Phase lock Optickle simulation

phaseLock.m

% Configuration:
%
%  [laser1] --->  [mod1] ---->  [    ]  <--- [mod2] <--- [laser2]
%                               [ BS ] 
%   [PD1] <-------------------  [    ]  ---------------> [PD2]
%
% PD1 and PD2 form a balanced homodyne detector for laser1 and laser2.  If
% you want to consider a "DC readout" type configuration (or a squeezer
% coherent control configuration) where you just have one PD, you can just
% ignore PD2.
%
% 
% Tobin Fricke
% 2012-08-23

% Initial carrier power (before modulation) in the two sources.  In the
% squeezer case, P2 will be zero, but just set it to some arbitrary value
% here so the modulators will have something to modulate.  There are ways
% around this if you want.

P1 = 1;            % Watts
P2 = 1;

% Modulation frequencies and depths for the two laser sources.

fmod1 = 10e6;      % Hz
fmod2 = 11e6;

gamma1 = 0.34;     % radians
gamma2 = gamma1;

% Create vector of RF frequencies to consider.  This needs to have all the
% modulation frequencies, plus any beat frequencies we want to consider.

vFrf = [0, fmod1, fmod2, (fmod2-fmod1)];
vFrf = unique([-vFrf, vFrf]);

opt = Optickle(vFrf);

% Put the power into the laser carrier.  Both sources have the same carrier
% frequency.

opt = addSource(opt, 'laser1', sqrt(P1) * (vFrf==0));
opt = addSource(opt, 'laser2', sqrt(P2) * (vFrf==0));

% Add a phase modulator for one of the sources.

opt = addModulator(opt, 'PM', 1i);

% Change the phase of the sidebands relative to the carrier by changing the
% phase of the modulation depth.  Phase modulation is made with a purely
% imaginary modulation depth, while a real modulation depth produces AM.

opt = addRFModulator(opt, 'Mod1', fmod1, 1i*gamma1);
opt = addRFModulator(opt, 'Mod2', fmod2,    gamma2);

% I set angle of incidence to 0 on the beamsplitter so that there won't be
% any sqrt(2) to deal with.

opt = addMirror(opt, 'BS', 0, 0, 0.5, 0, 0);

opt = addSink(opt, 'PD1');
opt = addSink(opt, 'PD2');

% Link everything together

opt = addLink(opt, 'laser1', 'out', 'PM',   'in', 0);
opt = addLink(opt, 'PM',     'out', 'Mod1', 'in', 0);

opt = addLink(opt, 'laser2', 'out', 'Mod2', 'in', 0);

opt = addLink(opt, 'Mod1', 'out', 'BS', 'fr', 0);
opt = addLink(opt, 'Mod2', 'out', 'BS', 'bk', 0);

opt = addLink(opt, 'BS', 'fr', 'PD1', 'in', 0);
opt = addLink(opt, 'BS', 'bk', 'PD2', 'in', 0);

% Add the DC and RF photodiodes 

opt = addProbeIn(opt, 'PD1_DC', 'PD1', 'in', 0, 0);
opt = addProbeIn(opt, 'PD2_DC', 'PD2', 'in', 0, 0);
opt = addProbeIn(opt, 'PD1_I',  'PD1', 'in', abs(fmod1-fmod2), 0);
opt = addProbeIn(opt, 'PD1_Q',  'PD1', 'in', abs(fmod1-fmod2), 90);
opt = addProbeIn(opt, 'PD2_I',  'PD2', 'in', abs(fmod1-fmod2), 0);
opt = addProbeIn(opt, 'PD2_Q',  'PD2', 'in', abs(fmod1-fmod2), 90);

%% Run the simulation (sweep)

Npos = 100;

dBS = getDriveNum(opt, 'BS');
dPM = getDriveNum(opt, 'PM');

pPD1_DC = getProbeNum(opt, 'PD1_DC');
pPD2_DC = getProbeNum(opt, 'PD2_DC');
pPD1_I  = getProbeNum(opt, 'PD1_I');
pPD1_Q  = getProbeNum(opt, 'PD1_Q');
pPD2_I  = getProbeNum(opt, 'PD2_I');
pPD2_Q  = getProbeNum(opt, 'PD2_Q');

d = dBS;

start_pos = zeros(opt.Ndrive, 1);
start_pos(d) = opt.lambda/2;
end_pos = -start_pos;

[pos, sigDC, fDC] = sweepLinear(opt, start_pos, end_pos, Npos);
 
plot(pos(d,:) / opt.lambda, sigDC(pPD1_DC,:), ...
     pos(d,:) / opt.lambda, sigDC(pPD1_I, :), ...
     pos(d,:) / opt.lambda, sigDC(pPD1_Q, :));    
 
xlabel('differential phase (wavelengths)'); 
ylabel('signal');
legend('DC','I','Q');
grid on 

pkpk = max(sigDC(pPD1_I, :)) - min(sigDC(pPD1_I, :));
fprintf('Expected optical gain is %g W/radian\n', pkpk/2);

%% Run the simulation (tickle)
pos = zeros(opt.Ndrive, 1);
f = linspace(0, 100, 10);

[fDC, sigDC, sigAC, mMech, noiseAC, noiseMech] = tickle(opt, pos, f);

dPM = getDriveNum(opt, 'PM');
pPD1_I  = getProbeNum(opt, 'PD1_I');

h = getTF(sigAC, pPD1_I, dPM);

fprintf('Optical gain is %g W/radian\n', h(1));