Angled-grating Distributed Feedback Lasers Research Articles

Properties of ion-implanted high-power angled-grating distributed-feedback lasers

An improvement of the linearity of the light-current characteristics and the beam quality of high-power /spl alpha/-distributed feedback lasers is achieved by an ion implantation of the regions outside the contact stripe. The linear part of the light-current characteristics of 4-mm-long devices emitting at 1060 nm is extended to P=1.8 W output power. The times-diffraction-limit factor M/sup 2/ remains constant, equal to 1.7 over the whole power range. Simulations of the electro-optical behavior reveal that the improvement is achieved by a suppression of optical field components which propagate inside the cavity perpendicular to the facets.

Virtual mesa and spoiler midinfrared angled-grating distributed feedback lasers fabricated by ion bombardment

It is demonstrated that the suppression of parasitic Fabry–Perot-like lasing modes substantially enhances the beam quality and brightness of wide-stripe angled-grating distributed feedback lasers emitting in the midwave infrared. The direct facet-to-facet gain path is blocked by loss regions that are created by ion bombardment with 900 keV silicon ions. Both virtual mesa structures, in which loss regions bound both sides of the 300-μm-wide angled gain path, and spoiler structures, in which loss is induced only near the facets, decrease the etendue of the output by nearly an order of magnitude, and increase the brightness by up to a factor of 3.

Limitations to beam quality of mid-infrared angled-grating distributed-feedback lasers

The far-field characteristics of mid-infrared angled-grating distributed-feedback (/spl alpha/-DFB) lasers with W active regions are studied as a function of etch depth, stripe width, and optical pumping intensity. Whereas near-diffraction-limited output is obtained for 50 /spl mu/m stripes at ten times threshold, the beam quality degrades rapidly when either the stripe width or the pump intensity is increased. A key finding is that most of the degradation may be attributed to the onset of Fabry-Perot-like lasing modes that propagate along the direct path normal to the facets. We further show that these parasitic modes may be effectively eliminated by using ion-bombardment to create angled virtual mesas surrounded by loss regions. The bombarded structures show substantial improvement of the beam quality for wide pump stripes and high pump intensities, although in this first demonstration the efficiency decrease was greater than expected.

Far-field characteristics of mid-infrared angled-grating distributed feedback lasers

The far-field emission characteristics of mid-infrared angled-grating distributed-feedback (α-DFB) lasers with W active regions are calculated using a self-consistent beam-propagation formalism that is more general than previous analyses. The theoretical projections are compared with the results of an experimental study of optically pumped α-DFB devices. Near-diffraction-limited beam quality is obtained both theoretically and experimentally for pump stripes ⩽50 μm wide. While simulations employing the theoretical linewidth enhancement factor of 1.7 for the homogeneously-broadened W-laser gain spectrum predict that the good beam quality should be retained for stripes as wide as ≈200 μm, the data indicate a much more rapid degradation. That finding can be reproduced only by assuming that inhomogeneous broadening increases the structure’s linewidth enhancement factor to ≈5. The experiments and theory also yield a steering of the output beam to off-normal angles as large as 6° when temperature tuning shifts the gain peak away from the grating resonance.

Power dependence of the injection lock band of angled-grating distributed feedback lasers

Experimental measurements of the injection lock band of an angled-grating distributed feedback laser have been performed systematically as a function of the unlocked slave laser power. Fringe visibility measurements were used to ascertain the quality of the lock between the master and slave laser as a function of master coupling level and frequency detuning. Experimental data show increasing spectral instabilities under optical injection as the slave laser power is increased, resulting in the stable portion of the lock band decreasing in width.

Mid-infrared angled-grating distributed feedback laser

We report near-diffraction-limited output from an angled-grating distributed feedback type-II W laser emitting near 3.4 μm. For pulsed optical pumping of a 50-μm-wide stripe at 78 K, the far-field beam divergence angle was only 1.4°. The slope efficiency was 64% of that for a conventional Fabry–Pérot laser on the same bar. However, the spectral linewidth decreased by only a factor of 2. The beam quality was substantially better than that for the Fabry–Pérot laser out to stripe widths of at least 800 μm.

Injection locking of broad-area angled grating DFB lasers

The injection locking properties of an angled-grating distributed feedback laser have been measured experimentally. Fringe visibility measurements were used to ascertain the quality of the phase lock between the master and slave laser as a function of master coupling level and frequency detuning. Experimental results show an asymmetric lockband with the stable lock region increasing in width as the coupling is increased.

Theory of grating-confined broad-area lasers

Angled-distributed-feedback semiconductor lasers have demonstrated 1-W diffraction-limited collimated output from a broad-area aperture. We present the first theoretical analysis of the modes of these devices, explaining their principle of operation and the reasons for their high spatial mode quality. A transfer matrix analysis is presented that can describe the general class of grating-guided waveguides with either finite and/or infinite grating boundaries. Lateral grating-confined broad-area waveguides are shown to have extremely high spatial mode selectivity. The theory is applied to describe the new angled-grating distributed feedback laser (/spl alpha/-DFB), predicting a broad near-Gaussian near field and a collimated diffraction-limited far field, in good agreement with experiment.