Proceedings Article | 3 February 2009
KEYWORDS: Calibration, Charge-coupled devices, Spectroscopy, Sensors, Precision calibration, Electroluminescence, Optical design, Ocean optics, Manufacturing, Mercury
An advanced wavelength calibration process with higher wavelength accuracy is developed based on the conventional
calibration method of micro-spectrometers with multichannel detectors. In the conventional method, the unit of pixel
data for calibration is pixel. A pixel unit usually has a length measured in μm, and the wavelength peak is not always in
the middle of a pixel. Thus, the location of a spectral line's peak can't be got accurately. The length of a pixel arouses a
measurement error of wavelength-peak location. And the error of wavelength-peak location results in error of pixel
wavelength calibration. A new method, applying triangular linetype to approach the real spectral linetype, which enhance
the wavelength-peak location accuracy, is introduced in this article. The method is proved useful in theory and a function
for calculating the accurate pixel location is produced from the method. Two steps are added to the conventional method
before the final pixel-wavelength fitting. First, three-pixel data collection is carried out. In the conventional method, only
the highest pixel of one spectral line is chosen for calibration, but that is not enough for getting more accurate
wavelength peak location. In the new method, three pixels, including the highest one and its two neighbors, are collected
for the more accurate wavelength-peak location process. Second, sub-pixel calculation is executed to enhance the peak
location accuracy. On the assumption that a triangular linetype can approximately replace the real linetype in theory, the
wavelength-peak location is calculated more accurately and the precision of the result is better than 0.5 pixel. When an
unknown spectral line is measured, accurate wavelength-peak location can be got in the same way. The experiment was
based on a compact spectrometer HR4000, with a crossed Czerny-Turner optical design, produced by Ocean Optics
Company. Its manufacturer's calibration precision, which is given by the company, is 0.24nm. Mercury lamp's line
spectra are used as wavelength standards. The results show that by applying the new method, the wavelength-peak
location accuracy improves from 1 pixel to around 0.5 pixel, and the wavelength accuracy improves from above 0.2nm to
around 0.1nm.
