Created by sebastien.popoff on 08/09/2020


Controlling multimode laser modes using wavefront shaping inside the cavity

[X. Wei et al., Light Sci. Appl., 9 (2020)]

Multimode cavity lasers, such as multimode fiber lasers, are attractive for the opportunity they offer to generate high energy pulsed lasers, provided that one can achieve spatiotemporal mode-locking. However, it can be complicated to control the laser properties as 1) spatiotemporal dispersion, nonlinearity, gain and loss can nonlinearly interact, and 2) dispersion and mode coupling in such a system are difficult to predict or control. In a typical wavefront shaping experiment, one modulates the output of a laser beam, which can come at the cost of a significant energy loss, and only allows to control the spatial profile of the beam. In this paper, the authors use a spatial light modulator, but inside the laser cavity to modulate its boundary conditions. Using a genetic algorithm, they are able to efficiently control the laser properties, namely the output power, the output mode profile, the optical spectrum, and mode-locking.

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Created by sebastien.popoff on 25/08/2020


Using prior information for speeding up the measurement of fiber transmission matrices

[S. Li et al., arxiv, 2007.15891, (2020)]

Due to disorder and dispersion, knowing the transmission matrix of a multimode fiber is usually required to reconstruct an input image for endoscopic applications. In the general case, its characterization for a fiber allowing \(N\) guided modes requires at least \(N\) complex measurements. However, we usually have additional information, the most common one being that the matrix is never totally random, and usually sparse, when expressed in the mode basis. In this study, the authors use such prior information to reduce drastically the number of measurements for the transmission matrix estimation using the framework of compressed sensing. They demonstrate the validity of such an approach for endoscopic imaging through multimode fibers.

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Created by sebastien.popoff on 11/08/2020

Job offers

Postdoctoral position at the Langevin Institute

Wavefront shaping and study of light propagation in disordered multimode fibers

We are recruiting a postdoc for 1+ year(s) to work on the study of light propagation in multimode fibers for telecommunication applications using wavefront shaping. Join un in Paris!

Contact: Sébastien Popoff - sebastien.popoff(at)

More information here.

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Created by hugo.defienne on 10/08/2020


Unscrambling entanglement through a complex medium

[N. H. Valencia, S. Goel, W. McCutcheon, H. Defienne and M. Malik, Nature Physics (2020)]

Quantum properties of light may enable unconditionally secure optical communications. In this respect, high-dimensional entangled states offer a way of exceeding the limitations of current approaches to quantum communication (e.g. larger information capacity and increased noise resilience). For example, the orbital angular momentum of photons was first used to establish high-dimensional quantum key distribution (HD-QKD) protocols in free-space, but with a limited range due to diffraction and the presence of atmospheric turbulence. Alternatively, multimode optical fibers (MMF) can be used to transport information encoded in parallel across many modes over large distances, and with limited losses. However, the complex mode mixing process occurring during light propagation through the fiber scrambles the encoded information, making it unusable by the receiver. In their work, N. H. Valencia and co-workers demonstrate the transport of six-dimensional spatial-mode entanglement through a 2m-long commercial MMF, by compensating the random mode mixing effect using a transmission matrix-based wavefront-shaping technique. Such an ability to certify the presence of high-dimensional entanglement between two parties (Alice and Bob) is an essential step towards the implementation of practical HD-QKD protocols in optical fibers.

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