Abstract
It is shown, by calculations calibrated against the authors’ recent experimental data, that an eye-safe wavelength range InGaAsP/InP high pulsed power laser design using a bulk active layer, which has a large refractive index step with respect to the optical confinement layer and is located close to the p-cladding, can provide substantial performance improvement compared to the best results achieved so far for this operating regime and wavelength. The dependence of the laser performance on the design parameters such as the thicknesses of the active layer and the waveguide, as well as the cavity length, are analysed. It is shown that the relatively thick bulk active layer in such InGaAsP/InP lasers allows the use of short cavity lengths (∼1 mm or even shorter), for achieving high pulsed power while maintaining a low p-cladding series resistance (making for high efficiency) and a narrow far field (making for high brightness). A single-asymmetry structure with the asymmetric active layer location but symmetric optical confinement layer/cladding refractive index steps gives performance only marginally inferior to that of a double-asymmetric one including asymmetric refractive index steps.
Highlights
High power broad area pulsed diode lasers operating in the eye-safe spectral range, i.e. within the wavelength range from 1400 to 1700 nm, find applications ranging from medical instrumentation to range finding/LIDAR systems [1]
It has been shown that by far the most efficient way to minimise the increase in the internal losses at high injection levels due to the inhomogeneous hole accumulation is to minimise the physical thickness of the p-Optical Confinement Layer (OCL), that is, the side of the OCL that is adjacent to the p-cladding
The two designs of high-power quasi-continuouswave lasers, at any wavelength, most widely used currently are the ultranarrow waveguide [5,6,7,8] and the broad asymmetric waveguide [12,13,14,15,16,17] designs. Both have been applied for the eye safe wavelength range [5,6,7,8, 12, 13]
Summary
High power broad area pulsed diode lasers operating in the eye-safe spectral range, i.e. within the wavelength range from 1400 to 1700 nm, find applications ranging from medical instrumentation to range finding/LIDAR systems [1]. In strongly asymmetric Large Optical Cavity waveguides, the single broad mode is achieved by using asymmetric refractive index steps at the n-OCL/n-cladding and p-OCL/p-cladding interfaces in addition to the asymmetry of the active layer position, resulting in double asymmetry or, in the most recent implementation, triple asymmetry to maximise the mode overlap with the active layer (the optical confinement factor Γ [17]). This last step was made necessary by the fact that most high-power laser structures used so far have used active layers consisting of only a few (1–3) Quantum Wells (QWs). We present a more systematic theoretical study of high-power laser design with bulk active layers with substantial waveguiding effect, and show that they offer new paths in laser design and optimisation
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