Wavelength references for 1300-nm wavelength-division multiplexing

We have conducted a study of potential wavelength calibration references for use as both moderate-accuracy transfer standards and high-accuracy National Institute of Standards and Technology (NIST) internal references in the 1280-1320-nm wavelength-division-multiplexing region. We found that most atomic and molecular absorption lines in this region are not ideal for use as wavelength references owing to factors such as weak absorption, complex spectra, or special requirements (for example, frequency-doubling or excitation with an additional light or discharge source). We have demonstrated one of the simpler schemes consisting of a tunable diode laser stabilized to a Doppler-broadened methane absorption line. By conducting a beat-note comparison of this reference to a calcium-based optical frequency standard, we measured the methane line center with an expanded uncertainty (2/spl sigma/) of /spl plusmn/2.3 MHz. This methane-stabilized laser now serves as a NIST internal reference.