Using principal modes (PMs) can avoid the inter-mode crosstalk in fiber-optic communication and reduce the complexity of digital signal processing. In this paper, a new detection method for PMs based on spatially and spectrally resolved imaging (S 2) is used to recover their intensity distributions and inter-mode dispersion parameters. This method collects the optical interference information on a two-dimensional plane at different frequencies. The collected data can be used to characterize the principal modes, including their patterns and differential mode group delays. Due to the frequency invariance of PMs even in mode coupling state, which is studied carefully, this proposed method is shown to be robust. Analyses based on a four-mode fiber show that the distributed fluctuation of the coupling coefficients break the frequency invariance of PMs. We experimentally measure the mode characteristics of a four-mode fiber with S 2 method. The results show that the mode group delays of degenerate modes can be separated in mode coupling state, which is exactly appropriate for the modified measurement method.

Based on the polarization interference technique, we propose a modified method for simultaneously measuring the beat length of all guided modes in a polarizationmaintaining few-mode fiber (PM-FMF). We experimentally demonstrate the effectiveness of our proposed method on a 3-mode PANDA-type PM-FMF. The simultaneous measurement results agree well with the results obtained by one-by-one measurement process. What's more, the modified measurement method is easier to be implemented and more scalable to a larger mode number.

We present simple, low loss and broadband mode scramblers for mode division multiplexed (MDM) transmission based on few-mode fibers. By simply shortening the length of the long-period fiber grating (LPFG), the optical bandwidth is significantly enhanced and >260 nm bandwidth is predicted in our simulations with a grating length of 0.613 cm. In an experimental demonstration we fabricate a mechanically induced LPFGs using a commercially available 3-dimentional (3D) printing technique and wideband operation is confirmed over the C band with a low loss (0.2 dB) and low mode dependent loss (0.1 dB).

Microchip electrophoresis (ME) is an ion detection system with low cost and portability, which is suitable for online analysis of environmental samples. However, the unresolved peaks in the detection signal of complex samples seriously affect the measurement accuracy of sample concentration. In this article, an efficient unresolved peaks analysis algorithm is proposed, which is based on the sigmoidal membership function, Lévy flight, and slime mould algorithm (SLSMA). First, the hyperbolic tangent function in the original slime mould algorithm (SMA) is replaced by the sigmoidal membership function to enhance the global optimization capability. Second, we use the Lévy flight sequences to further enhance the convergence speed of the SMA algorithm. Then, the performance of SLSMA is tested using synthetic peaks with different resolutions and noise levels. Finally, ME peaks are used to further validate the application of the proposed algorithm. The results show that the proposed algorithm has higher computational efficiency and can be used for the analysis of ME peaks.

We propose a new type of all-fiber mode scrambler for mode division multiplexed data transmission based on few mode fibers. By randomly placing multiple point-loads along the fiber length, low loss and wideband mode coupling is obtained amongst all the guided modes. The effect of mode coupling is simulated from a single point-load to multiple point-loads with a specific focus on the insertion loss and wavelength dependence. In an exemplar experimental demonstration we present a mode scrambler for step-index two mode fibers incorporating 150 randomly located point-loads. Uniform mode coupling is achieved over the C band with an insertion loss of less than 1 dB.