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.
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.
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.
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
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
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<sup>-6</sup> without any forward error correction (FEC) coding.
The Gemini Observatory and University of Hawaii are planning to install an 85-element curvature adaptive optics system with a laser guide star system on its Cerro Pachon telescope in 2001. This paper discusses the motivation, issues on implementing a laser guide star with a curvature-based system, the implementation of a laser guide star based on a commercially available 2W ring-dye laser, and the expected performance of the system. Detailed simulations show very promising results for system performance down to natural guide star magnitudes of 19 - 20th magnitude. The performance cross- over point between NGS and LGS is between 13 - 16th magnitude depending on the performance parameter of interest (e.g. Strehl, energy through a slit, etc.).
The UH 36 element curvature AO system, Hokupa'a-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.
The University of Hawaii adaptive optics program has recently moved its 36 actuators system, named 'Hokupa'a 36', to the Gemini North Telescope. First light for Hokupa'a 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, Hokupa'a 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.
Atmospheric turbulence distorts the wavefront of the incoming light from an astronomical object and so limits the ability of a telescope to form a perfect image. The AO systems for astronomy had come the most powerful tool for infrared observation in the near thermal domain. A conventional AO system requires quite a few reflections that are needed to transfer and correct an image. A typical system would have a collimator, deformable mirror and a camera at the bare minimum. For the thermal region the gains are substantial where one can eliminate extra optical surfaces and their associated thermal background, that occurs when you put the deformable mirror at the secondary. We study the possibility of development an adaptive secondary with the techniques of a Current Bimorph mirror with the necessaries number of actuators for control the edge slope. Also we simulate the performance of a 19 channels curvature adaptive optics system in order to demonstrate the gain achievable with an adaptive secondary. The adaptive secondary for the 2.1 m Telescope at SPM Observatory is designed for a f/50 beam, 100 mm in diameter with 19 actuators necessaries to control the edge slope and curvature.
The IRTF is a 3.0 meter, f/38, infrared optimized, cassegrain telescope operated under contract from NASA with the primary mission of providing ground-based support for NASA's planetary missions. We are currently in the design and construction phase of a 36 element, curvature-based, natural guide star, adaptive optics facility installation for the IRTF. System architecture will be modeled on the highly successful AO systems developed at the University of Hawaii. The system should achieve an AO efficiency, q >= 0.4. The Strehl ratio is expected to exceed 0.8 in the K band. We estimate a limiting guide star magnitude for full correction of m<SUB>R</SUB> equals 14.4.
All existing night-time astronomical telescopes, regardless of aperture, are blind to an important part of the universe - the region around bright objects. Technology now exist to build an unobscured 6.5 m aperture telescope which will attain coronagraphic sensitivity heretofore unachieved. A working group hosted by the University of Hawaii Institute for Astronomy has developed plans for a New Planetary Telescope which will permit astronomical observations which have never before ben possible. In its narrow-field mode the off-axis optical design, combined with adaptive optics, provides superb coronagraphic capabilities, and a very low thermal IR background. These make it ideal for studies of extra-solar planets and circumstellar discs, as well as for general IR astronomy. In its wide-field mode the NPT provides a 2 degree diameter field for surveys of Kuiper Belt Objects and Near-Earth Objects, surveys central to current intellectual interests in solar system astronomy.
We describe different works conducing to the adaptive optics system for the TIM 6.5m telescope. We show turbulence profiles result at our San Pedro Martir Observatory in Baja using the Generalized SCIDAR. We can conclude that the turbulence conditions in this site are comparable to the major observatories in the world. From these results and taken in account curvature AO simulations it is possible to predict the performances in limiting magnitude and sky coverage of different AO systems and telescopes in our observatory. We can also define the degree of the AO system for the TIM 6.5m telescope. We made a short description of our LOLA tip-tilt corrector system and the GUIELOA 19 elements curvature AO system. The calculation of the optics quality for the TIM 6.5m is briefly mentioned. Studies about the influence of the finite outerscale on the optical quality of AO corrected images are described.
The University of Hawaii adaptive optics program has scaled its previously successful 13 elements AO system to 36 actuators and named it 'Hokupa'a', meaning 'immovable star' in Hawaiian. First light for Hokupa'a in early November of 1997, was on the Canada France Hawaii Telescope on Mauna Kea, an f/35, 3.35 meter telescope. Performance at the telescope has now been measured and compares favorably with that predicted theoretically. The extension to 36 elements has now allowed the system to give diffraction limited performance down to I band on stars as faint as 12.5 magnitude in median 0.7 arcsecond seeing on Mauna Kea. Like our previous system, extensive computer simulations were carried out to achieve the best possible match between the curvature WFS and the deformable curvature mirror.
The University of Hawaii AO group has been actively carrying out astronomical AO observations for the last four years. The UHAO group and out collaborators have utilized the curvature AO system to obtain diffraction-limited images of asteroids, planets, moons, protoplanetary disks, young stars, young star clusters, planetary nebulae, black holes, galaxies and quasars. The current scientific capabilities of the new 36-actuator Hokupa'a AO curvature system will be briefly reviewed. Four key astronomical situations that are excellent for AO observations will be discussed. Examples of scientific observational techniques will be highlighted with actual AO astronomical results.
Wave-front reconstruction from defocused stellar images has now been widely applied to the testing of ground-based optical telescopes. We describe here the latest improvements to the technique and discuss how to reach a maximum accuracy. Statistics are given on the aberrations observed over 10 different telescopes.
A fast tip-tilt secondary is being implemented on the University of Hawaii 2.2-m telescope, to provide image quality to match the site characteristics of Mauna Kea, and complement the existing wide-field RC secondary.
In this paper we discuss the performance of low order adaptive optics (AO) systems. We present improved calculations of Strehl ratio achievable at various D/r<SUB>o</SUB> ratios for AO systems up to 7<SUP>th</SUP> order. Additionally we present calculations concerning the throughput of low order AO systems used in conjunction with spectrometers. We then show the results of a detailed simulation of the expected interaction of the University of Hawaii prototype AO system with spectrometers through the V,I,J,H,K optical bands. This simulation shows that AO spectroscopy performance should always be acceptable in the near IR (J,H,K), and often in the visible (V,I). We show the results of our initial efforts at deconvolving the AO PSF. These results indicate that deconvolution is likely to be quite widely applicable to AO images. Finally we discuss how it might be possible to extend the applicability and accuracy of deconvolution using the AO drive and wavefront error signals. The following results are for on-axis system, the effects of atmospheric anisoplanitism have not been addressed in this paper.
A photon counting wavefront curvature sensor (WFS) with 13 subapertures suitable for adaptive optics in astronomy has been developed at the University of Hawaii. This sensor is capable of using very faint point sources or slightly extended sources to derive the wavefront signal. The sensitivity of this sensor is continuously variable and can be adjusted in real time to match the seeing conditions at the time. The wavefront sampling geometry has been optimized for correcting the standard atmosphere up to 9 orders expressed in terms of Zernike's. Its output is used in conjunction with a newly developed deformable bimorph mirror for high efficiency correction capabilities. This WFS has successfully been used recently at the CFHT and UKIRT facilities on Mauna Kea on a variety of astronomical objects. Point sources, double stars, planetary nebula, galactic nuclei, and some of the moons of Jupiter have all been successfully attempted. Limiting magnitude has not been explored in great detail at the telescope, but we have taken the system down to magnitude R equals 13.7 (V equals 15) with a 3.6 meter aperture with success. This was achieved during bright time or whilst the full moon was present.
The University of Hawaii experimental adaptive optics system is controlled by dual SPARC single board computers on a VME backplane. One processor is dedicated to the feedback loop. The second processor manages loop data flow to a workstation and transfers new control parameters to the loop processor without stopping the loop. This system facilitates cause-effect analysis of the various system parameters.
The experimental adaptive optics system, currently developed at the University of Hawaii, is now equipped with a VME-based control system, and a high sensitivity wave-front sensor. The sensor uses an array of 13 photon-counting avalanche photodiodes which enable the system to work with faint reference or `guide' sources, as faint as magnitude 15. Results of the first successful observing runs are described here.
We report on the results of the system simulation software written at Canada-France-Hawaii Telescope, to predict and optimize the performance of our adaptive optics bonnette presently under construction. The individual simulation elements, atmospheric simulator, curvature sensor, bimorph mirror and control loop, are reviewed with an emphasis on the basic properties of curvature sensors. Optimization of the extra-focal distance parameter and its consequences are discussed. We then present results of whole system simulations, and quantify the main sources of error. Some results, including noise, are reported. In a second part, we present our view of modal control and detail the construction of the modal basis. We also report briefly on modal gain optimization.
This paper describes a low cost adaptive optics (AO) instrument that is being built for the f/31 focus of the UH 2.2m telescope. While operating within the low cost constraint, we have tried to maximize the flexibility and usefulness of the instrument, and minimize the impact of the necessary performance compromises. We have used off-the-shelf optical and electronic components wherever possible, and have emphasized simplicity of design throughout the instrument. The UH prototype AO system, on which the 2.2m AO system is based, is described elsewhere, thus the principles of operation of the UH 2.2m instrument will not be described in detail here.
A review of computer simulation of a low-order adaptive system based on curvature sensing and a bimorph mirror is given. The system was designed to accurately follow the lowest order Karhunen Loeve modes of the atmosphere. The purpose of the simulation was system design improvement and the determination of system performance limits. The four main areas of the simulation are described; atmospheric simulation, Fresnel propagation, bimorph model, and sensor feedback model. Results are presented and discussed.
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.