[Laser] Photodiodes in series

[F1AVYopto at aol.com]

Very good question !
The diodes are the same and receive the same energy.
Their Rshunts add and the equivalent new Rshunt increases.
The assembly internal capacitance at 0V reverse is divided by the  
photodiodes number.   
I did a test at once with 2 x BPW34.
 
Their FEM add but the photocurrent stays the same !

The Rshunt increasing should reduce the Johnson noise as the square root of  
the diodes number.
The Cdiodes reducing should increase the speed in the diode number  ratio.
73 Yves