IEC TR 61292-4:2010 pdf – Optical amplifiers – Part 4: Maximum permissible optical power for the damage-free and safe use ofoptical amplifiers, including Raman amplifiers.
The above information was made available from Furukawa Electric (Japan in Oct. 2002) and was reported (1) at the 2003 International Laser Safety Conference in Jacksonville, FL, USA. This issue was also discussed in other literature (21 (3j as follows.
The main physical mechanism responsible for the fibre fuse phenomenon and its propagation Is optical discharge propagation due to thermal conductivity. It can be initiated in most fibre types by launching a CW laser Into a fibre and ensuring contact of the fibre output end face with some absorbing surface or by heating a section of the fibre.
The temperature of the optical discharge plasma is about 5 000 K to 10 000 K The speed of its propagation is about lmls in typical single mode fibres at a laser power of approximately 1 W. Examination of the fibre core after such discharge reveals extensive damage in the form of voids which have the form of bubbles (sometimes periodic) o long non-periodic filaments.
Because the most probable reason for optical discharge is a contaminated end face, fusion splicing is the most reliable way to reduce the risk of high-power damage Optical isolators used in some schemes can also be damaged. Unfortunately, their survivability at high power is an open question.
The literature (3J includes a figure reporting the measured dependencies of threshold intensity for the propagation of optical discharge through the fibre (the power at which such propagation is terminated) on the mode field diameter of single-mode fibres of different core compositions
The figure includes 21 data points among which, however, just one experimental point using 1.48 micrometer wavelength for silica-based single-mode fibre is applicable 121 to typical optical transmission systems.
The threshold intensity ‘th for this experimental point was 1.0 (MW!cm2) for MFD (mode field diameter) L)m = 12,6 micrometer The threshold power is calculated as 1,3W.
4.2.3 Conclusion
The threshold optical powers of fibre fuse propagation reported in Figure 1 and Table 1 were found to be 1,4 W and 1,2 W for SMF and DSF respectively under the conditions tested. On the other hand, the fuse-initiation threshold varied significantly, although they well exceeded 1,4 W and 1.2W. Another report identified that 1.3 W could be allowed for SMF. although the information available on the fibre was limited.
4.3 Loss-lnduc.d h.atlng at conn•ctors or splIces
4.3.1 Introduction
In extremely high power optical amplifiers, the loss-induced heating at fibres and connectors or splices could lead to damage, including fibre-coat burning, fibre fuse. etc. This subclause provides experimental data (4) and considerations for information.
4.3.2 Experiment on the connector
Table 2 summarizes the measurement conditions. The experiment used MU type optical connectors for standard single mode fibre (SMF) and dispersion-shifted fibre (DSF). where loss was increased by optical fibre misalignment. The optical source used was a 2-W Raman pump at 1 480 nm. The connector temperature was measured by a thermocouple placed on the sleeve. Sinc, the MU ferrule diameter was only 1.25 mm. the sleeve temperature was almost the same as that of the ferrule; ferrule temperature is the most important factor determining the long-term reliability of optical connectors [5].
The data suggest that the temperature increase could be within 10 “C under realisticconditions of loss and power. A commercial dry-type connector cleaner was used each time.
During repeated connection-disconnection of the connectors,neither damage nor fibre fusewas observed.The experiments with the use of the cleaner identified no problems in terms offibrelconnector damage and reliability. Without the cleaner, however, the experiment with theDSF connector indicated that fibre fuse could occur after repeated connection-disconnectionof more than 200 times.
Such temperature increase,and accordingly the danger of fibre fuse,for non-zero dispersionshifted single-mode optical fibre (NZ-DSF)connectors will be worse than SMF connectors butbetter than DSF connectors; the effective areas are SMF>NZDSF>DSF.Further quantitativestudies are needed. Other types of physical contact (PC) connectors such as SC connectorswill show similar temperature responses because only their ferrule radi differ.