Achille Monteville

Casting method for producing low-loss chalcogenide microstructured optical fibers

We report significant advances in the fabrication of low loss chalcogenide microstructured optical fiber (MOF). This new method, consisting in molding the glass in a silica cast made of capillaries and capillary guides, allows the development of various designs of fibers, such as suspended core, large core or small core MOFs. After removing the cast in a hydrofluoric acid bath, the preform is drawn and the design is controlled using a system applying differential pressure in the holes. Fiber losses, which are the lowest recorded so far for selenium based MOFs, are equal to the material losses, meaning that the process has no effect on the glass quality.

Concentration dependence and self-similarity of photodarkening losses induced in Yb-doped fibers by comparable excitation

We report on an extensive investigation of photodarkening in Yb-doped silica fibers. A set of similar fibers, covering a large Yb concentration range, was made so as to compare the photodarkening induced losses. Careful measurements were made to ensure equal and uniform inversion for all the tested fibers. The results show that, with the specific set-up, the stretching parameter obtained through fitting has a very limited variation. This gives more meaning to the fitting parameters. Results tend to indicate a square law dependence of the concentration of excited ions on the final saturated loss. We also demonstrate self-similarity of loss evolution when experimental curves are simply normalized to fitting parameters. This evidence of self-similarity also supports the possibility of introducing a preliminary figure of merit for Yb-doped fiber. This will allow the impact of photodarkening on laser/amplifier devices to be evaluated.

Photobleaching of photodarkening in ytterbium doped aluminosilicate fibers with 633 nm irradiation

In the present study, we examined photodarkening loss reduction in Yb3+ doped aluminosilicate fibers by utilizing 633 nm light irradiation. It is demonstrated that the final photobleaching value is intensity dependent, but the percentage of photodarkening reduction does not depend on dopant concentrations for settled bleaching intensity. Further examination was committed to explore the photobleaching starting from different photodarkening loss levels while keeping the same dopant concentration and subsequently the other way around. This approach related photobleaching with the number of photodarkening induced color centers and also showed that photobleaching was dopant concentration dependent. In all experiments an unbleachable residual loss for the bleaching powers up to ~100 W/mm2 was found. To the best of our knowledge this is the most extensive investigation of photobleaching effect.

Temporal evolution and correlation between cooperative luminescence and photodarkening in ytterbium doped silica fibers.

The present work describes photodarkening from the viewpoint of cooperative luminescence. The temporal evolution of both effects was measured simultaneously by means of ytterbium doped aluminosilicate fibers for concentrations up to 1.8 wt% Yb3+. The quadratic dependence of photodarkening and cooperative luminescence versus dopant concentration was observed. The change in the photodarkening and cooperative luminescence mutual dynamics for highly and low doped fibers is ascribed to a different ion number which forms the cluster. Cooperative luminescence is proved to be a natural probe for photodarkening since it provides new pieces of information and contributes to the photodarkening mechanism description.

Evidence of Photodarkening Mitigation in Yb-Doped Fiber Lasers by Low Power 405 nm Radiation

In this letter, we investigate the impact of a 405 nm radiation on photodarkening generation in Yb-doped fiber laser. Simultaneous photodarkening and photobleaching effects induced by 976 and 405 nm radiations, respectively, were investigated in a 1070 nm laser and compared with the loss induced in an irradiated active fiber. We observed a significant photobleaching effect due to 405 nm radiation but not a complete recovery. A strong absorption of the 405 nm radiation by the excited ions was also observed and could be the limiting factor for the bleaching performance. We also observed for the first time, to the best of our knowledge, ground-state absorption induced photodarkening in pristine fiber irradiated at 405 nm. This effect could generate additional residual losses in the laser system.

Low loss, low OH, highly non-linear holey fiber for Raman amplification

We present a highly non-linear holey fiber with low loss and low OH absorption which enables us to demonstrate efficient Raman amplification in the C band with pump wavelengths of 1453 and 1480 nm.

Fabrication of low losses chalcogenide photonic crystal fibers by molding process

Chalcogenide glasses are known for their large transparency in the mid infrared and their high refractive index (>2). They present also a high non linear refractive index (n2), 100 to 1000 times larger than for silica. An original way to obtain single-mode fibers is to design photonic crystal fibers (PCFs). Until now, chalcogenide PCFs are realized using the stack and draw process. However this technique induces defects, like bubbles, at the capillaries interfaces, causing significant scattering losses. Until now, the best transmission obtained was 3dB/m at 1.55μm. The poor PCF transmission reduces significantly their application potential. So, we present a new efficient method to realize low-loss chalcogenide PCFs. This original method by molding permits to reduce the optical losses down to 1dB/m at 1.55μm and less than 0.5dB/m between 3 and 5μm for an As-Se PCF. Furthermore, this molding method can be used for different compositions. Single mode fibers were realized. Moreover, very small core fibers were realized with this method, obtaining a non linear coefficient of 15 000W-1km-1 with an As-Se PCF. We also observed self phase modulation at 1.55μm on a fiber with a 2.3μm2 mode area.

Fabrication and Applications of Low Loss Nonlinear Holey Fibers

Abstract We present the important fabrication issues involved with the realization of low loss, low water peak, nonlinear holey fibers based on the Stack and Draw technique. We have realized fibers with loss performances in the 1.38 μm spectral region that are limited by the intrinsic losses of the raw materials, opening up the possibility of using long lengths of such fibers to demonstrate phenomenon such as Raman amplification and supercontinuum generation using continuous wave pump sources.

Photodarkening: investigation, mitigation and figure of merit

This paper reviews and extends the work done on photodarkening by our project consortium and present our latest results on bleaching and photodarkening mitigation in fiber lasers. We shows the need for a standard set-up to avoid underestimation of photodarkening equilibrium losses and we suggest photodarkening losses scale with the square of Yb doping level. Investigation on visible light emission suggest an interplay of visible light with the Yb excited level. Finally we present an extensive investigation of photobleaching, both as post-irradiation and as simultaneous bleaching. We show evidence photobleaching can effectively mitigate the impact of photodarkening on laser performance when highly-doped Al-silicate fibers are used.

Photodarkening mitigation in Yb-doped fiber lasers by 405 nm irradiation

We investigate the impact of 405 nm radiation on photodarkening evolution in Yb-doped fiber. Simultaneous photodarkening and photobleaching effects induced by 976 nm and 405 nm radiations respectively were investigated in a 1070 nm laser.