Molecular transitions as medium-precision wavelength standards for optical communication

Molecular vibration-rotation transitions in overtone or combination bands are well suited as absolute wavelength standards throughout the wavelength range used for optical communication. In this paper, we describe two different implementations. In the first, radiation from a superluminescent diode is sent through a cell containing H¹³CN. This provides the spectrum with a characteristic signature from absorption in the 2ν₃ overtone band, and allows for calibration in the 1530-1560 nm range. In the second implementation, radiation from a distributed feedback (DFB) fiber laser is locked to a Doppler broadened absorption line at 1548.8193 nm in the ν₁+ν₃ combination band of ¹³C₂H₂. The resulting standard has a relative Allan deviation of less than 10^-8 beyond 100 s of integration time, and the signal can be disseminated through optical networks without degradation in stability. A novel feature of the fiber laser is all thermal control of the wavelength through resistive heating of a thin-film gold coating.