Single-mode operation of a broad-area semiconductor laser with an anamorphic external cavity: experimental and numerical results

Abstract

The emission of high-power broad-area semiconductor lasers inherently contains many lateral modes that increase the beam divergence and reduce the spatial coherence. Elimination of higher-order lateral modes from the output beams of commercially available broad-area lasers will be beneficial in many applications of these lasers. Experimental results obtained with a broad-area laser coupled to an anamorphic external cavity are presented and are compared with the predictions from our numerical model. We have predicted and observed with the anamorphic external cavity a greatly improved discrimination against high-order lateral modes. The measurement of the spectrally resolved near-field intensity patterns provides much more comprehensive information on their longitudinal- and lateral-mode content than do observations of near-field and far-field beam intensity profiles. With a broad-area laser of 100-mW nominal power, it has been possible to extract 40% of the maximal power in a stable single-lateral and single-longitudinal mode regime.

Structure, Stability, and Spectra of Lateral Modes of a Broad-Area Semiconductor Laser

“…The effect of carrier relaxation oscillations is seen as shoulders on the central peak at . The spectral dependence on the lateral position is in qualitative agreement with the experiments in [17]. The present calculation of the field power spectrum ignores the effects of gain dispersion.…”

“…We derive expressions for the relative intensity noise (RIN) spectrum, the frequency noise spectrum and the field power spectrum, and present numerical calculations for our BA laser example. The spectra depend on the lateral position as was also demonstrated experimentally in [17] and [18].…”

“…This is justified when the focus is on spectral details determined by the carrier dynamics on the scale of a few GHz. In reality the BA laser oscillates in several longitudinal modes [17]. In order to calculate the full longitudinal spectrum one may introduce a field equation like (6) for each longitudinal mode.…”

“…If the modes are stable they may be operating modes of the BA laser, and if they are unstable, they may still show up as attractors for the trajectories of the time domain solution in phase space. The experiments of Mailhot et al [17] and Mandre et al [18] show the presence of lateral modes even when the BA laser is not operating in a stationary state. The same behavior is seen in time domain computer simulations [13], [14].…”

Coherent beam combining of high power broad-area laser diode array with near diffraction limited beam quality and high power conversion efficiency

“…Applying low anti-reflection (AR) coating to a BALD and employing external optical feedback to a BALD can limit the number of transverse modes. A variety of external feedback designs can limit the number of transverse modes of BALD and improve the beam quality [26][27][28][29][30][31][32][33][34][35][36][37][38]. The off-axis optical feedback was introduced to enhance one transverse mode and significantly increase beam quality of BALD [33,34,36,38].…”