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R. M. Oldenbeuving, H. Song, G. Schitter, M. Verhaegen, E. J. Klein, C. J. Lee, H. L. Offerhaus, K.-J. Boller:
"High precision wavelength estimation method for integrated optics";
Optics Express, 21 (2013), 14; 11 S.

A novel and simple approach to optical wavelength measurement
is presented in this paper. The working principle is demonstrated using
a tunable waveguide micro ring resonator and single photodiode. The initial
calibration is done with a set of known wavelengths and resonator tunings.
The combined spectral sensitivity function of the resonator and photodiode
at each tuning voltage was modeled by a neural network. For determining
the unknown wavelengths, the resonator was tuned with a set of heating
voltages and the corresponding photodiode signals were collected. The
unknown wavelength was estimated, based on the collected photodiode
signals, the calibrated neural networks, and an optimization algorithm. The
wavelength estimate method provides a high spectral precision of about
8 pm (5·10−6 at 1550 nm) in the wavelength range between 1549 nm to
1553 nm. A higher precision of 5 pm (3·10−6) is achieved in the range
between 1550.3 nm to 1550.8 nm, which is a factor of five improved
compared to a simple lookup of data. The importance of our approach is
that it strongly simplifies the optical system and enables optical integration.
The approach is also of general importance, because it may be applicable
to all wavelength monitoring devices which show an adjustable wavelength
response.