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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Frequency and Phase-lock Control of a 3 THz Quantum Cascade Laser

We have locked the frequency of a 3 THz quantum cascade laser (QCL) to that of a far-infrared gas laser with a tunable microwave offset frequency. The locked QCL line shape is essentially Gaussian, with linewidths of 65 and 141 kHz at the -3 and -10 dB levels, respectively. The lock condition can be maintained indefinitely, without requiring temperature or bias current regulation of the QCL other than that provided by the lock error signal. The result demonstrates that a terahertz QCL can be frequency controlled with l-part-in-lO(exp 8) accuracy, which is a factor of 100 better than that needed for a local oscillator in a heterodyne receiver for atmospheric and astronomic spectroscopy.

Betz, A. L.↗
NASA NTRS1994

Internal impacted screw-locking pellet

An elongate fastener having an engaging surface engageable with an engaging surface of a fastener's mate includes a hole extending through a portion of the fastener and having a top opening and a bottom floor, a locking pellet disposed near the bottom floor, a discharge channel communicating between the pellet and through the engaging surface of the fastener and opening out toward the engaging surface of the fastener's mate, and an impact pin in the hole having a top portion protruding through the top opening and a bottom portion near the locking pellet, whereby the pin drives the locking pellet through the discharge channel against the engaging surfaces of the fastener and the fastener's mate whereby to lock the fastener against the fastener's mate.

MacMartin, Malcolm J.↗
NASA NTRS2008

Frequency-Tunable Pre-stabilized lasers for LISA via Stabilized Lasers for LISA via Sideband Locking

This viewgraph presentation discusses a major potential source of noise for the Laser Interferometer Space Antenna (LISA) that is the laser frequency noise and the proposed mechanism to suppress the unstabilized frequency fluctuations. These fluctuations must be suppresed by about 12 orders of magnitude to achieve a stability that is sufficient for the detection of gravitational waves. This presentation reviews present a modification to the traditional cavity locking technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This presentation also discusses measurements of the system stability, demonstrating that the pre-stabilization level satisfies LISA requirements and a demonstration of a phase-lock loop which utilizes the tunable sideband locking technique as a pre-stabilization stage.

Livas, Jeffrey↗
NASA NTRS2011

Time Domain Simulations of Arm Locking in LISA

Arm locking is a technique that has been proposed for reducing laser frequency fluctuations in the Laser Interferometer Space Antenna (LISA). a gravitational-wave observatory sensitive' in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that comprise LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of arm locking including the expected limiting noise sources (shot noise, clock noise. spacecraft jitter noise. and residual laser frequency noise). The effect of imperfect a priori knowledge of the LISA heterodyne frequencies and associated "pulling" of an arm locked laser is included. We find that our implementation meets requirements both on the noise and dynamic range of the laser frequency.

Thorpe, J. I.↗
NASA NTRS2008

Fundamental Noise-Limited Optical Phase Locking at Femtowatt Light Levels

We describe an optical phase lock loop (PLL) designed to recover an optical carrier at powers below one picowatt in a Deep Space optical transponder. Previous low power optical phase lock has been reported with powers down to about 1 pW. We report the demonstration and characterization of the optical phase locking at femtowatt levels. We achieved a phase slip rate below one cycle-slip/second at powers down to 60 femtowatts. This phase slip rate corresponds to a frequency stability of 1 10(exp -14) at 1 s, a value better than any frequency standard available today for measuring times equal to a typical two-way delay between Earth and Mars. The PLL shows very robust stability at these power levels. We developed simulation software to optimize parameters of the second order PLL loop in the presence of laser flicker frequency noise and white phase (photon) noise, and verified the software with a white phase noise model by Viterbi. We also demonstrated precise Doppler tracking at femtowatt levels.

Doppler ranging↗
NASA NTRS1971

Injection locking in IMPATT diode oscillators.

A model for an injection-locked IMPATT diode oscillator is presented and used to calculate the locking behavior of the oscillator at different operating points. The model is compared with earlier theories of injection locking in IMPATT diode oscillators and the calculated results are compared with experimental observations.

Gupta, M. S.↗
NASA NTRS1972

A class of all digital phase locked loops - Modelling and analysis.

An all digital phase locked loop which tracks the phase of the incoming signal once per carrier cycle is proposed. The different elements and their functions, and the phase lock operation are explained in detail. The general digital loop operation is governed by a non-linear difference equation from which a suitable model is developed. The lock range for the general model is derived. The performance of the digital loop for phase step, and frequency step inputs for different levels of quantization without loop filter, are studied. The analytical results are checked by simulating the actual system on the digital computer.

Reddy, C. P.↗
NASA NTRS1972

Orientation and resonance locks for satellites in the elliptic orbit.

In order to achieve the maximum strength of higher resonance locks for satellites in the elliptic orbit, the condition of satellite orientation during the process of deployment is established. It is shown that for maximum strength locks the axis of the minimum moment of inertia of satellites should point toward the attracting body at plus or minus (5/8) pi and 0 values of the true anomaly f. This condition of deployment is applicable to all cases of resonance rotation regardless of the value of lock number k and orbit eccentricity e.

Liu, H.-S.↗
NASA NTRS1973

A class of all digital phase locked loops - Modeling and analysis

An all digital phase locked loop which tracks the phase of the incoming signal once per carrier cycle is proposed. The different elements and their functions, and the phase lock operation are explained in detail. The general digital loop operation is governed by a nonlinear difference equation from which a suitable model is developed. The lock range for the general model is derived. The performance of the digital loop for phase step and frequency step inputs for different levels of quantization without loop filter are studied. The analytical results are checked by simulating the actual system on the digital computer.

Reddy, C. P.↗
NASA NTRS1974

Binary phase locked loops for Omega receivers

An all-digital phase lock loop (PLL) is considered because of a number of problems inherent in an employment of analog PLL. The digital PLL design presented solves these problems. A single loop measures all eight Omega time slots. Memory-aiding leads to the name of this design, the memory-aided phase lock loop (MAPLL). Basic operating principles are discussed and the superiority of MAPLL over the conventional digital phase lock loop with regard to the operational efficiency for Omega applications is demonstrated.

Chamberlin, K.↗
NASA NTRS1978

The false lock performance of Costas loops with hard-limited in-phase channel

The ability of a Costas loop to false lock on a data sideband is a problem which must be dealt with in the design of suppressed-carrier receivers which employ such loops for carrier reconstruction. For conventional Costas loops wherein the error signal is formed from the product of two analog signals, the false lock problem has recently been investigated by the author and others and is now well understood. For implementation reasons associated with the reduction of dc offsets, it is often desirable to hard-limit the output of the in-phase channel and replace the analog multiplier which forms the above product with a chopper-type device. The false lock behavior of such a Costas loop with hard-limited in-phase channel is quite different from that of the conventional Costas loop and is the subject of investigation in this paper. Results are also presented for a modified version of the Costas loop wherein the quadrature arm filter is removed.

Simon, M. K.↗
NASA NTRS1978

Spatially coherent beam formation and mode locking of an array of solid-state lasers

A study is reported on the spatially coherent beam formation from an array of four Nd-glass lasers and on mode locking of their longitudinal modes. The results indicate a nearly 16 times increase in radiance. For mode locking, only a single modulator is required. A spatial filter in the optical cavity performs the spatially coherent beam formation and the precision synchronization of the mode-locked pulses at the output mirror of the optical cavity.

Philipp-Rutz, E. M.↗
NASA NTRS1977

On the false lock behavior of polarity-type Costas loops with Manchester coded input

A modification of a Costas loop is described, and the false lock behavior of this system is studied. The modified Costas loop hard limits the output of the in-phase channel, replaces the analog multiplier with a chopper-type device, and is equipped with single-pole arm filters in the loop. The false lock behavior associated with the use of Manchester coded data is investigated; the results can be applied to the assessment of the false lock margin on the Ku-band uplink to the Space Shuttle Orbiter through the TURSS.

Simon, M. K.↗
NASA NTRS1978

Phase-locked loops and their application

A collection of papers is presented on the characteristics and capabilities of phase-locked loops (PLLs), along with some applications of interest. The discussion covers basic theory (linear and nonlinear); acquisition; threshold; stability; frequency demodulation and detection; tracking; cycle slipping and loss of lock; phase-locked oscillators; operation and performance in the presence of noise; AGC, AFC, and APC circuits and systems; digital PLL; and applications and miscellaneous. With the rapid development of IC technology, PLLs are expected to be used widely in consumer electronics.

Lindsey, W. C.↗
NASA NTRS1980

Analysis of first and second order binary quantized digital phase-locked loops for ideal and white Gaussian noise inputs

Specific configurations of first and second order all digital phase locked loops are analyzed for both ideal and additive white gaussian noise inputs. In addition, a design for a hardware digital phase locked loop capable of either first or second order operation is presented along with appropriate experimental data obtained from testing of the hardware loop. All parameters chosen for the analysis and the design of the digital phase locked loop are consistent with an application to an Omega navigation receiver although neither the analysis nor the design are limited to this application.

Blasche, P. R.↗
NASA NTRS1983

Control of mutual phase locking of monolithically integrated semiconductor lasers

The degree of phase locking between the individual laser apertures is the major issue in phase-locked laser arrays. A description is presented of a series of experiments in which the mutual coherence of two laser apertures is characterized by measuring the visibility of the far-field interference fringes. Attention is given to an approach which makes it possible to control continuously the degree of coherence by means of a separate contact configuration. An investigation was conducted of the far-field radiation patterns of pairs of lasers obtained under various conditions. The results of the present study demonstrate the feasibility of controlling the mutual phase locking between semiconductor lasers by varying the gain distribution between their pumped stripes.

Kapon, E.↗
NASA NTRS1985

New results on the PLL false lock phenomenon

Conditions, based on the multipliers of a linear differential equation with periodic coefficients, for the occurrence of false lock in a phase lock loop (PLL) are presented. Two new and powerful algorithms are presented for computing the frequency difference between the reference and voltage controlled oscillator when the loop is false locked. The first algorithm expresses omega f sup -1 as a power series in the closed loop gain. The second algorithm expresses omega sup -1 as part of a solution to a nonlinear algebraic system of equations which can be solved by numerical methods. The power of both algorithms is illustrated by application and comparison.

Stensby, J. L.↗
NASA NTRS1985

Self-locking mechanical center joint

A device for connecting, rotating and locking together a pair of structural half columns is described. The device is composed of an identical pair of cylindrical hub assemblies connected at their inner faces by a spring loaded hinge; each hub assembly having a structural half column attached to its outer end. Each hub assembly has a spring loading locking ring member movably attached adjacent to its inner face and includes a latch member for holding the locking ring in a rotated position subject to the force of its spring. Each hub assembly also has a hammer member for releasing the latch on the opposing hub assembly when the hub assemblies are rotated together. The spring loaded hinge connecting the hub assemblies rotates the hub assemblies and attached structural half columns together bringing the inner faces of the opposing hub assemblies into contact with one another.

Bush, H. G.↗