Joseph E. Sluz

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.

Optical communications in atmospheric turbulence

Recent experiments conducted under the Optical RF Communications Adjunct program demonstrate and validate the viability of hybrid free space optical communications links in heavy atmospheric turbulence. Long range air-to-mountain link closures were established under extreme atmospheric turbulence. The system implemented adaptive mechanisms such as adaptive optics, an optical automatic gain controller, forward error correction coding, and link-level retransmission to achieve low packet error rates for long distance links with heavy turbulence. The system, experiments, and results are presented and comparisons are made to statistical prediction models.

Fiber optic bundle array wide field-of-view optical receiver for free space optical communications

We propose a design for a free space optical communications (FSOC) receiver terminal that offers an improved field of view (FOV) in comparison to conventional FSOC receivers. The design utilizes a microlens to couple the incident optical signal into an individual fiber in a bundle routed to remote optical detectors. Each fiber in the bundle collects power from a solid angle of space; utilizing multiple fibers enhances the total FOV of the receiver over typical single-fiber designs. The microlens-to-fiber-bundle design is scalable and modular and can be replicated in an array to increase aperture size. The microlens is moved laterally with a piezoelectric transducer to optimize power coupling into a given fiber core in the bundle as the source appears to move due to relative motion between the transmitter and receiver. The optimum position of the lens array is determined via a feedback loop whose input is derived from a position sensing detector behind another lens. Light coupled into like fibers in each array cell is optically combined (in fiber) before illuminating discrete detectors.

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.

Long range field testing of free space optical communications terminals on mobile platforms

Ground and air testing of mobile FALCON free-space optical (FSO) communications terminals was performed in New Mexico by ITT Corporation, JHU/APL and AFRL. The testing verified the operation of the terminals pointing, acquisition, tracking and data transmission for ground to ground link distances up to 36 km and air to air and air to ground link distances up to 65 km. The FALCON terminals have a nominal 2.5 gbps bidirectional data link. Packet goodput was generally 90% or better for the tests. Data will be presented on the pointing and acquisition sequence, tracking performance, received power and packet throughput. In addition, analysis of the atmospheric conditions and a comparison of actual performance to expected performance will be presented.

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.

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.

Free-space optical channel propagation tests over a 147-km link

A free-space optical communications link spanning 147 km between the islands of Hawaii and Maui was studied as part of AFRLs IRON-T2 program and in support of risk reduction efforts for DARPAs ORCA program in September/October 2008. Over 14 days, the performance of a 10-Gbps bi-directional link was tested during different periods of the day. This paper will present the test configuration, discuss the effects of atmospheric turbulence on the 10 Gbps link, and compare its performance to the available turbulence measurements. Additionally, modeling of the link configuration will be presented and comparisons will be made to collected data including local Cn 2 to understand the impact of atmospheric turbulence on future long distance links.

High-sensitivity DPSK receiver for high-bandwidth free-space optical communication links

A high-sensitivity modem and high-dynamic range optical automatic gain controller (OAGC) have been developed to provide maximum link margin and to overcome the dynamic nature of free-space optical links. A sensitivity of -48.9 dBm (10 photons per bit) at 10 Gbps was achieved employing a return-to-zero differential phase shift keying based modem and a commercial Reed-Solomon forward error correction system. Low-noise optical gain was provided by an OAGC with a noise figure of 4.1 dB (including system required input loses) and a dynamic range of greater than 60 dB.

Analysis of link performance for the FOENEX laser communications system

A series of experiments were conducted to validate the performance of the free-space optical communications (FSOC) subsystem under DARPAs FOENEX program. Over six days, bidirectional links at ranges of 10 and 17 km were characterized during different periods of the day to evaluate link performance. This paper will present the test configuration, evaluate performance of the FSOC subsystem against a variety of characterization approaches, and discuss the impact of the results, particularly with regards to the optical terminals. Finally, this paper will summarize the impact of turbulence conditions on the FSOC subsystem and present methods for estimating performance under different link distances and turbulence conditions.