David Murrell

Analytical Modeling of the Temperature Performance of Monolithic Passively Mode-Locked Quantum Dot Lasers

This paper examines and models the effect of temperature on the mode-locking capability of monolithic two-section InAs/GaAs quantum dot passively mode-locked lasers. A set of equations based on an analytic net-gain modulation phasor approach is used to model the observed mode-locking stability of these devices over temperature. The equations used rely solely on static material parameters, measured on the actual device itself, namely, the modal gain and loss characteristics, and govern the limit describing the onset of mode-locking. Employment of the measured gain and loss characteristics of the gain material over temperature, wavelength and current injection in the model provides a physical insight as to why the mode-locking shuts down at elevated temperatures. Moreover, the model enables a temperature-dependent prediction of the range of cavity geometries (absorber to gain length ratios) where mode-locking can be maintained. Excellent agreement between the measured and the modeled mode-locking stability over a wide temperature range is achieved for an 8-stack InAs/GaAs quantum dot mode-locked laser. This is an attractive tool to guide the design of monolithic passively mode-locked lasers for applications requiring broad temperature operation.

A passively mode-locked quantum-dot laser operating over a broad temperature range

Broad temperature operation is demonstrated from 20 to 110 °C in a 5-GHz monolithic two-section InAs/GaAs quantum dot passively mode-locked laser with an optimized absorber to gain section length ratio of 0.11. Stable pulses of less than 19 ps full-width-half-maximum are measured over this entire temperature range. For a grounded absorber, mode-locking from the ground-state occurred over the range 20–92 °C, dual-mode lasing involving both ground and excited states from 93 to 98 °C and exclusively from the excited-state from 99 to 110 °C. The observed broad temperature operation agrees with theoretical analysis based on measured gain and absorption data that predicted improved temperature performance for a short absorber. The results are promising for the development of temperature-insensitive pulsed sources for uncooled applications such as data multiplexing and optical clocking.

Temperature Performance of Monolithic Passively Mode-Locked Quantum Dot Lasers: Experiments and Analytical Modeling

In this paper, a detailed study is presented on a series of quantum dot (QD) passively mode-locked lasers (MLLs) with variable absorber to gain-section length ratios. The effect of temperature on the stability of pulses emitted from the QD ground state is primarily examined and compared to an analytical model that predicts regions of mode-locking stability for a given device layout. The model correctly predicts the temperatures of maximum operability in each device for a variety of absorber voltages. Prediction of the regimes of excited-state operation from the QDs is also included and experimentally verified. For the first time, the unsaturated absorption is identified as a key parameter that strongly influences the range of biasing conditions that produce stable mode-locked pulses. This dataset offers valuable insight into design of future MLL devices for maximum optical pulse quality over a large range of temperature and biasing conditions.

Preliminary results from the AFRL-NASA W/V-band terrestrial link experiment in Albuquerque, NM

Atmospheric propagation models and the measurements that train them are critical to the design of efficient and effective space-ground links. As communication systems advance to higher frequencies in search of higher data rates and open spectrum, a lack data at these frequencies necessitates new measurements to properly develop, validate, and refine the models used for link budgeting and system design. In collaboration with the Air Force Research Laboratory (AFRL), NASA Glenn Research Center has deployed the W/V-band Terrestrial Link Experiment (WTLE) in Albuquerque, NM to conduct a measurement campaign at 72 and 84 GHz, among the first atmospheric propagation measurements at these frequencies. WTLE has been operational since October 1, 2015, and the system design shall be herein discussed alongside preliminary results and performance.

W/V-band terrestrial link experiment, an overview

The Air Force Research Laboratory in partnership with NASA Glenn Research Center and the University of New Mexico have initiated the W/V-band Terrestrial Link Experiment (WTLE) to conduct propagation analysis at W/V-band frequencies. An overview is provided of the system and ancillary equipment to facilitate the propagation experiment.

Terrestrial link rain attenuation measurements at 84 GHz

We present 560 m terrestrial link rain attenuation measurements at 84 GHz in Albuquerque, New Mexico. Both empirical and theoretical rain attenuation models such as ITU-R, Mie and Rayleigh will be examined with the measurements. This study will contribute to the understanding of signal propagation phenomena and the utilization of the W/V-bands for satellite communication.

Validation of the Mie theory for rain attenuation at 72 and 84 GHz

This paper presents the Mie theory for propagation loss resulting from atmosphere scattering and absorption for W/V frequency bands. The theory will be validated using experiment data collected on a 23-km test and measurement range, which is instrumented with an unmodulated transmitter, a receiver, and several meteorology instruments. This research is crucial for understanding signal propagation phenomena and enabling the utilization of the W/V-bands for satellite communication.

COMPARISON OF MONOLITHIC PASSIVELY MODE-LOCKED LASERS USING In(Ga)As QUANTUM DOT OR QUANTUM WELL MATERIALS GROWN ON GaAs SUBSTRATES

In this paper, a technology comparison between monolithic passively mode-locked lasers (MLLs) fabricated from 1.24 μm InAs dots-in-a-Well (DWELL) and 1.25 μm InGaAs single quantum well (SQW) structures grown using elemental source molecular beam epitaxy (MBE) is presented. 5 GHz optical pulses with sub-picosecond RMS jitter, high pulse peak power (1W) and narrow pulse width (< 10 ps) are typical of these monolithic two-section InAs DWELL passive MLLs. An InGaAs single quantum well MLL with the 42% indium is shown to exhibit a superior high-temperature performance. Compared with the typical operating range of the InAs DWELL devices (<60°C), the operation is in excess of 100 °C and is particularly attractive for clocking applications in next generation microprocessors. Based on an 8-band k.p analysis the reduction in the band edge density of states for such a quantum well is discussed.

Automated analysis of stable operation in two-section quantum dot passively mode locked lasers

In this paper, two-section mode-locked lasers consisting of monolithic quantum dot gain and absorber sections are studied as a function of absorber voltage, injected current to the gain region, and relative section lengths. We map the regions of stable mode-locking as measured by the electrical and optical spectra. A simple algorithm is presented that evaluates the quality of mode locking and allows automated characterization of devices. The relative advantages of increasing the absorber length compared to increasing the absorber reverse bias voltage are analyzed. Initial data indicate that doubling the absorber length from 1.4 to 2.8-mm in a 5 GHz repetition rate device increases the region of stable mode-locking by at least 25%, while increasing the absorber reverse bias can more than double the mode-locking regime. Nonetheless, in these devices, stable mode-locking over greater than a 100 mA bias range is realized with a grounded absorber making single bias control of a passively mode-locked semiconductor laser feasible.

Preliminary rain attenuation studies for W/V-band wave propagation experiment

The need to investigate higher frequencies for satellite communication led to the W/V-band Terrestrial Link Experiment (WTLE) project. This project is assessing atmospheric propagation effects at W/V-band frequencies, particularly rain-fade. In this paper, two rain attenuation models (i.e., the ITU-R and the Silva-Mello model) are compared to experimental measurements. The step-by-step comparison, along with all the tools used, is described herein.