Renshi Sawada

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...

An integrated laser blood flowmeter

We have constructed a very small and lightweight blood flowmeter using micromachining and surface mounting techniques for a wearable health monitoring system. The hybrid integrated structure of the optical system incorporates a InGaAsP-InP distributed feedback laser diode (DFB-LD) with a wavelength of 1310 nm, an edge-illuminated photodiode (PD) and a polyimide waveguide on silicon substrate (2 mm /spl times/ 3 mm). This integrated flowmeter can be positioned directly on the tissue and permits real-time monitoring of capillary microcirculation. In-vivo measurements of blood perfusion in a finger confirm the feasibility of the blood flowmeter.

Hybrid microlaser encoder

We have developed a microlaser encoder that can detect displacements relative to an external grating scale with a resolution on the order of 10 nm. Its size is only a few tens of a percent of a conventional encoders. A long-lasting InP laser diode with a wavelength of 1550 nm was bonded, along with several photodiode chips, within an alignment accuracy of 1 /spl mu/m onto a silicon planar lightwave circuit chip. The chip is 2.3 mm /spl times/ 1.7 mm and includes a fluorinated polyimide lightwaveguide fabricated in advance. A wide gap of more than 600 /spl mu/m was obtained between the external grating scale and the encoder despite the tiny size of the sensor. When used as a rotary encoder, the number of rotations could also be detected. Thus, this microencoder satisfies the market requirements for practical use.

Monolithically integrated optical displacement sensor based on triangulation and optical beam deflection

A monolithically integrated optical displacement sensor based on triangulation and optical beam deflection is reported. This sensor is simple and consists of only a laser diode, a polyimide waveguide, and a split detector (a pair of photodiodes) upon a GaAs substrate. The resultant prototype device is extremely small (750 microm x 800 microm). Experiments have shown that this sensor can measure the displacement of a mirror with resolution of better than 4 nm. Additionally, we have experimentally demonstrated both axial and lateral displacement measurements when we used a cylindrical micromirror (diameter, 125 microm) as a movable external object.

Highly accurate and quick bonding of a laser-diode chip onto a planar lightwave circuit

A method for accurately and quickly bonding a planar lightwaveguide circuit (PLC) and a laser diode is proposed. It is based on simultaneous auto-focusing on marks fabricated on the PLC and laser diode. Bonding equipment constructed to implement the method achieves alignment accuracy of ± 1 μm and greatly reduces the turn-around-time, i.e., the time from when the laser diode is picked up by the tweezers to completion of the bonding process.

Optically driven angular alignment of microcomponents made of in-plane birefringent polyimide film based on optical angular momentum transfer

The optically driven angular alignment of micromachined components (microlenses and microprisms) within a single-beam optical trap using a linearly-polarized laser is presented. This optically induced angular alignment around the laser beam axis results from the spin angular momentum of the laser beam produced by the birefringence of the trapped microcomponents. The microcomponents are fabricated by reactive ion etching of an in-plane birefringent polyimide film (retardation = Δnd = 0.76λ where Δn = nslow-nfast is the birefringence, d is the thickness and λ is the wavelength). The fabricated microlenses and microprisms are made to align at desired angular positions simply by changing the direction of the vibration plane of a linearly-polarized laser beam.

NANOMETER-DISPLACEMENT DETECTION OF OPTICALLY TRAPPED METALLIC PARTICLES BASED ON CRITICAL ANGLE METHOD FOR SMALL FORCE DETECTION

We have developed a method of measuring the displacement of optically trapped metallic particles (10 μm in diameter) in water with nanometer resolution to detect small forces. Metallic particles were optically trapped in two dimensions by focusing a laser beam below the particle using an objective lens with a numerical aperture of 0.9. Displacement of a trapped metallic particle was detected using the light reflected from the particle based on the critical angle method. The lateral spring constant was estimated from the equipartition theorem to be on the order of 10−6 N/m and found to increase as the incident laser power increased. Consequently, a trapped metallic particle can be used to detect small forces (10−13 N).

Axial and Lateral Displacement Measurements of a Microsphere Based on the Critical-Angle Method

A method has been developed for optically measuring nanometer-scale displacements of transparent and metal-coated microspheres in both the axial (vertical) and lateral (horizontal) directions. This method works by detecting changes in the internal reflection of a laser beam reflected from the microsphere after it passes through critical-angle prisms. For weakly reflective 10-µm-diameter polystyrene microspheres in water (relative refractive index n=1.2), the detection resolutions as estimated from the full-width at half maximum (FWHM) noise level in the frequency region above 500 Hz in the axial and lateral directions were experimentally found to be as good as 1.7 and 1.1 nm, respectively. Furthermore, the lateral displacement resolution (0.2 nm) of a 10-µm-diameter metal-coated microsphere was better than the axial displacement resolution (0.9 nm) of a conventional flat mirror by more than a factor of four.