Asynchronous optical sampling THz spectroscopy system based on monolithically modelocked laser diodes

基于单片锁模激光二极管的异步光学采样太赫兹光谱系统

• 批准号: 236759088
• 负责人: Professor Dr. Martin Hofmann
• 金额: --
• 依托单位: Ferdinand-Braun-Institut gGmbH, Leibniz-Institut für Höchstfrequenztechnik (FBH)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/236759088?language=en
• 关键词: Asynchronous; optical; sampling; THz; spectroscopy

Our fundamental goal in this continuation project remains the development and realization of an operating extremely compact THz Time-domain sampling measurement system. Our concept is based on monolithically modelocked diode lasers and asynchronous optical sampling. In our first approach, one laser diode in combination with a photoconductive antenna acts as THz sender, and a second identical laser diode is synchronized to the first but operates on a slightly different repetition frequency in order to sample the THz signal received at the receiver photoconductive antenna asynchronously. For an even more compact system, we aim to integrate sender and receiver laser on one chip and to address the photoconductive antennas with fibers. In our second and new approach, we will realize an ASOPS-system with only one monolithically modelocked laser diode. The repetition frequency of the laser diode will be slowly varied and the receiver will be gated with a signal that is delayed with respect to the sender. This principle (Optical Sampling by Cavity Tuning, OSCAT) shall be demonstrated here with compact diode lasers for the first time. In the first part of the project we have demonstrated the first diode laser based THz-ASOPS-system. After this first demonstration with compact modelocked external cavity laser diodes, a first system with monolithically modelocked diodes and synchronization electronics has been set up. In addition to the proof-of-principle, our studies have shown the major challenges of the concept which we plan to address in this continuation project. These challenges include the specifications of the used laser systems, in particular the output power, the pulse width of the emitted pulses, and he stability of the repetition frequency. For the output power, we plan a further increase to > 50 mW average power, in order to achieve a better signal to noise ratio for the THz signal. To optimize the pulse width of the pulses hitting the antennas, two steps are required: first, the gain material of the semiconductor has to support the generation of pulses with a sufficient spectral bandwidth, and second, the strongly chirped pulses emitted by the laser diodes have to be compressed. For that, we use optimized semiconductor material using chirped quantum wells for a large gain bandwidth and compress the pulses with fibers with tailored dispersion and length. We aim to achieve pulse widths below 500fs and a THz bandwidth above 1.5 THz. The stability of the repetition frequency is a further major challenge. We plan to realize pulse trains with temporal jitter below 500 fs by different approaches. First we will reduce the jitter in the current ASOPS approach by optimized electronics, optical feedback and integration of the two lasers on one chip. Second, we will analyze, as a new approach, Optical Sampling by Cavity Tuning (OSCAT) with only one monolithically modelocked diode laser with slow repetition frequency variation.

我们在这个延续项目中的基本目标仍然是开发和实现运行极其紧凑的太赫兹时域采样测量系统。我们的概念基于单片锁模二极管激光器和异步光学采样。在我们的第一种方法中，一个激光二极管与光电导天线结合充当太赫兹发送器，第二个相同的激光二极管与第一个激光二极管同步，但在重复频率略有不同的情况下工作，以便对接收器光电导天线处接收到的太赫兹信号进行异步采样。对于更紧凑的系统，我们的目标是将发送器和接收器激光器集成在一个芯片上，并用光纤处理光电导天线。在我们的第二种新方法中，我们将实现仅具有一个单片锁模激光二极管的 ASOPS 系统。激光二极管的重复频率将缓慢变化，接收器将通过相对于发送器延迟的信号进行选通。这一原理（腔调谐光学采样，OSCAT）将首次使用紧凑型二极管激光器进行演示。在该项目的第一部分，我们展示了第一个基于二极管激光器的 THz-ASOPS 系统。在使用紧凑型锁模外腔激光二极管进行首次演示之后，第一个具有单片锁模二极管和同步电子器件的系统已经建立。除了原理验证之外，我们的研究还表明了我们计划在这个延续项目中解决的概念的主要挑战。这些挑战包括所用激光系统的规格，特别是输出功率、发射脉冲的脉冲宽度以及重复频率的稳定性。对于输出功率，我们计划进一步提高到> 50 mW平均功率，以获得更好的太赫兹信号信噪比。为了优化到达天线的脉冲的脉冲宽度，需要两个步骤：首先，半导体的增益材料必须支持产生具有足够光谱带宽的脉冲，其次，必须压缩激光二极管发射的强啁啾脉冲。为此，我们使用优化的半导体材料，使用啁啾量子阱来获得大增益带宽，并使用具有定制色散和长度的光纤来压缩脉冲。我们的目标是实现低于 500fs 的脉冲宽度和高于 1.5 THz 的太赫兹带宽。重复频率的稳定性是另一个主要挑战。我们计划通过不同的方法实现时间抖动低于 500 fs 的脉冲序列。首先，我们将通过优化电子器件、光学反馈以及在一个芯片上集成两个激光器来减少当前 ASOPS 方法中的抖动。其次，我们将分析一种新方法，即仅使用一个具有缓慢重复频率变化的单片锁模二极管激光器的腔调谐光学采样（OSCAT）。