On-chip temperature-insensitive read-out

A photonic integrated chip for temperature-compensated wavelength monitoring of at least one spectral line in a predetermined range of operating temperatures of the photonic integrated chip, comprising:

• an optical filter having a spectral response curve comprising at least one of a wavelength passband, for selecting at least one spectral reference line from a wavelength continuum in a source signal applicable to the filter, and
• a first spectrometer having a spectral response curve comprising a plurality of wavelength channels, an input of the first spectrometer being connected to the optical filter to receive the at least one spectral reference line selected by the filter, the first spectrometer being configured for detecting wavelength drifts of each received spectral reference line in response to temperature variations of the photonic chip;
• wherein the first spectrometer or a further spectrometer of the photonic chip is configured for receiving said at least one spectral line to be monitored and for detecting wavelength shifts thereof,
• wherein the at least one wavelength passband of the optical filter is spectrally overlapping at least one wavelength channel of the plurality of wavelength channels of the first spectrometer for each temperature in said range of operating temperatures of the photonic integrated chip, and
• wherein a thermal wavelength drift rate for the spectral response curve of the optical filter differs from a thermal wavelength drift rate for the spectral response curve of the first spectrometer at least by an amount such that, over the entire range of operating temperatures of the photonic integrated chip, an effective resolving power associated with the spectrometer receiving said at least one spectral line to be monitored is at least 50% of a nominal resolving power in respect of that same spectrometer.