(a) coupling substantially monochromatic measurement radiation of a first wavelength λ into the first end of the segment in a manner effective for launching at least one propating mode of radiation, Setting at least one of the manufacturing steps in the manufacture of the first fiber, or setting at least one of the manufacturing steps for the subsequent production of another optical fiber, in accordance with the result of the comparison between λ c and the target value the actual cut-off wavelength λ c determined by a method comprising Single mode optical fiber manufacturing process comprising a multiplicity of manufacturing steps including forming an optical fiber preform, drawing first fiber from the preform, and grading of the drawn fiber, the process further comprisingĭetermining an actual cut-off wavelength λ c of a segment of the first fiber, where λ c is the actual cut-off wavelength of the LP 11 mode of electromagnetic radiation propagating axially through the segment of fiber, the fiber segment having a first and a second end and having a length effective to produce steady-state propagation conditions at the second end for electromagnetic radiation launched into the first end and propagating axially through the segment Ĭomparing λ c to a predetermined target value and (c) fitting a Gaussian function G(θ) to the radiation power distribution, or to a distribution derived from the radiation power distribution, andĢ. (b) measuring, as a function of a far-field angle θ, the radiation power at a multiplicity of values of θ in at least part of the central lobe of the far-field radiation field of the radiation emitted from the second end of said first fiber fiber end, the set of measured values of radiation power to be referred to as the radiation power distribution, (a) coupling substantially monochromatic measurement radiation of wavelength λ o into the first end of the fiber segment in a manner effective for launching the fundamental mode LP 01, The mode field radius ω determined by a method comprising Setting at least one of the manufacturing steps in the manufacture of the first fiber, setting of at least one of the manufacturing steps for the subsequent production of another optical fiber, in accordance with the result of the comparison between ω and the target value Single mode optical fiber manufacturing process comprising a multiplicity of manufacturing steps including forming a first optical fiber preform, drawing first fiber from the first preform and grading of the draw fiber, the process further comprisingĭetermining the mode field radius ω for radiation of wavelength λ o of a segment of the first fiber, λ o being a wavelength in the single mode regime of the segment of fiber, the fiber segment having a first and a second end and being of length effective to produce steady-state propagating conditions at the second end for radiation of wavelength λ o launched into the first end Ĭomparing ω to a predetermined target value of the mode field radius and Lazay, "Symposium on Optical Fiber Measurement", Boulder, Co., 1980, pp. Marcuse, "Principals of Optical Fiber Measurements", 1981, pp. Gambling et al., "Microwaves, Optics, and Acoustics," vol. Bhagavatula et al., "Electronics Letters", vol. Ghatak et al., "Electronics Letters", vol. Brinkmeyer et al., "Applied Optics", vol.
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