The Difference between VFL,OPM and OTDR

VFL

Visual Fault Locator is the most commonly used, easy to carry and easy to operate. Use a Visual Fault Locator to illuminate the optical fiber connector in the direction of the optical cable, and adjust the button to emit light all the time or pulse light. The other end of the optical cable arranges a person to stare at it. If it is glows, that means the optical fiber is connected.

Visual Fault Locator is very convenient to use. It can not only test the on-off of the optical fiber, but also find the line sequence corresponding to the two ends of the optical fiber without marking. The special Visual Fault Locator for optical fiber test bought for a few hundred yuan can play 20 kilometers.

Although the Visual Fault Locator is simple and convenient to use, its function is also very simple. It can only measure the on-off, and there is no data response.

OPM

Optical Power Meter refers to an instrument used to measure the relative loss of absolute optical power or optical power through a piece of optical fiber. The optical power meter is also relatively cheap, and you can buy it for a few dollars. When the builders finish the cables construction, then connect one end of the optical fiber with light source.  The other end is plugged into the optical power meter to check the light loss whether it is up to the standard and need to rectify or not. Sometimes Broadband maybe have no signal, serviceman need to use an OPM to connect the optical fiber to check the signal and verify whether the signal is weakened due to the bending.

The total amount of loss or attenuation in the observed optical fiber link can be calculated by using the OPM. The OPM detects and measures the signal's power level at the B end of the optical fiber after the stable light source at the A end of the fiber emits a signal made up of continuous optical waves at a particular wavelength.

OTDR

Optical Time Domain Reflector (OTDR) is an instrument that understands the uniformity, defects, fractures, joint coupling and other properties of optical fibers through the analysis of measurement curves. It is made according to the backward scattering and Fresnel reverse principle of light. It uses the backward scattering light generated when the light propagates in the optical fiber to obtain attenuation information. It can be used to measure the attenuation of optical fiber, joint loss, optical fiber fault point positioning and understand the loss distribution along the length of the optical fiber.

OTDR has two disadvantages.

Firstly, it is expensive.

Secondly, it has blind spot.

OTDR is inaccurate if the optical cable is too short, say, less than 100 meters. This is because OTDR cannot identify or precisely locate event sites and fault points in optical fiber links within a specified distance when it detects optical fiber links due to reflection (or time). We refer to this distance as the blind spot. It will also be constrained by its loss measurement precision and measurement range when testing with OTDR since the OTDR blind region will unavoidably affect the test accuracy at the starting point and the finish.

Compared with the optical power meter, OTDR mainly has two more functions:

1. OTDR can generate test curves and analyze each time on the curve to form different events.

2. OTDR can measure the length of the measured optical fiber and give the optical fiber length data.