Things To Note When Using OTDR Test Tools

The cost for huge fiber optic network maintenance is raising up since the popularity of FTTH and development of optical network end users. It is much more harder for operator to manage and maintenance PON network because network access information is incomplete, end users’ information is inaccurate,terminal signal release is incomplete. FCST have professional fiber optic test solution and related products, widely used in FTTH, LAN, metropolitan area optical fiber network, PON network construction, deployment, maintenance, certification and optical communication teaching & scientific research.

Among them, OTDR (optical time-domain reflectometer) is an instrument that can understand the uniformity, defects, fractures, connector coupling and other properties of optical fibers through the analysis of measurement curves. It is made based on the backscattering and Fresnel reverse principles of light. It uses the backscattered light generated when light propagates in the optical fiber to obtain attenuation information. It can be used to measure fiber attenuation, joint loss, locate fiber fault points and understand The loss distribution along the length of optical fiber is an indispensable tool in optical cable construction, maintenance and monitoring. Next we will introduce how to set the parameters when using OTDR.

1. Wavelength selection (λ):

Because different wavelengths correspond to different light characteristics (including attenuation, micro-bending, etc.), the test wavelength generally follows the principle corresponding to the system transmission communication wavelength, that is, if the system opens to 1550 wavelength, the test wavelength is 1550nm.

2. Pulse Width:

The longer the pulse width, the larger the dynamic measurement range and the longer the measurement distance, but the larger the blind zone in the OTDR curve waveform, and the pulse width period is usually expressed in ns.

3. Measuring range (Range):

The OTDR measurement range refers to the maximum distance over which the OTDR acquires data sampling. The selection of this parameter determines the sampling resolution. The optimal measurement range is between 1.5 and 2 times the length of the fiber to be measured.

4. Average time:

Since the backscattered light signal is extremely weak, statistical averaging is generally used to improve the signal-to-noise ratio. The longer the averaging time, the higher the signal-to-noise ratio. For example, a 3min acquisition will be 0.8dB more dynamic than a 1min acquisition. However, acquisition time exceeding 10 minutes does not significantly improve the signal-to-noise ratio. Generally, the average time does not exceed 3 minutes.

5. Optical fiber parameters:

The setting of fiber parameters includes the setting of refractive index, backscattering coefficient and backscattering coefficient eta. The refractive index parameter is related to distance measurement, and the backscattering coefficient affects the measurement results of reflection and return loss. These two parameters are usually given by the fiber manufacturer.

After the parameters are set, the OTDR can send light pulses and receive the light scattered and reflected back by the optical fiber link, sample the output of the photodetector, and obtain the OTDR curve. By analyzing the curve, you can understand the fiber quality. There are some caveats to pay attention to. 1) Simple judgment of optical fiber quality. Under normal circumstances, the slope of the main body of the light curve (single or several optical cables) tested by OTDR is basically the same. If the slope of a certain section is large, it indicates that the attenuation of this section is large; if the main body of the curve is not Regular shapes, large slope fluctuations, bends or arcs indicate that the quality of the optical fiber has seriously deteriorated and does not meet communication requirements. 2) Wavelength selection and single and bidirectional testing, the 550 wavelength test distance is farther, 1550nm fiber is more sensitive to bending than 1310nm fiber, 1550nm has smaller attenuation per unit length than 1310nm, and 1310nm has higher splicing or connector loss than 1550nm. In actual optical cable maintenance work, both wavelengths are generally tested and compared. For positive gain phenomena and over-distance lines, two-way test analysis and calculation must be performed to obtain good test conclusions. 3) Clean the fiber optical connectors. Before connecting the optical fiber union to the OTDR, it must be carefully cleaned, including the output connector of the OTDR and the union under test. Otherwise, the insertion loss will be too large, the measurement will be unreliable, the curve will be too noisy, and the measurement may even become impossible. It may also Damage the OTDR. Avoid using cleaning agents or refractive index matching fluids other than alcohol, as they can dissolve the adhesive within the fiber optic connector.

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We have been designing, manufacturing and supplying passive components for fiber optical networks since 2003. Everything we do in FCST is designed to provide efficient, simple and innovative solutions to solve complicated tasks.

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lFTTH ODN Solution

lUnderground Cable Installation Solution

lAerial Cable Installation Solution

lFiber Tools & Test Solution

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