IEC 61300-3-43 pdf download – Fibre optic interconnecting devices and passive components – Basic test and measurement procedures – Part 3-43: Examinations and measurements – Mode transfer function measurement for fibre optic sources
5.2 Test sample The test sample consists of a multimode patch cord attached to a light source. It should be recognised that the mode distribution at the output of the patch cord is a product of both the launch conditions of the source and of the patch cord itself. The resultant MTF is therefore not a parameter of either the light source or the patch cord individually but rather of the combination, including the particular conditions under which the patch cord is disposed, such as bend radius.
5.3 Sample positioning device A positioning device is required to ensure that the end of the patch cord under test is located on the optical axis of the instrument and also in the correct axial position to give a well- focussed image on the camera. For this purpose, an XYZ manipulation stage may be used or, preferably, a suitable connector receptacle mounted axially with the optics. An example is a standard 2,5 mm ferrule receptacle which is able to accommodate several connector types,such as FC,ST and SC. In this case,the xY positioning of the patch cord is well-defined andonly a focussing adjustment is required.
5.4Optical system
The optical system comprises magnifying optics to produce an image of the fibre end on thecamera. Tooptimise measurement resolution， it is recommended that the opticalmagnification shall be chosen so that the image of the fibre core fills a reasonable proportionof the camera.Typically, this might be between 20 % and 50 % of the vertical extent of thecamera.
The numerical aperture of the imaging system shall be greater than the numerical aperture ofthe fibre under test.
A means of illuminating the end face of the fibre in reflection may also be provided, such as abeam splitter and an LED source positioned between the focussing lens and the camera.
Neutral density (ND) filters may also be provided to control the amount of light reaching thecamera.
5.5Camera
A high quality camera shall be used that has demonstrable geometrical uniformity andintensity linearity.The pixel size of the camera,picsize，shall be sufficiently small comparedwith the magnified near-field image as to be less than the system diffraction limits by a factorof 2, given by
Picsin
IEC 61300-3-43 pdf download – Fibre optic interconnecting devices and passive components – Basic test and measurement procedures – Part 3-43: Examinations and measurements – Mode transfer function measurement for fibre optic sources
