Quasicontinuous tunable fiber-ring laser applied as local oscillator in an absolute calibrated spectrometer for WDM systems

A special tunable fiber-ring laser is introduced. With this laser as local oscillator, a calibrated optical spectrometer was realized, which allows the determination of the wavelength of all transmitters of a wavelet division multiplexing (WDM) system in one sweep. The system is based on a fiber ring laser including a high finesse Fabry-Perot resonator with a high free spectral range and a 1-km-long dispersion shifted fiber. To achieve a high wavelength determination accuracy two auxiliary signals are generated: one with a Krypton filled absorption tube and another with a simple, silica based, periodical filter. With that, the wavelength of every transmitter of a WDM signal can be determined with an absolute frequency accuracy of better than ±0.8 GHz in a range of 1527-1562 nm in one sweep. The relative frequency accuracy is better than ±0.3 GHz