Example 7 - squeezing and homodyne detection

This example shows a simple example of modelling squeezed light with Finesse.

The optical configuration

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 shot noise (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.

The Finesse model

import finesse
finesse.configure(plotting=True)

kat = finesse.Model()
kat.parse(
    """
    l l1 P=1
    s s1 l1.p1 bs1.p4 L=1
    sq sq1 db=10
    s s2 sq1.p1 bs1.p1
    bs bs1 R=0.5 L=0 alpha=45

    # Set a signal frequency to activate the signal simulation
    # (needed for squeezing effects to be observed)
    fsig(1)

    # Output the pure shot noise along with the qnoised detector
    # measuring the effects of the squeezing
    qnoised sqzd_noise bs1.p2.o
    qshot shot_noise bs1.p2.o

    xaxis(l1.phase, lin, -90, 90, 360)
    """
)

Output plots

out = kat.run()
out.plot(separate=False);

The plot shows that the qshot output is flat, whereas the qnoised output rises above and falls 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 give the desired effect (try for example to change the length of s1 and see what happens).