Youqiao Ma

Fiber refractometer based on a fiber Bragg grating and single-mode-multimode-single-mode fiber structure.

A refractive index (RI) sensor based on a novel fiber structure that consists of a single-mode-multimode-single-mode (SMS) fiber structure followed by a fiber Bragg grating was demonstrated. The multimode fiber in the SMS structure excites cladding modes within output single-mode fiber (SMF) and recouple the reflected cladding Bragg wavelength to the input SMF core. By measuring the relative Bragg wavelength shift between core and cladding Bragg wavelengths, the RI can be determined. Experimentally we have achieved a maximum sensitivity of 7.33 nm/RIU (RI unit) at RI range from 1.324 to 1.439.

Low Loss, High Extinction Ration and Ultra-Compact Plasmonic Polarization Beam Splitter

In this letter, an ultra-compact plasmonic polarization beam splitter (PBS) is proposed and investigated by numerical simulations using the finite element method. The PBS is based on a three-core plasmonic directional coupler, which uses a long range surface plasmon polaritons waveguide as the middle waveguide to achieve polarization selective coupling. The calculations show that with proper structural parameters, the PBS with low insertion losses of 0.17 and 0.25 dB for TE and TM polarizations, respectively, and high extinction ratios of 20.17 and 19.83 dB for TE and TM polarizations, respectively, can be realized at a telecommunication wavelength of 1550 nm. Furthermore, an insertion loss and an extinction ratio > 14 dB can be realized across the entire C-band for both TE and TM polarizations.

Hybrid nanowedge plasmonic waveguide for low loss propagation with ultra-deep-subwavelength mode confinement

In this Letter, a novel waveguide based on hybrid surface plasmon polaritons (HSPPs) is proposed and numerically analyzed. This waveguide consists of two dielectric nanowires placed on both sides of a nanowedge-patterned metal film, which can confine light in the ultra-deep-subwavelength region (ranging from λ²/4000 to λ²/400) with a long propagation length (ranging from 1200 to 3500 μm). Compared to a previous HSPPs waveguide without the nanowedges, with the same propagation length, our proposed structure has much higher mode confinement with 1 order of magnitude smaller normalized mode area. An investigation of the effect of structural perturbations indicates that our proposed waveguide also has good tolerance of fabrication errors. The proposed waveguide could be an interesting alternative structure to realize nanolasers and optical trapping.

White Light Trapping Using Supercontinuum Generation Spectra in a Lead-Silicate Fibre Taper

We experimentally investigate white light optical trapping by generating a supercontinuum in a lead silicate fibre pumped by femtosecond pulses from a Ti:Sapphire laser near the zero-dispersion wavelength of 1030 nm, before confining the light using a microfibre half taper with a final tip diameter of 75 nm. Due to the high intensity gradient at the output, robust optical trapping is possible, as demonstrated for individual yeast cells using an average pumping power of 100 mW.

Novel Dielectric-Loaded Plasmonic Waveguide for Tight-Confined Hybrid Plasmon Mode

In this paper, a novel metal-dielectric waveguide structure is proposed to support hybrid long range surface plasmon polaritons (LRSPPs) with a highly confined mode field. The simulation results showed that our proposed structure has better mode confinement and propagation length compared to that of conventional dielectric-loaded surface plasmon polaritons (DLSPPs) waveguides. This structure offers greater flexibility for the design of surface plasmon polaritons (SPPs) waveguides by altering the trade-off between mode confinement and propagation length. The proposed structure has significant potential for application in highly integrated photonic circuits.

Mach–Zehnder Interferometer-Based Integrated Terahertz Temperature Sensor

A plasmonic Mach–Zehnder interferometer (MZI) for temperature sensing is reported in the terahertz (THz) regime. The MZI is formed by embedding a semiconductor (SC) layer into a silicon membrane, where the SC layer supports two independent propagating surface plasmon polariton (SPP) waves on both surfaces. The temperature-sensitive phase difference between these two SPP waves gives rise to the modulation of the transmitted intensity. The results show that the MZI sensor possesses a sensitivity and a figure of merit as high as 8.9 × 10−3 THz/K and 117, respectively. Theoretical calculations indicate that the further improvement in sensing performance is still possible through optimization of the structure Moreover, an investigation of structural perturbations indicates that the MZI has a good tolerance to the fabrication errors. The compact MZI-based waveguide structure may find important applications in areas of sensing and integrated THz circuits.

A Hybrid Wedge-To-Wedge Plasmonic Waveguide With Low Loss Propagation and Ultra-Deep-Nanoscale Mode Confinement

The well-known tradeoff between the propagation loss and mode confinement is a critical consideration for the plasmonic waveguide structures. Aiming to overcome this limitation, in this paper, we propose a compact plasmonic waveguide consisting of two identical dielectric wedge waveguides symmetrically placed on each side of a nanowedge-patterned thin metal film. The systematical analysis has demonstrated that the light can be confined to approximate 3000th of the diffraction spot size (ranging from λ2/10 604 to λ2 /972) without sacrificing the propagation length (ranging from 1680 to 4724 μm). Compared to the recent published structure which achieved the best tradeoff, to the best of our knowledge, the proposed waveguide could achieve a 9-fold enhanced mode confinement for the same propagation length and a 2.4-fold outspread propagation length for the same mode confinement.

Evanescent field coupling between two parallel close contact SMS fiber structures

We proposed a novel optical coupling technique based on two parallel singlemode-multimode-singlemode (SMS) fiber structures. This technique utilizes one SMS structure to excite multiple cladding modes within an output singlemode fiber. The excited multiple cladding modes will be coupled to the input SMF in the second SMS structure by placing the two SMS fiber structures in parallel and in close contact each other. The coupled cladding modes will be re-coupled to a guided core mode by the second SMS fiber structure. Theoretical analysis for such technique was provided and experimentally we have achieved a pass band spectral response with an extinction ratio higher than 20 dB and a maximum coupling efficiency of 5.9%.

UV exposure on a single-mode fiber within a multimode interference structure

We experimentally study the effects of UV exposure on a single-mode fiber (SMF) with a fiber multimode interferometer (MMI) based on the singlemode-multimode-singlemode-multimode-singlemode (SMSMS) fiber structure. We observe a wavelength shift of over 33 nm when irradiating the central SMF in the SMSMS fiber structure with a 3-mm-width UV beam (the UV laser has a wavelength of 193 nm and pulse energy of 3 mJ). According to our numerical simulation, the SMSMS fiber structure can achieve a very high refractive-index (RI) sensitivity of 67670 nm/RIU with a very good linearity of R2≈0.9999. The structure can find potential application for high-sensitivity RI sensing by replacing the central SMF with a hollow-core optical fiber filled with the sample under test. The UV exposure technique can be used for tuning the characteristics of fiber MMI devices.

Enhanced refractive index sensor using a combination of a long period fiber grating and a small core singlemode fiber structure

An enhanced refractive index (RI) sensor based on a combination of a long period fiber grating (LPG) and a small core singlemode fiber (SCSMF) structure is proposed and developed. Since the LPG and SCSMF transmission spectra experience a blue and a red shift respectively as the surrounding RI (SRI) increases, the sensitivity is improved by measuring the separation between the resonant wavelengths of the LPG and SCSMF structures. Experimental results show that the sensor has a sensitivity of 1028 nm/SRI unit in the SRI range from 1.422 to 1.429, which is higher than individual sensitivities of either structure alone used in the experiment. Experimental results agree well with simulation results.