基于射频调制技术的宽谱太赫兹量子级联激光器研究

Homogeneous broadband and electrically pumped semiconductor radiation sources emitting in the terahertz regime are highly desirable for various applications, including spectroscopy, chemical sensing, and gas identification. In the frequency range between 1 and 5 THz, unipolar quantum cascade lasers employing electron inter-subband transitions in multiple-quantum-well structures are the most powerful semiconductor light sources. However, these devices are normally characterized by a narrow emission spectrum due to the narrow gain bandwidth of the inter-subband optical transitions. Terahertz quantum cascade lasers can be modulated by a RF signal. When the frequency of the signal is equal to laser mode spacing, each side mode will be enhanced, thus the emission spectrum will be broadened, even reach to the width of gain medium, and the laser mode spacing will be locked to the modulation frequency. If the active region has a wide gain spectrum, and a RF modulation is applied simultaneously, the laser is expected to output stable broadband emission spectrum..Here, we propose a homogeneous broad terahertz semiconductor quantum cascade laser. The active region with heterogeneous stacks provides a broadband gain medium. Under the radio frequency modulation, the emission spectrum spans to the gain spectrum width. A high-resolution homogeneous broadband spectrum with spectral bandwidth more than 1 THz and mode number more than one hundred, is expected.

均匀宽谱和电泵浦的太赫兹波段半导体辐射源应用前景广阔，包括光谱技术、化学传感和气体鉴定等。在1~5 THz频率范围内，量子级联激光器是一种重要的半导体辐射源，基本原理是电子在多量子阱结构中子带间跃迁辐射光子。然而正是由于这种有限的子带间跃迁特性限制了有源区增益带宽，结果影响了激光器发射谱谱宽。在太赫兹量子级联激光器上加入射频调制，当射频调制频率与纵模间隔相当时，边模得到增强，从而激光光谱范围变宽，几乎达到有源区增益谱范围，并且激光器模式间距将精确锁定到调制频率。如果以宽增益谱材料为有源区，外加射频调制，激光器有望实现稳定的宽发射谱输出。本项目提出一种宽谱太赫兹量子级联激光器，有源区由多个异质结构堆叠而成具有很宽的增益谱，在射频调制的作用下，光谱均匀展宽达到增益谱宽度，预期形成谱宽超过1THz、模数过百的高分辨率宽发射谱。

均匀宽谱和电泵浦的太赫兹波段半导体辐射源应用前景广阔，包括光谱技术、化学传感和气体鉴定等。在1~5 THz频率范围内，量子级联激光器是一种重要的半导体辐射源，其基本原理是电子在多量子阱结构中子带间跃迁辐射光子。激光器中有源区增益带宽、谐振腔特性以及外加射频调制等因素均会影响发射谱宽度。本项目研制了基于射频调制技术的宽谱太赫兹量子级联激光器，激射频率约4 THz，有源区具有很宽的增益谱，在射频调制作用下，发射谱均匀展宽，单个电流下谱宽达300 GHz，整个驱动电流下谱宽达700 GHz。另外采用15 mm超长谐振腔，激光模式间隔低至2.45 GHz，射频调制后单个电流下可激发90个纵模，整个驱动电流下纵模数约106个。这种高分辨的均匀宽发射谱在太赫兹光谱技术中具有重要的应用价值。最后，还开展了基于射频调制宽谱太赫兹量子级联激光器的太赫兹光频梳研究，实现了被动稳频太赫兹光频梳以及太赫兹双光梳。