Farzana I. Khatri

Overview and Results of the Lunar Laser Communication Demonstration

From mid-October through mid-November 2013, NASA’s Lunar Laser Communication Demonstration (LLCD) successfully demonstrated for the first time duplex laser communications between a satellite in lunar orbit, the Lunar Atmosphere and Dust Environment Explorer (LADEE), and ground stations on the Earth. It constituted the longest-range laser communication link ever built and demonstrated the highest communication data rates ever achieved to or from the Moon. The system included the development of a novel space terminal, a novel ground terminal, two major upgrades of existing ground terminals, and a capable and flexible ground operations infrastructure. This presentation will give an overview of the system architecture and the several terminals, basic operations of both the link and the whole system, and some typical results.

Models for self-limited additive pulse mode-locking

Abstract We analyze Self-Limited Additive Pulse Mode-locked (SLAPM) lasers. SLAPM is APM in which the effective fast saturable absorption rolls over to become fast saturable gain for the pulse peaks, providing an important stabilizing mechanism. The pulses in a SLAPM laser tend to look Gaussian at the top but maintain exponential wings and have time-bandwidth products larger than that of a sech2-shaped pulse. We compare a simple analytic theory with two discrete computer simulations of SLAPM lasers. We show that despite large nonlinear phase shifts per pass in the fiber (close to π) and the lumped nature of the elements in the laser, the analytic model is applicable. Both the simulated pulse parameters and shapes show good agreement with the theory.

Link analysis of Mars-Earth optical communications system

A systems-level analysis of a high data rate Mars to Earth optical communications link is presented. A feasibility of a minimum 10 Mb/s optical link with the possibility of achieving > 100 Mb/s under certain conditions will be shown. The link design employs a Pulse Position Modulated (PPM) 1.06 μm Mars transmitter with a photon-counting Earth receiver. This study will characterize system performance (link data rate) as a function of orbital position including the complex diurnal and annual variations in the Mars-Earth system. Key system impairments that vary diurnally/annually include loss and turbulence due to the Earths atmosphere, daytime/nighttime sky background noise, background noise from Mars itself, and space loss due to the relative planetary distances. In addition, transmitter/receiver design parameters and their impact on system performance are discussed.

A Hybrid Stabilization Approach for Deep-Space Optical Communications Terminals

Near-Earth laser communication system designs typically use the near-symmetric power levels in duplex links as bright sources upon which to base active beam stabilization. In deep space, it may be difficult to provide a constant, high-power laser beacon as a stabilization reference. We describe here several means, aimed at different frequency ranges of control, for generating a combined pointing reference and for actively controlling beam position. Such a blended approach gives a highly flexible system for performing beam stabilization in deep space, where distances, conditions, and power levels can vary widely.

Simulation of pulsed squeezing in optical fiber with chromatic dispersion

Pulsed squeezing in lossless optical fiber with Kerr nonlinearity and chromatic dispersion is numerically simulated by the use of the linearization approximation. The formalism developed here allows us to predict squeezing for an arbitrary initial complex pulse envelope in a fiber with nonlinearity and dispersion. The results show that squeezing is not necessarily reduced by large temporal and spectral distortions of the pulse caused by dispersion and can even be enhanced in certain cases.

Interaction of soliton with sinusoidal wave packet

The interaction of a soliton of the Nonlinear Schrodinger Equation (NSE) with a weak sinusoidal wave packet is treated analytically. The second-order soliton solution containing the original soliton and a perturbing soliton is expanded to first order in the amplitude of the perturbating soliton. From this expansion, one obtains the associate function of Gordon (1992) and a continuous change of position and phase of the perturbed soliton. One finds that the soliton experiences a second-order change of velocity under the influence of the perturbation. This result is then used to derive the displacement due to a wave packet of general shape, which is also confirmed by computer simulation.

The NASA Lunar Laser Communication Demonstration—Successful High-Rate Laser Communications To and From the Moon

The Lunar Laser Communication Demonstration (LLCD) is NASA’s first demonstration of the use of free-space optical communications for high-rate duplex communications between a lunar spacecraft and an Earth ground station. The LLCD system comprised a space terminal on the Lunar Atmosphere and Dust Environment Exploration (LADEE) spacecraft and three ground terminals developed by NASA and the European Space Agency. The primary mission occurred during the fall of 2013 and successfully demonstrated reliable data delivery over optical data links operating at rates as high as 20 Mbps on the uplink and 622 Mbps on the downlink.

Near-Sun free-space optical communications from space

Free-space optical communications offers expanded data return capacity, from probes distributed throughout the solar system and beyond. Space-borne and Earth-based optical transceivers used for communicating optically, will periodically encounter near-Sun pointing. This will result in an increase in the scattered background-light flux, often contributing to degraded link performance. The varying duration of near-Sun pointing link operations relative to the location of space-probes, is discussed in this paper. The impact of near-Sun pointing on link performance for a direct detection photon-counting communications system is analyzed for both ground- and space-based Earth receivers. Finally, the impact of near-Sun pointing on space-borne optical transceivers is discussed

A New Optical Communication Architecture for Delivering Extremely Large Volumes of Data from Space to Ground

Space-based laser communication has been demonstrated at rates ranging from 10’s of Mbps to a few Gbps for near-Earth crosslinks and for direct-to-Earth downlinks from ranges as far as the Moon. We describe a novel space-to-Earth communication architecture that can deliver many terabytes of data regularly, if the user is willing to accept certain amounts of delay. With careful design of space and ground terminals, and by tapping the recent advances in integrated extremely high rate modems developed by the fiber telecommunications industry, we believe that space terminal cost, ground terminal cost, and operations costs can be kept much lower than present day radio-frequency or proposed optical systems while increasing the amount of data delivery by orders of magnitude.

Extension of coupled-cavity additive pulse mode-locked laser theory

Abstract We present an extended theory for a coupled-cavity Additive Pulse Mode-locked (APM) laser. With filtering in the auxiliary (fiber) cavity, stable operation at higher powers is made possible. We present both numerical and analytic studies and compare them to experimental results.