Improvement of the beam quality of a broad-area diode laser using asymmetric feedback from an external cavity

Abstract

In this work, the use of an asymmetric feedback technique for improving the beam quality of a broad-area diode laser is investigated using numerical simulations. A mirror stripe is placed in the external cavity to select lateral mode and provide asymmetric feedback. The width and the position of the mirror stripe are optimized to improve the beam quality. The simulation results show a good beam quality of 0.7 • FWHM and M 2 value of 2.69.

Asymmetric feedback external cavity laser diodes: Comparison of experiment and simulation

“…However, these lasers suffer from poor beam quality, which can be a significant issue in applications such as telecommunications, medicine, displays and laser manufacturing. In this work, we present simulation work on an asymmetric feedback technique to improve the beam quality of a broad area laser diode [1]. We have realized this setup experimentally and have obtained good agreement with simulation.…”

Self-consistent simulation of high-brightness diode lasers with external optical feedback

“…In practise, however, they are almost always placed in a larger optical system, whereby even simple applications use multiple optical components to collimate, shape and focus the output beam -all of which can introduce optical feedback. In more complex systems, external feedback may be used to improve the beam quality through spatial mode filtering [1], wavelength stabilisation [2] or even phase locking for coherent beam combining (CBC) [3,4]. As the output power of laser diodes continues to increase, even small amounts of unintentional feedback can affect the performance and even the degradation/failure of the laser [5].…”

“…Even if the external feedback does not allow these modes to reach threshold, the additional stimulated emission and free-carrier absorption processes can reduce the laser's efficiency and cause self-heating. Several groups [1,4] have modelled external cavity laser diodes where optical feedback was used positively (e.g. beam quality improvement and phase locking for CBC) but much less focus has been given to modelling the negative impact of external optical feedback.…”

Spectral properties of a broad-area diode laser with off-axis external-cavity feedback

“…Among them, off-axis external-cavity feedback is an effective technique to improve the beam quality of BALs in the slow axis. [1][2][3][4][5][6][7][8] The off-axis external-cavity feedback technique is based on the fact that the output of a gain-guided BAL consists of a set of transverse spatial modes; each mode has a double-lobed far-field in the slow axis, and these modes are distinguished at different angles in the far field. 9,10 The offaxis external-cavity feedback technique is to select one lobe of a spatial mode at the far field and reflect it back into the laser cavity; thereby this lobe is amplified in the BAL and reflected at the back facet of the laser, finally it is coupled out of the laser as the other lobe (the output beam of the BAL system) of the same spatial mode.…”

“…9,10 The offaxis external-cavity feedback technique is to select one lobe of a spatial mode at the far field and reflect it back into the laser cavity; thereby this lobe is amplified in the BAL and reflected at the back facet of the laser, finally it is coupled out of the laser as the other lobe (the output beam of the BAL system) of the same spatial mode. All the other transverse modes are suppressed effectively, [1][2][3][4][5][6][7][8] thus, the spatial coherence of a BAL in the slow axis is improved significantly. But in order to achieve a compact laser system, normally for an off-axis external-cavity feedback set-up, the far field is imaged onto a pseudo-far-field plane by an imaging system, and different transverse spatial modes are distinguished at different positions in this plane, thus, the modeselection by angle in the real far field is changed to the mode-selection by position in the pseudo-far-field plane.…”