Chaotic oscillator in wavelength: a new setup for investigatingdifferential difference equations describing nonlinear dynamics

A generator of chaos in wavelength is reported. It is formed by a wavelength-tunable laser diode with a time delayed feedback loop in which a wavelength nonlinear-linear device is introduced. The dynamical regime of wavelength emission thus obtained is ruled by a differential difference equation. Experimental results are compared with numerical simulations and with previous theoretical and experimental results     

Coherence-multiplexed acousto-optic correlator for signal processing: theory and applications

A method of multichannel processing to compute correlation products simultaneously is introduced. The signals that process are encoded on a single light beam through the use of an electro-optic modulators that induce optical delays greater than the coherence length of light. The coherence-modulated light beam thus obtained is then spatially and temporally modulated through an acousto-optic Bragg cell. The potential number of channels is estimated to be approximately 5-10. The method can be combined with other existing systems, such as time-, space-, or frequency-multiplexed correlators, to increase the channel number. The method also applies to high-resolution spectral analysis.     

Photon counting in the 1540-nm wavelength region with a germaniumavalanche photodiode

Unexpected results have been obtained in measurements of dark-count rate and quantum efficiency (QE) for a germanium avalanche photodiode operating in the photon counting regime at 1540-nm wavelength. A liquid-nitrogen cooled Ge single-photon avalanche diode (SPAD) exhibited both a low dark-count rate and a QE of the order of 1%, which is at least one order of magnitude higher than the values reported for such a device. The data offer hope for future diodes that might match such performance. Reasons for the device's extraordinarily good performance, a performance level not matched by the other 17 APDs in the collection investigated, are not understood. Such high quantum efficiency germanium devices could be used in one-bit-per-photon communication systems operating in the 1540-nm telecommunications window     

Electrooptic modulation of multilongitudinal mode laser diodes: Demonstration at 850 nm with simultaneous data transmission by coherence multiplexing

An electrooptic modulation method based on signal coding through optical delays larger than the source coherence length is described. The method is illustrated with the simultaneous transmission of several signals by path-difference multiplexing. In this method, the signals are coded as a sequence of optical delays introduced by a series of electrooptic modulators working as delay lines. Decoding is carried out by temporal correlation performed by another sequence of optical delays introduced by birefringent plates, and matched to those used at the emission process. The permissible delays are shown to be ruled by the source coherence length and by the number of laser modes.     

AlGaAs-GaAs polarization converter with electrooptic phase mismatchcontrol

We designed and fabricated an electrooptic transverse magnetic-transverse electric mode converter with phase mismatch control integrated in AlGaAs-GaAs. The electrode scheme, which is reported for the first time in such a device, insures a high polarization conversion efficiency with low-driving voltages     

Experimental investigation of soliton optical phase jitter

The soliton optical phase stability versus amplified spontaneous noise is investigated in a recirculation loop experiment in the presence of in-line filters. The behavior of phase fluctuations is shown to be in good agreement with numerical simulations. The phase standard deviation is kept below 0.15×π for distances up to 8000 km. We, therefore, demonstrate the feasibility of phase-shift keying on solitons for long-haul transmission systems     

Wavelength tuning of a semiconductor laser using nematic liquidcrystals

The authors report a single frequency, extended cavity laser diode operating at 1500 nm wavelength and using an intracavity liquid cell wavelength filter to tune the wavelength over 6 nm by mode hopping. Continuous tuning over the free spectra range of the cavity is also demonstrated     

Transmission system using chaotic delays between lightwaves

We report a chaos-based transmission system that uses optical path differences between wavegroups produced by a short coherence source. Chaos synchronization is demonstrated in delay-differential equations involving optical delays larger than the coherence length of the source. The particular feature is all-optical chaos subtraction for message extraction and a very high masking efficiency.     

Influence of digitisation on master?slave synchronisation in chaos-encrypted data transmission

The impact of digitisation on chaos synchronisation and message decoding in a chaotic cryptosystem is described. The sampling rates and resolutions that lead to a good decoding of the message are determined numerically and experimentally. The results are interpreted in light of Shannon's sampling theory     

Erbium-doped fiber laser tuning using two cascaded unbalancedMach-Zehnder interferometers as intracavity filter: numerical analysisand experimental confirmation

We propose a new method for tuning an Er³⁺-doped continuous-wave fiber-ring laser. We present a novel numerical model and confirm the model with experimental results. The numerical model relies on the implementation of the analytical solution of signal propagation over small (elemental) segments of amplifier fiber rather than using the usual Runge-Kutta algorithm. The validity of the model is verified by the good agreement between computer results and experimental data. Experiments demonstrating a 11.2-nm wavelength tuning range have been conducted using an electrooptic intracavity filter composed of two cascaded unbalanced Mach-Zehnder interferometers (MZIs) integrated in lithium niobate. The numerical analysis shows that the tuning range obtained is limited by the combination of gain shape and filter characteristics. Increased tuning range can be obtained by decreasing losses or by using a more selective filter