Design of Low Voltage Unsaturated Ring Oscillator for a Sigma Delta Time to Digital Converter

This thesis investigates the phase noise of two different 2-stage cross-coupled pair unsaturated ring oscillators with no tail current source. One oscillator consists of top cross-coupled pair delay cells, and the other consists of top cross-coupled pair and bottom cross-coupled pair delay cells. Under a low supply voltage restriction, a phase noise model is developed and applied to both ring oscillators. Both top cross-coupled pair and top and bottom cross-coupled pair oscillators are fabricated with 0.13 um CMOS technology. Phase noise measurements of -92 dBc/Hz and -89 dBc/Hz ,respectively, at 1 MHz offset is obtained from the chip, which agree with theory and simulations. Top cross-coupled ring oscillator, with phase noise of -92 dBc/Hz at 1 MHz offset, is implemented in a second order sigma-delta time to digital converter. System level and transistor level functional simulation and timing jitter simulation are obtained

Generation of High-Energy Pulses by Managing the Kerr-Nonlinearity in Fiber-Based Laser Amplifiers

Increasing the pulse energy of ultrafast laser systems is an important field of laser development. High pulse energies simplify and accelerate most applications, such as the stimulation of optical parametric effects or the processing of materials. The amplification of ultrashort pulses in glass fibers is a prominent method, as fiber amplifiers are inexpensive, flexible and highly-integrated. Resulting from the strong confinement in the fiber core and the high peak intensities of the laser pulses, the amplification is often limited by the onset of a nonlinear deterioration of the pulses. Within this thesis, two methods of fiber-based pulse amplification by managing the Kerr-nonlinearity are presented. In the first method, the chirped-pulse amplification, nonlinear effects are suppressed by locally reducing the peak intensity. A chirped-pulse amplifier was realized that generated pulses with energies of 450 nJ and durations of 293 fs, limited by pump power. These pulse parameters were not sufficient for the intended application. In order to further decrease the pulse duration and increase pulse energy, the parameters of the amplified pulses had to be decoupled from the seed pulses. This is achieved in an amplifier based on the second approach. By enforcing the impact of Kerr-nonlinearity, the optical spectrum of self-similar pulses could be broadened by self-phase modulation during the amplification to generate pulses with 1 µJ pulse energy and a compressed duration of 50 fs at which level the amplification was limited by transverse mode instabilities. This improvement of pulse parameters by nonlinear techniques is also exploited in a pulse regenerator. By feeding back a part of the amplified pulse into a second amplifier, a so-called Mamyshev oscillator is formed. Its principle of alternating spectral filtering between sections of gain and spectral regeneration allowed for the generation of mode-locked pulses. This Mamyshev oscillator was optimized for the generation of high-energy pulses by the analysis of optimum band-pass filter parameters and the implementation of a few-mode gain fiber. A pulse with a maximum energy of 650 nJ and a compressed duration of <100 fs was achieved. This was the highest pulse energy achieved by a Mamyshev oscillator based on standard Yb-doped fibers to date, even surpassing the performance of state-of-the-art Titanium:Sapphire lasers. A transfer of the Mamyshev oscillator concept to the regime of Thulium-doped gain fibers with the wavelength 2 µm is challenging due to the anomalous dispersion of the gain fibers which prevents parabolic pulse evolution. Nevertheless, a realization of this design is feasible. Mode-locked pulses with durations of <200 fs and pulse energies of 6.4 nJ were achieved. At this pulse duration it was the highest output power from a Thulium-doped fiber oscillator to date. Due to the alteration of the pulse shape in the glass fibers, a characterization of the final pulses is necessary. A recently developed method for the required complete pulse analysis was transferred from the application in solid-state systems to fiber-based systems in this thesis, which involves the management of less precisely defined amounts of dispersion. The complete characterization by dispersion scans based on a grism compressor was achieved by the use of an adequate retrieval algorithm

NASA patent abstracts bibliography: A continuing bibliography. Section 1: Abstracts (supplement 11)

This continuing bibliography lists index for 3256 patents and patent applications introduced into the NASA scientific and technical informations system from January 1977 through June 1977. The index section contains fix indexes: subject, inventor, source, number, and accession number

New measurement of the 2S1/2-8D5/2 transition in atomic hydrogen, A

2021 Summer.Includes bibliographical references.High-precision spectroscopy of simple atoms provides input data that can be used to extract fundamental constants and to test Standard Model theory. Hydrogen, the simplest element, has played a historically significant role in the development of fundamental theory and, more recently, provides important data for the proton radius puzzle. In this thesis, we will describe a new measurement of the 2S1/2-8D5/2 transition on a cryogenic hydrogen beam. We will overview the measurement scheme and experimental apparatus, then present analysis and systematic characterization important to the spectroscopy. Finally, we will present our preliminary determination of the proton radius and the Rydberg constant using our value for the 2S1/2-8D5/2 combined with the previously measured 1S-2S transition

Fundamentals and applications of spatial dissipative solitons in photonic devices : [Chapter 6]

We review the properties of optical spatial dissipative solitons (SDS). These are stable, self‐localized optical excitations sitting on a uniform, or quasi‐uniform, background in a dissipative environment like a nonlinear optical cavity. Indeed, in optics they are often termed “cavity solitons.” We discuss their dynamics and interactions in both ideal and imperfect systems, making comparison with experiments. SDS in lasers offer important advantages for applications. We review candidate schemes and the tremendous recent progress in semiconductor‐based cavity soliton lasers. We examine SDS in periodic structures, and we show how SDS can be quantitatively related to the locking of fronts. We conclude with an assessment of potential applications of SDS in photonics, arguing that best use of their particular features is made by exploiting their mobility, for example in all‐optical delay lines

Semiconductor Laser Dynamics

This is a collection of 18 papers, two of which are reviews and seven are invited feature papers, that together form the Photonics Special Issue “Semiconductor Laser Dynamics: Fundamentals and Applications”, published in 2020. This collection is edited by Daan Lenstra, an internationally recognized specialist in the field for 40 years

Significant NASA inventions available for licensing in foreign countries

Abstracts of various NASA-owned inventions which are available for foreign licensing in the identified countries are listed in accordance with the NASA Patent Licensing Regulations. Instructions for requested applicatons are explained

Optical comb injection for optical demultiplexing and harmonic frequency locking

With the continued growth of internet traffic, new optical communication infrastructures capable of dramatically increasing network bandwidth are being considered. Optical superchannels consisting of densely packed channels will be required for future networks, which could potentially be implemented using optical frequency combs - optical sources which consists of a series of discrete, equally spaced frequency lines. Optical combs can increase the spectral efficiency of these superchannels by allowing the channels to be more densely packed, while simultaneously reducing the number of components required (decreasing the energy consumption), and simplifying the digital signal processing required. Despite these advantages, the trade-off between cost and performance must be favourable in order for optical combs to become feasible for use in future communication networks. Photonic integrated circuits integrate several components together on a single semiconductor chip. These photonic circuits reduce both the cost and power consumption of devices, and hence recent research has been focused on creating suitable on-chip coherent optical comb transmitters. This thesis investigates an approach which is being used to demultiplex narrowly spaced optical combs on a photonic integrated circuit. By injection locking a laser to one of the lines in the optical comb (i.e, forcing a laser to lase with the frequency of that comb line), the comb line can be amplified and demultiplexed. This work investigates the physics of these active demultiplexers, both experimentally and numerically. It is found that the optimal side mode suppression ratio is obtained when the ratio of the comb's power to the injected laser's power is small, which also indicates optimal performance occurs when the locking range of the injected laser is at its smallest. The relaxation oscillations of the injected laser affect how well the comb can be demultiplexed, and as a result better side mode suppression ratios can be achieved at larger comb spacings. Further, it is shown that the relaxation oscillations within the injected laser can become undamped due to the comb injection, and frequency lock to fractions of the optical comb spacing. The injected laser can even become locked at detunings between the comb lines, creating a new output optical comb through nonlinear processes. The above phenomena are investigated numerically using two dimensional maps, and it is found that Arnol'd tongues appear in the injected laser's locking map

Design of a Time Based Analog to Digital Converter

Analog to digital converter (ADC) plays a very important role in any mixed analog/digital system. Because digital CMOS technology can take advantage of technology scaling, system designers try to increase the percentage of the digital part of the system. This means moving the ADC more and more towards the input of the system which results in making the role of the ADC more and more critical. With technology scaling, the switching characteristics of MOS transistors offer superb timing accuracy at high frequencies. This makes the time based analog to digital converter (TADC) a good alternative to the conventional ADCs in sub-micron region. In this thesis, an all digital TADC structure is proposed. This TADC is based on an analog to time converter (ATC), followed by a time to digital converter (TDC). The TDC is based on sigma-delta modulation. A non-linear multi-bit internal quantizer in sigma-delta modulator is used to counteract the nonlinearity introduced when the VCO is used as the ATC. The novel TADC also uses an implicit sample and hold (S/H) circuit to reduce area. Dynamic element matching (DEM) is used to improve the robustness of the system against random mismatch in the multi-bit quantizer. Both first and second order sigma-delta modulator TADC are proposed. Simulations and measurements on the proposed TADC are provided. Measurements, from a prototype chip fabricated using 0.13um CMOS technology, show that the first order TADC has achieved a dynamic range of 11 bits for a bandwidth of 2MHz. While simulation results show a dynamic range of 12 bit. Simulations show that the second order TADC has achieved a dynamic range of 12bit for a bandwidth of 20MHz

Instrument and Application Development in Saturation Recovery and Rapid Scan Electron Paramagnetic Resonance

Enhanced signal sensitivity by the use of Rapid Scan (RS) electron paramagnetic resonance (EPR), a technique that allows for much faster magnetic field scans than traditional field-swept techniques, has facilitated improved data acquisition for many types of samples. For example, irradiated fingernails for radiation dosimetry have been studied using RS-EPR, which resulted in substantial decreases in detection limits. Samarium-mediated reduction mechanisms in organic synthesis have been investigated by RS-EPR providing evidence for a radical intermediate. Spectra of organic radicals exhibiting both narrow lines and closely spaced hyperfine interactions have been recorded via RS-EPR. Well-resolved spectra can be recorded at a rate of 40 spectra/minute to gain insight into molecular changes on this timescale. RS-EPR performed at low temperatures using a closed cycle helium system and a cryostat containing a region with low electrical conductivity provides very wide (\u3e9000 G) spectra free of passage effects near 5 K, expanding the capabilities of RS-EPR. Recent developments in arbitrary wave form generators (AWGs) provide digital waveform synthesis at high enough frequencies to be used in EPR experiments at ca. 9 GHz (X-band). A new saturation recovery (SR) EPR spectrometer has been constructed with an AWG as the microwave source. Circuit design focuses on implementation of an X-band crossed-loop resonator with a reduced quality factor (Q) to minimize dead time due to resonator ring down processes. Increased accuracy of the AWG instrument relative to conventional sources has made nitroxide spin-lattice relaxation time measurements possible via SR-EPR with S/N high enough to permit separation of electron and nuclear spin-lattice relaxation contributions. These results enabled more accurate estimation of the saturation factor in dynamic nuclear polarization (DNP) experiments