242 research outputs found
Signal-to-Noise Ratio in Squeezed-Light Laser Radar
The formalism for computing the signal-to-noise ratio (SNR) for laser radar
is reviewed and applied to the tasks of target detection, direction-finding,
and phase change estimation with squeezed light. The SNR for heterodyne
detection of coherent light using a squeezed local oscillator is lower than
that obtained using a coherent local oscillator. This is true for target
detection, for phase estimation, and for direction-finding with a split
detector. Squeezing the local oscillator also lowers SNR in balanced homodyne
and heterodyne detection of coherent light. Loss places an upper bound on the
improvement that squeezing can bring to direct-detection SNR.Comment: Typos correcte
The emergence of dynamic networks from many coupled polar oscillators. A model for Artificial Life
This work concerns a many-body deterministic model that displays life-like
properties as emergence, complexity, self-organization, spontaneous
compartmentalization, and self-regulation. The model portraits the dynamics of
an ensemble of locally coupled polar phase oscillators, moving in a
two-dimensional space, that in certain conditions exhibit emergent
superstructures. Those superstructures are self-organized dynamic networks,
resulting from a synchronization process of many units, over length scales much
greater than the interaction length. Such networks compartmentalize the
two-dimensional space with no a priori constraints, due to the formation of
porous transport walls, and represent a highly complex and novel non-linear
behavior. The analysis is numerically carried out as a function of a control
parameter showing distinct regimes: static, stable dynamic networks,
intermittency, and chaos. A statistical analysis is drawn to determine the
control parameter ranges for the various behaviors to appear.Comment: 14 pages, 8 figures and 4 movie
Private Communications Using Optical Chaos
After a brief summary of the basic methods for secure transmission using optical chaos, we report on most recent achievements, namely, on the comparison between the standard two-laser and the three-laser schemes and on the network architecture for multiuser secure transmission. From our investigations, we found that while both the basic two-laser and the three-laser schemes are suitable to secure data exchange, the three-laser scheme offers a better level of privacy due to its symmetrical topology. Moreover, while transmission based on optical chaos is usually restricted to point-to-point interconnections, a more advanced solution, derived from the well-known public key cryptography, allows for private message transmission between any couple of subscribers in a network
Distance measurement by delayed optical feedback in a ring laser
We numerically study the behavior of a semiconductor ring laser subject to bidirectional
delayed optical feedback, when the isolated laser is in the quasi-unidirectional regime.
The optical feedback, provided by two external refectors located in front of the ring output waveguides, can modify the laser regime produced by the cross-saturation between
the clockwise and the counter-clockwise mode. Thus, the system exhibits new diferent regimes, most of which are asymmetric and bidirectional, with alternating dominant
mode. Two of these regimes are of special interest in view of applications, because the
laser switching period, between the clockwise and the counter-clockwise mode, is linearly
related to the time of fight from the laser to one or both refectors. In these operating conditions, the laser is thus suitable to implement a telemeter. A convenient electrical output
signal is obtained by a photodiode located behind one (partially refecting) fxed mirror,
or by measuring the voltage drop across the laser junction. Simulations are performed by
mathematical models based on rate-equations, assuming typical literature parameters for a
1 mW ring laser
Overcoming laser diode nonlinearity issues in multi-channel radio-over-fiber systems
The authors demonstrate how external light injection into a directly modulated laser diode may be used to enhance the performance of a multi-channel radio-over-fiber system operating at a frequency of 6 GHz. Performance improvements of up to 2 dB were achieved by linearisation of the lasers-modulation response. To verify the experimental work a simulation of the complete system was carried out using Matlab. Good correlation was observed between experimental and simulated results
Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption
Optical chaos is a topic of current research characterized by
high-dimensional nonlinearity which is attributed to the delay-induced
dynamics, high bandwidth and easy modular implementation of optical feedback.
In light of these facts, which adds enough confusion and diffusion properties
for secure communications, we explore the synchronization phenomena in
spatiotemporal semiconductor laser systems. The novel system is used in a
two-phase colored image encryption process. The high-dimensional chaotic
attractor generated by the system produces a completely randomized chaotic time
series, which is ideal in the secure encoding of messages. The scheme thus
illustrated is a two-phase encryption method, which provides sufficiently high
confusion and diffusion properties of chaotic cryptosystem employed with unique
data sets of processed chaotic sequences. In this novel method of cryptography,
the chaotic phase masks are represented as images using the chaotic sequences
as the elements of the image. The scheme drastically permutes the positions of
the picture elements. The next additional layer of security further alters the
statistical information of the original image to a great extent along the
three-color planes. The intermediate results during encryption demonstrate the
infeasibility for an unauthorized user to decipher the cipher image. Exhaustive
statistical tests conducted validate that the scheme is robust against noise
and resistant to common attacks due to the double shield of encryption and the
infinite dimensionality of the relevant system of partial differential
equations.Comment: 20 pages, 11 figures; Article in press, Optics Communications (2011
Sudden chaotic transitions in an optically injected semiconductor laser
We study sudden changes in the chaotic output of an optically injected semiconductor laser. For what is believed to be the first time in this system, we identify bifurcations that cause abrupt changes between different chaotic outputs, or even sudden jumps between chaotic and periodic output. These sudden chaotic transitions involve attractors that exist for large regions in parameter space. © 2001 Optical Society of Americ
Experimental investigation of the impact of optical injection on vital parameters of a gain-switched pulse source
An analysis of optical injection on a gain-switched distributed feedback (DFB) laser and its impact on pulse parameters that influence the performance of the pulse source in high-speed optical communication systems is presented in this paper. A range of 10 GHz in detuning and 5 dB in injected power has been experimentally identified to attain pulses, from an optically injected gain-switched DFB laser, with durations below 10 ps and pedestal suppression higher than 35 dB. These pulse features are associated with a side mode suppression ratio of about 30 dB and a timing jitter of less than 1 ps. This demonstrates the feasibility of using optical injection in conjunction with appropriate pulse compression schemes for developing an optimized and cost-efficient pulse source, based on a gain-switched DFB laser, for high-speed photonic systems
Mechanical-Thermal Noise in Drive-Mode of a Silicon Micro-Gyroscope
A new closed-loop drive scheme which decouples the phase and the gain of the closed-loop driving system was designed in a Silicon Micro-Gyroscope (SMG). We deduce the system model of closed-loop driving and use stochastic averaging to obtain an approximate âslowâ system that clarifies the effect of thermal noise. The effects of mechanical-thermal noise on the driving performance of the SMG, including the noise spectral density of the driving amplitude and frequency, are derived. By calculating and comparing the noise amplitude due to thermal noise both in the opened-loop driving and in the closed-loop driving, we find that the closed-loop driving does not reduce the RMS noise amplitude. We observe that the RMS noise frequency can be reduced by increasing the quality factor and the drive amplitude in the closed-loop driving system. The experiment and simulation validate the feasibility of closed-loop driving and confirm the validity of the averaged equation and its stablility criterion. The experiment and simulation results indicate the electrical noise of closed-loop driving circuitry is bigger than the mechanical-thermal noise and as the driving mass decreases, the mechanical-thermal noise may get bigger than the electrical noise of the closed-loop driving circuitry
- âŠ