Semiconductor Laser Arrays Research Articles

A high-voltage optoelectronic GaAs static induction transistor

Experimental realization of an optically activated, high-voltage GaAs static induction transistor (SIT) is reported. In the forward blocking state, the breakdown voltage of the device was approximately 200 V, while in the conduction state, on-state current densities exceeding 150 A/cm/sup 2/ were obtained. In the floating-gate configurations (gate open), the specific on-resistance of the device was approximately 50 m Omega -cm/sup 2/. Optical modulation of the device was achieved using a compact semiconductor laser array as the triggering source. In this mode, a gate-coupled RC network was implemented, resulting in an average switching energy gain (load energy/optical energy) of approximately 30. This mode of operation is applicable to series-coupled devices for pulsed switching at higher power levels. >

Semiconductor laser array dynamics: numerical simulations on multistripe index-guided lasers

The space–time dynamical behavior of multistripe index-guided semiconductor laser arrays is studied by using an extension of the usual phenomenological laser model to include transverse diffraction of the counterpropagating optical fields and transverse diffusion of the excited carriers. Our results confirm that evanescently coupled multistripe lasers are a fascinating manifestation of spatiotemporal complexity in spatially extended nonlinear systems. Stabilization of the laser output can be achieved by injection locking the array with a weak external injected signal, and we show that the stability of the externally driven array depends on the transverse profile of the injected signal. A numerical algorithm is presented that takes advantage of high-performance parallel computing architectures to solve the coupled partial differential equations describing the light–matter interaction in the laser structure. Both the model and the numerical algorithm are sufficiently flexible and modular to support arbitrary laser geometries and to allow for inclusion of important many-body semiconductor effects in future studies.

Improved coupled-mode theory for the dynamics of semiconductor laser arrays

We present an improved coupled-mode model to describe the dynamics of weakly index-guided semiconductor laser arrays. The model is derived from a partial differential equation model that includes the effects of carrier diffusion and gain guiding. Results from the two models are compared, and good qualitative and quantitative agreement is obtained.

Propagation model for the dynamics of gain-guided semiconductor laser arrays

A model is presented for the spatiotemporal dynamics of gain-guided semiconductor laser arrays. The model goes beyond coupled mode theory and treats the array as a single entity. Numerical simulations of twin-stripe gain-guided arrays yield stable or pulsing outputs, depending on array parameters.

The effect of nonlinear gain on the stability of evanescently coupled semiconductor laser arrays

We show that nonlinear gain saturation can enhance the stability of evanescently coupled semiconductor laser arrays.

Surface-emitting semiconductor lasers and laser arrays

Various types of surface-emitting semiconductor lasers are reviewed along with their anticipated applications. The recent progress in grating-coupled surface-emitting (GSE) lasers is particularly emphasized. SuchGSE arrays have operated continuously to more than 3 W and pulsed to more than 30 W. They have obtainedCW threshold current densities of under 140 A/cm2 withCW differential quantum efficiencies of 20 to 40% per surface. Linewidths in the 40 MHz range have been obtained with output powers of 100 to 250 mW. The arrays typically consist of 10–30 mutually injection-coupled gain sections with 10 laterally coupled ridge-guided lasers in each gain section. A single GaInAs strained-layer quantum well with a graded index separate confinement heterostructure geometry allows junction down mounting with light emission through the transparent GaAs substrate. A surface relief grating is used for feedback and outcoupling.

Laterally coupled periodic semiconductor laser structures: Bloch function analysis

The Bloch function analysis is applied to the problem of periodical phase-locked semiconductor laser array structures. This method makes it possible to treat in the same manner both evanescent and leaky modes of such structures and to optimize these structures in order to get maximum content in the central lobe of emission far-field pattern. If one places high gain in the low-index array regions, the preferred array modes are leaky modes coupled either in-phase or out-of-phase depending on parameters of structure. The linear and nonlinear problems of the propagation of finite aperture beams in such laser structures are considered. Propagation of such a beam is described by the Schrodinger equation with 'photon mass' determined by a curvature of photon dispersion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

MATERIALS FOR DIODE PUMPED SOLID STATE LASERS

The advantages of semiconductor diode lasers and laser arrays as pump sources for solid state lasers are reviewed. The properties desired for solid state laser media for various diode pumping applications are discussed, and the characteristics of several promising media are summarized. 13 refs., 4 tabs.

Relative intensity noise of laser-diode arrays

Relative intensity noise in GaAs-GaAlAs semiconductor laser arrays was measured, compared with that in single-stripe lasers, and reviewed in the context of laser noise theory. When all the light is gathered and back reflections removed, all the arrays tested show comparable noise levels. Good agreement between theory and experiment is obtained for low drive currents where mode competition noise is relatively small. For low drive currents the noise is limited by the quantum noise, whereas for higher currents the noise saturates at about -145 dB/Hz under the best conditions, 10 dB below the level for a comparable single-stripe laser but 10 dB worse than for a single-mode distributed-feedback laser. The low noise in the array is explained quantitatively by considering the multiple transverse modes and the longer cavity length of the array.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Coupled broad-area mode theory of gain-guided laser arrays

Multiple-stripe semiconductor laser arrays are analyzed using a broad-area mode coupling approach. Rather than considering coupling between individual waveguide modes as in the conventional supermode theory, a basis of broad-area modes is chosen. These modes are coupled through a perturbation of refractive index and gain profiles caused by nonuniform carrier injection, thermal effects, and/or built-in weakly guiding or antiguiding profiles. Present theory reveals that earlier simplified analysis involving broad-area mode-coupling may lead to significant errors in modal gains of high-order array modes.

Frequency control using a complex effective reflectivity in laterally coupled semiconductor laser arrays

Frequency selectivity of a novel type of multielement, multisection laterally coupled semiconductor laser array is studied using the round-trip method. It is found that such a structure should lead to a strong frequency selectivity owing to a periodic dependency of the threshold gain on the frequency. A gain-guided two-coupledcavity device was fabricated. The experimental results show excellent agreement with the theoretical prediction.

Tunable diode-laser-pumped solid state LNA laser for helium spectroscopic experiments

We have designed, built, and tested a compact, integrated, single-mode solid state LNA laser pumped by a semiconductor laser array for exciting the He resonance line at lambda = 1.083 microm. The laser's three major components are mounted on a single aluminum base, and the diode laser and its beam shaping optics are mounted on a separate stage. This compact and stable structure provides good frequency stability and nearly pure TEM(00) transverse mode operation. The laser can be tuned around the metastable He resonance transition in a single longitudinal mode with linewidth congruent with 5 MHz using a solid, 60% coated intracavity 0.25-mm thick etalon. Saturated absorption signals on this transition have been used to measure the stability and tuning range. We have measured the properties for several crystals and calculated the expected performance characteristics to compare with the measured ones.

Spatiospectral and picosecond spatiotemporal properties of a broad area operating channeled-substrate-planar laser array

Spatiospectral and spatiotemporal properties of an eight-element channeled-substrate-planar laser array are investigated in both cw and pulsed operating conditions. The closely spaced CSP array with strong optical coupling between array elements is characterized by a broad area laserlike operation determined by its spatial mode spectra. The spatiotemporal evolution of the near and far field exhibits complex dynamic behavior in the picosecond to nanosecond domain. Operating parameters for the laser device have been experimentally determined. These results provide important information for the evaluation of the dynamic behavior of coherent semiconductor laser arrays.

High-power, cw, diffraction-limited, GaAlAs laser diode array in an external Talbot cavity

A 20-element linear array of single transverse mode semiconductor lasers is operated in an external Talbot cavity. A total cw output power of 250 mW in a diffraction-limited far field and 29% differential efficiency is obtained with a 50% output coupler. By decreasing the output mirror reflectivity to 20%, 900 mW cw in a 1.7 times diffraction-limited radiation pattern with an increased differential efficiency of 38% is obtained. The low fill factor of the array (1:12) acts as a spatial mode-selective filter resulting in strong mode discrimination.

Finite element analysis of semiconductor laser arrays

This article presents the analysis of semiconductor laser arrays based on the finite element method, with emphasis on nonuniform structures where the channel width and/or refractive index can vary across the array. The results show that the variation of channel width will have the same effect on the near-field intensity profile as the variation of channel refractive index. Based on this finding, a laser array structure devised to achieve a highly desirable uniform intensity distribution for the lowest-order mode is also presented. 8 refs.

Coherent beams from high efficiency two-dimensional surface-emitting semiconductor laser arrays

We have fabricated and operated large two-dimensional (2D) arrays of phase-locked surface-emitting semiconductor lasers. The arrays were fabricated by reactive ion beam etching of epitaxial Fabry–Perot resonators comprising GaAs/AlGaAs quantum wells surrounded by AlAs-AlGaAs quarter-wave mirrors. Different arrays corresponding to different pixel size (2–5 μm) and spacing (1–2 μm) were produced to investigate evanescent coupling between pixels. The arrays were photopumped so that the array size could be conveniently varied from 1×1, 2×2,... up to 20×20. Except for the 1×1 which emits a circular pattern, all arrays exhibit a well-defined four-lobed far-field pattern in agreement with our theoretical analysis of the optical modes which predicts domination by the 2D out-of-phase eigenmode. As a consequence this pattern can be understood with simple Fraunhofer diffraction theory. The angular spread of the lobes, determined by the periodicity of the array elements, is 10° for the array with element size/spacing of 4/1 μm. The widths of the lobes are 6.7° for the 2×2 and narrow to 3.2° with increasing number of pixels in the array. The array exhibits a sharp onset for lasing, operation on a single longitudinal mode, and a linewidth which narrows to ∼1 Å with increasing array size. The differential power efficiency is as high as 70%. These observations provide further impetus and guidance for the development of 2D laser diode arrays.

Two-dimensional phase-locked arrays of vertical-cavity semiconductor lasers by mirror reflectivity modulation

Coupling of two-dimensional (2D) vertical-cavity surface-emitting lasers (VCSELs) to give a coherent supermode is described. The top metal layer of a stained-layer InGaAs quantum well VCSEL structure was patterned laterally by depositing various metals with different optical reflectivities. This lateral reflectivity patterning defined a 2D laser array sharing the same ‘‘supercavity’’. It is shown that these 2D arrays oscillate in a stable single, coherent 2D supermode. This was achieved with a simple planar process and without significant deterioration of threshold current and efficiency relative to an equivalent broad-area VCSEL.

Tuneable multiwavelength semiconductor laser with single fibre output

A new multiwavelength semiconductor laser with singlemode fibre output is reported. The laser consists of a semiconductor laser array which is incorporated into an external cavity comprising a diffraction grating and a fibre loop mirror. This laser has five wavelength-locked output channels with a fixed separation of 2.5 nm. The centre wavelength may be tuned over 80 nm.

Uniform high power nine and 18 element individually addressable laser diode arrays

Results from the CW operation of uniform high power nine and 18 element addressable semiconductor laser arrays, that are applicable to parallel data processing in optical storage, communication, and imaging systems, are presented. A nine element array on 150 μm centres capable of emitting greater than 150 mW/element and 1.15 W of total power at λ ≃ 854.4 nm is demonstrated. In addition, power exceeding 80 mW/element and 1 W total power is obtained from an 18 element array on 50 μm centres. Variations in operating current and wavelength are limited on ≤5% for the nine element array and ≤9% for the 18 element array.

Coupling-loss-arrested misaligned semiconductor laser arrays

Coupling-loss-arrested misaligned semiconductor laser arrays are designed and fabricated by liquid-phase epitaxy. In these devices, the losses in the normal misaligned arrays is collected by a gain-induced positive waveguide, and then the collected light couples with light in the adjacent waveguides evanescently, therefore avoiding the coupling loss and strengthening the coupling. The constructed co-cavity element should have better characteristics with respect to transverse-mode selection. A clean single-lobe far field as narrow as 3° and a relatively low threshold of 130 mA for a seven-element array are obtained.