Zhang Jinchuan

Free-space communication based on quantum cascade laser*

A free-space communication based on a mid-infrared quantum cascade laser (QCL) is presented. A room-temperature continuous-wave distributed-feedback (DFB) QCL combined with a mid-infrared detector comprise the basic unit of the communication system. Sinusoidal signals at a highest frequency of 40 MHz and modulated video signals with a carrier frequency of 30 MHz were successfully transmitted with this experimental setup. Our research has provided a proof-of-concept demonstration of space optical communication application with QCL. The highest operation frequency of our setup was determined by the circuit-limited modulation bandwidth. A high performance communication system can be obtained with improved modulation circuit system.

High-Power and High-Efficiency Operation of Terahertz Quantum Cascade Lasers at 3.3 THz

A high-power and high-efficiency GaAs/AlGaAs-based terahertz (THz) quantum cascade laser structure emitting at 3.3 THz is presented. The structure is based on a hybrid bound-to-continuum transition and resonant-phonon extraction active region combined with a semi-insulating surface-plasmon waveguide. By optimizing material structure and device processing, the peak optical output power of 758 mW with a threshold current density of 120 A/cm2 and a wall-plug efficiency of 0.92% at 10K and 404mW at 77K are obtained in pulsed operation. The maximum operating temperature is as high as 115 K. In the cw mode, a record optical output power of 160 mW with a threshold current density of 178 A/cm2 and a wall-plug efficiency of 1.32% is achieved at 10 K.

Development of Surface Grating Distributed Feedback Quantum Cascade Laser for High Output Power and Low Threshold Current Density

We report on the room-temperature cw operation of a surface grating distributed feedback (DFB) quantum cascade laser (QCL) at ? ~4.7 ?m. Both grating design and material optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-?m-wide and 4-mm-long laser, high wall-plug efficiency of 6% is obtained at 20?C from a single facet producing over 1 W of cw output power. The threshold current density of DFB QCL is as low as 1.13 kA/cm2 at 10?C and 1.34 kA/cm2 at 30?C in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in the working temperature range of 20?50?C.

High Power Surface Metal Grating Distributed Feedback Quantum Cascade Lasers Emitting at λ ∼ 8.3 μm

We present a surface metal grating distributed feedback quantum cascade laser emitting at λ~8.3 μm and operating above 400 K in pulsed mode. A very high peak power of 463 mW at 290 K and still more than 18 mW at 400 K is achieved for a high-reflectivity-coated 13-μm-wide and 2.5-mm-long laser. Single-mode emission with a high side mode suppression ratio and wide temperature tuning range is observed. Such a high-power single-mode laser with a simple device process is important for practical applications.

High-Power High-Temperature Continuous-Wave Operation of Quantum Cascade Laser at λ∼4.6 μm without Lateral Regrowth

High-power quantum cascade lasers (λ = 4.6 μm) working in continuous wave (cw) up to 90°C are presented. The material was grown by solid-source molecular beam epitaxy and processed into narrow conventional ridge geometry without lateral regrowth. High cw output power of 850mW at 10°C and more than 200mW at 90°C were obtained with threshold current densities of 1.34 and 2.47 kA/cm2, respectively, for a high-reflectivity-coated 12-μm-wide and 3-mm-long laser.