Mode control of electrically injected semiconductor laser with parity-time symmetry

Abstract

The non-Hermitian description is of great significance for open systems, and the Hamiltonian which satisfies parity-time symmetry can make the energy have real eigenvalue within a certain range. The properties of parity-time symmetry have bright application prospects in optical systems. For semiconductor lasers, the parity-time symmetry can be constructed by adjusting the level of electrical injection to help achieve better mode control. Electric injection is easier to realize than optical pump when the device size is small and the structure is complex. Therefore, we hope to analyze the characteristics of the laser that satisfies the parity-time symmetry condition under the condition of electric injection. In this paper, we simulate the effects of different set loss values on parity-time symmetry. It is found that with the increase of set loss value, the imaginary part of the refractive index of the gain cavity corresponding to the parity-time symmetry breaking point so-called exceptional point will decrease, and the imaginary part of the characteristic frequency corresponding to the exceptional point will also decrease. We also simulate the effect of structural size ratio of gain region and loss region on parity-time symmetry. On condition that the total cavity length and the imaginary part of the refractive index of the loss region remain unchanged, as the gain cavity becomes longer and the loss cavity becomes shorter, the imaginary part of the refractive index of the gain cavity corresponding to the exceptional point will increase, and the imaginary part of the characteristic frequency corresponding to the exceptional point will also increase. And we qualitatively explain the above phenomenon through the coupled mode equations. Through experiments, metal organic chemical vapor deposition (MOCVD) and standard lithography techniques are used to fabricate asymmetric ridge lasers. Under thermoelectric cooler (TEC) refrigeration and by controlling the injection level of the gain area, the doubled mode spacing and halved mode number of ridge waveguide are found for the first time due to the parity-time symmetry breaking under the condition of electric injection. We believe that the study of parity-time symmetry in ridge laser under the condition of electric injection will be of great help in implementing the mode control.

Advances in Semiconductor Lasers Based on Parity–Time Symmetry

“…In 2020, Wang et al at the Institute of Semiconductors of the Chinese Academy of Sciences [26] introduced the concept of PT symmetry in electrically injected semiconductor lasers with stripe structures. They analyzed the impact of the gain-loss structure symmetry on the PT symmetry-breaking phenomenon and demonstrated experimentally that PT symmetry breaking could lead to a doubling of the mode spacing in electrically in- In 2017, Ke et al, from the Huazhong University of Science and Technology [56] proposed an external optical feedback DFB laser that utilized PT-symmetric complex coupling.…”

“…Currently, PT symmetry is widespread in laser applications. For example, single transverse mode operation can be achieved by the lateral introduction of a PT-symmetric coupling structure into a laser [24], and the longitudinal introduction of PT-symmetric Bragg gratings into lasers allows for the selection of longitudinal modes [25,26]. Additionally, at the PT-symmetric breaking points, peculiar phenomena such as unidirectional light transmission [27,28] are observed.…”

Electrically injected double‐taper semiconductor laser based on parity‐time symmetry

“…The simulation results of double‐taper PT‐symmetric laser are shown in Figure 2. The specific method of tuning PT‐symmetric breaking point has been elucidated in our previous work [7]. The widths of the two ends of the tapered cavity is 5.0 μ m and 8.0 μ m, respectively.…”

“…In our previous work, we have analysed how to control the position of PT‐symmetric breaking point through simulations and experiments [6]. We have also realized longitudinal and lateral PT‐symmetric electrically injected semiconductor lasers through experiments, and verified the robustness of the structures [6, 7]. Our previous experiments were all limited in single‐ridge or double‐ridge structure to control mode.…”