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International audience; Laser spectra are strongly modified by the optical feedback which is provided by external cavities; here we give a preliminary experimental result describing the optical spectrum of a fibre laser having two identical end cavities, which appear between the external mirrors and fibre ends. One observes a channelled spectrum including mode clusters separated by empty regions. We use the optical Airy function defined in the pure frequency domain to study these spectra. An optical Vernier effect allows the description of this structure. The linewidth of each mode is calculated as a function of the gain, by using the same Airy function.

In this paper, we analyze an indoor wireless communications system using optical spatial modulation (OSM) when is subject to inter-symbol interference (ISI). An array of light emitting diodes (LEDs) is used in transmitter and an array of photo diodes (PDs) is used in receiver. Each group of k information bits selects a unique transmitting LED from the 2k total number of available LEDs. In the receiver, an optimal maximum likelihood (ML) detector is used to identify the transmitting LED. A channel model with ISI is introduced and the OSM system performances are tested in presence of additive white Gaussian noise (AWGN). The signal-to-interference-and-noise ratio (SINR) is estimated as function of channel path gains. The bit error rate (BER) is analyzed by simulation as function of SINR for different distances between transmitter and receiver. The simulation results reveal that for SINR values closer to the upper limit, SM receiver performs better than in the only presence of AWGN.

Indoor wireless optical communications (IWOC) can offer in certain applications a valuable alternative to wireless radio. Its main advantages being: low cost, medical safety and unlicensed band- width. The most suitable band- width seems to be 1550nm because of low noise and WDM solutions accessible by the current technology. In this paper we show a synthesis of some original results obtained last few years: impulse response simulation and measurement of IWOC channels, WDMA access solutions and Er doped spherical concentrator and amplifiers for IWOC.

In this paper we present a new “dynamical” spectral encoding method for the optical code division multiple access (OCDMA) indoor wireless communication system. In contrast with the classical OCDMA systems, where one user transmits all the information bits using the same spreading code sequence, in the proposed “dynamical” case one user transmits a fixed number of bits using one code sequence, and thereafter the code sequence is changed. According to obtained results, the performances of the system are better because of multipath interference reduction.

The Free Space Optic (FSO) communication is a daily reality used by an increasing number of companies. For indoor environment, optical wireless communication becomes a good alternative with respect to radio proposals. For both technologies, the architecture is similar: emission/reception base station (Gateway or Bridge) are installed to cover zones, which are defined to ensure a quality of service. The customers may be connected to the Wireless Local Area Network (WLAN) with an adapter or module that emits and receives on this network. But due to its specific characteristics, wireless optical technology could present important advantages such as: Transmitted data security, medical immunity, high data rate, etc... Nevertheless, the optical system may have a limit on the network management aspect and link budget. The scope of this paper is to present a proposal at crossroads between optical fibre telecom system and data processing. In this document, we will present a prototype developed in Brittany during a regional collaborative project (Techim@ges). In order to answer to the management aspect and the link budget, this prototype uses an optical multiplexing technique in 1550 nm band: the Wavelength Division Multiple Access (WDMA). Moreover it also proposes a new class 1 high power emission solution. This full duplex system transmits these various wavelengths in free space, by using optical Multiplexer/Demultiplexer and optical modules. Each module has a defined and personal wavelength associated to the terminal identification (addresses MAC or IP). This approach permits a data rate at a minimum of a ten's Mbit/s per customer and potentially hundred Mbps for a line of sight system. The application field for the achieved and proposed prototype is potentially investigated from WLAN to WPAN.

We propose recently in a pan to use these objects as optical amplifiers. This aim requires working in a complete different direction. Firstly it is not suitable to have a good quality factor for the micro-sphere, because we want to avoid the lasing effect and the interferences between the many round-trip fields that will give a severe limitation to the optical bandwidth. Secondly, it could be interesting to have bigger sphere in order to have a higher gain. We present in this communication the fabrication of optical amplifiers [3] using 6000 ppm Er3+ Al-doped silica micro-spheres of diameters ranging from 200 mum to 3 mm. In a first step, 46 samples have been made in order to realize this study.

topic « Lasers and laser applications »; International audience; We present the experiment that allows multiwavelength operation and tunability of a neodymium-doped fiber laser with an intracavity polarizer. Then, we present the experimental method to extract the Jones matrix of the fiber as a function of the wavelength. Hence, using the round-trip operator method, we compare both experimental and theoretical wavelength selection and find a excellent agreement.

conference 5452 « Semiconductor Lasers and Laser Dynamics », session 4 « Short Pulses and Mode-Locking » [5452-18]; International audience; A semiconductor laser coupled to a gallium-made non linear mirror may exhibit pulse regime. In order to better understand this coupled cavity, stationary solutions and dynamics are described following the standard Lang and Kobayashi equations for a semiconductor laser submitted to nonlinear optical feedback. It is shown that the nonlinearity distorts the ellipse on which lied the stationary solutions, with a "higher" part corresponding to lower reflectivity and a "lower" part to higher reflectivity. Bifurcation diagrams and nonlinear analysis are presented while the conditions for pulsed operation are discussed.

International audience; A multi mode channeled emission spectrum of Nd3+ and Er3+ doped fiber lasers with two symmetric free space external cavities is experimentally demonstrated. An optical Vernier effect depending on the relative length difference between the two end cavities leads to a controlled number of clusters of oscillating modes.

International audience; We report that a bubble with a radius of a few micrometers may be created at a precise location on a metal-coated optical fiber tip immersed in liquid nitrogen by microsecond optical pulses with peak powers of less than 20 mW. Dynamic optical measurements reveal that after termination of the optical pulse the bubble exhibits stable oscillations for several tens of microseconds, at frequencies up to several megahertz, as it slowly collapses.

The purpose of this paper is to calculate the radiation from bent single-code optical fibers along arbitrarily oriented curved shape, which we call 'single-mode optical fiber antennas' (SMOFA). A generalized voluie current cethod (VCM) is used in order to determine the radiated power of a N-iultiturn optical fiber antenna in the fore of circular helix. The resulting loss formula reduces in the case of N1 to the well known atennuation forsula of the the bent single-code fibers.