Reliable mid-infrared laterally-coupled distributed-feedback interband cascade lasers

Abstract

We report on the performance and reliability of laterally-coupled distributed-feedback (DFB) interband cascade lasers designed to operate at 3.6 μm wavelength. A two-step ridge etch process ensures single-transverse-mode operation with minimal lateral current spreading, and a second-order Bragg grating etched alongside the ridge waveguide imposes single-mode DFB operation. Life tests performed on four randomly selected lasers, continuously operating at 40 °C with output power >10 mW, showed no measurable degradation after each laser was operated continuously for more than 1500 h.

The Interband Cascade Laser

“…Intrinsic limits to the device performance are best evaluated from measurements in pulsed mode (with a low duty cycle to preclude significant lattice heating) on ridges wide enough to minimize current leakage and optical scattering losses at the sidewalls. The ridge should be etched to a depth stopping below the entire active core, since significant lateral current spreading otherwise occurs due to the core's high impedance to vertical transport at current densities well below the lasing threshold [92]. Unless otherwise specified, the broad-area lasers discussed in this work are 150 µm wide and 2 mm long, with uncoated facets.…”

InAs-based distributed feedback interband cascade lasers

“…Therefore, to enable cw operation while still maintaining sufficient coupling to the grating, we realized a double ridge approach, which is similar to the one presented in Ref. 19. In this work, however, we used a metal grating instead of an index grating, which is placed on the waveguide layers above the active region, as sufficient coupling can be achieved here.…”

Laterally coupled distributed feedback lasers emitting at 2 μm with quantum dash active region and high-duty-cycle etched semiconductor gratings

“…[22][23][24][25] In additional recent work, improvements in low-loss, high-power operation have been achieved by etched lateral grating fabrication, 13 or by use of a twostep ridge etch process for minimal lateral current spreading. 26 On the other hand, higher side mode discrimination in relatively short cavities has been achieved by operation with a narrower ridge waveguide of 1.7 lm width, 27 introducing first-order 28,29 or optimized third-order [30][31][32][33][34] Bragg gratings on the ridge waveguide sidewalls, or by use of focused ion beam lithography (FIB) in LC-DFB 35 and LC-DBR 36,37 configurations. Notably, chirped CRW gratings for the better control over the coupling coefficient have been also investigated.…”