Squeezing and homodyne detection

(An optics simulation with Finesse)

The following shows a simple example for modelling squeezed light with Finesse, including the text input file, a brief explanation and the resulting plot.

The input file

%------------------------------------------------------------------------ 
% Finesse input file to model a squuezed light source and an
% unbalanced homodyne detector.
% Daniel Brown 17.05.2014
%------------------------------------------------------------------------ 
l l1 1 0 n1
s s1 0 n1 n2
sq sq1 0 10 0 n3
s s2 0 n3 n4
bs bs1 0.5 0.5 0 45 n4 nout1 nout2 n2

# Setting the frequency at which we compute the quantum noise
# and signals. We aren't applying any signal, we just need
# to set the frequency value and give it a name.
fsig noise 1

# output the pure shot noise along with the qnoised detector 
# measuring the effects of the squeezing 
qnoised sqzd_noise 1 $fs 0 nout1
qshot   shot_noise 1 $fs 0 nout1

xaxis l1 phase lin -90 90 360
 

The optical layout

The optical layout shows a laser and a squeezed light source whose beams are superimposed on a beam splitter. Two quantum noise detectors are used for detection, the qshot detector measuring only the shotnoise (ignoring the squeezing) and the qnoised detector measuring the correct quantum noise. We mix a 10dB squeezed source and a 1W laser at the beamsplitter and measure the result at the photodiode, varying the phase of the laser field.

Output graphs

Quantum noise of a squeezed field, measured with a qnoised detector. For comparison a qshot detector is used, showing the unchanged shotnoise. The noise scaling for this plot has been set to 'Power spectral density in units of hf' via the `quantum_scaling' setting in the `kat.ini' file.

The graph shows that the qshot output is flat whereas the qnoised detector output shows and increase or reducing below the shot noise, depending on the phase. You should also see here that you must be careful to ensure that any squeezed field and laser fields have the correct phase and squeezing angle to ensure that you have the effect you desire (try for example to change the length of `s1' and see what happens).