Abstract
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.
Highlights
Measuring and controlling the wavelength of lasers is essential to a vast number of applications
Examples range from multichannel wavelength division-multiplexing (WDM) [1], optical communication [2], linear and nonlinear spectroscopic applications [3,4,5,6], to laser based metrology [7]
We present a new method for wavelength and power estimation, based on the calibrated transmission spectra of a micro-ring resonator (MRR), providing high precision and extended measurement range suitable for integrated optics
Summary
Measuring and controlling the wavelength of lasers is essential to a vast number of applications. State-of-the-art wavemeters, such as double-folded Michelson interferometers [8], can readily provide a high spectral resolution of better than 10−6 This comes at the cost of a fairly large instrument size (in the order of 106 wavelengths, i.e., typically a meter). Miniaturization can be achieved by using the transmission functions of integrated optical wavelength filters [10], such as thin-film interference filters, photonic crystal waveguides [11], or multimode interference couplers [12]. This allows the laser and its wavelength monitor to be integrated into a single device [13]. The operational range is confined to the region where the spectral sensitivities of all channels are either strictly increasing or decreasing
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