D. Uttamchandani

University of Strathclyde, Glasgow, SCT, United Kingdom

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Publications (130)127.08 Total impact

  • Micro & Nano Letters 06/2014; 9:399–402. · 0.85 Impact Factor
  • A. Dudus, R. Blue, M. Zagnoni, G. Stewart, D. Uttamchandani
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    ABSTRACT: We report an in-line, fiber optic, broadband variable optical attenuator employing a side-polished, single-mode optical fiber integrated on a digital microfluidics platform. The system is designed to electrically translate a liquid droplet along the polished surface of an optical fiber using electrowetting forces. This fiber optic device has the advantage of no moving mechanical parts and lends itself to miniaturization. A maximum attenuation of 25 dB has been obtained in the wavelength range between 1520 nm and 1560 nm.
    Applied Physics Letters 01/2014; 105(2):021105-021105-4. · 3.52 Impact Factor
  • G. Brown, R. Bauer, W. Lubeigt, D. Uttamchandani
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    ABSTRACT: MEMS scanners are of interest for their potential as low-cost, low operating power devices for use in various photonic systems. The devices reported here are actuated by the electromagnetic force between a static external magnetic field and a current flowing through an SOI MEMS scanner. These scanners have several modes of operation: their mirrors may be rotated and maintained at a static angle (up to +/- 1.4 degrees), scanned rapidly (up to 500 Hz); or may be operated in a resonance mode, at the device's mechanical resonance frequency (~1.2 kHz) for higher rate scanning. The use of these scanners as a Q-switching element within a Nd:YAG laser cavity has been demonstrated. Pulse durations of 400 ns were obtained with a pulse energy of 58 μJ and a pulse peak power of 145 W. The use of an external magnetic field, generated by compact rare-earth magnets, allows a simple and cost-effective commercial fabrication process to be employed (the multi-user SOI process provided by MEMSCAP Inc) and avoids the requirement to deposit magnetic materials on the MEMS structure.
    Proc SPIE 03/2013;
  • A. Dudus, R. Blue, D. Uttamchandani
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    ABSTRACT: A simple theoretical analysis is undertaken to compare the change of guided mode index of microfiber and side-polished single mode fiber sensors to the refractive index of surrounding fluids. This is followed by an experimental investigation using a broadband Mach-Zehnder interferometer to compare the sensitivity of the two types of sensing fibers by measuring the interferometer response to fluid refractive indices ranging from 1.330 to 1.451. The experiments show that a microfiber sensor of diameter close to 5 $mu{rm m}$ and an average length of around 500 $mu{rm m}$ generates a response similar to that generated from a side-polished fiber sensor of length 7 mm. A compact microfluidic cell is fabricated to enable a microfiber based refractive index sensor to be used in a microfluidics environment. Experimental refractometric results obtained using this arrangement are reported.
    IEEE Sensors Journal 01/2013; 13(5):1594-1601. · 1.48 Impact Factor
  • Li Li, Ran Li, W. Lubeigt, D. Uttamchandani
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    ABSTRACT: A 1.2-mm-diameter gold-silicon bimorph varifocal micromirror (VFM) has been designed and investigated for imaging applications. Several prototypes have been fabricated in a 10-μm-thick single-crystal silicon-on-insulator material. Controlled variation of the radius of curvature using electrothermal and optothermal actuation has been demonstrated. A finite-element-based simulation of the device behavior has been undertaken. Experimental characterization has shown that the device focusing power varied from an initial 87 dioptre to 69 dioptre by applying dc electrical power of 33 mW and produced a focusing power value of 59 dioptre when optothermally actuated with a normally incident laser beam of 488-nm wavelength and 43 mW. When electrothermally driven, the mechanical rise and fall times of the device were measured as 130 and 120 ms, respectively. Experimental and theoretical analyses using Zernike coefficients show that, throughout the actuation range, the aberration of the VFM is mainly a small defocus term, with negligible higher order aberrations. A compact active imaging system incorporating the VFM has been also demonstrated. This system was capable of focusing several objects located along the optical axis with a maximum tracking range of 134 mm.
    Journal of Microelectromechanical Systems 01/2013; 22(2):285-294. · 2.13 Impact Factor
  • R. Bauer, G. Brown, Li Li, D. Uttamchandani
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    ABSTRACT: An angular vertical comb-drive (AVC) with electrically controllable initial comb-offset is presented in the context of a single crystalline silicon scanning micromirror. The electrothermal actuated control of the variable offset is used to investigate the influence of the initial comb offset on the dynamic resonance behavior of the scanning mirror. With possible maximum vertical comb-offsets between 10 μm and 5 μm a higher dynamic mirror scan angle at the mechanical resonance frequency of 6 kHz is found for higher initial offsets. The same behavior of higher scan angles for higher offsets is also shown when mechanically controlling the initial comb-offset including negative offset values and offsets close to 0 μm.
    Micro Electro Mechanical Systems (MEMS), 2013 IEEE 26th International Conference on; 01/2013
  • Li Li, Ran Li, W. Lubeigt, D. Uttamchandani
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    ABSTRACT: A close-loop-controlled miniature Peltier element was used to vary the temperature of a 1.2 mm diameter silicon-gold bimorph varifocal micromirror (VFM), thereby changing its radius of curvature due to differential thermal expansion of the two materials. By varying the VFM temperature from 10°C to 100°C, the radius of curvature (ROC) of the micromirror was measured to vary from 19.2mm to 30.9mm. The Zernike coefficients over this operational range were analysed to be less than a few micrometres. An imaging system utilising the VFM was assembled, and examples of the near aberration-free images obtained are presented.
    Optical MEMS and Nanophotonics (OMN), 2013 International Conference on; 01/2013
  • A. Unamuno, R. Blue, D. Uttamchandani
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    ABSTRACT: We report on the modeling and testing of a Vernier latched MEMS variable optical attenuator (VOA) which uses chevron electrothermal microactuators to control fiber-to-fiber optical power coupling. The use of microlatches has the advantage of holding the mechanical position of the fiber, and therefore the level of attenuation, with no electrical energy supplied except only to change the attenuation. Results of analytical electro-thermo-mechanical models of the device are obtained and compared with experimental test results, showing a good agreement. A step resolution of 0.5 μm for this multi-state latched device is achieved using a Vernier latch approach. This incremental step size is smaller than previously reported latched microactuators. The VOA demonstrated an attenuation range of over 47 dB and an insertion loss of 1 dB. The wavelength dependent loss across the optical communications C-band is 1.4 dB at 40 dB attenuation and the 10-90% transition time of the unlatched VOA is measured to be 1.7 ms.
    Journal of Microelectromechanical Systems 01/2013; 22(5):1229-1241. · 2.13 Impact Factor
  • A. Dudus, R. Blue, M. Zagnoni, D. Uttamchandani
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    ABSTRACT: We report for the first time a broadband variable optical attenuator employing a side-polished single-mode optical fiber integrated on an electrowetting-on-dielectric platform. This in-line fiber optic device has the advantage of no moving mechanical parts and lends itself to miniaturization.
    Optical MEMS and Nanophotonics (OMN), 2013 International Conference on; 01/2013
  • E.J. Boyd, D. Uttamchandani
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    ABSTRACT: In (100) silicon wafers, the most commonly used in microelectromechanical systems (MEMS) fabrication, the value of Young's modulus of a MEMS structure can vary by over 20%, depending on the structure's orientation on the wafer surface. This anisotropy originates from the crystal structure of silicon. We have directly measured the anisotropy of Young's modulus in the (100) plane of silicon from the measured resonance frequencies of a “wagon-wheel” test structure comprising an arc of identical microcantilevers fabricated in the structural layer of a (100) silicon-on-insulator wafer. The direction of the principal axis of the cantilevers increased from 0° to 180 ° in 10° steps with respect to the [110] direction, allowing the angular dependence of Young's modulus to be experimentally mapped out. The Young's modulus was measured to have a value of 170 GPa ± 3 GPa at 0° and 90 ° to the [110] direction and a value of 131 GPa ± 3 GPa at ±40° and ±50° to the [110] direction. The measured values of Young's modulus and their angular dependence agree very well with the theoretical values that were recently reported, thereby experimentally verifying the theoretical calculations.
    Journal of Microelectromechanical Systems 01/2012; 21(1):243-249. · 2.13 Impact Factor
  • Li Li, R. Bauer, G. Brown, D. Uttamchandani
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    ABSTRACT: A hybrid two-axis scanning micromirror combining electrostatic and electrothermal actuators was fabricated using SOIMUMPs. Experimental evaluation shows the device is capable of scan in two orthogonal directions and produces a rectangular raster-scan pattern.
    Optical MEMS and Nanophotonics (OMN), 2012 International Conference on; 01/2012
  • R. Bauer, W. Lubeigt, D. Uttamchandani
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    ABSTRACT: A comb-drive actuated MEMS scanning mirror is used to actively Q-switch a side-pumped Nd:YAG laser. Minimum pulse durations of 38 ns are observed and maximum average output powers of 55 mW at 17.625 kHz pulse repetition frequency.
    Optical MEMS and Nanophotonics (OMN), 2012 International Conference on; 01/2012
  • E. J. Boyd, B. Choubey, I. Armstrong, D. Uttamchandani
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    ABSTRACT: This paper reports on a simple technique to measure the anisotropy of the Young's modulus of single crystal silicon using a coupled cantilever structure fabricated in the silicon. We demonstrate that it is possible to determine the Young's modulus of five silicon micro-cantilevers, whose orientations range from 30γ to 55γ to the wafer flat, by measuring the resonance frequencies of just one single cantilever of the coupled structure in a “perturbed” and “unperturbed” state. In this work the perturbation of the coupled system was achieved by shortening one of the cantilevers using focused ion beam milling. The resulting Young's modulus values from this experiment agree very well with the theoretical values with a difference of less than 2.5%.
    Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS) 01/2012;
  • B. Choubey, E.J. Boyd, I. Armstrong, D. Uttamchandani
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    ABSTRACT: This paper reports a simple technique to measure the anisotropy of the Young's modulus of MEMS materials using coupled cantilevers. The technique is demonstrated in single-crystal silicon with an array of cantilevers fabricated in (100) silicon following a “wagon wheel” configuration. The long axis of the cantilevers had different angular orientations to the [110] direction. The parasitic coupling due to undercut below the cantilevers, which is often observed during etching of MEMS, led to a collective behavior in the frequency response of the cantilevers. This collective behavior was used in association with an inverse eigenvalue analysis to obtain the Young's moduli for the different orientations. Further analysis of the technique relating to accuracy and precision required in the resonance frequency measurement has also been presented.
    Journal of Microelectromechanical Systems 01/2012; 21(5):1252-1260. · 2.13 Impact Factor
  • A. Dudus, R. Blue, D. Uttamchandani
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    ABSTRACT: Broadband interferometry was used to evaluate microfiber and side-polished fiber sensors for refractive index sensing of fluids. Refractive indices ranging from 1.33 to 1.451 were measured. Sensor behaviour agreed with a simple theoretical analysis.
    Optical MEMS and Nanophotonics (OMN), 2012 International Conference on; 01/2012
  • Z. Vobecka, R. Blue, F. Vilela, P. J. Skabara, D. Uttamchandani
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    ABSTRACT: This Letter describes a fabrication of a microsensor incorporating a novel customised nitro-sensitive polymer derived from the propylenedioxythiophene family. Electrochemical polymerisation was used to selectively grow different types of localised polymer films on interdigitated electrode arrays, thereby fabricating miniature sensors that exhibited a highly selective and reversible response to chemical vapours containing 'nitro' (NO2) groups. Such nitro-bearing vapours are also present in trace quantities in the atmosphere in the presence of explosives. Vapours of nitropropane and nitrobenzene, serving as model analytes for explosives, were used for sensor testing. The sensors were demonstrated to have up to three orders of magnitude higher signal response to vapours from nitro compounds compared to other vapours commonly found in the atmosphere. The authors believe this is the highest selectivity to nitro compounds reported from a polymer-based chemicapacitor sensor.
    Micro & Nano Letters 01/2012; 7(9):962-964. · 0.85 Impact Factor
  • Source
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    ABSTRACT: A novel and efficient absorption line recovery technique is presented. A micro-electromechanical systems (MEMS) mirror driven by an electrothermal actuator is used to generate laser intensity modulation through the mirror reflection. Tunable diode laser spectroscopy (TDLS) and photoacoustic spectroscopy (PAS) are used to recover the target absorption line profile which is compared with the theoretical Voigt profile. The target gas is 0.01% acetylene (C2H2) in a nitrogen host gas. The laser diode wavelength is swept across the P17 absorption line of acetylene at 1535.4 nm by a current ramp, and an erbium-doped fibre amplifier (EDFA) is used to enhance the optical intensity and increase the signal-to-noise ratio (SNR). A SNR of about 35 is obtained with 100 mW laser power from the EDFA. Good agreement is achieved between the experimental results and the theoretical simulation for the P17 absorption line profile.
    Guang pu xue yu guang pu fen xi = Guang pu 07/2011; 31(7):1814-8. · 0.29 Impact Factor
  • R. Bauer, G. Brown, D. Uttamchandani
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    ABSTRACT: Experimental investigations on the influence of a frame structure around an electrostatic comb-drive actuated micromirror are presented. The comparison between two 800 m diameter mirrors, one framed and the other frameless, fabricated with a multi-user silicon-on-insulator process was carried out in relation to the dynamic movement behaviour and the static and dynamic curvature of the mirror surfaces. Both mirror types used in the study were carefully chosen to have a similar diameter and torsional resonant frequency of the order of 7 kHz and are actuated with 10 pairs of comb-fingers. The inclusion of the frame structure is shown to increase the homogeneity of the curvature of the mirror, with a difference of radius of curvature between the main axes of 1 compared to a 10 difference for the frameless mirror. The frame also increases the achievable maximum resonant tilt angle around the second main axis by a factor of three, at the same time avoiding nonlinear frequency responses (such as hysteresis) in the tilt angle against frequency curve.
    Micro & Nano Letters 07/2011; · 0.85 Impact Factor
  • R. Blue, Li Li, G.M.H. Flockhart, D. Uttamchandani
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    ABSTRACT: A MEMS electrothermally actuated platform is described to allow tunable coupling between optical spherical resonators and optical waveguides. The platform is experimentally characterised and selective wavelength dropping from an optical fibre waveguide is demonstrated.
    Optical MEMS and Nanophotonics (OMN), 2011 International Conference on; 01/2011
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    E. J. Boyd, V. Nock, X. Li, D. Uttamchandani
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    ABSTRACT: The use of micro-cantilever test structures for determining the density of thin film materials is reported. A range of micro-cantilever test structures has been fabricated using silicon, silicon nitride and silicon carbide which are materials that are commonly used in the fabrication of micro-electromechanical systems. The density of each material was determined by combining load–deflection and resonant frequency measurements, and using the Euler–Bernoulli equation for single clamped beams. The density values obtained were 2.35, 3.16 and 3.18g/cm3 for silicon, silicon carbide and silicon nitride respectively. These values of density for these thin films agree very well with the values quoted in the literature.
    Thin Solid Films 01/2011; 519(22):7932-7935. · 1.87 Impact Factor