C. A. Zmudzinski

Anomalous temperature dependence of threshold for thin quantum well AlGaAs diode lasers

Thermally induced threshold wavelength shifts of 50 nm have been observed in short cavity length diode lasers fabricated from thin quantum well AlGaAs. Analysis suggests that the high‐energy radiation is generated by transitions between the n=2 level in the conduction band and the n=2 heavy hole level in the valence band. The threshold characteristic temperature (T0) of the laser material is found to be a strong function of cavity length.

Coherent 1 W continuous wave operation of large-aperture resonant arrays of antiguided diode lasers

Near‐diffraction‐limited cw operation at 1 W power level is demonstrated, for the first time, from all‐monolithic, phase‐locked diode‐laser arrays. In pulsed operation purely diffraction‐limited beams (0.4° lobewidth) are obtained from relatively large‐aperture (120 μm) devices to power levels of 1 W, with 70%–75% of the energy in the central lobe at low drives. These record‐high coherent powers are achieved from 20‐element resonant‐optical‐waveguide arrays of antiguided diode lasers by significantly increasing the aperture width while maintaining strong discrimination against high‐order array modes via Talbot‐type spatial filters.

Resonant self‐aligned‐stripe antiguided diode laser array

Resonant‐optical‐waveguide (ROW) arrays with a self‐aligned‐stripe (SAS) geometry have been realized for the first time. Resonance is achieved by holding the array element/interelement widths constant and varying the aluminum composition of the passive guide layer. External differential quantum efficiencies as high as 47% have been achieved from longitudinally uniform 20‐element 1000 μm‐long devices. Diffraction‐limited‐beam operation is obtained up to 13×threshold, and 2.1 W output power level from devices with Talbot‐type spatial filters. The front‐facet emitted coherent uniphase power is 1.6 W, with 1.15 W in the central lobe.

Antiresonant reflecting optical waveguide‐type, single‐mode diode lasers

Antiresonant reflecting optical waveguide (ARROW)‐type diode lasers have been demonstrated for the first time. The ARROW structure is made in the lateral direction (i.e., the plane of the junction) by two‐step metalorganic chemical vapor deposition. Stable, diffraction‐limited beam operation is achieved to 0.6 W peak pulsed power and 20× threshold. The power contained within the diffraction‐limited beam pattern is 420 mW with 60% of the energy residing in the central, diffraction‐limited lobe. Modal calculations for ARROW lasers confirm very strong intermodal discrimination. Theoretical calculations and preliminary experimental data show that up to 90% of the energy can be obtained in the central lobe (475 mW diffraction‐limited power).

Simple description of laterally resonant, distributed‐feedback‐like modes of arrays of antiguides

The Bloch‐function method is used to provide a simple, yet accurate treatment of the leaky modes of infinite‐extent antiguided arrays. Laterally resonant modes of infinite arrays are described for the first time. Bloch‐function solutions for infinite arrays are used to explain key characteristics of the modes of finite‐extent antiguided arrays. It is found that the resonant modes of antiguided arrays satisfy the second‐order lateral Bragg condition, and consequently are analogous to the modes of second‐order distributed‐feedback (DFB) lasers. In effect, the resonant‐optical‐waveguide (ROW) array is a second‐order lateral DFB structure with the radiative component along the longitudinal device axis, and zero stopband.

High‐power phase‐locked InGaAs strained‐layer quantum well heterostructure periodic laser array

Data are presented on high‐power strained‐layer InGaAs quantum well heterostructure laser arrays. These devices are periodic nonplanar arrays, formed by a single metalorganic chemical vapor deposition growth over a selectively etched corrugated GaAs substrate. The corrugation serves to provide both stripe definition and index guiding while suppressing lateral lasing perpendicular to the stripes. Maximum pulsed optical powers of 2.5 W/facet (width=1600 μm, length=440 μm) for an emission wavelength of 1.03 μm have been obtained from uncoated devices having threshold current densities in the range 290–600 A/cm2. Far‐field radiation patterns indicate that the arrays are phase locked.

Optimization and characterization of index-guided visible AlGaAs/GaAs graded barrier quantum well laser diodes

Index-guided, single and multiple stripe, visible laser diodes ( \lambda = 6950-7150 A) have been fabricated and characterized. These structures utilize a graded barrier quantum well laser structure having high aluminum composition ( x = 0.60-0.85 ) confining layers to obtain low threshold current. The use of thin AlAs quantum well barrier layers allows short wavelengths to be obtained from the quantum size effect in binary GaAs wells without the need for alloy Al x Ga 1-x As wells. Index-guiding is accomplished by use of either a complementary self-aligned structure or a shallow mesa laser structure allowing stabilized single-mode laser operation.

Phase-locked arrays of antiguides: analytical theory II

By employing a variational technique on the eigenvalue equation for finite arrays of antiguides we obtain accurate analytical expressions for key parameters characterizing the resonant array modes: the radiation loss at resonance, /spl alpha//sub RR/, and the propagation constant at resonance. The previously empirical finding that /spl alpha//sub RR/ is equal to the radiation loss of a single antiguide divided by the number of array elements is found to be a good approximation only for large element/interelement width ratios (/spl ges/3) and for, high-index-step (/spl Delta/n/spl ges/0.05) devices. By using an expansion, the radiation loss versus index-step curve is well approximated near resonance by a parabola, which gives curve halfwidths at half intensity only 10 to 15% less than numerically calculated values. An extremely accurate approximation formula is obtained for the resonant-mode propagation constant over large ranges in index-step variation around the resonance point. The obtained formulae are discussed in light of device design. >

Above‐threshold behavior of high‐power, single‐mode antiresonant reflecting optical waveguide diode lasers

Above‐threshold analysis of antiresonant reflecting optical waveguide (ARROW) diode lasers has been performed. One key finding is that preferential pumping of the (central) low‐index core region dramatically enhances the device single‐mode power capability, as a result of defocusing and subsequent radiation‐loss increase for the first‐order spatial mode. Stable, single‐mode operation to drive levels ≳10× threshold is predicted for 6‐μm wide core devices, in excellent agreement with experiment. Similar performance is found to hold true for ARROW devices with cores as wide as 10 μm, although due to gain spatial hole burning, the far‐field beam pattern experiences mild broadening. Study of triple‐core ARROW structures of 20‐μm‐wide aperture shows stable fundamental‐mode operation to ≳10× threshold, thus raising the prospect for stable, single‐mode reliable operation to power levels as high as 1 W cw.

Temperature‐dependent factors contributing to T0 in graded‐index separate‐confinement‐heterostructure single quantum well lasers

The temperature dependence of threshold current in graded‐index, separate‐confinement‐heterostructure, single quantum well lasers has been investigated and analyzed. The conventional parameter used to describe this temperature dependence, T0, is measured and shown to increase with cavity length. The temperature dependences of the loss coefficient α and the differential gain β have also been measured. Both parameters decrease linearly with temperature in the range 20–70 °C. Competition between α(T) and β(T) is shown to account for the dependence of T0 on cavity length and to suggest guidelines for designing high T0 lasers.