Publications

We report the first successful demonstration of a photomixer local oscillator (LO) integrated with a superconducting heterodyne detector. The photomixer LO generated the difference frequency of two diode lasers by optical heterodyne conversion in low-temperature-grown GaAs. The measured receiver noise temperature, 331 K at 630 GHz, compares favorably with that achieved using a varactor-multiplier LO. We also report the design of a high-power distributed photomixer structure.

High-power diode lasers consisting of a ridge-waveguide section coupled to a tapered region have been fabricated in 1.5um InGaAsP-InP multiple-quantum-well material. Self-focusing at high current densities and high-intensity input into the taper section has been identified as a fundamental problem in these devices that has to be dealt with. To date, continuous-wave output powers>1 W with=80% of the power in the near-diffraction-limited central lobe of the far field have been obtained through a judicious choice of device parameters.

A monolithic two-dimensional array of surface-emitting AlGaAs diode lasers with dry-etched vertical facets and parabolic deflecting mirrors was mounted junction-side up on a W / Cu microchannel heatsink and evaluated under continuous-wave (CW) operating conditions. Both the facets and parabolic deflecting mirrors were etched using chlorine ion-beam-assistd etching. Threshold current densities of different sections of the array were consistently around 240 A/cm (to the second power), and measured CW differential quantum efficiencies were in the 46-48% range. CW power densities as high as 148 W/cm (to the second power) were achieved with an average temperature rise of less than 25 degrees C in this junction-side-up configuration.

Runway 4-R at Logan Airport cannot now be used with full effectiveness because of tall ships passing through the runway's approach clearance zone. The key to utilizing the full length of Runway 4-R at Logan Airport for longer periods of time is to establish a channel surveillance system that would allow both ships and aircraft to safely share the air space above the channel. A laser-gate alarm system across the channel, at the approaches to the clearance zone, has been proposed for alerting tower operators to the passage of tall ships. A surface detection (ASDE) radar would maintain surveillance during passage of the ship. This ship detection concept was explored and developed within Lincoln Laboratory with cooperation and encouragement from MASSPORT and members of the FAA Burlington office. This report completes the study and field measurements program, sponsored by MASSPORT, for the evaluation of an experimental laser-gate ship-detection system. The study and field Measurements program supports the conclusion that a reliable, fail-safe, laser-gate system can be designed, installed and operated to detect ships entering the clearance zone of Runway 4-R. System feasibility has been established for visual meteorological conditions both day and night. Ship masts of 1-inch diameter at speeds up to 15 knots can be reliably detected under visual meteorological conditions for laser-path-lengths up to 3000 feet. An operational system can be de signed for visibility ranges down to 1/4 mile with laser path lengths of 1800 feet and with the expectation that performance would be substantially the same. The system design is amenable to various balance s between mast-height margin, VFR runway length and displaced threshold duty factor. In the recommended system, the laser-gates may be placed at a height of about 45 feet, which will detect ships tall enough to intrude the clearance zone, while allowing small craft to pass without alarm. This configuration would permit full use of the 10,000-foot runway, while providing an 11- to 21-foot margin for narrow objects which might be less than one-inch wide at the laser-gate height. Analysis of ship traffic indicates that the use of a laser-gate system at the 40- to 50-foot height under nighttime visual meteorological conditions would permit the full-length use of Runway 4-R throughout the night except for the times of passage of 4 to 7 ships on the average. During the early nighttime hours having the heaviest nighttime air traffic, less than one ship alarm would be expected on the average. Operational system design relations are presented which permit a spectrum of design options. False alarms would be at a negligible level in a multiple-parallel-beam operational system and an infrequent false alarm could be checked with the ASDE radar. Recommendations are made for a program which would lead to an operational laser-gate ship-detection system fully integrated with airport facilities and activities. This program would initially involve the design and installation of one prototype laser-gate, which would be integrated with the airport surface detection radar to establish optimum system configuration, develop operational procedures, and to test more extensively the reliability and fail-safe features of the surveillance system. Upon satisfactory completion of the tests and studies, the prototype could be used as one element of an operational system. This report contains in Appendix B engineering guidelines for the recommended prototype laser-gate system.