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ABSTRACT: Theory and experiments of single-mode ridge waveguide GaAs-AlGaAs semiconductor ring lasers are presented. The lasers are found to operate bidirectionally up to twice the threshold, where unidirectional operation starts. Bidirectional operation reveals that just above threshold, the lasers operate in a regime where the two counterpropagating modes are continuous wave. As the injected current is increased, a new regime appears where the intensities of the two counterpropagating modes undergo alternate sinusoidal oscillations with frequency in the tens of megahertz range. The regime with alternate oscillations was previously observed in ring lasers of the gas and dye type, and it is here reported and investigated in semiconductor ring lasers. A theoretical model based on a mean field approach for the two counterpropagating modes is proposed to study the semiconductor ring laser dynamics. Numerical results are in agreement with the regime sequence experimentally observed when the injected current is increased (i.e., bidirectional continuous-wave, bidirectional with alternate oscillations, unidirectional). The boundaries of the different regimes are studied as a function of the relevant parameters, which turn out to be the pump current and the conservative and dissipative scattering coefficients, responsible for an explicit linear coupling between the two counterpropagating field modes. By a fitting procedure, we obtain good numerical agreement between experiment and theory, and also an estimation for the otherwise unknown scattering parameters.
IEEE Journal of Quantum Electronics 11/2003; · 1.88 Impact Factor
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ABSTRACT: This work performs numerical and experimental studies of coupled mode dynamics for monolithic semiconductor ring lasers. This study presents numerical analysis and experimental results of the different operating regimes, namely: bidirectional CW, bidirectional with harmonic oscillations of the mode intensities, and unidirectional.
Quantum Electronics Conference, 2003. EQEC '03. European; 07/2003
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ABSTRACT: We report on fabrication and characterization of single-longitudinal- and transverse-mode semiconductor ring lasers. A bifurcation from bidirectional stable operation to a regime with alternate oscillations of the counterpropagating modes was observed experimentally and is theoretically explained through a two-mode model. Analytical expressions for the onset and the frequency of the oscillations are derived, and L-I curves numerically evaluated. Good quantitative agreement between theory and measurements made over a large number of tested devices is obtained.
Optics Letters 12/2002; 27(22):1992-4. · 3.40 Impact Factor
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ABSTRACT: In testing MEMS and MOEMS, one can use the direct observation of
the device under a microscope and the functionality test in the intended
mode of operation. A new diagnostic tool, also useful since the initial
design phases, is presented in this paper. It is based on injection
interferometry and provides the actual amplitude of displacement and
related parameters, e.g. the maximum frequency of operation and the
mechanical quality-factor of the structure. We present the basic idea
and the measurements (vibration amplitude, resonant frequency, Q and
hysteresis effects) performed on a MEMS gyro structure with the aid of
the injection interferometer
Optical MEMS, 2000 IEEE/LEOS International Conference on; 02/2000
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IEEE Journal of Selected Topics in Quantum Electronics 10/1999; 5(5):1225-1225. · 3.78 Impact Factor
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ABSTRACT: In this paper, we analyze the phenomena arising when a monomode
semiconductor laser is subjected to external injection from another
laser. The system stability is investigated as a function of detuning
and of the relative injected power. Different regimes, spanning from
phase locking to chaos and coherence collapse, are described by
analytical and numerical methods for weak and moderate injection.
Previous theoretical studies are extended by describing the inverse
transition from chaos to stability and by deriving the final locking
condition. Also, further investigation on the coherence collapse regime
has been performed. Besides contributing to the exploration of an
interesting fundamental phenomenon, the results of this analysis are
useful for different applications, including coherent detection and
chaotic cryptography
IEEE Journal of Quantum Electronics 01/1999; · 1.88 Impact Factor
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ABSTRACT: We propose a new procedure for evaluating the complex refractive index of a metal film, based on transmission measurements at different incidence angles. The method is simpler and faster than standard ellipsometry and performs the accuracy required for the design of fiber-optic attenuators for telecommunications. As an example, we report on a device showing a constant attenuation on the 1200-1600-nm wavelength range.
Applied Optics 09/1998; 37(22):5298-301. · 1.41 Impact Factor
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ABSTRACT: We propose a new scheme for synchronization of the optical chaos
generated by a semiconductor laser subjected to external reflection. The
scheme is based on optical feedback and will be analyzed from the
viewpoint of static and dynamic properties and of robustness to external
perturbations and noise. An application to cryptographic communications
(chaotic shift keying) is finally proposed
IEEE Journal of Quantum Electronics 10/1997; · 1.88 Impact Factor
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ABSTRACT: Using a laser-diode feedback interferometer, we show how to
reconstruct without ambiguity the displacement waveform of an external
target from a single interferometric signal. We present the underlying
theory with numerical simulations and report an example of actual
reconstruction from experimental data. Reconstruction accuracy is on the
order of tens of nanometers for displacements of a few micrometers
IEEE Journal of Quantum Electronics 05/1997; · 1.88 Impact Factor
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ABSTRACT: We have analyzed the failure data of a standard telecommunication
optical fiber under static bending stress. Experimental data have been
collected on a 468 day period, observing more than 7000 turns, with a
bend radius ranging from 1.25 to 6 mm. The statistical analysis has been
carried out by both the least-square and the maximum likelihood method.
We have found that data are fitted by a Weibull distribution, as
expected theoretically. Moreover, we have determined the scale and shape
parameters and tested their dependence on the bend radius. According to
our results, we conclude that in sensor applications silica fibers can
be safely bent down to a radius less than 5 mm
Journal of Lightwave Technology 03/1997; · 2.78 Impact Factor
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ABSTRACT: We describe a laser-diode feedback interferometer for displacement
measurements with directional discrimination and resolution better than
10<sup>-6</sup> m. This new, compact instrument consists of a small
optical head and a signal processing board, which is interfaced to a
personal computer. The prototype developed has a dynamic range of 2 m
and an accuracy of about 5 μm/m, using a corner cube as a remote
reflector. Thanks to PC interfacing, the displacement is directly
available in metric units and errors due to temperature fluctuations can
be corrected with software signal processing
IEEE Transactions on Instrumentation and Measurement 01/1997; · 1.21 Impact Factor
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ABSTRACT: We show that, in studying eye-head coordination, the rotation of
the head can be measured with the aid of a fiber optics gyroscope
mounted on a helmet worn by the subject, and that the performances of
this approach are considerably better than those of currently used
sensors. After presenting the specifications required in head rotation
measurements, we report details on the gyroscope used and on its
interconnection to the acquisition system, and discuss experimental
results of head rotation measurements made by the gyroscope and the
potentiometer sensor
IEEE Journal of Selected Topics in Quantum Electronics 01/1997; · 3.78 Impact Factor
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IEEE Photonics Technology Letters 10/1996; 8(9):1278-. · 2.19 Impact Factor
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ABSTRACT: We demonstrate that two chaotic systems, each made by two coupled
semiconductor lasers, can be synchronized using direct-optical feedback.
The robustness of the proposed synchronization scheme against mismatch
of source parameters and difference in starting conditions is tested by
numerical simulations. Applications to secure data transmission are
proposed, namely chaotic masking and chaotic shift keying (CSK)
IEEE Journal of Quantum Electronics 07/1996; · 1.88 Impact Factor
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ABSTRACT: A quarter-wave retarder made by a small loop of fiber on the laser pigtail is an effective means to protect the laser from retroreflections. Suppression factors of about 20 dB have been achieved with negligible insertion losses. An example of application is given. A method to measure the isolation is also presented.
IEEE Photonics Technology Letters 05/1996; · 2.19 Impact Factor
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ABSTRACT: With a figure-of-eight winding of monomode fiber, we have been
able to build multiturn (>100) coils which can be easily trimmed to
match the condition of exactly one wavelength-per-turn birefringence. As
an example, we report a 45° Faraday rotator intended for an
all-fiber optical isolator at λ=1300 nm
Journal of Lightwave Technology 01/1996; · 2.78 Impact Factor
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ABSTRACT: Phase noise due to thermodynamic fluctuations in the optical path length is evaluated in this paper for basic fibre interferometers. In Mach-Zehnder and Michelson interferometers, where the temperature phase fluctuation (TPF) is that intrinsic to the fibre, this noise has been reported to be comparable to shot noise and a possible limit to sensor sensitivity in practical cases. We show that in Sagnac interferometers, used in fibre gyro and in Faraday current sensors, the TPF noise is decreased with respect to that intrinsic to the fiber because propagation in the same optical path leads to a correlation of the phase fluctuations. In addition, we show that in Fabry-Perot and ring resonators, as multiple reflections increase the effective path length, TPF noise is enhanced and can be dominant over shot noise even for moderate fibre lengths.
Optical and Quantum Electronics 12/1995; 28(1):43-49. · 0.82 Impact Factor
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ABSTRACT: We report what, to our knowledge, is the first example of laser
feedback interferometer capable of measuring displacements of arbitrary
form using a single interferometric channel. With a GaAlAs laser diode
we can measure 1.2-m displacements, with interferometric resolution,
simply by means of the backreflection from the surface (reflective or
diffusive) under test. The operation is performed at moderate (i.e., not
very weak) levels of feedback, such that a two-level hysteresis is found
in the amplitude modulated signal. This is shown to allow the recovery
of displacement without sign ambiguity from a single interferometric
signal. Experimental results are reported, which are found to be in good
agreement with the underlying theory. Performances of the developed
feedback interferometer are finally presented
IEEE Journal of Quantum Electronics 02/1995; · 1.88 Impact Factor
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ABSTRACT: We have analyzed the behavior of a semiconductor laser subjected
to increasing external injection. Numerical simulations show the
well-known nonlinear modulation and locking regimes, followed by an
intermediate chaotic region that precedes definitive locking to the
external source at significantly higher injection levels
IEEE Journal of Quantum Electronics 08/1994; · 1.88 Impact Factor
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ABSTRACT: New results on the polarization properties of a matched fiber-coil
(i.e. one beat length per turn) immersed in a magnetic field are
described. It is shown that both components H <sub>y</sub> and
H <sub>z</sub>, perpendicular to the coil axis, can be
simultaneously measured. Sensing coils of 1-cm diameter, with multiple
turns of fiber, were fabricated. Using 100-turn heads, a sensitivity of
0.01 G was achieved for the vectorial fiber sensor
Journal of Lightwave Technology 01/1993; · 2.78 Impact Factor
