We have made improvements for QCL in the thermal management to produce high output power. Unlike the previous literature, we use epilayer-down mounting and buried heterostructures to achieve high output power by improving the heat dissipation and reducing the thermal resistance. At 20 K, the continuous wave threshold current density is 110 A·cm-2 and the maximum current density is 210 A·cm−2. The maximum output power is about 250 mW at single facet. The central frequency is approximately ∼4 THz, which matches the energy band design. The thermal simulation shows that, compared with the traditional device, the heat removal performance of the optimized device is significantly improved, and the core temperature is reduced by about 20 K. It improves the heat extraction through epilayer-down mounting and buried heterostructures and leads also to significant lateral heat fluxes. The ways can facilitate the heat extraction in all in-plane directions. In conclusion, this method is beneficial to the development of high continuous wave power, especially for thick active region design. The demonstration of buried heterostructure terahertz quantum cascade lasers for epilayer-down mounting can promote the development of high-power terahertz source in continuous wave.
Quantum cascade lasers (QCLs) are relevant optical sources for free-space communication because they can emit in the long-wave infrared (LWIR) domain, i.e. in the 8-12 µm region. The advantage of this optical domain is that it combines a high atmosphere transmission1 with a reduced distortion for propagating beams,2 thus the superiority of LWIR lasers in comparison with existing near-infrared systems is very dependent on link availability.3 Furthermore, QCLs are characterized by the absence of relaxation oscillation resonance.4 This peculiarity could imply a very large modulation bandwidth, even if QCL structures still need to be optimized to avoid parasitic effects.5 Recent experimental efforts have highlighted the potential of QCL-based free-space communication systems6–8 and the current 4 Gbits/s record rate is expected to be outperformed in the near future with bandwidth-enhanced structures.9 This work describes a free-space live video broadcasting with a room-temperature QCL emitting at 8.1 µm. The video file is encoded in uncompressed high-definition format (1280 pixels x 720 pixels) and this corresponds to a data rate of 1.485 Gbits/s with on-off keying scheme. This high-speed electrical signal is directly injected in the QCL via the AC port of a bias tee. The modulated optical signal from the QCL is retrieved with a Mercury-Cadmium-Telluride detector and the resulting electrical signal is sent to a TV monitor where the video can be watched in live. The current findings demonstrate the versatility of a communication system with QCLs and this paves the way for real-field applications
We report nonlinear dynamics in directly connected twin circular-sided square microcavity semiconductor lasers with mutual optical injection. Rich nonlinear dynamics including injection locking, four-wave fixing, and multi-period oscillation states are observed experimentally by adjusting the mode frequency offset between two circular-side square microcavities. Internal optical injection or mode coupling can be realized directly in the connected twin circular-sided square microcavity lasers, which effectively relaxes device processing techniques of the integrated microcavities for photonic integration.
A numerical scheme for calculating phase noise is proposed for hybrid square-rectangular semiconductor lasers. By establishing a two-section single-mode rate equation model driven by Langevin noise sources and considering the nonlinear gain effect, we numerically studied the phase noise characteristics and linewidth of the hybrid-cavity laser. The time-varying spectra of carrier density, photon density and phase are simulated and the frequency spectra of phase noise are presented with the help of the fast Fourier transform. With the increase of the bias current, the frequency noise has an obvious downward trend and a narrower linewidth is obtained. The linewidth of the hybrid square-rectangular laser is calculated according to the phase noise at low frequency. The simulated linewidth of the hybrid-cavity semiconductor laser is 0.36 MHz at the linewidth enhancement factor of 3 when the square microcavity bias current is 20 mA and the FP cavity bias current is 100 mA.
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