Office-based endoscopic laser surgery is an increasingly popular option for the treatment of many benign and premalignant tumors of the vocal folds. While these procedures have been shown to be generally safe and effective, recent clinical studies have revealed that there are a number of challenging locations inside the larynx where laser light cannot be easily delivered due to line-of-sight limitations. In this paper, we explore whether these challenges can be overcome through the use of side-firing laser fibers. Our study is conducted in simulation, using three-dimensional models of the human larynx generated from X-ray microtomography scans. Using computer graphics techniques (ray-casting), we simulate the application of laser pulses with different types of laser fibers and compare the total anatomical coverage attained by each fiber. We consider four fiber types: a traditional “forward-looking” fiber - not unlike the ones currently used in clinical practice - and three side-firing fibers that emit light at an angle of 45, 70, and 90 degrees, respectively. Results show that side-firing fibers enable a ∼70% increase in accessible anatomy compared to forward-looking fibers.
Tapered optical fibers can deliver guided light into and carry light out of micro/nanoscale systems with low loss and high spatial resolution, which makes them ideal tools in integrated photonics and microfluidics. Special geometries of tapered fibers are desired for probing monolithic devices in plane as well as optical manipulation of micro particles in fluids. However, for many specially shaped tapered fibers, it remains a challenge to fabricate them in a straightforward, controllable, and repeatable way. In this work, we fabricated and characterized two special geometries of tapered optical fibers, namely fiber loops and helices, that could be switched between one and the other. The fiber loops in this work are distinct from previous ones in terms of their superior mechanical stability and high optical quality factors in air, thanks to a post-annealing process. We experimentally measured an intrinsic optical quality factor of 32,500 and a finesse of 137 from a fiber loop. A fiber helix was used to characterize a monolithic cavity optomechanical device. Moreover, a microfluidic "roller coaster" was demonstrated, where microscale particles in water were optically trapped and transported by a fiber helix. Tapered fiber loops and helices can find various applications ranging from on-the-fly characterization of integrated photonic devices to particle manipulation and sorting in microfluidics.
KEYWORDS: Sensors, Temperature metrology, Silicon, Resonators, Finite element methods, Transducers, Near field optics, Optical resonators, Near field, Neck
There exists a tradeoff between the mechanical resonant frequency (fm) and the mechanical quality factor (Qm) of a nanomechanical transducer, which resulted in a tradeoff between the band width and sensitivity. Here, we present monolithic silicon nitride (Si3N4) cavity optomechanical transducer, in which high fmand Qmare achieved simultaneously. A nanoscale tuning fork mechanical resonator is near-field coupled with a microdisk optical resonator, allowing the displacement of mechanical resonator to be optically read out. Compared with a single beam with same length, width, and thickness, the tuning fork simultaneously increases fmand Qmby up to 1.4 and 12 times, respectively. A design enabled, on-chip stress tuning method is also demonstrated. By engineering the clamp design, we increased the stress in the tuning fork by 3 times that of the Si3N4 film. A fundamental mechanical in-plane squeezing mode with fm ≈ 29 MHz and Qm ≈ 2.2×105 is experimentally achieved in a high-stress tuning fork device, corresponding to a fmQm product of 6.35×1012 Hz. The tuning fork cavity optomechanical sensors may find applications where both temporal resolution and sensitivity are important such as atomic force microscopy.
In this work, we developed fiber based optical trapping system and explored its applications in biology and physics. We aim to replace objective lenses with optical fibers, both for optical trapping and particle position detection. Compared with objective lens based counterparts, fiber based optical trapping systems are small, low-cost, integratable, independent of objective lenses, and can work in turbid mediums. These advantages make fiber optical trapping systems ideal for applications in tightly confined spaces as well as integration with various microscopy techniques.
We demonstrate the applications of fiber optical trapping systems in both single-cell mechanics and microrheology study of asphalt binders. Fiber optical trapping system is being used to study mechanical properties of viscoelastic hydrogel, as an important extra cellular matrix (ECM) material that is used to understand the force propagation on cell membranes on 2D substrates or in 3D compartments. Moreover, the fiber optical trapping system has also been demonstrated to measure the cellular response to the external mechanical stimuli. Direct measurements of cellular traction forces in 3D compartments are underway. In addition, fiber optical trapping systems are used to measure the microscale viscoelastic properties of asphalt binders, in order to improve the fundamental understanding of the relationship between mechanical and chemical properties of asphalt binders. This fundamental understanding could help targeted asphalt recycling and pavement maintenance. Fiber optical trapping systems are versatile and highly potential tools that can find applications in various areas ranging from mechanobiology to complex fluids.
Inclined dual-fiber optical tweezers (DFOTs) are investigated both numerically and experimentally. In simulations, the
trapping forces of the inclined DFOTs and the single-fiber optical tweezers (SFOTs) are studied along two directions. By
comparing the simulation results of the inclined DFOTs and the SFOTs, the inclined DFOTs are found to have more
symmetric performance, stronger trapping forces, and more reliable functionality. The spring constant of the DFOTs was
calibrated experimentally along one direction. The calibration results agree with those obtained in simulations. Moreover,
we created multiple optical traps with an inclined dual-fiber optical tweezers setup. Multiple optical traps were formed at
different vertical levels. We demonstrated that this fiber-based trapping system can perform multiple functions, such as
particle grouping and stacking. Compared with those formed with objective-based optical tweezers, the multiple traps
presented here are small in size and independent of the objective or the substrate, and hence hold the promise to be
integrated in microfluidic systems. The inclined DFOTs capable of multiple trapping can be used for on-chip parallel
manipulation.
Experimental measurements of the strain and pressure of rotor blades are important for understanding the aerodynamics
and dynamics of a rotorcraft. This understanding can help in solving on-blade problems as well as in designing and
optimizing the blade profiles for improved aerodynamics and noise attenuation in the next generation rotorcraft. The
overall goal of our research is to develop a miniature wireless optical sensor system for helicopter on-blade pressure and
strain measurements. In this paper, leveraging past and current experiences with fiber optic sensor development, a proof-of-
concept of fiber optic pressure/strain sensor system with wireless data acquisition and transfer capability is
demonstrated. The recently developed high-speed, real-time fiber optic sensor demodulation techniques based on low
coherence interferometry and phase-shifting interferometry is used. This scheme enables a Spatial Division Multiplexing
configuration that consists of multiple Fabry-Perot strain and pressure sensors. Calibration of the strain and pressure
sensors is carried out by using commercially available sensors as references. Spin chamber testing of the sensor system
for simultaneous on-blade pressure and strain field measurements is also performed. It is expected that such a sensor
system will result in enhanced robustness and performance for on-blade pressure and strain field measurements.
Three dimensional cell manipulation using two inclined fibers with lensed tips is demonstrated. For the first time, the
relationship between optical forces and cell positions is experimentally characterized in such an optical fiber trap, which
exhibits a good linearity in the vicinity of the equilibrium. The system is capable of being a force sensor with a
resolution of around 1 pN/&mgr;m. The spring constant is found to be dependent on the cell's shape: a prolate cell entails a
larger spring constant than that of a round cell with a similar size. Numerical analysis is carried out by using a modified
ray optics model with a spheroidal object in the trap. The spring constant obtained from the analysis also depends on the
shape of a cell, which agrees with the experimental results. The fiber optical tweezers have great potential for threedimensional
manipulation and force measurement of cells.
In this article, recently developed high-speed, real-time fiber optic sensor demodulation techniques based on low coherence interferometry and phase-shifting interferometry are presented. The demodulation schemes are used in a pressure sensor system that consists of a Fabry-Perot sensing interferometer and an integrated optical circuit (IOC) phase modulator that is used as a reference interferometer. Various conventional phase-stepping algorithms and novel algorithms with error compensations are investigated in order to reduce the errors in the demodulated phase signals. The errors introduced in the phase demodulation arise from many sources, including random intensity measurement errors, phase-shifting errors, and signal-related errors associated with time delays. Numerical analyses are conducted to compare the performances of the demodulation schemes based on different phase-shifting algorithms. These analyses will provide guidelines for choosing appropriate algorithms in sensor demodulation schemes and improving the sensor accuracy and bandwidth.
In this letter, we propose the new theoretical investigation on the optical forces and torques on complex microrotors. On the basis of R. C. Gauthier’s hybrid ray-wave model, the optical forces and toques on two complex asymmetric micro-objects, the conical microrotor and the helical microrotor, are analyzed. The viscous drag torque is estimated by Stokes flow to obtain the rotational speed. The results of our computation agree well with the previously published experimental results, which indicates that our approach of the optical torque calculation is suitable for other complex microrotors and that the theoretical calculation is very helpful to optimum design of light-driven microrotors.
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