Recently we proposed the concept of so-called Light Robotics including the new and disruptive 3D-fabricated micro-tools coined Wave-guided Optical Waveguides that can be real-time optically manipulated and remote-controlled with a joystick in a volume with six-degrees-of-freedom. Exploring the full potential of this new ‘drone-like’ light-driven micro-robotics in challenging microscopic geometries requires a versatile and real-time reconfigurable light addressing that can dynamically track a plurality of tiny micro-robots in 3D to ensure continuous optimal light coupling on the fly. Our latest developments in this new and exciting research area will be reviewed.
Early detection of diseases can save lives. Hence, there is emphasis in sorting rare disease-indicating cells within small dilute quantities such as in the confines of lab-on-a-chip devices. However, before diseased cells can be studied in isolation, it is necessary to identify them against normal healthy cells. With the richness of visual information, a lot of microscopy techniques have been developed and have been crucial in biological studies. To utilize their complementary advantages we adopt both fluorescence and brightfield imaging in our optical cell sorter. Brightfield imaging has the advantage of being non-invasive, thus maintaining cell viability. Fluorescence imaging, on the other hand, takes advantages of the chemical specificity of fluorescence markers and can validate machine vision results from brightfield images. Visually identified cells are sorted using optical manipulation techniques. Scattering forces from beams actuated via efficient phase-only efficient modulation has been adopted. This has lowered the required power for sorting cells to a tenth of our previous approach, and also makes the cell sorter safer for use in clinical settings. With the versatility of dynamically programmable phase spatial light modulators, a plurality of light shaping techniques, including hybrid approaches, can be utilized in cell sorting.
We show a simplified method of generating extended regions of destructive interference with near arbitrary shapes using the generalized phase contrast (GPC) method. For Gaussian input beams, GPC typically results in a 3× intensified user-defined input mask shape against a dark background. In this work, we investigate conditions wherein GPC’s synthetic reference wave destructively interferes with what is typically the foreground pattern. Using alternate conditions for the input phase mask, the locations of light and darkness are interchanged with respect to typical GPC output mappings. We show experimentally how “dark GPC” allows the dark regions to be easily reshaped using a binary-only phase mask encoded on a spatial light modulator. Similar to standard GPC, the method does not require complex calculations or the fabrication of complex gray-level phase elements. The simplified approach and flexibility in the output shapes make dark GPC attractive for applications such as optical trapping of low-index particles or superresolution microscopy like stimulated emission depletion.
As celebrated by the Nobel Prize 2014 in Chemistry light-based technologies can now overcome the diffraction barrier for imaging with nanoscopic resolution by so-called super-resolution microscopy1. However, interactive investigations coupled with advanced imaging modalities at these small scale domains gradually demand the development of a new generation of disruptive tools, not only for passively observing at nanoscopic scales, but also for actively reaching into and effectively handling constituents in this size domain. This intriguing mindset has recently led to the emergence of a novel research discipline that could potentially be able to offer the full packet needed for true "active nanoscopy" by use of so-called light-driven micro-robotics or Light Robotics in short.
Generalized Phase Contrast (GPC) is a light efficient method for generating speckle-free contiguous optical distributions using binary-only or analog phase levels. It has been used in applications such as optical trapping and manipulation, active microscopy, structured illumination, optical security, parallel laser marking and labelling and recently in contemporary biophotonics applications such as for adaptive and parallel two-photon optogenetics and neurophotonics. We will present our most recent GPC developments geared towards these applications. We first show a very compact static light shaper followed by the potential of GPC for biomedical and multispectral applications where we experimentally demonstrate the active light shaping of a supercontinuum laser over most of the visible wavelength range. Finally, we discuss how GPC can be advantageously applied for Quantitative Phase Imaging (QPI).
Early detection of diseases can save lives. Hence, there is emphasis in sorting rare disease-indicating cells within small
dilute quantities such as in the confines of lab-on-a-chip devices. In our work, we use optical forces to isolate red blood
cells detected by machine vision. This approach is gentler, less invasive and more economical compared to conventional
FACS systems. As cells are less responsive to plastic or glass beads commonly used in the optical manipulation
literature, and since laser safety would be an issue in clinical use, we develop efficient approaches in utilizing lasers and
light modulation devices. The Generalized Phase Contrast (GPC) method that can be used for efficiently illuminating
spatial light modulators or creating well-defined contiguous optical traps is supplemented by diffractive techniques
capable of integrating the available light and creating 2D or 3D beam distributions aimed at the positions of the detected
cells. Furthermore, the beam shaping freedom provided by GPC can allow optimizations in the beam’s propagation and
its interaction with the catapulted cells.
Generalized Phase Contrast (GPC) is an efficient method for efficiently shaping light into speckle-free contiguous
optical distributions useful in diverse applications such as static beam shaping, optical manipulation and recently, for
excitation in two-photon optogenetics. GPC typically results in a 3x intensified user defined input mask shape against a
dark background. In this work, we emphasize GPC’s capability of optimal destructive interference, normally used to
create the dark background surrounding the shaped light. We also study input parameters wherein the locations of light
and darkness are interchanged with respect to typical GPC output, thus resulting to a well-defined structured darkness.
The conditions that give destructive interference for the output are then applied to near-arbitrary shapes. Preliminary
experimental results are presented using dynamic spatial light modulator to form scaled arbitrary darkness shapes.
Supporting demonstrations that reverse the light and dark regions of amplitude-modulated input are also presented as a
related case of structuring destructive interference. Our analysis and experimental demonstrations show a simplified
approach in the generation of extended regions of destructive interference within coherent beams.
Material transport is an important mechanism in microfluidics and drug delivery. The methods and solutions found in
literature involve passively diffusing structures, microneedles and chemically fueled structures. In this work, we make
use of optically actuated microtools with embedded metal layer as heating element for controlled loading and release.
The new microtools take advantage of the photothermal-induced convection current to load and unload cargo. We also
discuss some challenges encountered in realizing a self-contained polymerized microtool. Microfluidic mixing, fluid
flow control and convection currents have been demonstrated both experimentally and numerically for static metal thin
films or passively floating nanoparticles. Here we show an integration of aforementioned functionalities in an optically fabricated
and actuated microtool. As proof of concept, we demonstrate loading and unloading of beads. This can be
extended to controlled transport and release of genetic material, bio-molecules, fluorescent dyes. We envisioned these
microtools to be an important addition to the portfolio of structure-mediated contemporary biophotonics.
We have previously demonstrated on-demand dynamic coupling to optically manipulated microtools coined as wave-guided optical waveguides using diffractive techniques on a “point and shoot” approach. These microtools are extended microstructures fabricated using two-photon photopolymerization and function as free-floating optically trapped waveguides. Dynamic coupling of focused light via these structures being moved in three-dimensional space is done holographically. However, calculating the necessary holograms is not straightforward when using counter-propagating trapping geometry. The generation of the coupling spots is done in real time following the position of each microtool with the aid of an object tracking routine. This approach allows continuous coupling of light through the microtools which can be useful in a variety of biophotonics applications. To complement the targeted-light delivery capability of the microtools, the applied spatial light modulator has been illuminated with a properly matched input beam cross section based on the generalized phase contrast method. Our results show a significant gain in the output at the tip of each microtool as measured from the fluorescence signal of the trapping medium. The ability to switch from on-demand to continuous addressing with efficient illumination leverages our microtools for potential applications in stimulation and near-field-based biophotonics on cellular scales.
We originally proposed and experimentally demonstrated the targeted-light delivery capability of so-called Wave-guided
Optical Waveguides (WOWs) three years ago. As these WOWs are maneuvered in 3D space, it is important to maintain
efficient light coupling through their integrated waveguide structures. In this work we demonstrate the use of real-time
diffractive techniques to create focal spots that can dynamically track and couple to the WOWs during operation in a
volume. This is done by using a phase-only spatial light modulator to encode the needed diffractive phase patterns to
generate a plurality of dynamic coupling spots. In addition, we include our proprietary GPC Light Shaper before the
diffractive setup to efficiently illuminate the rectangular shaped spatial light modulator by a Gaussian laser beam. The
method is initially tested for a single WOW and we have experimentally demonstrated dynamic tracking and coupling
for both lateral and axial displacements of the WOWs. The ability to switch from on-demand to continuous addressing
with efficient illumination leverages our WOWs for potential applications in near-field stimulation and nonlinear optics
at small scales.
We have previously proposed and demonstrated optimal beam shaping of contiguous light patterns using the Generalized Phase Contrast (GPC) method. The concept has been packaged into a compact add-on module, which we call the GPC light shaper (LS) that can be conveniently integrated to existing optical setups requiring optimal illumination of devices such as spatial light modulators (SLMs). In this work, we integrated the GPC LS into a holography setup to generate more intense focal spots and extended patterns. The output of the holography setup with the GPC LS is compared with a similar setup but using only hard-truncated beams. Our results show that, we get a ~3x gain in intensity of the generated patterns when using GPC LS.
We have previously demonstrated on-demand dynamic coupling of an optically manipulated wave-guided optical waveguide (WOW) using diffractive techniques on a “point and shoot” approach. In this work, the generation of the coupling focal spots is done in real-time following the position of the WOW. Object-tracking routine has been added in the trapping program to get the position of the WOW. This approach allows continuous coupling of light through the WOWs which may be useful in some application. In addition, we include a GPC light shaper module in the holography setup to efficiently illuminate the spatial light modulator (SLM). The ability to switch from on-demand to continuous addressing with efficient illumination leverages our WOWs for potential applications in stimulation and nonlinear optics.
We have previously proposed and demonstrated the targeted-light delivery capability of wave-guided optical waveguides (WOWs). The full strength of this structure-mediated paradigm can be harnessed by addressing multiple WOWs and manipulating them to work in tandem. We propose the use of diffractive techniques to create multiple focal spots that can be coupled into light manipulated WOWs. This is done by using a spatial light modulator to project the necessary phase to generate the multiple coupling light spots. We incorporate a diffractive setup in our Biophotonics Workstation (BWS) and demonstrate holographic shaping, tracking of light in 3D with the purpose of coupling light in the WOWs.