Abstract: A light-emitting device is provided which includes a gain medium having an optically-active phosphosilicate glass, wherein the phosphosilicate glass includes at least one active ion dopant and from about 1 to 30 mol % of phosphorus oxide. The phosphorous oxide may be present in an effective amount for reducing any photodarkening effect and increasing the saturation energy of the system. The active ion dopant may be a rare earth dopant. The light-emitting device may include an optical waveguide, the optical waveguide including the gain medium. The optical waveguide may have a core and at least one cladding, and the gain medium having the phosphosilicate glass may be found in the core and/or in one of the cladding.

Abstract: A light-emitting device is provided which includes a gain medium having an optically-active phosphosilicate glass, wherein the phosphosilicate glass includes at least one active ion dopant and from about 1 to 30 mol % of phosphorus oxide. The phosphorous oxide may be present in an effective amount for reducing any photodarkening effect and increasing the saturation energy of the system. The active ion dopant may be a rare earth dopant. The light-emitting device may include an optical waveguide, the optical waveguide including the gain medium.

Abstract: An optically active glass and an optical fiber comprising such glass, having reduced photodarkening properties are provided. The optically active glass is mainly composed of silica representing from about 50 to 98 mol % of the glass. It also includes at least one active ion, such as a rear-earth ion, which induces a photodarkening effect in optical properties of the glass. Moreover, the glass includes an effective amount of phosphorus oxide providing the photodarkening reducing effect, preferably in an amount of from about 1 to 30 mol %. A method for reducing a photodarkening effect in optical properties of an optically active glass including the step of introducing phosphorus oxide to the glass is also provided.

Abstract: A large mode field diameter optical fiber is disclosed. It is a single mode optical fiber which has a core and a cladding. The core of this fiber has two regions, an inner core region and an outer core region which has a refractive index lower than that of the inner core region. The inner core region is doped with a rare-earth element, such as Er2O3, and a co-dopant, such as Al2O3, and the outer core region is doped with a dopant such as GeO2. The types and amounts of the dopants and co-dopants are adjusted to obtain a fiber with a mode field diameter greater than 5.5 ?m at a wavelength of 1550 nm.

Abstract: A double-clad optical fiber has an inner cladding with a pentagonal or heptagonal cross-section. The core of this fiber can be in the center or off-center. Moreover, the fiber may comprise stress field portions within the inner cladding which cause further distortions for deflecting pumped light to the core. In addition, the core may have a dual structure with an inner portion and an outer portion surrounding the inner portion. It is preferable that the inner cladding should have a lower index of refraction than the core and the outer cladding which surrounds the inner cladding should have a lower index of refraction than the inner cladding.

Abstract: A large mode field diameter optical fiber is disclosed. It is a single mode optical fiber which has a core and a cladding. The core of this fiber has two regions, an inner core region and an outer core region which has a refractive index lower than that of the inner core region. The inner core region is doped with a rare-earth element, such as Er2O3, and a co-dopant, such as Al2O3, and the outer core region is doped with a dopant such as GeO2. The types and amounts of the dopants and co-dopants are adjusted to obtain a fiber with a mode field diameter greater than 5.5 ?m at a wavelength of 1550 nm.