I am trying to perform an experiment to determine the spectral response of grating-coupler. I am measuring the output power while changing the input light wavelength. With the measured output power, I calculated the loss.
But, I can see a lot of fluctuations in my measurement. Sometimes there are no fluctuations, but most of time I can see them. I tried cleaving the fiber again and also cleaning the chip. But nothing worked.
Does someone have similar experience? If yes, how was it solved?
Actually, this is very ordinary in case of grating as it satisfies the grating equation of interference. So, where is the error?
I'm NOT familiar with your system, but I tentatively wonder:
Might the effects relate to a need for better temperature control, somewhere in the system?
Thanks Dr. Vincent Lecoeuche for the detailed answer. I am going through the paper and trying to relate it with my work.
Hello Dr. Oday Hammadi , thanks for insighting on grating equation but I also dont think that the gratings alone could be the reason behind that high fluctuations. Anyways thanks for the response.
Hello Dr. Stephen A. Langford , I tried to check the temperature on the device and around, but it is cool. So, I dont think that the temperature was the culprit. Thanks for reminding about the temperature.
UPDATE: I recently cleaved the fiber again, this time the fluctuation was much settled, but the tendency looks completely different. Previously, although it had fluctuations, the tendency was what we were expecting. This recent update has added more confusion.
How closely is temperature controlled in your experiment?
I have had an additional thought, which might pertain:
My RI data looked like yours, until I sampled at *much* finer X increments.
Hoping this helps, Bishal. -Steve-
I think this fluctuations comes from fabry perot effect either from the fiber and the grating coupler or from the input and output grating coupler (due to that each of these elements has weak reflection)
you can check which effect is causing the fluctuation, by roughly estimating the distance between fiber and grating, and the distance between the grating, then, compare the periodicity of this fluctuation by the famous fabry perot law lambda^2/2nL.
Thank you everyone. I have tried all the methods you have explained here. I even added some epoxy in between the fiber tip and the chip but none works. 1 more thing I found is the effect is more prominent in structures with both end with GC. If one end is SSC then the effect is negligible. Also, in case of both end GC based structures, the effect is lower for those structure having longer length.
So, still I am looking for the solution to this issue.
Thank you Jun Zou
for pointing out a specific issue. In simulation the fluctuation in the spectrum is not seen.
We are suspecting, since we did only single coupler simulation, we didn't see any fluctuation. Now my point of concern is how can I see/measure the fabry perot resonance in the simulation using two couplers. I use FDTD simulation tool from Lumerical for my simulation.