I need to detect the "DC offset level" from the signal and "four stage band pass filter".

I am trying to measuring the Fluorescence decay time which is come from the Fiber optic thermometer. I am driving the LED by square pulse, then the square pulse is changed depending on the temperature and the signal behaves like exponential curve. But the problem is when I m bending the fiber cable, the dc offset level is changing. So, I need to "detect the dc offset level" as fast as possible and need to set the reference voltage depending on the dc offset level. Also, the signal is so noisy. So, I need to filter the signal by "four stage band pass filter".

So, please help me!

Thank you so much!