Harnessing Microwave Photonics for Low Noise and Cryogenic Applications

In many cases, optical systems exhibit orders of magnitude improved performance over their microwave counterparts. For example, optical clocks have much better stability than microwave clocks, and generating picosecond pulses is easy in optics while it is very challenging with electronics. The field of microwave photonics aims to bring such advantages of optical systems to the microwave domain, achieving performance levels beyond the capabilities of conventional electronics. In the work presented here, we show how microwave photonics can be harnessed for low noise microwave generation and cryogenic applications. For low noise microwaves, focus is given to the behavior of photodiode flicker noise, the dominant noise contributor at long timescales, under short pulse illumination. Due to the cyclostationary nature of the noise process, flicker phase noise was found to be lower than flicker amplitude noise by as much as 10 dB, in agreement with our noise model. The cryogenic photonic link experiments were performed with the goal of driving Josephson junction arrays with photonically generated electrical pulse patterns, as required for producing AC voltage standards. This approach can potentially achieve system bandwidths as wide as 100 GHz, which is very difficult to achieve in cryogenic systems driven with traditional methods. With optically driven Josephson junctions, we synthesized a 1 kHz bipolar sine wave. An optical arbitrary pulse pattern generator based on a 2D line-by-line pulse shaper is also shown. The pulse shaper exhibits the highest resolution among programmable pulse shapers of similar designs. With these experiments, we show how microwave photonics can continue to push the state-of-the-art in low noise microwave generation and high-bandwidth signal generation in cryogenic environments.</p

Compact, Portable, Thermal-Noise-Limited Optical Cavity with Low Acceleration Sensitivity

We develop and demonstrate a compact (less than $6$ mL) portable Fabry-P\'{e}rot optical reference cavity. A laser locked to the cavity is thermal noise limited at $2\times10^{-14}$ fractional frequency stability. Broadband feedback control with an electro-optic modulator enables near thermal-noise-limited phase noise performance from $1$ Hz to $10$ kHz offset frequencies. The additional low vibration, temperature, and holding force sensitivity of our design makes it well suited for out-of-the-lab applications such as optically derived low noise microwave generation, compact and mobile optical atomic clocks, and environmental sensing through deployed fiber networks.Comment: 12 pages, 6 figure

Chip-Based Laser with 1 Hertz Integrated Linewidth

Lasers with hertz-level linewidths on timescales up to seconds are critical for precision metrology, timekeeping, and manipulation of quantum systems. Such frequency stability typically relies on bulk-optic lasers and reference cavities, where increased size is leveraged to improve noise performance, but with the trade-off of cost, hand assembly, and limited application environments. On the other hand, planar waveguide lasers and cavities exploit the benefits of CMOS scalability but are fundamentally limited from achieving hertz-level linewidths at longer times by stochastic noise and thermal sensitivity inherent to the waveguide medium. These physical limits have inhibited the development of compact laser systems with frequency noise required for portable optical clocks that have performance well beyond conventional microwave counterparts. In this work, we break this paradigm to demonstrate a compact, high-coherence laser system at 1548 nm with a 1 s integrated linewidth of 1.1 Hz and fractional frequency instability less than 10$^{-14}$ from 1 ms to 1 s. The frequency noise at 1 Hz offset is suppressed by 11 orders of magnitude from that of the free-running diode laser down to the cavity thermal noise limit near 1 Hz$^2$/Hz, decreasing to 10$^{-3}$ Hz$^2$/Hz at 4 kHz offset. This low noise performance leverages wafer-scale integrated lasers together with an 8 mL vacuum-gap cavity that employs micro-fabricated mirrors with sub-angstrom roughness to yield an optical $Q$ of 11.8 billion. Significantly, all the critical components are lithographically defined on planar substrates and hold the potential for parallel high-volume manufacturing. Consequently, this work provides an important advance towards compact lasers with hertz-level linewidths for applications such as portable optical clocks, low-noise RF photonic oscillators, and related communication and navigation systems

Photonic chip-based low noise microwave oscillator

Numerous modern technologies are reliant on the low-phase noise and exquisite timing stability of microwave signals. Substantial progress has been made in the field of microwave photonics, whereby low noise microwave signals are generated by the down-conversion of ultra-stable optical references using a frequency comb. Such systems, however, are constructed with bulk or fiber optics and are difficult to further reduce in size and power consumption. Our work addresses this challenge by leveraging advances in integrated photonics to demonstrate low-noise microwave generation via two-point optical frequency division. Narrow linewidth self-injection locked integrated lasers are stabilized to a miniature Fabry-P\'{e}rot cavity, and the frequency gap between the lasers is divided with an efficient dark-soliton frequency comb. The stabilized output of the microcomb is photodetected to produce a microwave signal at 20 GHz with phase noise of -96 dBc/Hz at 100 Hz offset frequency that decreases to -135 dBc/Hz at 10 kHz offset--values which are unprecedented for an integrated photonic system. All photonic components can be heterogeneously integrated on a single chip, providing a significant advance for the application of photonics to high-precision navigation, communication and timing systems

From the Circle to the Square: Symmetry and Degeneracy in Quantum Mechanics

The relationship between degeneracy and symmetry in quantum mechanics is explored using two dimensional infinite potential wells with boundaries |x|^n + |y|^n = an for n = 2, whose limiting cases are circular (n = 2) and square (n ¿ 8) well. Analytic solutions for the circular and square cases are derived from separation of variables. Boundary element method (BEM) is a numerical method that solves PDEs using boundary conditions. The BEM is used to solve potential well problems. The method is first tested by comparing numerical solutions with analytic solutions for the circular and square wells. For the ground state of the circular well, the error as a function of the number of discretization points N decreased like 1/N^2. As the potential well changed shape from circle to square, energy eigenvalues and degeneracies are tracked. Energy levels split (when degeneracies are lifted), merge, and cross

Successful Smoking Cessation among Women Smokers Based on Utilizing National Smoking Cessation Service Type in Korea

Background: This study aimed to evaluate the successful smoking cessation across different national smoking cessation services. Methods: This study included data that had been previously entered into the integrated information system for smoking cessation services and comprised 144,688 participants after excluding missing data. These clinics provide face-to-face counseling, phone calls, text messages, and e-mail services for six months and nine sessions. Results: The women-only program had the lowest success rate (11.3%). Compared with the women-only program, the six-month success rate of smoking cessation clinic at public health centers (OR = 3.72, CI = [3.52, 3.92]), visiting-type smoking cessation clinics (OR = 2.97, CI = [2.79, 3.16]), the residential 4 -night 5-day program (OR = 7.79, CI = [6.49, 9.35]), and a program for inpatients (OR = 2.36, CI = [1.89, 2.94]) showed a significant increase. Conclusions: Emotional labor workers who participated in the women-only program had low smoking cessation success rates, while those who participated in the residential 4-night 5-day program had high success rates

Spent fuel simulation during dry storage via enhancement of FRAPCON-4.0: Comparison between PWR and SMR and discharge burnup effect

Spent fuel behavior of dry storage was simulated in a continuous state from steady-state operation by modifying FRAPCON-4.0 to incorporate spent fuel–specific fuel behavior models. Spent fuel behavior of a typical PWR was compared with that of NuScale Power Module (NPM™). Current PWR discharge burnup (60 MWd/kgU) gives a sufficient margin to the hoop stress limit of 90 MPa. Most hydrogen precipitation occurs in the first 50 years of dry storage, thereby no extra phenomenological safety factor is identified for extended dry storage up to 100 years. Regulation for spent fuel management can be significantly alleviated for LWR-based SMRs. Hydride embrittlement safety criterion is irrelevant to NuScale spent fuels; they have sufficiently lower plenum pressure and hydrogen contents compared to those of PWRs. Cladding creep out during dry storage reduces the subchannel area with burnup. The most deformed cladding outer diameter after 100 years of dry storage is found to be 9.64 mm for discharge burnup of 70 MWd/kgU. It may deteriorate heat transfer of dry storage by increasing flow resistance and decreasing the view factor of radiative heat transfer. Self-regulated by decreasing rod internal pressure with opening gap, cladding creep out closely reaches the saturated point after ∼50 years of dry storage

Radial hydride fraction with various rod internal pressures and hydrogen contents for Zr-Nb alloy cladding tube

Hydride reorientation experiments for unirradiated Zr-Nb alloy cladding tubes under multi-axial stress states induced by internal pressurization were performed with peak cladding temperature set to 400 degrees C. Applied internal pressure was held constant during cooling down stage. PROPHET was used to analyze Radial Hydride Fraction (RHF) of tested cladding tubes. The attained RHF behavior for a wide range of rod internal pressure (7.5-18.5 MPa) and hydrogen content (0-1100 wppm) were investigated. Empirical models for RHF with respect to rod internal pressure and hydride contents were developed. Ring com-pression tests (RCTs) were conducted to investigate toughness (strain energy density) change with radial hydride formation. In order to take the multi-axial stress effect into account, rod internal pressure-based regulation is necessary. Hydride reorientation threshold rod internal pressure is-9.32 MPa. The rod in-ternal pressure corresponding to hoop stress of 90 MPa is 11.5 MPa, indicating that hydride reorientation in multi-axially stressed Zircaloy cladding tube occurs at hoop stresses below 90 MPa. The presented thermodynamic model for threshold rod internal pressure gives improved agreement with experimen-tally measured threshold with input the directly measured orientation relationship between 8-hydride and a-Zr.(c) 2022 Elsevier B.V. All rights reserved.N

Substance P Hinders Bile Acid-Induced Hepatocellular Injury by Modulating Oxidative Stress and Inflammation

Liver failure is an outcome of chronic liver disease caused by steatohepatitis and cholestatic injury. This study examined substance P (SP) effect on liver injury due to cholestatic stress caused by excessive bile acid (BA) accumulation. Chenodeoxycholic acid (CDCA) was added to HepG2 cells to induce hepatic injury, and cellular alterations were observed within 8 h. After confirming BA-mediated cellular injury, SP was added, and its restorative effect was evaluated through cell viability, reactive oxygen species (ROS)/inflammatory cytokines/endothelial cell media expression, and adjacent liver sinusoidal endothelial cell (LSEC) function. CDCA treatment provoked ROS production, followed by IL-8 and ICAM-1 expression in hepatocytes within 8 h, which accelerated 24 h post-treatment. Caspase-3 signaling was activated, reducing cell viability and promoting alanine aminotransferase release. Interestingly, hepatocyte alteration by CDCA stress could affect LSEC activity by decreasing cell viability and disturbing tube-forming ability. In contrast, SP treatment reduced ROS production and blocked IL-8/ICAM-1 in CDCA-injured hepatocytes. SP treatment ameliorated the effect of CDCA on LSECs, preserving cell viability and function. Collectively, SP could protect hepatocytes and LSECs from BA-induced cellular stress, possibly by modulating oxidative stress and inflammation. These results suggest that SP can be used to treat BA-induced liver injury