Philippe Signoret

Radiation-resistant erbium-doped-nanoparticles optical fiber for space applications

We demonstrate for the first time a radiation-resistant Erbium-Doped Fiber exhibiting performances that can fill the requirements of Erbium-Doped Fiber Amplifiers for space applications. This is based on an Aluminum co-doping atom reduction enabled by Nanoparticules Doping-Process. For this purpose, we developed several fibers containing very different erbium and aluminum concentrations, and tested them in the same optical amplifier configuration. This work allows to bring to the fore a highly radiation resistant Erbium-doped pure silica optical fiber exhibiting a low quenching level. This result is an important step as the EDFA is increasingly recognized as an enabling technology for the extensive use of photonic sub-systems in future satellites.

Correlation between electrical and optical photocurrent noises in semiconductor laser diodes

The low and medium frequency (1 Hz/spl les/f/spl les/10 MHz) electrical noise characteristics of 0.98, 1.3, and 1.55 micrometer semiconductor lasers have been investigated. We show that the electrical noise is connected to the optical noise behavior. The correlation between electrical and optical noises is obtained by using the coherence function between these noise sources. This confirms the theoretical predictions issued from Haugs model that this correlation, which originates in the dipole interaction between the optical field and electron-hole pairs, can be extended to the laser diode characterization by using electrical noise measurements. >

Direct printing of gratings on sol-gel layers

The sol-gel process is an interesting alternative for making glass integrated-optics components. Reasonable performance can be reached with low-cost fabrication. We show a one-step method for imprinting gratings on a thin layer made through the sol-gel process, thus enlarging the field of application in integrated optics to filters, out-ofplane connections, etc. The efficiency of the grating is studied through diffraction measures and computations.

Low-frequency FM-noise-induced lineshape: a theoretical and experimental approach

Linewidth determination by self-heterodyne or self-homodyne methods may lead to mistaken interpretation, because these measurements often include significant broadening due to low-frequency FM noise. The effects of FM noise on these linewidth measurement schemes are investigated. An analytical formulation of the photocurrent autocorrelation function is given for different frequency noise signatures, the lineshape being extracted from numerical implementation. We apply these results to linewidth prediction for 850-nm commercial vertical-cavity surface-emitting lasers and get almost perfect agreement between the theoretical and the experimental approaches.

Theoretical explanation of enhanced low dose rate sensitivity in erbium-doped optical fibers

A new theoretical framework is proposed to explain the dose and dose-rate dependence of radiation-induced absorption in optical fibers. A first-order dispersive kinetics model is used to simulate the growth of the density of color centers during an irradiation. This model succeeds in explaining the enhanced low dose rate sensitivity observed in certain kinds of erbium-doped optical fiber and provides some insight into the physical reasons behind this sensitivity.

Strongly sub-Poissonian electrical noise in 1.55-/spl mu/m DBR tunable laser diodes

We report terminal electrical noise measurements on 1.55-/spl mu/m DBR tunable laser diodes in the 1 Hz-1 MHz frequency range, performed using an electrical correlation method. These measurements are compared with a comprehensive electrical model based on rate equation formalism. Taking into account diffusion phenomenon and structural parameters, we obtain a complete agreement between the model and the measurements above threshold and a quite similar tendency below threshold. The influence of Bragg section bias is also discussed.

Correlation between tuning section electrical noise and optical amplitude fluctuations in DBR two- and three-section tunable lasers emitting around 1.55 μm

Most common monomode tunable laser diodes use carriers injection to change a bulky semi-conductor materials optical index (through absorption), with the aim of switching the emission wavelength, thanks to the phasis comb spectrum or Bragg filtering evolution. This index change existe in the active, phase and Bragg section. Independently, current injection in a laser diode involves the existance of a fundamental shot noise and of excess 1/f noise. This noise power creates optical index fluctuations in all of the 3 sections, and so modulates the lasers light field. As there is a close link between absorption and refraction index in semiconductors, through Kramers-Kronig relationships this modulation has an influence on both phase and amplitude of the laser field. The aim of this paper is to establish the correlations existing between electrical shot noise and 1/f noise of the tuning sections and the laser fields optical noise.

Frequency noise in 850-nm oxidized VCSELs

The spectral purity of laser radiation is a key point in the performance of coherent optical network. As 850nm VCSELs are being used in short distance interconnections, the evaluation of the frequency noise level is essential. Using a Fabry-Perot cavity as a frequency discriminator, the frequency noise spectrum is being investigated in the medium frequency and high frequency range (up to 1GHz). Frequency noise spectra show a 1/fn part in the medium frequency domain and a traditional white noise part in the high frequency domain. The aim of this paper is to present our measurements concerning 850nm-selectively-oxidized VCSELs and to investigate the different factors which have a quantitative influence on the frequency noise spectrum.

Single frequency free-running low noise compact extended-cavity semiconductor laser at high power level

We present a highly coherent semiconductor laser device formed by a ½-VCSEL structure and an external concave mirror in a millimetre high finesse stable cavity. The quantum well structure is diode-pumped by a commercial single mode GaAs laser diode system. This free running low noise tunable single-frequency laser exhibits >50mW output power in a low divergent circular TEM00 beam with a spectral linewidth below 1kHz and a relative intensity noise close to the quantum limit. This approach ensures, with a compact design, homogeneous gain behaviour and a sufficiently long photon lifetime to reach the oscillation-relaxation-free class-A regime, with a cut off frequency around 10MHz.

Broadband Radiation-Resistant Erbium-Doped Optical Fibers for Space Applications

We explore how radiation-resistant broadband erbium-doped fibers (EDFs) can be achieved by using a carefully selected chemical composition, without specific coating or specific packaging. In this framework, we define a factor of merit, an appropriate and effective tool to design a radiation-hardened EDF amplifier (EDFA) based on a mature technology. We focus on specialty fibers, with a finely tuned composition in aluminum and erbium, guaranteeing the optimal operation of an EDFA (a 20-nm bandwidth and an optical output power level of at least 18 dBm) in the classical booster configuration throughout the entire geostationary mission. These performances are estimated thanks to a standard accelerated test, with a 300-Gy dose deposition at a dose rate of 0.4 Gy/h. We also confirmed, based on experiments and modeling, the importance of the radiation-induced absorption at pump wavelength on the EDFA degradation under irradiation.