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US 4,636,071 AGranted
Method and apparatus for measuring single mode fiber mode field radius
AssigneeNorthern Telecom Limited
InventorsRichard S. Lowe, Constantine Saravanos
Life of this patent
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AssigneeNorthern Telecom Limited
InventorsRichard S. Lowe, Constantine Saravanos
Estimating the term…
The fundamental-mode field radius `w` is a key parameter in characterizing optical fibers. `w` is a function of P, .theta. and .lambda. where P is the far-field power passing through a circular aperture subtending a solid angle of 2.theta. at the fiber end face and .lambda. is the center wavelength of transmitted length. `w` is derived by moving a fixed diameter aperture along an axis extending between the test fiber end surface and a photodetector so as effectively to vary .theta.. At each location the power P incident on the photodetector and the corresponding acceptance angle .theta. are measured. A microprocesor is programmed to compute from the range of measured values of .theta. and P, the value of mode field radius for a particular transmission wavelength .lambda..
A method for determining the mode field radius `w`, of a single mode optical fiber comprising projecting light of wavelength .lambda. through the optical fiber, positioning a fixed diameter aperture in front of an exit face of the optical fiber in the far field pattern of light emitted therefrom, moving the aperture on the axis of emitted light through a series of acceptance angles .theta., measuring the power P passing through the aperture corresponding to said acceptance angles, and obtaining a value of mode field radius in terms of .lambda., P and .theta..
A test set for determining the mode field radius `w`, of a single mode optical fiber comprising projection means for projecting light through the fiber, a fixed diameter aperture located in front of an exit face of the optical fiber within a far-field pattern of light emitted therefrom, carriage means for moving the aperture on the axis of light emitted from the fiber through a series of acceptance angles .theta., means for measuring the power P passing through the aperture corresponding to the acceptance angles, and signal processing means for obtaining a value of mode field radius `w` in terms of .lambda., P and .theta..
Dependencies are inferred from the claim text.