0.45 W diffraction-limited beam and single-frequency operation from antiguided phase-locked laser array with distributed feedback grating

Abstract

A second-order diffraction grating placed below the active region of a phase-locked resonant antiguided array selects the in-phase array mode in addition to its role as a single-longitudinal-mode selector. This type of array-mode discrimination relies on the fact that the resonant in-phase array mode has significantly better field overlap with the grating region than nonresonant array modes. Furthermore, it eliminates the need for a conventional array-mode discriminator: interelement loss; which can cause self-pulsations. Diffraction-limited beam and single-frequency operation is obtained to at least 0.45 W peak pulsed power from 20 element, InGaAs/InGaP/GaAs structures (ϭ0.97 m) of 120-m-wide aperture. Distributed-feedback operation is confirmed over the 20-40°C temperature range. The results are in good agreement with theory. © 1998 American Institute of Physics. ͓S0003-6951͑98͒02531-5͔The ability to produce high-power, single-frequency, single-spatial-mode light sources is of fundamental importance to applications such as coherent free-space optical communications, blue-light generation via frequency doubling, midinfrared light generation via parametric frequency conversion, and low-noise sources for high-fidelity rf optical links. Large-aperture ͑у100 m͒ devices such as the fanouttype master-oscillator power amplifier ͑MOPA͒ 1 and the ␣-distributed-feedback ͑DFB͒ laser 2 have displayed high diffraction-limited, single-frequency powers. However, such devices, having weak or no lateral-mode confinement, possess inherent instabilities, 3-6 thus raising serious issues of long-term stability and reliability. Therefore, there is a need for coherent large-aperture devices which not only select fundamental-mode operation but also maintain a stable mode to high drive levels.As in the case of single-element devices, large-aperture emitters can achieve lateral-mode stability only by introducing strong built-in index guiding (⌬nу0.01). Resonant antiguided diode laser arrays ͑ROW arrays͒ 7 with 100-200-m-wide apertures have demonstrated the ability to operate in-phase with stable, diffraction-limited or near-diffractionlimited beams to record-high pulsed and cw output powers.7-10 Such performances are due primarily to the devices' high effective-index step (⌬n eff ϳ0.05) and inherent stability against multimoding via gain spatial hole burning ͑GSHB͒.11 Discrimination against higher order spatial modes is usually provided by placing loss in the high effectiveindex interelement regions, 7 in turn suppressing modes with significant interelement field. However, it has been shown 12 that the presence of interelement loss could trigger selfpulsations due to saturable absorption at high power levels. Therefore, in order to assure stable, coherent high powers from antiguided arrays, there is a need for a novel spatialmode selector that does not rely on interelement loss.Here we present the first experimental proof of the concept 13 that a DFB grating placed below the active region of a ROW array selects both a single longitudina...

High-power (>10 W) continuous-wave operation from 100-μm-aperture 0.97-μm-emitting Al-free diode lasers

“…1,2 Furthermore, the low oxidation rate of InGaP permits high-quality epitaxial regrowths over gratings for longitudinal-mode control ͑i.e., distributed-feedback lasers͒ 3,4 or over etched structures for lateral-mode control. [5][6][7][8][9] Thus, the Al-free material system is highly desirable for both broad-stripe spatially incoherent devices as well as for temporally and/or spatially coherent index-guided diode lasers.…”

Technologies and applications of Al‐free high‐power laser diodes

“…Thus, we developed laser diodes using InGaAsP, which do not contain aluminum in the active region (thus called "Al-free"). Using InGaAsP instead of AlGaAs has the following advantage: (1) the lower surface recombination velocity leads to higher maximum optical power with decreased nonradiative recombination [1], (2) the low oxidation of Al-free material makes it easy to fabricate indexguided structures and DFB structures [2], (3) the reduction of threshold current and improvement of characteristic temperature can be realized by introduction of strained quantum well structures and strain-compensating barrier layers [3,4], and (4) higher efficiency can be obtained by reduction of the electric resistance and thermal resistance [5].…”