This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Hello all,
I am using ultra-mobile near-infrared (NIR) spectrometer in reflectance measurements using optical fibers. My signal is very weak, I believe it is very close to the noise level.
I need to define if I am measuring reliable signal or it is just noise. I have access to Optical Power meter thus my question is:
What is minimal optical power that I could detect? Preferably in Watts. If it is not possible to define it exactly, could you please provide the range, eg. nW, µW.
So far I have found SNR equal to 6000:1. However I cannot use it (or I don't know how to adapt it) for my puprose, link below.
Thank you and best wishes, Lucas.
Hello Paul,
Thank you for quick answer.
I am currently using 15 W IR halogen lamp, which should be stronger than built-in two small IR lamps. Fiber core in my setup has 125 µm of diameter. On one side of the fibers I have just 'raw' polished fiber tips, lets call this detector's side. On the other side those optical fibers are connected to the module and lamp using SMA 905 connectors. No lenses / sophisticated coupling.
Yes, I understand your point with dependency on wavelength. As far as I checked I should not receive more than 100 µW on this range.
50, 000 counts in reflectance measurements? Is this possible to achieve with optical fibers? I am using Spectralon as a standard sample for calibration and even with this I cannot achieve amplitude higher than 1,200 units. Please find CSV file and a plot attached.
To be precise, 50,000 counts on average or peak points? I am now not sure if I got that much even with transmittance measurements.
Could you please provide me some hints how I could improve signal strength?
Thank you again!
Best, Lucas.
Hi Paul,
sorry for delayed answer but I needed some time more time to test. First of all I updated software after your idea to change PGA gain, which I couldn't in previous version.
I checked Hadamard with biggest possible PGA (equal to 64). I believe it slightly improved SNR as the signal become less noisy. Meaning amplitude of 'spikes' decreased. However overall amplitude of the signal is not much better. I would say it improved by 200 units/counts. Meaning it is equal to ~2300 units/counts in highest peak.
I think your solution with optical fibers may be the key. However, before I start I would ask you, if your team in TI conducted successful reflectance measurements with Nano, using optical fibers. If detector is able to detect signal on milliWatt range I'm not sure if I will provide much more than µW even with round-to-flat optical fibers. If you already did it, could you please provide more details on how measurement setup was made, e.g. fibers used(core size, type), light source(optical power), distance from the sample to fibers, sample type, reference sample type.
Another theoretical solution would be changing the photo-detector, would you recommend this solution? I believe I would need to change ADC as well.
Thank you for your time and help!
Best, Lucas.
Paul,
thanks a lot for your help. You clarified several issues. I hope that I will be able to push it from this point.
Best, Lucas