Three-dimensional microfabrication with two-photon-absorbed photopolymerization

We propose a method for three-dimensional microfabrication with photopolymerization stimulated by two-photon absorption with a pulsed infrared laser. An experimental system for the microfabrication has been developed with a Ti:sapphire laser whose oscillating wavelength and pulse width are 790 nm and 200 fs, respectively. The usefulness of the proposed method has been verified by fabrication of several kinds of microstructure by use of a resin consisting of photoinitiators, urethane acrylate monomers, and urethane acrylate oligomers.     

Generation of sub-Poissonian light by a four-level microlaser with a high-Q cavity

We develop a kinetic theory that describes the behavior of a monatomic four-level laser when the atom is fixed inside a high-Q optical cavity. Such a statement of the problem is similar to that used in the experiment of G. M. Meyer, H.-J. Briegel, and H. Walther [Europhys. Lett. 37, 317 (1997)]. The condition that the number of photons is large and the photon fluctuations are small is employed. We show that by selecting the parameters of the periodic electromagnetic pulses exciting the atom one can achieve regular pumping of the upper laser level and generate sub-Poissonian laser light. We also discuss the reasons why the statistical pattern of the radiation differs from the micromaser pattern with regular injection of atoms. Zh. éksp. Teor. Fiz. 116, 485–502 (August 1999)     

Three-dimensional photochemical microfabrication of conductive polymers in transparent polymer sheet

By focused illumination at the wavelength of 800 nm using a femtosecond laser, the tris(2,2′-bipyridyl)ruthenium complex displayed a two-photon excitation as observed by the quadratic dependence of the emission intensity on the incident laser power. Since the oxidation of pyrrole is induced by the oxidative quenching of the excited state, polypyrrole can be formed by a continuous illumination. The polymerization area showed a high spatial selectivity which can be scanned in the XYZ axis by a piezo device. In the present study, three-dimensional (3D) polypyrrole microstructures were formed in the transparent polymer sheet.     

Array of a dye-doped polymer-based microlaser with multiwavelength emission

This Letter reports a convenient method of fabricating a polymer-based microlaser array. Laterally aligned plastic micropillars equipped with an optical resonator were fabricated by using a lithographic technique with an organic-dye-doped photopolymer, which operated as a laser element with a vertical cavity. Under optical pumping, very fine emission spectra showing a Fabry-Perot-type lasing oscillation were observed. Using this technique, integrated laser cavities with desired operation wavebands can be produced easily.     

Metal-cavity surface-emitting microlaser with hybrid metal-DBR reflectors

We demonstrate a metal-cavity surface-emitting microlaser at room temperature using hybrid metal/distributed Bragg reflectors as well as substrate removal. Our devices operate under continuous-wave current injection at room temperature. The smallest laser is 1.0 μm in radius and ~4.0 μm in height with a circular beam shape and an output over 8 μW. The device lases at 995 nm wavelength with a threshold current of about 2.6 mA.     

Fast solvent-driven micropump fabricated by two-photon microfabrication

A solvent-driven micropump was developed using three-dimensional two-photon microfabrication. The actuation of micropump is utilizing the bending behavior of hydrogel film under asymmetric solvent-stimulus. The micropump could absorb and discharge fluid reversibly by simply alternating solvent composition. Contributing to the thin hydrogel film with the thickness of 2.5 μm, the response time was significantly improved to 0.17 s. The discharge capacity of fluid was estimated to be as low as 9.2×10⁻² pL. The pumping of such ultra-low-volume fluid will be useful for further miniaturization of micro-nanofluidic devices.     

Amplification of the emission of a liquid-crystal microlaser by means of a uniform liquid-crystal layer

The amplification of the emission of a microlaser based on a cholesteric liquid crystal by means of a uniformly oriented layer of a laser-dye-doped nematic liquid crystal is demonstrated. The nematic liquid crystal is characterized by the anisotropy of optical properties, including the amplification coefficient, which opens the possibility of creating amplifiers controlled by a low electric field.     

Coherence of a single mode InAlGaAs/InP cylinderical microlaser with two output ports

We experimentally investigate the coherence of a single mode InAlGaAs/InP cylindrical microlaser with two output waveguides. For a cylindrical microlaser with a radius of 15 μm and two 2 μm-wide output waveguides, single mode operation with a side mode suppression ratio of 30 dB is realized, and a far-field interferometric pattern similar to a Young's interferometer is observed. The results indicate that the microlasers with two output waveguides can be used as the light source for an optical sensor by monitoring the phase change of the output emission from one port versus that of the other port.     

Arbitrary-lattice photonic crystals created by multiphoton microfabrication

We used voxels of an intensely modified refractive index generated by multiphoton absorption at the focus of femtosecond laser pulses in Ge-doped silica as photonic atoms to build photonic lattices. The voxels were spatially organized in the same way as atoms arrayed in actual crystals, and a Bragg-like diffraction from the photonic atoms was evidenced by a photonic bandgap (PBG) effect. Postfabrication annealing was found to be essential for reducing random scattering and therefore enhancing PBG. This technique has an intrinsic capability of individually addressing single atoms. Therefore the introduction of defect structures was much facilitated, making the technique quite appealing for photonic research and applications.     

Effect of dissipative forces on the theory of a single-atom microlaser

A single-atom microlaser involving Poissonian input of atoms with a fixed flight time through an optical resonator is described. The influence of the cavity reservoir during the interactions of successive individual atoms with the cavity field is included in the analysis. Atomic decay is also considered, as it is nonnegligible in the optical regime. During the random intervals of absence of any atom in the cavity, the field evolves under its own dynamics. The steady-state characteristics of the cavity field are discussed. Away from laser threshold, the field can be nonclassical in nature.     

Three dimensional microfabrication in ceramics by solid state lasers

Nano- and picosecond laser radiation offers better possibilities by achieving higher accuracy in microstructuring because of much lower heat load compared to larger pulses. The influence of wavelength, pulse energy, overlap and the properties of processing gas atmosphere on material removal and roughness of ceramics are investigated for ns-pulses. The removal threshold and the removal rate per pulse for ns- and ps- laser pulses are presented. Strategies, which reduce the surface roughness and enhance the efficieny of the production of three dimensional structures are reported. These results show the parameter field which permits a precise material removal during the production of microstructures without damaging the remaining structure.     

Three-dimensional particle image velocimetry: a low-cost 35 mm angular stereoscopic system for liquid flows

A low-cost 35 mm PIV stereoscopic system for liquid flows is presented which has an imaging component cost under US$9000. The system uses an angular configuration, rotating mirror image shifting and in-situ calibration techniques. Image processing algorithms based on cross correlation and bicubic interpolation are also used to calculate the 3D data from the PIV images. Results from an error analysis have shown the system to have in plane errors ranging from 4.15 to 5.95% and out of plane errors of 7.01% providing an f-number of f2 is fixed for all imaging. Subsequent application of the system to a flow field generated by a free falling sphere in wheat syrup have produced results which when compared to previous flow visualisation give good qualitative agreement. Suggested improvements to the PIV system costing US$1300 would allow operation at f-numbers down to f by modifying the cameras for the Scheimpflug condition and using a corrective liquid prism.     

Observation of microlaser with Er-doped phosphate glass coated microsphere pumped by 780 nm

The silica microspheres coated with a thin layer of Er-doped phosphate glass are fabricated and whispering-gallery modes (WGMs) with quality factor of 8 × 10⁶ in the 780 nm band are obtained. We demonstrate that the microsphere can form single-mode and multi-mode microlaser in communication-band with a pumping laser of wavelength 780 nm band. Moreover, the representative lateral emission distributed modes in the microsphere can be directly observed via the upconverted photoluminescence.     

Three-dimensional simulation of free-radical block polymerization of diallyl isophthalate by the Monte Carlo method

A model of the three-dimensional free-radical block polymerization of diallyl isophthalate to a limiting degree of conversion is developed. The core of the model is a reactor built on a cubic lattice of size 100 × 100 × 100. The influence of chain transfer to the monomer and of diffusion effect on the kinetic characteristics of the polymerization process is examined.     

Highly effective three-dimensional large-scale microfabrication using a continuous scanning method

Effective scanning is an important issue in two-photon induced stereolithography (TPS) for the reduction of the processing time required to fabricate three-dimensional (3D) nano/microstructures. In large-scale TPS based on a stage-scanning system, the large processing time due to the intrinsic slow response in the stage scanning system is a major obstacle to its use as a practical nanofabrication process. To overcome this drawback, we propose a continuous scanning method (CSM) for a stage-scanning system. In CSM, a pattern is generated with continuous movement of the stage during laser beam exposure. A stable fabrication window (SFW), which enables uniform motion of the stage without errors considering the stage characteristics, was obtained from fundamental experiments. Within the condition of a SFW, 2D and 3D microstructures having nanoscale details were fabricated with a whole scale range of several hundred micrometers using CSM.     

Optical trapping microfabrication with electrophoretically delivered particles inside glass capillaries

We have developed a new technique for rapid microfabrication that uses electrophoretically delivered particles and an optical trap. The material particles, micrometer- and nanometer-sized polystyrene beads in aqueous solution, are continuously delivered to an optical trap by means of the electrophoretic effect inside glass capillaries or similar microstructures. The optical trap is used to manipulate and deposit the polystyrene beads onto a substrate. The continuous, on-demand delivery of particles allows for microfabrication in two and three dimensions with high speed and high efficiency and without material waste. This new technique has many potential applications in microelectronics and biotechnology.     

Femtosecond laser microfabrication of periodic structures using a microlens array

A microlens array (MLA) was applied for femtosecond laser microfabrication. Two-dimensional periodic patterns that corresponded to the arrangement of lenses in the MLA were recorded by ablation on a glass surface. The two-dimensional periodic patterns were recorded by a single exposure without scanning of the laser beam or the sample, and worked as a grating. Optical resizing of the patterns and high efficiency of fabrication are demonstrated and discussed. PACS 42.82.Cr; 07.60.Pb; 42.62.Cf     

Single-mode hybrid Al Ga In As/Si octagonal-ring microlaser with stable output

Hybrid octagonal-ring microlasers are investigated for realizing a stable output from a silicon waveguide based on a two-dimensional simulation. The inner radius of the ring is optimized to achieve single-mode and low-threshold operation. Using the divinylsiloxane-benzocyclobutene(DVS-BCB) bonding technique, a hybrid Al Ga In As/Si octagonal-ring microlaser vertically coupled to a silicon waveguide is fabricated with a side length of 21.6 μm and an inner radius of 15 μm. A single transverse-mode operation is achieved with a threshold current density of 0.8 k A∕cm~2and a side-mode suppression ratio above 30 d B, and a stable output from the lower silicon waveguide is obtained.     

Simplified radio-over-fiber transport systems with a low-cost multiband light source

In this Letter, low-cost radio-over-fiber (ROF) transport systems are proposed and experimentally demonstrated. By utilizing a laser diode (LD) and a local oscillator (LO) to generate coherent multiband optical carriers, as well as a self-composed wavelength selector to separate every two carriers for different ROF transport systems, no any other dedicated LD or electrical frequency upconverting circuit/process is needed in the central station (CS). Compared with current ROF systems, the required numbers of LDs, LOs, and mixers in a CS are significantly reduced. Reducing the number of components not only can simplify the network structure but can also reduce the volume and complexity of the relative logistics. To demonstrate the practice of the proposed ROF transport systems, clear eye diagrams and error-free transmission performance are experimentally presented.     

Phase stability theory of Bloch eigenstates in active photonic lattices with coupled microlaser arrays

An generic model for the lattice dynamics of coupled microlaser arrays is employed for the lattice stability analysis. Nonlinear cross-cavity gain-coupling effects, characterizing active lattices, are included via the gain dependence on carrier depletion and cross-cavity hole burning. Passive near neighbor interactions (inter-cavity absorption and mirror reflection interference) are also included. The introduction of lattice-orthogonal modes simplifies the derivation of the coupled rate equations. The interaction phase among sites exhibits spontaneous long range “crystallization" into periodic Bloch states whereby the cavity radiation envelopes behave as laser “macro-atoms". The sign of the coupling coefficients as a function of geometry determines in- vs. out-of-phase locking and has practical implications for array design. Emphasis is placed on the stability analysis of Bloch states by including earlier omitted [1] effects of phase perturbations. The importance of the linewidth factor ι is uncovered: unconditional stability results for ι ≤1, otherwise a stability threshold exists for the coupling strength among sites. Choice of low ι gain material permits phase stability with high coupling strength, beneficial in overcoming manufacturing variations among array cavity parameters.