mW Input Research Articles

Near-Field Radiation from a Ridge Waveguide Transducer in the Vicinity of a Solid Immersion Lens

A near-field optical system is investigated to improve the transmission efficiency of near-field transducers. A ridge waveguide is placed adjacent to a solid immersion lens (SIL) but separated by a low-index dielectric layer. The incident electric field near the focus of the SIL is determined by the Richards-Wolf vector field equations. The finite element method is used to solve Maxwell's equations. A spot size of 31 nm is obtained. The maximum value of the absorbed optical power density in the recording medium is 7.51 x 10(-4) mW/nm3 for a 100 mW input power.

High-Power Er3+/Yb3+ Codoped Double-Cladding FibreAmplifier with More Than 2 W Output Power

A high-power Er3+/Yb3+-codoped double-cladding all-fibreamplifier was successfully demonstrated and experimentallyinvestigated. The amplifier could be operated with amaximum output power of 2.18 W and 2.11 W at 1541 nm and 1550 nmwavelengths, respectively, when the maximum pump power was6.07 W. The power conversion efficiency was up to 35.6%and 34.4% at the two wavelengths, respectively. The output power andthe gain were greater than 2.00 W and 20.0 dB, respectively, in thewavelength range from 1539 nm to 1565 nm for 20.0 mW input signalpower. The gain fluctuation and the noise figure around 1550 nmwavelength were less than 0.3 dB and 6.0 dB, respectively.

High-power optical microswitch based on direct fiber actuation

An optical microswitch is presented for high-power switching applications. The device, capable of switching several watts of optical power, employs large-core multimode fibers to switch output from a laser diode operating at a wavelength of 810 nm. Switching is achieved through the direct deflection of an on-chip fiber using a high force electrothermal actuator. Optical losses in the system are identified, and optical efficiency is predicted and verified with experimental measurements. The switch demonstrated in this work requires an electrical current of 120 mA and has an electrical power consumption of 5280 mW. The optical efficiency is found to be on the order of 88% (0.55–0.60 dB loss) with a maximum power transfer of 1690 mW from a 1930 mW input. Switching time is 40 ms with channel isolation between the on and off states of 55 dB.

Comparison between strip and rib SOI microwaveguides for intra-chip light distribution

A comparative analysis of the strip and rib geometries guided wave devices (waveguides, bends, mirrors, beam splitters) is performed to realize an optical distribution to several outputs. For the strip structures, the optical losses are strongly sensitive to sidewall roughness due to processing, whereas for slightly etched submicron rib waveguides, optical losses are lower than 0.4 dB/cm. The design, realization and characterization of an H-tree optical distribution from one input to 16 output points using 1 cm long rib waveguides, four compact T-splitters and two mirrors are presented. A 2.6lW optical power is obtained at each output for a 3 mW input power. This corresponds to an excess loss of 14 dB which seems to be sufficient for an integrated photodetector. � 2004 Elsevier B.V. All rights reserved.

Design and fabrication of a micro thermal actuator for cellular grasping

The development of a novel polymer-based micro robotic gripper that can be actuated in a fluidic medium is presented in this paper. Our current work is to explore new materials and designs for thermal actuators to achieve micromanipulation of live biological cells. We used parylene C to encapsulate a metal heater, resulting in effectively a tri-layered thermal actuator. Parylene C is a bio-compatible dielectric polymer that can serve as a barrier to various gases and chemicals. Therefore, it is suitable to serve as a thermal/electrical/chemical isolation material for protecting the metal heater from exposing to an aqueous environment. We have demonstrated parylene actuators (2 mm×100 μm×0.5 μm) to operate in an aqueous environment using 10 to 80 mW input power. The temperature of these actuators at full deflection was estimated to be ∼60°C, which is much lower than the typical requirement of >100°C to actuate other conventional MEMS actuators.Danio rerio follicles in fluidic medium were captured successfully using these actuators. Moreover, these actuators were found to be responsive to moderate rise in environmental temperature, and hence, we could vary the fluidic medium temperature to actuate trimorphs on a chip without any input of electrical energy, i.e., raising the fluidic temperature from 23°C to 60°C could actuate the trimorphs to grasp follicles of ∼1 mm size in diameter. At 60°C, the embryos inside the follicles were observed to be alive, i.e., they were still moving in the biological fluid isolated by the follicle membrane. The smallest follicles grasped were ∼500 μm in diameter using 800 μm×130 μm×0.6 μm actuators. The fabrication process, modeling, and optimization of the trimorph actuators are presented. Based on the successful operation of these polymer-based actuators, we are currently developing multifinger thermal microgrippers for cellular grasping and manipulation, which can potentially be hybridly integrated with circuits for computer control.

A global design of an erbium-doped fiber and an erbium-doped fiber amplifier

A global design of an erbium-doped fiber and an open-loop erbium-doped fiber amplifier (EDFA) in a steady-state operation is discussed by applying genetic algorithms. Taking a signal gain and a bandwidth as objective functions, 7 parameters of the EDFA (erbium concentration, core radius, erbium-doped radius, refractive index difference, fiber length, pumping wavelength and signal power) are optimized by solving optical propagation equations, assuming a homogenous two-level active medium and a single-mode propagation. There is evidence to show that the 1480 nm pump utilized in usual EDFAs is not an optimal choice, which should be chosen around 1460 nm . The optimal core radius ranges 0.465 –0.548 μm on pumping power 50 –200 mW . Under different design objects and with different pumping powers, however, there are different optimal Er-doped concentrations, reflective index differences and fiber lengths. As a single fiber EDFA, 35 dB signal gain or 35 nm bandwidth is obtained with the 7 optimal parameters, 100 mW pumping power and 0.001 mW input signal power.

Condenser-Transducer Configuration for Improving Radiation Efficiency of Near-Field Optical Transducers

ABSTRACTNear-field radiation efficiency of the ridge waveguide transducer is investigated in the vicinity of a recording magnetic medium. Near-field radiation from a ridge waveguide transducer is expressed in terms of power density quantities. This allows us to quantify the near-field radiation efficiency from the near-field transducer with respect to the input optical power. Finite element method (FEM), which is capable of modeling focused beams, is used to simulate various geometries involving ridge waveguides. The incident electric field near the focal region is determined using a Gaussian beam expression and Richards-Wolf vector field equations for low NA and high NA beams, respectively. First, the ridge waveguide transducer is placed at the focal point of an optical lens system. The maximum value of the absorbed optical power in the recording medium is 1.6*10-4 mW/nm3 for a 100 mW input optical power. Finally, the ridge waveguide is placed adjacent to a solid immersion lens but separated by a low-index dielectric layer. For this case, the maximum value of the absorbed optical power in the recording medium is 7.5*10-4 mW/nm3 for a 100 mW input optical power. The improvement in the transmission efficiency is a result of two factors: 1. Increased incident electric field over the transducer surface due to increased NA of the optical system, 2. Surface plasmon enhancement obtained by placing a low-index dielectric material between the solid immersion lens and ridge waveguide.

Stable dissipative solitons in semiconductor optical amplifiers.

We have observed for the first time stable spatial solitons in semiconductor optical amplifiers. Soliton destabilization due to the growth of background noise was suppressed by using patterned electrodes on the device. Numerical simulations fit very well with the experiment results. We show that it is possible to excite these solitons with about 60 mW input power.

Second-harmonic generation in two-dimensional periodically poled lithium niobate using second-order quasiphase matching

Two-dimensional nonlinear photonic crystals of lithium niobate with square lattices were fabricated. In these crystals, efficient quasiphase-matched second-harmonic generation was demonstrated by using second-order quasiphase matching. As a mode-locked Nd:yttritium–aluminum–garnet laser at 1064 nm with 35 ps pulse was used, we obtained an average power of 0.86 mW at 532 nm with 2.73 mW input, which corresponds to 42% internal conversion efficiency. The variations of second-harmonic output with crystal temperature and incident angle were measured. In addition, the relation between the second-harmonic output and reversed duty cycle was studied. All the experimental results are well consistent with simulations.

A high-flow thermopneumatic microvalve with improved efficiency and integrated state sensing

This paper reports a thermopneumatic microvalve featuring a corrugated diaphragm. A sealed cavity below the diaphragm contains a volatile fluid, the vapor pressure of which can be increased by resistive heating to deflect the diaphragm, thus closing the valve. Silicon heater grids are elevated 9 /spl mu/m above the cavity floor, and the cavity is only partially filled with fluid, to increase thermal efficiency. A vacuum-sealed, capacitive pressure sensor on the floor allows direct monitoring of the cavity pressure. Pentane-filled actuators sustain a 2070 torr pressure rise above atmospheric with 500 mW input power. A device tested in situ closes with 350 mW at 1000 torr inlet pressure (venting to vacuum) and maintains closure with 30 mW input. Valves conduct 400 sccm under 1500 torr differential pressure, while maintaining leak rates as low as 10/sup -3/ sccm, yielding a dynamic range of 10/sup 5/. A thermodynamic model has been developed that matches experimental power, pressure, and transient response data to within a few percent. This model is used to suggest an optimized structure capable of a 2000 torr pressure rise with 50 mW input and a 1 s response time. The glass-and-silicon valve structure is suitable for integration into complete microfluidic systems.

Experimental demonstration of pattern effect compensation using an asymmetrical Mach-Zehnder interferometer with SOAs

We propose an asymmetrical interferometer to compensate the pattern effect in semiconductor optical amplifier (SOA) as an inline amplifier in dense wavelength-division-multiplexing (DWDM) system. Experiments are demonstrated with a commercial integrated Mach-Zehnder interferometer (MZI)-SOA. The experiments showed that in a 16/spl times/10-Gb/s DWDM system, the power penalty induced by the SOA decreased from 6.8 to 0.9 dB by the interference at 1 mW input power, and the input power dynamic range of the SOA was efficiently extended.

Microwave plasma characteristics of a circulating fluidized bed-plasma reactor for coating of powders

Coating of powders by Plasma-CVD is an adequate way to protect particles from environmental attack or to provide a large catalytic surface on carrier particles. The μ-SLAN® microwave plasma source is placed into the riser of a circulating fluidized bed, and its performance as a particle-coating reactor is evaluated for silicon oxide deposition on glass beads. Fluctuations of the particle concentration reduce the efficiency of MW coupling. The minimum MW input power for stable plasma generation is 4 times higher in the presence of particles and increases with oxygen partial pressure. The temperature of the entrained particles can be adjusted to very low values, but higher temperatures are achieved near the MW-coupling slots. The conversion ratio of HMDSO only depends on the specific power ( P/ F). It is slightly lower with particles and 5 W/sccm are required for 80% conversion.

Bent-beam electrothermal actuators-Part I: Single beam and cascaded devices

This paper describes electrothermal microactuators that generate rectilinear displacements and forces by leveraging deformations caused by localized thermal stresses. In one manifestation, an electric current is passed through a V-shaped beam anchored at both ends, and thermal expansion caused by joule heating pushes the apex outward. Analytical and finite element models of device performance are presented along with measured results of devices fabricated using electroplated Ni and p/sup ++/ Si as structural materials. A maskless process extension for incorporating thermal and electrical isolation is described. Nickel devices with 410-/spl mu/m-long, 6-/spl mu/m-wide, and 3-/spl mu/m-thick beams demonstrate 10 /spl mu/m static displacements at 79 mW input power; silicon devices with 800-/spl mu/m-long, 13.9-/spl mu/m-wide, and 3.7-/spl mu/m-thick beams demonstrate 5 /spl mu/m displacement at 180 mW input power. Cascaded silicon devices using three beams of similar dimensions offer comparable displacement with 50-60% savings in power consumption. The peak output forces generated are estimated to be in the range from 1 to 10 mN for the single beam devices and from 0.1 to 1 mN for the cascaded devices. Measured bandwidths are /spl ap/700 Hz for both. The typical drive voltages used are /spl les/12 V, permitting the use of standard electronic interfaces that are generally inadequate for electrostatic actuators.

Active optical waveguides based on Er- and Er/Yb-doped silicate glasses

The growing interest for the use of integrated optical (IO) amplifiers in optical fibre telecom systems has led to depth search for ever better rare-earth-doped glassy materials. In the present paper we report some properties of a set of Er 3+/Yb 3+-doped soda-lime silicate glasses. Several batches were prepared, all with the same base mol% composition (73SiO 2–1Al 2O 3–0.4P 2O 5–14Na 2O–0.6K 2O–11CaO) containing Er 2O 3 (0.32–0.48%) and Yb 2O 3 (0.63 and 0.78%). The resulting glasses were cut into rectangular plates about 1 mm thick, and one surface was optically polished. Planar and channel waveguides were subsequently obtained in these plates by Ag +–Na + ion-exchange. Spectroscopic analysis showed that the fluorescence emission peak for all the samples was observed at 1532±1 nm, with a full-width at half-maximum equal to 19 nm. Measurements of the lifetime of the metastable state of Er 3+ were performed upon excitation by laser pumps at 514.5 and 980 nm, and times of the order of 7 ms were measured in most samples. The intensity of the up-conversion fluorescence was less in Er 3+/Yb 3+ co-doped glasses than in Er 3+-doped ones. Preliminary measurements of the transmitted power at 1540 nm in channel waveguides made in the glass doped with nominal 0.32 mol% of Er 2O 3 have confirmed their potential of achieving optical gain; in fact, a signal enhancement (internal gain) >1 dB/cm was measured with more than 1 mW input signal.

Integrated atomic force microscopy array probe with metal–oxide–semiconductor field effect transistor stress sensor, thermal bimorph actuator, and on-chip complementary metal–oxide–semiconductor electronics

A microfabricated 2×1 array of active and self-detecting cantilevers is presented for applications in atomic force microscopy (AFM). The integrated deflection sensor is based on a stress sensing metal–oxide–semiconductor transistor. Full custom complementary metal–oxide–semiconductor amplifiers for signal readout are combined on the same chip. A sensor sensitivity of 2.25 mV/nm, or a change in current ΔId/Id=2.8×10−6/nm, was obtained at the final output stage. Three Al–Si thermal bimorph actuators are integrated on each cantilever for self-excitation and feedback actuation. The efficiencies of the heaters are 2.4–4.7 K/mW. In the experimental setup, a maximum displacement of 8 μm was achieved at 45 mW input. A pair of parallel AFM images in the constant height mode, a typical tapping mode image, and a constant force image with 1.3 μm high features have been successfully taken with the array probe.

Highly Efficient Frequency Doubling with a KNbO3 Semi-Monolithic Resonator

A semi-monolithic standing-wave resonator has been constructed and employed for frequency doubling of a Ti:sapphire laser. The resonator consists of a 5 mm long KNbO3 crystal with dielectric coatings on both end faces and a spherical mirror with 20 mm radius of curvature. With 31.2 mW input power at 861.4 nm second harmonic power of 11.4 mW has been generated corresponding to the conversion efficiency of 36.5%.

Low-loss 1.3-/spl mu/m MQW electroabsorption modulators for high-linearity analog optical links

Low-loss InAsP-GaInP multiquantum-well electroabsorption waveguide modulators have been developed for transmitting microwaves as subcarriers over optical fibers. The fiber-to-fiber insertion loss is only 5 dB at 1.32-/spl mu/m wavelength. The electrooptic slope efficiency of an 185-/spl mu/m-long 11-GHz bandwidth device is equivalent to a Mach-Zehnder modulator with a V/sub /spl pi// of 2.2 V. The linearity performance was characterized for a test link without any form of amplification. A RF-to-RF link efficiency of -25.5 dB, noise figure of 27 dB and suboctave spurious-free dynamic range of 114 dB.Hz/sup 4/5/ have been achieved with 16 mW input optical carrier power. The measured 3-dB electrical bandwidth exceeds 20 GHz for a 90-/spl mu/m-long device.

Gain flattening of erbium-doped fibre amplifierusing fibre Bragg gratings

A new technique, using fibre-Bragg gratings with different centre frequencies to reflect the different channel signals at different positions, is proposed for flattening the gain spectrum of an erbium-doped fibre amplifier. A designed gain excursion of <0.1 dB can be achieved for 16 channel multiplexed signals with 0.1 mW input power in the 1532-1562 nm wavelength region.

Micromechanical fiber-optic attenuator with 3 μs response

Optomechanical fiber-optic attenuators are bulky and slow. The mechanical antireflection switch (MARS) modulator offers a high-speed alternative for applications including dynamic gain control in fiber amplifiers. This paper describes a compact electrically controlled variable attenuator using a micromechanical device where electrostatic deflection of a silicon nitride quarter-wave dielectric layer suspended over a silicon substrate creates a variable reflectivity mirror. This device is packaged with two fibers in one ceramic ferrule placed in contact with a gradient index (GRIN) collimation lens, so that the input light reflects from the modulator in the collimated beam plane and couples into the output fiber. Using a 300 /spl mu/m diameter MARS attenuator and a 500 /spl mu/m diameter collimation lens, the total insertion loss at 1550 nm was 3.0 dB with no applied voltage, increasing to 31 dB at 35.2 V. The polarization dependent loss was less than 0.06 dB. Full attenuation with more than 100 mW input power produced no damage. The response time was 2.8 /spl mu/s to move from maximum to minimum transmission and 1.1 /spl mu/s to return to maximum transmission.

Structure and properties of a complex crystal for laser diode frequency doubling: Cadmium mercury thiocyanate

The crystal structure of cadmium mercury thiocyanate [CdHg(SCN)4] is determined by means of a four circle diffractometer. The structural features and properties of the crystal are described. Blue-violet light output by frequency doubling of a 809 nm GaAlAs laser diode using a cadmium mercury thiocyanate crystal device that is 3 mm thick at the phase matching angle: θ=47.7°, φ=0°, is realized at room temperature with input power lower than 200 mW. A 404.5 nm light output power of 1.8 mW is also measured for a 576 mW input power of the GaAlAs laser diode.