Dedicated optical instruments for ultrasonic welder inspection and control

Two different optical instruments for real-time vibration measurements, inspection and control of ultrasonic welders were designed, realized and characterized: a self-mixing laser interferometer and an optical triangulator, both studied for achieving high bandwidth and very good resolution within a short dynamic range. The implemented instruments can solve the problem of measurement and control of ultrasonic welders that until now has no low-cost solutions available on the market. The performance of the two developed instruments was compared in order to assess which is the most appropriate for this specific application. Finally, results of the real-time characterization of an ultrasonic welder are given and discussed.     

Noise evolution along optically amplified links in presence ofnonlinear parametric gain

With a semiclassical model of the optical amplifier, we calculate the evolution of noise along optically amplified lines in presence of nonlinear interaction between signal and amplified spontaneous emission, amplifier saturation, fiber dispersion and vacuum field fluctuations associated with attenuation of the fiber. The noise figure (NF) is calculated for two representative cases of long and short-distance links with different numbers of optical amplifiers and for several fiber dispersions. Results indicate that the optimum number of optical amplifiers is limited by the increase of nonlinear effects with signal power     

Testing of "Venetian-Blind" silicon microstructures with optical methods

In this paper, we illustrate the design and testing of new silicon microstructures, fabricated by means of a conventional planar process. These "Venetian-blind" structures consist of arrays of narrow, rectangular suspended masses (width =31 /spl mu/m, length =400 /spl mu/m, thickness =15 /spl mu/m), which can be tilted using electrostatic actuation. Characterization of their static and dynamic behavior was performed with optical methods. The diffraction patterns in monochromatic light were analyzed and vibration measurements were performed by means of semiconductor laser feedback interferometry: experimental data on the tilt angle as a function of the applied voltage and on the resonance frequencies are reported. A maximum tilt angle of approximately 1.9/spl deg/ was obtained with a driving voltage in the range of 70-95 V. All the tested devices showed resonance frequencies higher than 80 kHz, which is fast enough (i.e., switching time in the millisecond range) for future use in optical interconnections. Numerical analyses were performed to evaluate the coupled electromechanical behavior of the microstructures, confirming the observed experimental behavior.     

Self-mixing vibrometer with real-time digital signal elaboration

This work describes the development of an optical sensor for measurement of vibration without contact. The realized vibrometer is based on real-time digital elaboration of the signal obtained by a self-mixing interferometer, with an embedded autofocus system. Two different algorithms are implemented, for the continuous working on diffusive surfaces, with different levels of optical reflectivity. Thanks to the autofocus and the digital processing, the proposed sensor is easy to use and requires no assistance of a skilled operator.     

A displacement-measuring instrument utilizing self-mixing interferometry

We develop a self-mixing laser interferometer for the measurement of displacements on a generic target surface. The measurement is based on the bright-speckle tracking, a technique we have recently proposed to solve amplitude fading associated with the speckle statistics when the displacement to be covered is well in excess of the speckle longitudinal size. We implement the dynamical tracking of speckle maxima with piezo actuators and a phase-sensing loop. Also, we use an automatic gain control, based on a liquid crystal attenuator, to improve the amplitude statistics. Details of digital signal acquisition with adaptive signal processing through a field programmable gate array are discussed. The resulting instrument offers sub-/spl mu/m resolution in the measurement of displacement up to 500 mm of total shift, has virtually no need for alignment, and has very relaxed target-surface requisites, yet works with a very simple and inexpensive set-up.     

Measurement of Water Jet Velocity Distribution Using Laser Velocimetry

A laser Doppler velocimetry technique has been implemented in this work to evaluate the water jet velocity distribution in water jet and abrasive water jet cutting applications. Knowledge of the water jet velocity is fundamental to determine the system cutting efficiency; in particular, it allows us to experimentally determine the specific performance of the orifices employed in the cutting process.      

Hybrid opto-mechanical gyroscope with injection-interferometerreadout

A hybrid micromachined-optoelectronic mechanical system (MOEMS) gyroscope is proposed. It consists of an electrically excited micro-mechanical resonator and an optical readout performed by a laser diode operating as an injection interferometer. An analysis of the system, validated by preliminary experimental results, indicates an attainable performance of 1 deg/h√Hz     

Measurements on a micromachined silicon gyroscope by feedbackinterferometry

Feedback interferometry is a useful tool to characterize micromachined devices. We consider a silicon vibrating gyroscope, in which the angular rotation is transduced into the vibration amplitude of a small suspended mass. Measurements of the mass displacement at submicrometer resolution are reported on a 400×400 μm sensor, using an 800-nm 20-mW laser diode. The resonance curves of the device have been determined for different values of pressure and other parameters, which allows us to tune the resonance frequency and maximize the Q factor. Hysteresis and other nonlinear phenomena on specific samples also have been detected. The proposed method provides a direct inspection tool and represents a practical alternative to the standard electrical measurements     

Three-Dimensional Reconstruction and Image Processing in Mandibular Distraction Planning

Mandible or facial bone reconstruction is a serious challenge in craniomaxillofacial surgery. Careful presurgical planning or availability of objective methods to evaluate the three-dimensional (3-D) shape of the patient mandible is necessary to achieve predictable outcomes. The aim of this paper is to apply 3-D techniques of volumetric reconstruction and image processing for planning distraction osteogenesis of the mandible, involving the use of 3-D modeling. To accomplish this task, suitable two-dimensional (2-D)-to-3-D image processing is used in order to obtain a 3-D model of the mandible from standard 2-D computed tomography images. The goal of this paper is to provide the surgeon with a 3-D model of the patient mandible, where it would be possible to find, in the presurgical phase, the exact point of implant with respect to the patient's anatomy and to build a custom-made prosthesis that properly fits the bone surface of the patient for correct control of the vector during the progressive traction of the bone segments     

Spot optical measurements on micromachined mirrors for photonic switching

This paper describes and compares three optical methods for performing spot measurements on micromachined mirrors, designed for photonic switching in fiberoptic networks. For static characterization, two spot-position detection systems, one based on a vidicon camera and the other based on a bidimensional silicon position sensitive detector (PSD), are illustrated, tested, and compared. Moreover, the dynamic behavior has been monitored with the PSD-based detection arrangement and with a semiconductor laser feedback interferometer. Advantages and drawbacks of these methods are highlighted. Testing is reported on torsional, silicon micromachined mirrors, with a single degree of freedom. High dc voltage for static measurements, and sinusoidal or white-noise or step excitation for dynamic characterization, have been used for mirror driving.