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V-grooved quantum wire (QWR) lasers were studied by near-field optical microscopy with 0.1 /spl mu/m spatial resolution. We mapped the electroluminescence from the quantum structures and measured the lasing mode evolution. Localized photocurrent measurements show spectral features consistent with the QWR lateral confinement.

Operation of a new triple fused long wavelength VCSEL structure is demonstrated for the first time. In this structure both highly resistive p-AlGaAs/GaAs DBR and strained p-GaAs/p-InP fused junction are replaced with a composite mirror comprising a p-InGaAsP/InP partial DBR fused to an undoped AlGaAs/GaAs DBR and an isoperiodic, low barrier p-InP/p-InGaAsP fused junction.

Quantum wire (QWR) semiconductor lasers, grown by organometallic chemical vapor deposition OMCVD) on nonplanar substrates, exhibit two dimensional (2D) quantum confinement and sub-mA threshold currents. The in situ formation of the wires in these lasers eliminates excessive nonradiative recombination at their interfaces, which is essential for the efficient operation of these devices. One of the expected advantages of QWR heterostructures is the enhanced optical gain and absorption resulting from the increased density of states at the quasi-1D subbands. This feature would make QWR heterostructures useful for applications in low power consumption integrated optoelectronics. Here, we report the first measured gain and absorption spectra of QWR lasers. The multi-QWR lasers discussed here were grown by OMCVD on V- grooved substrates. Their active regions consist of 4 crescent-shaped GaAs wires, placed at the center of a 2D, graded index AlGaAs optical waveguide. A band structure model of these wires yields electron-heavy hole QWR subband transitions separated by 19meV, with an effective wire width of 15nm for the ground electron state, The subband structure was evident in the amplified spontaneous emission and lasing spectra of the devices, with observed transition energies in good agreement with the calculated values.

1.52 µm double fused InGaAsP/AlGaAs vertical cavity surface emitting lasers with in-situ built-in lateral current confinement were fabricated using localised wafer fusion process. These devices operate at room temperature in quasi-CW regime at 10% duty cycle. Operation characteristics of these lasers are limited by the high resistivity of p-InP/p-GaAs fused junctions which is a result of using carbon-doped p-AlGaAs/GaAs distributed Bragg-mirrors.

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 waveguiding 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.

The supermode structure of index-guided, phase-locked arrays of diode lasers with nonuniform laser spacing is investigated theoretically. It is shown that in a variable spacing array, the super-mode field patterns can be significantly different from those of a uniform array. However, in a variable-spacing array with N elements, supermodes ν and N + 1 - \nu(\nu = 1, 2, ..., N) have similar near-field intensity patterns and modal gains, as in the case of uniform arrays. As a result, the discrimination between the fundamental (0° phase shift) and the highest order (180° phase shift) supermodes is small and depends sensitively on the amount of gain in the interchannel regions, as for uniform arrays. This may explain the inefficient supermode discrimination and the wide beams exhibited by variable-spacing diode laser arrays, in contrast to the strong discrimination and the narrow beams obtained with chirped (variable channel width) arrays structures.

Perturbation theory is used in order to calculate the effective-index distribution in dielectric waveguides that exhibit slow lateral variations. As an example, the method is employed to find the optical modes in diode lasers with lateral spatial variations in thickness. Very good agreement with experiment is obtained for the case of GaAlAs double heterostructure lasers with a crescent-shaped waveguide.

We have studied the OMCVD growth of GaAs/AlGaAs quantum well heterostructures on non-planar substrates in the temperature range of 625 to 750°C. The lateral variation in layer thickness and other growth features were found to depend not only on the growth temperature but also on the aluminum content of the layer. An example of the application of this technique of producing lateral thickness variations in quantum well heterostructures to a quantum well semiconductor laser is given. A unique feature of this laser is the formation of a quantum-wire-like crescent shaped active region at the center of a two-dimensional optical waveguide.

Distributed Bragg-reflector (DBR) diode lasers were designed and fabricated from lattice-matched Pb 1-x Sn x Te/PbSe y Te 1-y single heterostructures grown by liquid-phase epitaxy. These DBR lasers operated in a single longitudinal mode within a limited range of heat-sink temperatures, 8.5-38 K, with a threshold current density of ∼3 kA/cm2at 20 K. Single longitudinal mode operation was maintained up to more than three times the threshold current. Continuous tuning of the laser output frequency over a range of ∼6 cm-1, near 775 cm-1(12.9 μm), was acheived by varying the heat-sink temperature. The average tuning rate was 0.21 cm-1/K, and it was much smaller than the rate for corresponding Fabry-Perot lasers, which was 2.3 cm-1/K. The measured effective mode index of the DBR lasers agrees well with the calculated one.

The effect of complex coupling coefficients on the performance of distributed feedback (DFB) lasers is studied. The physical origins of a complex coupling coefficient are specified, and its relation with gain or loss mechanisms which occur inside the laser is discussed. Numerical results are presented for the oscillation frequencies, threshold gains, and intensity patterns of the longitudinal modes of the DFB laser.

We demonstrate a single contact tailored gain-guided array in which the gain profile across the array is made strongly asymmetric by varying the width of the contact stripes. A proton isolated array of six (GaAl)As lasers with 5-µm separations and widths varying linearly between 3 and 8 µm had a single lobed far field 2° wide, close to the diffraction limit for a single supermode. Fabrication of this device is simple, and suited to large-scale processing techniques. We also show that in such an asymmetric gain-guided array the fundamental mode is favored over higher order modes, and that higher order modes can have single lobed far-field patterns differing only slightly from that of the fundamental.

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-µm-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.

Inverted‐V chirped arrays of multiple quantum well GaAs/GaAlAs lasers were grown by molecular beam epitaxy. These arrays consisted of seven gain‐guided lasers whose stripe widths decreased, from the central laser to the outermost ones, symmetrically. This structure makes it possible to discriminate against the higher order array supermodes, which results in diffraction limited beams with a single lobe directed perpendicular to the laser facet. Single lobed far‐field patterns, 3°–4° wide, were obtained from inverted‐V chirped arrays operated up to 1.5Ith. The supermode structure of these arrays was identified by studying their spectrally resolved near fields.

A new type of buried heterostructure InGaAsP/InP lasers grown by a single-step liquid phase epitaxy on Cd diffused mesa substrate is described. These lasers exhibit excellent current and optical confinement. Threshold currents as low as 15 mA are achieved for a laser with a 2-µm-wide active region.

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 ~50 Å, with tuning rate of ~5 Å/mA, 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.

The spatial mode characteristics of gain‐guided broad‐area quantum well lasers grown by organometallic chemical vapor deposition were investigated experimentally. GaAs/AlGaAs quantum well lasers grown on 6°‐off (100) oriented substrates exhibit excellent material uniformity, which allows study of their modal behavior. Gain‐guided broad‐area lasers fabricated on such uniform material demonstrate nearly ideal gain‐guiding modal behavior. These lasers tend to lase in the fundamental mode near threshold and emit single‐lobed far‐field patterns. In these well‐behaved broad‐area lasers, we have identified the mechanism for degradation in the spatial coherence at high pumping levels as the onset of higher order lateral modes.

Phase‐locked arrays of buried‐ridge InP/InGaAsP lasers, emitting at 1.3 μm, were grown by liquid phase epitaxy. The arrays consist of index‐guided, buried‐ridge lasers which are coupled via their evanescent optical fields. This index‐guided structure makes it possible to avoid the occurrence of lower gain in the interchannel regions. As a result, the buried‐ridge arrays oscillate mainly in the fundamental supermode, which yields single lobed, narrow far‐field patterns. Single lobed beams less than 4° in width were obtained from buried‐ridge InP/InGaAsP phased arrays up to more than twice the threshold current.

It is shown that a gain-guided laser array couples via propagating fields rather than the evanescent mode coupling typically responsible for directional coupling in passive (directional couplers) and active (laser array) devices. We show that these phase-locked modes exhibit an interference pattern, in the junction plane, which arises from the curvature of the phase fronts of optical fields of the interacting lasers. The experimental results are interpreted with the aid of a simple theoretical model, and the effect of the observed mode pattern on the coupling of gain-guided lasers is discussed.

Coherent combination of the power of several semiconductor lasers fabricated on the same substrate has been the subject of an intense research effort in recent years, the main motivation being to obtain higher power levels than those available from a single laser in a stable radiation pattern. Best results reported so far include 2.6 watts CW emitted power and less than 1 deg far-field angle (in the array plane) in arrays where all the lasers are electrically connected in parallel. A different type of coherent array, where each element has a separate contact, has been recently demonstrated. While requiring the more complex two-level metallization technology, applying a separate contact to each laser provides an additional degree of freedom in the design and the operation of monolithic arrays. The separate contacts can be employed to tailor the near-field and far-field distributions and to compensate for device-to-device nonuniformities. Furthermore, the control of the currents of the array elements allows the performance of a variety of other functions, such as beam scanning, spectral mode control, wavelength tuning and control of the mutual coherence between array elements.

Infrared transmitting silver halide fibers 0.3 - 1 mm diameter were fabricated by extrusion, and were found to have losses of about 6 dB/m, at λ = 10.6 µm. Infrared heterodyne experiments have been carried out using these fibers. Two stabilized CO2 lasers, of frequencies ωl and ω2, were used. The two laser beams were coupled into a single infrared fiber, using a Y coupler, with no other optics. Both beams were transmitted through this fiber to a fast IR detector. A heterodyne signal at a beat frequency ω1 - ω2 was obtained from the detector.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The operation of a new type of tunable laser, where the two separately controlled individual lasers are placed vertically in parallel, has been demonstrated. One of the cavities (‘‘control’’ cavity) is operated below threshold and assists the longitudinal mode selection and tuning of the other laser. With a minor modification, the same device can operate as an independent two‐wavelength laser source.

Uniform semiconductor laser arrays tend to oscillate in a superposition of their supermodes, thus leading to large beam divergence and spectral spread. Discrimination among the supermodes in phase-locked arrays is discussed theoretically. It is shown that supermode discrimination in gain-guided arrays, in favor of the fundamental supermode, is made possible by the near-field interference patterns which result from the complex optical fields of the gain-guided lasers. A fundamental supermode operation is demonstrated, for the first time, in GaAlAs/GaAs gain-guided laser arrays. This is achieved by control of the current (gain) profile across the array by means of individual laser contacts.

The phase‐locking characteristics of two coupled, ridge waveguide InP/InGaAsP diode lasers emitting at 1.2 μm were investigated experimentally. The phase locking of the lasers was verified by the observation of phase‐locked modes (supermodes) in the spectrally resolved near fields and distinct diffraction patterns in the far field. By independent control of the laser currents it was possible to vary continuously the mutual phase shift between the two phase‐locked lasers and thus steer the far‐field diffraction lobes. In addition, the separate current control could be utilized to obtain single longitudinal mode oscillation of the phase‐locked lasers. Variation in one of the laser currents resulted then in tuning of the wavelength of this single mode over a range of 90 A.

Distributed Bragg-reflector (DBR) diode lasers were fabricated from lattice-matched Pb0.817Sn0.183 Te/PbSe0.08Te0.92 wafers grown by liquid phase epitaxy. The DBR lasers operated within a limited range of heat-sink temperatures, 8.5°-38°K, with threshold current density of 3kA/cm2 at 20°K. Single longitudinal-mode operation was obtained up to more than three times the threshold current. The DBR lasers exhibited continuous tuning range of 6 cm-1 near 775 cm-1 (12.9 μm). The average tuning rate was 0.21 cm-1/°K and was much smal-ler than that of the corresponding Fabry-Perot lasers, which was 2.3 cm-1/°K.

Lateral patterning of the bandgap in semiconductor quantum well (QW) lasers is essential for achieving lateral carrier confinement and for integrating diode lasers with other optoelectronic components having a different bandgap. In particular, lateral carrier confinement into extremely narrow (µm) dimensions is required for the realization of low-dimensional quantum wire and quantum dot lasers. We have developed a new technique for lateral patterning of semiconductor QW lasers.1 The technique consists of growing otherwise conventional QW laser structures on patterned, nonplanar substrates. The resulting patterned QW heterostructures exhibit lateral variations in the effective QW bandgap. Patterned QW lasers grown by molecular beam epitaxy2 have active region widths of ~1 µm and exhibit threshold currents as low as 0.7 mA. Patterned QW lasers grown by organometallic chemical vapor deposition have crescent-shaped quantum wire active regions µm wide. Lasing due to transitions between quasi 1-D subbands in these quantum wires has been observed.3

An eight‐element phase‐locked array of index‐guided separate confinement ridge AlGaAs diode lasers is fabricated. In this array the absorption of light in the region between lasers is negligible and the gain profile across the array is nearly uniform. Unlike most other arrays, this array oscillates in its fundamental mode. Stable radiation patterns of near diffraction‐limited single narrow beam with 1.6° width are obtained. The beam width approaches the theoretical limit for the present array structure.

Coupled-wave formalism is developed to describe the coupling between modes that are guided by gain variation and by refractive-index discontinuities in two mutually perpendicular directions. The formalism is used to analyze distributed-feedback (DFB) stripe-geometry diode lasers, which are characterized by gain-induced lateral wave-guiding. Analytical models for the gain distribution parallel to the junction plane are employed to evaluate the coupling coefficient, and results for various coupled-mode pairs and different gain profiles are presented and discussed. The effect of grating tilt is studied as well, and it is found that misaligned gratings may enhance the oscillation of DFB lasers in a single lateral mode.

The optical characteristics of phase-locked semiconductor laser arrays are formulated in terms of the array supermodes, which are the eigenmodes of the composite-array waveguide, by using coupled-mode theory. These supermodes are employed to calculate the near fields, the far fields, and the difference in the longitudinal-mode oscillation wavelengths of the array. It is shown that the broadening in the far-field beam divergence, as well as the broadening of each of the longitudinal modes that were observed in phase-locked arrays, may arise from the excitation of an increasing number of supermodes at increasing pumping levels.

Expressions are derived for the number of guided TE modes in periodic multichannel waveguides. Both symmetrical and nonsymmetrical cases are treated. Simple formulas are given for the number of modes in multiple-quantum-well lasers.

A new design of nonuniform phased arrays of diode lasers is described. In these nonuniform arrays both the channel widths and the channel spacings are properly varied across the array. This design results both in effective discrimination against the higher-order supermodes as well as in a more uniform near-field distribution. Such nonuniform arrays should therefore yield single-lobe, diffraction-limited beams up to higher output power levels.