Wavelength dependence of non-linearity of optical fibre power meters

This study discusses wavelength dependence of non-linearity of optical fibre power meters (OFPMs). The non-linearity for several kinds of OFPMs was measured at various wavelengths used in optical communication to determine its wavelength dependence. The response of OFPMs was intrinsically linear and the linearity seemed to be wavelength independent for a certain wavelength range that probably meets the conditions that almost all electron-hole pairs generated by incident light reach the space-charge region of a photodiode and contribute to photocurrent. This suggests that linearity calibration at a single or a few wavelength(s) would be sufficient to derive the linearity at arbitrary wavelength around the calibration point(s). The non-linearity of OFPMs appeared when carrier recombination is not negligible during carrier diffusion into the space-charge region, and it was probably wavelength dependent, as it can be described theoretically. It was also found that using a modulated test light source revealed whether the non-linearity measured for a continuous wave (CW) source is an intrinsic one (because of supraresponsivity, photodiode saturation) or range discontinuity.