Sensitive control of broad-area semiconductor lasers by cavity shape

Abstract

The ray dynamics of optical cavities exhibits bifurcation points: special geometries at which ray trajectories switch abruptly between stable and unstable. A prominent example is the Fabry–Perot cavity with two planar mirrors, which is widely employed for broad-area semiconductor lasers. Such cavities support lasing in a relatively small number of transverse modes, and the laser is highly susceptible to filamentation and irregular pulsations. Here, we demonstrate experimentally that a slight deviation from this bifurcation point (planar cavity) dramatically changes the laser performance. In a near-planar cavity with two concave mirrors, the number of transverse lasing modes increases drastically. While the spatial coherence of the laser emission is reduced, the divergence angle of the output beam remains relatively narrow. Moreover, the spatiotemporal lasing dynamics becomes significantly more stable compared to that in a Fabry–Perot cavity. Our near-planar broad-area semiconductor laser has higher brightness, better directionality, and hence allows shorter integration times than an incandescent lamp while featuring sufficiently low speckle contrast at the same time, making it a vastly superior light source for speckle-free imaging. Furthermore, our method of controlling spatiotemporal dynamics with extreme sensitivity near a bifurcation point may be applied to other types of high-power lasers and nonlinear dynamic systems.

Coherence‐adjustable, high‐directional, electrically pumped semiconductor lasers around 650 nm

“…The coherence and directionality of the laser can be changed by controlling the number of lasing spatial modes through tuning the shape of the resonant cavity [1][2][3]. For the low-coherence or adjustable-coherence lasers, there are already some successful cases.…”

Spatiotemporal lasing dynamics in a Limaçon-shaped microcavity

“…For edge-emitting semiconductor lasers, the resonator geometry can have a profound impact on the lasing dynamics [17,18]. Carefully designed cavity shapes for semiconductor quantumwell lasers can suppress the intrinsic spatio-temporal instabilities [19][20][21] and control the nonlinear light-matter interactions [22].…”

“…Figure 1(a) is the scanning electron microscope (SEM) image of a Limaçon-shaped disk with R = 86 µm. It is fabricated with a commercial GaAs/AlGaAs quantum-well wafer (Q-Photonics QEWLD-808) by photolithography and inductively coupled plasma etching [21]. Top and bottom metal contacts are deposited for electric current injection (See Supplement).…”

“…Each singular vector has its own characteristic scales in space and time. The spatial scale is given by the correlation length l α , which is defined as the full-width-at-half-maximum (FWHM) of the spatial correlation function for u α (x) [21]. Correspondingly, the temporal scale is the correlation time τ α given by the FWHM of the temporal correlation function for v α (t).…”

Spatio-temporal lasing dynamics in a Limaçon-shaped microcavity

“…For edge-emitting semiconductor lasers, the resonator geometry can have a profound impact on the lasing dynamics [17,18]. Carefully designed cavity shapes for semiconductor quantumwell lasers can suppress the intrinsic spatio-temporal instabilities [19][20][21] and control the nonlinear light-matter interactions [22].…”