Optical trapping and directional high-speed rotation by radiation pressure are demonstrated for anisotropic micro-objects fabricated by reactive ion-beam etching. These micro-objects, which have shape dissymmetry (not bilateral symmetry but rotational symmetry) in the horizontal cross section, rotate about the laser beam axis in the designed direction in a liquid medium (e.g., water or alcohol). The rotation speed is almost proportional to the input laser power.

Fluorinated polyimide micro-objects (6–7.5 μm cross-sectional radius) fabricated using reactive ion etching have been both optically trapped and simultaneously rotated in both high and low relative–refractive index surrounding media. Symmetrical micro-objects with a low relative–refractive index were optically trapped by exerting optical radiation pressure through their center openings by using a strongly focused trapping laser beam. Micro-objects were both trapped and rotated by the radiation pressure when the horizontal cross sections of these objects showed dissymmetry (that is, not bilateral but rotational symmetry). In the case of micro-objects with a high relative–refractive index, the pressure is exerted on the outer walls. For objects with a low relative–refractive index, the pressure is exerted on the inner walls. The rotation speed versus optical power (typically, 0.4–0.7 rpm/mW) and the axial position of the laser focal point were investigated for high relative–refractive index micro-objects. The optically induced torque generated by a TEM01* (doughnut)-mode laser beam was found to be greater than that generated by a TEM00-mode laser beam.

A cantilever resonant microbeam, laser diodes, and a photodiode have been fabricated on the surface of a gallium arsenide substrate. The microbeam is excited photothermally by light from a laser diode. The vibration is detected with a photodiode as the variation in light output caused by the difference in optical length between the microbeam and another laser diode. A high carrier-to-noise ratio (45 decibels) is achieved with a short (3 micrometers) external cavity length. Such a small distance allows a lensless system, which increases the ease of fabrication. This work could lead to applications in which photomicrodynamic systems are monolithically integrated on a gallium arsenide substrate with surface micromachining technology.

An optically driven microrotator is proposed for fluidic mixing in future micrototal analysis systems (-TAS). The rotation mechanism, optical torque and microflow around the rotator are analyzed, and the rotator is fabricatied both by photolithography and photoforming methods. The microflow fields generated by the optical rotation are then experimentally visualized by both tracer and optical methods, and the velocity vectors and flux amount around the rotator are analyzed for the evaluation of the mixing performance of the microfluids.

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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.

A supersmall optically switched laser (OSL) head is proposed. A laser diode attached to an air bearing slider forms a complex cavity together with a recording medium, and its light output is detected by a photodetector placed at the other end of the laser facet. Data signals and track error signals read from the sampled servo marks are successfully detected. The signal amplitude variation caused by the flying height change is much reduced, and the SNR is increased to 36 dB (40 kHz to 20 MHz for a phase change medium) by decreasing the reflectivity of the laser facet facing the medium to <5%.

A composite-cavity laser diode is used to monitor the reflectivity or the displacement of the external-cavity mirror for micromechanical photonics devices. Optical disk bits are read out in the near field from the difference in medium reflectivity with an antireflection-coated laser diode and a photodiode. Microbeam vibration is also detected in the near field from the phase difference with an uncoated laser diode and a photodiode. In both cases the carrier-to-noise ratio is very high (more than 45 dB) because of the lack of mode-hopping noise resulting from the extremely short (less than 3 µm) external-cavity length and strong light feedback. These composite-cavity laser diode microdevices are fabricated on a gallium arsenide substrate to eliminate the need for optical alignment.