Application of OTDR Optical Time Domain Reflectance Technology in Optical Fiber Communication

The development of optical fiber communication has played an important role in China's economic construction. Optical fiber communication has incomparable advantages: the transmission frequency is wide and the loss is less. The construction of optical fiber communication started in the 1990s and has been developed on a large scale.

As a transmission network carrying a large amount of information, optical fiber communication has certain risks and instability. In order to ensure the smooth operation and safety of optical fiber communication, it is necessary to develop a tool or instrument that can accurately measure the characteristics of optical fiber communication. In order to meet the requirements for optical fiber diagnosis in optical fiber communication, an optical time-domain reflectometer (OTDR) with back Rayleigh scattering as the measurement signal was produced.

OTDR technology can detect the link loss and health status of the optical fiber because it has the ability to test the loss at different positions of the entire optical fiber link, so that the health status of the optical cable can be evaluated based on the loss at different positions measured by the OTDR.

According to the intensity of the back Rayleigh scattered light generated by the pulsed light in the fiber, the attenuation along the fiber can be measured at the single end of the fiber; according to the time difference between the arrival time of the scattered light and the launch time of the pulsed light, the attenuation points of the fiber can be measured Perform spatial positioning. The two characteristics of single-ended, non-destructive fiber attenuation measurement and "optical radar" effect make OTDR technology not only quickly replace conventional methods, but also show unique superior performance in the application of field fiber fault diagnosis and location.

Researchers continue to improve and perfect the OTDR measurement technology, so that its measurement dynamic range, spatial resolution, signal-to-noise ratio, automatic protection, automatic identification and measurement performance have been greatly improved. The OTDR system can solve the health problems of optical fiber communication operations to a large extent.

OTDR uses the backscattering phenomenon generated when optical pulses are transmitted in the optical fiber to inject high-power narrow pulse light into the fiber under test, and then detect the scattered light power returning along the fiber axis at the same end, as shown in the figure below. When the incident light pulse is transmitted in the line, Rayleigh scattered light and Finier reflection light will be generated along the way. Most of the Rayleigh scattered light will be refracted into the cladding and attenuated. Among them, the back Rayleigh scattering is opposite to the propagation direction of the light pulse. The light will be transmitted along the optical fiber to the light inlet port of the line. The wavelength of Rayleigh scattered light is the same as the wavelength of incident light, and its optical power is proportional to the incident light power at the scattering point. Measuring the power of the back Rayleigh scattered light returning along the axis of the optical fiber can obtain information about the transmission loss along the optical fiber, thereby measuring the attenuation of the optical fiber.

In the process of optical time domain reflectometer (OTDR) testing the optical cable, the instrument injects a higher power laser or optical pulse from one end of the optical cable, and receives the reflected signal through the same side. When the light pulse is transmitted through the optical cable, part of the scattering and reflection will return to the transmitting end. Optical Time Domain Reflectometer (OTDR) will only measure the high intensity of the reflected optical signal. By recording the time from transmission to return of the signal and the transmission speed of the signal in the glass material, the length of the optical cable can be calculated by the formula .

Compared with the power supply and electric energy meter that can directly measure the loss of optical cable equipment, the optical time domain reflectometer (OTDR) works indirectly. The Optical Time Domain Reflectometer (OTDR) is made according to the principle of backscattering and Fresnel reverse of light. It uses the backscattered light generated when the light propagates in the optical fiber to obtain the attenuation information, thereby indirectly measuring the loss and failure of the optical cable Location..