Biomechanics plays a central role in breast epithelial morphogenesis. In this study we have used 3D cultures in which
normal breast epithelial cells are able to organize into rounded acini and tubular ducts, the main structures found in the
breast tissue. We have identified fiber organization as a main determinant of ductal organization. While bulk rheological
properties of the matrix seem to play a negligible role in determining the proportion of acini versus ducts, local changes
may be pivotal in shape determination. As such, the ability to make microscale rheology measurements coupled with
simultaneous optical imaging in 3D cultures can be critical to assess the biomechanical factors underlying epithelial
morphogenesis. This paper describes the inclusion of optical tweezers based microrheology in a microscope that had
been designed for nonlinear optical imaging of collagen networks in ECM. We propose two microrheology methods and show preliminary results using a gelatin hydrogel and collagen/Matrigel 3D cultures containing mammary gland
We explore the possibility of using optical tweezers to enable all optical control of optofluidic circuits. Optically trapped microspheres can be used as microlenses for optical signal switching and steering. By using cantilevers instead of microspheres we provide a method for robust and stable placement of switching elements in the optofluidic circuits. Cantilevers made of tapered optical fiber and polydimethyl siloxane are demonstrated. We also show that it is possible to use transverse optical tweezer beams to load silica beads into the hollow core photonic crystal fibers for tuning their transmission properties.
Optofluidics offers new functionalities that can be useful for a large range of applications. What microfluidics can bring
to microphotonics is the ability to tune and reconfigure ultra-compact optical devices. This flexibility is essentially
provided by three characteristics of fluids that are scalable at the micron-scale: fluid mobility, large ranges of index
modulation, and adaptable interfaces. Several examples of optofluidic devices are presented to illustrate the achievement
of new functionalities onto (semi)planar and compact platforms. First, we report an ultra-compact and tunable
interferometer that exploits a sharp and mobile air/water interface. We describe then a novel class of optically controlled
switches and routers that rely on the actuation of optically trapped lens microspheres within fluid environment. A tunable
optical switch device can alternatively be built from a transversely probed photonic crystal fiber infused with mobile
fluids. The last reported optofluidic device relies on strong fluid/ light interaction to produce either a sensitive index
sensor or a tunable optical filter. The common feature of these various devices is their significant flexibility. Higher
degrees of functionality could be achieved in the future with fully integrated optofluidic platforms that associate complex
microfluidic delivery and mixing schemes with microphotonic devices.
We introduce a novel method of attaining all-optical beam control in an optofluidic device by displacing an optically trapped silica micro-sphere though a light beam. The micro-sphere causes the beam to be refracted by various degrees as a function of the sphere position, providing tunable attenuation and beam-steering in the device. The device itself consists of the manipulated light beam extending between two buried waveguides which are on either side of a
microfluidic channel. This channel contains the micro-spheres which are suspended in water. We simulate this geometry using the Finite Difference Time Domain method and find good agreement between simulation and experiment.
Lambda DNA is used to tether polystyrene microspheres to an optical substrate, thus eliminating the need for high numerical aperture trapping lenses in single beam optical tweezers to provide axial trapping. The tethered particle may be used as a sensor probe to measure local viscosity and forces on the trapped particle such as those induced by fluid flow.
One dimensional photonic bandgap structures can be used to enhance the efficiency of nonlinear optical parametric processes. Structural dispersion can be used to achieve phase matching, and resonant effects can be used to increase the intensity of the pump beams in the nonlinear optical material. In this paper these ideas are used to derive for the a continuous wave or a quasicontinuous wave THz signal and show that an improvement of three orders of magnitude in the
output intensity can be achieved for a structure involving as few as four layers of ZnTe.
Confocal microscopy and optical tweezers were combined to develop a minimally invasive instrument capable of making hydrodynamic measurements more rapidly than is possible with other devices. This result leads to the possibility of making scanning images of the viscosity distribution of materials around bipolymer producing cells. An image of the viscosity distribution around a pullulan producing cell of Aureobasidium pullulans is shown as an example. We present results from experiments supporting a linearized model for the motion of a trapped bead in an oscillating harmonic potential. Fluid velocity measurements are tested by comparing to an independent video based measurement. We apply the technique to obtain a 2-D map of the flow past a microscopic wedge and compare to a theoretical solution for the stream lines assuming potential flow. Since the velocity is measured simultaneously with the trap relaxation time, it requires practically no calibration and is independent of the trap stiffness and the particle size.
Coherent population trapping can be used to achieve efficient optical phase conjugation in a double-(Lambda) system at pump intensities well below the saturation intensity of the optical transitions. Experimental evidence for this process in sodium vapor qualitatively verifies this prediction.
Baseband demodulation, lock-in detection, noise reduction, compression/expansion nonlinearities, and correlation receivers are common subjects in communication theory. In this paper we use photorefractive materials to show how real-time holography can be used to implement these temporal electronic signal processing techniques as spatio-temporal optical signal processing on images.
An all optical nonlinear joint transform correlator is proposed and demonstrated. A hard- limiting quadratic nonlinearity is used in the Fourier plane to allow the first implementation of a phase only filter using photorefractive materials.
Nonlinear optical thresholding in the Fourier plane produces optically adaptive noise-cleaning masks that reduce additive signal-dependent noise, such as scalar multiplicative noise. We demonstrate the two-beam coupling artifact noise-reduction technique and achieve performance comparable to the Wiener filter.
Signal recovery from multiplicative complex noise is proposed and demonstrated. The recovery is achieved by using two phase conjugators in series to produce a photorefractive quadratic nonlinear processor.