Optical selection, manipulation, trapping, and activation of a microgear structure for applications in micro-optical-electromechanical systems

Micro-optical pattern-based selective transmission mechanism

This paper presents a micro-optical pattern-based selective transmission mechanism with a simple modulation principle. The mechanism is composed of a patterned plate and liquid medium, and it does not contain a transparent conductor. The pattern uses 50 μm rectangular pyramid shapes that satisfy a retro-reflection condition. An ultraprecision diamond-cutting machine is used to precisely fabricate the metallic patterned mold, and a hot embossing process creates the micro-optical pattern. The measurement results show that the proposed mechanism displays a much higher optical performance and more durability than the existing switchable glasses in the specific condition. It has specular transmittances of 84.1% in the transparent state and 0.2% in the translucent state, and its total reflectance is 50.4%. An optical simulation verifies the measurement results with a specific analysis.

Contactless and non-invasive delivery of micro-particles lying on a non-customized rigid surface by using acoustic radiation force

In the existing acoustic micro-particle delivery methods, the micro-particles always lie and slide on the surface of platform in the whole delivery process. To avoid the damage and contamination of micro-particles caused by the sliding motion, this paper deals with a novel approach to trap micro-particles from non-customized rigid surfaces and freely manipulate them. The delivery process contains three procedures: detaching, transporting, and landing. Hence, the micro-particles no longer lie on the surface, but are levitated in the fluid, during the long range transporting procedure. It is very meaningful especially for the fragile and easily contaminated targets. To quantitatively analyze the delivery process, a theoretical model to calculate the acoustic radiation force exerting upon a micro-particle near the boundary in half space is built. An experimental device is also developed to validate the delivery method. A 100 μm diameter micro-silica bead adopted as the delivery target is detached from the upper surface of an aluminum platform and levitated in the fluid. Then, it is transported along the designated path with high precision in horizontal plane. The maximum deviation is only about 3.3 μm. During the horizontal transportation, the levitation of the micro-silica bead is stable, the maximum fluctuation is less than 1 μm. The proposed method may extend the application of acoustic radiation force and provide a promising tool for microstructure or cell manipulation.

The self-orientation of mammalian cells in optical tweezers--the importance of the nucleus

Here we present the first evidence showing that eukaryotic cells can be stably trapped in a single focused Gaussian beam with an orientation that is defined by the nucleus. A mammalian eukaryotic cell (in suspension) is trapped and is re-oriented in the focus of a linearly polarized Gaussian beam with a waist of dimension smaller than the radius of the nucleus. The cell reaches a position relative to the focus that is dictated by the nucleus and nuclear components. Our studies illustrate that the force exerted by the optical tweezers at locations within the cell can be predicted theoretically; the data obtained in this way is consistent with the experimental observations.

Optical rotor capable of controlling clockwise and counterclockwise rotation in optical tweezers by displacing the trapping position

A clockwise rotor and a counterclockwise rotor (a clockwise rotor placed upside down) are linked on the optical axis to control the rotation direction in optical tweezers by displacing the trapping (focus) position. The dependence of optical torque on the trapping position of this linked rotor is analyzed using an upward-directed focused beam as illumination, via an objective lens with a numerical aperture of 1.4, using a ray optics model under the condition that laser light is incident to not only the lower surfaces, but also to the side surfaces of both rotors. The rotation rate in water is also simulated for an SU-8 linked rotor with 20 microm diameter at a laser power of 200 mW, with rotor thickness as a parameter, by balancing the optical torque with the drag force evaluated using computational fluid dynamics. It is confirmed that the rotation direction changes from clockwise to counterclockwise with the displacement of the trapping position, that almost the same rotation speed is possible in both directions, and that both speeds increase, reach a maximum at a rotor thickness of 9 microm, and then decrease as the thickness increases.

Probing technique using circular motion of a microsphere controlled by optical pressure for a nanocoordinate measuring machine

A new surface probing technique using the circular motion of an optically-trapped microsphere is proposed for a nanocoordinate measuring system. The probe sphere is oscillated circularly in the plane perpendicular to the probe axis and the circular orbit of the probe sphere is monitored for the detection of the position and normal vector direction of the surface. The principle of detection is based on changes in the circular orbit of the microsphere. When the probe approaches a work surface, the orbit of the probe sphere becomes elliptical. The minor-axis length and the minor-axis angle of the ellipse are then used as parameters to detect the position and normal vector direction of the surface, respectively. In this study, the circular motion probe is shown to have a resolution of position detection of 39 nm, and the accuracy of measuring a normal vector to the surface is on the order of 3 degrees.

Parallel photopolymerisation with complex light patterns generated by diffractive optical elements

Photopolymerisation by scanning a focused laser beam is a powerful method to build structures of arbitrary complexity with submicrometer resolution. We introduce parallel photopolymerisation to enhance the efficiency. Instead of multidimensional scanning of a single focus, the structure is generated simultaneously with diffractive patterns. We used fixed diffractive optical elements (DOEs), kinoforms, and Spatial Light Modulators (SLMs). The possibilities of photopolymerisation using SLM were investigated: the added flexibility using the programmable device is demonstrated. By using these DOEs, straight and helical cross shaped columns were produced with a single scan at a rate about an order of magnitude faster than by simple scanning. The produced helical structures could be rotated by optical tweezers.

Integrated optical motor

A light-driven micrometer-sized mechanical motor is created by laser-light-induced two-photon photopolymerization. All necessary components of the engine are built upon a glass surface by an identical procedure and include the following: a rigid mechanical framework, a rotor freely rotating on an axis, and an integrated optical waveguide carrying the actuating light to the rotor. The resulting product is a most practical stand-alone system. The light introduced into the integrated optical waveguide input of the motor provides the driving force: neither optical tweezers or even a microscope are needed for the function. The power and efficiency of the motor are evaluated. The independent unit is expected to become an important component of more complex integrated lab-on-a-chip devices.

Self-centering of a ball lens by laser trapping: fiber-ball-fiber coupling analysis

Fiber-to-fiber coupling through use of a laser-trapped microball lens is examined. A model based on radiation pressure predicts that the ball lens will align axially between the fiber endfaces. Laser manipulation of the ball lens axial position results in a configuration in which the ball lens optically bridges the gap between the fibers. Experimental results are presented for several fiber endface separations, and it is found that the presence of the microball lens can increase the coupling by a factor of 2 above the level expected by direct fiber-to-fiber coupling for the same fiber endface separation.

Laser-trapping properties of dual-component spheres

The optical trapping properties of dual-component spheres consisting of a cocentered outer transparent dielectric spherical shell and internal solid sphere are examined on the basis of the enhanced ray optics model. It is shown that stable trapping can occur on axis, off axis, or at multiple axial positions and depends on the dual-sphere and laser beam parameters. Computation results are also presented for an internal reflecting sphere surrounded by an outer dielectric spherical shell.

Microfluidic control using colloidal devices

By manipulating colloidal microspheres within customized channels, we have created micrometer-scale fluid pumps and particulate valves. We describe two positive-displacement designs, a gear and a peristaltic pump, both of which are about the size of a human red blood cell. Two colloidal valve designs are also demonstrated, one actuated and one passive, for the direction of cells or small particles. The use of colloids as both valves and pumps will allow device integration at a density far beyond what is currently achievable by other approaches and may provide a link between fluid manipulation at the macro- and nanoscale.