Bidirectional ring laser: Stability analysis and time-dependent solutions

Square-wave oscillations in a semiconductor ring laser subject to counter-directional delayed mutual feedback

Square-wave (SW) switching of the lasing direction in a semiconductor ring laser (SRL) is investigated using counter-directional mutual feedback. The SRL is electrically biased to a regime that supports lasing in either counter-clockwise (CCW) or clockwise (CW) direction. The CCW and CW modes are then counter-directionally coupled by optical feedback, where the CCW-to-CW and CW-to-CCW feedback are delayed by τ₁ and τ₂, respectively. The mutual feedback invokes SW oscillations of the CCW and CW emission intensities with a period of T≈τ₁+τ₂. When τ₁=τ₂, symmetric SWs with a duty cycle of 50% are obtained, where the switching time and electrical linewidth of the SWs can be reduced to, respectively, 1.4 ns and 1.1 kHz by strengthening the feedback. When τ₁≠τ₂, asymmetric SWs are obtained with a tunable duty cycle of τ₁/(τ₁+τ₂). High-order symmetric SWs with a period of T=(τ₁+τ₂)/n can also be observed for some integer n. Symmetric SWs of order n=13 with a period of T=10.3  ns are observed experimentally.

Diffusion stabilizes cavity solitons in bidirectional lasers

We study the influence of field diffusion on the spatial localized structures (cavity solitons) in bidirectional lasers. We find threefold positive role of the diffusion: 1) it allows for the existence of solitons in cavities with equal losses for the two fields; 2) it increases the stability range of the individual (isolated) solitons; and 3) it reduces the long-range interaction between cavity solitons, allowing for the independent manipulation (writing and erasing) of individual structures.

Phase-space approach to directional switching in semiconductor ring lasers

We show that a topological investigation of the phase space of a semiconductor ring laser can be used to devise switching schemes which are alternative to optical pulse injection of counterpropagating light. To provide physical insight in these switching mechanisms, a full bifurcation analysis and an investigation of the topology is performed on a two-dimensional asymptotic model. Numerical simulations confirm the topological predictions.

Topological insight into the non-arrhenius mode hopping of semiconductor ring lasers

We investigate both theoretically and experimentally the stochastic switching between two counterpropagating lasing modes of a semiconductor ring laser. Experimentally, the residence time distribution cannot be described by a simple one-parameter Arrhenius exponential law and reveals the presence of two different mode-hop scenarios with distinct time scales. In order to elucidate the origin of these two time scales, we propose a topological approach based on a two-dimensional dynamical system.

Optical injection in semiconductor ring lasers: backfire dynamics

We report on directional mode switching in semiconductor ring lasers through optical injection co-propagating with the lasing mode. The understanding of this novel feature in ring lasers is based on the particular structure of a two-dimensional asymptotic phase space. Our theoretical results are verified numerically and experimentally.

Could cavity solitons exist in bidirectional ring lasers?

We show numerically that bright and dark cavity solitons can be obtained in bidirectional class A ring lasers only if the phase invariance of the electromagnetic field is broken. The phase invariance symmetry is responsible for the existence of phase waves, which generate long-range interactions destroying the property of independence among otherwise localized structures. We improved the usual model describing such types of lasers, and we prove that it leads to genuine cavity solitons.

Cavity solitons in bidirectional lasers

We show theoretically that a broad area bidirectional laser with slightly different cavity losses for the two counterpropagating fields sustains cavity solitons (CSs). These are complementary; i.e., there is a bright (dark) CS in the field with larger (smaller) losses. Interestingly, the CSs can be written or erased by injecting suitable pulses into any of the two counterpropagating fields.

Mode-coupling control in resonant devices: Application to solid-state ring lasers

We report the theoretical and experimental investigation of the effects of mode coupling in a resonant macroscopic quantum device, in the case of a solid-state ring laser. This is achieved by introducing an additional coupling source whose interplay with the already-existing nonlinear effects ensures the coexistence of two counterpropagating cavity modes yielding a rotation-sensitive beat note. The determination of the condition for rotation sensing, both theoretically and experimentally, allows a quantitative study of the role of various mode-coupling mechanisms, in particular, the gain-induced mode coupling. We point out the connection between our work and the theoretical work on mode coupling in superfluid devices. This work opens up the possibility of new types of active rotation sensors.

Chaotic alternation of waves in ring lasers

We intend to give an analytic description of the mechanisms involved in the periodic and chaotic wave alternation frequently observed in ring lasers. A set of amplitude equations is derived from the Maxwell-Bloch equations. These equations are studied analytically and numerically.