Abstract: An optical fiber measurement system includes an optical time-domain reflectometer, a wavelength division multiplexer, and a signal generator. The signal generator sends a signal light ray to the wavelength division multiplexer. The optical time-domain reflectometer sends two measurement light rays whose wavelengths are respectively longer than and shorter than a wavelength of the signal light ray to the wavelength division multiplexer. The wavelength division multiplexer combines the two measurement light rays and the signal light ray, sends a combined light ray to an optical fiber, and sends a light ray returned by the optical fiber to the optical time-domain reflectometer, so that the optical time-domain reflectometer determines performance of the optical fiber based on the returned light ray.

Abstract: Embodiments of an optical amplification apparatus are disclosed which include a first optical amplifier, a second optical amplifier, and a mode exchanger. The first optical amplifier is connected to an input port of the mode exchanger, and the second optical amplifier is connected to an output port of the mode exchanger. The first optical amplifier is configured to amplify optical signals carried in a plurality of transmission modes of a few-mode fiber, the plurality of transmission modes of the few-mode fiber may be grouped into N groups, each group includes two transmission modes, and N is a positive integer greater than or equal to 1. The mode exchanger is configured to exchange the two transmission modes carrying optical signals in each group. The second optical amplifier is configured to amplify the optical signals that are carried in the two transmission modes in each group and whose modes are exchanged.

Abstract: A communication system is provided. The communication system may include few mode fibers of at least two spans and a mode converter. The few mode fiber is configured to transmit M received mode groups, where group delays of the M mode groups during transmission in the few mode fiber are symmetrically distributed about a center. The mode converter is configured to: receive the M mode groups from the few mode fiber, perform mode group exchange between a first mode group and a second mode group in the M mode groups to obtain M exchanged mode groups, where a group delay of the first mode group and a group delay of the second mode group are symmetric about the center.

Abstract: A fiber amplifier is provided, including a pump laser (202), a pump and signal combiner (203), and a few-mode doped fiber (204). The pump laser (202) is configured to output pump light. The pump and signal combiner (203) is configured to couple input few-mode signal light and the pump light into the few-mode doped fiber (204). Refractive indexes of a fiber core of the few-mode doped fiber (204) are distributed to be gradient along a radial direction of a cross section, the fiber core is etched with periodic gratings along an axial direction, and periods of the gratings satisfy a phase matching condition. The fiber amplifier achieves strong coupling and co-amplification between optical signal modes, thereby reducing a differential gain between mode groups.