How to synchronise the IQ modulator with the asg generator

[Ayoub-elec]

Hello
I am working on frequency laser stabilization loop using PyRPL. The first step is top use the IQ module. I have tried to multiply sin ( 2pi*1e6t) with the same sine and then use a low pass filtrer so the result should be a constant signal with value equal to 0.5. However the Real result is a voltage signal which fluctuates between 0,5 and -0,5. How Can i fixe this issue ?