Enhancing Chaotic Communication Performances by Manchester Coding

A numerical analysis of an optical chaotic transmission system, based on the synchronization of two chaotic lasers, in a master-slave closed loop configuration is presented. At the transmitter, the master chaotic wave is superposed on the information message; at the receiver, the message is recovered by subtracting the synchronized slave chaotic wave from the received signal. The performances are analyzed in terms of the Q-factor, considering two different message modulation formats: the nonreturn-to-zero and the Manchester coding. The Manchester coding shows enhanced performances due to the shift of the signal spectrum to higher frequencies.     

Optical Characterization of High-Order 1-D Silicon Photonic Crystals

In this paper, we present numerical and experimental results on the spectral reflectivity of hybrid, high-order (up to 22nd) 1-D silicon photonic crystals (PCs) in the near-infrared region (wavelength range 1- 1.7 mum). Mechanically robust, vertical 1-D PCs with high aspect ratio and spatial period of 8 mum were fabricated by electrochemical micromachining of silicon, and tested in reflection with an improved optical setup, incorporating standard telecommunication single-mode optical fibers and a lensed fiber pigtail. A detailed theoretical, numerical analysis was performed to assess the effects of both non-idealities of the structures under test and constraints of the optical setup, on the spectral reflectivity. Experimental data were found in very good agreement with theoretical calculations, performed by using the characteristic matrix method, keeping into account an in-plane porosity variation for 1-D PCs, due to surface roughness of silicon walls, and the limited resolution bandwidth of the spectrum analyzer. Best optical performances, measured on the fabricated 1-D PC mirrors, consist of optical losses less than 0.8 dB in a bandgap around 1.5 mum and a -35 dB reflectivity minimum at a bandgap edge.     

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.     

A semiclassical model for noise propagation in depleted-pumpoptical amplifiers

Erbium-doped and parametric fiber-optic amplifiers can be modeled as a cascade of “amplifying” beamsplitters, each representing a short fiber section in which the pump is approximately constant. Each beamsplitter obeys simple noise combination relations and its gain is calculated from the standard rate equations. The proposed model allows for the management of pump depletion in a very simple way by numerical analysis, avoiding direct quantum mechanical calculations. Sample noise propagation diagrams are reported for technically significant values of the parameters. For the four-wave-mixing amplifier, it has been found that the 3-dB noise limit can be reached even for a strong gain compression     

Synchronization of chaotic lasers by optical feedback forcryptographic applications

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     

All-fiber Faraday rotator made by a multiturn figure-of-eight coilwith matched birefringence

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     

Dynamic behavior and locking of a semiconductor laser subjected toexternal injection

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     

Synchronization of chaotic injected-laser systems and itsapplication to optical cryptography

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)     

Mechanical–thermal noise in micromachined gyros

In this paper we investigate the effect of mechanical–thermal fluctuations on a vibrating-mass surface-micromachined gyroscope. It is found that this noise source represents a practical sensitivity limit in such devices and is likely to restrict their performances to the automotive grade.     

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