Abstract
The linewidth of regenerative oscillators is enhanced by amplitude–phase coupling of the oscillator field [Phys. Rev. 160, 290 (1967)]. In laser oscillators, this effect is well known for its impact on semiconductor laser performance. Here, this coupling is studied in Brillouin lasers. Because their gain is parametric, the coupling and linewidth enhancement are shown to originate from phase mismatch. The theory is confirmed by measurement of linewidth in a microcavity Brillouin laser, and enhancements as large as 50 × are measured. The results show that pump wavelength and device temperature should be carefully selected and controlled to minimize linewidth. More generally, this work provides a new perspective on the linewidth enhancement effect.
Highlights
The linewidth of stimulated Brillouin lasers (SBLs) has received considerable attention for some time
While the conventional Schawlow–Townes laser linewidth [21] is insensitive to temperature, the fundamental SBL linewidth is proportional to the number of thermomechanical quanta in the phonon mode and to the Boltzmann energy kBT [13]
The parametric nature of the process means that pump phase noise couples through to the laser linewidth, it is strongly suppressed by the phonon damping [24]
Summary
The linewidth of stimulated Brillouin lasers (SBLs) has received considerable attention for some time. The parametric nature of the process means that pump phase noise couples through to the laser linewidth, it is strongly suppressed by the phonon damping [24]. The linewidth enhancement factor is studied in SBLs. The parametric nature of Brillouin gain is shown to strongly influence this parameter.
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