A summary of the fiber transmittance measurements
Yokogawa, Sugimoto, Izumi
The below is a summary table of the fiber transmittance measurements performed today (the 9th) before the fibers were layed. The measurement was done by using the setup for the X arm green beam.
| Measured output power | Estimated core transmittance* | |
| CCH-948-63 A (63 m duplex fiber, A) | 14 mW (36%) | 60% |
| CCH-948-63 B (63 m duplex fiber, B) | 12 mW (31%) | 51% |
| CCH-948-58 (58 m duplex fiber, A) | 16 mW (41%) | 68% |
| CCH-948-58 (58 m duplex fiber, B) | 16 mW (41%) | 68% |
* core tranmissttance = (measured output power) / (incident power) / (coupling efficiency). The input power was set to 39 mW and the coupliing efficiency was assumed to be 60%.
The fibers themself are made of Nufern PM-S405-XP whose core attenuation are nominally 30 dB/km @630 nm and @488 nm. From this value we were expecting the transmittance to be at least 65 % ( = 10^{-30 dB/1000 m x 58 m / 1000 m / 10}) in power for the 63 m fibres while 67% for the 58 m fibers. While the 58 m fibers barely meet the catalog spefication, the 63 m fibers do not match the catalog specification.
One thing we thought after the measurements was that we could have tried to adjust the input polarization. So, there may be some small room to improve the transmittance.