On-chip CMOS-compatible all-optical integrator

One reason for using photonic devices is their speed—much faster than electronic circuits—but there are many challenges in integrating the two technologies. Ferrera et al. construct a CMOS-compatible monolithic optical waveform integrator, a key building block for photonic circuits

Corrigendum

Nelson DA, Burgansky-Eliash Z, Barash H, Loewenstein A, Barak A, Bartov E, Rock T, Grinvald AHigh-resolution widefield imaging of perfused capillaries without the use of contrast agentClinical Ophthalmology. 2011;5:1095-1106.The authors of this paper and their affiliations are as follows.Darin A Nelson1Amit Ruf1Jacob Oaknin1Zvia Burgansky-Eliash1,2Hila Barash1David Izhaky1Anat Loewenstein3Adiel Barak4Elisha Bartov2Tali Rock2Amiram Grinvald51Optical Imaging Ltd, Rehovot, Israel; 2Department of Ophthalmology, Edith Wolfson Medical Center, Holon, Israel; 3Department of Ophthalmology, Tel Aviv Medical Center and Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel; 4Department of Ophthalmology, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel; 5Department of Neurobiology, The Weizmann Institute of Science, Rehovot, IsraelOriginal Articl

Differential detection of dual traps improves the spatial resolution of optical tweezers

The drive toward more sensitive single-molecule manipulation techniques has led to the recent development of optical tweezers capable of resolving the motions of biological systems at the subnanometer level, approaching the fundamental limit set by Brownian fluctuations. One successful approach has been the dual-trap optical tweezers, in which the system of study is held at both ends by microspheres in two separate optical traps. We present here a theoretical description of the Brownian limit on the spatial resolution of such systems and verify these predictions by direct measurement in a Brownian noise-limited dual-trap optical tweezers. We find that by detecting the positions of both trapped microspheres, correlations in their motions can be exploited to maximize the resolving power of the instrument. Remarkably, we show that the spatial resolution of dual optical traps with dual-trap detection is always superior to that of more traditional, single-trap designs, despite the added Brownian noise of the second trapped microsphere

Using mechanical force to probe the mechanism of pausing and arrest during continuous elongation by Escherichia coli RNA polymerase

Escherichia coli RNA polymerase translocates along the DNA discontinuously during the elongation phase of transcription, spending proportionally more time at some template positions, known as pause and arrest sites, than at others. Current models of elongation suggest that the enzyme backtracks at these locations, but the dynamics are unresolved. Here, we study the role of lateral displacement in pausing and arrest by applying force to individually transcribing molecules. We find that an assisting mechanical force does not alter the translocation rate of the enzyme, but does reduce the efficiency of both pausing and arrest. Moreover, arrested molecules cannot be rescued by force, suggesting that arrest occurs by a bipartite mechanism: the enzyme backtracks along the DNA followed by a conformational change of the ternary complex (RNA polymerase, DNA and transcript), which cannot be reversed mechanically

CMOS-compatible integrated optical hyper-parametric oscillator

Integrated multiple-wavelength laser sources, critical for important applications such as high-precision broadband sensing and spectroscopy, molecular fingerprinting, optical clocks and attosecond physics, have recently been demonstrated in silica and single-crystal microtoroid resonators using parametric gain. However, for applications in telecommunications and optical interconnects, analogous devices compatible with a fully integrated platform do not yet exist. Here, we report a fully integrated, CMOS-compatible, multiple-wavelength source. We achieve optical hyper-parametric oscillation in a high-index silica-glass microring resonator with a differential slope efficiency above threshold of 7.4% for a single oscillating mode, a continuous-wave threshold power as low as 54mW, and a controllable range of frequency spacing from 200GHz to more than 6THz. The low loss, design flexibility and CMOS compatibility of this device will enable the creation of multiple-wavelength sources for telecommunications, computing, sensing, metrology and other areas

Assessment of potential vessel segmentation pitfalls in the analysis of blood flow velocity using the Retinal Function Imager

PURPOSE: The purpose of our study was to investigate the potential pitfalls linked to different vessel segmentation methods when using the built-in software of the Retinal Function Imager (RFI) for the analysis of retinal blood flow velocities (BFVs). METHODS: Ten eyes of nine healthy subjects were enrolled in the study. Retinal blood flow measurements were obtained with the RFI device with a 20° field of view imaging. The same grader segmented the retinal vasculature using the RFI software in two sessions with segments ranging from 50 to 100 pixels (“short segments”) or 100-200 pixels long (“long segments”). The blood flow velocities for the arteriolar and venular system were calculated and the percentage of excluded vessel segments with high coefficients of variation (>45%) was recorded and compared by paired t-test. Spearman correlation was used to analyze the link between the two measurements by the two vessel segmentation methods. RESULTS: The number of analyzed vessel segments did not differ significantly in the two groups (28.6±2.6 short and 26.7±4.6 long segments, respectively), while the percent of acceptable segments was significantly higher in the long segment group (65.2±11.4% vs 85.2±5.87%, p=0.001). All subjects in the short segment group had more than 15% of vessel segments rejected, while in the long segment group only three subjects had a rejection rate of 15% (16.7%, 18.7% and 28%). Both arteriolar and venular velocities were lower in the short segment group, although it reached significance only in the case of the arteriolar velocities (3.93±0.55 vs 4.45±0.76 mm/s, p=0.036 and 2.95±0.56 vs. 3.17±0.84 mm/s, p=0.201 for arterioles and venules, respectively). Only the venular velocities showed significant correlation (p=0.003, R(2)=0.67) between the two groups. CONCLUSIONS: Our results suggest that BFV measurements by the RFI may be affected by the segment length and therefore care should be taken when choosing the vessel segment lengths used during the analysis of RFI data. Long segments of 100-200 pixels (400-800 μm) seem to provide more robust measurements which can be explained by the analysis methodology of the RFI device