Optical frequency stabilisation and line width reduction of a multielectrode DFB laser with current feedback

This study employs an experimental setup with a variable feedback fraction (fext), external cavity length (ECL), and pump current (J) to investigate their relationships with optical linewidth and external optical feedback-induced speckle contrast (SC) reduction in a visible laser diode. In total, speckle contrast and optical linewidth data for seven feedback fractions, two pump currents, and three external cavity lengths were collected. Achieving optical linewidths up to 3.90 nm (1/e2 width) and a reduction in speckle contrast of up to 41.6%, we also revealed negative correlations between speckle contrast and optical linewidth, and speckle contrast and feedback fraction, and a positive correlation between optical linewidth and feedback fraction.

The proton magnetic resonance absorption in anhydrous potassium stearate has been measured over the temperature range −190 °C to 182 °C. Abrupt changes in line width have been found between 55 °C and 62 °C, and between 170 °C and 171 °C; these changes correspond approximately to known phase transitions. The reduction in line width and second moment with rising temperature is discussed.

Extreme ultra-violet lithography (EUVL) has been prepared for next generation lithography for several years. We could get sub-22 nm line and space (L/S) pattern using EUVL, but there are still some problems such as roughness, sensitivity, and resolution. According to 2007 ITRS roadmap, line edge roughness (LER) has to be below 1.9 nm to get a 22 nm node, but it is too difficult to control line width roughness (LWR) because line width is determined by not only the post exposure bake (PEB) time, temperature and acid diffusion length, but also the component and size of the resist. A new method is suggested to reduce the roughness. The surface roughness can be smoothed by applying the resist reflow process (RRP) for the developed resist. We made resist profile which has surface roughness by applying exposure, PEB and development process for line and space pattern. The surface roughness is calculated by changing parameters such as the protected ratio of resin. The PEB time is also varied. We compared difference between 1:1 L/S and 1:3 L/S pattern for 22 nm. Developed resist baked above the glass transition temperature will flow and the surface will be smoothed. As a result, LER and LWR will be much smaller after RRP. The result shows that the decreasing ratio of LER due to RRP is larger when initial LER is large. We believe that current ~ 5 nm LWR can be smoothed to ~ 1 nm by using RRP after develop.

This paper presents the design of fully differential second-order delta-sigma modulator. A current feedback technique is used in the proposed switched-current feedback memory cell (FMC) to decrease the input impedance and to improve the transmission error in the memory cell. Furthermore, the entire memory cell is designed in a coupled differential replicate (CDR) form to eliminate the clock feedthrough (CFT) error. In this paper, the SDM is simulated with TSMC 0.35 micrometre CMOS process technology. The simulation results reveal that the peak signal to noise plus distortion ratio (SNDR) is 75 dB at 10.24 MHz sampling rate with 40 kHz bandwidth, and the power dissipation is 16 mW.

19F NMR spectroscopy has recently witnessed a resurgence as an attractive analytical tool for the study of the structure and dynamics of biomolecules in vitro and in cells, despite reports of its applications in biomolecular NMR since the 1970s. The high gyromagnetic ratio, large chemical shift dispersion, and complete absence of the spin 1/2 19F nucleus from biomolecules results in background-free, high-resolution 19F NMR spectra. The introduction of 19F probes in a few selected locations in biomolecules reduces spectral crowding despite its increased line width in comparison to typical 1H NMR line widths and allows rapid site-specific measurements from simple 1D spectra alone. The design and synthesis of novel 19F probes with reduced line widths and increased chemical shift sensitivity to the surrounding environment, together with advances in labeling techniques, NMR methodology, and hardware, have overcome several drawbacks of 19F NMR spectroscopy. The increased interest and widespread use of 19F NMR spectroscopy of biomolecules is gradually establishing it as a sensitive and high-resolution probe of biomolecular structure and dynamics, supplementing traditional 13C/15N-based methods. This Review focuses on the advances in 19F solution NMR spectroscopy of proteins in the past 5 years, with an emphasis on novel 19F tags and labeling techniques, NMR experiments to probe protein structure and conformational dynamics in vitro, and in-cell NMR applications.

CMOS scaling affects the subthreshold current per IC, and it directly impacts the utility of Iddq testing for CMOS devices. Continued IC manufacturing refinements enable a factor of /spl radic/2 reduction in line widths every three years. This in conjunction with an increase in chip size makes it possible to increase the number of transistors per IC by a factor between two and three. This trend in CMOS technology is expected to continue over at least the next ten years. The scaling of devices affects numerous device parameters, one being the subthreshold current commonly known as the leakage current. Assuming defect size scales with technology, it will be explained why it will become increasingly difficult to differentiate good and defective devices based upon an Iddq test methodology.

A novel feed-forward phase noise reduction scheme is introduced to reduce the phase noise of an optical frequency comb. The phase noise of a single comb line is measured using a heterodyne technique, and the inverse of this signal is then applied to the entire comb. The method is capable of simultaneously reducing the phase noise of multiple lines and is limited only by the correlation of phase noise across the comb. Experimentally, we demonstrate a reduction in the optical linewidth of a 16-mode optical frequency comb derived from a mode-locked semiconductor laser from around 20 MHz to less than 300 kHz, with 11 of the 16 output spectral modes possessing optical linewidths less than 100 kHz.

We analyze the possibility of linewidth reduction of a semiconductor laser when a feedback signal is obtained directly from the noise voltage at the electrical terminal, rather than indirectly from the optical field. For sufficiently large gain in a feedback loop we find, by solving the linearized laser rate equations, that the spectral fluctuations of the instantaneous frequency are suppressed for frequencies less than a value dependent on the width of the feedback gain response. If the suppressed width is sufficiently large, the power spectrum of the field is a lorentzian of width uf=uf0[1+α2/ΓIΚo/Ω 2)2], where dr() is one half the Schawlow-Townes width, a is the linewidth parameter, 0 is the relaxation oscillation frequency, Ko is the DC gain of the feedback loop and F1 is the damping rate of the photon number fluctuations. Thus, for large Ico, this method of linewidth reduction appears capable of removing the a2 contribution to the laser frequency spread. For values of the feedback response band width, u w, less than that required for full suppression of the a2 contribution to the line width, the line shape may deviate considerably from a lorentzian form but with a central peak of width uf = ufo.

Absolute performance and price/performance of computing systems have advanced at an extremely rapid rate since the early 1950’s. The rapid decrease in the cost per operation has caused the computer industry’s designers to begin thinking of “computers as commodities”. High volume manufacturing and mass markets have even challenged mission-oriented government agencies to consider commercial off-the-shelf technology as the best path to ever higher performance at a reasonable cost. The reduction of printable line widths for integrated circuits has been primarily responsible for this trend. While the projected improvements in line width continue, there has been a decline in the rate of minimum feature improvement. Short of a revolutionary breakthrough, it is generally believed that only modest gains (relative to the historical trends) will come with higher gate and clock speeds alone. Rather, higher density active devices coupled with scalable architectures and three-dimensional packaging technologies will provide the new high performance solutions.

Carrier frequency offset (CFO) destroys the orthogonality of the subcarriers and causes intercarrier interference (ICI). ICI self-cancellation scheme proposed by Zhao et al. is the simplest scheme to mitigate the effect of ICI. It repeats the same data symbol on two adjacent subcarriers with phase inversion and therefore does not provide any frequency diversity. To achieve frequency diversity Tang et al. proposed a symmetric data conjugate transmission scheme to mitigate the effect of ICI but its BER performance degrades at higher values of CFO. In order to improve its BER performance, a phase rotated symmetric data conjugate transmission scheme to mitigate the effect of ICI has been proposed in this paper. Like symmetric data conjugate scheme, proposed scheme also repeats the same data symbol with phase rotation on two symmetrically located subcarriers to achieve frequency diversity. The analytical expression for optimal phase rotation factor to optimize the carrier-to-interference ratio (CIR) performance of the proposed scheme is also derived. It has been shown that proposed scheme provides better performance than that of the conventional symmetric data conjugate scheme especially at high CFO.

Current haptic feedback techniques on handheld devices are applied to the finger pad or the palm of the user. These state-of-the-art approaches are coarse-grained and tend to be intrusive, rather than subtle. In contrast, we present a new feedback technique that applies stimuli around the periphery of the finger pulp, demonstrating how this can provide rich, nuanced haptic information. We use a reconfigurable haptic device employing a ferromagnetic marble for back-of-the device handheld use, which, for the first time, probes, without instrumenting the user, the periphery of the distal phalanx with localised stimulation. We present the design-space afforded by this new technique and evaluate the human-factors of finger-peripheral touch interaction in a controlled user-study. We report results with marbles of different diameters, speeds and a combination of poking, lateral vibration and patterns; present the resulting design guidelines for finger-periphery haptic feedback; and, illustrate its potential with use case scenarios.

We consider a binary discrete channel with phase inversion and with random errors. Such a channel is a cascade of two channels. We also consider a continuous channel with phase inversion. For both channels, we wish to correct a phase inversion error when it occurs as well as random errors. For this purpose, we introduce a special metric to describe combinations of these errors. We call this metric the phase rotating metric (PR-metric). In this paper, we consider constructions of PR-metric codes together with their hard decision decoding for a discrete channel and their soft decision decoding for a continuous channel with phase inversion.

We calculate the effect of nonlinear interactions among solar acoustic modes upon the modal frequencies and energy loss rates (or line widths). The frequency shift for a radial p-mode of frequency 3 mHz is found to be about -0.5 µHz. The magnitude of nonlinear frequency shift increases more rapidly with frequency than the inverse mode mass (mode mass is defined as the ratio of energy in the mode to its surface velocity amplitude squared). This frequency shift is primarily due to nonresonant three-mode interactions and is dominated by high l surface gravity waves (ƒ-modes) and p-modes. The line width of a radial p-mode of frequency 3 mHz, due to resonant nonlinear interactions, is about 0.3 µHz. This result is consistent with that of Kumar & Goldreich (1989). We also find, in agreement with these authors, that the most important nonlinear interactions of trapped p-modes involve ƒ-modes and high-frequency p-modes (frequency greater than about 5 mHz) which propagate in the solar photosphere. Thus, using the arguments advanced by Kumar & Goldreich (1989), we conclude that nonlinear couplings cannot saturate the overstable solar p-modes at their small observed amplitudes. Both the nonlinear frequency shifts and line widths, at a fixed frequency, are proportional to the inverse of mode mass which for modes of degree greater than about 100 is ~ l^(0.8). Therefore, the frequency of an ƒ-mode of l = 1000, due to nonlinear interactions, is decreased by approximately 0.4%.

Diode laser spectroscopy of complex molecules with enclosive flow cooling for spectral simplification

Electrical negative frequency feedback control has been shown to reduce frequency modulation (FM) noise linewidth in semiconductor lasers. The method is based on the direct frequency modulation capability of a semiconductor laser. An error signal is extracted through optical heterodyne frequency discrimination detection using a stable master laser. FM noise is reduced by more than 20 dB and linewidth is reduced by one order of magnitude.