Biomedical subjects

Sadik C Esener

Publications and source records attributed to Sadik C Esener.

10 recordsLinked to original sources

PubMed2006

Size tunable three-dimensional annular laser trap based on axicons.

A three-dimensional (3D) ring-shaped laser trap has been built using axicons. The diameter of this laser trap ranges from 70 to 140 mum and is adjusted by simply changing the position of one axicon in the optical path. Parallel 3D trapping of 5 mum silica microspheres and 3D confinement of cells along the ring are demonstrated. In this system the special optical properties of axicons are used to create a continuous annular trap with high power efficiency and a constant numerical aperture. This new approach, without any mechanical scanning, offers significant potential for applications in cell motility analysis and biotropism studies.

Equipment Design↗

PubMed2006

Optical bistability in vertical-cavity semiconductor optical amplifiers.

We present an overview of the properties and applications of optical bistability in vertical-cavity semiconductor optical amplifiers (VCSOAs). The basic physics and analytical models of this optical nonlinearity are discussed. Experimental results obtained from a VCSOA operated in the 850 nm wavelength region are presented. Counterclockwise hysteresis loops are obtained over a range of initial phase detuning and bias currents. One hysteresis loop is observed experimentally with an input power as low as 2 muW when the device is biased at 98% of its lasing threshold. Numerical simulations based on the Fabry-Perot resonator model and rate equations we developed show good agreement with our experimental observations. In addition, a low input intensity high contrast (10:1) optical and gate and 2R regeneration are demonstrated. We believe that bistable VCSOAs can significantly advance the prospect of a dense two-dimensional array of low-switching-intensity all-optical logic and memory elements.

Journal Article↗

PubMed2006

Dynamically adjustable annular laser trapping based on axicons.

To study the chemotactic response of sperm to an egg and to characterize sperm motility, an annular laser trap based on axicons is designed, simulated with the ray-tracing tool, and implemented. The diameter of the trapping ring can be adjusted dynamically for a range of over 400 microm by simply translating one axicon along the optical axis. Trapping experiments with microspheres and dog sperm demonstrate the feasibility of the system, and the power requirement agrees with theoretical expectation. This new type of laser trapping could provide a prototype of a parallel, objective, and quantitative tool for animal fertility and biotropism study.

Animals↗

PubMed2006

Self-aligned spatial filtering using laser optical tweezers.

We present an optical spatial filtering device that has been integrated into a microfluidic system and whose motion and alignment is controlled using a laser optical tweezer. The lithographically patterned micro-optical spatial filter device filters out higher frequency additive noise components by automatically aligning itself in three dimensions to the focus of the laser beam. This self-alignment capability is achieved through the attachment of a refractive optical element directly over the circular aperture or pinhole of the spatial filter. A discussion of two different spatial filter designs is presented along with experimental results that demonstrate the effectiveness of the self-aligned micro-optic spatial filter.

Equipment Design↗

PubMed2005

Laser-tweezer-controlled solid immersion microscopy in microfluidic systems.

We describe the creation and implementation of a near-field scanning solid immersion microscope that is specifically tailored for use in microfluidic systems. The microscope comprises a newly fabricated Weierstrass solid immersion lens (SIL), which is detached from its substrate and is free floating in the fluid, and a laser optical tweezer, which serves both as a trapping beam for alignment and positioning of the SIL and as a near-field scanning beam that images the sample through the SIL. A discussion of the SIL's fabrication method is presented along with experimental results that demonstrate the effectiveness of our microscope design.

Equipment Design↗

PubMed2005

Counter-propagating optical trapping system for size and refractive index measurement of microparticles.

We propose and demonstrate a novel approach to measure the size and refractive index of microparticles based on two beam optical trapping, where forward scattered light is detected to give information about the particle. The counter-propagating optical trap measurement (COTM) system exploits the capability of optical traps to measure pico-Newton forces for microparticles' refractive index and size characterization. Different from the current best technique for microparticles' refractive index measurement, refractometry, a bulk technique requiring changing the fluid composition of the sample, our optical trap technique works with any transparent fluid and enables single particle analysis without the use of biological markers. A ray-optics model is used to explore the physical operation of the COTM system, predict system performance and aid system design. Experiments demonstrate the accuracy of refractive index measurement of Deltan=0.013 and size measurement of 3% of diameter with 2% standard deviation. Present performance is instrumentation limited, and a potential improvement by more than two orders of magnitude can be expected in the future. With further development in parallelism and miniaturization, the system offers advantages for cell manipulation and bioanalysis compatible with lab-on-a-chip systems.

Biopolymers↗

PubMed2005

Two-beam optical traps: refractive index and size measurements of microscale objects.

A counter-propagating optical trap measurement (COTM) system is proposed and analyzed based on the ray-optics model. In this system, refractive index and size of trapped objects can be estimated by using forward scattered light from the two-beam laser trap with resolution Delta n = 0.013 for the refractive index measurements and 3.3% for the size measurements, which is comparable with current bulk techniques, such as refractometry, and flow cytometry. The unique advantage of the COTM system over conventional approaches lies in its capability of marker-free single-particle characterization in whatever transparent buffer required by living cell, eliminating the necessity of changing the fluid composition of the sample in refractometry, and of tagging target with toxic fluorescence dyes in flow cytometry. Noise analysis predicts a potential improvement in the system resolution by more than two orders of magnitude. This non-invasive and sterile tool complements lab-on-a-chips with single cell manipulation and analysis in living friendly ambient.

Biopolymers↗

PubMed2004

Use of moving optical gradient fields for analysis of apoptotic cellular responses in a chronic myeloid leukemia cell model.

To facilitate quantitation of cellular apoptotic responses to various antineoplastic agents, a laser-based technology, Optophoresis, has been developed to provide analysis of cells without any need for labeling or cell processing. Optophoresis is defined as the analysis of the motion of cells, where the motion is either induced or modified by a moving optical gradient field, which produces radiation pressure forces on the cells in an aqueous suspension. Quantitation of the induced motion provides a basis for distinguishing one population of cells from another. One Optophoretic technique, Fast Scan, measures the distribution of distances traversed by a population of cells when exposed to a fast-moving optical gradient. Fast Scan was validated using a cell-based model of chronic myeloid leukemia treated with Gleevec, a specific inhibitor of aberrant Bcr-Abl protein kinase. The Optophoretic measurements were quantitatively comparable to reference assays with regard to drug selectivity and potency and to target specificity, demonstrating the suitability of this technology for pharmaceutical and clinical applications.

Antineoplastic Agents↗

PubMed2002

Misalignment tolerance analysis of free-space optical interconnects via statistical methods.

System-level packaging is one of the critical issues that need to be addressed for free space optical interconnections (FSOI) to become useful in desktop systems. The performance of FSOI, e.g., in terms of system bit-error rate, is greatly affected by misalignments in the optical system. Therefore tolerancing, i.e., the ability to analyze and predict the effects of misalignments in the system, is of prime importance to system designers. We introduce an approach in which we study the effects of optical misalignments and other tolerance factors using statistical methods. We use Monte Carlo simulations, design of the experiments, and regression techniques to fit a polynomial equation that expresses the relationship between the system performance and the tolerance factors. This prediction model can be used for design, cost optimization, and quality control purposes. In addition, we perform a sensitivity analysis to determine those tolerance variables that have the greatest effect on system performance.

Journal Article↗

PubMed2002

Three-dimensional optoelectronic stacked processor by use of free-space optical interconnection and three-dimensional VLSI chip stacks.

We present a demonstration system under the three-dimensional (3D) optoelectronic stacked processor consortium. The processor combines the advantages of optics in global, high-density, high-speed parallel interconnections with the density and computational power of 3D chip stacks. In particular, a compact and scalable optoelectronic switching system with a high bandwidth is designed. The system consists of three silicon chip stacks, each integrated with a single vertical-cavity-surface-emitting-laser-metal-semiconductor-metal detector array and an optical interconnection module. Any input signal at one end stack can be switched through the central crossbar stack to any output channel on the opposite end stack. The crossbar bandwidth is designed to be 256 Gb/s. For the free-space optical interconnection, a novel folded hybrid micro-macro optical system with a concave reflection mirror has been designed. The optics module can provide a high resolution, a large field of view, a high link efficiency, and low optical cross talk. It is also symmetric and modular. Off-the-shelf macro-optical components are used. The concave reflection mirror can significantly improve the image quality and tolerate a large misalignment of the optical components, and it can also compensate for the lateral shift of the chip stacks. Scaling of the macrolens can be used to adjust the interconnection length between the chip stacks or make the system more compact. The components are easy to align, and only passive alignment is required. Optics and electronics are separated until the final assembly step, and the optomechanic module can be removed and replaced. By use of 3D chip stacks, commercially available optical components, and simple passive packaging techniques, it is possible to achieve a high-performance optoelectronic switching system.

Journal Article↗