off-set joint Fig. 6.1-19 Offset technique for mode field measurement-a block diagram; CMS, cladding mode stripper. Reprinted from Ref. [18], p. 426, courtesy of Marcel Dekker Inc. Optical fiber, cable and connectors CHAPTER 6.1 test fiber introduction He-No ALIGNMENT LASER of small bend detector SPATIAL FILTER launching system P,(A) FIBER reference MONOCHROMATOR TOTAL LENGTH OF FISER power SCALE MICRO SCOPE VARIABLE DELAY PATH (TROMBONE) TO LOCK-IN AMPLIFIER TRANSDUCER AND Y AXIS MOTOR OF RECORDER TO x AXIS OF RECORDER 10.34 wavelength Fig. 6.1-20 Typical setup of cutoff wavelength measurement: (a) bending and (b) typical measurement of graph of the cutoff wavelength, single-mode reference (bending method). Reprinted from Ref. [18], (a) p. 430, and (b) p. 431, courtesy of Marcel Dekker Inc. loads. Additionally, a screen test is performed on long samples of the fibers to find the effective strength [19]. WAVELENGTH IN um Fig. 6.1-21 Optical arrangement of dispersion measured by the interferrometric technique and the delay curve. Reprinted from 6.1.2.5 Measurement techniques Ref. [20], p. 351, courtesy of Academic Press. In this section I will briefly introduce one measurement method each for measuring attenuation, mode field Cutoff Wavelength (the Single-Bend diameter, cutoff wavelength, and chromatic dispersion. Attenuation Method) In this method the power transmission is measured as Attenuation (the cutback method) a function of wavelength for two different fiber bending The transmission is measured as a function of wavelength situations. In the first measurement a prescribed bend for the full-length fiber, PL(X). The fiber is then cut diameter of 28 cm is used (CCITT and EIA standards). approximately 1 or 2 m away from the input end and a new transmission measurement is performed, Pr(A) Glass Fiber (Fig. 6.1-18). The attenuation constant a is then calcu- 125 um Diameter lated as follows [20]: PL(2) Empty or Strength a = 10.log Pr(A) (6.1.39) Members Soft, UV-cured Primary Plastic Tube Hard Secondary Coating Co