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We demonstrate a novel system that uses a piezoelectric transducer (PZT)-actuated mirror for laser stabilization. A combination of a simple mechanical design and electronic circuits is used to realize an ultra-flat frequency response, which enables an effective feedback bandwidth of 500 kHz. The PZT also performed well when used in a mode-locked laser with a GHz repetition rate, to which it is difficult to apply an electro-optic modulator (EOM).Lying between optical and microwave ranges, the terahertz band in the electromagnetic spectrum is attracting increased attention. Optical fibers are essential for developing the full potential of complex terahertz systems. In this manuscript, we review the optimal materials, the guiding mechanisms, the fabrication methodologies, the characterization methods and the applications of such terahertz waveguides. We examine various optical fiber types including tube fibers, solid core fiber, hollow-core photonic bandgap, anti-resonant fibers, porous-core fibers, metamaterial-based fibers, and their guiding mechanisms. The optimal materials for terahertz applications are discussed. The past and present trends of fabrication methods, including drilling, stacking, extrusion and 3D printing, are elaborated. Fiber characterization methods including different optics for terahertz time-domain spectroscopy (THz-TDS) setups are reviewed and application areas including short-distance data transmission, imaging, sensing, and spectroscopy are discussed.Coherent optical communication provides optical links with a high spectral efficiency and sensitivity. An essential feature of a coherent optical receiver is to phase lock the optical local oscillator to the carrier of the incoming signal. In this work, we propose and demonstrate, for the first time, a novel coherent optical receiver, where the relative instantaneous phase between the incoming optical carrier and a semiconductor laser (SCL), serving as the optical local oscillator, is first detected using a balanced photodiode, filtered, and used in a feed-forward scheme to modify the phase of the optical local oscillator, effectively recovering the input carrier, which is then used for data recovery. The proposed architecture leverages high-performance on-chip photonic devices to realize a low-power coherent optical receiver without utilizing a phase-locked loop and eliminates the required high data-rate ADC, lowering the complexity of the backend DSP. The photonic part of the implemented prototype was integrated on a 180 nm silicon-on-insulator photonic process within a footprint of 1.0 mm × 0.8 mm. Clock and data recovery at 10 GBaud/s with bit-error-rates better than 10-6 and 10-3 for optical BPSK and QPSK have been demonstrated, respectively.W centers are trigonal defects generated by self-ion implantation in silicon that exhibit photoluminescence at 1.218 µm. We have shown previously that they can be used in waveguide-integrated all-silicon light-emitting diodes (LEDs). Here we optimize the implant energy, fluence and anneal conditions to maximize the photoluminescence intensity for W centers implanted in silicon-on-insulator, a substrate suitable for waveguide-integrated devices. After optimization, we observe near two orders of magnitude improvement in photoluminescence intensity relative to the conditions with the stopping range of the implanted ions at the center of the silicon device layer. The previously demonstrated waveguide-integrated LED used implant conditions with the stopping range at the center of this layer. We further show that such light sources can be manufactured at the 300-mm scale by demonstrating photoluminescence of similar intensity from 300 mm silicon-on-insulator wafers. selleck chemical The luminescence uniformity across the entire wafer is within the measurement error.Reliable sensing and accurate location of a weak and small hot spot are critical for applications in industrial infrastructure monitoring. We propose and experimentally demonstrate a practical and reliable distributed hot spot detection method using ultra-weak fiber Bragg gratings (UWFBGs) array and optical time-domain reflectometry (OTDR) based interrogator. To reliably detect the hot spots, the grating spacing of the sensor array is decreased to a similar size of the hot spot. All UWFBGs within a fiber section (FS) are considered as one sensing element, and the wavelength-division multiplexing technique is introduced to reduce crosstalk between adjacent FSs. To retrieve the sensing information, the proposed FS spectrum interrogation method based on OTDR technology is numerically analyzed and experimentally demonstrated. The interrogator exploits the reflection spectrum of each FS instead of each grating, enabling the low-speed hardware implementation of the whole demodulation method. Experimental results show that the expected hot spot can be successfully detected with a sensing resolution of 10 cm and a location resolution of 1 m over a range of 2 km by exploiting 10-ns pulsewidth. Besides, the temperature measurement can be demonstrated with a temperature sensing precision of ± 1°C and a measurement time of 1.5 s, which are meaningful for the early warning of centimeters-sized fire source in some oil and gas pipelines monitoring applications.The changing of snow and glaciers in mountainous areas is a sensitive signature to global warming, and satellite photon-counting laser altimeters provide an effective way to monitor the changing thickness of the snow and ice. Based on the background noise difference between snow/ice-covered areas and bare lands, we proposed a classification method to distinguish snow-covered areas from the raw photons measured by photon-counting laser altimeters in mountainous areas. First, a theoretical noise model was established considering the influence of the sunlight incident direction, the terrain slope, and reflection characteristics of different surfaces. Second, the dynamic thresholds from the proposed theoretical model and the trained thresholds were calculated and tested to classify the along-track land-cover types for the Ice, Cloud, and Elevation Satellite-2 (ICESat-2) photon-counting laser altimeter. Then, the study areas in Aksai Chin in autumn and near Pamirs plateau in winter were selected and the classification method was verified to achieve an overall accuracy of over 93% for both thresholds and areas.
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