Spectrally resolved modal characteristics of leaky-wave-coupled quantum cascade phase-locked laser arrays

Abstract

Abstract. The modal characteristics of nonresonant five-element phase-locked arrays of 4.7-μm emitting quantum cascade lasers (QCLs) have been studied using spectrally resolved near-and far-field measurements and correlated with results of device simulation. Devices are fabricated by a two-step metal-organic chemical vapor deposition process and operate predominantly in an in-phase array mode near threshold, although become multimode at higher drive levels. The wide spectral bandwidth of the QCL's core region is found to be a factor in promoting multispatial-mode operation at high drive levels above threshold. An optimized resonant-array design is identified to allow sole in-phase array-mode operation to high drive levels above threshold, and indicates that for phase-locked laser arrays full spatial coherence to high output powers does not require full temporal coherence.

Tapered Quantum Cascade Laser Arrays Integrated with Talbot Cavities

“…Phase-locked arrays have been skillfully applied in the wide ridge and low divergence semiconductor lasers since the 1980s [ 13 ]. In previous works, phase-locked QCL arrays have been studied in the Y-junction arrays, resonant leaky-wave-coupled arrays, and evanescent wave-coupled arrays, as the near-infrared laser did in the past [ 14 – 18 ]. These structures either bring about large losses in the waveguide [ 15 ] or result in heat accumulation by pursuing a short adjacent distance to obtain the coupling [ 16 – 18 ].…”

“…In previous works, phase-locked QCL arrays have been studied in the Y-junction arrays, resonant leaky-wave-coupled arrays, and evanescent wave-coupled arrays, as the near-infrared laser did in the past [ 14 – 18 ]. These structures either bring about large losses in the waveguide [ 15 ] or result in heat accumulation by pursuing a short adjacent distance to obtain the coupling [ 16 – 18 ]. Recently, diffraction-coupled QCL arrays that integrated a side cavity based on diffraction-coupled Talbot effects were reported [ 19 ].…”

Reverse-Taper Mid-Infrared Quantum Cascade Lasers for Coherent Power Scaling

“…Many approaches have been investigated for achieving highpower (>1 W) single-mode CW output powers, among them are the use of monolithic phase-locked laser array structures and multimode-interferometer (MMI)-combined tree-array structures. Leaky-wave-coupled phase-locked antiguided-laser arrays [2]- [8] have successfully achieved single-spatial-mode operation from large emitting apertures. Such devices possess a large built-in index contrast and operate in an in-phase array mode with uniform intensity profile across the emitting aperture, which ensures mode stability even under CW operation.…”