Showing papers on "Single-mode optical fiber published in 2016"

Broadband robustly single-mode hollow-core PCF by resonant filtering of higher-order modes.

Abstract: We report a hollow-core photonic crystal fiber that is engineered so as to strongly suppress higher-order modes, i.e., to provide robust LP01 single-mode guidance in all the wavelength ranges where the fiber guides with low loss. Encircling the core is a single ring of nontouching glass elements whose modes are tailored to ensure resonant phase-matched coupling to higher-order core modes. We show that the resulting modal filtering effect depends on only one dimensionless shape parameter, akin to the well-known d/Λ parameter for endlessly single-mode solid-core PCF. Fabricated fibers show higher-order mode losses some ∼100 higher than for the LP01 mode, with LP01 losses 110 THz bandwidth.

Manipulation of Group-Velocity-Locked Vector Solitons From Fiber Lasers

Abstract: Manipulation of group-velocity-locked vector solitons (GVLVSs) is numerically proposed and experimentally demonstrated. A pseudo-high-order GVLVS could be generated from a fundamental GVLVS with the help of a polarization-resolved system. Specifically, a pseudo-high-order GVLVS with a two-humped pulse along one polarization and a single-humped pulse along the orthogonal polarization could be obtained. The phase difference between the two humps could be 180°.

Single-Mode Parametric-Down-Conversion States with 50 Photons as a Source for Mesoscopic Quantum Optics.

Abstract: We generate pulsed, two-mode squeezed states in a single spatiotemporal mode with mean photon numbers up to 20. We directly measure photon-number correlations between the two modes with transition edge sensors up to 80 photons per mode. This corresponds roughly to a state dimensionality of 6400. We achieve detection efficiencies of 64% in the technologically crucial telecom regime and demonstrate the high quality of our measurements by heralded nonclassical distributions up to 50 photons per pulse and calculated correlation functions up to 40th order.

Use of complex frequency plane to design broadband and sub-wavelength absorbers.

Abstract: The reflection of sound of frequency below 1 kHz, by a rigid-backed structure that contains sub-wavelength resonators is studied in this work. In particular, only single mode reflected waves are considered, an approximation which is accurate in this low frequency regime. A method of analysis of absorption that uses the structure of the reflection coefficient in the complex frequency plane is proposed. In the absence of losses, the reflection coefficient supports pairs of poles and zeros that are complex conjugate and which have imaginary parts linked to the energy leakage by radiation. When losses are introduced and balanced to the leakage, the critical coupling condition is satisfied and total absorption is obtained. Examples of a slot resonator and of multiple Helmholtz resonators are analyzed to obtain both narrow and broadband total absorption.

Monolithically Integrated High-β Nanowire Lasers on Silicon

Abstract: Reliable technologies for the monolithic integration of lasers onto silicon represent the holy grail for chip-level optical interconnects. In this context, nanowires (NWs) fabricated using III–V semiconductors are of strong interest since they can be grown site-selectively on silicon using conventional epitaxial approaches. Their unique one-dimensional structure and high refractive index naturally facilitate low loss optical waveguiding and optical recirculation in the active NW-core region. However, lasing from NWs on silicon has not been achieved to date, due to the poor modal reflectivity at the NW-silicon interface. We demonstrate how, by inserting a tailored dielectric interlayer at the NW-Si interface, low-threshold single mode lasing can be achieved in vertical-cavity GaAs–AlGaAs core–shell NW lasers on silicon as measured at low temperature. By exploring the output characteristics along a detection direction parallel to the NW-axis, we measure very high spontaneous emission factors comparable to n...

Ultrasensitive vector bending sensor based on multicore optical fiber.

Abstract: In this Letter, we demonstrate a compellingly simple directional bending sensor based on multicore optical fibers (MCF). The device operates in reflection mode and consists of a short segment of a three-core MCF that is fusion spliced at the distal end of a standard single mode optical fiber. The asymmetry of our MCF along with the high sensitivity of the supermodes of the MCF make the small bending on the MCF induce drastic changes in the supermodes, their excitation, and, consequently, on the reflected spectrum. Our MCF bending sensor was found to be highly sensitive (4094 pm/deg) to small bending angles. Moreover, it is capable of distinguishing multiple bending orientations.

Fiber-chip edge coupler with large mode size for silicon photonic wire waveguides.

Abstract: Fiber-chip edge couplers are extensively used in integrated optics for coupling of light between planar waveguide circuits and optical fibers. In this work, we report on a new fiber-chip edge coupler concept with large mode size for silicon photonic wire waveguides. The coupler allows direct coupling with conventional cleaved optical fibers with large mode size while circumventing the need for lensed fibers. The coupler is designed for 220 nm silicon-on-insulator (SOI) platform. It exhibits an overall coupling efficiency exceeding 90%, as independently confirmed by 3D Finite-Difference Time-Domain (FDTD) and fully vectorial 3D Eigenmode Expansion (EME) calculations. We present two specific coupler designs, namely for a high numerical aperture single mode optical fiber with 6 µm mode field diameter (MFD) and a standard SMF-28 fiber with 10.4 µm MFD. An important advantage of our coupler concept is the ability to expand the mode at the chip edge without leading to high substrate leakage losses through buried oxide (BOX), which in our design is set to 3 µm. This remarkable feature is achieved by implementing in the SiO2 upper cladding thin high-index Si3N4 layers. The Si3N4 layers increase the effective refractive index of the upper cladding near the facet. The index is controlled along the taper by subwavelength refractive index engineering to facilitate adiabatic mode transformation to the silicon wire waveguide while the Si-wire waveguide is inversely tapered along the coupler. The mode overlap optimization at the chip facet is carried out with a full vectorial mode solver. The mode transformation along the coupler is studied using 3D-FDTD simulations and with fully-vectorial 3D-EME calculations. The couplers are optimized for operating with transverse electric (TE) polarization and the operating wavelength is centered at 1.55 µm.

A New Type Circular Photonic Crystal Fiber for Orbital Angular Momentum Mode Transmission

Abstract: We proposed a new circular photonic crystal fiber (C-PCF), which can support 14 orbital angular momentum (OAM) modes transmission, with the good features of wide bandwidth, low confinement loss, and all OAM modes at the same size. At 1.55 μm, the designed C-PCF has a very low confinement loss of 3.434 × 10 -9 dB/m for HE41 mode and a relatively low nonlinear coefficient of 3.979 W -1 km -1 for EH 31 mode. The common bandwidth for the four orders of OAM modes is as large as 560 nm (about 1.25 μm-1.81 μm), which does cover all bands of optical fiber communication. Flat dispersion (a total dispersion variation of <;46.38 ps nm -1 km -1 over a 750-nm bandwidth from 1.25 μm to 2 μm for TE 01 mode) is another feature. With all these good features, the proposed C-PCF could be a well-promising OAM fiber for mode division multiplexing in high capacity fiber communication systems.

4 Tb/s Transmission Reach Enhancement Using 10 × 400 Gb/s Super-Channels and Polarization Insensitive Dual Band Optical Phase Conjugation

Abstract: In this paper, we experimentally demonstrate the benefit of polarization insensitive dual-band optical phase conjugation for up to ten 400 Gb/s optical super-channels using a Raman amplified transmission link with a realistic span length of 75 km. We demonstrate that the resultant increase in transmission distance may be predicted analytically if the detrimental impacts of power asymmetry and polarization mode dispersion are taken into account.

Narrow linewidth, single mode 3 kW average power from a directly diode pumped ytterbium-doped low NA fiber amplifier

Abstract: We report on a newly designed and fabricated ytterbium-doped large mode area fiber with an extremely low NA (~0.04) and related systematic investigations on fiber parameters that crucially influence the mode instability threshold. The fiber is used to demonstrate a narrow linewidth, continuous wave, single mode fiber laser amplifier emitting a maximum output power of 3 kW at a wavelength of 1070 nm without reaching the mode-instability threshold. A high slope efficiency of 90 %, excellent beam quality, high temporal stability, and an ASE suppression of 70 dB could be reached with a signal linewidth of only 170 pm.

Room temperature continuous wave, monolithic tunable THz sources based on highly efficient mid-infrared quantum cascade lasers.

Abstract: A compact, high power, room temperature continuous wave terahertz source emitting in a wide frequency range (ν~1-5 THz) is of great importance to terahertz system development for applications in spectroscopy, communication, sensing, and imaging. Here, we present a strong-coupled strain-balanced quantum cascade laser design for efficient THz generation based on intracavity difference frequency generation. Room temperature continuous wave emission at 3.41 THz with a side-mode suppression ratio of 30 dB and output power up to 14 μW is achieved with a wall-plug efficiency about one order of magnitude higher than previous demonstrations. With this highly efficient design, continuous wave, single mode THz emissions with a wide frequency tuning range of 2.06-4.35 THz and an output power up to 4.2 μW are demonstrated at room temperature from two monolithic three-section sampled grating distributed feedback-distributed Bragg reflector lasers.

A fiber-coupled diamond quantum nanophotonic interface

Abstract: Color centers in diamond provide a promising platform for quantum optics in the solid state, with coherent optical transitions and long-lived electron and nuclear spins. Building upon recent demonstrations of nanophotonic waveguides and optical cavities in single-crystal diamond, we now demonstrate on-chip diamond nanophotonics with a high efficiency fiber-optical interface, achieving > 90% power coupling at visible wavelengths. We use this approach to demonstrate a bright source of narrowband single photons, based on a silicon-vacancy color center embedded within a waveguide-coupled diamond photonic crystal cavity. Our fiber-coupled diamond quantum nanophotonic interface results in a high flux of coherent single photons into a single mode fiber, enabling new possibilities for realizing quantum networks that interface multiple emitters, both on-chip and separated by long distances.

Spatiotemporal Control of Light Transmission through a Multimode Fiber with Strong Mode Coupling.

Abstract: We experimentally generate and characterize eigenstates of the Wigner-Smith time-delay matrix, called principal modes, in a multimode fiber with strong mode coupling. The unique spectral and temporal properties of principal modes enable global control of temporal dynamics of optical pulses transmitted through the fiber, despite random mode mixing. Our analysis reveals that well-defined delay times of the eigenstates are formed by multipath interference, which can be effectively manipulated by spatial degrees of freedom of input wave fronts. This study is essential to controlling dynamics of wave scattering, paving the way for coherent control of pulse propagation through complex media.

Single mode lasing in transversely multi-moded PT-symmetric microring resonators

Abstract: Conventional techniques for transverse mode discrimination rely on introducing differential external losses to the different competing mode sets, enforcing single-mode operation at the expense of additional losses to the desirable mode. We show how a parity-time (PT) symmetric design approach can be employed to achieve single mode lasing in transversely multi-moded microring resonators. In this type of system, mode selectivity is attained by judiciously utilizing the exceptional point dynamics arising from a complex interplay of gain and loss. The proposed scheme is versatile, robust to deviations from PT symmetry such as caused by fabrication inaccuracies or pump inhomogeneities, and enables a stable operation considerably above threshold while maintaining spatial and spectral purity. The experimental results presented here were obtained in InP-based semiconductor microring arrangements and pave the way towards an entirely new class of chip-scale semiconductor lasers that harness gain/loss contrast as a primary mechanism of mode selectivity.

High sensitivity humidity sensor based on cladding-etched optical fiber and lossy mode resonances

Abstract: In this work a high sensitivity optical fiber humidity sensor (OFHS) is presented. The configuration chosen for this purpose is a cladding-etched single mode optical fiber (CE-SMF) coated with a thin film of tin oxide (SnO2). The etching has been made using hydrofluoric acid (HF) and the coating has been fabricated by means of sputtering. Tin oxide was used to build the nano-coating which produces the Lossy Mode Resonance (LMR) and works as sensitive material. Theoretical and experimental results are shown and compared. The device was tested using a climatic chamber in order to obtain the response of the OFHS to relative humidity. Changes greater than 130 nm have been obtained for relative humidity varying from 20% to 90%, which gives a sensitivity of 1.9 nm/%RH.

Spatial beam intensity shaping using phase masks on single-mode optical fibers fabricated by femtosecond direct laser writing

Abstract: Submicrometer dielectric phase masks allow for the realization of the miniaturization of high-quality optical elements. In this Letter we demonstrate spatial intensity beam shaping using phase masks attached to optical single-mode fibers. The phase masks are directly fabricated onto the end facet of optical fibers using femtosecond two-photon direct laser writing, achieving, therefore, submicrometer alignment accuracy. We observe high-quality intensity patterns and find excellent agreement with simulations. Our results prove that 3D printing of diffractive micro-optics can achieve sufficient performance to enable compact devices.

Highly Tm(3+) doped germanate glass and its single mode fiber for 2.0 μm laser.

Abstract: Highly Tm3+ doped optical fibers are urgently desirable for 2.0 μm compact single-frequency fiber laser and high-repetition-rate mode-locked fiber laser. Here, we systematically investigated the optical parameters, energy transfer processes and thermal properties of Tm3+ doped barium gallo-germanate (BGG) glasses. Highly Tm3+ doped BGG glass single mode (SM) fibers were fabricated by the rod-in-tube technique. The Tm3+ doping concentration reaches 7.6 × 1020 ions/cm3, being the reported highest level in Tm3+ doped BGG SM fibers. Using ultra short (1.6 cm) as-drawn highly Tm3+ doped BGG SM fiber, a single-frequency fiber laser at 1.95 μm has been demonstrated with a maximum output power of 35 mW when in-band pumped by a home-made 1568 nm fiber laser. Additionally, a multilongitudinal-mode fiber laser at 1.95 μm has also been achieved in a 10 cm long as-drawn active fiber, yielding a maximum laser output power of 165 mW and a slope efficiency of 17%. The results confirm that the as-drawn highly Tm3+ doped BGG SM fibers are promising in applications that require high gain and high power from a short piece of active optical fiber.

Low-loss single-mode hollow-core fiber with anisotropic anti-resonant elements

Abstract: A hollow-core fiber using anisotropic anti-resonant tubes in the cladding is proposed for low loss and effectively single-mode guidance. We show that the loss performance and higher-order mode suppression is significantly improved by using symmetrically distributed anisotropic anti-resonant tubes in the cladding, elongated in the radial direction, when compared to using isotropic, i.e. circular, anti-resonant tubes. The effective single-mode guidance of the proposed fiber is achieved by enhancing the coupling between the cladding modes and higher-order-core modes by suitably engineering the anisotropic anti-resonant elements. With a silica-based fiber design aimed at 1.06 µm, we show that the loss extinction ratio between the higher-order core modes and the fundamental core mode can be more than 1000 in the range 1.0-1.65 µm, while the leakage loss of the fundamental core mode is below 15 dB/km in the same range.

Surface enhanced raman spectroscopy using a single mode nanophotonic-plasmonic platform

Abstract: We demonstrate the generation of Surface Enhanced Raman Spectroscopy (SERS) signals from integrated bowtie antennas, excited and collected by the fundamental TE mode of a single mode silicon nitride waveguide. Due to the integrated nature of this particular single mode SERS probe one can rigorously quantify the complete enhancement process. The Stokes power, generated by a 4-nitrothiophenol-coated antenna and collected into the fundamental TE mode, exhibits an 8 × 106 enhancement compared to the free space Raman scattering of a 4-nitrothiophenol molecule. Furthermore, we present an analytical model which identifies the relevant design parameters and figure of merit for this new SERS-platform. An excellent correspondence is obtained between the theoretically predicted and experimentally observed absolute Raman power. This work paves the way toward a new class of fully integrated lab-on-a-chip systems where the single mode SERS probe can be combined with other photonic, fluidic, or biological functionalities.

Broadband mode division multiplexer using all-fiber mode selective couplers.

Abstract: We report an all-fiber mode division multiplexer formed with cascaded mode selective couplers with significantly broadened bandwidth potentially spanning S, C and L band. This was achieved by matching the effective refractive indices over a wide wavelength range for the few mode fiber and the single mode fiber used in the coupler. The multiplexer provides high coupling efficiency (>55% for the worst case) for the 4 spatial modes over the entire wavelength range of 1515-1590 nm. The all-fiber construction provides mechanical stability. Experimental results for the coupling efficiency and the mode extinction ratio for each spatial mode are presented along with the far field radiation patterns.

Dual-Wavelength Soliton Mode-Locked Fiber Laser With a WS 2 -Based Fiber Taper

Abstract: Recently, few-layer WS2, as a novel two-dimensional (2D) material, has been discovered to possess both the saturable absorption effect and the huge nonlinear refractive index. In experiment, by taking advantage of the unique optical properties of 2D WS2, we fabricated a highly nonlinear photonic device using the pulsed laser beam to deposit the WS2 film onto a fiber taper. With the WS2-based fiber taper, we have demonstrated the single- and dual-wavelength soliton pulses in the erbium-doped fiber laser (EDFL) by properly adjusting the pump strength and the polarization state. According to the soliton theory, the pulse width is $\sim 220$ fs for the single-wavelength soliton, and $\sim 585$ and $\sim 605$ fs for the dual-wavelength soliton, respectively. The dual-wavelength soliton fiber laser exhibits the maximum output power of 10.1 mW and the pulse energy of $\sim 1.14$ nJ, when the pump power is increased to $\sim 420$ mW. Our findings suggest that WS2-based fiber taper could operate as both an excellent saturable absorber for obtaining a femtosecond pulse and a promising highly nonlinear photonic material for the multi-wavelength generation.

Mode Coupling Effects in Ring-Core Fibers for Space-Division Multiplexing Systems

Abstract: An optical fiber with weak mode coupling is desirable for future ultrahigh capacity space-division multiplexing (SDM) systems because mode coupling in an optical fiber results in extrinsic loss of the fiber and crosstalk between guided optical modes. To study the feasibility of a ring-core fiber (RCF) for SDM systems, in this paper, we investigate the mode coupling in the RCF supporting five or seven guided mode groups (MGs) at a wavelength of 1550 nm. For this purpose, the coupled mode/power theory with identified spatial power spectrum of random perturbations of fiber axis is used to estimate the bend loss/crosstalk of the RCF due to microbending. It is shown that based on the identified parameters for the spatial power spectrum in the 5/7-MG RCF, the estimated bend loss/crosstalk of the RCF agrees well with experimental results. In addition, the impact of the gradient parameter α and refractive index contrast Δ of the fiber refractive index profile on bend loss and crosstalk of the RCF is explored. Simulation results indicate that the Δ instead of the α significantly affects bend loss and crosstalk of the RCF. The magnitude improvement in bend loss by increasing the Δ is dependent on the spatial power spectrum.

Fiber Bragg gratings in heterogeneous multicore fiber for directional bending sensing

Abstract: We present the fabrication of fiber Bragg gratings (FBGs) in a trench-assisted heterogeneous multicore fiber (MCF). Two obviously different Bragg reflection peaks are obtained due to the slight difference of refractive indices between the center core and the outer cores. To investigate the reflections of the two FBGs simultaneously, only a segment of multimode fiber is inserted between the lead-in single mode fiber and the MCF. The experimental results confirm that the curvature sensitivity of the FBG in the outer core is a sinusoidal function of the bending orientation angle. The maximum linear curvature sensitivity is about 0.128 nm/m?1. The cross sensitivity to temperature or externally applied axial strain can be eliminated by discriminating the different responses of FBGs inscribed in outer cores and the center core. Thus this MCF with FBGs can be utilized as a directional bending sensor. Moreover, the proposed sensor offers several advantages, such as low cost and flexibility in fabrication.

Optical vortex generation with wavelength tunability based on an acoustically-induced fiber grating.

Abstract: We presented a method to actualize the optical vortex generation with wavelength tunability via an acoustically-induced fiber grating (AIFG) driven by a radio frequency source. The circular polarization fundamental mode could be converted to the first-order optical vortex through the AIFG, and its topological charges were verified by the spiral pattern of coaxial interference between the first-order optical vortex and a Gaussian-reference beam. A spectral tuning range from 1540 nm to 1560 nm was demonstrated with a wavelength tunability slope of 4.65 nm/kHz. The mode conversion efficiency was 95% within the whole tuning spectral range.

Temperature Insensitive Liquid Level Sensor Based on Antiresonant Reflecting Guidance in Silica Tube

Abstract: We propose and demonstrate an optical fiber sensor based on a section of silica tube fusion spliced between single mode fibers. When light is conducted into the hollow core of the silica tube, anti-resonant reflecting guidance occurs, which leads to the periodic attenuation dips in the transmission spectra of the structure. The transmission intensity of the attenuation dips can be influenced by the surrounding medium, which gives rise to the application for liquid level sensing. A liquid level sensitivity of 0.4 dB/mm is achieved by immersing the sensor head vertically into water. Experimental results also prove that such a sensor is insensitive to temperature, eliminating the requirement for temperature compensation.

Design and fabrication of elliptical-core few-mode fiber for MIMO-less data transmission

Abstract: We propose a design strategy of elliptical core few-mode fiber (e-FMF) that supports three spatial modes with enhanced mode spacing between LP11a and LP11b, to suppress intra-mode coupling during mode-division multiplexing (MDM) transmission. Our theoretical investigations show that there exist two optimization regimes for the e-FMF, as a comparison with traditional circular core FMF(c-FMF). At the regime of three-mode operation, there occurs a trade-off between mode spacing and bending-induced loss. Meanwhile, in terms of five-mode regime, a trade-off between mode spacing and high-order mode crosstalk happens. Finally, we fabricate 7.94 km e-FMF with the optimal parameters, based on the commercial fiber manufacture facility. The primary characterizations at 1550 nm show that three spatial modes of e-FMF can be transmitted with a loss less than 0.3 dB/km. Meanwhile, −22.44 dB crosstalk between LP11a and LP11b is observed, even when the 2 km e-FMF is under stress-induced strong perturbation.

Selective transverse mode operation of an all-fiber laser with a mode-selective fiber Bragg grating pair.

Abstract: We propose a novel approach for achieving selective transverse mode operation of few-mode all-fiber lasers. Lasing in a specific transverse mode is enabled by employing a pair of few-mode fiber Bragg gratings as an efficient transverse mode selector. As a proof-of-principle, we have implemented a ytterbium-doped all-fiber laser operating in the second-order (LP11) transverse mode. The achieved output power is 81 mW, and the slope efficiency is as high as 54%. This simple and compact all-fiber laser is also capable of delivering cylindrical vector beams through appropriate polarization control. Furthermore, the approach has great scalability and can be applied to other working modes and spectral regimes.

Low-Differential-Mode-Group-Delay 9-LP-Mode Fiber

Abstract: We report the optimization of a few-mode fiber, adapted to multiple-input multiple-output mode division multiplexing, that supports 9 LP modes (15 spatial modes). The fiber is fabricated using standard multimode processes, which allows for tight process tolerances, yielding low differential mode group delays (<155 ps/km) with low attenuations (<0.22 dB/km), large effective areas (≥95 μm2) and low bend losses.