RICERCA ITALIANA     

Integrated amplifiers e laser sources within soliton waveguides in Er:LiNbO3

Università degli Studi di Roma "La Sapienza"

Abstract

The present project will realise laser sources at 1.55 um, integrated within single-mode soliton waveguide, buried inside single crystals on lithium niobate doped in volume by erbium. Both single and arrays of lasers will be realised.
Even if waveguide integrated laser have been already realised in the past (the first Er:LiNbO3 laser was built in 1992), their construction, because of the fabrication techniques, was always performed close to the surface of a bulk material, that for this reason got the name "substrate", i.e. lower layer. Indeed until now only superficial structures have been realised, because the whole integrated optics is indeed superficial: any test to get buried waveguides inside any substrate gave unsatisfactory results, being not able to overpass a depth for the external surface larger than 100-200 um. Only recently such a limit has been overcome by using new writing techniques coming from nonlinear optics. In fact, within nonlinear materials like photorefractive lithium niobate, spatial soliton formation, i.e. formation of self-confined undiffracting beams, was both theoretically and experimentally demonstrated. Such beams permanently modify the material refractive index writing, as a consequence, a perfect single-mode waveguide. These waveguides will be used to realise integrated lasers within erbium doped lithium niobate.
Soliton waveguides start a new technology for using the whole volume of a material, because they can be written >>>

Principal Investigator

Eugenio FAZIO Università degli Studi di ROMA "La Sapienza"

Research Objectives

The proposed project would realise laser sources at 1.55 um, integrated in single-mode waveguides with soliton refractive index profile, buried inside single-crystals of lithium niobate doped with erbium in volume by means of the Czochralski technique. Both single sources and arrays of laser cavities will be realised in the same crystal.
The project would also write soliton waveguides in single-crystal fibres of lithium niobate doped with erbium grown by means of the MicroPullingDown technique. Such soliton waveguides would act as cores for the fibres, within which the light can be propagated and optically amplified.
The primary task of the entire project will be caught up by following intermediate advance steps of the job, that they can therefore be defined as:
1) growing up of single crystals of lithium niobate doped in volume with erbium by means of the Czochralski technique. During the initial step the growing of single-crystal samples of lithium niobate with concentrations of erbium, distributed in homogenously in the inner volume, ranging between 0 and 1mol%. Such samples must have optical and crystalline quality comparable with undoped crystals of the same material available in the market. Secondary task, in case of successful growing of single-crystals with the previous characteristics, is the determination of the growing protocol in order to obtain reproducible samples. In a second step of such a task, using the protocol set up before >>>

Timescale

24 months

National and international background

The exploding demand for internet access, telecommunications and broadband services is pushing for lightwave transmission, that had intrinsically shown much larger capacity than electronic technologies, which shortly will not likely be able to comply with the increasing request of high-speed systems. In order to meet this demand, more and more sophisticated and compact optical components are required, such as bulk- or directly fibre-type devices. The key point of this technology is based on "optical waveguides", which mean zones of larger refractive index than the surrounding, in order to confine the light inside by means of total internal reflection phenomenon. The present technology has successfully developed both 1-dimensional and 2-dimensional structures, while the 3-dimensional ones are still unexplored, being any suitable ad innovative technology for volume-waveguide writing still unavailable. Different techniques are usually adopted for constructing 1-dimensional and 2-dimensional structures: for example optical fibres are drawn from a larger preform until the desired dimension is reached; optical waveguides instead can either be grown as thin films on substrate or be realised by chemical-physical treatment of the external surface of the material to locally modify the refractive index. Such a procedure can use suitable masks for getting planar or channel waveguides. However the possibility of increase the number of complex functions on the same chip will greatly >>>