All-fiber active tractor beam generator and its application

Xiaoyun Tang, Yu Zhang, Yaxun Zhang, Zhihai Liu, Xinghua Yang, Zhang Jianzhong, Jun Yang, Libo Yuan

We propose and demonstrate an all-fiber probe to generate an active tractor beam by changing the gradients of optical intensity distributions. We grind the tip of a seven-core fiber (SCF) into a truncated hexagonal pyramid shape to integrate three equivalent two-core fiber optical tweezers in an SCF. Three optical tweezers produce three trapping locations along the fiber main axis. By adjusting and controlling the incident laser power in each core, we may perform multiple functions, including microparticles optical trapping, long-distance attraction, bidirectional transportation, and axial-direction position controllable adjustment. The proposed all-fiber active tractor beam generator is convenient to integrate and low cost. The all-fiber probe has the compatibility of optical tweezers and optical tractor beams. The increased effective range of optical pull broadens the scope of feasible optical trapping and will pave the way towards more efficient light-powered miniature machines, tools and applications.

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Generalized Modeling of Optomechanical Forces Applied to PT-Symmetric Optical Microscale Resonators

Martino De Carlo; Francesco De Leonardis; Luciano Lamberti; Vittorio M. N. Passaro

We propose an innovative optomechanical device, exploiting the force enhancement due to a quasi-PT symmetry in resonant coupled optical cavities. In order to perform the study, we develop a generalized modeling of the response theory of optical forces, including the loss and the gain effects in optical systems. The enhancement of optical force appears to be limited only by non-linearity and by the resolution of the gain/loss mechanism.

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Optomechanical Self-Regulated Coupling of a Suspended Microsphere Cavity and a Waveguide in the Aqueous Medium

Te-Chang Chen; Ming-Chang M. Le

Optomechanics of colloidal microparticles has wide applications in biological analysis and sensing. For colloidal microspheres or microdroplets, the optomechanical force can be magnified through the cavity enhancement effect. However, it is difficult to analyze the force since the colloidal microspheres are suspended in liquid, and addressing a movable microsphere at a specific position in three-dimensional space is also challenging. An on-chip integrated operating platform comprising waveguides and microelectromechanical systems is employed to study the cavity-enhanced optical gradient force on colloidal microspheres, owing to the ability to precisely control the distance between a suspended microsphere and a waveguide through dielectrophoretic force. We introduce two kinds of optomechanical coupling mechanisms at resonance, depending on the initial coupling gap without inclusion of the optical gradient force. One is self-adjusted coupling, where the coupling gap of a suspended microsphere continuously varies with the optical input power, and the other is bistable coupling, where the coupling gap hops from one state to the other as the input power exceeds over a threshold value, which is caused by the nature of nonlinear gap-dependent optical gradient force.

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Multiple Particles 3-D Trap Based on All-Fiber Bessel Optical Probe

Yaxun Zhang, Xiaoyun Tang, Yu Zhang, Zhihai Liu, Enming Zhao, Xinghua Yang, Jianzhong Zhang, Jun Yang, Libo Yuan

We propose and demonstrate an all-fiber Bessel optical tweezers for multiple microparticles (yeast cells) three-dimensional (3-D) trap. To the best knowledge of us, it is the first time to achieve the 3-D stable noncontact multiple microparticles optical traps with long distance intervals by using a single all-fiber probe. The Bessel beam is produced by splicing coaxially a single-mode fiber and a step index multimode fiber. The convergence of the output Bessel beam is performed by molding the tip of the multimode fiber into a special semiellipsoid shape. The effective trapping range of the all-fiber probe is 0 to 60 μm, which is much longer than normal single fiber optical tweezers probes. The all-fiber Bessel optical probe is convenient to integrate and suitable for the lab on the chip. The structure of this fiber probe is simple, high precision, low cost, and small size, which provides new development for biological cells experiment and operation.

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Multiple particles 3D trap based on all-fiber Bessel optical probe

Yaxun Zhang, Xiaoyun Tang, Yu Zhang, Zhihai Liu, Enming Zhao, Xinghua Yang, Jianzhong Zhang, Jun Yang, Libo Yuan

We propose and demonstrate an all-fiber Bessel optical tweezers for multiple microparticles (yeast cells) 3 dimensional trap. To the best knowledge of us, it is the first time to achieve the 3 dimensional stable non-contact multiple microparticles optical traps with long distance intervals by using a single all-fiber probe. The Bessel beam is produced by splicing coaxially a single mode fiber and a step index multimode fiber. The convergence of the output Bessel beam is performed by molding the tip of the multimode fiber into a special semi-ellipsoid shape. The effective trapping range of the all-fiber probe is 0 to 60μm, which is much longer than normal single fiber optical tweezers probes. The all-fiber Bessel optical probe is convenient to integrate and suitable for the lab on the chip. The structure of this fiber probe is simple, high-precision, low-cost, and small size, which provides new development for biological cells experiment and operation.

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Dual-Mode Fiber Optofluidic Flowmeter With a Large Dynamic Range

Yuan Gong ; Liming Qiu ; Chenlin Zhang ; Yu Wu ; Yun-Jiang Rao ; Gang-Ding Peng

A dual-mode fiber optofluidic flowmeter with a large dynamic range of four orders of magnitude is developed. The sensing mechanism is based on the force balance on an optically trapped polystyrene microparticle. As the optical force is at piconewton level, the flowmeter is very sensitive with a lower detection limit of 10 nl/min. In the open-loop mode, the manipulation length is used as the sensing output and the flowmeter has an inverse sensitivity so that it has higher sensitivity at lower flow rate. In the closed-loop mode, the manipulation length is set constant and a feedback signal, tuning the laser power for the force balance, is used as the sensing output. The closed-loop mode is helpful for extending the upper detection limit of flow rate and also enhancing the sensitivity at higher flow rate. This paper introduces a new kind of high-performance optofluidic sensors based on optical forces.

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Theoretical Study on Surface Mode in Photonic Crystal Fishbone Nanocavity

Tsan-Wen Lu; Po-Tsung Lee

We propose and theoretically investigate a novel 1-D photonic crystal fishbone (FB) that can sustain surface waves. By designing a nanocavity in an FB, the confined surface mode with a high quality factor (~ 105) and extremely concentrated field near the FB surface (small mode volume, ~ 2.3 × 10-2 (λ/2)3) cause strong interactions between light and the surrounding medium for optical sensing and manipulation. In simulation, as an optical sensor, the proposed design achieved a high index sensitivity of 650 nm/RIU and minimum detectable index variation of 2 × 10-5. As optical tweezers, a simulated injected optical threshold power of only 80 μW is needed for stably trapping a polystyrene sphere (PS) 100 nm in diameter. In addition, a method of selectively trapping a PS of specific size is theoretically proposed via our design. We believe that our proposed FB nanocavity with a surface mode would provide enhanced features for on-chip optical sensors and tweezers.

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New Trends on Optical Fiber Tweezers

Rodrigues Ribeiro, R.S.; Soppera, O.; Gonzalez Oliva, A.; Guerreiro, A.; Jorge, P.A.S.

In the last few decades, optical trapping has played an unique role concerning contactless trapping and manipulation of biological specimens. More recently, optical fiber tweezers (OFTs) are emerging as a desirable alternative to bulk optical systems. In this paper, an overview of the state of the art of OFTs is presented, focusing on the main fabrication methods, their features and main achievements. In addition, new OFTs fabricated by guided wave photo polymerization are reported. Their theoretical and experimental characterization is given and results demonstrating its application in the manipulation of yeast cells and the organelles of plant cells are presented.

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Designing a Plasmonic Optophoresis System for Trapping and Simultaneous Sorting/Counting of Micro- and Nano-particles

Ghorbanzadeh, M.; Moravvej-Farshi, M.; Darbari, S.

We are proposing a plasmonic-based optophoresis system that can trap and simultaneously sort and count metallic and dielectric micro- and nano-particles, in a simple microfluidic system. The operating principles of the proposed system are based on the particles intrinsic properties that modulate the in-duced optical force and the transmitted power. Particle manipu-lations, in this system, are based on the near-field optical forces excreted by leaky surface plasmons modes, excited on a gold stripe. Simulations show that the maximum potential depth sensi-tivity to the trapped PS/Au particles’ radius is ~ 0.09/0.03 (kBT / nm). The maximum transmission sensitivity in response to a change in radii of trapped Au and PS spheres are both ~0.01% per nm. Moreover, it is also shown that a minute change of ±1% in a refractive index of a 250-nm trapped dielectric particle re-sults in ±0.26 kBT and ∓0.13% variations in the potential depth and transmission, respectively. Furthermore, the proposed sys-tem that can be implemented simply and inexpensively, benefits from its small footprint for integration into lab-on-a-chip devices and low power consumption, with promising potentials for bio-logical applications.

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A Novel Temperature Sensor Based on Optical Trapping Technology

Yu Zhang, Peibo Liang, Zhihai Liu, Jiaojie Lei, Jun Yang, and Libo Yuan

We propose and fabricate a novel temperature sensor based on the optical trapping technology. The temperature sensing cell is constructed by putting a “test-micro-particle” enclosed in a space built by a quartz capillary tube and two opposite-inserted optical fibers. In order to make the temperature sensor have the ability of auto-ready and easy-reset, we design and fabricate the special concavities in the ends of two fibers. This ability of auto-ready and easy-reset makes the sensor convenient to be applied in industrial fields for long-term-use. These properties provide a new probably development direction in sensing research fields for the optical tweezers technology, and solve the optical tweezers measurement repeatability problems.

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Multi-Dimensional Manipulation of Yeast Cells Using a LP_11 Mode Beam

Zhang, Y.; Liang, P. ; Lei, J. ; Wang, L. ; Liu, Z. ; Yang, J. ; Yuan, L.

We report a new method for constructing a single fiber optical tweezers, which can realize multi-dimensional manipulation of trapped yeast cells by using a LP$_{bf 11}$ mode beam excited in a normal communication single core optical fiber. This allows a simple and convenient orientation control on the trapped yeast cells. The LP$_{bf 11}$ mode beam, both for generating trap and orientation manipulation, has been modulated by using the tension and twisting loaded on the fiber. We present experimental results of controllable deflection and orientation manipulation of the yeast cells. To the best of our knowledge, it is the first report about the trapped yeast cells being driven by the normal single fiber optical tweezers in multi dimensions, and it constitutes a new development for single fiber optical trapping and makes possible of more practical applications in the biomedical research fields.

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

Pengfei Wang; Lee, T. ; Ming Ding ; Zhenggang Lian ; Xian Feng ; Youqiao Ma ; Lin Bo ; Qiang Wu ; Semenova, Y. ; Wei Loh ; Farrell, G. ; Brambilla, G.

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.

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Enhanced Optical Forces by Hybrid Long-Range Plasmonic Waveguides

Lin Chen, Tian Zhang, and Xun Li
Compared with optical resonant structures, current plasmonic waveguides have the advantage of enhancing optical forces in a broad range of wavelengths, but the enhancement can only be maintained for several dozens of microns at 1.55 μm. Here, a hybrid long-range plasmonic waveguide, consisting of two identical dielectric nanowires symmetrically placed on each side of a thin metal film, is proposed for optical forces. Strong optical coupling between the dielectric waveguide mode and long-range plasmonic mode leads to enhanced optical forces on the dielectric nanowire at low input optical power due to the deep subwavelength optical energy confinement. The enhancement can be maintained for distances of 1∼2 orders of magnitude larger than that of previous plasmonic waveguides. The deep subwavelength optical confinement as well as enhanced field gradient also allows eff icient trapping of single nanoscale particle, while the smaller propagation loss ensures a much larger trapping region at the same input optical power. The present results enable the potential applications of precisely controlling the positions of dielectric nanowires as well as manipulating a single nanoparticle such as a biomolecule and one quantum dot.
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