Jesse Mee

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.

Total Dose Test Results for CubeSat Electronics

CubeSats are increasingly important for space research. Their low orbits and short mission durations permit using electronics with modest radiation failure thresholds. Total ionizing dose irradiation results are presented for microelectronics interesting for CubeSat applications.

Pulse Characterization of Passively Mode-Locked Quantum-Dot Lasers Using a Delay Differential Equation Model Seeded With Measured Parameters

A delay differential equation-based model for passive mode locking in semiconductor lasers is shown to offer a powerful and versatile mathematical framework to simulate quantum-dot lasers, thereby offering an invaluable theoretical tool to study and comprehend the experimentally observed trends specific to such systems. To this end, mathematical relations are derived to transform physically measured quantities from the gain and loss spectra of the quantum-dot material into input parameters to seed the model. In the process, a novel approach toward extracting the carrier relaxation ratio for the device from the measured spectra, which enables a viable alternative to conventional pump-probe techniques, is presented. The simulation results not only support previously observed experimental results, but also offer invaluable insight into the device output dynamics and pulse characteristics that might not be readily understood using standard techniques such as autocorrelation and frequency-resolved optical gating.

CubeFlow: Training for a New Space Community

Many organizations (academia, industry and government) make high quality satellite components; however, very few organizations make entire satellites well. Those that can successfully create entire satellites, often take years to design and deploy “Swiss watch,” one-of-a-kind satellites. The federal government wants a way to capitalize on all of these organization’s quality components in a quick and efficient manner. To be more responsive to the military and emergency responder’s needs, rapid satellite development and deployment is critical. There is a need for a method to go from pushbutton mission design to off the shelf components (that all seamlessly integrate) in a rapid fashion. Under sponsorship by the Operationally Responsive Space (ORS) office, the Air Force Research Laboratory (AFRL) developed a modular, nanosatellite, plug-and-play (PnP) approach where hardware and software modules can be rapidly merged to form functional satellites. The Stanford/Cal Poly CubeSat and Poly-Picosatellite Orbital Dispenser (PPOD) standards have revolutionized the way that small satellites are developed and deployed. AFRL wants to capitalize on this momentum to advance the concepts and goals of rapid space. Small satellites are an excellent test bed for larger spacecraft. The combination of the AFRL’s PnP design paradigm and the CubeSat standards has resulted in the creation of a CubeFlow program and CubeFlow training. The basis of the electrical and software infrastructure is the AFRL Space PnP Avionics (SPA) technology. Many have complained about the complexity of developing components that conform to the SPA standards. To alleviate this, a secure, web-based, design system has been created that allows convenient access for developing design configurations and coordinating the offerings of a community of component developers. This system provides a simple development flow through which component manufacturers can easily and efficiently create a PnP module. This stems from the idea that minimizing the amount of code that a developer must produce and also minimizing human error through constant validation will greatly increase efficiency. The hope is that those trained in the CubeFlow courses will gain the skills needed to produce useful PnP components and allow the PnP community to expand. Currently, there are a number of organizations and universities that have expressed interest in nano-satellite programs and rapid space development. CubeFlow is intended to address the issue that, due to lack of funding or capability, it is rare that a single organization or university would be able to research and develop all the necessary components for a small satellite. If a community can be built around an accepted standard such as PnP, then it may be possible to coordinate efforts in such a way that no longer would a single entity be tasked with the development of an entire satellite - but rather a single module or component. It is believed that this will not only lead to faster development, but higher quality satellites.

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.

Trailblazer: Proof of Concept CubeSat Mission for SPA-1

The Space Plug-and-play Architecture (SPA) concept of rapid satellite development has progressed exponentially over the past several years. The team at the Configurable Space Microsystems Innovations and Applications Center (COSMIAC) in conjunction with the Space Dynamics Laboratory (SDL) and the Air Force Research Laboratory have trained over 500 individuals on this rapid bus architecture related to satellite development. This paper will outline the first CubeSat satellite proof of concept flight for a SPA only spacecraft. The Trailblazer mission is designed to fly a 1U CubeSat that is based entirely on a SPA bus implementation. Trailblazer will consist of Commercial Off The Shelf (COTS) parts converted to be SPA compliant. This allows not only a demonstration of the bus reliability in a space environment, but also the ease in converting existing components to be SPA compliant. With the dimensional constraints and power budget of Trailblazer, we have elected to use the SPA-1 standard. SPA-1 is the most recent addition to the AFRL SPA family. The SPA-1 data transfer protocol is based on 400 kbit/s I2C making it the lowest power, and lowest bandwidth option for SPA. Given the power constraints of typical satellite architecture, it is generally advantageous to interface devices/modules which do not require high data transfer rates to a SPA network via the SPA-1 Applique Sensor Interface Module (ASIM). This ASIM is logic that enables SPA Plug-and-Play for hardware components. It contains all the information needed for the system to automatically discover and automatically configure the hardware component. SPA-1 ASIMs can be any microcontroller that supports I2C and has enough memory to contain the needed logic. This allows the standard to remain open to a variety of dynamic implementations. The Trailblazer mission is being launched under the National Aeronautics and Space Administration (NASA) Educational Launch of Nanosatellite (ELaNA) program. This NASA program is designed to provide affordable access to space through collaborative efforts with academic institutions. The ELaNA program provides manifesting and launch of CubeSats for

The advent of the PnP Cube satellite

30,000 per 1U module. The proposed orbit is 325 km with an inclination of 51 degrees for a launch in 2011.

Benchmarking image processing for space: Introducing the SPACER architecture laboratory

In terms of time and budget, integration is a significant time-consuming component of spacecraft development. While many useful COTS spacecraft components are available, interfacing and controlling these components in an integrated satellite system remains a complex engineering task. The Stanford/Cal Poly CubeSat and Poly-Picosatellite Orbital Dispenser (PPOD) standards have begun to standardize small satellite mechanical systems and revolutionize the way small satellites are deployed. NASA has recognized this as evident by their Educational Launch of Nanosatellites (ELaNa) program which recently selected 17 CubeSats for the ELaNa-4 launch in 2012 (including one high school). To capitalize on this momentum, the Air Force Research Lab (AFRL) has organized and supported a team of commercial and academic laboratories to develop and test an over-arching Space Plug-and-play Architecture (SPA) set of standards to support the rapid integration of independently developed satellite modular systems. SPA represents not only an electrical inter-connection and communication scheme, but a complete model for a self-organizing and self-configuring system to support the rapid assembly of mission-specific small satellites. Rather than forcing existing modules to be re-developed to a common messaging standard, SPA utilizes an XTEDS (eXtended Transducer Electronic Data Sheet) model. Each satellite module contains an electronic document describing its interface, capabilities, messages, data formats, etc. By reading a components XTEDS, other systems can quickly integrate and utilize a new module. While designed to initially take advantage of nanosatellites, everything developed can easily scale to larger spacecraft, UAVs or other aerospace and defense systems. This paper discusses our experience in developing the CubeSat Trailblazer, a 1U SPA-only spacecraft - launching in 2012 as a testbed for SPA technology. The mechanisms of self-organization for independent modules as a cooperating communications system are discussed. The simplifications associated with software development of a Command and Data Handler (CDH) is also presented.

Reduced group delay dispersion in quantum dot passively mode-locked lasers operating at elevated temperature

In order to better make investment decisions for future space processing, we are equipping an architectures laboratory to investigate the power and computing performance of candidate computing architectures for future space applications. The picture for future space processing is increasingly complicated by ever increasing data rates/sizes and limited communications bandwidth, both of which will require more data processing, in the form of either data reduction or compression, to be performed on orbit rather than on the ground. Candidate architectures for the laboratory are being drawn from a range of COTS processing architectures including low power multicore processors, FPGAs, and GPUs. As the drivers for these investments are likely to be data-intensive image processing applications, we have selected two representative applications, Synthetic Aperture Radar (SAR) and Hyper-Temporal Imaging (HTI), and tested them on a variety of low-power multicore processors, and for comparison, on modern conventional processors. Both applications were parallelized using OpenMP and/or pthreads. The processors employed include from four to eight cores. State-of-the-art numerical libraries were used to extract the most performance possible. The multi-core processors selected included examples of both homogeneous and heterogeneous computing architectures. Effects of varying the parameters such as the amount of memory made available to the processors, which affects how data decomposition is accomplished, are also studied. In general, homogeneous computing architectures performed better than heterogeneous ones. In some cases, better performance could be achieved with a single processor core with large memory than with multiple processors. These results are a function of the employed algorithms ability to efficiently utilize architecture features, and cannot be attributed to all application/architecture pairings, thus highlighting the need for a concerted effort to explore processing requirements for future space missions.

On the energy consequences of information for spacecraft systems

A detailed study of the pulse characteristics emitted from a monolithic Quantum Dot (QD) passively Mode-Locked Laser (MLL) has been performed using a state-of-the-art Frequency Resolved Optical Gating (FROG) pulse measurement system. While traditionally the time-domain pulse characteristics of semiconductor MLLs have been studied using digital sampling oscilloscope or intensity autocorrelation techniques, the FROG measurements allow for simultaneous characterization of time and frequency, which has been shown to be necessary and sufficient for true determination of mode-locked stability. In this paper, FROG pulse measurements are presented on a two-section QD MLL operating over wide temperature excursions. The FROG measurement allows for extraction of the temporal and spectral intensity and phase profiles from which the Group Delay Dispersion (GDD) can be determined. The magnitude of the GDD is found to decrease from 16.1 to 3.5 ps/nm when the temperature is increased from 20 to 50 oC, mirroring the trend of pulse width reduction at elevated temperature, which has been shown to correlate strongly with reduced unsaturated absorption. The possibility to further optimize pulse generation via intra-cavity dispersion compensation in a novel three-section MLL design is also examined, and shows strong potential toward providing valuable insight into the optimal cavity designs and operating parameters for QD MLLs.