Electrically tunable THz QCLs

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 113-118).In this thesis, microelectromechanical systems (MEMS) assisted electrically tunable terahertz quantum cascade lasers (THz QCLs) are designed and demonstrated. Two MEMS tuner devices are proposed to achieve electrically tunable THz QCLs. One is the electrostatic comb drive actuated tuner design and the other one is a two-stage flexure design that is actuated by an external piezo nano-positioning actuator. The MEMS tuner devices are all fabricated using standard foundry process SOIMUMPs from MEMSCAP Inc. with some additional in-house post-processings. First order distributed-feedback (DFB) THz wire QCLs with robust mode selectors are designed and fabricated at the MIT Microsystems Technology Laboratories (MTL) using processes developed at our group. By integrating the MEMS tuner chips with the THz QCL chips, broadband electrically tunable THz QCLs are successfully demonstrated. This thesis work provides an important step towards realizing turn-key tunable THz coherent sources for a variety of applications such as THz spectroscopy and THz coherent tomography.by Ningren Han.S.M

Synthetic biology and microbioreactor platforms for programmable production of biologics at the point-of-care

Current biopharmaceutical manufacturing systems are not compatible with portable or distributed production of biologics, as they typically require the development of single biologic-producing cell lines followed by their cultivation at very large scales. Therefore, it remains challenging to treat patients in short time frames, especially in remote locations with limited infrastructure. To overcome these barriers, we developed a platform using genetically engineered Pichia pastoris strains designed to secrete multiple proteins on programmable cues in an integrated, benchtop, millilitre-scale microfluidic device. We use this platform for rapid and switchable production of two biologics from a single yeast strain as specified by the operator. Our results demonstrate selectable and near-single-dose production of these biologics in <24 h with limited infrastructure requirements. We envision that combining this system with analytical, purification and polishing technologies could lead to a small-scale, portable and fully integrated personal biomanufacturing platform that could advance disease treatment at point-of-care

Computational and statistical approaches to optical spectroscopy

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 223-236).Compact and smart optical sensors have had a major impact on people's lives over the last decade. Although the spatial information provided by optical imaging systems has already had a major impact, there is untapped potential in the spectroscopic domain. By transforming molecular information into wavelength-domain data, optical spectroscopy techniques have become some of the most popular scientific tools for examining the composition and nature of materials and chemicals in a non-destructive and non-intrusive manner. However, unlike imaging, spectroscopic techniques have not achieved the same level of penetration due to multiple challenges. These challenges have ranged from a lack of sensitive, miniaturized, and low-cost systems, to the general reliance on domain-specific expertise for interpreting complex spectral signals. In this thesis, we aim to address some of these challenges by combining modern computational and statistical techniques with physical domain knowledge. In particular, we focus on three aspects where computational or statistical knowledge have either enabled realization of a new instrument-with a compact form factor yet still maintaining a competitive performance-or deepened statistical insights of analyte detection and quantification in highly mixed or heterogeneous environments. In the first part, we utilize the non-paraxial Talbot effect to build compact and high-performance spectrometers and wave meters that use computational processing for spectral information retrieval without the need for a full-spectrum calibration process. In the second part, we develop an analyte quantification algorithm for Raman spectroscopy based on spectral shaping modeling. It uses a hierarchical Bayesian inference model and reversible-jump Markov chain Monte Carlo (RJMCMC) computation with a minimum training sample size requirement. In the last part, we numerically investigate the spectral characteristics and signal requirements for universal and predictive non-invasive glucose estimation with Raman spectroscopy, using an in vivo skin Raman spectroscopy dataset. These results provide valuable advancements and insights in bringing forth smart compact optical spectroscopic solutions to real-world applications.by Ningren Han.Ph. D

Microelectromechanical control of the state of quantum cascade laser frequency combs

Chip-scale frequency combs such as those based on quantum cascade lasers (QCLs) or microresonators are attracting tremendous attention because of their potential to solve key challenges in sensing and metrology. Though nonlinearity and proper dispersion engineering can create a comb - light whose lines are perfectly evenly spaced - these devices can enter into different states depending on their history, a critical problem that can necessitate slow and manual intervention. Moreover, their large repetition rates are problematic for applications such as dual comb molecular spectroscopy, requiring gapless tuning of the offset. Here, we show that by blending midinfrared QCL combs with microelectromechanical comb drives, one can directly manipulate the dynamics of the comb and identify new physical effects. Not only do the resulting devices remain on a chip-scale and are able to stably tune over large frequency ranges, but they can also switch between different comb states at extremely high speeds. We use these devices to probe hysteresis in comb formation and develop a protocol for achieving a particular comb state regardless of its initial state.United States. Defense Advanced Research Projects Agency (Grant W31P4Q-16-1-0001

Frequency comb ptychoscopy

Frequency-comb-based multiheterodyne spectroscopy requires that total bandwidth of the measured spectrum covers less than half the comb spacing, which is usually not the case for incoherent spectra. Here, the authors propose a technique that lifts this requirement, and demonstrate it in the microwave regime

Compact and high-precision wavemeters using the Talbot effect and signal processing

Precise knowledge of a laser’s wavelength is crucial for applications from spectroscopy to telecommunications. Here, we present a wavemeter that operates on the Talbot effect. Tone parameter extraction algorithms are used to retrieve the frequency of the periodic signal obtained in the sampled Talbot interferogram. Theoretical performance analysis based on the Cramér–Rao lower bound as well as experimental results are presented and discussed. With this scheme, we experimentally demonstrate a compact and high-precision wavemeter with below 10 pm single-shot estimation uncertainty under the 3–σ criterion around 780 nm

Effective mode selector for tunable terahertz wire lasers

We demonstrate an effective mode selector design that enables a terahertz quantum cascade wire laser to have a robust single-mode operation at frequencies much lower than the gain peak. This is achieved by selectively guiding the undesired modes into a lossy session while keeping the desired lasing mode largely unperturbed. The large mode discrimination obtained by this mode selector is necessary to further extend the tuning range to the lower half of the gain curve. Additionally, the connectors of this mode selector conveniently provide electrical bias to the wire lasers without degrading the lasing performance.National Science Foundation (U.S.)United States. National Aeronautics and Space AdministrationUnited States. Dept. of Energy (Office of Basic Energy Sciences, Energy’s National Nuclear Security Administration, contract DE-AC04-94AL85000

Optomechanical control of quantum cascade laser frequency combs

© 2019 SPIE. Quantum cascade laser-based frequency combs have attracted much attention as of late for applications in sensing and metrology, especially as sources for chip-scale spectroscopy at mid-infrared fingerprint wavelengths. A frequency comb is a light source whose lines are evenly-spaced, and only two frequencies are needed to describe the system - the offset and the repetition rate. Because chip-scale combs have large repetition rates, for many spectroscopic applications is important to be able to change both parameters independently, without substantially changing the comb spectrum or spectral structure. Although it is possible to modulate both the offset and the repetition rate of a comb by tuning the laser current and temperature, both properties affect the laser by changing its index of refraction, and both frequencies will be affected. Here, we show that by integrating a mirror onto a MEMS comb drive, the dispersion and group delay associated with a quantum cascade comb's cavity can be modulated at kilohertz speeds. Because the MEMS mirror primarily affects the group delay of the cavity, it is able to adjust the comb's repetition rate while leaving the offset frequency mostly unaffected. Since this adjustment is linearly independent from current adjustments and can be adjusted quickly, this provides an avenue for mutual stabilization of both parameters. In addition, we show that dynamic modulation of the comb drive is able to allow the laser to recover from comb-destroying feedback, making the resulting comb considerably more robust under realistic conditions