The concept and the realization of the high-power laser diodes with multi-stripe-gain distribution

Abstract

Abstract-Slow axis far-field widening (far-field blooming) is one of the factors which decrease the quality of an emitted beam of high-power laser diodes. This effect is connected with a rising number of maintained lateral optical modes in the laser waveguide. In this paper the design of the gain distribution by the steering of a current flow is presented as a way to restrict the far-field blooming. Numerical and experimental results are presented. An almost constant slow-axis width of optical field distribution in the far-field is obtained up to four times above the threshold current.The implementation of high-power laser diodes (LDs) in many applications requires high stability of an emitted beam. In standard construction of these devices a broad active (BA) stripe is used to obtain high power. Unfortunately, in this solution the quality of the emitted beam in a lateral direction (slow axis) is poor. It is due to the multimode character of the beam and its low stability. One of the symptoms of low stability is the far-field widening (also called: far-field blooming). It is connected with self-heating which leads to variations of the refractive index. The rise of the refractive index with temperature in an active region enhances the waveguide effect. Consequently, higher order lateral modes can appear. It is well known that higher order modes have wider distribution in the far-field [1][2][3]. This effect is restricted in the Phase Locked Arrays (PLA) of semiconductor lasers [4][5][6]. In these devices, the BA stripe is replaced by an array of narrow waveguides and the optical fields from the neighboring active stripes are coupled to each other. As a result of the coupling, the optical field forms a set of supermodes propagating over the whole structure. The PLA radiation usually forms two beams located symmetrically with respect to the device optical axis. These beams are highly-stable and nearly diffraction limited. However, the PLA structures prove to be technologically difficult. In this paper the concept of the BA laser with a limited effect of slow-axis far-field blooming is presented. The numerical results are obtained using the FIMMWAVE program (by Photon Design), which had been successfully * E-mail: grzegorz.sobczak@itme.edu.pl used in earlier investigations [7][8] to predict the distributions in the near-and far-field (NF, FF respectively). Confirming experimental results are presented as well. The idea is to form by ion implantation a laterallyperiodic gain distribution in the active region of LD (here such a construction will be called a multi-stripe-gain laser diode: MSG-LD). The goal is that the inducted variations in the gain distribution should provide a low threshold current (I th ) of the higher order lateral mode but should not be able to form supermodes as in the PLA structures. To fulfill these assumptions, the ion implantation should cause only a small difference between the effective indices (n eff ) in implanted (n eff2 ) and unimplanted (n eff1 ) regions (n eff =n eff1 -n eff2 0); a...

High-power broad-area laser diode performance improvement with a double pedestal structure

“…4) Previous studies have shown that thermal lensing [5][6][7][8] due to the lateral refractive index gradient causes generation of higher-order lateral modes and narrowing of the near-field profile of each guided mode resulting in the far-field blooming. [9][10][11][12] In order to solve this problem, the pedestal heat-sinking structure has been demonstrated for reducing the far-field blooming 13,14) and numerically analyzed. 15) However, with this pedestal structure, the active region temperature is actually higher than without it, resulting in the lower slope efficiency and the thermal rollover at the lower current.…”