A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

We examine the current performance and future demands of interconnects to and on silicon chips. We compare electrical and optical interconnects and project the requirements for optoelectronic and optical devices if optics is to solve the major problems of interconnects for future high-performance silicon chips. Optics has potential benefits in interconnect density, energy, and timing. The necessity of low interconnect energy imposes low limits especially on the energy of the optical output devices, with a ~ 10 fJ/bit device energy target emerging. Some optical modulators and radical laser approaches may meet this requirement. Low (e.g., a few femtofarads or less) photodetector capacitance is important. Very compact wavelength splitters are essential for connecting the information to fibers. Dense waveguides are necessary on-chip or on boards for guided wave optical approaches, especially if very high clock rates or dense wavelength-division multiplexing (WDM) is to be avoided. Free-space optics potentially can handle the necessary bandwidths even without fast clocks or WDM. With such technology, however, optics may enable the continued scaling of interconnect capacity required by future chips.

Device Requirements for Optical Interconnects to Silicon Chips

Single-molecule surface-enhanced Raman scattering (SM-SERS) is one of the vital applications of plasmonic nanoparticles. The SM-SERS sensitivity critically depends on plasmonic hot-spots created at the vicinity of such nanoparticles. In conventional fluid-phase SM-SERS experiments, plasmonic hot-spots are facilitated by chemical aggregation of nanoparticles. Such aggregation is usually irreversible, and hence, nanoparticles cannot be re-dispersed in the fluid for further use. Here, we show how to combine SM-SERS with plasmon polariton-assisted, reversible assembly of plasmonic nanoparticles at an unstructured metal–fluid interface. One of the unique features of our method is that we use a single evanescent-wave optical excitation for nanoparticle assembly, manipulation and SM-SERS measurements. Furthermore, by utilizing dual excitation of plasmons at metal–fluid interface, we create interacting assemblies of metal nanoparticles, which may be further harnessed in dynamic lithography of dispersed nanostructures. Our work will have implications in realizing optically addressable, plasmofluidic, single-molecule detection platforms. Plasmonic hot-spot generation in solution is not reversible for single-molecule surface-enhanced Raman scattering, which limits its applications. Patra et al.tackle this problem by integrating this technique with thermo-plasmon-assisted reconfiguration of nanoparticles at a metal–fluid interface.

/pdf/plasmofluidic-single-molecule-surface-enhanced-raman-39t0v43usg.pdf

Plasmofluidic single-molecule surface-enhanced Raman scattering from dynamic assembly of plasmonic nanoparticles

The fact that light carries both linear and angular momentum is well-known to physicists. One application of the linear momentum of light is for optical tweezers, in which the refraction of a laser beam through a particle provides a reaction force that draws the particle towards the centre of the beam. The angular momentum of light can also be transfered to particles, causing them to spin. In fact, the angular momentum of light has two components that act through different mechanisms on various types of particle. This Review covers the creation of such beams and how their unusual intensity, polarization and phase structure has been put to use in the field of optical manipulation.

Tweezers with a twist

The silicon chip has been the mainstay of the electronics industry for the last 40 years and has revolutionized the way the world operates. Today, a silicon chip the size of a fingernail contains nearly 1 billion transistors and has the computing power that only a decade ago would take up an entire room of servers. As the relentless pursuit of Moore's law continues, and Internet-based communication continues to grow, the bandwidth demands needed to feed these devices will continue to increase and push the limits of copper-based signaling technologies. These signaling limitations will necessitate optical-based solutions. However, any optical solution must be based on low-cost technologies if it is to be applied to the mass market. Silicon photonics, mainly based on SOI technology, has recently attracted a great deal of attention. Recent advances and breakthroughs in silicon photonic device performance have shown that silicon can be considered a material onto which one can build optical devices. While significant efforts are needed to improve device performance and commercialize these technologies, progress is moving at a rapid rate. More research in the area of integration, both photonic and electronic, is needed. The future is looking bright. Silicon photonics could provide low-cost opto-electronic solutions for applications ranging from telecommunications down to chip-to-chip interconnects, as well as emerging areas such as optical sensing technology and biomedical applications. The ability to utilize existing CMOS infrastructure and manufacture these silicon photonic devices in the same facilities that today produce electronics could enable low-cost optical devices, and in the future, revolutionize optical communications

http://ieeexplore.ieee.org/iel5/6668/34347/01638290.pdf

Silicon photonics

We present a study into the small particle size and resolution limits of Light Induced Dielectrophoresis (LIDEP). Here the illumination of a photoconductive layer creates virtual electrodes whose associated electric field gradients cause the dielectrophoretic response of the particles. In this way a potential energy landscape can be created that is optically controlled giving reconfigurable control over a large area [1]. In this paper we discuss the interlinked limits of size of particle it is possible to manipulate and the resolution these particles can be manipulated with. We compare traditional dielectrophoresis (DEP) experiments with LIDEP experiments, and discuss the mechanisms behind the physical limits comparing the effects of carrier diffusion verses the spreading of the electric fields in the medium.

Size resolution with Light Induced Dielectrophoresis (LIDEP)

Raman spectroscopy provides a non-invasive method to study biological samples. We demonstrate the powerful capabilities of our novel Raman modulation technique to detect weak Raman signals hidden by a strong fluorescent background.

/pdf/fluorescence-background-suppression-in-raman-spectroscopy-pay6xvs8p6.pdf

Fluorescence background suppression in Raman spectroscopy

Raman spectroscopy is a non-invasive technique offering great potential in the biomedical field for label-free
discrimination between normal and tumor cells based on their biochemical composition. First, this contribution describes
Raman spectra of lymphocytes after drying, in laser tweezers, and trapped in a microfluidic environment. Second,
spectral differences between lymphocytes and acute myeloid leukemia cells (OCI-AML3) are compared for these three
experimental conditions. Significant similarities of difference spectra are consistent with the biological relevance of the
spectral features. Third, modulated wavelength Raman spectroscopy has been applied to this model system to
demonstrate background suppression. Here, the laser excitation wavelength of 785 nm was modulated with a frequency
of 40 mHz by 0.6 nm. 40 spectra were accumulated with an exposure time of 5 seconds each. These data were subjected
to principal component analysis to calculate modulated Raman signatures. The loading of the principal component shows
characteristics of first derivatives with derivative like band shapes. The derivative of this loading corresponds to a
pseudo-second derivative spectrum and enables to determine band positions.

Raman spectra of single cells with autofluorescence suppression by modulated wavelength excitation

Optical chromatography is a powerful technique, capable of separating micron-sized particles within a fluid flow, based
on their intrinsic properties, including size, shape and refractive index. Briefly, particles in a fluid flow are subject to two
forces, the Stokes drag force due to the fluid and then an introduced optical force as supplied by a laser beam, acting in
opposite but collinear directions. According to the particle's intrinsic hydrodynamic and optical properties, equilibrium
positions may form where the two forces balance, which is highly dependent on the properties of the particle and as a
result provides a means for spatial separation in a sample mixture. Optical chromatography is a passive sorting
technique, where pre-tagging of the particles of interest is not required, allowing for non-discrete distributions to be
evaluated and/or separated. Firstly we review the current stage of optical chromatography. We present a new advance in
optical chromatography potentially enabling the unique beam delivery properties of photonic crystal fiber (PCF) to be
employed and integrated into microfluidic chips. Also, for the first time a finite element method is applied to the optical
field in the theoretical analysis of optical chromatography, which is found to be in excellent agreement with the current
ray optics model, even for particles much smaller than the optical wavelength. This will pave the way for the technique
to be extended into the nanoparticle regime.

Towards integrated optical chromatography using photonic crystal fiber

It is known that a properly arranged distribution of nanoholes on a metallic slab is able to produce, in far field conditions, light confinement at sub-diffraction and even sub-wavelength scale. The same effect can also be implemented by the use of Optical Eigenmode (OEi) technique. In this case, a spatial light modulator (SLM) encodes phase and amplitudes of N probe beams whose interference is able to lead to sub-wavelength confinement of light focused by an objective. The OEi technique has been already used in a wide range of applications, such as photoporation, confocal imaging, and coherent control of plasmonic nanoantennas. Here, we describe the application of OEi technique to a single valve of a marine diatom. Diatoms are ubiquitous monocellular algae provided with an external cell wall, the frustule, made of hydrated porous silica which play an active role in efficient light collection and confinement for photosynthesis. Every frustule is made of two valves interconnected by a lateral girdle band. We show that, applying OEi illumination to a single diatom valve, we can achieve unprecedented sub-diffractive focusing for the transmitted light.

Michael Mazilu

Papers

Size resolution with Light Induced Dielectrophoresis (LIDEP)

Fluorescence background suppression in Raman spectroscopy

Raman spectra of single cells with autofluorescence suppression by modulated wavelength excitation

Towards integrated optical chromatography using photonic crystal fiber

Combining focusing properties of a single diatom valve with optical eigenmodes in ultra-shrinking of light