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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Colliding Pulse Mode Locking and Nonequilibrium Carrier Dynamics within Vertical External-Cavity Surface-Emitting Lasers

The complex nonlinear dynamics of colliding counterpropagating ultrashort laser pulses circulating in a vertical external-cavity surface-emitting ring laser cavity are captured by a first-principles quantum-mechanical microscopic model coupled to an intracavity beam propagator. Furthermore, our numerical simulations establish that overall mode locking stability is sensitive to relative phases and delays of the pulses impinging on the semiconductor saturable absorber mirror. Delay offsets of the counterpropagating pulses lead to asymmetric carrier recovery and instability, often leading in turn to single unidirectional circulating pulses. Although computationally challenging, we also include transverse effects and show that the influence of interference patterns from spatial gratings written by the counterpropagating pulses is significant in stabilizing the modelocked pulses.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1975

Symbol synchronizer assembly instability study, part 2

Data processing to develop a third-order phase model and to translate all such processed data to the frequency realm for further analysis was described. The frequency study yields a long frequency modulation (FM) drift sinusoid (1600-sec period), an impressed secondary drift wave with a period of about 116 sec, and a set of even harmonics of twice the ramp period-the latter arising from, and used to modify, the phase detector model. The result is applied secondarily to estimate the strong-signal SSA phase detector response "out-of-lock." Finally, the main drift components are verified against all available data, and the result is used to estimate minimum lock conditions and the SSA drift effect under normal operating modes. The instability problem appears marginally resolvable if the acquisition technique is modified.

Bunce, R. C.↗
NASA NTRS1982

Developments in mode-locked lasers and their applications

The most important recent advance with respect to mode locking has been the development of 'colliding-pulse' mode locking. An important extension to this method is reported. According to this extension, the colliding pulse function is obtained by making use of an 'antiresonant ring' laser cavity. The new concept has been applied to a flash-pumped passively mode-locked Nd:YAG laser in a number of experiments. Attention is given to mode locking of a self-pumped phase conjugate laser, picosecond photoacoustic experiments, and picosecond pulses on semiconductor surfaces.

Siegman, A. E.↗
NASA NTRS1988

Airborne lidar global positioning investigations

The Global Positioning System (GPS) network of satellites shows high promise of revolutionizing methods for conducting surveying, navigation, and positioning. This is especially true in the case of airborne or satellite positioning. A single GPS receiver (suitably adapted for aircraft deployment) can yield positioning accuracies (world-wide) in the order of 30 to 50 m vertically, as well as horizontally. This accuracy is dramatically improved when a second GPS receiver is positioned at a known horizontal and vertical reference. Absolute horizontal and vertical positioning of 1 to 2 m are easily achieved over areas of separation of tens of km. If four common satellites remain in lock in both receivers, then differential phase pseudo-ranges on the GPS L-band carrier can be utilized to achieve accuracies of + or - 10 cm and perhaps as good as + or - 2 cm. The initial proof of concept investigation for airborne positioning using the phase difference between the airborne and stationary GPS receivers was conducted and is examined.

Krabill, W. B.↗
NASA NTRS1992

Electronic Control Of Slow Rotations

Digital/analog circuit controls both angular position and speed of rotation of motor shaft with high precision. Locks angular position of motor to phase of rotation-command clock signal at binary submultiple of master clock signal. Circuit or modified version used to control precisely position and velocity of robotic manipulator, to control translation mechanism of crystal-growing furnace, to position hands of mechanical clock, or to control angular position and rate of rotation in any of large variety of rotating mechanisms.

Howard, David E.↗
NASA NTRS1992

Behavior Of Costas Loop In Reception Of Telemetry

Report presents study of behavior of Costas loop in reception of binary non-return-to-zero telemetry signal phase-shift-modulated onto sinusoidal or square-wave subcarrier signal in turn phase-modulated onto carrier signal. Equations describe degradation of performance of Costas loop in terms of phase jitter, conditions causing loss of lock, and other effects. Costas loop used to track telemetry signal with residual carrier in presence of Doppler shift. Performance optimized by suitable choice of bit rate, waveform and frequency of subcarrier, and noise bandwidth of filters in arms of Costas loop.

Nguyen, Tien Manh↗
NASA NTRS1991

Low data rate coherent optical link demonstration using frequency stabilized solid state lasers

A low data rate laboratory heterodyne link demonstration operating at 1.06 micron using frequency stabilized Nd:YAG lasers was implemented. The data was modulated onto the optical carrier at 100 kbps using binary pulse position modulation. Phase coherent reception was achieved by closing the receiver phase tracking loop around the piezo-electric and temperature-tuned local oscillator laser. Initial frequency acquisition was accomplished by linearly scanning the LO frequency over the uncertainty range while a combined frequency and phase tracking loop searches for a lock indicator signal. The link performance was experimentally evaluated and compared to the theoretical predictions.

Chen, CHIEN-C.↗
NASA NTRS2008

Combined GMSK Communications and PN Ranging

A document discusses a method by which GMSK (Gaussian minimum shift keying) modulation and a pseudonoise (PN) ranging signal may be combined. By isolating the in-phase and quadrature components after carrier lock, and extracting their low-pass and band-pass filtered components, there is enough information available to both demodulate data and track the PN signal. The proposed combined GMSK communications and PN ranging is one potential approach to address emerging requirements for simultaneous high data rate communications from and tracking of vehicles in deep space or at the Moon.

Orr, Richard↗
NASA NTRS1998

Recent results with coupled opto-electronic oscillator

We present experimental results of coupled opto-electronic oscillators (COEO) constructed with a semiconductor optical amplifier based ring laser, a semiconductor Fabry-Perot laser, and a semiconductor colliding pulse mode-locked laser.

coupled↗
DOE OSTI2023

A high-resolution clock phase shifter circuitry for ALTIROC

Abstract A high-resolution clock phase shifter is implemented to adjust the phase of multiple clocks at 40 MHz, 80 MHz, or 640 MHz in the ALTIROC chip. The phase shifter has a coarse-phase shifter and a fine-phase shifter to achieve a step size of 97.7 ps and an adjustable range of 25 ns. The fine delay unit is based on a Delay Locked Loop (DLL) operating at 640 MHz. The phase shifter is fabricated in a 130 nm CMOS process. The area of the phase shifter is 725 µm × 248 µm. The Differential Non-Linearity (DNL) and the Integral Non-Linearity (INL) are ±0.6 LSB and ±0.75 LSB, respectively. The jitter from −25 °C to 20 °C is less than 15.5 ps (RMS), including the contributions from the FPGA clock source and the PLL. The power consumption is 11.2 mW.

Instruments & Instrumentation↗
NASA NTRS2004

An exact solution for the steady state phase distribution in an array of oscillators coupled on a hexagonal lattice

When electronic oscillators are coupled to nearest neighbors to form an array on a hexagonal lattice, the planar phase distributions desired for excitation of a phased array antenna are not steady state solutions of the governing non-linear equations describing the system. Thus the steady state phase distribution deviates from planar. It is shown to be possible to obtain an exact solution for the steady state phase distribution and thus determine the deviation from the desired planar distribution as a function of beam steering angle.

injection locking↗
NASA NTRS1999

Two-dimensional Array Beam Scanning via Externally and Mutually Injection Locked Coupled Oscillators

Some years ago, Stephan proposed an approach to one dimensional (linear) phased array beam steering which requires only a single phase shifter. This involves the use of a linear array of voltage-controlled electronic oscillators coupled to nearest neighbors. The oscillators are mutually injection locked by controlling their coupling and tuning appropriately.Stephan's approach consists of deriving two signals from a master oscillator, one signal phase shined with respect to the other by means of a single phase shifter. These two signals are injected into the end oscillators of the array as shown in Figure 1. The result is a linear phase progression across the oscillator array. Thus, if radiating elements are connected to each oscillator and spaced uniformly along a line, they will radiate a beam at an angle to that line determined by the phase gradient which is, in turn, determined by the phase difference between the injection signals. The beam direction is therefore controlled by adjusting this phase difference.

Pogorzelski, Ronald J.↗
NASA NTRS2000

Two-Dimensional Array Beam Scanning Via Externally and Mutually Injection Locked Coupled Oscillators

Some years ago, Stephan proposed an approach to one dimensional (linear) phased array beam steering which requires only a single phase shifter. This involves the use of a linear array of voltage-controlled electronic oscillators coupled to nearest neighbors. The oscillators are mutually injection locked by controlling their coupling and tuning appropriately. Stephan's approach consists of deriving two signals from a master oscillator, one signal phase shifted with respect to the other by means of a single phase shifter. These two signals are injected into the end oscillators of the array. The result is a linear phase progression across the oscillator array. Thus, if radiating elements are connected to each oscillator and spaced uniformly along a line, they will radiate a beam at an angle to that line determined by the phase gradient which is, in turn, determined by the phase difference between the injection signals.The beam direction is therefore controlled by adjusting this phase difference. Recently, Pogorzelski and York presented a formulation which facilitates theoretical analysis of the above beam steering technique. This was subsequently applied by Pogorzelski in analysis of two dimensional beam steering using perimeter detuning of a coupled oscillator array. The formulation is based on a continuum model in which the oscillator phases are represented by a continuous function satisfying a partial differential equation of diffusion type. This equation can be solved via the Laplace transform and the resulting solution exhibits the dynamic behavior of the array as the beam is steered. Stephan's beam steering technique can be similarly generalized to two-dimensional arrays in which the beam control signals are applied to the oscillators on the perimeter of the array. In this paper the continuum model for this two-dimensional case is developed and the dynamic solution for the corresponding aperture phase function is obtained. The corresponding behavior of the resulting far-zone radiation pattern is displayed as well.

Pogorzelski, Ronald J.↗
NASA NTRS1980

Alias lock behavior of sampled-data Costas loops

The potential false-lock problem associated with the sampled data type of Costas loop implementation is addressed in this paper. The term 'alias lock' is used here to differentiate this type of false lock behavior from the data sideband false lock behavior of analog Costas loops. It is shown that the sampled-data version of the conventional Costas loop, sampled at a rate 1/T(s), can alias lock at frequencies that are multiples of 1/2T(s) away from the carrier frequency. It is also shown that the alias lock problem of the sampled data version of the Costas loop with hard-limited in-phase channel is further compounded by the potential occurrence of false lock frequencies at rational multiples of 1/2T(s) away from the carrier. The false lock S-curves of I-Q loops and decision-directed I-Q loops are investigated in detail, with and without additive noise. Close agreement between theory and earlier experimental results is also demonstrated.

Simon, M. K.↗
NASA NTRS1994

Optical Heterodyne With Lower Phase Noise

Proposed improvement enhances utility of optical-heterodyne apparatus used to generate radio signal at chosen frequency between 1 and 1,000 GHz. Two lasers injection-locked to third, mode-locked laser. Beat-frequency heterodyne output contains much less phase noise if generated from outputs of two independent lasers, and phase-coherent with reference signal. Potential applications include phased-array radar, fiber-optic communication systems, fiber-optic stabilized oscillators, and other applications involving conversions between optical and millimeter-wave signals.

Logan, Ronald T.↗
DOE OSTI2025

Unified ELM Suppression on KSTAR and DIII-D via Adaptive Feedback Control Strategies

This paper reports on the extension of our amplitude-based resonant magnetic perturbation (RMP) edge localized mode (ELM) controller to support phasing control (relative toroidal phases of RMP waveforms between rows of coils), multiple toroidal mode numbers, and new ‘jump’ and ‘probing’ strategies, all deployed on KSTAR and DIII-D. By treating the control algorithm as device-independent and adjusting only the real-time interfaces to sensors and power supplies, we have confirmed that the same finite state machine—based feedback logic can be ported between machines with minor modifications. In experiments using n = 2 RMPs on KSTAR and n = 3 on DIII-D, the controller successfully modulated RMP amplitudes in real time to sustain ELM suppression while minimizing confinement degradation. Phasing control broadened the suppression window, as it permitted the system to avoid locked-mode regions and safely access ELM-free conditions. A rotating RMP phasing scheme, integrated into the same framework, distributes divertor heat loads more uniformly, making it a promising strategy for protecting plasma-facing components during long discharges. New ‘jump’ and ‘probing’ techniques demonstrate the possibility for the controller to preempt imminent ELMs and refine the minimum required RMP amplitude without returning to ELMy conditions. Taken together, these upgrades enable extended ELM-free operation while mitigating confinement degradation, providing a practical framework for real-time ELM control in future high-performance tokamaks.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Thermal quench in ITER locked mode disruptions

Simulations and theory are presented of an ITER locked mode thermal quench(TQ). In present experiments, locked mode disruptions have a long precursor phase,followed by a rapid termination and thermal quench, which can be identified with a resistive wall tearing mode (RWTM). In ITER, the RWTM will be slowed by the highly conductive vacuum vessel. Here, the rapid termination might be absent, and the plasma could remain in the precursor phase. If the edge temperature is in the collisional regime, the TQ would proceed on a long timescale, limited by the RWTM to almost100ms. This is an important self mitigating effect.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗