NIST demonstrates hybrid wavelength calibration reference. (General Developments).

NIST scientists have have developed a multiple-wavelength calibration reference that incorporates the wavelength flexibility of fiber Bragg grating artifact references and the stability of fundamental molecular absorption references. A prototype wavelength calibration unit was demonstrated at the Navy Primary Standards Laboratory, San Diego, CA, in December 2002.

Wavelength calibration references are needed to calibrate wavelength-measuring instruments such as optical spectrum analyzers. Atomic and molecular absorption lines are very stable under changing environmental conditions and are excellent references for this purpose. Unfortunately, good atomic or molecular candidates are not available in all wavelength regions. Customized multiple wavelength reflectors can be generated by writing multiple superimposed fiber Bragg grating (FBG) reflectors into optical fiber using ultraviolet light. Each grating is a reflector for a specific wavelength of light; the wavelengths are selected during the grating fabrication process. Strain and temperature changes, however, can cause the center wavelength of these reflectors to change; the temperature sensitivity is about 0.01 nm/[degrees]C. If one of the FBG reflectors is located near an atomic or molecular absorption line, it can be actively stabilized to that line. This stability is then transferred to the other gratings, becaus e they are super-imposed at the same location in the fiber. Once the wavelength of each FBG reflection peak is measured at NIST, all of the peaks can be used as calibration references. The NIST prototype uses interleaved sampled FBGs to produce multiple peaks in the 1300 nm and 1550 nm regions. The unit provides eight calibration references between 1297 nm and 1306 nm and 12 references between 1531 nm and 1550 nm, each with a stability of a few picometers. NIST scientists are now investigating methods to incorporate calibration references in the 850 nm region.

CONTACT: Sarah Gilbert, [phone]; [e-mail].