A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

An optical vortex having an isolated point singularity is associated with the spatial structure of light waves. A polarization vortex (vector beam) with a polarization singularity has spatially variant polarizations. A phase vortex with phase singularity or screw dislocation has a spiral phase front. The optical vortex has recently gained increasing interest in optical trapping, optical tweezers, laser machining, microscopy, quantum information processing, and optical communications. In this paper, we review recent advances in optical communications using optical vortices. First, basic concepts of polarization/phase vortex modulation and multiplexing in communications and key techniques of polarization/phase vortex generation and (de)multiplexing are introduced. Second, free-space and fiber optical communications using optical vortex modulation and optical vortex multiplexing are presented. Finally, key challenges and perspectives of optical communications using optical vortices are discussed. It is expected that optical vortices exploiting the space physical dimension of light waves might find more interesting applications in optical communications and interconnects.

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Advances in communications using optical vortices

The growing maturity of integrated photonic technology makes it possible to build increasingly large and complex photonic circuits on the surface of a chip. Today, most of these circuits are designed for a specific application, but the increase in complexity has introduced a generation of photonic circuits that can be programmed using software for a wide variety of functions through a mesh of on-chip waveguides, tunable beam couplers and optical phase shifters. Here we discuss the state of this emerging technology, including recent developments in photonic building blocks and circuit architectures, as well as electronic control and programming strategies. We cover possible applications in linear matrix operations, quantum information processing and microwave photonics, and examine how these generic chips can accelerate the development of future photonic circuits by providing a higher-level platform for prototyping novel optical functionalities without the need for custom chip fabrication. The current state of programmable photonic integrated circuits is discussed, including recent developments in their building blocks, circuit architectures, electronic control and programming strategies, as well as different application spaces.

https://biblio.ugent.be/publication/8677857/file/8677861.pdf

Programmable photonic circuits.

Wave front shaping, the ability to manipulate light fields both spatially and temporally, in complex media is an emerging field with many applications. This review summarizes how insights from mesoscopic scattering theory have direct relevance for optical wave control experiments and vice versa. The results are expected to have an impact on a number of fields ranging from biomedical imaging to nanophotonics, quantum information, and communication technology.

Light fields in complex media: Mesoscopic scattering meets wave control

Multi-plane light conversion is a method of performing spatial basis transformations using cascaded phase plates separated by Fourier transforms or free-space propagation. In general, the number of phase plates required scales with the dimensionality (total number of modes) in the transformation. This is a practical limitation of the technique as it relates to scaling to large mode counts. Firstly, requiring many planes increases the complexity of the optical system itself making it difficult to implement, but also because even a very small loss per plane will grow exponentially as more and more planes are added, causing a theoretically lossless optical system, to be far from lossless in practice. Spatial basis transformations of particular interest are those which take a set of spatial modes which exist in the same or similar space, and transform them into an array of spatially separated spots. Analogous to the operation performed by a diffraction grating in the wavelength domain, or a polarizing beamsplitting in the polarization domain. Decomposing the Laguerre-Gaussian, Hermite-Gaussian or related bases to an array of spots are examples of this and are relevant to many areas of light propagation in free-space and optical fibre. In this paper we present our work on designing multi-plane light conversion devices capable or operating on large numbers of spatial modes in a scalable fashion.

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Laguerre-Gaussian mode sorter.

We designed and built a new type of spatial mode multiplexer, based on Multi-Plane Light Conversion (MPLC), with very low intrinsic loss and high mode selectivity. In this first demonstration we show that a typical 3-mode multiplexer achieves a mode selectivity better than −23 dB and a total insertion efficiency of −4.1 dB (optical coating improvements could increase efficiency to −2.4 dB), across the full C-band. Moreover this multiplexer is able to perform any mode conversion, and we demonstrate its performance for the first 6 eigenmodes of a few-mode fiber: LP01, LP11a, LP11b, LP02, LP21a and LP21b.

Efficient and mode selective spatial mode multiplexer based on multi-plane light conversion.

Efficient and mode selective spatial mode multiplexer based on multi-plane light conversion

We report a 10 spatial mode multiplexer based on the technique of Multi-Plane Light Conversion. The device shows average 4.4 dB insertion loss and 21 dB mode selectivity across the full C+L-band.

Mode selective 10-mode multiplexer based on multi-plane light conversion

We designed and built a new type of spatial mode multiplexer, based on Multi-Plane Light Conversion (MPLC), with very low intrinsic loss and high mode selectivity. In this first demonstration we show that a typical 3-mode multiplexer achieves a mode selectivity better than -23 dB and a total insertion efficiency of -4.1 dB (optical coating improvements could increase efficiency to -2.4 dB), across the full C-band. Moreover this multiplexer is able to perform any mode conversion, and we demonstrate its performance for the first 6 eigenmodes of a few-mode fiber: LP$_{01}$, LP$_{11\mathrm{a}}$, LP$_{11\mathrm{b}}$, LP$_{02}$, LP$_{21\mathrm{a}}$ and LP$_{21\mathrm{b}}$.

Efficient and mode selective spatial mode multiplexer based on Multi-Plane Light Conversion

We demonstrate 4 × 10 Gbit/s error-free bidirectional transmission over 2 km of conventional OM1 graded-index multimode fiber using OOK modulation and direct detection. We also perform field transmission to show reach and capacity boosts on legacy multimode infrastructure. Such transmission is enabled by selective mode group division multiplexing, based on multi-plane light conversion over 4 mode groups of the multimode fiber.

Bertrand Denolle

Papers

Efficient and mode selective spatial mode multiplexer based on multi-plane light conversion.

Efficient and mode selective spatial mode multiplexer based on multi-plane light conversion

Mode selective 10-mode multiplexer based on multi-plane light conversion

Efficient and mode selective spatial mode multiplexer based on Multi-Plane Light Conversion

4×10 Gbit/s bidirectional transmission over 2 km of conventional graded-index OM1 multimode fiber using mode group division multiplexing