Hi gang,I decide to focuse laser into the SMF ( single mode fiber ),but found that the following system would produce a fluctuating intensity at the exit end of the fiber(Fig 1):
Helium-Neon laser (633 nm, 35 mW, DA(Divergence Angle)=0.66mrad, BD(Beam diameter)=1.23mm) --> lens(20X)--> single mode FC fiber (NA=0.14, 125 micron cladding, 3.6m length)-->power meter. The lens and SMF are all fixed on two separate 5-dimensional positioner(from Newport: http://search.newport.com/?q=*&x2=sku&q2=LP-05A) And all the system are fixed on the optical table.
Here is the problem:
The intensity reaching the power meter is about 26mW with fluctuations as large as 1mW with a frequency of 0.5-1Hz. Since the He-Ne laser has been on for hours and is rather stable at the time of measurement (as measured directly at the laser output), this fluctuation could be caused by the fiber coupling system described above? It is strange that when I vibrate the floor, the intensity doesn’t seem to change much. I suspect it is cause by mechanical deformation of the 5-dimensional positioned, while placed the whole system over a night, the fluctuations is still there. Furthermore, the intensity seems swing with the central point——26mW, and the swing trend seems no rules to follow——sometimes larger than 1mW, sometimes smaller than 0.5mW.
Since the laser is used for scientific experiments, this kind of fluctuating is unbearable. I am curious to know where the disturbance come from and how to eliminate it.
Thanks in advance!
Helium-Neon laser (633 nm, 35 mW, DA(Divergence Angle)=0.66mrad, BD(Beam diameter)=1.23mm) --> lens(20X)--> single mode FC fiber (NA=0.14, 125 micron cladding, 3.6m length)-->power meter. The lens and SMF are all fixed on two separate 5-dimensional positioner(from Newport: http://search.newport.com/?q=*&x2=sku&q2=LP-05A) And all the system are fixed on the optical table.
Here is the problem:
The intensity reaching the power meter is about 26mW with fluctuations as large as 1mW with a frequency of 0.5-1Hz. Since the He-Ne laser has been on for hours and is rather stable at the time of measurement (as measured directly at the laser output), this fluctuation could be caused by the fiber coupling system described above? It is strange that when I vibrate the floor, the intensity doesn’t seem to change much. I suspect it is cause by mechanical deformation of the 5-dimensional positioned, while placed the whole system over a night, the fluctuations is still there. Furthermore, the intensity seems swing with the central point——26mW, and the swing trend seems no rules to follow——sometimes larger than 1mW, sometimes smaller than 0.5mW.
Since the laser is used for scientific experiments, this kind of fluctuating is unbearable. I am curious to know where the disturbance come from and how to eliminate it.
Thanks in advance!
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