Kabir Udeshi

A bi-stable electro-thermal RF switch for high power applications

This paper reports on the development of a bi-stable electro-thermal RF switch which can be operated with zero standby power (and bias) in either latched state. The device includes a bi-stable structure, which electrically shorts the input and output signal lines. Two electro-thermal actuators are used to switch it on and off. The entire structure is fabricated from 27 /spl mu/m thick electroplated Cu, suspended 3 /spl mu/m above a glass substrate. Typical actuation of the driving engine is performed by a 20 ms single pulse, corresponding to power and energy consumption of 33 mW and 662 /spl mu/J, respectively. Bursts of pulses of 0.1 ms width, used in sets of various durations, can reduce the total switching energy to <210 /spl mu/J. Measurements show that at 2.2 GHz, the device offers -0.5 dB insertion loss and -38 dB isolation, whereas at 3.5 GHz it offers -1 dB insertion loss and -30 dB isolation. Power handling capability tests for cold switching show that the device can be easily switched even after flowing >1 W RF power, suggesting that any micro-welding that may occur does not impede switching.

Impact behavior and energy transfer efficiency of pulse-driven bent-beam electrothermal actuators

This paper investigates the dynamics of bent-beam electrothermal actuators and their use in impact actuation of other micromechanical elements, and in particular the issue of energy efficiency achieved by temporal variations in electrical drive signals. A transient thermal model of an actuator beam shows that the uniformity of temperature profile is greater when activating with short electrical pulses, which results in larger achievable displacements and forces. A dynamic force analysis reveals that using a train of pulses, referred to as a burst pulse, for activation achieves significant impact forces due to high velocities at the point of impact. The analytical trends are confirmed through experimental observations of microfabricated metal test structures in which actuators work against bistable mechanisms. Measurements of 2 mm and 3mm long actuators show that pulsed activation results in >5/spl times/ reduction in energy consumption, with the activation energy falling from over 1000 /spl mu/J at dc activation, to less than 200 /spl mu/J using a 0.2-ms voltage pulse. The actuators however consume higher instantaneous power levels at shorter pulses, which may inhibit the use of pulses less than 1 ms in width. Further, the energy consumption through burst activation is 70% that of a single pulse, if sufficient impact forces are generated.

A DC-powered, tunable, fully mechanical oscillator using in-plane electrothermal actuation

This paper describes a fully mechanical micromachined oscillator that is driven using only a DC power source. The oscillator is made using an electrothermal actuator, that when actuated, opens a switch to cut off its supply current. Two versions of this oscillator have been designed using distinct hysteresis mechanisms: one structural, and the other thermal. The devices have 30 /spl mu/m thick electroplated copper structures and 3 /spl mu/m minimum features, fabricated using a single mask low temperature UV-LIGA process, with a footprint of 1 mm/spl times/1 mm. Measured results confirm the operation and show that the oscillators are capable of generating a tunable signal with a frequency range from 38 Hz to 1200 Hz and a duty cycle between 0.3 and 0.7, while requiring an operating voltage less than 0.5 V. The maximum power consumption is 180 mW.

A DC-Powered High-Voltage Generator using a Bulk Pt-Rh Oscillating Micro-Relay

This paper reports a high voltage generator formed by the hybrid assembly of a micromachined relay and a wound-wire inductor or transformer. The relay is micro-electrodischarge machined from Pt-Rh bulk metal foil, and consists of a normally-closed switch that is part of a DC-powered electrothermal relaxation oscillator. The use of this material permits the relay to be operated in air, without the need for inert packaging. It also provides a resistance of <2 Omega (including both the actuator and the contact), which makes it amenable to low drive voltages. Using an input of 5 V and a 56 mH transformer with a turns-ratio of 46, peak pulsed outputs of 1200 V are obtained. A DC output of 276.5 V is obtained for an output power of 76 mW.

Programmable optical wave form shaper on a microchip

This letter reports a device for in-fiber programmable optical pulse shaping, that consists of a chirped fiber grating and a micromachined array of Si actuators integrated on a 1×5mm2 chip. The pulse spectrum is longitudinally imaged inside a chirped fiber Bragg grating, thus permitting spectral components to be accessed inside the fiber by individual actuators. The demonstration of controlled optical pulse spectrum and temporal-width changes shows that the silicon microactuators, fabricated using a standard lithographic process, can tune the local refractive index of the grating by inducing localized fiber core strain gradients at a rate of >1μStrain per 1mW of actuator driving power.

A DUAL-EDM REVERSE DAMASCENE PROCESS FOR RF SWITCHES AND OTHER BULK METAL DEVICES

This paper reports a manufacturing process suitable for lithography-compatible fabrication of suspended micro-structures from any conductive material (including bulk metal) that is available in sheet form. It uses two aligned steps of batch mode micro-electro-discharge machining followed by a series of filling and lapping steps similar to a damascene process. The process is demonstrated by the fabrication of a bi-stable RF switch from #302 stainless steel foil. The fabricated devices have a footprint of 5 × 5 mm2 , with 25 μm thickness, and a minimum feature size of 5 μm.Copyright

A micromachined platform for localized index modulation in chirped fiber Bragg gratings and its application to ultrafast optical pulse shaping

This paper reports the development of a micromachined platform that locally modifies the refractive index of a chirped fiber Bragg grating (CFBG). This platform, composed of an array of electrothermal actuators, has been used to make an ultrashort optical pulse shaper. The micromachined array, with a footprint of 5 mm /spl times/ 1 mm, has 75 actuators spaced 60 /spl mu/m apart, and has been used to demonstrate pulse shaping both in the time and frequency domain. A normalized intensity peak of 1.5 at 1550 nm is obtained by applying about 2 mN of force using a single actuator. The intensity peak can be shifted by over 3 nm to the edge of the CFBG spectrum by using different actuators. The pulse width is modulated from 1.5 ps to 4 ps by application of 500 mW of power. System simulations track experimental data that show the individual actuators addressing distinct frequency components. Thermal experiments verify that heat generated by the electrothermal actuators has no measurable effect on the optical pulse spectrum obtained.

Bragg gratings in femtosecond fiber lasers: from programmable pulse shapers to compact volume-grating pulse compressors

Fiber-based lasers constitute next-generation in the ultrashort-pulse sources due to the significant practical advantages offered by fibers, such as high efficiency, compactness and robust all-fiber packaging of complex laser systems. In fact fiber technology has led to the first truly practical and compact mode-locked laser oscillators, which are fully compatible with rigorous reliability requirements of industrial use. However, majority of pulse-shaping and compression techniques conventionally employed for ultrashort pulse generation and control are based on using various bulk optical components (diffraction gratings in particular) and, therefore, are poorly compatible with fiber based laser systems. Here we describe our recent work on developing novel compact pulse-shaping and pulse-compression devices, which are fully compatible with fiber technology. The unifying theme of these efforts is that they use various implementations of chirped Bragg-reflection gratings. The first class of devices, pulse shapers, use combination of chirped fiber gratings and programmable MEMS arrays integrated into a single chip, to arbitrary manipulate the phase of ultrashort optical pulses on a temporal and absolute-phase magnitude scales exceeding those of conventional diffraction-grating based pulse shapers. In contrast, the second type of devices are based on volume chirped Bragg gratings to achieve pulse stretching and recompression between femtosecond to subnanosecond time scales. Use of volume gratings here offers a unique advantage of providing with compact devices which are also compatible with very high pulse energies. We have demonstrated that broad-bandwidth high-reflectivity gratings can be made in photo-thermal glass with apertures of several millimeters (and potentially much larger) thus permitting /spl sim/mJ fiber-amplified and recompressed ultrashort-pulse energies. Fiber-based chirped pulse amplification systems demonstrated using these novel pulse stretchers and compressors, combine advantages of being compact, robust, efficient, and providing with very high average power and high pulse energy ultrashort pulses.

Monolithic fiber-grating and MEMS based devices for controllable ultrafast pulse shaping

A new type of optical pulse shaper for arbitrary waveform generation is demonstrated, based on fiber Bragg grating and micro-electro-mechanical system (MEMS) technologies. This is an on-chip device which is compact, robust, monolithic, and programmable and can be used for a variety of applications such as higher order dispersion compensation in fiber communication links and high-energy pulse amplification.