The fiber connected to the 2nd stage photodiode was broken.
Thus, one connected the Auxilary output which is placed on the front cover, coming from a 10% tap of the 2nd stage, with a fiber to this photodiode.
for that, one drilled a small hole on the side to the crate to let the fiber in.
as the power is quite big, the 2nd stage photodiode is used with a filter to avoid its saturation.
one used also a 1kohms resistor to connect it to the scope.
one get more than 65mV when the output of the amplifier with only 2nd stage is about 350mW.
after about 30 minutes, the power increases slowly to more than 550mW.
summary :
- photodiode from the fiber coupling should read more than 60mV on 1kohms
- photodiode from the 1st amplifier stage should read more than 200mV on 50ohms
- photodiode from the 2nd amplifier stage should read more than 65mV on 1kohms
| Ronic Chiche wrote: |
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Today with Titouan, we installed a 10-90% fiber coupler between the EOM and the amplifier to have a diagnostic of the fiber injection power level.
65mV on 1kohms on the diagnostic photodiode is equivalent to 1.3mW injected to the 1st stage of the amplifier.
One has to get at least 50mV on the photodiode to inject 1mW to the 1st stage of the amplifier.
we used the included 1st stage photodiode which has to be above 200mV on 50 ohms.
one has 250mV on this photodiode
the 2nd stage photodiode seems to be broken.
one can use an internal tap for diagnotic or open the amplifier box and try to fix the photodiode.
to be done...
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