Semiconductor Laser Structures Research Articles

Analysis of laser-structure anisotropic semiconductors by the Bloch-function method

The method of Bloch functions is used to obtain the radiation makeup of a semiconductor laser structure consisting of periodically alternating waveguide and antiguide regions, and the differntial gains for the different modes are determined. Pumping of antiguide regions with different structure parameters makes it possible to obtain the maximum gains of a Bloch mode made up of “outflowing” waveguide modes at the center of the brillouin lobe. The directivity pattern contains in this case sideband satellites in addition to the central lobe. When the structure is optimized, the intensity of the central lobe amounts to 70% of the total emission intensity.

Resonant periodic gain surface-emitting semiconductor lasers

A surface-emitting semiconductor laser structure with a vertical cavity, extremely short gain medium length, and enhanced gain at a specific design wavelength is described. The active region consists of a series of quantum wells spaced at one half the wavelength of a particular optical transition in the quantum wells. This special periodicity allows the antinodes of the standing-wave optical field to coincide with the gain elements, enhancing the frequency selectivity, increasing the gain in the vertical direction by a factor of two compared to a uniform medium or a nonresonant multiple quantum well, and substantially reducing amplified spontaneous emission. Optically pumped lasing was achieved in a GaAs/AlGaAs structure grown by molecular-beam epitaxy, with what is believed to be the shortest gain medium (310 nm) ever reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Model calculations of diffusion limited trapping dynamics in quantum well laser structures

We present a phenomenological theoretical model to treat the trapping of carriers into quantum wells of semiconductor laser structures. We consider explicitely the transport within the barrier layers by solving the continuity equation with the appropriate boundary conditions taking into account surface recombination, radiative and nonradiative recombination in the barrier layers and trapping of carriers into the quantum wells. The experimental findings for the trapping dynamics in GaAs/AlGaAs quantum well structures can be consistently interpreted by the model calculations.

Patterned quantum well semiconductor injection laser grown by molecular beam epitaxy

A novel quantum well semiconductor laser structure is described. This patterned quantum well laser utilizes the thickness variations and nonplanarity exhibited by quantum wells grown on grooved substrates in order to achieve lateral carrier confinement and real index waveguiding. Index guided GaAs/AlGaAs patterned quantum well lasers with ∼1-μm-wide active layer stripes and threshold currents as low as 6 mA have been grown by molecular beam epitaxy. This patterned quantum well laser configuration is particularly attractive for fabricating quantum wire and quantum box semiconductor injection lasers.

Two numerical techniques of the analysis of complex dielectric waveguides

The scalar wave equation with a complex dielectric constant describes the propagation of light in a waveguide having parallel stratification with gain or loss. Unlike their passive and lossless counterparts, complex dielectric waveguides no longer have the self-adjoint (Hermitian) form when described by the wave equation. The lack of the self-adjoint property makes the standard methods for analysis of the wave equation inapplicable. This paper describes two numerical methods for solving the wave equation. The first technique described performs an integration in the direction of propagation by the beam propagation method (BPM) with adaptive step-size control. The second technique is an eigenmode analysis using a finite-difference formulation of the wave equation with the inverse power method used to determine the eigenmodes of interest. As examples of the techniques' applications to semiconductor laser structures are developed.

Analysis of mode separation in multichannel branching waveguides

Spatial separation of modes is important in multiport switching and wavelength multiplexing for integrated optics, and in controlling the spatial modes in multimode semiconductor laser structures. It has been recently shown that the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> normal modes of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> - mode channel waveguide can be separated by branching into <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> single-mode channels whose propagation constants are all different. By means of examples, we answer two questions about this mode separation scheme. 1) How widely separated must the channels be in order for each mode to be concentrated in a different one of the channels? 2) How small must the branching angle be in order for the power to remain in the launched mode? The effects of wavelength, dimensions, and refractive index step are discussed. Important conclusions are that the branching angle must be rather small, of the order of a few milliradians, and that it is helpful to have the largest possible difference in the widths of the guiding channels, thereby giving them the largest possible difference in uncoupled propagation constants.

Semiconductor lasers: A choice structure for lightwave communications

The advantages that the semiconductor laser offers over gas or solid-state lasers are presented, and the multilayer structure of semiconductor lasers is described. Attention is also given to some of the new growth techniques that are now being used. The author then describes how semiconductor lasers are being used in lightwave communications technology. The description covers propagating modes and photodetectors.

Model for semiconductor laser structures incorporating longitudinal and transverse variations

A description is given of a computer model for the analysis of semiconductor lasers in which longitudinal variations in such devices are taken into account. The construction of the model ensures that a detailed description of the transverse variations in the device is also maintained, and, furthermore, that a variety of cross-sectional geometries may be examined. Numerical results are presented to illustrate longitudinal variations occurring in the device due to asymmetries in facet reflectivities.

The effective index method and its application to semiconductor lasers

By the effective index method a two-dimensional field problem is transformed to a problem for a one-dimensional effective waveguide. This method is applied to semiconductor lasers having a gradual lateral variation in the complex permittivity. For the special case of a parabolic variation, analytical formulas for the required gain in the center and the half width of the intensity distribution are derived. The results are compared with a numerical method and very good agreement is found except in some cases where convergence problems occur for the numerical method. This agreement is taken as evidence for the validity of results obtained using the effective index method for analysis of semiconductor laser structures.

Semiconductor Laser Diodes: A User's Handbook

M E Fabian 1981 Ayr: Electrochemical Publications viii + 136 pp price £24 Of all the applications of semiconductor laser diodes, their use in the context of optical fibre systems is currently one of the most challenging and rapidly developing. For this reason the author, after outlining the fabrication, structure and operation of semiconductor lasers, goes on later in the book to devote a chapter to this particular topic.

Beamwidth for asymmetric and multilayer semiconductor laser structures

An expression for the far field of the fundamental TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> mode in an asymmetrical dielectric slab waveguide is derived. By using normalized waveguide parameters, universal plots of the beamwidth are presented. These plots include the obliquity factor correction. Experimental results for symmetrical GaInAsP lasers at wavelengths near 1.3 μm are compared with theoretical predictions by Buus and Adams. Calculated results for the 1.55 μm wavelength are presented. A numerical method for the calculation of the far field for structures where four or more layers must be included is outlined.

Evaluation of dielectric optical waveguides from their far-field radiation patterns

An experimental technique for determining the characteristics of dielectric optical waveguides is presented. The far-field pattern of a passive waveguide excited by an external source is measured and compared with a theoretical pattern. The presence of spurious light in the fax field complicates the measurement, but this difficulty can be minimized for many structures. Application to semiconductor laser structures is discussed. Determining the waveguiding properties of laser structures prior to processing can result in the early detection of faults for increased yield.

TJS Semiconductor Lasers

A new structure of semiconductor laser which is designated as the transverse-junction-stripe (TJS) laser has been developed. In TJS laser, a very thin GaAs homojunction laser is sandwiched by GaAIAs layers. The minimum threshold current is 36mA at room temperature for continuous operation. The TJS laser shows the fundamental transverse mode up to three times of the threshold current and nearly single longitudinal mode.

Transverse-junction-stripe lasers with a GaAs p-n homojunction

A new semiconductor laser structure named the transverse-junction-stripe (TJS) laser, in which the active region is a GaAs p-n homojunction sandwiched between GaAlAs layers, has been developed. It is possible to operate the laser continuously at room temperature below 100 mA. The minimum threshold current is 34 and 50 mA in pulsed and continuous operation, respectively. Relatively high efficiencies have been obtained, comparable to those of conventional double-heterostructure (DH) lasers. The transverse mode is fundamental in both directions and is almost independent of input current up to three times the threshold current. The longitudinal mode stays nearly single over a wide range of input current. The TE/TM power ratio exceeds 100 at 1.5 times the threshold current.