FBG Fiber Optic Reflector is the Ideal Optical End of FTTX Network Link Monitoring

Fiber optic reflector, also known as fiber Bragg grating filter, is usually installed in the front end of optical network ONU. Combined with OTDR equipment, optical link point-to-point (PTP) or point-to-multipoint (PTMP) network monitoring can be realized, and network anomalies can be reflected quickly and accurately.

Ⅰ. What is fiber grating?

FBG is called Fiber Bragg Grating, which is also referred to as Fiber Grating. Fiber grating is a kind of diffraction grating, which mainly increases the probability of refraction of the optical fiber core inside it through certain methods, so as to form a kind of all-fiber device formed by periodic modulation.

Fiber grating has the characteristics of small volume, good wavelength selectivity, good compatibility, and mature production process, good practicability and low cost, so it is widely used in the field of communication and sensing, and devices based on fiber grating become the ideal key devices in the all-optical network.

The FBG reflector uses the wavelength selectable feature of the fiber grating to embed the fiber grating in the adapter. It can be conveniently installed in the front end of the     optical network (ONU), and combined with optical time domain reflector (OTDR), it can quickly and accurately detect optical network faults. Due to the excellent wavelength selection characteristics of fiber Bragg grating, it is anti-electromagnetic interference, and the central wavelength shift is very small with the change of external temperature. When the coverage range and depth of optical network are increasing, the fault point of the entire optical network can be detected quickly and accurately.

Ⅱ. Application of fiber optic reflector

With the application of optical splitters in passive optical network (PON) network, the complexity of ODN deployment environment is increased. FTTX terminal Splitter applies trunk optical cable signal Splitter, and meanwhile, the identification difficulty of OTDR technology for attenuation events on ODN branch optical fiber is increased. The application of fiber optic reflector is a wavelength selective reflector based on this environment, which aims to improve the fast and accurate detection of optical link fault events by OTDR.

Fiber reflector is usually installed on the ONU side. OTDR can detect the optical signal intensity reflected by this reflector and judge whether the optical fiber in the link is damaged or broken by comparing the return loss value between the normal line and the faulty link. However, the normal working wavelength of passive optical network (PON) system does not meet the reflector condition, so the reflector can achieve the monitoring function without interference or loss of flow. Grating reflection wavelength of 1650nm fiber optic reflector is 1645-1650nm, and the light signal satisfying this Bragg condition will return along the input path, and all other wavelengths (1260-1625nm) can pass through. If the fiber Bragg grating reflection peak of the band can be detected in the input optical signal section, the transmission path can be judged to be normal. Otherwise, it is abnormal.

End-to-end OTDR measurements from OLT to ONT are often difficult because of the high losses and complex networks that splitters introduce. The application of fiber reflector is an economical and effective scheme to help OTDR detection, and it is an ideal way to realize real-time end-to-end (OLT to ONT) monitoring of optical network in FTTX network.