Optical tweezers (infrared laser-based optical traps) have emerged as a powerful tool in molecular and cell biology. However, their usefulness has been limited, particularly in vivo, by the potential for damage to specimens resulting from the trapping laser. Relatively little is known about the origin of this phenomenon. Here we employed a wavelength-tunable optical trap in which the microscope objective transmission was fully characterized throughout the near infrared, in conjunction with a sensitive, rotating bacterial cell assay. Single cells of Escherichia coli were tethered to a glass coverslip by means of a single flagellum: such cells rotate at rates proportional to their transmembrane proton potential (Manson et al.,1980. J. Mol. Biol. 138:541-561). Monitoring the rotation rates of cells subjected to laser illumination permits a rapid and quantitative measure of their metabolic state. Employing this assay, we characterized photodamage throughout the near-infrared region favored for optical trapping (790-1064 nm). The action spectrum for photodamage exhibits minima at 830 and 970 nm, and maxima at 870 and 930 nm. Damage was reduced to background levels under anaerobic conditions, implicating oxygen in the photodamage pathway. The intensity dependence for photodamage was linear, supporting a single-photon process. These findings may help guide the selection of lasers and experimental protocols best suited for optical trapping work.

Abstract-The design and performance of next-generation chip multiprocessors (CMPs) will be bound by the limited amount of power that can be dissipated on a single die. We present photonic networks-on-chip (NoC) as a solution to reduce the impact of intrachip and off-chip communication on the overall power budget. The low loss properties of optical waveguides, combined with bit-rate transparency, allow for a photonic interconnection network that can deliver considerably higher bandwidth and lower latencies with significantly lower power dissipation than an interconnection network based only on electronic signaling. We explain why on-chip photonic communication has recently become a feasible opportunity and explore the challenges that need to be addressed to realize its implementation. We introduce a novel hybrid microarchitecture for NoCs that combines a broadband photonic circuit-switched network with an electronic overlay packet-switched control network. This design leverages the strength of each technology and represents a flexible solution for the different types of messages that are exchanged on the chip; large messages are communicated more efficiently through the photonic network, while short messages are delivered electronically with minimal power consumption. We address the critical design issues including topology, routing algorithms, deadlock avoidance, and path-setup/teardown procedures. We present experimental results obtained with POINTS, an event-driven simulator specifically developed to analyze the proposed design idea, as well as a comparative power analysis of a photonic versus an electronic NoC. Overall, these results confirm the unique benefits for future generations of CMPs that can be achieved by bringing optics into the chip in the form of photonic NoCs.

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Recent remarkable advances in nanoscale siliconphotonic integrated circuitry specifically compatible with CMOS fabrication have generated new opportunities for leveraging the unique capabilities of optical technologies in the on-chip communications infrastructure. Based on these nano-photonic building blocks, we consider a photonic network-on-chip architecture designed to exploit the enormous transmission bandwidths, low latencies, and low power dissipation enabled by data exchange in the optical domain. The novel architectural approach employs a broadband photonic circuit-switched network driven in a distributed fashion by an electronic overlay control network which is also used for independent exchange of short messages. We address the critical network design issues for insertion in chip multiprocessors (CMP) applications, including topology, routing algorithms, path-setup and teardown procedures, and deadlock avoidance. Simulations show that this class of photonic networks-on-chip offers a significant leap in the performance for CMP intrachip communication systems delivering low-latencies and ultra-high throughputs per core while consuming minimal power.

We observe polarization-locked vector solitons in a mode-locked fiber laser. Temporal vector solitons have components along both birefringent axes. Despite different phase velocities due to linear birefringence, the relative phase of the components is locked at 6p͞2. The value of 6p͞2 and component magnitudes agree with a simple analysis of the Kerr nonlinearity. These fragile phaselocked vector solitons have been the subject of much theoretical conjecture, but have previously eluded experimental observation. [S0031-9007(99) The observation of temporal solitons in optical fiber [1] has resulted in a huge amount of research. This has been motivated by both fundamental interest and the potential for applications in telecommunications. Despite the fact that "single" (radial) mode optical fiber supports two orthogonal polarization modes, soliton propagation in optical fiber is often treated as a scalar problem, and the vector nature of light is ignored [2]. Although this would be valid if the fiber were truly isotropic, in reality it is always slightly birefringent due to strain, bends, etc. The presence of birefringence lifts the degeneracy between the two modes, resulting in coupling and differing phase and group velocities. Because of differing phase velocities, the soliton polarization will evolve as it propagates. A differing group velocity causes the energy propagating in each mode to temporally separate, destroying the soliton. Clearly, the very observation of solitons in fiber implies that the group velocity of the modes lock together. This occurs via a slight shift in the frequencies of the two orthogonal components, which shifts their group velocities, and has been the subject of both theory and experiment [3,4]. Normally, the polarization state of solitons propagating through low birefringence fiber remains uniform across the pulse but evolves with position [4,5].For solitons to propagate with a uniform, nonevolving polarization state, the phase velocities must lock. This was also predicted, resulting in a soliton that preserves its polarization state in the presence of birefringence. However, phase velocity locking is more difficult to obtain than group velocity locking because the phase velocity difference is larger in standard fiber. Furthermore, since the birefringence of standard single mode fiber is generally randomly distributed and propagation over long distances is accompanied by losses, experimental study of polarization-locked solitons in transmission systems is difficult. Here, we report the observation of such polarization-locked vector solitons (PLVS) in a mode-locked fiber laser. This mode-locked fiber laser provides a unique system that is nearly conservative, has well-controlled birefringence, and allows monitoring of the pulse during propagation over an essentially infinite distance. This makes it well suited for observing vector solitons in a controlled environment.The use of temporal vector solitons for communications [4] and all-optical switching [6] has been explored. Recently, the n...