Dear all,
I perform a phase modulation technique of an optical signal. The amplitude of my optical signal is modulated at fm = 1GHz and reads sm*cos(2pi*fm*t). The signal passes through a sample and I am interested in the resulting phases (phi) acquired such as sm*cos(2*pi*fm*t+phi).
The phase (phi(t)) varies quickly in roughly 10 ns. This variation is simultaneous with a variation of the amplitude (sm(t)).
What I am interested in is the phase phi(t). The problem is that both the phase and the amplitude vary quickly in time, what broadens my signal in frequency.
I perform the detection with a detector with a cut-off frequency of 2.5 GHz. Since my signal is kind of broad (roughly 10 - 100 MHz around 1 GHz), the phase that I measure in the time domain (using a RF scope to measure the detected signal in time) is the superposition of the phase that I want and an extra phase from the detector (convolution of the broad spectrum and the phase response of my detector). Indeed the phase change (phi(t)) that I want to see if rather small (few degrees), while I picture that by working so close to the cut-off of my detector the residual shift would be about tens of degrees.
Since I cannot change either my carrier frequency or my detector, I am looking for an electronic method to get rid of the residual phase coming from my detector. I was told that an IQ demodulation might do the trick. By IQ demodulation I mean multiplying the signal by cos(2*pi*fm*t) and sin(2*pi*fm*t) and combining the two to extract independently the amplitude sm(t) and phi(t).
Can someone confirm that this technique will get rid of the influence of my detector? Otherwise is there a way to retrieve the contribution from the detector?
Best
I perform a phase modulation technique of an optical signal. The amplitude of my optical signal is modulated at fm = 1GHz and reads sm*cos(2pi*fm*t). The signal passes through a sample and I am interested in the resulting phases (phi) acquired such as sm*cos(2*pi*fm*t+phi).
The phase (phi(t)) varies quickly in roughly 10 ns. This variation is simultaneous with a variation of the amplitude (sm(t)).
What I am interested in is the phase phi(t). The problem is that both the phase and the amplitude vary quickly in time, what broadens my signal in frequency.
I perform the detection with a detector with a cut-off frequency of 2.5 GHz. Since my signal is kind of broad (roughly 10 - 100 MHz around 1 GHz), the phase that I measure in the time domain (using a RF scope to measure the detected signal in time) is the superposition of the phase that I want and an extra phase from the detector (convolution of the broad spectrum and the phase response of my detector). Indeed the phase change (phi(t)) that I want to see if rather small (few degrees), while I picture that by working so close to the cut-off of my detector the residual shift would be about tens of degrees.
Since I cannot change either my carrier frequency or my detector, I am looking for an electronic method to get rid of the residual phase coming from my detector. I was told that an IQ demodulation might do the trick. By IQ demodulation I mean multiplying the signal by cos(2*pi*fm*t) and sin(2*pi*fm*t) and combining the two to extract independently the amplitude sm(t) and phi(t).
Can someone confirm that this technique will get rid of the influence of my detector? Otherwise is there a way to retrieve the contribution from the detector?
Best
