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Fusion splicing single-mode G.655, G.656 or G.657 onto G.652D

Fusion splicing single-mode G.655, G.656 or G.657 onto G.652D 
It appears as if an OTDR knows not its A from its E, when testing G.652D Non-Dispersion-Shifted Fibre (NDSF), connected to the following fibre types: (a) G.655D or G.656, variants of non-zero dispersion-shifted fibre (NZDSF) and (b) G.657A bend insensitive fibre. It is a difference in backscatter just before and just after the splice that confuses an OTDR:

a) The issue here is mode field diameters (MFDs). When splicing G.652D (smaller MFD) onto G.655/6 (larger MFD) a negative contribution (gainer) is incorrectly reported and G.655/6 onto G.652D reports an exaggerated loss… e.g. a real splice of 0.05 dB could bi-directionally measure -0.10 dB and +0.20 dB. These phenomena are well known, and operating procedures calling for bi-directional OTDR measurements and averaging the results has been a time-honoured tradition. More importantly though, using either Fujikura SM or NZ splicing modes, averaged dB splice losses as low as 0.04 to 0.02 are accomplishable without any obvious effort.

I recently subjected my field (who all happened to be novices) to splicing G.652D onto G.657A, using Auto, SM and NZ splice modes and below, the outcome:

Auto, SM and NZ modes all deliver decent-looking splices, with the true loss being the average of bi-directional measurements. NZ proved to be superior by a whisker. Experienced splice techs are predisposed not to like Auto-mode because for them, it is intolerably slow. Note that while BI G.657.A-compliant fibres are required to be backward compatible with G.652.D - G.657.B-compliant fibres (called bend-tolerant), are not.

OPTICAL FIBER NETWORK: Example cable tension calculation method

OPTICAL FIBER NETWORK: Example cable tension calculation method: Example cable tension calculation method The following are example formulae used in tension calculation.

OPTICAL FIBER NETWORK: TOPOLOGY AND POWER LOSS POINT ANALYSIS

OPTICAL FIBER NETWORK: TOPOLOGY AND POWER LOSS POINT ANALYSIS: TOPOLOGY AND POWER LOSS POINT ANALYSIS

TOPOLOGY AND POWER LOSS POINT ANALYSIS

TOPOLOGY AND POWER LOSS POINT ANALYSIS

Example cable tension calculation method

Example cable tension calculation method

The following are example formulae used in tension calculation.

Example overhead trunk installation method

Example overhead trunk installation method

• Use an anti-twist fitting or the like to avoid twisting in the optical cable during installation.
• Hanger rollers tend to cause twisting in the cable for structural reasons. If you are using hanger rollers, use them with the utmost care during the installation of a long cable since hanger rollers are likely to affect the cable in such installation.
• Place the cable drum 2H or more apart from the utility pole (H: cable roller mounting height), as shown above, to avoid sharp bends in the optical cable. It is recommended to use an 11-wheel cable roller with a 300 mm corner radius to avoid squashing the cable during installation.
• To lay an optical cable over a long distance, pull the tension member instead of the cable sheath and monitor the tension in the cable to avoid over-tension. Over-tension can result in detaching the pulling eye or squashing the cable. The maximum allowable tension differs according to the cable type, and specifications are given for individual cables. For more detailed information, refer to relevant specifications.
• If it is unavoidable to use a ribbon slotted-core cable (helical), always secure the fibers in order to prevent them from moving due to vibration after installation.
• Figure 8 cables need to be twisted once every 10 m or so to reduce vibration caused by winds.