IEC 60793-1-43:2001 pdf download

IEC 60793-1-43:2001 pdf download.optical fibres -Part 1-43: Measurement methods and test procedures -Numerical aperture.
NA can be determined from a far-field radiation pattern measurement on a short length of fibre or from a measurement of a flbre’s refractive Index profile. Using the tar-field method, the intensity pattern. 1(0), of a fibre is acquired, and the NA (numerical aperture in the tar field) is defined as the sine of the halt-angle where the intensity has decreased to 5 % of its maximum value.
4 Reference test method
Because there is only one method for measuring numerical aperture, there is no reference test method (RTM) as of the publication date of this standard. Additional methods may be added in the future, however.
5 Apparatus
5.1 Input system
5.1.1 Light source
Use an Incoherent light source capable of producing an area of substantially constant radiance (variations of less than 10 % in intensity) on the endface of the specimen, It shall be stable in intensity and position over a time Interval sufficient to perform the measurement.
5.1.2 Input optIcs
Use a system of optical components to create a monochromatic (<100 nm full width half maximum), substantially constant radiance spot larger in diameter than the endface of the specimen and with a numerical aperture greater than that of the specimen Unless otherwise specified, the centre wavelength shall be 850 nm ± 25 nm. Provide a means of verifying the alignment of the endface, Optical filters may be used to limit the spectral width of the source. 5.1.3 Fibre Input end support and alignment Provide a means of supporting the Input end of the specimen to allow stable and repeatable positioning without introducing significant fibre deformation. Provide suitable means to align the Input endlace with respect to the launch radiation. 5.1.4 Cladding mode stripper Provide means to remove cladding light from the specimen. Often the fibre coating is sufficient to perform this function. Otherwise, it will be necessary to use cladding mode strippers near both ends of the test specimen. 5.2 Output system and detection Three equivalent techniques may be used to detect the angular radiant intensity (far field) distribution from the specimen. Techniques I and 2 are angular scans of the far-field pattern. Technique 3 is a scan of the spatial transform of the angular intensity pattern (a small or large area scanning detector may be used.) 5.2.1.1 FIbre output end support and alignment Use a means of supporting and aligning the output end of the specimen that allows alignment of the endface normal to and coincident with the axis of rotation of the optical detector and coincident with the plane of rotation of the optical detector. For example, a vacuum chuck mounted on X-Y-Z micropositloners with a microscope fixture for aligning the fibre end would be suitable. Examples include a gonionieter or stepper-motor driven rotational stage. 5.2.1.2 Detection system mechanics Use a suitable means for rotation of the optical detector that allows the detector to scan an arc sufficient to cover essentially the full radiation cone from the specimen (for example, a calibrated gonlometer). The axis of rotation of the mechanism shall Intercept the endface of the specimen and shall be perpendicular to the specimen axis, and the rotation plane of this mechanism shall be coincident with the axis of the specimen. Provide means for recording the relative angular position of the detector with respect to the specimen output axis. 5.2.2 TechnIque 2 — Angular scan (see figure 2) Use a means of supporting the specimen such that the output endface is perpendicular to, and coincident with, the axis of rotation of the specimen. This mechanism (e.g. a gonlometer or precision rotating stage) shall rotate sufficiently to allow the full radiation cone in the plane of rotation to sweep past the fixed detector. That Is. the rotation shall be greater than the total angle of the specimen output radiation. Provide means to record the included angle formed by the specimen axis and the imaginary line between the detector and specimen endface. 5.2.3 TechnIque 3 — Scan of the spatial field pattern (see figure 3) 5.2.3.1 Fibre output end support apparatus Provide a means of supporting and aligning the specimen output end that allows stable and repeatable positioning. 5.2.3.2 Far-field transformation and projection Create a spatial representation of the far field of the specimen by suitable means (for example. by using a microscope objective or other well corrected lens to obtain the Fourier transform of the fibre output near-field pattern). Scan this pattern or Its image using a pinhole aperture as to enable the far-field intensity to be recorded. The size of the pinhole aperture shall be less than, or equal to, one-half the diffraction limit of the system.