Three-step OTDR for fiber measurements

With OTDR for optical measurements can be divided into three steps: parameter setting, data acquisition and curve analysis. Manually set the measurement parameters include:
(1) wavelength (λ):
   Due to different wavelengths of light corresponding to different characteristics (including attenuation, slightly curved, etc.), the test wavelength transmission communication with the system generally follows the wavelength corresponding to the principle that the system is open to 1550 wavelength, the test wavelength of 1550nm.

(2) Pulse Width (Pulse Width):
    The longer pulse width, the greater the dynamic range, measuring distances, but the waveform generated in the OTDR trace blind greater; short pulses of light into the lower level, but can reduce the blind spot. Ns pulse cycle is usually expressed.

(3) Range (Range):
    OTDR OTDR measurement range is the maximum distance for data sampling, the choice of this parameter determines the size of the sampling resolution. The best measurement range of the length of the fiber under test between 1.5 to 2 times the distance.

(4) Average time:
    As the backscattering light signal is extremely weak, commonly used statistical methods to improve the average signal to noise ratio, the longer the average, the higher signal to noise ratio. For example, 3min 1min access to get access to take to improve than 0.8dB dynamic. But more than 10min to get to take time to improve signal to noise ratio is not significant. General average of no more than 3min.

(5) Optical parameters:
    Parameter settings, including fiber-optic refractive index n and n backscattering coefficient and backscattering coefficient η settings. Distance to measure the refractive index parameters, the backscattering coefficient of reflection and return loss is affecting the measurement results. These two parameters are usually given by the fiber manufacturer.

    After setting parameters, OTDR can send and receive light pulses from the fiber link back to the light scattering and reflection, the output of the photodetector sampling, get OTDR curve, the curve analysis to understand the optical quality.