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At least 127 records · Page 7

Single longitudinal mode operation of semiconductor laser arrays with etalon control

A simple method is devised to obtain a single longitudinal output beam from high-power multilongitudinal mode diode laser arrays. Mode control is achieved by simply placing a thin etalon in front of the laser. The three-cavity laser formed by addition of the etalon favors a single longitudinal mode. This technique is applicable to both continuous wave and pulsed laser modes of operation. Experimental results demonstrating the technique along with future work and possible applications are discussed.

Hemmati, H.↗

Optical communication with semiconductor laser diodes

A 25 megabit/sec direct detection optical communication system that used Q=4 PPM signalling was constructed and its performance measured under laboratory conditions. The system used a single-mode AlGaAs laser diode transmitter and low noise silicon avalanche photodiode (APD) photodetector. Comparison of measured performance with the theoretical revealed that modeling the APD output as a Gaussian process under conditions of negligible background radiation and low (less than 10 to the -12 power A) APD bulk leakage currents leads to substantial underestimates of optimal APD gain to use and overestimates of system bit error probability. A procedure is given to numerically compute system performance which uses the more accurate Webb's Approximation of the exact Conradi distribution for the APD ouput signal that does not require excessive amounts of computer time (a few minutes of VAX 8600 CPU time per system operating point). Examples are given which illustrate the breakdown of the Gaussian approximation in assessing system performance. This system achieved a bit error probability of 10 to the -6 power at a received signal energy corresponding to an average of 60 absorbed photons/bit and optimal APD gain of 700.

Davidson, F.↗

Electrical and optical study of semiconductor laser diodes and materials

The characterization of a 2-D diode laser array from McDonald Douglas has been completed. The array consisted of 8 linear arrays of approximately 11 mm x 0.18 mm. Each array has between 7 and 8 diodes per mm. The threshold current is approximately 15 amps. The power output vs drive current (above threshold) of the array was measured. A peak power of 50 W was obtained at a drive current of 26 amps. Its far field pattern has a double lobe.

Albin, Sacharia↗

Confocal unstable-resonator semiconductor laser

GaAs/GaAlAs heterostructure lasers with a monolithic confocal unstable resonator were demonstrated. The curved mirrors satisfying the confocal condition were fabricated by etching. Close to threshold, the lasers operate in a single lateral mode with a nearly collimated output beam. A single-lobe far-field intensity distribution as narrow as 1.9-deg full width at half maximum was measured.

Salzman, J.↗

Single longitudinal mode operation of semiconductor laser arrays with etalon feedback

The multiple longitudinal mode output of high-power diode-laser arrays is converted into single mode with 97 percent efficiency by optical feedback from a thin (less than 200-micron thick) etalon external to the laser. The coupled cavities formed by addition of the etalon favor a single longitudinal mode. Single-mode operation is retained at 0.1 MHz pulsed rates. Both the near-field and the far-field patterns of the laser array remain nearly unchanged while the array operates in a single longitudinal mode.

Hemmati, H.↗

Diffraction-Coupled, Phase-Locked Semiconductor Laser Array

Stable, narrow far field produced. Array of lasers fabricated on single chip. Individual laser waveguides isolated from each other except in end portions, where diffraction coupling takes place. Radiation pattern far from laser array has single, sharp central lobe when all lasers operate in phase with each other. Shape of lobe does not vary appreciably with array current. Applications include recording, printing, and range finding.

Katz, Joseph↗

Optical communication with semiconductor laser diodes

Slot timing recovery in a direct detection optical PPM communication system can be achieved by processing the photodetector waveform with a nonlinear device whose output forms the input to a phase lock group. The choice of a simple transition detector as the nonlinearity is shown to give satisfactory synchronization performance. The rms phase error of the recovered slot clock and the effect of slot timing jitter on the bit error probability were directly measured. The experimental system consisted of an AlGaAs laser diode (lambda = 834 nm) and a silicon avalanche photodiode (APD) photodetector and used Q=4 PPM signaling operated at a source data rate of 25 megabits/second. The mathematical model developed to characterize system performance is shown to be in good agreement with actual performance measurements. The use of the recovered slot clock in the receiver resulted in no degradation in receiver sensitivity compared to a system with perfect slot timing. The system achieved a bit error probability of 10 to the minus 6 power at received signal energies corresponding to an average of less than 60 detected photons per information bit.

Davidson, F.↗

Monolithic narrow-linewidth InGaAsP semiconductor laser for coherent optical communications

A design for a monolithic narrow-linewidth InGaAsP diode laser has been developed using a multiple-quantum-well (MQW) extended-passive-cavity distributed-Bragg-reflector (DBR) laser design. Theoretical results indicate that this structure has the potential for a linewidth of 100 kHz or less. To realize this device, a number of the fabrication techniques required to integrate low-loss passive waveguides with active regions have been developed using a DBR laser structure. In addition, the MOCVD growth of InGaAs MQW laser structures has been developed, and threshold current densities as low as 1.6 kA/sq cm have been obtained from broad-stripe InGaAs/InGaAsP separate-confinement-heterostructure MQW lasers.

Palfrey, S. L.↗

Incoherent GaAlAs/GaAs semiconductor laser arrays

The fabrication of an incoherent laser array is reported. The main features of the arrays are low threshold index-guided laser elements, single-lobe far-field pattern, low astigmatism, low current operation, dense packing, and total electrical and optical isolation. With further development, this device should have applications in multihead optical-disk reading and writing, multifiber optical communications, and line-of-sight communications.

Hwang, C. J.↗

Lateral modes of broad area semiconductor lasers - Theory and experiment

Calculations of the lateral modes of an ideal broad area laser, including the nonlinear interaction between the carriers and the optical field, are made. The results include periodically modulated near fields and single- and double-lobed far fields similar to those previously measured. The unsaturable losses are higher and quantum efficiencies are lower than those determined from plane-wave approximations. Broad area InGaAs-GaAlAs-GaAs quantum-well lasers were fabricated and measured and found to closely agree with the theory in near, far, and spectrally resolved near fields. An occultation experiment on the far field confirms previously predicted unstable resonatorlike modes with V-shaped fronts.

Lang, Robert J.↗

Long wavelength semiconductor lasers development for infrared heterodyne applications

PbSnTe single crystals were grown in a new 3 zone furnace. Molecular beam epitaxy (MBE) growth parameters have been established, including beam flux vs. temperature, and growth rates and dopant vs. PbTe flux ratios for the various effusion sources involved. Lattice matching studies were conducted and doping studies were completed. Broad area Pb(1-x)Sn(x)Te double heterostructure lasers were fabricated with active layer compositions up to x equals 0.04 at percent Sn in the active layers. Electrical and optical test data are presented.

Feit, Zeev↗

Development of simplified external control techniques for broad area semiconductor lasers

The goal of this project was to injection lock a 500 mW broad area laser diode (BAL) with a single mode low power laser diode with injection beam delivery through a single mode optical fiber (SMF). This task was completed successfully with the following significant accomplishments: (1) injection locking of a BAL through a single-mode fiber using a master oscillator and integrated miniature optics; (2) generation of a single-lobed, high-power far-field pattern from the injection-locked BAL that steers with drive current; and (3) a comprehensive theoretical analysis of a model that describes the observed behavior of the injection locked oscillator.

Davis, Christopher C.↗

High speed semiconductor lasers and integrated receivers for microwave and millimeter wave signal transmission

This project was proposed to be a three-year contract, but was cut off after one year (1987) of support. Sufficient progress was made to allow continuation for a year on minimal internal funds before proper support levels were received from a combination of ONR, RADC, and IBM contracts at about the start of 1989. A major DARPA grant, expected to start August 1, 1990, will sharply expand this effort to include several faculty members. During the course of this project, two students did thesis research, one Ph.D. on lasers and one M.S. on high speed photodetectors. These theses were finished in September 1988, nine months after the contract was cut off. This report covers excerpts from those theses as well as information obtained on other programs since that time.

Eastman, L. F.↗

Flight demonstration of flight termination system and solid rocket motor ignition using semiconductor laser initiated ordnance

Solid State Laser Initiated Ordnance (LIO) offers new technology having potential for enhanced safety, reduced costs, and improved operational efficiency. Concerns over the absence of programmatic applications of the technology, which has prevented acceptance by flight programs, should be abated since LIO has now been operationally implemented by the Laser Initiated Ordnance Sounding Rocket Demonstration (LOSRD) Program. The first launch of solid state laser diode LIO at the NASA Wallops Flight Facility (WFF) occurred on March 15, 1995 with all mission objectives accomplished. This project, Phase 3 of a series of three NASA Headquarters LIO demonstration initiatives, accomplished its objective by the flight of a dedicated, all-LIO sounding rocket mission using a two-stage Nike-Orion launch vehicle. LIO flight hardware, made by The Ensign-Bickford Company under NASA's first Cooperative Agreement with Profit Making Organizations, safely initiated three demanding pyrotechnic sequence events, namely, solid rocket motor ignition from the ground and in flight, and flight termination, i.e., as a Flight Termination System (FTS). A flight LIO system was designed, built, tested, and flown to support the objectives of quickly and inexpensively putting LIO through ground and flight operational paces. The hardware was fully qualified for this mission, including component testing as well as a full-scale system test. The launch accomplished all mission objectives in less than 11 months from proposal receipt. This paper concentrates on accomplishments of the ordnance aspects of the program and on the program's implementation and results. While this program does not generically qualify LIO for all applications, it demonstrated the safety, technical, and operational feasibility of those two most demanding applications, using an all solid state safe and arm system in critical flight applications.

Schulze, Norman R.↗

Semiconductor Laser Line-width Measurements for Space Interferometry Applications

This work discusses results using the self-heterodyne delay atechnique to measure 1.3 um InP based DFB lasers. We will also address practical issues concerning detection and elimination of back reflections, choice of fiber length and resolution, and measurement of laser 1/f and current supply noise.

DFB laser delayed self-heterodyne interferometer l↗

Low SWaP Semiconductor Laser Transmitter Modules For ASCENDS Mission Applications

The National Research Council's (NRC) Decadal Survey (DS) of Earth Science and Applications from Space has identified the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) as an important atmospheric science mission. NASA Langley Research Center, working with its partners, is developing fiber laser architecture based intensity modulated CW laser absorption spectrometer for measuring XCO2 in the 1571 nm spectral band. In support of this measurement, remote sensing of O2 in the 1260 nm spectral band for surface pressure measurements is also being developed. In this paper, we will present recent progress made in the development of advanced transmitter modules for CO2 and O2 sensing. Advanced DFB seed laser modules incorporating low-noise variable laser bias current supply and low-noise variable temperature control circuit have been developed. The 1571 nm modules operate at >80 mW and could be tuned continuously over the wavelength range of 1569-1574nm at a rate of 2 pm/mV. Fine tuning was demonstrated by adjusting the laser drive at a rate of 0.7 pm/mV. Heterodyne linewidth measurements have been performed showing linewidth ~200 kHz and frequency jitter ~75 MHz. In the case of 1260 nm DFB laser modules, we have shown continuous tuning over a range of 1261.4 - 1262.6 nm by changing chip operating temperature and 1261.0 - 1262.0 nm by changing the laser diode drive level. In addition, we have created a new laser package configuration which has been shown to improve the TEC coefficient of performance by a factor of 5 and improved the overall efficiency of the laser module by a factor of 2.

Prasad, Narasimha S.↗

Subpicometer Length Measurement Using Semiconductor Laser Tracking Frequency Gauge

We have demonstrated heretofore unattained distance precision of 0:14pm (2pm) incremental and 14nm (2.9 micrometers) absolute in a resonant (nonresonant) interferometer at an averaging time of 1 s, using inexpensive telecommunications diode lasers. We have controlled the main source of error, that due to spurious reflection and the resulting amplitude modulation. In the resonant interferometer, absolute distance precision is well under lambda/6. Therefore, after an interruption, an absolute distance measurement can be used to return to the same interferometer order.

Thapa, Rajesh↗