A present embodiment relates to a MDL measurement method and the like including a structure for enabling MDL measurement without increasing a processing load. The present embodiment sequentially executes, for N (2) spatial modes, light-input operation of inputting light of a predetermined intensity to an arbitrary spatial mode, and intensity measurement operation of measuring an output light intensity of each of the N spatial modes including the arbitrary spatial mode, to generate a transfer matrix relating to transmission loss in an optical fiber as a measurement target, and determine at least a linear value of MDL per unit fiber length by using each component value of the generated transfer matrix.

An on-silicon integrated test structure for characterizing the PDL of a 1 to 2 fiber/silicon optical coupler with a two-dimensional diffraction grating (2DGC), includes the 2DGC to be tested configured as an output coupler, mirrored with another 1 to 2 fiber/silicon optical coupler configured as an input coupler, via planar waveguides coupling their respective guided optical terminals. An adjustable phase shifter is arranged at one of these waveguides. A p- or s-polarized optical signal is input via the input coupler. The adjustable phase shifter is controlled to apply a pure phase shift between 0 and to the optical signal propagating in this waveguide. The optical signal input to the 2DGC under test then sweeps through all the mixed polarization states. The variation in optical transmission in the 2DGC under test during this sweep gives the PDL.

A digital processor (DP) is configured to obtain a temporal sequence of digital phase distortion measurements of a first optical signal received by a coherent optical receiver (COR) from an optical fiber link, where the first optical signal co-propagates with a second, power-modulated, optical signal in different frequency channels. The DP is configured to estimate a cross-correlation between the temporal sequence of digital measurements and a temporal sequence of powers of the second optical signal for a plurality of relative time shifts between the sequences, and to identify a location along the optical fiber link based on a magnitude of the cross-correlation exceeding a threshold for a particular time shift.

Disclosed in the present invention is a polarity, insertion loss and return loss tester for a multi-core optical fiber, the tester comprising an integrating sphere, wherein the integrating sphere has an incident light channel, the incident light channel comprising an incidence end, an integrating sphere cavity and a receiving end, which are sequentially in communication with each other; the integrating sphere is further provided with a reflected light channel in communication with the incident light channel, a lens assembly and an imaging device being provided in the reflected light channel; a semi-transparent and semi-reflective reflector is fixedly arranged in the incident light channel, or a movable reflective mirror is provided in the incident light channel; and incident light is reflected by the reflective mirror or the semi-transparent and semi-reflective reflector, and is then converged by the lens assembly onto the imaging device for imaging. In the present invention, return loss testing, insertion loss testing, and polarity testing of a winding-free multi-core optical fiber patch cord are carried out on one apparatus, such that the cost is reduced, and the efficiency is improved. Moreover, the reliability and accuracy of the measurement of an insertion loss value and a return loss value are also ensured on the premise of improving efficiency.