Browsing by Subject "Mode filtering"
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Item Open Access Single-mode engineering in semiconductor lasers using parity-time-symmetry and coupled-cavity structures(Bilkent University, 2021-07) Şeker, EnesHigh power single spatial mode semiconductor lasers are of interest for various applications, including optical communication, material processing, and pumping single-mode optical fibers. The output power of a typical index guided ridge waveguide single-mode laser is limited by its narrow waveguide width required to cut off higher-order optical modes. To overcome the output power limitation, conventional techniques rely on structures increasing the mode size without introducing new modes. These methods are based on lateral mode discrimination in a single waveguide to enforce single-mode operation. In contrast to the conventional methods, our work utilizes the concept of parity-time-symmetry (PTS) and coupled-cavity (CC) structures. By exploiting these two approaches, we employ multi-mode waveguides to achieve single-mode lasing in edge-emitting laser diodes. The PTS laser is based on coupling two identical waveguides. By electrically tuning the gain and loss in each waveguide, the optical modes are manipulated to realize a single-mode operation. On the other hand, the CC approach is based on the resonant coupling of waveguides with different widths to realize single-mode operation. In contrast to the PTS method, CC lasers have an unpumped waveguide to introduce loss instead of tuning the loss with an electrical pump. Towards this goal, the design parameters are numerically explored by detailed optical simulations, and their sensitivities are investigated for PTS and CC methods. I fabricated and experimentally demonstrated the control of the optical mode profiles promising single-mode operation for PTS and CC structures. The results are encouraging for future research and industrial applications.Item Open Access Single-mode operation of electrically pumped edge-emitting lasers through cavity coupling of high order modes(SPIE, 2022-03-04) Şeker, Enes; Şengül, Serdar; Dadashi, Khalil; Olyaeefar, Babak; Demir, AbdullahThe output power of a typical single-mode semiconductor laser is limited by its narrow waveguide width required to cut off high-order spatial modes. Conventional techniques rely on engineering the waveguide without introducing higherorder modes. In contrast, this work utilizes the concept of coupled-cavity (CC) structures. A single-mode lasing is achieved by employing a multi-mode and a neighboring single-mode waveguide. The CC approach is based on the resonant coupling of the high-order mode in the wide waveguide to the fundamental mode of a narrower lossy waveguide. First, geometrical dispersion of the CC lasers, such as their width, spacing, and their sensitivity to the resonance, was investigated. After optimizing the design, edge-emitting-lasers were fabricated using high-efficiency GaAs-based structures. Optical mode control and single-mode operation of the design are demonstrated through fundamental optical characterization measurements. The output power curves for the single and CC designs show similar slope efficiencies suggesting the proposed method as a promising approach towards high-power single lateral mode operation of edge-emitting lasers.