Method for determining calibration parameters for a spectrometer
An imaging spectrometer includes a Fabry-Perot interferometer and an image sensor having color-sensitive pixels. The interferometer has a first transmission peak and a second transmission peak (PEAK2). A method calibrating the spectrometer includes providing first calibration light, which has a narrow spectral peak, obtaining first detector signal values from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak is near a first spectral position, obtaining second detector signal values from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak is near a second spectral position, providing second calibration light, which has a broad bandwidth, and obtaining third detector signal values from the image sensor by coupling the second calibration light into the spectrometer.
1. A method for determining calibration parameters for a spectrometer, wherein the spectrometer comprises a Fabry-Perot interferometer having an adjustable mirror gap, and an image sensor, the image sensor comprises a plurality of first pixels and a plurality of second pixels, the pixels are arranged to detect light transmitted through the Fabry-Perot interferometer, the first pixels have a first sensitivity function, the second pixels have a second different sensitivity function, the Fabry-Perot interferometer has a first transmission peak and a second transmission peak, the first pixels are arranged to detect light at the spectral position of the first transmission peak and the at the spectral position of the second transmission peak,
the method comprising:
providing first calibration light, which has a reference spectral peak at an adjustable spectral position,
obtaining first detector signal values from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak is substantially at a first spectral position,
obtaining second detector signal values from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak is substantially at a second spectral position,
determining a first group of calibration parameters from the first detector signal values and from the second detector signal values,
providing second calibration light, wherein the spectral width of a spectral band of the second calibration light is broader than the spectral width of the reference spectral peak,
obtaining third detector signal values from the image sensor by coupling the second calibration light into the spectrometer, and
determining a second group of calibration parameters from the third detector signal values and from the first group of calibration parameters.
2. The method of claim 1 comprising obtaining a set of detector signal values from the image sensor by scanning the spectral position of the reference spectral peak over a spectral range, which comprises the first spectral position, and summing said set of detector signal values.
3. The method of claim 1 comprising obtaining a set of detector signal values from the image sensor by scanning the spectral position of the first transmission peak over a spectral range, which comprises the spectral position of the reference spectral peak, and summing said set of detector signal values.
4. The method according to the claim 1 wherein the first calibration light is provided by filtering light of a broadband light source by using a monochromator.
5. The method according to the claim 1 comprising forming a first matrix from said first group of calibration parameters, determining a second matrix by inverting the first matrix, and determining the second group of calibration parameters from the second matrix and from said third detector signal values.
6. The method according to the claim 1 wherein a spectral band of the second calibration light includes the first spectral position, and wherein the spectral width of the spectral band of the second calibration light is substantially broader than spectral width of the first transmission peak.
7. The method according to the claim 1 comprising obtaining fourth detector signal values from the image sensor by forming an image of an object on the image sensor, and determining intensity values from the fourth detector signal values by using the second group of calibration parameters.
8. The method of claim 7 comprising comparing an intensity value with a reference value.
9. The method of claim 7 comprising comparing a ratio of intensity values with a reference value.
10. The method according to the claim 1 comprising:
defining a cut-off wavelength with an optical filter,
coupling light into the spectrometer,
adjusting the mirror gap, and
monitoring the detector signal as a function of the mirror gap in order to determine a feedback signal value associated with the cut-off wavelength.
11. The method according to the claim 1 comprising:
defining a cut-off wavelength with an optical filter,
coupling light into the spectrometer,
adjusting the mirror gap, and
monitoring the detector signal as a function of the mirror gap in order to determine a mirror gap value associated with the cut-off wavelength.
12. A computer program product embodied on a non-transitory computer readable medium, comprising computer program code for determining calibration parameters of a spectrometer, wherein the spectrometer comprises a Fabry-Perot interferometer having an adjustable mirror gap, and an image sensor, the image sensor comprises a plurality of first pixels and a plurality of second pixels, the pixels are arranged to detect light transmitted through the Fabry-Perot interferometer, the first pixels have a first sensitivity function, the second pixels have a second different sensitivity function, the Fabry-Perot interferometer has a first transmission peak and a second transmission peak, the first pixels are arranged to detect light at the spectral position of the first transmission peak and the at the spectral position of the second transmission peak,
wherein the computer program code is configured to, when executed on at least one processor, cause an apparatus or a system to:
provide first calibration light, which has a reference spectral peak at an adjustable spectral position,
obtain first detector signal values from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak is substantially at a first spectral position,
obtain second detector signal values from the image sensor by coupling the first calibration light into the spectrometer when the reference spectral peak is substantially at a second spectral position,
determine a first group of calibration parameters from the first detector signal values and from the second detector signal values,
provide second calibration light, wherein the spectral width of a spectral band of the second calibration light is broader than the spectral width of the reference spectral peak,
obtain third detector signal values from the image sensor by coupling the second calibration light into the spectrometer, and
determine a second group of calibration parameters from the third detector signal values and from the first group of calibration parameters.