Test procedures of Measurement methods and test procedures Numerical aperture 3.2.3. 5 Recording system Provide means to record El), the detected intensity as a function of the scan position, y, and to correct the detected intensity as follows: (0)=E cos 8 where r(0) is the angular intensity distribution as detected by the angular scan lens El is the radiance at distance y from the axis of the spatial pattern y is the distance from the axis to the spatial field pattern; a is the angle with respect to the axis of the specimen output 3.2.4 Optical detector Use a detector that is linear within 5 % over the range of intensity encountered A pinhole aperture ma be used to restrict the effective size of the detector in order to achieve increased resolution the detector or aperture size can be determined according to the angular resolution that is desired for the apparatus according to the formul BR (9) where D is the detector aperture diameter, in um; e is the desired angular resolution, in degrees o R is the distance from the sample output endface to the detector or aperture, in mm. A resolution of +0, 5 is typically used. R shall also meet the far-field requiremen R≥ R is the distance from the sample output endface to the detector or aperture in mm d is the diameter of the emitting region of the specimen, in_m n is the centre wavelength of the optical source, in nm Equation(5) gives the appropriate detector or aperture size for technique 3 Sampling and specimens 4. 1 Specimen length 4. specimen shall be a representative sample of fibre 2, 0 m +0, 2 m in length Prepare a flat end face orthogonal to the fibre axis, at the input and output ends of each specimen. The accuracy of these measurements is affected by a non-perpendicular endface End angles less than 2 are recommended Procedure 5.1 Place the specimen ends in the support devices. The input end shall be approximately at the centre of the input place of the focused image of the constant radiance spot 5.2 Set the optical source to the desired wavelength and spectral width 5.3 Scan the far-field radiation pattern along a diameter and record intensity versus angular position Calculations 6.1 Far field versus maximum theoretical value The relationship between the far-field numerical aperture and the maximum theoretical numerical aperture is dependent upon the measurement wavelength of the far-field and profile measurements Most far-field measurements are made at 850 nm, whereas profile measurements are commonly made at 540 nm or 633 nm. For these wavelengths, the relationshipbetween NAff and NAth is given by NAff= k NAth (11) where NAff is the na in the far field k=0, 95 when the profile measurement is made at 540 nm, and k=0, 96 when the measurement is made at 633 nm:Test procedures Page: 4 of 5 Subject: Originated by: Wu Jia Measurement methods and test procedures – Numerical aperture 3.2.3.5 Recording system Provide means to record E(y), the detected intensity as a function of the scan position, y, and to correct the detected intensity as follows: I (θ) = E(y) cos θ (8) where I(θ) is the angular intensity distribution as detected by the angular scan lens; E(y) is the radiance at distance y from the axis of the spatial pattern; y is the distance from the axis to the spatial field pattern; θ is the angle with respect to the axis of the specimen output. 3.2.4 Optical detector Use a detector that is linear within 5 % over the range of intensity encountered. A pinhole aperture may be used to restrict the effective size of the detector in order to achieve increased resolution. The detector or aperture size can be determined according to the angular resolution that is desired for the apparatus according to the formula: where D is the detector aperture diameter, in µm; θ is the desired angular resolution, in degrees (°); R is the distance from the sample output endface to the detector or aperture, in mm. A resolution of ±0,5° is typically used. R shall also meet the far-field requirement: where R is the distance from the sample output endface to the detector or aperture, in mm; d is the diameter of the emitting region of the specimen, in _m; λ is the centre wavelength of the optical source, in nm. Equation (5) gives the appropriate detector or aperture size for technique 3. 4 Sampling and specimens 4.1 Specimen length The specimen shall be a representative sample of fibre 2,0 m ± 0,2 m in length. 4.2 Specimen end face Prepare a flat end face, orthogonal to the fibre axis, at the input and output ends of each specimen. The accuracy of these measurements is affected by a non-perpendicular endface. End angles less than 2° are recommended. 5 Procedure 5.1 Place the specimen ends in the support devices. The input end shall be approximately at the centre of the input place of the focused image of the constant radiance spot. 5.2 Set the optical source to the desired wavelength and spectral width. 5.3 Scan the far-field radiation pattern along a diameter and record intensity versus angular position. 6 Calculations 6.1 Far field versus maximum theoretical value The relationship between the far-field numerical aperture and the maximum theoretical numerical aperture is dependent upon the measurement wavelength of the far-field and profile measurements. Most far-field measurements are made at 850 nm, whereas profile measurements are commonly made at 540 nm or 633 nm. For these wavelengths, the relationshipbetween NAff and NAth is given by NAff = k NAth (11) where NAff is the NA in the far field; k = 0,95 when the profile measurement is made at 540 nm, and k = 0,96 when the measurement is made at 633 nm;