Alcatel Lucent Reveals Manufacturing Process for Photonic Crystal Fibers with Nanoparticles

Alcatel Lucent (Paris, FR) earned U.S. Patent 7,657,142 for a method for making a optical fiber containing nanoparticles.  Owing to the broad diversity of nanoparticles that can be implemented in a preform, the uses of such fibers may be very diverse. For example, the following applications are possible: rare earth-doped fiber for amplifiers or optical lasers, Raman fibers for amplifiers or optical lasers, heavily non-linear fibers, saturable absorbent fibers and/or polarizable fibers, say inventors Laurent Gasca, Stephanie Blanchandin, Alain Pastouret and Christian Simonneau. 

It is also possible to manufacture photonic crystal fibers (PCF) that include holes obtained by forming fiber out of the performs obtained through a glass assembly method. To manufacture such PCF fibers, the fiber-forming should be performed with the non-oxidizing gas having pressure on the same order of magnitude as the atmospheric pressure, if not slightly higher. When the fiber is formed using non-oxidizing gas in the recesses with pressure lower than atmospheric pressure, the previously described fibers are obtained.

It should be noted that the nanoparticle-free material may be glass formed of silica or another type of glass, and that the doped zone comprises nanoparticles bearing an active element and/or a component such as erbium (Er), ytterbium (Yb), thulium (Tm), europium (Eu), cerium (Ce), chromium (Cr), manganese (Mn), bismuth (Bi), antimony (Sb), tellurium (Te), tantalum (Ta), zircon (Zr), niobium (Nb), vanadium (V), lead (Pb), tungsten (W), indium (In), gallium (Ga), tin (Sn), molybdenum (Mo), boron (B), arsenic (As), titanium (Ti), or aluminum (Al).

In particular, the usage of Si nanoparticles is advantageous for erbium-doped amplifying fibers. The actual section where such nanoparticles are absorbed is in fact three orders of magnitude higher than that of erbium, which makes it possible to transfer optical energy to the erbium ions more efficiently.

Manufacturing fiber requires heat-treating the preform, which in the present case may contain nanoparticles. However, hear treatment is performed with temperatures greater than 500 degree C., and usually greater than 1000 degree C. These high temperatures lead to alterations in the composition and/or structure of these nanoparticles, and therefore in their properties.

The Alcatel invention also includes the observation that the alteration of the nanoparticles at high temperatures is mainly due to the oxidation of at least one of its components, such as silicon or germanium, whose form is stable in the form of oxides.

The method of manufacturing an optical fiber comprising the following steps: a preform is created, containing nanoparticles bearing an active element comprising at least one recess in the vicinity of at least part of the nanoparticles. The preform is made into fibers by introducing a non-oxidizing gas into the recess, thereby limiting the chances that the nanoparticles in the preform will oxidize.

The manufacture of an optical fiber includes first manufacturing a preform, which is drawn in a fiber-forming step to obtain a fiber. The preform which is implemented in the fiber-forming step normally takes the form of a cylindrical bar made of bulky material created from SiO2 silica. To manufacture preforms, a Modified Chemical Vapor Deposition (MCVD) method is commonly used inside a rotating silicate tube, depositing oxide particles which transform into silica glass. The bar obtained in this manner is heat-shrunk in order to obtain a solid preform.

Another known method (called OVD, for Outside Vapor Deposition) involves depositing silica-based particles on the outside surface of a part, such as a tube, so as to create overlapping layers of porous glass. The tube is then drawn, and the bar is heat-shrunk to obtain a solid preform, which will be implemented during the fiber-forming step. 

FIG. 1 depicts the obtaining of an optical fiber 18 via a method for forming fiber from a preform 10 in accordance with the Alcatel process, meaning that a non-oxidizing gas 11, such as a reducing gas, is kept in the vicinity of the doped zone 12 of the preform 10 by flowing into a recess 14 that is coaxial to the axis 13 of the preform 10.

The optical fiber (18) including the following steps: producing a preform (10) containing nanoparticles provided with an active element including at least one recess (14) proximate at least part of the nanoparticles; fiber drawing of the preform (10) by introducing a non-oxidizing gas in the recess (14), thereby limiting the risks of oxidizing the nanoparticles of the preform (10). The preform (10) designed to the manufacture of an optical fiber (18) by the inventive method comprises nanoparticles provided with an active element in a doped zone (12) and at least one recess (14) proximate the doped zone (12). 

In this manner, the nanoparticles included in the doped zone 12 of the material 16 of the preform 10 are protected from oxidization by the presence of this non-oxidizing gas 11 during the step in which fiber is formed from the preform 10, which is conducted using devices 15 that heat said preform.

By these means, the alteration of the composition and/or structure of the nanoparticles present in the doped areas 12 is heavily limited. In other words, the conditions to which the nanoparticles are subjected are less hostile, so that nanoparticles with various compositions can be used in the preform 10, and consequently, in the fiber 18 obtained from this preform 10.

In one embodiment, the non-oxidizing gas 11 is a mixture of a gas which is non-explosive at a high temperature, comprising hydrogen and a neutral gas such as helium. For example, the gas sold by the company Air Liquide under the name NOXAL may be used.

The preform 10 implemented in the method described with the assistance of FIG. 1 is depicted in cross-section in FIG. 2a, which, from a new perspective, shows the presence of the recess 14 in the vicinity of the doped zone 12 of the preform 10.

Using the Alcatel method, it is also possible to manufacture photonic crystal fibers (PCF) that include holes obtained by forming fiber out of the performs obtained through a glass assembly method. To manufacture such PCF, the fiber-forming should be performed with the non-oxidizing gas having pressure on the same order of magnitude as the atmospheric pressure, if not slightly higher. When the fiber is formed using non-oxidizing gas in the recesses with pressure lower than atmospheric pressure, the PCF are obtained.