Compact Package Research Articles

Recent Advances in 100+nm Ultra-Wideband Fiber-Optic Transmission Systems Using Semiconductor Optical Amplifiers

We report on the use of semiconductor optical amplifiers (SOAs) to extend the optical bandwidth of next generation optical systems to 100 nm and beyond. After discussing the technological progress and the motivation for rekindling the interest in SOAs for line amplification, we describe the innovative approach developed for the realization of ultra-wideband (UWB) SOAs. Leveraging custom design of singly polarized SOAs to provide gain over 100+ nm bandwidth, we developed a polarization diversity architecture to realize UWB-SOA modules. Embedded in a compact package, the UWB amplifier modules have been successfully used to demonstrate 100+ Tb/s transmissions. We subsequently review recent experimental transmission results based on such novel 100+ nm wide semiconductor optical amplifiers, including our first demonstration of 100+Tb/s transmission over 100 km distance, our field trial using real-time traffic, and finally the transmission of 107 Tb/s throughput over three spans of standard single mode fiber (SSMF) using hybrid UWB Raman/SOA amplification technique.

Chip-based soliton microcomb module using a hybrid semiconductor laser

Photonic chip-based soliton microcombs have shown rapid progress and have already been used in many system-level applications. There has been substantial progress in realizing soliton microcombs that rely on compact laser sources, culminating in devices that only utilize a semiconductor gain chip or a self-injection-locked laser diode as the pump source. However, generating single solitons with electronically detectable repetition rates from a compact laser module has remained challenging. Here we demonstrate a current-initiated, Si3N4 chip-based, 99-GHz soliton microcomb driven directly by a compact, semiconductor-based laser. This approach does not require any complex soliton tuning techniques, and single solitons can be accessed by tuning the laser current. Further, we demonstrate a generic, simple, yet reliable, packaging technique to facilitate the fiber-chip interface, which allows building a compact soliton microcomb package that can benefit from the fiber systems operating at high power (> 100 mW). Both techniques can exert immediate impact on chip-based nonlinear photonic applications that require high input power, high output power, and interfacing chip-based devices to mature fiber systems.

Optical design and fabrication of an all-aluminum unobscured two-mirror freeform imaging telescope

Freeform optics offers more degrees of freedom to optical design that can benefit from a compact package size and a large field of view for imaging systems. Motivated by the advances in modern optical fabrication and metrology, freeform optics has been found in many applications. In this paper, we will describe the challenging optical design, fabrication, metrology, and assembly of an all-aluminum unobscured two-mirror freeform imaging telescope. The telescope has a large field of view of 20∘×15∘. The freeform aluminum mirrors are manufactured by diamond turning based on a feedback modification strategy. The freeform mirrors are measured by a computer-generated hologram-based interferometric null test method. All-aluminum configuration has the advantages of being athermal and cost-effective.

AlGaN/GaN High-Electron-Mobility Transistors on a Silicon Substrate Under Uniaxial Tensile Strain

This paper reports pulsed DC and RF characteristics of GaN high-electron-mobility transistors (HEMTs) on a silicon substrate under external mechanical tensile strain. Tensile strain enhanced two-dimensional electron gas (2DEG) density resulted in increasing ID, fT and fmax at CW measurement. Eliminating self-heating by pulse measurement, DC and RF characteristics between flat and bend devices were slightly increased for small-width devices, and decreased for wide-width devices. This was because maximum electron drift velocity was reduced by a hot phonon effect while 2DEG density increased by tensile strain for wide-width devices. Results indicated that the tensile strain on thinner substrates decreased the DC and RF performances of wide-width GaN-based RF power devices. This phenomenon should be considered while using GaN-based RF power devices for compact packages, especially in high-power applications.

Robotilter: An automated lens/CCD alignment system for the Evryscope

Camera lenses are increasingly used in wide-field astronomical surveys due to their high performance, wide field-of-view (FOV) unreachable from traditional telescope optics, and modest cost. The machining and assembly tolerances for commercially available optical systems cause a slight misalignment (tilt) between the lens and CCD, resulting in PSF degradation. We have built an automated alignment system (Robotilters) to solve this challenge, optimizing 4 degrees of freedom - 2 tilt axes, a separation axis (the distance between the CCD and lens), and the lens focus (the built-in focus of the lens by turning the lens focusing ring which moves the optical elements relative to one another) in a compact and low-cost package. The Robotilters remove tilt and optimize focus at the sub 10 micron level, are completely automated, take 2 hours to run, and remain stable for multiple years once aligned. The Robotilters were built for the Evryscope telescope (a 780 MPix 22-camera array with an 8150 sq.deg. field of view and continuous 2-minute cadence) designed to detect short timescale events across extremely large sky areas simultaneously. Variance in quality across the image field, especially the corners and edges compared to the center, is a significant challenge in wide-field astronomical surveys like the Evryscope. The individual star PSFs (which typically extend only a few pixels) are highly susceptible to slight increases in optical aberrations in this situation. The Robotilter solution resulted in a limiting magnitude improvement of .5 mag in the center of the image and 1.0 mag in the corners for typical Evryscope cameras, with less distorted and smaller PSFs (half the extent in the corners and edges in many cases). In this paper we describe the Robotilter mechanical and software design, camera alignment results, long term stability, and image improvement.

Using Field-Effect Gas Sensors for Monitoring H2 in Transformer Oil

Hydrogen can be released during the thermal decomposition of organic materials, therefore, monitoring its level in the working industrial high-voltage transformer oil allows you to identify the development of degenerative processes in advance, because these processes can lead to an accident in the future. In experiments has shown that highly sensitive and small-sized field effect gas sensor based on the metal-insulator-semiconductor structure can be used for measuring of Hydrogen in oil with direct contact of its structure with transformer oil. Given the harsh environmental conditions of hydrogen measurement the field effect capacity type gas sensor were fabricated by using laser micromilling technique for fabrication compact ceramic surface mounting device package and microheater for sustentation working temperature of metal-insulator-semiconductor structure.

Design, modeling, analysis and development of deployable tubular metallic booms for space application

Deployable space structures have always fascinated space scientist and engineers. They serve the purpose of compact packaging volume during launch and a large deployed length in space subsequent to satellite ejection in orbit. Booms are any kind of deployed cantilever arms stretching out of satellite or any other spacecraft’s main body to perform several tasks. Prediction of booms working stress in stowed as well as deployed state is a governing parameter for booms functioning and its operational life. The ability and accuracy of modeling tools for prediction of system dynamics and its behavior at various operating conditions has increased to a greater extent and becoming extremely popular these days. This paper presents the design, analysis and development of Deployable Tubular Metallic Booms. Theory of plates and shells with advanced mechanics concept are software coded for prediction of overlap angle and shear centre of booms. Slit cross-section overlapped section booms are considered here, which are stowed on a drum or spool during launch and deployed into the forms of huge cantilever arms using motor. Sincere efforts are made to simulate actual operating conditions, to achieve best possible analysis results. A working technology model is also made to validate analysis outcomes and to have a better know how of the physics involved in assembly, manufacturing and working of Deployable Booms. Geometrical parameters are extracted from analysis and are then utilized for generating technology model and results are found encouraging.

Electrical and Thermal Characterization of an Inductor-Based ANPC-Type Buck Converter in 14 nm CMOS Technology for Microprocessor Applications

Integrated Voltage Regulators (IVRs) are attractive substitutes for conventional voltage regulators located on the motherboards, due to outstanding dynamic performances and superior power densities. IVRs operate with switching frequencies in the range of 100 MHz and are assembled in highly compact packages close to the microprocessor load. This paper presents a comprehensive characterization of a PCB and inductor-based four-phase ANPC-type IVR that uses a Power Management IC (PMIC) implemented in a 14 nm CMOS technology node. The characterization is based on the results of electrical measurements, thermal inspections of the chip surface, and simulations, which enables the separation of the total losses into on-chip and off-chip loss components and the allocation of important loss components inside the chip. The investigated IVR achieves a maximum efficiency of 84.1% at an output power of P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> = 640 mW and a switching frequency of f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 50 MHz. The thermal measurements reveal that the maximum efficiency of the PMIC itself is between 88 % and 90 % at f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 50 MHz and P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> ∈ [500 mW, 600 mW]; at P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> = 890 mW, a chip current density of 24.7 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is achieved. The findings in particular point out that the losses in the chip-internal interconnections, i.e., the conductors of the Power Distribution Network (PDN) and the twelve stacked metal layers below the PDN, have a substantial contribution to the total losses. Furthermore, the combination of Cadence post-layout simulations with impedance networks obtained from an appropriate software tool, e.g., FastHenry, is found to establish a suitable toolbox for estimating losses in IVRs.

Moles power-walk with their thumbs

Moles are busy creatures. When not digging their tunnels, eastern moles (Scalopus aquaticus) are living, foraging and traversing through their labyrinthine territories. In a single day, a mole may walk 400 m through pitch-dark, cramped, narrow tunnels; that's a lot of (under) ground to cover. Moles do this in their own particular style – with their palms facing outwards. This unusual forelimb posture is probably an adaptation to a digging lifestyle; equipped with an extra ‘false’ thumb on their spade-like hands, moles push soil away from their body and against the tunnel walls. But how does an animal specialised for digging deal with the demands of walking such long distances?Yi-Fen Lin at the University of Massachusetts (UMass) Amherst and colleagues at UMass Lowell and the University of California Merced, USA, set out to record high-precision measurements of how moles walk. The team studied three eastern moles, a species that lives close to Lin's lab. To measure how the moles’ skeletons move, the scientists turned to a technique known as X-ray Reconstruction of Moving Morphology, or XROMM for short. XROMM combines X-ray videos of the moving moles with 3D models of their bones and then splices the data together using Hollywood-standard animation software to reconstruct the moles’ motion. For the experiment, the moles walked back and forth through a purpose-built tunnel, positioned in front of the X-ray cameras. When the motion was reconstructed from the X-ray videos, the resulting 3D animations were beautiful and precise.Analysing the movies, Lin found that moles power-walk in a most unusual manner, probably a by-product of their digging tendencies. Whereas all other quadrupeds place their feet on the ground behind their shoulder joint, moles break the rules by holding their feet in front. With each step, they load their weight fleetingly onto their thumbs and false thumbs, way out in front of their body. This instance of weight bearing was so brief that the moles’ walking gait almost approached some definitions of running and was more like human power-walking, where people walk as fast as possible without actually breaking into a run. This might seem like an awkward way to get about, but considering that moles walk with shovels permanently attached to their forearms, awkward seems normal.The XROMM animations also show that moles point their improbably shaped upper-arms to the ceiling, not downwards like other quadrupeds – effectively staging the action high above the shoulder joint instead of below it. As each foot lifts off the ground, the limb moves forward in line with the body, then retracts back. This is a very different motion from that seen in digging, where the moles shovel earth either side by twisting their arms outwards. This walking configuration means that moles fold their limbs into a nice compact package, perfect for squeezing down narrow tunnels.Lin's moles show us how demanding life can be, sometimes right beneath our feet. Whilst it's incredible that moles have evolved such effective digging modifications at the ends of their limbs, it's even more astonishing that they still perform all of their other daily activities while burdened with these apparently cumbersome appendages. Sometimes a strange lifestyle leads to a unique way of getting around – no other known animal walks quite like a mole.

Development of Resilient Seismic Solutions for Timber Structures in New Zealand Using Innovative Connections

There is increasing public pressure for damage avoidance structural systems using new engineered wood products, especially cross-laminated timber (CLT), in countries with high levels of seismic activity, such as New Zealand, to minimise the destruction after severe earthquakes with no post-event maintenance. This study presents damage avoidance lateral load-resisting systems (LLRSs) using rocking timber panels and the innovative resilient slip friction joint (RSFJ) technology. RSFJs can be used as hold-downs or as ductile links between adjacent walls or between the walls and boundary columns. These joints are capable of providing a self-centring behaviour (the main deficiency of conventional friction joints) in addition to a high rate of energy dissipation, all in one compact package. In addition, a novel type of shear-transferring device is introduced to be used as the shear key for rocking structural members. The proposed concepts are described and verified by large-scale experimental tests and numerical simulations. The results confirm that the introduced systems can be considered as the new generation of resilient LLRSs for timber construction.

Mechanical tensile strain for AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors on a silicon-on-insulator substrate

The impacts of various tensile strains on both DC and RF performance of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) on a silicon-on-insulator (SOI) substrate were investigated using pulsed-IV and pulsed-S-parameter tests. The sensitivity of MIS-HEMTs to various tensile strains was observed via pulse measurements because of the improved self-heating effect. The DC and RF performance of MIS-HEMTs on a SOI substrate were found to be enhanced with the pulse width decreasing under small tensile strain. A significant hot phonon effect was observed for MIS-HEMTs under larger tensile strain, particularly for shorter pulse widths. Additionally, an obvious reduction of fmax was observed under larger tensile strain because the channel resistance increased via the hot phonon effect, despite the increase in ft. The results indicated that tensile strain in the ultra-thin thinned substrate of AlGaN/GaN HEMTs should be carefully monitored in compact packages for high-power and high-frequency applications.

ULPAC: A Miniaturized Ultralow-Power Atomic Clock

This article introduces a chip-scale ultralow-power atomic clock (ULPAC) in the microwave frequency region. A new suspended quantum package architecture along with a fully integrated frequency probing and locking loop implemented in CMOS technology results in a compact package and ultralow-power consumption. In addition, dedicated low-noise magnetic field and temperature control loops are incorporated for isolating and mitigating the internal and external factors affecting the frequency stability. The output frequency of a crystal oscillator is continuously compensated and stabilized by locking to the peak of a coherent population trapping signal, thereby inheriting the superior frequency stability of the atomic resonance. The proposed ULPAC system achieves a frequency stability of $2.2 \times 10^{-12}$ at an averaging time of 105 s, while consuming 59.9 mW. The frequency probing and locking circuits implemented in a standard 65-nm CMOS process node occupy an area of 2.55 mm2. The prototype of this atomic clock occupies a volume of 15 cm3.

Glass Optical Connector Ferrule for Solder-Reflow-Compatible Photonic IC Edge Interconnections

A glass-tube-based MT-style fiber array ferrule is presented that provides a compact interface to PIC (Photonic Integrated Circuit) edge waveguides. The approach aligns and attaches a glass ferrule on the PIC substrate top surface using solder-reflow-resistant UV curable adhesives. A mating fiber array connector ferrule is attached to the PIC after solder reflow. Mate/demate experiments on pairs of matching glass-based connector ferrules demonstrated IL (insertion loss) values across eight single mode fiber array channels of less than 1.5 dB without using index matching fluid between coupled arrays. A compact connector packaging housing compatible with glass tube-based ferrules is also presented.

A Novel Capacitance-Based In-Situ Pressure Sensor for Wearable Compression Garments.

This paper pertains to the development & evaluation of a dielectric electroactive polymer-based tactile pressure sensor and its circuitry. The evaluations conceived target the sensor’s use case as an in-situ measurement device assessing load conditions imposed by compression garments in either static form or dynamic pulsations. Several testing protocols are described to evaluate and characterize the sensor’s effectiveness for static and dynamic response such as repeatability, linearity, dynamic effectiveness, hysteresis effects of the sensor under static conditions, sensitivity to measurement surface curvature and temperature and humidity effects. Compared to pneumatic sensors in similar physiological applications, this sensor presents several significant advantages including better spatial resolution, compact packaging, manufacturability for smaller footprints and overall simplicity for use in array configurations. The sampling rates and sensitivity are also less prone to variability compared to pneumatic pressure sensors. The presented sensor has a high sampling rate of 285 Hz that can further assist with the physiological applications targeted for improved cardiac performance. An average error of ± 5.0 mmHg with a frequency of 1–2 Hz over a range of 0 to 120 mmHg was achieved when tested cyclically.

Design of a Hybrid Power Unit for Formula SAE Application: Packaging Optimization and Thermomechanical Design of the Electric Motor Case

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;This paper presents the development of a parallel hybrid power unit for Formula SAE application. In particular, the system is made up of a brand new, single-cylinder 480 cc internal combustion engine developed on the basis of the Ducati “959 Superquadro” V90 2-cylinders engine. The thermal engine is assisted by a custom electric motor (30 kW), powered by a Li-Ion battery pack. The performance of the ICE has been optimized through CFD-1D simulation (a review of this activity is reported in a parallel paper). The main design goal is to get the maximum amount of mechanical energy from the fuel, considering the car typical usage: racing on a windy track. The Ducati “959 Superquadro” engine is chosen because of its high power-to-weight ratio, as well as for its V90 2-cylinder layout. In fact, the vertical engine head is removed and it is subsequently replaced by the electric motor directly engaged to the crankshaft using the original valvetrain transmission chain, thus achieving a very compact package. The mechanical behaviour of the original chain is investigated for this purpose. A specific electric motor case is then designed and manufactured via Additive Manufacturing technology, in order to include the chain housing, the electric motor cooling system and the lubrication system. Furthermore, the case flange is designed to perfectly fit to the original engine deck in order to allow the engine cooling circuit to match with the electric motor cooling circuit. Several types of circuit layout - around the stator - are analysed via CFD simulations comparing pressure drop and heat transfer coefficients. Finally, a thermo-structural analysis is performed in order to assess the mechanical strength of the electric motor case.&lt;/div&gt;&lt;/div&gt;

Electrochemical Pumping for Carbon Dioxide Removal in Automotive Hydroxide Exchange Membrane Fuel Cell Systems

Hydroxide exchange membrane fuel cells (HEMFCs) suffer unacceptable efficiency losses when exposed to the carbon dioxide in ambient air1. Despite rapid progress on power density and stability, the need to remove carbon dioxide from the air feed of the fuel cell has been a major roadblock for HEMFCs, especially in space-constrained automotive systems. Conventional sorbent-based carbon dioxide removal systems are complex and bulky, with multiple beds and careful thermal integration required to operate continuously. Herein, we propose the electrochemical carbon dioxide pump2,3 (ECP) as a compact, efficient, and highly effective method for carbon dioxide removal in HEMFC systems (Figure 1). Model-based projections indicate than an optimized ECP could remove 99.9% of CO2 from air in an active area half as large as the HEMFC it feeds, powered by a continuous 2% purge of hydrogen from the HEMFC anode. The module would contribute zero parasitic electrical load, add <15 kPa pressure drop, and be packaged efficiently to further minimize volume. The cost contribution to a 100-kW automotive HEMFC system would be less than $2 kW-1 at large scale. The ECP operates as a H2-air HEMFC at low current density (e.g. 20 mA cm-2). Given the low concentration of CO2, even a low current density generates a large excess of hydroxide anions. When in excess, hydroxide reacts rapidly with CO2 to produce carbonate and bicarbonate anions, which are electrochemically transported to the anode. At the anode, bicarbonate accumulates, lowering the pH and triggering its own decomposition. In this way, steady-state CO2 transport is rapidly established, with performance usually controlled by CO2 diffusion and reaction with hydroxide. The performance of a single-cell 25 cm2 ECP is shown in Figure 2. With the first-order processes of CO2 diffusion and chemical reaction with hydroxide as the rate-limiting steps, the cell shows an exponential relationship between residual CO2 and the inverse of the air flow rate. As a consequence of this behavior, the ECP area required for a given rated flow is proportional to the logarithm of residual CO2 level, and very high removal fractions are possible. In addition to results and theory, a technoeconomic roadmap for ECPs in automotive HEMFC systems will be presented. Without optimization, an ECP could add the cost and bulk of a second electrochemical stack. However, such a design would deliver electrochemical performance in the ECP that is orders of magnitude greater than necessary to remove only 400 ppm of CO2. The true potential of the ECP is realized with a distinct architecture that sacrifices unnecessary electrochemical performance for rapid CO2 transport, compact packaging, and low cost. References Ziv, W. E. Mustain, and D. R. Dekel, ChemSusChem, 11, 1136–1150 (2018).Winnick, Adv. Electrochem. Sci. Eng., 1, 205–248 (1990).A. Rigdon et al., J. Electrochem. Energy Convers. Storage, 14, 020701 (2017). Figure 1

(Invited) Capillary Electrophoresis Instrumentation and Methods for Spaceflight Missions of Exploration

The search for evidence of life beyond Earth is among the highest level goals in planetary exploration. However, despite multiple orbiter and landed missions to extraterrestrial bodies in the solar system, we still haven’t found evidence of life. A powerful approach in this search involves seeking biochemical signatures of life at the molecular level, as distributions of organic molecules. The separation techniques capillary electrophoresis (CE) and its miniaturized version, microchip electrophoresis (ME) overcome the limitations of gas-phase techniques and hold unique promise in the search for signatures of life on other worlds. These techniques offers high resolution separations of molecules dissolved in water and are the simplest of all liquid separation methods to implement for flight. Here we describe CE and ME instrumentation developed at JPL and the steps we are taking to someday enable the its implementation on other worlds. Although multiple detection methods can be coupled to CE and ME, we focus on three detection modes: laser-induced fluorescence (LIF) for state-of-the-art measurements of amino acids, mass spectrometry (MS) for broad detection of ionizable organics, and contactless conductivity detection (C4D) for measurements of inorganic and organic ions. These techniques are complementary of each other and would allow full characterization of the chemical composition of a sample in situ. We are not only developing instrumentation but also analytical methods that could be implemented on a mission scenario. Here we also describe a system we dub The Chemical Laptop, which would provide the sample processing capabilities required for in situ analysis on extraterrestrial destinations with ultra-high sensitivity in a compact, low-mass, and low-power package. The Chemical Laptop is a truly portable, battery-powered, automated, and reprogrammable microchip electrophoresis instrument coupled to laser-induced fluorescence detection. This instrument concept could be adapted to the environmental requirements of a variety of astrobiologically interesting targets like Europa, Enceladus, or Titan. This system also serves as a general prototype that could be reprogrammed for terrestrial-based analyses as well.

High-transmission fiber ring resonator for spectral filtering of master oscillator power amplifiers

We experimentally characterize a fiber-based ring resonator constructed from two commercially available 2x2 polarization-maintaining directional couplers. This ring resonator has a maximum noise suppression of 25 dB and resonant transmission of 80% at 1550 nm. Its high transmission means this ring resonator is ideally suited for the spectral filtering of master oscillator power amplifier light sources in a robust, compact, and all-fiber package. The limits of such a ring resonator for use in gravitational-wave detectors are discussed, and we show how it could be used to filter the low-power amplifier section and reduce the noise suppression requirements for the final free-space mode-cleaner.

Long Shape Memory Alloy Tendon-based Soft Robotic Actuators and Implementation as a Soft Gripper

Shape memory alloy (SMA) wire-based soft actuators have had their performance limited by the small stroke of the SMA wire embedded within the polymeric matrix. This intrinsically links the bending angle and bending force in a way that made SMA-based soft grippers have relatively poor performance versus other types of soft actuators. In this work, the use of free-sliding SMA wires as tendons for soft actuation is presented that enables large increases in the bending angle and bending force of the actuator by decoupling the length of the matrix and the length of the SMA wires while also allowing for the compact packaging of the driving SMA wires. Bending angles of 400° and tip forces of 0.89 N were achieved by the actuators in this work using a tendon length up to 350 mm. The tendons were integrated as a compact module using bearings that enables the actuator to easily be implemented in various soft gripper configurations. Three fingers were used either in an antagonistic configuration or in a triangular configuration and the gripper was shown to be capable of gripping a wide range of objects weighing up to 1.5 kg and was easily installed on a robotic arm. The maximum pulling force of the gripper was measured to be 30 N.

Design, Control, and Preliminary Assessment of a Multifunctional Semipowered Ankle Prosthesis

This paper describes the design, control, and preliminary assessment of a novel microprocessor-controlled multifunction ankle prosthesis that provides three microprocessor-controlled behaviors—a selectable stiffness equilibrium angle, lockable conformal damping, and swing-phase repositioning. Following a description of the motivation for providing these behaviors, the authors provide a detailed description of the device and walking controller design. This device utilizes a power-asymmetric linear actuator to provide the desired functionality in a compact and lightweight package through a combination of both hydraulic and electromechanical actuation approaches. The device is controlled for level ground walking via a finite-state machine. The functionality of the prosthesis is demonstrated by a set of benchtop experiments that characterize the ability of the prosthesis to provide the three desired behaviors and by an experiment in which the prosthesis was worn by a transtibial amputee during walking. Both sets of experiments indicate that the prosthesis provides the functionality for which it was designed.