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.Until now,a universal AO solution-one that can be readily transferred between microscope modalities-has not been deployed.We propose versatile and fast aberration correction using a physics-based machine learning assisted wavefront-sensorless AO control(MLAO)method.Unlike previous ML methods,we used a specially constructed neural network(NN)architecture,designed using physical understanding of the general microscope image formation,that was embedded in the control loop of different microscope systems.The approach means that not only is the resulting NN orders of magnitude simpler than previous NN methods,but the concept is translatable across microscope modalities.We demonstrated the method on a two-photon,a three-photon and a widefield three-dimensional(3D)structured illumination microscope.Results showed that the method outperformed commonly-used modal-based sensorless AO methods.We also showed that our ML-based method was robust in a range of challenging imaging conditions,such as 3D sample structures,specimen motion,low signal to noise ratio and activity-induced fluorescence fluctuations.Moreover,as the bespoke architecture encapsulated physical understanding of the imaging process,the internal NN configuration was no-longer a"black box",but provided physical insights on internal workings,which could influence future designs.

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.However,their high-level of coherence can result in the formation of noise,referred to as speckle,that can corrupt and degrade images.Here,we demonstrate a new electro-optic technology for combatting laser speckle using a chiral nematic liquid crystal(LC)dispersed with zwitterionic dopants.Results are presented that demonstrate when driven at the optimum electric field conditions,the speckle noise can be reduced by>90%resulting in speckle contrast(C)values of C=0.07,which is approaching that required to be imperceptible to the human eye.This LC technology is then showcased in an array of different display and imaging applications,including a demonstration of speckle reduction in modern vectorial laser-based imaging.

Adaptive optics in laser processing

Adaptive optics are becoming a valuable tool for laser processing,providing enhanced functionality and flexibility for a range of systems.Using a single adaptive element,it is possible to correct for aberrations introduced when focusing inside the workpiece,tailor the focal intensity distribution for the particular fabrication task and/or provide parallelisation to reduce processing times.This is particularly promising for applications using ultrafast lasers for threedimensional fabrication.We review recent developments in adaptive laser processing,including methods and applications,before discussing prospects for the future.

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.Several recent breakthroughs,development trends,and potential multimodal uses in conjunction with other techniques are also presented.The primary goal of the review is to give the reader a general overview in the use of vectorial information that can be obtained by polarisation optics for applications in biomedical and clinical research.

Subcellular spatial resolution achieved for deep-brain imaging in vivo using a minimally invasive multimode fiber

Achieving intravital optical imaging with diffraction-limited spatial resolution of deep-brain structures represents an important step toward the goal of understanding the mammalian central nervous system1–4.Advances in wavefrontshaping methods and computational power have recently allowed for a novel approach to high-resolution imaging,utilizing deterministic light propagation through optically complex media and,of particular importance for this work,multimode optical fibers(MMFs)5–7.We report a compact and highly optimized approach for minimally invasive in vivo brain imaging applications.The volume of tissue lesion was reduced by more than 100-fold,while preserving diffraction-limited imaging performance utilizing wavefront control of light propagation through a single 50-μm-core MMF.Here,we demonstrated high-resolution fluorescence imaging of subcellular neuronal structures,dendrites and synaptic specializations,in deep-brain regions of living mice,as well as monitored stimulus-driven functional Ca2+responses.These results represent a major breakthrough in the compromise between high-resolution imaging and tissue damage,heralding new possibilities for deep-brain imaging in vivo.

Revealing complex optical phenomena through vectorial metrics

Advances in vectorial polarization-resolved imaging are bringing new capabilities to applications ranging from fundamental physics through to clinical diagnosis.Imaging polarimetry requires determination of the Mueller matrix(MM)at every point,providing a complete description of an object’s vectorial properties.Despite forming a comprehensive representation,the MM does not usually provide easily interpretable information about the object’s internal structure.Certain simpler vectorial metrics are derived from subsets of the MM elements.These metrics permit extraction of signatures that provide direct indicators of hidden optical properties of complex systems,while featuring an intriguing asymmetry about what information can or cannot be inferred via these metrics.We harness such characteristics to reveal the spin Hall effect of light,infer microscopic structure within laser-written photonic waveguides,and conduct rapid pathological diagnosis through analysis of healthy and cancerous tissue.This provides new insight for the broader usage of such asymmetric inferred vectorial information.

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.We observed that these waveguides have high refractive index contrast of 0.017,low propagation loss of 0.14 dB/cm,and very low coupling loss of 0.19 dB coupled from a single-mode fiber.SPIM-WG devices were easily fabricated that were able to perform on-chip beam rotation through varying angles,or manipulate the polarization state of propagating light for target wavelengths.We also demonstrated SPIM-WG mode converters that provide arbitrary adiabatic mode conversion with high efficiency between symmetric and asymmetric nonuniform modes;examples include circular,elliptical modes,and asymmetric modes from ppKTP(periodically poled potassium titanyl phosphate)waveguides which are generally applied in frequency conversion and quantum light sources.Created inside optical glass,these waveguides and devices have the capability to operate across ultra-broad bands from visible to infrared wavelengths.The compatibility with optical fiber also paves the way toward packaged photonic integrated circuitry,which usually needs input and output fiber connections.

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 recordhigh six-dimensional encoding in an ultra-dense nanoscale volume.