SPECTROCHIMICA ACTA PART A ELSEVIER Spectrochimicd Acta Part A 53 (1997) 1547- 1551 Defect induced emission in germanolosilicate fibres P S R Prasad **I, Ranita Saha, J. Lavanya, Ranjit Singh . . . Srhool of Physics. Unicersity of Hyderabad, Hyderabad SO0 046, India Received 29 January 1996; accepted 25 January 1997 Abstract The emission spectra of fresh and photosensitized fibres pumped with second harmonic of ND:YAG laser is reported. An additional line at around 444 nm has been observed in photosensitized fibres. The blue emission line (478 nm) shows an enhancement in the UV exposed fibre as compared to the fresh one. The Raman lines also show anomalous enhancement in photosensitized fibre. 0 1997 Published by Elsevier Science B.V. Kqwords: Emission spectra; Photosensitized fibres; Raman lines 1. Introduction Low-loss optical fibres are being used in the field of optical communication and are also useful to verify a variety of nonlinear optical effects [ 1.21. The losses in the visible part of EM spec- trum in fibres are mainly due to metal ion and other defects inherently present during the pro- cessing. Advances in technology resulted in re- moving metal ions in the fibres. However, structural defects still play an important role in the fibres. In germanosilicate fibres the main emis- sion bands in the range 600-660 nm (depending on core combination) have been attributed to the defects created during the fibre drawing process [3-- 51. The other bands at 400-460 nm and 700- * Corresponding author. Present address: Mineral Physics, National Geophysical Research Institute, Hyderabad, 500 007, India. ’ Laser Programme, Centre for Advanced Technology, In- dore 451 013. (India). 940 nm are also due to the defects and strongly depend on index profile and Ge doping levels. On the other hand, exposure to gamma or neutron radiation will create other defects in the fibres [5-lo]. The GeE’ type defects created in the fibres due to UV exposures, however, play an important role in creating the permanent intra-core Bragg gratings in the germanosilicate fibres [11,12]. The technological applications of these devices have matured to a great extent [13]. However, the physical cause and its implications for nonlinear optical effects are still of interest [13- 1.51. In the present paper we present a systematic compara- tive study of some of the emission lines in fresh and UV treated germanosilicate fibres. 2. Experimental setup The fibres consist of about lo- 12 mol% of germania in their core with an index difference of l386-1425:97:$17.00 0 1997 Published by Elsevier Science B.V. All rights reserved PfZSl386-1425(97)00047-4