Malcolm J. Northcott

Images of Neptune's ring arcs obtained by a ground-based telescope

Neptune has a collection of incomplete narrow rings, known as ring arcs, which should in isolation be destroyed by differential motion in a matter of months. Yet since first discovered by stellar occultations in 1984, they appear to have persisted, perhaps through a gravitational resonance effect involving the satellite Galatea. Here we report ground-based observations of the ring arcs, obtained using an adaptive optics system. Our data, and those obtained using the Hubble Space Telescope (reported in a companion paper), indicate that the ring arcs are near, but not within the resonance with Galatea, in contrast to what is predicted by some models.

80 Gb/s free-space optical communication demonstration between an aerostat and a ground terminal

A free-space optical (FSO) communication demonstration was conducted with JHU/APL and AOptix at the TCOM Test Facility in Elizabeth City, NC in May 2006. The primary test objective was to evaluate the performance of an FSO link from a fiber-tethered aerostat to a ground platform at effective data rates approaching 100 Gigabits/sec using wavelength division multiplexing (WDM) techniques. (Multiple optical channels operating near 1550 nm were modulated at data rates of 1, 10 and 40 Gbps). The test was conducted with a 38 meter aerostat raised to an altitude of 1 km and a ground platform located 1.2 km from the aerostat (limited by property boundary). Error free data transfers of 1.2 Terabits in 30 seconds at 40 Gbps were demonstrated. The total data transferred during the test was greater than 30 Terabits with an average BER of 10-6 without any forward error correction (FEC) coding.

First light for Hokupa'a 36 on Gemini North

The University of Hawaii adaptive optics program has recently moved its 36 actuators system, named Hokupaa 36, to the Gemini North Telescope. First light for Hokupaa 36 was in time for the dedication of this telescope during June 1999 and most of the images presented were taken with this adaptive optics system. This paper will cover the modifications to the CFHT, Hokupaa 36 system that were necessary to accommodate the larger 8 meter aperture of the Gemini Telescope. Performance at the telescope has now been measured and compares favorably with that predicted.

Long distance laser communications demonstration

AOptix demonstrated a simulated air-to-air laser communications (laser-com) system over a 147Km distance by establishing a laser communication link between the islands of Hawaii and Maui. We expect the atmospheric conditions encountered during this demonstration to be representative of the worst seeing conditions that could be expected for an actual air to air link. AOptix utilized laser-com terminal incorporating Adaptive Optics (AO) to perform high speed tracking and aberration correction to reduce the effects of the seeing. The demonstration showed the feasibility of establishing high data rate point to point laser-com links between aircraft. In conjunction with Johns Hopkins University Applied Physics Laboratory networking equipment we were able to demonstrate a 40Gbit DWDM link, providing significantly more data throughput than is available using RF technologies. In addition to being very high data rate, the link demonstrates very low beam spread, which gives very high covertness, and a high degree of data security. Since the link is based on 1550nm optical wavelengths it is inherently resistant to jamming.

Optical RF Communications Adjunct

The capacity to integrate RF and free space optical hybrid communications now feasible given advances in adaptive optics and optical automated gain control. The ORCA program is developing on operationally capable of highly reliable hybrid communications. This paper provides an overview of the ORCA systems and discusses some of the key developments in making the systems a reality.

Hybrid optical radio frequency airborne communications

Optical RF Communications Adjunct Program flight test results provide validation of the theoretical models and hybrid optical radio frequency (RF) airborne system concepts developed by the Defense Advanced Research Projects Agency and the U.S. Air Force Research Laboratory. Theoretical models of the free-space optical communications (FSOC), RF, and network components accurately predict the flight test results under a wide range of day and night operating conditions. The FSOC system, including the adaptive optics and optical modem, can operate under high turbulence conditions. The RF and network mechanisms of Layer 2 retransmission and failover provide increased reliability, reducing end-to-end packet error rates. Overall the test results show that stable, long-range FSOC is possible and practical for near-term operations.

Demonstration of high-data-rate wavelength division multiplexed transmission over a 150-km free space optical link

A 150 km free-space optical (FSO) communication link between Maui (Haleakala) and Hawaii (Mauna Loa) was demonstrated by JHU/APL and AOptix Technologies, Inc. in September 2006. Over a 5 day period, multiple configurations including single channel 2.5 Gbps transmission, single channel 10 Gbps, and four wavelength division multiplexed (WDM) 10 Gbps channels for an aggregate data rate of 40 Gbps were demonstrated. Links at data rates from 10 to 40 Gb/s were run in excess of 3 contiguous hours. Data on the received power, frame synchronization losses, and bit error rate were recorded. This paper will report on the data transfer performance (bit error rates, frame synchronization issues) of this link over a 5 day period. A micropulse lidar was run concurrently, and on a parallel path with the FSO link, recording data on scattering loss and visibility. Comparisons between the state of the link due to weather and the data transfer performance will be described.

Demonstration of High Data Rate Wavelength Division Multiplexed Transmission over a 150 km Free Space Optical Link

A 150 km free-space optical (FSO) communication link between Maui (Haleakala) and Hawaii (Mauna Loa) was demonstrated by JHU/APL and AOptix Technologies, Inc. in September 2006. Over a 5 day period, multiple configurations including single channel 2.5 Gbps transmission, single channel 10 Gbps, and four wavelength division multiplexed (WDM) 10 Gbps channels for an aggregate data rate of40 Gbps were demonstrated. Links at data rates from 10 to 40 Gb/s were run in excess of 3 contiguous hours. Data on the received power, frame synchronization losses, and bit error rate were recorded.

University of Hawaii adaptive optics system: I. General approach

The adaptive optics system being developed to sharpen images produced by telescopes at Mauna Kea is discussed. An approach based on new components developed and optimized for astronomical applications is described. The approach is limited to low-order wavefront compensation and is used for image stabilization. Avalanche photodiodes were used as sensors and reference stars were employed for sensing wavefront errors in a novel sensing technique based on wavefront curvature measurements. The instrument is described and expected performance is discussed.

Design and performance of an 85 actuator curvature system

The UH 36 element curvature AO system, Hokupaa-36, was recently moved to the Gemini 8m telescope, where it was used with great success obtaining images for the telescope dedication. Since the 36 actuator system was optimized for performance on a 4 m (CFHT) telescope it does not provide full near IR wavelength converge on the Gemini 8m telescope. In order to address this issue we are planning to upgrade the system to 85 actuators. Given the slightly better seeing expected at the Gemini telescope, the move to 85 actuators will give Strehl ratios commensurate to those obtained with 36 actuators on the CFHT. The limiting magnitude will scale with the telescope aperture giving considerably better sky coverage than at the CFHT. Curvature AO systems can scale considerably beyond 85 actuators, at this point technology presents the most important limitations to scaling.