THz sources based on intracavity difference frequency generation (DFG) in mid-IR QCL have shown considerable progress in the past few years . When a QCL active region is designed with strong coupling between the lower lasing levels and injector levels; which results in a large nonlinear susceptibility ê•^2, THz emission can be generated within the cavity , Thus, this type of THz source is free from the temperature limitation suffered by the THz QCLs based on direct optical transition, and ideally its working temperature is only limited by the mid-IR QCL which can work well even above 100 Â°C , and can be tuned over a broad waveguide range with broadband heterogeneous active region design . It not only shares the common features of the mid-IR QCLs which are mass reproducible, room temperature operation, low cost, compact size, and high efficiency, but also carries the potential of delivering THz emission with high power in a wide frequency range (4).
An optical frequency comb is a coherent light source whose spectrum consist of a series of discrete, equally spaced frequency lines. A THZ frequency comb capable of high resolution measurement will significantly advance the application of THZ technology in communication spectroscopy, metrology and sensing.
We elaborated a room temperature THZ harmonic frequency comb in 2.2-3.3 THZ based on different â€“frequency generation from a mid-IR QCL comb. The THZ comb is intracavity generated via down converting a mid-IR QCL multimode comb with and integrated single mode mid-IR source based on distributed feedback without using external optical elements (5).
Emerging as high-precision tools, mid-infrared frequency combs based on semiconductor technology platform are exhibiting unique advantages in waveform synthesizing, chemical sensing and biomedical diagnostics. However, they show high instability and strong phase decoherence under external factors such as electrical perturbations or temperature fluctuations, preventing their practical uses in high-precision applications for industrial explorations. we demonstrated experimentally and numerically that by resonantly injecting a radio-frequency (RF) into a high-performance mid-infrared quantum cascade laser (QCL), we are able to greatly stabilize the frequency comb down to hertz level. (6)
This talk will cover recent advances and future trends of semiconductor THZ sources and frequency combs at center for quantum devices (CQD) at Northwestern University.
1- Razeghi. M . Recent progress of widely tunable, CW, THZ sources based QCLs at room temperature. THz Science and Tech. 10.87. (2017)
2- Bai, Y. Bandyopadhyay, N. TSao,S. Slivken, S. and Razeghi, M.
Room temperature quantum cascade lasers with 27% wall plug efficiency. Appl. Phys. Lett. 98, 181102 (20110
3- Bandyopadhyay, N. Bai, Y. Slivken, S. and Razeghi, M. Appl. Phys. Lett, 105, 071106 (2014)
4- S. Slivken, N. Bandyopadhyay, Y. Bai, Q. Y. Lu, and M. Razeghi. Extended electrical turning of quantum cascade lasers with digital concatenated gratings. Appl. Phys. Lett. 103, 231110 (2013)
5- Q. Lu, F. Wang, D. Wu, S Slivken, and M. Razeghi. room temperature terahertz semiconductor frequency comb nature communications (accepted 2019)
6- F. Wang, Q. Lu, S. Slivken, D. Wu, R. McClintock, and M. Razeghi. Stabilization of QCL frequency combs via radio-injection. Submitted to Nature light (2019).
Dr. Razeghi, currently serving as the Director of the Center for Quantum Devices, Northwestern University. She created the Graduate and Undergraduate Programs in Solid State Engineering (SSE) in the ECE Department at Northwestern University, a 12 .course curriculum and also supervised 50 PhD dissertations, 19 MS theses while at Northwestern. Currently supervises approximately 15 PhD students, Post-Docs, Visiting Researchers, and Faculty. Dr. Razeghi is a pioneer in the area of III-V compound semiconductors and optoelectronic devices from the deep ultraviolet to the far infrared spectral bands, including in particular InP and GaAs based semiconductors and devices, which were at the heart of the optical fiber telecommunication revolution of the late 20th Century and the rise of the information age. She is also an expert in quantum devices operating in the deep ultraviolet spectral band, with the demonstration of novel light-emitting diodes, photo detectors and focal plane arrays with world record characteristics. Based on her scientific research work, Dr. Razeghi is the author of 18 books and the author of 31 book chapters. She is the author or co-author of more than 1000 papers and has given more than 1000 invited and plenary talks. She holds 55 patents.