Effects of Spin-Dependent Interactions on Polarization of Bright Polariton Solitons

We report on the spin properties of bright polariton solitons supported by an external pump to compensate losses. We observe robust circularly polarized solitons when a circularly polarized pump is applied, a result attributed to phase synchronization between nondegenerate TE and TM polarized polariton modes at high momenta. For the case of a linearly polarized pump, either ${\sigma }^{+}$ or ${\sigma }^{-}$ circularly polarized bright solitons can be switched on in a controlled way by a ${\sigma }^{+}$ or ${\sigma }^{-}$ writing beam, respectively. This feature arises directly from the widely differing interaction strengths between co- and cross-circularly polarized polaritons. In the case of orthogonally linearly polarized pump and writing beams, the soliton emission on average is found to be unpolarized, suggesting strong spatial evolution of the soliton polarization. The observed results are in agreement with theory, which predicts stable circularly polarized solitons and unstable linearly polarized solitons.

Figure 1

(a) Schematic of soliton excitation in a microcavity consisting of distributed Bragg reflectors (DBRs) and a quantum well (QW). The cw pump and pulsed WB are incident along the $X$ direction. (b) Schematic of soliton spectrum and excitation in $E\text{−}k$ space with TE (dotted) and TM (solid) polarized polariton dispersions.

Figure 2

Soliton emission intensity recorded as a function of time and position across the sample in ${\sigma }^{+}$ (a),(d),(g),(j) and ${\sigma }^{-}$ (b),(e),(h),(k) circular polarizations. Soliton CPD ${\rho }_c$ as a function of time and position (c),(f),(i),(l). The pump polarization is ${\sigma }^{+}$ in (a)–(c) and TM linear in (d)–(l). The WB polarization is ${\sigma }^{+}$ in (a)–(f), ${\sigma }^{-}$ in (g)–(i), and TE linear in (j)–(l). The WB arrives at time $t=0\mathrm{ps}$ at position $x\sim -10\mu \mathrm{m}$.

Figure 3

(a) Thin grey lines show the CPD ${\rho }_c$ of polariton field vs the pump amplitude corresponding to a homogeneous pump polariton field. The dashed (solid) lines correspond to unstable (stable) soliton branches. (b),(d) Spatiotemporal trajectories of solitons when the pump and WB are orthogonally (b) and parallelly (d) linearly polarized. (c),(e) Soliton intensities and CPD ${\rho }_c$ as a function of position at time $t=30\mathrm{ps}$ (c) and 60 ps (e) after the WB pulse.

Figure 4

(a) Soliton CPD ${\rho }_c$ as a function of pump CPD ${\rho }_p$ recorded for the case of ${\sigma }^{+}$, ${\sigma }^{-}$ circularly polarized, and TE linearly polarized WB (circles, squares, and triangles, respectively). (b) Numerical modeling of soliton CPD ${\rho }_c$ as a function of ${\rho }_p$ recorded for the case of ${\sigma }^{+}$ polarized WB for different pump amplitudes and different pump angles.