Hiroo Ukita

Optically induced rotation of dissymmetrically shaped fluorinated polyimide micro-objects in optical traps

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. T...

A photomicrodynamic system with a mechanical resonator monolithically integrated with laser diodes on gallium arsenide.

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.

Supersmall flying optical head for phase change recording media

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 shuttlecock optical rotator-its design, fabrication and evaluation for a microfluidic mixer

An optically driven microrotator is proposed for fluidic mixing in future micrototal analysis systems (/spl mu/-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.

A Speckle Pattern Velocimeter Using a Periodical Differential Detector

A new method for non-contact velocimeter is proposed. A one-dimensional photodiode array, whose diodes are connected differentially, is used instead of a parallel slit array, in order to remove the low frequency noise. Then, the output signal of the differential detector is restricted to a narrow band signal, whose center frequency is proportional to the velocity of a rough surface. Since the output can be directly fed to a frequency counter, the restriction of the measurement range due to the cut-off frequency of the high pass filter is lifted. The characteristics of the proposed velocimeter are studied with the aid of spectrum analysis and some experimental results are shown.

Ion beam sputtered (SiO 2 )x(Si 3 N 4 ) 1− x antireflection coatings on laser facets produced using O 2 –N 2 discharges

The chemical composition of a (SiO(2))(x)(Si(3)N(4))(1-x) film produced by ion beam sputtering was precisely controlled by the ratio of O(2) and N(2) flow rates under a discharge current kept constant to within an accuracy of +/-0.05 A. The reproducibility of the refractive index was improved to +/-0.01. This film was applied to form antireflection coatings with extremely low reflectivity on facets of 830-nm AlGaAs double heterostructure lasers. The minimum reflectivity was 6.8 x 10(-5), and a reflectivity of 1 x 10(-4) was achieved reproducibly. Experimental studies show that antireflection coatings are effective for suppressing the interferometric light output variation of composite cavity lasers.

Optical tweezers and fluid characteristics of an optical rotator with slopes on the surface upon which light is incident and a cylindrical body

The characteristics of the optical trapping force, optical torque, and viscous drag force for a newly proposed cylindrical optical rotator are analyzed. The optical trapping force and torque are evaluated by use of a ray optics model for both parallel and focused laser beam illumination. The drag force is calculated from computational fluid dynamics to be the sum of the components of both the pressure and the shearing stress on all the surfaces of the rotator. We analyze the rotation rate by balancing the optical torque with the drag force. A cylindrical optical rotator is expected to rotate at a high speed because of its highly efficient generation of optical torque and its small viscous drag force.

Optical pregroove dimensions: design considerations

This paper describes the designing pregroove dimensions to achieve stable data read-out. The spot size detection method and the push-pull method are used for focusing and tracking error signal detection, respectively. Experimental and theoretical results show that pregroove crosstalk and decrease in light intensity due to groove diffraction become smaller as the edge gradient of the pregroove decreases. The permissible range of the depth for a triangular pregroove is 40% larger than that of a rectangular pregroove. The triangular pregroove depth to attain the maximum tracking signal efficiency is about 100 nm for a refractive index of 1.5.

Applications of an extremely short strong-feedback configuration of an external-cavity laser diode system fabricated with GaAs-based integration technology

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.

Read/write performance and reliability of a flying optical head using a monolithically integrated LD–PD

A flying head using the switching characteristics of an optically switched laser diode is shown to have an excellent read/write performance and head-disk interface. This head consists of an aluminum nitride slider and a 1.3-microm wavelength InGaAsP laser diode monolithically integrated with a photodetector (LD-PD). A ridged waveguide is fabricated on top of the LD facet to converge the light beam. The lensless flying head has a minimum power of 18 mW for writing information (at 1 MHz) at a medium velocity of 7 m/s. The disk has a SiN protective layer over a SbTeGe phase-change recording medium. The head signal remains good after more than 5 x 10(4) contact start/stop cycles and 4.4 x 10(8) passes in an experimental room environment.