Multimeter Application: Fiber Optic Test Parameters and Test Methods
Key physical parameters of fiber optic links
attenuation:
1. Attenuation is the reduction of optical power during light transmission along the optical fiber.
2. Calculation of the total attenuation of the optical fiber network: Optical fiber loss (LOSS) refers to the ratio of the power Powerout at the output end of the optical fiber to the power Powerin when transmitted to the optical fiber.
3. The loss is proportional to the length of the fiber, so the total attenuation not only indicates the fiber loss itself, but also reflects the length of the fiber.
4. Fiber loss factor (α): In order to reflect the characteristics of fiber attenuation, we introduce the concept of fiber loss factor.
5. Measure attenuation: Because the fiber is connected to the light source and the optical power meter inevitably introduces additional losses. Therefore, during on-site testing, you must first set the test reference point of the tester (ie, zero setting). There are several methods for testing reference points, which are mainly selected based on the link objects being tested. In optical fiber cabling systems, since the length of the optical fiber itself is usually not long, more attention will be paid to the connection in the testing method. On the instrument and test jumpers, the method is more important.
Return loss: Reflection loss is also called return loss. It refers to the decibel ratio of the back-reflected light to the input light at the fiber connection. The larger the return loss, the better, in order to reduce the impact of reflected light on the light source and system. Impact. The method to improve return loss is to process the fiber end face into a spherical or oblique spherical surface as much as possible. This is an effective method to improve return loss.
Insertion loss: Insertion loss refers to the decibel ratio of the output optical power to the input optical power after the optical signal in the optical fiber passes through the movable connector. The smaller the insertion loss, the better. Insertion loss is measured in the same way as attenuation.
To measure the loss of a fiber optic link, calibrated, stable light is emitted at one end and the output power is read at the receiving end.
This equipment constitutes an optical loss tester. When a light source and power meter are combined into one instrument, it is often called an optical loss tester (some people also call it an optical multimeter). When we measure the loss of a link, one person needs to operate the test light source at the transmitting end and another person uses an optical power meter to measure at the receiving end. In this way, we can only get the loss value in one direction.
Usually, we need to measure the loss in two directions (because of the existence of directional connection loss or due to the asymmetry of fiber transmission loss). At this time, technicians must exchange equipment and perform measurements in another direction. But what should we do when they are separated by more than ten floors or dozens of kilometers? Obviously, if these two people each have a light source and an optical power meter, then they can measure on both sides at the same time. The current optical fiber test kits used for certification testing can realize bidirectional dual-wavelength testing, such as: Fluke's CertiFiber and DSP cable test series FTA optical fiber test packages.
