Modification methods of optical fibers with rare earth elements and their spectral characteristics

Topicality and demand of the theme of dissertation. In the global arena, the relation of information and communication technologies directly from throughput capacity of fiber-optical communication networks and a rapid development of market of telecommunications, radio and mobile communication system detects the necessity of implementing modification methods of optical fibers with rare earth elements in order to increase the bandwidth of backbone of optical network which connects convergence nodes of communication systems with high-speed traffic. In the main segments of the communication networks -urban, trunk, international and local area networks, according to the statistics of 2005, the use of the optical fiber was more than 68 million km and increased by industry in general by 15%. At the end of 2012 the index of manufactured and applied optical fibers was 225 million km, 35-36 million km of which belongs to Japan, China People’s Republic 100 million km, the United States 32 million km and the countries of the European Union 26 million km.
Broadband LTE (Long Term Evolution) mobile technology of fourth generation began to be applied all over the world. According to the 3GPP (3rd Generation Partnership Project) and the International Organization IMT-Advanced requirements in fourth generation mobile networks the information transmission rate to a single subscriber should not fall below IGbps. The application of modified optical fibers in optical communication systems provides base stations of mobile operators with high data rate traffic and contributes to the growth of the number of subscribers.
In this regard, the solution of issues such as modification of the optical fiber with rare earth elements, modification of optical fiber with the application the methods of the quartz resonator and controlled thermal vacuum deposition, high-precision control of the thickness and composition of the deposited multicomponent optical film to locally open core optical fiber, simultaneously controlled vacuum deposition of oxides of erbium, ytterbium, silicon and aluminum, the creation of samples with suppressed the clustering of erbium ions and obtainment of high concentrations of the active ions of rare earth element (102°-1021) cm'3 in formed optical structures, the study of spectral characteristics of modified optical fibers doped with a multicomponent layers ЕГ2О3 - АЬОз - SiOx and ЕГ2О3 - УЬгОз - АЬОз - SiOx, (l<x<2) obtained by thermal vacuum deposition, the creation efficient planar and fiber optical amplifiers with high (102°-1021) cm'3 content of the active ions of rare earth elements, the development of methods of processing fiber-optic materials and development on their basis of optoelectronic data transmission systems in order to solve the problems of low noise figure and high-factor parameter of OSNR (Optical signal noise ratio) in optical amplifiers created based on modified optical fibers with a high concentration of erbium are topical for telecommunications, radio and mobile communication systems.
In order to create high range erbium ions concentrations in modified optical fibers, enhance the processes of effective modification of optical fibers with rare earth elements and create effective short-distance fiber optical amplifiers there is a representing special interest for the development methods for multicomponent vapor deposition, and modification of optical fibers by the controlled thermal deposition erbium oxide, ytterbium, silicon and aluminum on the optical fiber opened surface.
The subject of current dissertation is serving to provide the practical implementation tasks identified in the Decree of the President of the Republic of Uzbekistan «On measures to further the implementation and development of modern information and communication technologies» on March 21, 2012, № PR-1730 and in the resolution of the Cabinet of Ministers «On approval of the concept of e-commerce in the Republic of Uzbekistan for the period 2016-2018 years» on December 4, 2015, № 353.
Purpose of research is the development of methods of optical fibers with rare earth elements modification by means of thermal vacuum deposition multicomponent films of complex geometry, the fabrication locally modified optical fibers with high concentration of rare earth elements, as well as parameters measurement of modified optical fibers by creation of the complex of optical and mechanical devices.
Scientific novelty of research consists in the followings:
the method of controlled vacuum deposition in modification purposes of optical fibers with rare earth elements by the implementation of quartz resonator and thermal vacuum deposition methods has been developed;
the method of simultaneously controlled vacuum deposition of erbium, ytterbium, silicon and aluminum oxides on locally opened optical fiber core surface with high thickness measurement accuracy of deposited multicomponent (ЕвО; - АЬОз - SiOx and ЕГ2О3 - УЬгОз - АЬОз - SiOx) planar optical films has been developed;
the method of vacuum modification of optical fibers providing high concentration of active erbium ions (IO20 - 1021) cm'3 by formation of erbium ions clustering suppressed structures have been created and experimentally tested;
have been proved that modified optical films manufactured on base vacuum thermal deposition by simultaneously evaporation of metallic erbium, aluminum and silicon oxides at the atmosphere of reactive gas (oxygen) and at the vacuum pressure 0,25-0,35Pa ((2-3)'10"3mmHg) are causing the intense
photoluminescence of Er3’ ions in the range of -1540 nm, which represents the practical value for the field of fiber-optical communication;
the method of manufacturing activated optical fiber preforms for the fabrication of a long distance modified optical fibers and creation of effective planar and fiber optical amplifiers which include high concentration (102°-1021) cm'3 of active rare earth ions using in high speed fiber-optical communication networks have been created;
for the erbium ions activization purposes the technique of transverse pumping of planar optical amplifiers on base modified optical mediums for integrated fiberoptical systems has been offered;
measuring methods for study and investigation throughput characteristics of modified optical fibers and amplification properties of short-distance optical amplifiers with observing and registration possibility of spectral characteristics on computer monitor have been proposed;
practical recommendations by choosing the methodology of modification optical fibers and the creation of short-distance optical amplifiers based on the modified optical mediums have been developed;
it is established that, optical amplifiers created on base of modified optical fibers with a high concentration of erbium have a low noise figure and provide high value of OSNR (Optical signal noise ratio).
Conclusion
The main obtained results during the researches are follows:
1. It is established that, by the method of vacuum thermal evaporation could be obtained optically homogeneous dielectric erbium oxide ЕвОз thin film structures with a high concentration of active erbium ions (102<)-1021 cm'3) with a high degree of transparency (-80%) in the visible and infra red bands and also have a high resistivity value -109 Ohm cm.
2. Additional doping erbium oxide (EbOj) with aluminum oxide (АЬОз) promotes the suppression the erbium ions clustering which lead to decrease up-conversion and modified samples fabricated by means of vacuum thermal deposition methods have an extremely high concentration of active erbium ions up to (102O-1021 cm'3) in a small active modified section (2-5 cm) have been experimentally proved.
3. By controlled vacuum thermal deposition ЕГ2О3 - 8Юг-АЬОз and ЕгоОз -УЬзОз - SiOi - АЬОз planar optical waveguides on a local fragment of the optical fiber have been manufactured. It is established that, pumping of locally modified mediums with 980 nm wavelength radiation the deposited films are excited infrared radiation at -1540 nm which represents practical importance for FOCN.
4. Amplification properties of ЕвОз - ЗЮг-АЬОз and ЕвОз - УЬ20з - SiO2 -АЬОз planar optical structures created by vacuum controlled thermal deposition on an optical fiber fragment and on silicon substrates (SIO2) are investigated. In modified optical structures obtained by vacuum deposition methods the melting treatments causes clustering of erbium ions. As a result in the modified samples the luminescence spectrum becomes wider and occurring up-conversion processes in the photoluminescence kinetics.
5. Light emitting properties of modified planar samples with direct transverse optical pumping (based on xenon lamp at 980 nm) are studied. It is established that additional doping erbium (Er) with ytterbium (Yb) promotes the narrowing luminescence spectrum bandwidth. This phenomenon is explained by the fact that, ytterbium ions transfer their energy to the erbium ions during the transition to a lower energy level.
6. Proved that the optical structures modified by vacuum deposition methods demonstrate the maximum intensity of the photoluminescence (Er+3) ions at room temperature (T = 300K.). Observed result explained by the fact modifying optical structure on the optical fiber or silicon substrate is directly formed from the deposited phase, avoiding melting stage. Furthermore, using the dopants as Al and SiO can create higher concentrations of the optically active ions Er, compared with chemical modifying methods or magnetron sputtering.
7. Modified optical fibers and planar optical structures for creation sensors, optical detectors and optical fiber amplifiers implementing in FOCN are manufactured. It is revealed, that deposited multicomponent optical structures have adjustment efficiency with fiber core around 65% to 75%. As a result of this adjustment increases the efficiency of the laser transitions «fiber core - modified medium - fiber core» providing effective signal gain around 5-10 dB from locally modified section size 2-5 cm.
8. Short-distance optical amplifiers for DWDM systems based on modified optical structures on base silicon substrate have been fabricated. Such kind of optical amplifiers have the opportunity to amplify a DWDM group optical signal in the range of C-Band (1529 - 1565 nm). The group signal at the output of this amplifier is adjusted and linearized without implementing broadband smoothing filters.
9. Its is experimentally proved that short distance optical amplifiers based on the modified optical mediums with an extremely high concentration of active rare earth ions have a low noise-figure parameter which increases the overall budget of OSNR (Optical signal noise ratio) DWDM systems.