RESUMO
Mode-group multiplexing (MGM) can increase the capacity of short-reach few-mode optical fiber communication links while avoiding complex digital signal processing. In this paper, we present the design and experimental demonstration of a novel mode-group demultiplexer (MG DeMux) using Fabry-Perot (FP) thin-film filters (TFFs). The MG DeMux supports low-crosstalk mode-group demultiplexing, with degeneracies commensurate with those of graded-index (GRIN) multimode fibers. We experimentally demonstrate this functionality by using a commercial six-cavity TFF that was intended for 100 GHz channel spaced wavelength-division multiplexing (WDM) system.
RESUMO
We present a few-mode frequency-modulated receiver for light detection and ranging (LiDAR). We show that using a few-mode local oscillator (LO) with spatial modes at different frequencies at the receiver can significantly improve the performance of the LiDAR detection range. A preferred receiver architecture features LO modes with unequal frequency separations based on optical orthogonal codes (OOC) to allow range detection via cross correlation. The required signal-to-noise ratio (SNR) for the frequency-modulated continuous wave (FMCW) LiDAR decreases with the number of LO modes. This receiver can have a potential impact in the area of automotive LiDARs.
RESUMO
We evaluate the coupling efficiency from free space to few-mode fibers (FMF). A theoretical coupling model is developed based on the imaging properties of free-space modes and the inner products between the free-space modes and the FMF modes. Numerical results for six- and ten-mode free-space-to-FMF coupling are presented. It is found that in order to maximize the total coupling efficiency, the size of the highest-order free-space and fiber modes should be approximately matched, and there is an optimum value for the V number of the FMF. In addition, the axial alignment tolerance for free-space-to-FMF coupling is more stringent than for single-mode cases.
