Daniel V. Murphy

Coherent combining of a 4 kW, eight-element fiber amplifier array.

Commercial 0.5 kW Yb-doped fiber amplifiers have been characterized and found to be suitable for coherent beam combining. Eight such fiber amplifiers have been coherently combined in a tiled-aperture configuration with 78% combining efficiency and total output power of 4 kW. The power-in-the-bucket vertical beam quality of the combined output is 1.25 times diffraction limited at full power. The beam-combining performance is independent of output power.

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.

Enhanced Raman scattering from silicon microstructures

Electromagnetic-structure-resonance enhancement of scattering from Si phonon modes is reported for a number of submicrometer structures. Enhancements of greater, similar100 over the Raman intensity from bulk Si are observed for ~0.1-microm-diameter Si spheres. An analytic calculation of the Raman intensity for this geometry is in good qualitative agreement with the experiment and demonstrates that the enhancement arises from the coupling of both the incident and the scattered fields with the low-order-structure resonances in this high-index dielectric.

The lunar laser communications demonstration

The Lunar Laser Communications Demonstration represents NASAs first attempt to demonstrate optical communications from a lunar orbiting spacecraft to an Earth-based ground receiver. A low size, weight and power optical terminal will be integrated onto the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft, presently scheduled to launch in 2013. LLCD will demonstrate duplex optical communications between this small space terminal and a multi-aperture photon-counting ground terminal at downlink data rates of up to 622 Mbps and uplink data rates of up to 20 Mbps.

Beam control of a 2D polarization maintaining fiber optic phased array with high-fiber count

We demonstrate, for the first time to our knowledge, successful beam control of a fiber optic phased array containing a large number of polarization maintaining fibers. As many as forty-eight fibers have been coherently combined via individual all-fiber phase modulators. The residual phase error is less than 1/30th of a wave. Results with both near-field interferometric control and target-in-the-loop control have been obtained. Experimental results are compared with numerical simulations and excellent agreement has been achieved. We investigated propagation of this phased array output through a turbulent atmosphere, and used the all-fiber phase modulators for the compensation of turbulence effects on the array output. This work paves the way towards scaling such fiber optic phased arrays to very high fiber count. Eventually thousand of fibers can be controlled via such a scheme.

LDORA: a novel laser communications receiver array architecture

We present a new laser communications receiver architecture. It consists of an array of individually mounted telescopes, each with a Geiger-mode photon counting detector array. The detector outputs are sent to a central processor using standard digital networking hardware. The concept has many benefits including low cost and scalability.

Overview and status of the Lunar Laser Communications Demonstration

The Lunar Laser Communications Demonstration (LLCD), a project being undertaken by MIT Lincoln Laboratory, NASAs Goddard Space Flight Center, and the Jet Propulsion Laboratory, will be NASAs first attempt to demonstrate optical communications between a lunar orbiting spacecraft and Earth-based ground receivers. The LLCD space terminal will be flown on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft, presently scheduled to launch in 2013. LLCD will demonstrate downlink optical communications at rates up to 620 Mbps, uplink optical communications at rates up to 20 Mbps, and two-way time-of-flight measurements with the potential to perform ranging with sub-centimeter accuracy.

Design of a ground-based optical receiver for the lunar laser communications demonstration

In this paper we present a design for a photoncounting optical receiver—based on superconducting NbN nanowire detector arrays—that will be employed in the ground terminal for the NASA Lunar Laser Communications Demonstration. The ground receiver is designed with four, 40 cm apertures, each coupled to a novel multi-mode polarization-maintaining fiber. The receiver is designed to receive a variable-rate pulse-position-modulated signal with a maximum data rate of 622 Mb/s.

LLCD operations using the Lunar Lasercom Ground Terminal

The Lunar Lasercom Ground Terminal (LLGT) is the primary ground terminal for NASA’s Lunar Laser Communication Demonstration (LLCD), which demonstrated for the first time high-rate duplex laser communication between Earth and satellite in orbit around the Moon. The LLGT employed a novel architecture featuring an array of telescopes and employed several novel technologies including a custom PM multimode fiber and high-performance cryogenic photon-counting detector arrays. An overview of the LLGT is presented along with selected results from the recently concluded LLCD.

Overview of the lunar laser communications demonstration

The Lunar Laser Communications Demonstration (LLCD), a project being undertaken by MIT Lincoln Laboratory and NASAs Goddard Space Flight Center, represents NASAs first attempt to demonstrate optical communications from a lunar orbiting spacecraft to an Earth-based ground receiver. The LLCD space terminal will be flown on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft, presently scheduled to launch in 2013. LLCD will demonstrate downlink optical communications at rates up to 620 Mbps, uplink optical communications at rates up to 20 Mbps, and two-way time-of-flight measurements with the potential to perform ranging with sub-centimeter accuracy. We describe the objectives of the LLCD program and discuss key technologies employed in the space and ground terminals.