Optical experience and skills

(1) optical quality of the simple discrimination:
   Under normal circumstances, OTDR test light curve of the main (single disk or optical disk a few) are basically the same slope, if a large section of the slope, it indicates that a larger attenuation of this section; if the curve of the main body of irregular shape, the slope of undulating curved or rounded in, it indicates that a serious deterioration of optical quality, does not meet the communication requirements.

(2) single-wavelength selection and two-way test:
   1550 farther away from the test wavelength, 1550nm 1310nm optical fiber to bend than the more sensitive, 1550nm attenuation per unit length than smaller 1310nm, 1310nm 1550nm measured than the connector or splice loss higher. Maintenance work in the actual cable in the two wavelengths are generally tested and compared. Phenomenon and positive gain for more than two-way test must be conducted away from the line analysis and calculation, in order to obtain good test results.

(3) joint Clean:
   Fiber OTDR union access before, must be carefully cleaned, including OTDR's output connector and the measured union, or insertion loss is too large, the measurement is not reliable, noise and even more so the curve can not be measured, it may damage the OTDR. Avoid alcohol or cleaning agents other than the refractive index matching fluid, because they can dissolve the adhesive within the fiber optic connectors.

(4) refractive index and scattering coefficient of the correction: the fiber length measurement, the refractive index of 0.01 for each deviation will cause 7m/km many errors, the light for a longer section should be used in the refractive index of fiber optic cable manufacturer value.

(5) The ghost of the identification and treatment:
   Peak on the OTDR trace from the incident side is sometimes due to close and strong reflections caused by the echo, this peak is called ghosting. Identify ghost: the ghost at the curve does not cause significant loss; along the curve and the ghost is the beginning of the strong reflections from the beginning of the event and a multiple of the distance, into a symmetrical shape. Eliminate ghost: Choose a short pulse width, reflecting the strong front-end (such as the OTDR output) increase the attenuation. If the ghosting caused by the end of the event in the fiber, can "play a small bend" to attenuate the beginning of the light reflected back.

(6) is the phenomenon of processing gain:
   In the OTDR traces may produce a positive gain on the phenomenon. Positive gain is due to splice the fiber after the fiber before the splice point than to produce more after the formation of astigmatism. In fact, the optical fiber at the splice is splice loss. Often appear in a different mode field diameters or different backscattering coefficient of optical fiber fusion process, therefore, need to measure in both directions and the results are taken as the average splice loss. In practice, cable maintenance, but also can be used ≤ 0.08dB simple principle is qualified.

(7) the use of additional optical fiber:
  Additional fiber is used to connect a test OTDR and fiber, the fiber length 300 ~ 2000m, and its main role is to: front-end processing and blind terminal connector into the measurement.

   In general, OTDR and fiber under test caused by the connector between the biggest blind spot. Actual measurement in optical fiber, the OTDR and fiber under test then added a transition between the optical fiber, optical fiber to the front blind spot falls within the transition, while the fiber under test OTDR trace the beginning of fall on the linear stable region. Beginning of fiber optic connector system insertion loss increases by a transitional fiber OTDR to measure. To measure the first and last ends of the connector insertion loss, in the transition at each end plus one optical fiber.