Adrian Mihaescu

Indoor Free Space Optic: a new prototype, realization and evaluation

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 tens 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.

Effects of external cavities on laser spectra: application to a fibre laser

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.

Indoor wireless optical communications

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.

Realizing optical amplifiers with micro-sphere: A 15 dB gain, 2 dB noise-figure, tiny amplifier

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.

Harmonic Passive Mode-Locking of a Single-Frequency Semiconductor Laser Submitted to Nonlinear Optical Feedback

We report on a theoretical analysis of the dynamical performance of a single-frequency semiconductor laser under the influence of nonlinear optical feedback. It is shown that the modal structure of such a laser is both dependent on the mirror characteristics and on the pump current. The analysis concentrates on the self pulsating regimes that can be observed, and more precisely on the occurrence of harmonic passive mode-locking. Generation of short pulses, characterized by a duration around 10 ps and a repetition rates as high as 20 GHz, have been demonstrated. The characteristics of this mode-locking strongly depend on the nonlinear mirrors temporal response

Controlled spectral emission of fiber lasers using two external cavities

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.