In support of the optical fiber telecommunications and optical fiber sensor industries, we provide basic metrology support in group delay and dispersion measurements, polarization characterization (including polarization-mode dispersion) and spectral and group delay characterization of Fiber Bragg Gratings (FBG).

Supporting metrology needs to be in the form of well-characterized measurement techniques, artifact standards, and education on measurement best practices. Generally, the metrology needs in telecommunications are of well-known parameters. But, in order to enable the current and future high-data-rate and high-spectral-efficiency systems, many parameters need to be characterized with high temporal and/or spectral resolutions. We are developing new measurement techniques for these parameters and are working to increase the spectral and temporal resolution of existing methods.

Chromatic dispersion in optical fiber arises from the variation of the light's propagation velocity as a function of wavelength; it is the derivative of the relative group delay (RGD) versus wavelength. This variation in propagation velocity results in broadening of the optical pulses used in communication systems. Broadened pulses interfere with each other and are difficult to distinguish, causing communication errors. System chromatic dispersion must be dealt with by managing its spectral profile (through dispersion-tailored fibers, choice of zero-dispersion wavelength, and dispersion compensating fibers). This requires accurate measurement of the wavelength dependence of chromatic dispersion. Similarly, wavelength-dependent relative group delay in components degrades system performance. Often, RGD must be measured in components that have sub-nanometer optical bandpass regions (requiring < 100 pm spectral resolution). At the same time, high data rates require that RGD be measured with sub-picosecond temporal resolution. These two requirements are in opposition - fundamentally, spectral and temporal resolution are inversely related. A challenge is to optimize the mutual resolution of these quantities. We use the techniques of modulation phase shift and low-coherence interferometry to characterize dispersion and group delay in components and fibers, and are improving uncertainties of these measurements.

This same dilemma is experienced in polarization-mode dispersion (PMD) metrology where propagation velocity depends on the polarization state of the light. Communication systems can require PMD measurement with temporal resolutions of a few tens of femtoseconds and spectral resolutions of a few tens of picometers. In addition, PMD is a statistical quantity, making reference artifact stability difficult. Artifact standards are useful to isolate statistical and environmental variations from measurement inaccuracies. At higher data rates, systems are less tolerant to PMD and can be impacted by its wavelength dependence-Second-Order PMD (SOPMD). In support of higher spectral densities in transmission systems and SOPMD measurements, we are working to develop PMD measurement techniques with improved spectral efficiencies (temporal resolution per bandwidth).