Long-working-distance grating coupler for integrated optical devices

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Distortion-corrected phase demodulation using phase-generated carrier with multitone mixing

We present a novel phase generated carrier (PGC) demodulation technique for homodyne interferometers which is robust to modulation depth variations and source intensity fluctuations. By digitally mixing the waveform with a multitone synthetic function (a linear combination of harmonics of the modulating signal), distortion can become negligible even in presence of large variations of the modulation depth. The technique only requires two mixers and can also provide the DC component of the phase in real time, without needing any previously recorded data or ellipse-fitting algorithms. We validate the technique with simulated waveforms and with experimental data from a wavelength metering experiment using an integrated unbalanced interferometer on-chip, showing that the technique corrects distortion without increasing the noise with respect to the standard PGC technique

FPGA-Based High-Speed Optical Fiber Sensor Based on Multitone-Mixing Interferometry

We report a real-time high-speed fiber Bragg grating (FBG) interrogator based on a fiber-optic interferometer. The signal processing is performed by using a low-cost field-programmable gate array (FPGA) system, which is programed to implement a phase-generated carrier (PGC) demodulation algorithm with multitone mixing (MTM) to provide distortion-free signals with high tolerance to modulation depth variations and light intensity fluctuations. The system can stream data at rates up to 1 MS/s and allows multiplexed processing up to two channels. Experimental results show simultaneous measurements of two FBGs, one of which was actuated at frequencies up to 100 kHz. The system features a 3-dB bandwidth of 280 kHz, and a dynamic wavelength resolution of 4.7 fm/Hz ^{mathrm {1/2}}. We also demonstrate a strong reduction of distortion using the MTM approach with respect to the standard technique. Finally, we study the origin of the noise, demonstrating a reduction in common noise sources by using one of the FBGs as a reference. The system can measure FBGs centered at any position within the spectral band of the source, is polarization-independent, and is easily scalable to more than two measurement channels from the same interferometer

Comparison of flipped learning and traditional lecture method for teaching digestive system diseases in undergraduate medicine: A prospective non-randomized controlled trial

Introduction: This study examined the effects of a large-scale flipped learning (FL) approach in an undergraduate course of Digestive System Diseases. Methods: This prospective non-randomized trial recruited 404 students over three academic years. In 2016, the course was taught entirely in a Traditional Lecture (TL) style, in 2017 half of the course (Medical topics) was replaced by FL while the remaining half (Surgical topics) was taught by TL and in 2018, the whole course was taught entirely by FL. Academic performance, class attendance and student’s satisfaction surveys were compared between cohorts. Results: Test scores were higher in the FL module (Medical) than in the TL module (Surgical) in the 2017 cohort but were not different when both components were taught entirely by TL (2016) or by FL (2018). Also, FL increased the probability of reaching superior grades (scores >7.0) and improved class attendance and students’ satisfaction. Conclusion: The holistic FL model is more effective for teaching undergraduate clinical gastroenterology compared to traditional teaching methods and has a positive impact on classroom attendances

High-Speed FBG Interrogation with Electro-Optically Tunable Sagnac Loops

We report high-speed Fiber Bragg Grating (FBG) interrogation based on fiber interferometry. An electro-optical modulator, used as a tunable retarder, is implemented in a fiber Sagnac loop, enabling fast tuning of the interference fringes. Applying an active modulation scheme, the wavelength of the FBG can be retrieved without any requirement of the spectral position of the FBG with respect to the fringes, with no need of tunable sources or spectral analysis. We report experimental results of wavelength measurements with a bandwidth of 100 kHz (only limited by our data acquisition rate) and a dynamic wavelength resolution of σ = 3.7 fm/√Hz (corresponding to a strain resolution of 3.1 nϵ/√Hz). We also show that the system can track a continuous tunable laser sweep of 40 nm along the C-band. The technique is polarization-independent and allows wavelength division multiplexing schemes using only one interferometer for all the sensing points. The system is fully based on low-cost off-the-shelf fiber-optical components, and the free-spectral-range of the interferometer can be easily modified by just changing the length of the polarization-maintaining fiber segment

High-speed FBG interrogator based on fiber interferometry and FPGA real-time processing

We present a high-speed fiber Bragg grating interrogator based on an active Sagnac interferometer and phase-generated-carrier demodulation performed in real time by a low-cost FPGA system. The system has 280kHz detection bandwidth and 1MS/s sampling rate, and implements a multitone-mixing scheme to reduce distortion

Tunneling escape process from a spin-polarized two-dimensional electron system

In this work, we have numerically integrated in space and time the effective-mass nonlinear Schrödinger equation for an electron wave packet in a double barrier heterostructure. Considering both polarized and unpolarized magnetic phases, we have studied the tunneling escape process from the two-dimensional electron gas. Due to the nonlinear effective-mass equation, it is found that the charge trapped dynamically in the quantum well produces a reaction field, which modifies the tunneling escape process in the quantum well. At different electronic sheet densities, we have shown the possibility of having magnetic phase-dependent tunneling rates. © 2001 Elsevier Science Ltd