Starting from Fresnel diffraction theory, we derive analytic expressions for the lateral spatial dependence of feedback fields for the cases of conventional and phase-conjugate optical feedback. By using numerical simulations we show that for narrow-stripe gain-guided lasers, both types of optical feedback from an external cavity can convert the twin-lobed far fields into a nearly single-lobed far field. We also find that conventional and phase-conjugate feedbacks in broad-area lasers induce a spatial modulation of the lateral field that increases the tendency for filamentation at moderate (-30 dB) feedback levels.
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