Monolithically integrated 112 Gbps PAM4 optical transmitter and receiver in a 45†nm CMOS-silicon photonics process.

We demonstrate a transmitter and receiver in a silicon photonics platform for O-band optical communication that monolithically incorporates a modulator driver, traveling-wave Mach-Zehnder modulator, control circuitry, photodetector, and transimpedance amplifier (TIA) in the GlobalFoundries Fotonix (45SPCLO) platform. The transmitter and receiver show an open 112 Gbps PAM4 eye at a 4.3 pJ/bit energy efficiency, not including the laser. Extensive use of gain-peaking enables our modulator driver and TIA to achieve the high bandwidths needed in the 45 nm CMOS-silicon photonics process. Our results suggest an alternative to the frequent approach of bump-bonding BiCMOS drivers and TIAs to silicon photonics.

Angular orientation of nanorods using nanophotonic tweezers.

Near-field optical techniques have enabled the trapping, transport, and handling of nanoscopic materials much smaller than what can be manipulated with traditional optical tweezers. Here we extend the scope of what is possible by demonstrating angular orientation and rotational control of both biological and nonbiological nanoscale rods using photonic crystal nanotweezers. In our experiments, single microtubules (diameter 25 nm, length 8 µm) and multiwalled carbon nanotubes (outer diameter 110-170 nm, length 5 µm) are rotated by the optical torque resulting from their interaction with the evanescent field emanating from these devices. An angular trap stiffness of κ = 92.8 pN·nm/rad(2)·mW is demonstrated for the microtubules, and a torsional spring constant of 22.8 pN·nm/rad(2)·mW is measured for the nanotubes. We expect that this new capability will facilitate the development of high precision nanoassembly schemes and biophysical studies of bending strains of biomolecules.

Controlled photonic manipulation of proteins and other nanomaterials.

The ability to controllably handle the smallest materials is a fundamental enabling technology for nanoscience. Conventional optical tweezers have proven useful for manipulating microscale objects but cannot exert enough force to manipulate dielectric materials smaller than about 100 nm. Recently, several near-field optical trapping techniques have been developed that can provide higher trapping stiffness, but they tend to be limited in their ability to reversibly trap and release smaller materials due to a combination of the extremely high electromagnetic fields and the resulting local temperature rise. Here, we have developed a new form of photonic crystal "nanotweezer" that can trap and release on-command Wilson disease proteins, quantum dots, and 22 nm polymer particles with a temperature rise less than ~0.3 K, which is below the point where unwanted fluid mechanical effects will prevent trapping or damage biological targets.

DNA transport and delivery in thermal gradients near optofluidic resonators.

Heat generation and its impact on DNA transport in the vicinity of an optofluidic silicon photonic crystal resonator are studied theoretically and experimentally. The temperature rise is measured to be as high as 57 K for 10 mW of input power. The resulting optical trapping and biomolecular sensing properties of these devices are shown to be strongly affected by the combination of buoyancy driven flow and thermophoresis. Specifically, the region around the electromagnetic hot spot is depleted in biomolecules because of a high free energy barrier.

Nanomanipulation using silicon photonic crystal resonators.

Optical tweezers have enabled a number of microscale processes such as single cell handling, flow-cytometry, directed assembly, and optical chromatography. To extend this functionality to the nanoscale, a number of near-field approaches have been developed that yield much higher optical forces by confining light to subwavelength volumes. At present, these techniques are limited in both the complexity and precision with which handling can be performed. Here, we present a new class of nanoscale optical trap exploiting optical resonance in one-dimensional silicon photonic crystals. The trapping of 48 nm and 62 nm dielectric nanoparticles is demonstrated along with the ability to transport, trap, and manipulate larger nanoparticles by simultaneously exploiting the propagating nature of the light in a coupling waveguide and its stationary nature within the resonator. Field amplification within the resonator is shown to produce a trap several orders of magnitude stronger than conventional tweezers and an order of magnitude stiffer than other near-field techniques. Our approach lays the groundwork for a new class of optical trapping platforms that could eventually enable complex all-optical single molecule manipulation and directed assembly of nanoscale material.

Nanophotonic detection of freely interacting molecules on a single influenza virus.

Biomolecular interactions, such as antibody-antigen binding, are fundamental to many biological processes. At present, most techniques for analyzing these interactions require immobilizing one or both of the interacting molecules on an assay plate or a sensor surface. This is convenient experimentally but can constrain the natural binding affinity and capacity of the molecules, resulting in data that can deviate from the natural free-solution behavior. Here we demonstrate a label-free method for analyzing free-solution interactions between a single influenza virus and specific antibodies at the single particle level using near-field optical trapping and light-scattering techniques. We determine the number of specific antibodies binding to an optically trapped influenza virus by analyzing the change of the Brownian fluctuations of the virus. We develop an analytical model that determines the increased size of the virus resulting from antibodies binding to the virus membrane with uncertainty of ± 1-2 nm. We present stoichiometric results of 26 ± 4 (6.8 ± 1.1 attogram) anti-influenza antibodies binding to an H1N1 influenza virus. Our technique can be applied to a wide range of molecular interactions because the nanophotonic tweezer can handle molecules from tens to thousands of nanometers in diameter.

Localized opto-mechanical control of protein adsorption onto carbon nanotubes.

Chemical reactions can be described by an energy diagram along a reaction coordinate in which an activation barrier limits the rate at which reactants can be transformed into products. This reaction impedance can be overcome by reducing the magnitude of the barrier through the use of catalysis, increasing the thermal energy of the system, or through macroscopic mechanical processes. Here, we demonstrate direct molecular-scale control of a reaction through the precise application of opto-mechanical work. The method uses optical gradient forces generated in the evanescent field surrounding hybrid photonic-plasmonic structures to drive an otherwise unlikely adsorption reaction between proteins and carbon nanotubes. The adsorption of immunoglobulins on carbon nanotubes is used as a model reaction and investigated with an extended DLVO theory. The technique is also used to force a Förster resonance energy transfer between fluorophores on mismatched immunoglobulin proteins and is expected to lead to novel forms of chemical synthesis.

Nanomanipulation using near field photonics.

In this article we review the use of near-field photonics for trapping, transport and handling of nanomaterials. While the advantages of traditional optical tweezing are well known at the microscale, direct application of these techniques to the handling of nanoscale materials has proven difficult due to unfavourable scaling of the fundamental physics. Recently a number of research groups have demonstrated how the evanescent fields surrounding photonic structures like photonic waveguides, optical resonators, and plasmonic nanoparticles can be used to greatly enhance optical forces. Here, we introduce some of the most common implementations of these techniques, focusing on those which have relevance to microfluidic or optofluidic applications. Since the field is still relatively nascent, we spend much of the article laying out the fundamental and practical advantages that near field optical manipulation offers over both traditional optical tweezing and other particle handling techniques. In addition we highlight three application areas where these techniques namely could be of interest to the lab-on-a-chip community, namely: single molecule analysis, nanoassembly, and optical chromatography.