Continuously tuneable single electrode pair liquid crystal optical vortex generators.

In this work, we demonstrate the use of two-photon polymerization direct laser writing in the production of continuously tuneable optical vortex beam (OV) generators in a liquid crystal (LC) layer sandwiched between glass substrates. Results are presented that show how an OV generator can be inscribed into a 20 μm-thick LC layer and how the order of the OV beam can be tuned with the application of a voltage. Importantly, only a single pair of electrodes is needed to tune the order of the vortex as the required phase profile is generated through the 3D structuring of the polymer network using the laser writing process.

Topological protection of optical skyrmions through complex media.

Optical Skyrmions have many important properties that make them ideal units for high-density data applications, including the ability to carry digital information through a discrete topological number and the independence of spatially varying polarization to other dimensions. More importantly, the topological nature of the optical Skyrmion heuristically suggests a strong degree of robustness to perturbations, which is crucial for reliably carrying information in noisy environments. However, the study of the topological robustness of optical Skyrmions is still in its infancy.

Extended-period AOSLO imaging in the living human retina without pupil dilation: a feasibility study.

imaging using an adaptive optics scanning laser ophthalmoscope (AOSLO) is challenging, especially over extended periods. Pharmacological agents, administered as eye drops, are commonly used to dilate the pupil and paralyse accommodation, to improve image quality. However, they are contraindicated in some scenarios.

Low cross-talk optical addressing of trapped-ion qubits using a novel integrated photonic chip.

Individual optical addressing in chains of trapped atomic ions requires the generation of many small, closely spaced beams with low cross-talk. Furthermore, implementing parallel operations necessitates phase, frequency, and amplitude control of each individual beam. Here, we present a scalable method for achieving all of these capabilities using a high-performance integrated photonic chip coupled to a network of optical fibre components.

study of defect interactions between the negatively charged nitrogen vacancy centre and the carbon self-interstitial in diamond.

Fabrication techniques for nitrogen-vacancy centres in diamond require the creation of Frenkel defects (vacancy-interstitial pairs) the components of which can interact with formed NV centres affecting their photophysical properties. Here we use Density Functional Theory simulations of inter-defect electronic and strain interactions to explore how the NV centre and carbon self-interstitial interact in different configurations. We find that hybridization occurs between the NV centre e-orbitals and the carbon self-interstitial when an interstitial is present on the vacancy side of the NV centre.

Universal adaptive optics for microscopy through embedded neural network control.

The resolution and contrast of microscope imaging is often affected by aberrations introduced by imperfect optical systems and inhomogeneous refractive structures in specimens. Adaptive optics (AO) compensates these aberrations and restores diffraction limited performance. A wide range of AO solutions have been introduced, often tailored to a specific microscope type or application.

Laser-Written Tunable Liquid Crystal Aberration Correctors.

In this Article, we present a series of novel laser-written liquid crystal (LC) devices for aberration control for applications in beam shaping or aberration correction through adaptive optics. Each transparent LC device can correct for a chosen aberration mode with continuous greyscale tuning up to a total magnitude of more than 2π radians phase difference peak to peak at a wavelength of λ = 660 nm. For the purpose of demonstration, we present five different devices for the correction of five independent Zernike polynomial modes (although the technique could readily be used to manufacture devices based on other modes).

Zwitterion-doped liquid crystal speckle reducers for immersive displays and vectorial imaging.

Lasers possess many attractive features (e.g., high brightness, narrow linewidth, well-defined polarization) that make them the ideal illumination source for many different scientific and technological endeavors relating to imaging and the display of high-resolution information.

Deflectometry based calibration of a deformable mirror for aberration correction and remote focusing in microscopy.

Adaptive optics (AO) techniques enhance the capability of optical microscopy through precise control of wavefront modulations to compensate phase aberrations and improves image quality. However, the aberration correction is often limited due to the lack of dynamic range in existing calibration methods, such as interferometry or Shack-Hartmann (SH) wavefront sensors. Here, we use deflectometry (DF) as a calibration method for a deformable mirror (DM) to extend the available range of aberration correction.

Adaptive optics for optical microscopy [Invited].

Optical microscopy is widely used to visualize fine structures. When applied to bioimaging, its performance is often degraded by sample-induced aberrations. In recent years, adaptive optics (AO), originally developed to correct for atmosphere-associated aberrations, has been applied to a wide range of microscopy modalities, enabling high- or super-resolution imaging of biological structure and function in complex tissues.

Dynamic phase measurement of fast liquid crystal phase modulators.

We present dynamic time-resolved measurements of a multi-pixel analog liquid crystal phase modulator driven at a 1 kHz frame rate. A heterodyne interferometer is used to interrogate two pixels independently and simultaneously, to deconvolve phase modulation with a wide bandwidth. The root mean squared optical phase error within a 30 Hz to 25 kHz bandwidth is <0.

On-chip beam rotators, adiabatic mode converters, and waveplates through low-loss waveguides with variable cross-sections.

Photonics integrated circuitry would benefit considerably from the ability to arbitrarily control waveguide cross-sections with high precision and low loss, in order to provide more degrees of freedom in manipulating propagating light. Here, we report a new method for femtosecond laser writing of optical-fiber-compatible glass waveguides, namely spherical phase-induced multicore waveguide (SPIM-WG), which addresses this challenging task with three-dimensional on-chip light control. Fabricating in the heating regime with high scanning speed, precise deformation of cross-sections is still achievable along the waveguide, with shapes and sizes finely controllable of high resolution in both horizontal and vertical transversal directions.

Single-mode sapphire fiber Bragg grating.

Sapphire optical fiber has the ability to withstand ultrahigh temperatures and high radiation, but it is multimoded which prevents its use in many sensing applications. Problematically, Bragg gratings in such fiber exhibit multiple reflection peaks with a fluctuating power distribution. In this work, we write single-mode waveguides with Bragg gratings in sapphire using a novel multi-layer depressed cladding design in the 1550 nm telecommunications waveband.

Generalised adaptive optics method for high-NA aberration-free refocusing in refractive-index-mismatched media.

Phase aberrations are introduced when focusing by a high-numerical aperture (NA) objective lens into refractive-index-mismatched (RIM) media. The axial focus position in these media can be adjusted through either optical remote-focusing or mechanical stage translation. Despite the wide interest in remote-focusing, no generalised control algorithm using Zernike polynomials has been presented that performs independent remote-focusing and RIM correction in combination with mechanical stage translation.

Democratising "Microscopi": a 3D printed automated XYZT fluorescence imaging system for teaching, outreach and fieldwork.

Commercial fluorescence microscope stands and fully automated XYZt fluorescence imaging systems are generally beyond the limited budgets available for teaching and outreach. We have addressed this problem by developing "Microscopi", an accessible, affordable, DIY automated imaging system that is built from 3D printed and commodity off-the-shelf hardware, including electro-mechanical, computer and optical components. Our design features automated sample navigation and image capture with a simple web-based graphical user interface, accessible with a tablet or other mobile device.

Laser induced forward transfer isolating complex-shaped cell by beam shaping.

Beam shaping techniques have been widely used in holographic optical tweezers to accurately manipulate tiny particles and hologram optimization algorithms have also been widely reported to improve the optical trapping performance. In this paper, we presented a beam shaping laser induced forward transfer (BS-LIFT) technique to isolate complex-shaped cells. To do this, we built up a BS-LIFT instrument which combined beam shaping methods and laser induced forward transfer using liquid-crystal-on-silicon spatial light modulator.

Extended range and aberration-free autofocusing via remote focusing and sequence-dependent learning.

Rapid autofocusing over long distances is critical for tracking 3D topological variations and sample motion in real time. Taking advantage of a deformable mirror and Shack-Hartmann wavefront sensor, remote focusing can permit fast axial scanning with simultaneous correction of system-induced aberrations. Here, we report an autofocusing technique that combines remote focusing with sequence-dependent learning via a bidirectional long short term memory network.

Tomographic refractive index profiling of direct laser written waveguides.

The fabrication of complex integrated photonic devices via direct laser writing is a powerful and rapidly developing technology. However, the approach is still facing several challenges. One of them is the reliable quantitative characterization of refractive index (RI) changes induced upon laser exposure.

Shrinking multiplexed orbital angular momentum to the nanoscale.

Orbital angular momentum interactions at the nanoscale have remained elusive because the phase structure becomes unresolved. Now researchers have shown how to overcome this with tightly focused beams, demonstrating a record-high six-dimensional encoding in an ultra-dense nanoscale volume.

Polarisation optics for biomedical and clinical applications: a review.

Many polarisation techniques have been harnessed for decades in biological and clinical research, each based upon measurement of the vectorial properties of light or the vectorial transformations imposed on light by objects. Various advanced vector measurement/sensing techniques, physical interpretation methods, and approaches to analyse biomedically relevant information have been developed and harnessed. In this review, we focus mainly on summarising methodologies and applications related to tissue polarimetry, with an emphasis on the adoption of the Stokes-Mueller formalism.

Python-Microscope - a new open-source Python library for the control of microscopes.

Custom-built microscopes often require control of multiple hardware devices and precise hardware coordination. It is also desirable to have a solution that is scalable to complex systems and that is translatable between components from different manufacturers. Here we report Python-Microscope, a free and open-source Python library for high-performance control of arbitrarily complex and scalable custom microscope systems.