Principal modes in multimode fibers: exploring the crossover from weak to strong mode coupling

Abstract

We present experimental and numerical studies on principal modes in a multimode fiber with mode coupling. By applying external stress to the fiber and gradually adjusting the stress, we have realized a transition from weak to strong mode coupling, which corresponds to the transition from single scattering to multiple scattering in mode space. Our experiments show that principal modes have distinct spatial and spectral characteristic in the weak and strong mode coupling regimes. We also investigate the bandwidth of the principal modes, in particular, the dependence of the bandwidth on the delay time, and the effects of the mode-dependent loss. By analyzing the path-length distributions, we discover two distinct mechanisms that are responsible for the bandwidth of principal modes in weak and strong mode coupling regimes. Their interplay leads to a non-monotonic transition of the average principal mode bandwidth from weak to strong mode coupling. Taking into account the mode-dependent loss in the fiber, our numerical results are in qualitative agreement with our experimental observations. Our study paves the way for exploring potential applications of principal modes in communication, imaging and spectroscopy.

Coherent Wave Propagation in Multimode Systems with Correlated Noise

“…Optical fibers have revolutionize many modern technologies ranging from medical imaging and information-transfer technologies to modern communications. Along these lines, multi-mode fibers (MMFs) [13][14][15][16] have recently been exploited as alternatives to single mode fibers-the latter experiencing information capacity limitations, imposed by amplifier noise and fiber non-linearities. What makes MMFs attractive is the possibility to utilize the multiple modes as extra degrees of freedom in order to carry additional information -thus increasing the information capacity of a single fiber.…”

Space-time adaptive control of femtosecond pulses amplified in a multimode fiber

“…The two spatial PMs are associated with the shortest pulses, and hence the highest peak powers, that can be delivered by the MMF. In the case of weak coupling, [17] shows that the fastest PMs are composed of low order fiber eigenmodes and are characterized by few wide speckle grains close to the core center. We modeled the propagation through the MMF amplifier according to the concatenated sections approach [17,21] with ten straight multimode fiber sections connected by unitary random coupling matrices.…”

“…Without coupling, the PMs simply correspond to the MMF eigenmodes. PMs were studied recently in the weak and strong mode coupling regimes [17]. However, the use of a PM to deliver a short pulse at the end of a MMF has not been yet reported.…”

Multimode-fiber-based single-shot full-field measurement of optical pulses

“…As these degrees of freedom are coupled, an MMF provides a versatile and multi-functional platform for communication [3,4], imaging [5][6][7][8] and sensing applications [10][11][12][13][14][15][16]. The abundant spatial degrees of freedom have been utilized for controlling linear [17][18][19][20] and nonlinear light propagation [21][22][23][24][25] in an MMF. The spatial, temporal, spectral or polarization states of transmitted light are manipulated by shaping the spatial wavefront of an incident beam.…”