1 OTDR Studies • First look with SM OTDR failed: not enough sensitivity to see RBS signal. • Nice clear signals visible with MM OTDR (on free loan until 11/05/07). • Next slides show typical traces – RBS signal clearly visible above noise floor can measure attenuation length of fibre in cable with laser at 856 nm – Higher resolution with 665 nm laser allows clear separation of the Fresnel peaks from the MT-12 at PPB1 and the p-i- n diode on the dogleg.
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1 OTDR Studies First look with SM OTDR failed: not enough sensitivity to see RBS signal. Nice clear signals visible with MM OTDR (on free loan until 11/05/07).
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Transcript
1
OTDR Studies
• First look with SM OTDR failed: not enough sensitivity to see RBS signal.
• Nice clear signals visible with MM OTDR (on free loan until 11/05/07).
• Next slides show typical traces– RBS signal clearly visible above noise floor can
measure attenuation length of fibre in cable with laser at 856 nm
– Higher resolution with 665 nm laser allows clear separation of the Fresnel peaks from the MT-12 at PPB1 and the p-i-n diode on the dogleg.
2
OTDR Measurements
MM v OTDR
p-i-n diode
5m 3.2m or 2m
FUT (Fibre under test)~ 2m
ST MT MT
MT
APC
3
Connectors at start of cable and fan-out
RBS Signal abovebackground
MT-12 at PPB1
p-i-n diode on dogleg
4
Use delay setting to avoid peaks from start of cable & fan-out
5
Use 665 nm laser for higher resolution to see loss at MT-12 at PPB1
6
Use 856 nm laser to measure attenuation length of fibre in cable
7
Measurements
• Measured attenuation length of fibres in cable and loss at MT-12 at PPB1 for– All fibres in 4 ribbons associated with “problematic”
channels, all channels have < 90 A p-i-n current.– All fibres in 4 ribbons associated with “good”
channels. All channels have >= 90 A p-i-n current.
• Also checked that there was no excess loss near PPB1 due to micro-bending.
• Measured attenuation length of 4 ribbons in spare cable.
• Loss at MT-12 PPB1– <good channels> = 0.13 +/- 0.02 dB– <bad channels> = 0.17 +/- 0.03 dB
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Discussion
• There are systematic errors on the absolute values of these measurements but the relative measurements of good and problematic channels should be meaningful.
• Losses at PPB1 appear to be very small and no significant difference between problematic and good channels.
• The attenuation length for problematic channels is slightly longer than for good channels. Marginally statistically significant (2.7 )
• Attenuation length for fibes in spare cables is significantly longer.
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Averages for ribbons• Look at average attenuation lengths for