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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Separate-contact phase-locked semiconductor laser arrays

The novel optoelectronic devices discussed, phase-locked semiconductor laser arrays with separate contacts can perform a variety of near field and far field pattern tailoring functions and control mutual coherence among array elements, as well as lasing wavelength selectivity and tunability. Attention is presently given to experimental results from such arrays, which indicate that the threshold currents of the 4-micron wide lasers employed are typically 60 mA. The separate contacts to each one of them are provided by means of two-level metallization.

Katz, J.↗
NASA NTRS1988

Semiconductor lasers for space sensor applications

Despite their intrinsic power limitations, semiconductor laser diodes are essential for laser-based spaceborne sensor systems covering a wide spectral range, fulfilling such roles as pumping and injection-locking. They may also be used as direct sources in shorter-range operations. AlGaAs laser arrays have been developed for 810-nm band pumping in Nd:YAG lasers otherwise emitting at 1.064 nm. Additional roles include their use as low-power injection seeds, locking a solid-state laser into a specific desired wavelength.

Katz, Joseph↗
NASA NTRS1989

Increasing And Combining Outputs Of Semiconductor Lasers

Paper reviews methods of increasing and combining outputs of semiconductor lasers, with references to literature of recent years (mostly 1986 and 1987). This is a field of great practical importance: Necessary to increase or combine outputs of individual lasers to obtain sufficient power for such uses as communication, ranging, remote sensing, printing, and pumping solid-state lasers.

Katz, Joseph↗
NASA NTRS2000

Semiconductor Laser Linewidth Measurements for Space Interferometry Applications

Narrow linewidth (<100KHz) semiconductor lasers are expected to be a key technology in NASA's stellar interferometry missions to search for planets around nearby stars. Long coherence length lasers are needed for precise (20 pm to 5 mn) measurements of the optical path difference. This work discusses results using the self-heterodyne delay technique to measure 1.3 micrometer 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.

Dougherty, D. J.↗
NASA NTRS1996

Semiconductor Laser Low Frequency Noise Characterization

This work summarizes the efforts in identifying the fundamental noise limit in semiconductor optical sources (lasers) to determine the source of 1/F noise and it's associated behavior. In addition, the study also addresses the effects of this 1/F noise on RF phased arrays. The study showed that the 1/F noise in semiconductor lasers has an ultimate physical limit based upon similar factors to fundamental noise generated in other semiconductor and solid state devices. The study also showed that both additive and multiplicative noise can be a significant detriment to the performance of RF phased arrays especially in regard to very low sidelobe performance and ultimate beam steering accuracy. The final result is that a noise power related term must be included in a complete analysis of the noise spectrum of any semiconductor device including semiconductor lasers.

SEMICONDUCTOR LASERS↗
NASA NTRS1983

Phase-locked semiconductor laser array with separate contacts

A new monolithic phase-locked semiconductor laser array has been fabricated. Employing two-level metallization, each of the eight elements in the array has a separate contact, thus making it possible to compensate for device nonuniformities and control the near-field and far-field patterns. Threshold currents are approximately 60 mA for each 5-micron-wide laser in the array. Phase locking has been observed via the narrowing of the far-field pattern. Experimental results are compared to those obtained from the same arrays operated with all the lasers connected in parallel.

Katz, J.↗
NASA NTRS1984

Longitudinal-mode control in integrated semiconductor laser phased arrays by phase velocity matching

The spectrum of semiconductor-laser arrays with separate contacts is investigated. It is demonstrated that the individual laser currents can be selected such that the array operates in a single longitudinal mode, in contrast to the multimode nature of its individual constituents. Moreover, it is possible to tune the lasing frequency by varying the laser currents. Wavelength tuning range of about 50 A, with tuning rate of about 5 A per milliampere, is demonstrated. It is suggested that these spectral features, characteristic of lasers which are coupled in parallel, result from the strong frequency dependence of their spatial mode pattern near the phase-matching frequency of their coupled waveguides.

Kapon, E.↗
NASA NTRS2009

Electron beam pumped semiconductor laser

Electron-beam-pumped semiconductor ultra-violet optical sources (ESUVOSs) are disclosed that use ballistic electron pumped wide bandgap semiconductor materials. The sources may produce incoherent radiation and take the form of electron-beam-pumped light emitting triodes (ELETs). The sources may produce coherent radiation and take the form of electron-beam-pumped laser triodes (ELTs). The ELTs may take the form of electron-beam-pumped vertical cavity surface emitting lasers (EVCSEL) or edge emitting electron-beam-pumped lasers (EEELs). The semiconductor medium may take the form of an aluminum gallium nitride alloy that has a mole fraction of aluminum selected to give a desired emission wavelength, diamond, or diamond-like carbon (DLC). The sources may be produced from discrete components that are assembled after their individual formation or they may be produced using batch MEMS-type or semiconductor-type processing techniques to build them up in a whole or partial monolithic manner, or combination thereof.

Hug, William F.↗
NASA NTRS1993

Self-collimated unstable resonator semiconductor laser

Self-collimation of the output is achieved in an unstable resonator semiconductor laser by providing a large concave mirror M sub 1 and a small convex mirror M sub 2 on opposite surfaces of a semiconductor body of a material having an effective index of refraction denoted by n, where the respective mirror radii R sub 1, R sub 2 and beam radii r sub 1, r sub 2 are chosen to satisfy a condition (R sub 2)/(1 + r sub 1) = (n - 1)/n, with a value of geometric magnification 1 less than or equal to M less than or equal to (n + 1)/(n - 1) where r sub 1 and r sub 2 are the radii of counterpropagating beams at respective mirrors of radii R sub 1 and R sub 2.

Lang, Robert J.↗
NASA NTRS1991

Quantum correlation between the junction-voltage fluctuation and the photon-number fluctuation in a semiconductor laser

The photon-number fluctuation of the external field from a semiconductor laser - which was reduced to below the standard quantum limit - is shown to be correlated with the measured junction-voltage noise. The spectral density of the sum of the photon-number fluctuation and junction-voltage fluctuation falls below the squeezed photon-number fluctuation. This confirms the theoretical predictions that this correlation, which originates in the dipole interaction between the internal field and electron-hole pairs, extends into the quantum regime.

Richardson, W. H.↗
NASA NTRS1988

Semiconductor laser technology for remote sensing experiments

Semiconductor injection lasers are required for implementing virtually all spaceborne remote sensing systems. Their main advantages are high reliability and efficiency, and their main roles are envisioned in pumping and injection locking of solid state lasers. In some shorter range applications they may even be utilized directly as the sources.

Katz, Joseph↗
NASA NTRS1984

Rate equations analysis of phase-locked semiconductor laser arrays under steady state conditions

Rate equations analysis of phase-locked semiconductor laser arrays has been carried out. It was found that for given (laser) current densities, the photon density distribution in the array elements is that particular one which maximizes the total photon density. The results of this analysis were then combined with the waveguide properties of the laser array waveguide, yielding a basic model of phase-locked diode laser arrays. This model explains the effects of the variation of the current combination through the array elements on its mode structure that were observed recently.

Katz, J.↗
NASA NTRS2005

Ring resonator based narrow-linewidth semiconductor lasers

The present invention is a method and apparatus for using ring resonators to produce narrow linewidth hybrid semiconductor lasers. According to one embodiment of the present invention, the narrow linewidths are produced by combining the semiconductor gain chip with a narrow pass band external feedback element. The semi conductor laser is produced using a ring resonator which, combined with a Bragg grating, acts as the external feedback element. According to another embodiment of the present invention, the proposed integrated optics ring resonator is based on plasma enhanced chemical vapor deposition (PECVD) SiO.sub.2 /SiON/SiO.sub.2 waveguide technology.

Ksendzov, Alexander↗
NASA NTRS2000

Plasma Heating and Ultrafast Semiconductor Laser Modulation Through a Terahertz Heating Field

Electron-hole plasma heating and ultrafast modulation in a semiconductor laser under a terahertz electrical field are investigated using a set of hydrodynamic equations derived from the semiconductor Bloch equations. The self-consistent treatment of lasing and heating processes leads to the prediction of a strong saturation and degradation of modulation depth even at moderate terahertz field intensity. This saturation places a severe limit to bandwidth achievable with such scheme in ultrafast modulation. Strategies for increasing modulation depth are discussed.

Li, Jian-Zhong↗
NASA NTRS1982

Phase control and beam steering of semiconductor laser arrays

The operational principles and a possible device configuration of one dimensional monolithically integrated semiconductor laser arrays are described. The output beam of the array can be electronically steered. Devices of the type can find applications in optical communication systems where the power levels needed are above the capability of a single laser device.

Katz, J.↗
NASA NTRS1985

Gain saturation effects in supermodes of phase-locked semiconductor laser arrays

A basic modal analysis that includes gain saturation effects in phase-locked semiconductor laser arrays is presented. For a particular supermode operation, different lasers in the array emit different amounts of light, and hence their (waveguide) propagation constants are modified differently. Solving the lasers' rate equations self-consistently with the coupled-mode wave equations seems to provide an answer that is in much better agreement with experimental results than the result using only the coupled-mode analysis.

Katz, J.↗
NASA NTRS1979

Optical feedback effects on the performance of Pb/1-x/Sn/x/Se semiconductor lasers

The effects of optical feedback on the performance of Pb(1-x)Sn(x)Se semiconductor lasers are reported. Experimental results are presented to demonstrate that uncontrolled optical feedback can occur from optics external to the laser cavity and that these external optical elements can result in the formation of a composite cavity. This composite cavity can sustain a number of narrow closely spaced emission modes with the spectral characteristics of these modes dependent upon the parameters of the cavity. With weak feedback, the spectral width of the amplitude envelope of the new lasing modes resembles that of the original laser mode with no optical feedback. With strongly coupled feedback the envelope of the external cavity modes substantially broadens the apparent linewidth of the laser. It is shown that these effects can be eliminated, and, moreover, they offer the potential for obtaining spectrally narrow single-mode emission from Pb-salt lasers through the use of carefully designed external cavities.

Harward, C. N.↗
NASA NTRS1981

Theory of active mode locking of a semiconductor laser in an external cavity

An analytical treatment is given for the active mode locking of a semiconductor laser in an external resonator. The width of the mode-locked pulses is obtained as a function of the laser and cavity parameters and the amount of frequency detuning. The effects of self-modulation and saturation are included in the treatment. The pulse output is compared with that obtained by a strong modulation of the laser diode with no external cavity.

Yeung, J. A.↗