Mode-Locked Topological Insulator Laser Utilizing Synthetic Dimensions

Abstract

We propose a system that exploits the fundamental features of topological photonics and synthetic dimensions to force many semiconductor laser resonators to synchronize, mutually lock, and under suitable modulation emit a train of transform-limited mode-locked pulses. These lasers exploit the Floquet topological edge states in a 1D array of ring resonators, which corresponds to a 2D topological system with one spatial dimension and one synthetic frequency dimension. We show that the lasing state of the multielement laser system possesses the distinct characteristics of spatial topological edge states while exhibiting topologically protected transport. The topological synthetic-space edge mode imposes a constant-phase difference between the multifrequency modes on the edges, and together with modulation of the individual elements forces the ensemble of resonators to mode lock and emit short pulses, robust to disorder in the multiresonator system. Our results offer a proof-of-concept mechanism to actively mode lock a laser diode array of many lasing elements, which is otherwise extremely difficult due to the presence of many spatial modes of the array. The topological synthetic-space concepts proposed here offer an avenue to overcome this major technological challenge and open new opportunities in laser physics.

Highlighting photonics: looking into the next decade

“…Thus, it seems that the goal of locking together many semiconductor lasers to act as a single coherent laser will be achieved and is well on its way to become a real application. From all of this activity, it is now quite clear that currently the topological insulator lasers are the most promising application of topological photonics, with many new ideas emerging, for example, utilizing topology in synthetic dimensions to force an array of semiconductor lasers to emit mode-locked pulses [109], which could overcome a challenge of three decades.…”

Quantum Topological Photonics

“…Even when a ring resonator is removed, light can still propagate along the edge of the resonator array. The CROW configuration has been used widely in topological photonics to realize topological lasers, [ 79–85 ] the quadrupole topological state [ 86 ] and corner state, and reconfigurable topological phases. [ 87 ]…”

Topological photonics: Where do we go from here?

“…Importantly, very recent theoretical work [83] showed that indeed the topological design greatly improves the coherence of a large array of emitters, as envisioned by [34,76]. From all of this activity, it is now quite clear that currently the topological insulator laser is the most promising application of topological photonics, with many new ideas emerging, for example, utilizing topology in synthetic dimensions to force an array of semiconductor lasers to emit mode-locked pulses [87], which could overcome a challenge of three decades.…”