This paper presents a broadband THz generation and detection technique based on high-speed bipolar transistors and PIN diodes that act as fast switches. Traditionally, fsec lasers and photo-conductive antennas are used to produce psec pulses in the time domain. These techniques require an expensive and bulky laser, optical alignment, and moving parts that add to the complexity of the system. To alleviate these issues, laser-free fully electronic THz sources and detectors are designed and fabricated. The source technology can produce THz signals up to 1.1THz with linewidth of 2Hz. The detector technology can capture THz signals up to 500GHz.
To produce and radiate THz pulses, a DC current is passed through an on-chip antenna that acts as an inductor in low frequencies and stores magnetic energy. The DC current is then disconnected with a bipolar transistor in a few psec. This event causes a large voltage transient on the antenna resulting in radiation of pulses with duration of less than 2psec. The produced THz pulse is then radiated with an on-chip antenna. With this method, THz pulses with repetition rate up to 15GHz are generated and radiated. To detect the THz pulses, a silicon-based detector is designed and fabricated. The detector captures THz pulses with an on-chip antenna. The received THz pulse is then sampled by a fast bipolar transistor. In addition to the transistor-based approaches, this presentation will also introduce silicon-based PIN diodes as alternative solutions for THz pulse generation and detection.
Using the source and detector technology developed in this work, several systems are implemented. These systems include a THz gas spectrometer, a hyper-spectral imaging system, a micro-doppler radar, and a wireless communication link. In this presentation, the design, implementation, and performance of these systems will be reported as well.
Here we show two PIC-based prototypes of a photonic convolution layer. System 1) is a Fourier-optics based 4F system integrated into a PIC. Unliked our earlier demonstration of a massively-parallel optical DMD-based CNN layer (Miscuglio, Sorger et al. OPTICA 2020), which processes 1000x1000 pixel matrices in a single time-step at 20KHz update rates (8x faster than SOW GPUs), this first-ever PIC-based 4F processor processes only 10’s of pixels, but at GHz rates (10^6 times faster than DMD, and 10^8 times faster than SLM). System 2) is a PIC-based joint-transform correlator where both the data and the convolution kernel are fed front-end and auto-convolve in the Fourier domain (autocorrelation). Note, the rapid 10GHz update rate of the kernel using foundry PIC components allows to perform online training on the system as well. Rapid and low SWaP ASICs are powerful tools for network edge processing and enable ns-short latency for rapid target tracking, for example.
There is a need for embedded sensor technologies to monitor wellbore integrity in real-time for carbon storage and geothermal applications. Emerging sensing technologies such as optical fiber sensors and wireless sensors have been studied for physical parameter monitoring (e.g. temperature, vibration, and strain) and chemical parameter monitoring (e.g. pH, CO2, corrosion) to monitor structural health of the wellbore. The desirable sensors need to be able to withstand the harsh environments relevant for carbon storage and geothermal wellbores, and they must not inadvertently cause potential sources of wellbore failures. Therefore, we investigated the cement properties with embedded sensors to compare with baseline cement properties, including porosity, permeability, mechanical properties (e.g. Young’s modulus, Poisson’s Ratio, etc), and 3D computed tomography (CT) scans. The sensor devices (optical fiber sensors [OFS] and wireless chip sensors) were embedded in cement cores under wellbore relevant conditions. Then, the cement samples were examined using AutoLab 1500, nitrogen permeability testing, helium porosity testing, and 3D CT scanners. Results show that the cement samples with embedded sensor devices had a slight increase in porosity of 1.5% to 3.6% compared to the blank cement samples. Permeability slightly increased by 0.001 mD with embedded chip sensors. The embedded chip sensors did not significantly change the cement mechanical properties; whereas, the embedded OFS prototypes improved the cement mechanical strengths, e.g. increasing the Young’s modulus by as much as 10% and the bulk modulus by up to 25.5%. CT scans confirmed the proper embedding and good bonding between sensor devices and cement.
Radiation and detection of ultra-short terahertz pulses with picosecond duration advance a variety of applications, including imaging, spectroscopy, and wireless communication. Silicon-based integrated circuits can replace bulky, expensive femtosecond lasers with low-cost solutions to generate and detect THz pulses with GHz repetition rates. In this paper, we present laser-free fully electronic THz pulse sources and detectors to radiate and detect broadband frequency combs in mm-wave and terahertz regimes. A THz pulse radiator chip based on the reverse recovery of a PIN diode is presented. This chip radiates pulses with a tunable repetition rate that can go up to 10.5 GHz. In the frequency domain, the radiated pulses generate a frequency comb that extends up to 1.1 THz. The spacing between the THz tones can be tuned by changing the repetition rates of the pulses to cover the desired frequency range. In addition to the THz comb source, a broadband frequency comb detector chip is presented. The detector chip uses a tunable frequency comb as a reference to sense the spectrum over a wide bandwidth. Single-tone measurements were performed using the detector from 50 GHz to 280 GHz. The source and detector technologies are used to implement a dual-comb sensing system, in which the mm-wave/THz frequency components of the radiated combs are compressed to a small bandwidth in the RF regime.
Performing feature extractions in convolution neural networks for deep-learning tasks is computational expensive in electronics. Fourier optics allows convolutional filtering via dot-product multiplication in the Fourier domain similar to the distributive law in mathematics. Here we experimentally demonstrate convolutional filtering exploiting massive parallelism (10^6 channels, 8-bit at 1kHz) of digital mirror display technology, thus enabling 250 TMAC/s. An FPGA-PCIe board controls the ‘weights’ and handles the data I/O, whereas a high-speed camera detects the inverse-Fourier transformed (2nd lens) data. Gen-1 processes with a total delay (including I/O) of ~1ms, while Gen-2 at 1-10ns leveraging integrated photonics at 10GHz and changing the front-end I/O to a joint-transform-correlator (JTC). These processors are suited for image/pattern recognition, super resolution for geolocalization, or real-time processing in autonomous vehicles or military decision making.
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