Omni-Resonance in Broadband Photonics

• Omni-resonance is a wave-engineering paradigm that transforms narrowband resonances into broadband enhancements by tailoring the incident field’s spatiotemporal and spectral-angular structure.
• It employs angular dispersion and precise field pre-conditioning to achieve achromatic resonances, enabling high-fidelity imaging, enhanced nonlinear optical processes, and robust quantum light-matter interactions.
• Experimental realizations in Fabry–Pérot cavities and metamaterial systems demonstrate omni-resonance through broadband imaging, quantum photon coupling, and improved solar cell absorption.

Omni-resonance is a wave-engineering paradigm in which the narrow resonant bandwidth of a photonic, phononic, or electromagnetic system is effectively “unlocked”—enabling broadband field enhancement or absorption while preserving the characteristic benefits of high-Q or high-finesse resonant structures. This is achieved not by modifying the cavity or resonant medium itself, but by tailoring the spatiotemporal or spectral–angular structure of the incident field to match the resonance condition across a broad bandwidth. Omni-resonance breaks the conventional link between cavity photon lifetime and resonance bandwidth, thereby opening new possibilities for broadband nonlinear optics, imaging through resonant structures, quantum light-matter interactions, and unconventional magneto-electric effects.

1. Fundamental Concepts and Definitions

Omni-resonance refers to the transformation of a fundamentally narrow cavity or resonant mode into a broadband (achromatic) resonance by external “pre-conditioning” of the incident field (Shabahang et al., 2016, Hall et al., 2022, Turo et al., 2 Oct 2025, Shiri et al., 13 Oct 2025). In a conventional Fabry–Pérot (FP) or microresonator system, only those spectral components satisfying the resonance condition—set by the longitudinal mode number, cavity thickness, refractive index, and angle of incidence—are transmitted or enhanced. The canonical resonance condition for the FP cavity is: $$\chi(\lambda, \varphi) = \frac{4\pi d}{\lambda} \sqrt{n^2 - \sin^2\varphi} = 2\pi m,$$ where $d$ is the cavity thickness, $n$ is refractive index, $\lambda$ is wavelength, $\varphi$ is external angle, and $m$ is mode index. Omni-resonance is realized by correlating each spectral component with a distinct angle (or spatial frequency) such that the resonance condition is satisfied simultaneously across a broadband spectrum.

This principle extends beyond classical optics. In quantum optics, it allows broadband entangled-photon states—normally filtered out by the narrow resonance—to be fully coupled to a single cavity mode (Turo et al., 2 Oct 2025). In metamaterial systems, “superdimensional” modal engineering can also produce a high-density spectrum of resonances, loosely termed omni-resonance in this context (Greenleaf et al., 2014).

2. Physical Mechanisms and Theoretical Framework

The signature mechanism underlying omni-resonance is the introduction of angular dispersion (AD) or spatiotemporal correlations into the incident field. This is mathematically configured such that the resonance trajectory in wavelength–angle (or frequency–wavevector) space is “de-slanted,” rendering it horizontal and hence achromatic (Shabahang et al., 2016, Hall et al., 2022, Turo et al., 2 Oct 2025). Specifically, for a fixed cavity order $m$,

$$\lambda_m(\varphi) = \frac{2 d}{m} \sqrt{n^2-\sin^2\varphi}.$$

To render the resonance achromatic over bandwidth $\Delta\lambda$, an angular map

$$\varphi(\lambda) = \psi + \beta_m(\lambda - \lambda_c)$$

is imparted, with $\beta_m$ carefully chosen to satisfy the local derivative of the resonance trajectory, and $\psi$ set to align the central wavelength. Nonlinear corrections may be employed for optimal matching (Hall et al., 2022).

In the ultrafast and quantum regimes, spatiotemporally structured pulses (space–time wave packets, STWPs) are synthesized such that each temporal frequency is uniquely paired with a transverse spatial frequency (e.g., via phase-only synthesis on an SLM) (Shiri et al., 2019, Shiri et al., 13 Oct 2025). These pulses obey a hyperbolic constraint: $$n^2(\omega/c)^2-k_x^2 = \left(\frac{m\pi}{d}\right)^2,$$ ensuring all spectral components satisfy the cavity mode condition. In nonlinear systems or nanophotonics, spatial resonance or multidimensional resonance occurs when both spatial phase and frequency of the drive are optimally matched to a normal mode (Wang et al., 2016).

In multi-resonant media, the presence of several closely spaced resonances can lead to constructive interference in the magneto-electric Tellegen response, lifting the usual bound and giving rise to “giant” omni-resonant effects (Seidov et al., 11 Nov 2024).

3. Experimental Realizations

Omni-resonance has been experimentally demonstrated in a range of photonic platforms:

• Broadband imaging and color relay: Using SiO₂ FP cavities (thickness ~2.2 μm; finesse ~85), a 0.5 nm resonance is “stretched” to 130 nm by applying angular dispersion through combinations of gratings and customized lens systems. Two setups—one with aspheric lenses for nonlinear corrections, another with afocal telescopes—deliver broadband imaging over 100 nm with minimal aberrations (Hall et al., 2022).
• Quantum light: In FP cavities (finesse ~100; linewidth ~0.3 nm; FSR ~22 nm), single- and entangled-photon pairs (bandwidth ~20 nm) are rendered omni-resonant via AD pre-conditioning optics and imaging systems, preserving the biphoton spectral/anticorrelation structure (Turo et al., 2 Oct 2025).
• Ultrafast pulses: Space–time wave packets are generated by dispersive optics and SLM-based phase locking, enabling ultrashort pulses to transmit through cavities with linewidths an order of magnitude narrower than their bandwidth, with no temporal broadening (Shiri et al., 2019, Shiri et al., 13 Oct 2025).
• Solar cell integration: Omni-resonant coherent perfect absorption, by matching angular dispersion, doubles the near-infrared photocurrent in thin-film amorphous silicon solar cells embedded in FP cavities over 660–740 nm (Villinger et al., 2019).

A summary table of selected system parameters:

System	Achromatic Bandwidth (nm)	Intrinsic Linewidth (nm)	Free Spectral Range (nm)	Reference
Imaging FP cavity	130	0.5	45	(Hall et al., 2022)
Quantum FP cavity	20	0.3	22	(Turo et al., 2 Oct 2025)
Solar cell FP cavity	80	~0.5	—	(Villinger et al., 2019)

4. Applications and Implications

Omni-resonance has significant implications across wave physics and photonics:

• Broadband resonant imaging: Enables high-fidelity color imaging and relay through high-finesse resonators that would otherwise act as narrowband spectral filters (Hall et al., 2022, Shiri et al., 2022).
• Nonlinear optics: Permits intra-cavity peak intensity enhancement proportional to finesse for entire ultrashort or broadband pulses. This allows resonant broadband enhancement of nonlinear processes such as harmonic generation and two-photon absorption, maintained along cavity lengths much greater than the free-space Rayleigh range (Shiri et al., 13 Oct 2025).
• Photovoltaics and energy harvesting: Overcomes absorption-bandwidth limitations in ultrathin films by leveraging omni-resonant perfect absorption, which directly translates to quantum efficiency gains (Villinger et al., 2019).
• Quantum photonics: Omn-resonant cavities facilitate broadband entangled-photon interactions and quantum-enhanced metrology with preserved nonclassical correlations (Turo et al., 2 Oct 2025).
• Nonreciprocal and Tellegen metamaterials: In multi-resonant atomic or artificial meta-atom systems, omni-resonance underpins unbounded magneto-electric coupling, crucial for nonreciprocal devices (Seidov et al., 11 Nov 2024).

5. Spatial Resolution and Trade-offs

One of the distinctive features of omni-resonant imaging is the interplay between spatial resolution, bandwidth, and cavity finesse:

• Resolution formula: Spatial resolution along the dispersion axis follows

$$\delta x(\lambda) = \frac{\lambda}{\sin\varphi_+ - \sin\varphi_-}$$

where $\varphi_+$ and $\varphi_-$ delimit the angular window set by cavity linewidth and AD (Shiri et al., 2022). Increasing the cavity finesse narrows the spectral linewidth and angular acceptance, potentially degrading resolution, but yields stronger resonant field buildup.

• Negative angular dispersion: Unlike conventional imaging, omni-resonant systems exhibit negative angular dispersion: spatial resolution improves at longer wavelengths, inverting the usual diffraction-limit scaling (Shiri et al., 2022).

6. Limitations, Challenges, and Future Prospects

Despite its promise, omni-resonance faces several challenges:

• Aberration control: Realizing precise angle–wavelength mapping over broad bandwidths requires sophisticated optics (e.g., aspheric, free-form, or metasurface lenses) to minimize spherical and chromatic aberrations (Hall et al., 2022).
• Integration and miniaturization: Most demonstrations rely on bulk optics. Future research will focus on implementing AD using metasurfaces or thin-film photonics for integrated devices, essential for applications such as “solar windows” or on-chip quantum processors (Hall et al., 2022, Turo et al., 2 Oct 2025).
• Bandwidth extension: Practical deployments require further extending omni-resonant operation beyond the full visible or near-infrared, necessitating advanced spectral tailoring and recycling (Hall et al., 2022, Turo et al., 2 Oct 2025).
• Multi-dimensional and multimode control: While most current approaches use one-dimensional angle–wavelength mapping, multidimensional or conical angular dispersions could unlock additional control degrees of freedom for multimode cavities or complex wave manipulation (Turo et al., 2 Oct 2025).
• Optimizing trade-offs: The balance between resonant enhancement (field buildup), bandwidth, spatial resolution, and system complexity must be engineered based on application-specific constraints.

7. Relation to Broader Resonant Phenomena

The concept of omni-resonance is deeply intertwined with other forms of resonance engineering:

• Superdimensional metamaterial resonators: Modal engineering yields high-density resonance spectra by designing spatially varying medium parameters, enabling “superdimensional” omni-resonance for broadband antennas and focusing (Greenleaf et al., 2014).
• Multidimensional resonance: Simultaneous frequency and spatial mode matching yields multidimensional resonance that greatly boosts energy transfer rates in oscillatory systems—a phenomenon related to, though distinct from, angular-dispersion-based omni-resonance (Wang et al., 2016).
• Optomechanical dark modes: In multimode optomechanics, forms of resonance hybridization—distinct but structurally analogous to spectral–angular matching—can produce long-lived dark modes and tripartite resonances (Damskägg et al., 2016).

Omni-resonance thus provides a unifying framework applicable to photonic, quantum-optical, optomechanical, and metamaterial systems, forming the foundation for broadband, resonantly enhanced wave-matter interactions unconstrained by conventional cavity bandwidth limitations.