Calorimetric measurements of absorption and scattering losses in optical fibers

Simple method of measuring scattering losses in optical fibers

A simple method of measuring the scattering losses of optical fibers was developed. The method permits the measurement of the scattering-loss spectra by use of photon counting. Measurement is based on right-angle scattering, which is dominated by Rayleigh scattering, a material-intrinsic loss. A reference fiber for which the scattering loss is known is used to cancel out the unknown factors that are dependent on the optical setup. The scattering-loss measurement was demonstrated by use of two different low-loss fibers and was found to agree with predetermined figures to within 10% over the wavelength range 0.44-1.0 microm. Finally, the method was applied to a new high-numerical-aperture optical fiber to find its material scattering loss.

Optical time-domain reflectometer specifications and performance testing

From a researcher's as well as a user's point of view, it is highly desirable to adopt a common basis for specifying optical time-domain reflectometer performance parameters. This paper proposes some procedures and test methods which permit these devices to be characterized in a consistent way. Passive test fixtures are also described which may facilitate measurements of dynamic range and other reflectometer properties.

Separation of total-loss data into its absorption and scattering components: a more accurate model for fiber loss

A technique is presented that uses total-loss data from a conventional monochromator-based spectral-loss measurement set to obtain not only the Rayleigh and wavelength-independent scattering of a fiber but also the UV-band-edge absorption. That absorption causes the total-loss data to deviate significantly from a straight line when the data are plotted vs lambda on a 1/lambda(4) scale. Including the absorption term accounts for the deviation from a straight line over an extended wavelength region (0.66-1.16 microm) and materially affects the A and B coefficients obtained. For one fiber examined in detail A went from 1.30 to 1.13 microm(4) dB/km and B from 0.22 to 0.32 dB/km when the UV absorption was included. This technique also eliminates the problem of negative B coefficients and allows processing variables that affect absorption to be separated from those that affect scattering.

Calorimetric measurements of weakly absorbing materials: theory

The time-dependent heat equation is solved in a cylindrical geometry of finite length with heat loss by radiation and conduction. Exact expressions are derived for the time constants of radial and longitudinal modes. The steady-state solution is obtained in longitudinal modes and used as the initial state for the decay. A simple expression is presented for the ratio of the amplitude of the first-order longitudinal order mode A(1) and the corresponding time constant tau(1)fit with the separate expressions for A(1) and tau(1). These parameters are experimentally readily accessible and directly yield the absorption coefficient alpha of rod-shaped compound glass from which optical fibers are to be drawn.

Launch dependent loss in short lengths of graded-index multimode fibers

In this paper we describe the effect of different launching conditions on the loss measured with a calorimeter in short (~1-m) lengths of multimode optical fiber. A qualitative description of the relation between the energy distribution in the fiber and various excitation variables is given, and many examples are presented that illustrate the effect that launch conditions have on the fiber loss. The use of launch-dependent loss phenomena to diagnose loss mechanisms in optical fibers is discussed. In particular, loss plots are shown for two germania-doped silica-core fibers that indicate a strong absorption loss mechanism located deep within the fiber core.