High powered optical amplifiers (HPOAs) are a key subassembly in free-space optical communication systems. As these free-space optical communications systems are being introduced into space applications, it is critical to assess the impact of the radiation environment present in space on the reliability of these systems. One key component in HPOAs is multimode laser diodes, which are used to pump gain fibers in the HPOA. The reliability of these laser diodes is very dependent on optical output power, with increases in optical power causing dramatic reductions in lifetime. At the same time, radiation darkening is a well-known problem that reduces the efficiency in HPOAs operating in environments with high radiation levels. We use Monte Carlo simulation to evaluate the impact of radiation darkening on the reliability of multimode pump ensembles over time. At radiation fields related to geostationary earth orbits (2 to 5 krad / year) radiation effects reduce multimode pump lifetime by a factor of 7-220 under typical use conditions. Use of redundant pumps operating under derated conditions can mitigate the impact of radiation.
We report on the design, development, and testing of the high-power Laser Transmitter Assembly (LTA) supporting the Deep Space Optical Communications (DSOC) demonstration hosted on the Psyche Discovery class mission, due to launch in 2022. The DSOC project, under development by NASA’s Jet Propulsion Laboratory, will test space-to-ground high-bandwidth laser communications while en route to the Psyche-16 asteroid in the main asteroid belt, in what will be the longest range high rate optical communications link in history. The LTA is based on a master-oscillator power-amplifier optical architecture, using highly-efficient cladding-pumped amplification. The transmitter is designed to deliver average optical output powers <4 W at 1550 nm for low power consumption data links at <100 Mbps. The output signal operates across multiple pulse-position modulation (PPM) orders and pulse-widths to optimize the space-to-ground link. The architecture is designed for high-reliability and radiation hardness, and features hardware interlocks and secondary signal/pumping paths to reduce single points of failure. We also detail the effective management of optical nonlinearities which could damage the LTA or impact the communications link. These include the suppression of stimulated Brillouin scattering, self-phase modulation, and pulseto- pulse energy variation (PEV), which arises from the gain dynamics of the power amplifier, and will manifest when the LTA is configured for large pulse energies and long inter-pulse delays. The LTA also incorporates hardware and software controls to enable autonomous operation, including closed-loop control of intra-stage and output power levels, modulator bias control, and detailed reporting of LTA status through telemetry.
High power optical amplifiers (HPOAs) are utilized in many high reliability applications. The need for greater bandwidth in flight and space missions is driving the development of free space optical transmission systems which require high reliability HPOAs over mission lifetimes which may exceed 10 years. One challenge in developing such models is that typically when designing HPOAs, redundancy and derating approaches are utilized to augment reliability and avoid single points of failure. In these designs, redundant components experience a stress profile which depends on statistical failure probabilities of its sister components. For example, in the case of HPOA gain stages, typically several multimode pumps are combined to pump a gain fiber. These multimode pumps are typically run derated when the mission begins, but in the event of a component failure, the power to each remaining operational pump is increased to maintain constant output. As such it is more important to characterize when the entire ensemble of pumps fails. Accurate models for ensemble reliability require an approach which accounts for time and stress profile dependent failure rates which are hard to access experimentally (due to high component reliability) or analytically. In order to address this problem, we have utilized a Monte Carlo simulation approach which can rapidly simulate ensemble failures for any given stress profile. By running several simulations, we are able to build up the failure function for the ensemble, thus providing a more reliable model for failure rate for the ensemble. This failure model can be used to build a more accurate picture for HPOA reliability.
Sensing devices based on Graphene Field Effect Transistors (G-FET) have been demonstrated by several groups to show excellent sensitivity for a variety of chemical agents. These devices are based on measuring changes in the electrical conductivity of graphene when exposed to various chemicals. However, because of its unique band structure, graphene also exhibits changes in its optical response upon chemical exposure. The conical intersection of the valence and conduction bands results in a low density of states near the Dirac point. At this point, chemical doping resulting from molecular binding to graphene can result in dramatic changes in graphene’s optical absorption. Here we will discuss our recent work in developing a graphene planar lightwave circuit (PLC) sensor which exploits these optical and electronic properties of graphene to demonstrate chemical sensitivity. The devices are based on a strong evanescent coupling of graphene via electrically gated silicon nanowire waveguides. A strong response in the form of a reversible optical attenuation change of 6 dB is shown when these devices interact with toxic industrial chemicals such as iodine and ammonia. The optical transition can also be tuned to the optical c-band (1530-1565 nm) which enables these devices to operate at telecom wavelengths.
Dielectric electroactive polymers respond to an applied electric field by deformation as described by the Maxwell effect.
The response depends on the polymers' dielectric constant and stiffness. Addition of a high dielectric filler material has
been shown to enhance the strain response. We report preliminary results on the enhancement of p(EGPEA) polymer
films by addition of 1 w/v% of gold-capped, 500 nm SiO2 Janus particles (JP-SiO2). In comparison to pure p(EGPEA)
and p(EGPEA) filled with unmodified SiO2 particles, JP-SiO2 p(EGPEA) films show an up to 24 times enhanced
response. Measurement of the relative dielectric constant and the Young's Modulus indicate that the Janus particle
additive increases the relative dielectric constant of the films, while at the same time decreasing the Young's Modulus
leading to an overall larger electrostrictive coefficient for the JP-SiO2 p(EGPEA) films.
Conference Committee Involvement (1)
Smart Photonic and Optoelectronic Integrated Circuits XXIII
6 March 2021 | Online Only, California, United States