Invited Speakers - Special Sessions

Microfabricated alkali vapor cells are an asset for compact atomic devices but are limited by traditional sealing methods and single-axis optical designs. This work introduces two scalable solutions. First, we present an approach for collectively filling and sealing cesium cells, potentially supporting higher purity and compatibility with anti-relaxation coatings. Then, we report a wafer-level method that creates three orthogonal optical paths using laser-assisted etched glass and thermal reflow. 

We present a fully-integrated, scalable platform for the integration of photonic integrated circuits (PICs) and microfabricated atomic vapor cells. We demonstrate the device performance by interrogation of the rubidium D2 lines via free-space, grating-coupled, and evanescent spectroscopy. 

 We present a simple framework for the ensemble option (Option 2) in the redefinition of the SI second, showing that it corresponds to fixing the barycenter of a constellation of residuals associated with the contributing transitions when expressed in fractional frequency deviations. This linear formulation clarifies the definition, enables straightforward uncertainty propagation using the CCTF recommended frequencies, and naturally supports a full ensemble-based realization of the SI second. 

 This presentation on behalf of the CCTF Task Force on the Roadmap to the Redefinition of the Second will give an update on the work of the task force. The mission is to provide an analysis of the different types of options for the redefinition and of the specific atomic transitions and species that might be used to implement these options. 

 Integrated high power (Watt-level) sources are desired for frequency and time metrology and various other applications such as telecom, medical devices, and remote sensing. We use large-mode-area (LMA) gain waveguides in rare-earth doped gain media to achieve Watt-level output power devices on a SiN on insulator (SiNOI) fabrication platform. We demonstrate a DBR laser with more than 1 Watt output power and various other devices ranging from Q-switched lasers to on-chip mode-locked lasers. 

 The paper reviews the development of photonic integrated circuits integrated with MEMS vapor cells for atomic systems with examples of saturated absorption spectroscopy and cold-atoms in a MEMS cells as demonstrators. 

We showcase the potential for ultralow-noise integrated photonic lasers based on seed laser stabilization to an on-chip spiral interferometer. We achieve a record low Allan deviation for an integrated-chip laser of 5.6×10^-14 corresponding to a linewidth of 12 Hz centered at 1348 nm. 

Photonic integrated circuits based on silicon nitride have been developed that attain losses below 3dB/meter, unlocking applications from microcombs, frequency agile low noise lasers, to parametric amplfiers and femtosecond laser frequency combs on chip based on Erbium. 

 The paper reviews the development of photonic integrated circuits integrated with MEMS vapor cells for atomic systems with examples of saturated absorption spectroscopy and cold-atoms in a MEMS cells as demonstrators. 

 Compact ultrastable lasers have a variety of out-of-the-lab applications in low noise signal synthesis and sensing. We review our work in sub-1 mL vacuum-gap cavities that achieve 4x10-14 fractional frequency stability and on robust laser locking methods for chip-scale lasers. 

Laser cavity-solitons (LCS) arise in nested laser–microresonator systems as self-localized pulsed states sustained by the interplay of Kerr nonlinearity, gain dynamics, and slow nonlocal effects. Here we review their properties, including robust and long-term operation and present our recent results on their metrological features

High-Q microresonators enable access to nonlinear optical phenomena at milliwatt power levels. This capability, now available on CMOS foundry lines, is enabling a new generation of remarkable chip-integrated devices and systems. Following a brief overview of their history and early nonlinear demonstrations, this presentation will highlight recent advances in devices and systems driven by high-Q microresonator technology. Particular emphasis will be placed on the discovery of the photogalvanic effect in silicon nitride, which has unlocked access to second-order nonlinearities in this workhorse photonic integration platform. This capability, previously restricted to non-centrosymmetric dielectrics, is combined with self-injection locking of near-IR telecom lasers to generate high-coherence visible light on chip. The recent demonstration of ultra-high-Q Ge–silica resonators in the visible and violet bands will also be discussed, enabling direct generation of high-coherence visible light. 

This paper reviews the technical influences between MEMS and quartz crystal timing industries in the past two decades. The symbiotic growth between two very different technologies enabled smaller, better, cheaper, and more reliable timing devices.
 

We are in a new era of timing component expansion. ​We are seeing dramatic growth in AI server synchronization, high bandwidth data communication, RF networking, system clocking, and countless internet-of-things. Application complexity is increasing, with higher data rates, tighter synchronization, more protocols, more complex systems, and higher power densities. ​This is driving improvements in stability, holdover, phase noise, jitter, phase alignment, programmability, reliability, size, and power. Innovation is rapid and accelerating.
 

This talk will explore the development of advanced timing references at HRL, focusing on chip-scale quartz clocks and atomic clocks. We will highlight recent progress in quartz oscillators and phononic combs, followed by an introduction to the design and integration of chip-scale atomic beam clocks. These efforts represent significant advancements toward compact, high-performance timing solutions for next-generation technologies.
 

Microwave phononic frequency combs generated with piezoelectric micro-resonators offer a compact route to microwave comb sources and pulse-train synthesis. In this work, we demonstrate phononic frequency comb formation in thin-film lithium niobate (LN) over-moded acoustic resonators, where thermal nonlinearity and strong multi-mode coupling enable cascaded three-wave interactions. By driving a high-frequency acoustic mode near the sum of two lower-frequency modes, we first observe parametric down-conversion into two tones and, at higher drive levels, evenly spaced comb lines around the driven tone and the parametric tones. The comb spacing is tunable with drive conditions and follows the detuning between the driven tone and the parametric sum. In addition to presenting our baseline demonstration, the invited talk will highlight our latest results toward lower-threshold power, broader combs, and improved stability/repeatability, as well as an updated perspective on the role of thermal dynamics and mode coupling in determining the observed operating regimes.
 

This paper reviews CMOS-MEMS technology leveraging internal resonance to exceed linear resonator limits for sensing, security, and communication. By engineering precise frequency ratios between modes, these devices generate mechanical frequency combs via coherent energy transfer. Tracking internal resonance-induced comb spacing enables ultrasensitive thermometers with a temperature coefficient of frequency (TCF) enhancement >30× compared to linear versions. Bistable attractor branches enable "memory-embedded" sensors that record thermal events without continuous power. Security innovations include true random number generators (TRNGs) exploiting chaotic bifurcation and physical unclonable functions (PUFs) using process-variant comb patterns. Finally, the platform demonstrates mechanical feedforward demodulation of BPSK/QPSK signals, eliminating complex PLLs in RF front-ends. Collectively, these works establish internal resonance-driven frequency combs as a versatile mechanism for next-generation integrated CMOS-MEMS hardware.
 

In recent years, our group designed and realized various phononic frequency combs (PFC) and soliton frequency combs in electrostatic and piezoelectric micro and nano electromechanical systems (MEMS & NEMS) [1, 2]. In some case, those realizations exploited opto-electro-mechanical interactions. In others, the interaction was strictly electromechanical. In this talk, I will compare and contrast among the techniques we used to realize them, draw conclusions, lessons learned, and attempt to chart a way forward.

Phononic frequency combs (PFCs) have attracted significant attention recently as analogues of the optical frequency combs (OFCs) with minimal size, weight and power (SWAP) and with electrical in/output, making them attractive candidates for integration with electronics. We report on various methods of generating phononic frequency combs (PFCs) in piezoelectric membrane resonators, both theoretically and experimentally. Our group has shown generation of narrow-bandwidth frequency combs with tunable frequency spacings generated close to the pump frequency, as well as robust wideband frequency combs generated at harmonics of the pump frequency. In this work, I will discuss the essential ingredients in the equations of motion to generate frequency combs in piezoelectric resonators theoretically and provide insight on how to accurately extract the required parameters such as the nonlinear terms and modal couplings. I will then discuss the applications of PFCs, from sensing and metrology to timing.
 

We consider the underlying nonlinear dynamics of mechanical systems that generate time signatures associated with phononic frequency combs (PhFCs). Of particular interest are amplitude and phase modulated responses and the generic bifurcations that produce them as system parameters are varied. Experimentally observed PhFCs are described in terms of canonical models that exhibit these bifurcations. The analysis is centered on use of the rotating wave approximation that expose FCs as limit cycles in a rotating frame of reference. We consider PhFCs in Si-based MEMS and MoS2 membranes that demonstrate Hopf bifurcations, period doubling, and homoclinic connections. Comb properties such as finger spacing, frequency spread, and hysteresis are considered in light of the evolution of the limit cycles.
 

This work presents experimental studies of phononic frequency comb generation in microelectromechanical system (MEMS) resonators. Using piezoelectric circular membrane devices, frequency combs are generated through nonlinear modal interactions under strong electrical excitation. Both degenerate and non-degenerate parametric regimes are observed, leading to multimode spectral response. These results provide an experimental perspective on phononic frequency comb formation in MEMS resonators governed by nonlinear dynamics.

Analog neural networks promise to significantly improve power-efficiency for artificial intelligence computation. However, their deployment is impeded by accuracy limitations stemming from analog component variability and drift. To address these challenges, an in-situ trained MEMS-based analog neural network was developed and shown to achieve more than two orders of magnitude improvement in speed and energy efficiency and exhibit resilience to hardware failures.

In this talk, we describe the operation and modelling of PO-based IMs, showcasing how MEMS technology offers a pathway to enhanced accuracy, shorter time-to-solution, and easier scalability to large scale manufacturing. Next, we will show how PO-based IMs also provide a sustainable pathway to “intelligence” and edge computing in wireless sensing, a crucial priority to successfully and sustainably augment the Internet of Things with Artificial Intelligence. To this end, we will describe the first MEMS-based passive wireless sensor – namely the first “Sensing Parametric Ising Node (SPIN)” –able to implement threshold sensing, accurately and autonomously and directly at the edge, by relying on Ising dynamics.

Photonic Ising machines have the potential to find optimal solutions to combinatorial optimization problems. However, photonic hardware implementations that are simultaneously scalable, reconfigurable, fast, and stable remain elusive. Here, we demonstrate a 200 GOPS programmable, stable, room-temperature photonic Ising machine using cascaded thin-film lithium niobate (TFLN) modulators, a semiconductor optical amplifier, and a digital signal processing engine. Our architecture supports 256 fully connected and >41,000 sparsely connected Ising problems and achieves optimal solutions for benchmarking problems, number partitioning, and lattice protein folding.

This talk will focus on the design challenges that arise in building practical oscillator-based Ising machines, and on the hardware- and algorithm-aware strategies used to address them.