in the range from 1.33 to 1.37, which is compatible with those of bio-liquids.A special silica coreless optical fiber with an open V-groove was used as an optical sensing medium, which provided a high sensitivity for a minute liquid volume in the nanoliter scale.The V-groove fiber (VGF) was serially concatenated between two single-mode fibers (SMFs).The LPOi mode guided along the input SMF excited the higherorder inodes in the VGF to generate multimode interference,whose spectrum was transmitted through the output SMF. A single liquid droplet with volume of ~80 nanoliters wet the entire hydrophilic surface of the VGF, and the transmission spectra shifted corresponding to its refractive index in a very linear manner. The sensor also showed a negligible temperature cross-sensitivity in the range 25℃-75℃, which overlaps with the biological temperature window such that the sensitivity of 159.696 nm per refractive index unit(nm/RIU) remained independent of the temperature variation. Modal properties of VGF were thoroughly analyzed numerically, and detailed processes for the sensor fabrication and sensing experiments were reported.