Cavity Loss Research Articles

Stimulated emission from hexagonal silicon-germanium nanowires

Hexagonal crystal phase silicon-germanium (hex-SiGe) features efficient direct bandgap emission between 1.5 and 3.4 µm. For expanding its application potential, the key challenge is to demonstrate material gain for enabling a hex-SiGe semiconductor laser. Here we report the transition from the spontaneous emission regime to the stimulated emission-dominated amplified spontaneous emission regime in the optically excited part of a hexagonal Si0.2Ge0.8 nanowire. We observe narrow resonance peaks arising above a spontaneous emission background, which show lasing signatures such as a threshold and a superlinear increase of the emission. A Hakki-Paoli analysis of the height of the cavity resonances provides the gain spectrum of hex-SiGe, showing evidence for a positive material gain. Measurements of the cavity line widths provide an independent assessment of the total cavity loss. While lasing has not been reached, the observation of optical amplification and amplified spontaneous emission provides a clear roadmap toward lasing in hexagonal SiGe. This opens a new pathway for the monolithic integration of a Si-compatible laser within electronic chips.

A gas sensor scheme for CO based on optical-feedback linear-cavity enhanced absorption spectroscopy

Trace gases, especially some toxic trace gases, such as carbon monoxide, are of great value for high-precision detection of their concentration in environmental, safety, and health monitoring. To accurately measure CO gas, a novel spectral technique scheme is developed and demonstrated based on cavity-enhanced absorption spectroscopy with a high-quality linear cavity. The scheme can achieve the equal noise absorption sensitivity of 2.37 × 10−8 cm−1 at the cavity loss of 186 ppm, which can achieve the concentration measurement of 11.7 ppm of CO gas at 1564 nm in the near-infrared band. This approach has the potential for expansion to other gas concentration detection applications and can achieve ppb-ppt level concentration detection.

Black phosphorus film as Q-switcher in neodymium-doped fiber laser

We present the successful development of a 1089.4 nm Q-switched laser employing a neodymium-doped fiber (NDF) as the active fiber and black phosphorus (BP) as the saturable absorber (SA). The BP SA was fabricated by inserting BP compound into a polyvinyl alcohol (PVA) host polymer, exhibiting a saturable absorption of 2.8 %. Integrated into an NDFL ring cavity, the SA modified the cavity loss, enabling the production of Q-switched pulses. With an increase in the 808 nm pumping power from 108.6 to 155.9 mW, the laser output pulse duration decreased from 3.74 to 3.54 μs, while the repetition rate improved from 40.6 to 51.0 kHz. The laser demonstrated a stable pulse train output, with a fundamental frequency signal to background noise ratio of 45.78 dB. The highest pulse energy of 1.3 nJ was recorded at 155.9 mW pump power. To the best of our knowledge, this represents the first utilization of BP as a SA or Q-switcher within an NDFL cavity.

Quantum phase transitions and cat states in cavity-coupled quantum dots

We study double quantum dots coupled to a quasistatic cavity mode with high mode-volume compression allowing for strong light-matter coupling. Besides the cavity-mediated interaction, electrons in different double quantum dots interact with each other via dipole-dipole (Coulomb) interaction. There is a first-order cavity-induced ferroelectric quantum phase transition when the attractive dipolar interaction is smaller than the critical value defined by the energy splitting in DQDs and a smooth transition, otherwise. We show that, in the smooth transition region, both the ground and the first excited states of an array of double quantum dots are cat states. Such states are actively discussed as high-fidelity qubits for quantum computing, and thus our proposal provides a platform for semiconductor implementation of such qubits. We also calculate gauge-invariant observables such as the net dipole moment, the optical conductivity, and the absorption spectrum beyond the semiclassical approximation. The results are robust against cavity losses and variations of system parameters. Published by the American Physical Society 2024

Dynamics of spin-momentum entanglement from superradiant phase transitions

Exploring operational regimes of many-body cavity QED with multilevel atoms remains an exciting research frontier for their enhanced storage capabilities of intralevel quantum correlations. In this work, we consider an experimentally feasible many-body cavity QED model describing a four-level system, where each of those levels is formed from a combination of different spin and momentum states of ultracold atoms in a cavity. The resulting model comprises a pair of Dicke Hamiltonians constructed from pseudospin operators, effectively capturing two intertwined superradiant phase transitions. The phase diagram reveals regions featuring weak and strong entangled states of spin and momentum atomic degrees of freedom. These states exhibit different dynamical responses, ranging from slow to fast relaxation, with the added option of persistent entanglement temporal oscillations. We discuss the role of cavity losses in steering the system's dynamics into such entangled states and propose a readout scheme that leverages different light polarizations within the cavity. Our work paves the way to connect the rich variety of non-equilibrium phase transitions that occur in many-body cavity QED to the buildup of quantum correlations in systems with multilevel atom descriptions. Published by the American Physical Society 2024

Purcell-modified Doppler cooling of quantum emitters inside optical cavities

Standard cavity cooling of atoms or dielectric particles is based on the action of dispersive optical forces in high-finesse cavities. We investigate here a complementary regime characterized by large cavity losses, resembling the standard Doppler cooling technique. For a single two-level emitter a modification of the cooling rate is obtained from the Purcell enhancement of spontaneous emission in the large cooperativity limit. This mechanism is aimed at cooling quantum emitters without closed transitions, which is the case for molecular systems, where the Purcell effect can mitigate the loss of population from the cooling cycle. We extend our analytical formulation to the many-particle case governed by small individual coupling, but exhibiting large collective coupling. Published by the American Physical Society 2024

Weak to strong coupling conditions for a microcavity–quantum dot system under incoherent pumping

We theoretically study the power spectra of a microcavity–quantum dot system under incoherent pumping of photons and excitons, considering two models: one with linked cavity loss rate and pumping, and one with independent cavity loss rate and pumping. We investigate the transition from strong to weak coupling under low and high incoherent pumping in each model and determine sets of parameters necessary to achieve these regimes of light–matter interaction. Despite their differences, both models exhibit a sequence of transitions between weak, strong, and weak coupling as the pumping is increased. This prediction has not yet been observed.

Generation of wavelength-switchable nanosecond mode-locked pulses in an Erbium/Ytterbium co-doped fiber laser cavity

This article experimentally demonstrates the generation of mode-locked (ML) pulses, which can operate either at 1568 nm or 1608 nm in an Erbium/Ytterbium co-doped fiber laser cavity (EYDF). The wavelength switching was achieved by adjusting the cavity loss. Depending on the cavity length and losses, the laser could operate in either mode-locked (ML) or Q-switched (QS) regimes. We explored the characteristics of the QS and ML pulses, based on the pump power, cavity length and loss. The laser produced stable QS pulses with a repetition rate of 22.73 kHz and a width of 12.2 μs at a pump power of 3.1 W at 1608 nm, for a 30 m long cavity. The laser produced 520 ns ML pulses at 1568 nm with a repetition rate of 877 kHz, average output power of 2.15 mW, and energy of 2.45 nJ with an additional single-mode fiber (SMF) length 200 m at the same pump power. The laser could switch to 1608 nm wavelength when the cavity losses were adjusted.

Nonreciprocal routing of microwave photons with broad bandwidth via magnon-cavity chiral coupling.

We propose a scheme for realizing nonreciprocal microwave photon routing with two cascaded magnon-cavity coupled systems, which work around the exceptional points of a parity-time (PT)-symmetric Hamiltonian. An almost perfect nonreciprocal transmission can be achieved with a broad bandwidth, where the transmission for a forward-propagating photon can be flexibly controlled with the backpropagating photon being isolated. The transmission or isolated direction can be reversed via simply controlling the magnetic field direction applied to the magnons. The isolation bandwidth is improved by almost three times in comparison with the device based on a single PT-symmetric system. Moreover, the effect of intrinsic cavity loss and added thermal noises is considered, confirming the experimental feasibility of the nonreciprocal device and potential applications in quantum information processing.

Engineering the passband shape of coupled-cavity filters for low loss and/or narrow bandwidth.

Emerging applications of photonic integrated circuits are calling for extremely narrowband and/or low-insertion-loss bandpass filters. Both properties are limited by cavity losses or intrinsic quality factors. However, the choice of inter-cavity and bus couplings establishes trade-offs between these two properties and the passband shape, which have been little explored. Using the widely used second-order resonant system as an example, we present new, to the best of our knowledge, classes of filter passband shapes that provide the lowest insertion loss and the narrowest bandwidth for a given loss Q. A normalized design and novel properties based on a temporal coupled-mode theory model are presented, including a design tool to apply these results. These results may benefit loss-sensitive filtering applications such as quantum-correlated photon pair sources and RF-photonic integrated circuits.

Extraction method for superimposed coherent transition radiation using Fresnel reflection in a ring-type resonator

To generate terahertz pulses with a high peak power, a pulse train of coherent transition radiation (CTR) is superimposed by circulating it in a ring-type resonator at an L-band electron linear accelerator facility at the Kyoto University Institute for Integrated Radiation and Nuclear Science. By extracting the superimposed CTR pulses from the ring-type resonator via Fresnel reflection on a low-loss parallel substrate, we show that the cavity loss can be suppressed without being affected by the wavenumber of the CTR pulses. The power of the superimposed CTR pulse is increased to approximately four times that of a CTR generated by plane mirrors in the resonator at a wavenumber of 8.5cm−1, where the diffraction loss of the resonator is lower. Using shorter electron bunches to generate CTR pulses with higher wavenumbers increases the amplification factor caused by superposition and allows CTR pulses with a higher peak power to be generated.

Flying-cat parity checks for quantum error correction

Long range, multiqubit parity checks have applications in both quantum error correction and measurement-based entanglement generation. Such parity checks could be performed using qubit-state-dependent phase shifts on propagating pulses of light described by coherent states |α〉 of the electromagnetic field. We consider “flying-cat” parity checks based on an entangling operation that is quantum nondemolition for Schrödinger's cat states |α〉±|−α〉. This operation encodes parity information in the phase of maximally distinguishable coherent states |±α〉, which can be read out using a phase-sensitive measurement of the electromagnetic field. In contrast to many implementations, where single-qubit errors and measurement errors can be treated as independent, photon loss during flying-cat parity checks introduces errors on physical qubits at a rate that is anticorrelated with the probability for measurement errors. We analyze this trade-off for three-qubit parity checks, which are a requirement for universal fault-tolerant quantum computing with the subsystem surface code. We further show how a six-qubit entangled “tetrahedron” state can be prepared using these three-qubit parity checks. The tetrahedron state can be used as a resource for controlled quantum teleportation of a two-qubit state or as a source of shared randomness with potential applications in three-party quantum key distribution. Finally, we provide conditions for performing high-quality flying-cat parity checks in a state-of-the-art circuit QED architecture, accounting for qubit decoherence, internal cavity losses, and finite-duration pulses, in addition to transmission losses. Published by the American Physical Society 2024

Tunable gain clamping L-band erbium-doped fiber amplifier based on FBG and BBM

An improved structure for the L-band Erbium-doped fiber amplifier (EDFA) with gain clamping is suggested to address gain instability resulting from variations in the number of optical channels and the compromised gain clamping performance due to misalignment in the center wavelength of the grating. Here, a linear resonant cavity is formed by a broad-band mirror (BBM) and fiber Bragg grating (FBG), and a variable optical attenuator (VOA) is used for cavity loss adjustment. Experimental results show that the L-band EDFA solves the problem that the center wavelength of the narrowband grating pairs needs to be consistent. The 20 dB gain bandwidth is 42 nm(1582 ∼ 1623 nm). For signal at 1605 nm, the gain can be tuned from 28.8 to 34.8 dB, and a 40 dB (−50 to −10 dBm) gain clamped dynamic range is obtained at the gain of 28.8 dB, with stability of ± 0.25 dB, for which noise figure (NF) is less than 5.3 dB.

Quantum catalysis in cavity quantum electrodynamics

Catalysis plays a key role in many scientific areas, most notably in chemistry and biology. Here we present a catalytic process in a paradigmatic quantum optics setup, namely the Jaynes-Cummings model, where an atom interacts with an optical cavity. The atom plays the role of the catalyst, and it allows for the deterministic generation of nonclassical light in the cavity. Considering a cavity prepared in a “classical” coherent state, and choosing appropriately the atomic state and the interaction time, we obtain an evolution with the following properties. First, the state of the cavity has been modified, and it now features nonclassicality, as witnessed by sub-Poissonian statistics or Wigner negativity. Second, the process is catalytic in the sense that the atom is deterministically returned to its initial state exactly, and it can be reused multiple times. What is more, we also show that our findings are robust under dissipation and can be applied to scenarios featuring cavity loss and atomic decay. Finally, we investigate the mechanism of this catalytic process, in particular highlighting the key role of correlations and quantum coherence. Published by the American Physical Society 2024

Improvement of photothermal heating efficiency of Si plasmonic waveguide heaters with ring resonators

We report improved photothermal heating efficiency of Si plasmonic waveguide heaters integrated with ring resonators by enhancing the interaction of the propagating light and metal with a thinner buffer layer. The resonance wavelength was shifted towards a longer wavelength by inputting transverse magnetic mode light, and the amount of shift was influenced by the length of the region deposited with the Co thin film and the gap of the directional coupler. The local temperature rise of 580 K was achieved by injecting 6.3 mW of light, and photothermal conversion efficiency as high as 106 K mW−1 was obtained in a Si plasmonic waveguide deposited with 0.5 μm long Co thin films, showing improvement compared with previous devices. Discussion on the heating efficiency based on the propagation loss and cavity loss in the ring resonators is given based on experimental results, to realize compact photothermal waveguide heaters for various applications.

Design and Analysis of a Narrow Linewidth Laser Based on a Triple Euler Gradient Resonant Ring

We designed a narrow-linewidth external-cavity hybrid laser leveraging a silicon-on-insulator triple Euler gradient resonant ring. The laser’s outer cavity incorporates a compact, high-Q resonant ring with low loss. The straight waveguide part of the resonant ring adopts a width of 1.6 μm to ensure low loss transmission. The curved section is designed as an Euler gradient curved waveguide, which is beneficial for low loss and stable single-mode transmission. The design features an effective bending radius of only 26.35 μm, which significantly improves the compactness of the resonant ring and, in turn, reduces the overall footprint of the outer cavity chip. To bolster the laser power and cater to the varying shapes of semiconductor optical amplifier (SOA) spots, we designed a multi-tip edge coupler. Theoretical analysis indicates that this edge coupler can achieve an optical coupling efficiency of 85%. It also reveals that the edge coupler provides 3 dB vertical and horizontal alignment tolerances of 0.76 μm and 2.4 μm, respectively, for a spot with a beam waist radius of 1.98 μm × 0.99 μm. The outer cavity, designed with an Euler gradient micro-ring, can achieve a side-mode suppression ratio (SMSR) of 30 dB within a tuning range of 100 nm, with a round-trip loss of the entire cavity at 1.12 dB, and an expected theoretical laser linewidth of 300 Hz.

Osteological profiling of femoral diaphysis and neck in aquatic, semiaquatic, and terrestrial carnivores and rodents: effects of body size and locomotor habits

The increased limb bone density documented previously for aquatic tetrapods has been proposed to be an adaptation to overcome buoyancy during swimming and diving. It can be achieved by increasing the amount of bone deposition or by reducing the amount of bone resorption, leading to cortical thickening, loss of medullary cavity, and compaction of trabecular bone. The present study examined the effects of locomotor habit, body size, and phylogeny on the densitometric, cross-sectional, and biomechanical traits of femoral diaphysis and neck in terrestrial, semiaquatic, and aquatic carnivores, and in terrestrial and semiaquatic rodents (12 species) by using peripheral quantitative computed tomography, three-point bending, and femoral neck loading tests. Groupwise differences were analyzed with the univariate generalized linear model and the multivariate linear discriminant analysis supplemented with hierarchical clustering. While none of the individual features could separate the lifestyles or species adequately, the combinations of multiple features produced very good or excellent classifications and clusterings. In the phocid seals, the aquatic niche allowed for lower femoral bone mineral densities than expected based on the body mass alone. The semiaquatic mammals mostly had high bone mineral densities compared to the terrestrial species, which could be considered an adaptation to overcome buoyancy during swimming and shallow diving. Generally, it seems that different osteological properties at the levels of mineral density and biomechanics could be compatible with the adaptation to aquatic, semiaquatic, or terrestrial niches.

Extracting kinetic information from short-time trajectories: relaxation and disorder of lossy cavity polaritons

Abstract The emerging field of molecular cavity polaritons has stimulated a surge of experimental and theoretical activities and presents a unique opportunity to develop the many-body simulation methodology. This paper presents a numerical scheme for the extraction of key kinetic information of lossy cavity polaritons based on the transfer tensor method (TTM). Steady state, relaxation timescales, and oscillatory phenomena can all be deduced directly from a set of transfer tensors without the need for long-time simulation. Moreover, we generalize TTM to disordered systems by sampling dynamical maps and achieve fast convergence to disordered-averaged dynamics using a small set of realizations. Together, these techniques provide a toolbox for characterizing the interplay of cavity loss, disorder, and cooperativity in polariton relaxation and allow us to predict unusual dependences on the initial excitation state, photon decay rate, strength of disorder, and the type of cavity models. Thus, using the example of cavity polaritons, we have demonstrated significant potential in the use of the TTM toward both the efficient computation of long-time polariton dynamics and the extraction of crucial kinetic information about polariton relaxation from a small set of short-time trajectories.

From weak to strong coupling: quasi-BIC metasurfaces for mid-infrared light-matter interactions.

Thanks to their giant, yet tunable, Q-factor resonances, all-dielectric metasurfaces supporting the quasi-bound states in the continuum (q-BIC) resonances are well-suited to provide a promising platform for quantum-coherent light-matter interactions. Yet, the strong coupling regime, characterized by the hybrid light-matter states - polaritons, has not yet been fully explored in the mid-infrared regime. This paper investigates the parameter space of vibrational strong coupling (VSC) between material and metasurface cavities supporting q-BIC resonances in the mid-infrared spectral range. We outline the effects of transition dipole strength, damping rate, and the number of molecules coupled to a single cavity, as well as the cavity damping rates, to understand their respective impacts on VSC. By tuning the Q-factor of the metasurface and material parameters, a new transition light-matter coupling zone is introduced, bridging the gap between weak and strong coupling, where polaritons form but their linewidths prohibit their spectral identification. The study further identifies the effects of cavity linewidth on polariton peak separability in strongly coupled systems, highlighting that the cavities with smaller nonradiative losses and narrower linewidths facilitate better polariton separability. Moreover, we found that matching cavity and material loss, satisfying the critical strong coupling condition, enhances the coupling strength between cavity and material. Overall, these findings can guide the design of photonic cavities suited for VSC experiments, contributing to the burgeoning fields of polaritonic chemistry, light-mediated modulation of chemical reactivity, and highly sensitive molecular spectroscopy.

An In Situ-Gelling Conductive Hydrogel for Potential Use in Neural Tissue Engineering.

Cerebral cavitation is usual following acute brain injuries, such as stroke and traumatic brain injuries, as well as after tumor resection. Minimally invasive implantation of an injectable scaffold in the cavity is a promising approach for potential regeneration of tissue loss. This study aimed at designing an in situ-gelling conductive hydrogel containing silk fibroin (SF), brain decellularized extracellular matrix (dECM), and carbon nanotubes (CNT) for potential use in brain tissue regeneration. Two percent w/v SF hydrogels with different concentrations of dECM (0.1%, 0.2%, or 0.3% w/v) and CNTs (0.05%, 0.1%, or 0.25% w/v) were fabricated and characterized. It was observed that with the addition of dECM, the porosity decreased, whereas swelling and electrical conductivity tended to increase. The addition of dECM also led to a faster resorption rate, but no significant change in compressive modulus. Addition of CNTs, on the other hand, led to a denser, stronger, and more regular porous structure, higher swelling ratio, faster gelation time, slower degradation rate, and a significant increase in electrical conductivity. dECM and CNTs combined together resulted in superior porosity, swelling, resorption rate, mechanical properties, and electrical conductivity compared with SF scaffolds containing only dECM or CNTs. Hydrogel samples containing 2% SF, 0.3% dECM, and 0.1% CNTs had a high porosity (58.9%), low swelling ratio (15.9%), high conductivity (2.35 × 10-4 S/m), and moderate degradation rate (37.3% after 21 days), appropriate for neural tissue engineering applications. Cell evaluation studies also showed that the hydrogel systems support the cell adhesion and growth, with no sign of significant cytotoxicity. Impact statement Tissue loss and formation of a fluid-filled cavity following stroke, traumatic brain injury, or brain tumor resection lead to sensorimotor and/or cognitive deficits. The lack of a healthy extracellular matrix in the cavity avoids the endogenous cell migration and axonal sprouting and may also worsen the secondary injuries to peri-lesional tissue. Due to the brain anatomy, simple implantation of tissue engineering scaffolds to the injured site is not possible in many cases. Therefore, the development of injectable scaffolds that support neural growth and differentiation is crucial for tissue repair or limiting the expansion of damage region.