Search

This review essay addresses the major themes of Ghanaian theologian Kwame Bediako’s thought, as presented in Tim Hartman, Kwame Bediako: African Theology for a World Christianity. Bediako advocated examining the traditional spirituality of African peoples, studying the Bible in vernacular languages, and asking how the person and work of Jesus Christ engage local cultures. He insisted that Western theology was not central and normative to the Christian faith, and that African theology provided a better model for the development of contextual theologies worldwide.

We introduce recently developed space division multiplexing (SDM)-associated technologies into optical wireless communications (OWC) and propose to use incoherent and low-coherence spatial modes to realize optical broadcasting with reliable performance by mitigating coherent interference. We experimentally demonstrate reconfigurable optical beam steering using a programmable multi-plane light conversion (MPLC)-based mode multiplexer (MMUX) and realize point-to-multi-point optical wireless communications with low-loss up-link optical beam combining and reach extension using multimode fiber (MMF). Both incoherent and low-coherence spatial modes can be generated employing cost-efficient components such as a multimode vertical cavity surface emitting laser (MM-VCSEL) and broadband amplified spontaneous emission (ASE) noise source.

We designed, fabricated, and tested a 90° optical hybrid using multiplane light conversion. The device supports an octave of bandwidth (900–1800 nm) in simulations. The measured phase errors are below 3° for free space output, and below 8° with a fiber array output, across a measurement bandwidth of 390 nm. The fully-packaged device (with input and output fiber arrays) has a measured insertion loss of 5.52 dB at 1550 nm. A high-speed transmission experiment with QPSK format was conducted to verify the performance of the fully-packaged device.

Lossless linear wave propagation is symmetric in time, a principle which can be used to create time reversed waves. Such waves are special “pre-scattered” spatiotemporal fields, which propagate through a complex medium as if observing a scattering process in reverse, entering the medium as a complicated spatiotemporal field and arriving after propagation as a desired target field, such as a spatiotemporal focus. Time reversed waves have previously been demonstrated for relatively low frequency phenomena such as acoustics, water waves and microwaves. Many attempts have been made to extend these techniques into optics. However, the much higher frequencies of optics make for very different requirements. A fully time reversed wave is a volumetric field with arbitrary amplitude, phase and polarisation at every point in space and time. The creation of such fields has not previously been possible in optics. We demonstrate time reversed optical waves with a device capable of independently controlling all of light’s classical degrees of freedom simultaneously. Such a class of ultrafast wavefront shaper is capable of generating a sequence of arbitrary 2D spatial/polarisation wavefronts at a bandwidth limited rate of 4.4 THz. This ability to manipulate the full field of an optical beam could be used to control both linear and nonlinear optical phenomena., Truly arbitrary spatiotemporal wavefront shaping has many potential applications in optics. Here the authors develop a system capable of arbitrary waveshaping to the extent of full time reversal of spatiotemporal optical beams.

We demonstrate a device for measuring the generalized Stokes parameters of a six spatial mode beam. The device is a single-shot wavefront sensor measuring spatial complex amplitude and coherence without an external phase reference.

Higher-order Poincaré sphere (HOPS) beams with spatially variable polarization and phase distributions are opening up a host of unique applications in areas ranging from optical communication to microscopy. However, the flexible generation of these beams with high peak power from compact laser systems remains a challenge. Here, we demonstrate the controlled generation of HOPS beams based on coherent beam combination from an Yb-doped multicore fiber (MCF) amplifier. Using a spatial light modulator to adaptively adjust the wavefront and polarization of the signals seeded into the individual cores of the MCF various structured beams (including cylindrical vector beams and first- and second-order vortex beams) were generated with peak powers up to 14 kW for ∼ 92 ps pulses.

Optical angular momentum (OAM)-based structured light beams provide an additional degree of freedom for practical applications ranging from optical communication to laser-based material processing. Many techniques exist for generating such beams within laser sources and these primarily rely upon the use of specially designed optical components that limit laser power scaling and ready tunability of the topological charge and polarization of the output OAM beams. Here we show that some of these limitations can be overcome by employing a computer controlled reflective phase-only spatial light modulator to adaptively tailor the input (and subsequent output) beam wavefront and polarization in a few-mode fiber amplifier. In this way modal-coupling-induced beam distortion within the fiber amplifier can be mitigated and we are able to generate at will any desired supported spatial mode guided in the fiber, including conventional linearly polarized (LP) modes, scalar OAM modes, and cylindrical vector modes, at average powers > 10 W and with a peak power of > 11 kW . Our results pave the way to the realization of practical high-power structured laser sources with tunable chirality and polarization.

We describe an approach capable of generating structured light beams from a compact laser source based on the coherent combination of multiple tailored Gaussian beams emitted from a multicore fiber (MCF) amplifier. We report a proof-of-concept structured light generation experiment, using a cladding-pumped 7-core MCF amplifier as an integrated parallel amplifier array and a spatial light modulator to actively control the amplitude, polarization and phase of the signal light input to each fiber core. We demonstrate the generation of various structured light beams including high-order linearly polarized spatial fiber modes, cylindrical vector beams and helical phase front optical vortex beams.

We present a multi-plane light conversion based mode multiplexer supporting 1035 Hermite-Gaussian modes. It is characterized using spot scanning at the input and digital holography at the output.

We demonstrate a device for measuring the generalized Stokes parameters of a six spatial mode beam. The device is a single-shot wavefront sensor measuring spatial complex amplitude and coherence without an external phase reference.

We demonstrate how to generate arbitrary optical vector fields in the full C band (1535nm – 1570nm), with a new class of ultrafast wavefront shaper. A device capable of generating a sequence of arbitrary 2D spatial/polarization wavefronts at a bandwidth-limited rate of 4.4 THz.