In the past, this project concentrated on the measurement needs of the optical fiber communications industry. More recently our focus has expanded to include broader need for metrology in the near infrared region, including free space communications, LIDAR, and optical fiber sensors.

In an optical fiber communication system, wavelength division multiplexing (WDM) increases bandwidth by using many wavelength channels. Most systems employ 50 or 100 GHz channel spacing (0.4 or 0.8 nm, respectively) in the 1540 to 1560 nm region, but narrower channel spacing may be used in the future. It appears likely that systems will be implemented in other wavelength regions as well. For effective system operation, the wavelength dependence of WDM optical components must be characterized and controlled. We have developed wavelength calibration transfer standards in the 1510-1630 nm region to help industry evaluate optical components and calibrate wavelength-measuring instruments. We have also been developing high accuracy wavelength standards for in house calibration and, in collaboration with the NIST Time and Frequency Division have recently demonstrated two optical frequency combs in the near infrared. Ultimately, NIST-traceable optical frequency combs may meet wavelength calibration needs throughout the visible and near infrared regions.

Future communication systems will increase the total bandwidth by increasing both the number of WDM channels and the bit rate per channel. Both increases will lead to higher optical power in the fiber, and will in turn increase the importance of nonlinear effects. These nonlinear effects, such as cross-phase modulation, self-phase modulation, and 4-wave mixing can cause pulse broadening, pulse distortion, and crosstalk, and ultimately limit system performance. On the other hand, beneficial nonlinear effects, such as Raman amplification, can be used to improve overall system performance through lower noise and the ability to amplify over the full WDM region. Another beneficial nonlinear effect is supercontinuum generation in optical fiber, which allows the development of broad optical frequency combs and may have applications to LIDAR and optical coherence tomography.