A.Douglas Stone

• Professor
• Yale University

Over the past two decades there have been tremendous advances in high-power fiber lasers, which have provided a powerful tool for science, engineering and defense. A major roadblock for further power scaling of single-frequency fiber laser amplifiers is stimulated Brillouin scattering. Intense efforts were devoted to mitigate this nonlinear process...

In many linear and nonlinear systems, time-reversal symmetry makes it possible to control the output waves by appropriately shaping the input waves. However, time-reversal symmetry is broken in systems with energy dissipation, necessitating a different approach for relating the input and output fields. We theoretically consider a saturated multimod...

Filter synthesis is an inverse problem that is traditionally approached rationally by engineering the coupling between selected pairs of lumped resonators. The implicit restriction to spatially disjoint resonators strongly limits the design space, making it challenging to build extremely tunable filters. Here, agile free‐form signal filtering and r...

Wavefront shaping has become a powerful tool for manipulating light propagation in various complex media undergoing linear scattering. Controlling nonlinear optical interactions with spatial degrees of freedom is a relatively recent but fast growing area of research. A wavefront-shaping-based approach can be used to suppress nonlinear stimulated Br...

Multimode fibers provide a promising platform for realizing high-power laser amplifiers with suppressed nonlinearities and instabilities. The potential degradation of optical beam quality has been a major concern for highly multimode fiber amplifiers. We show numerically that the beam propagation factor M2 of a single-frequency multimode fiber ampl...

Stimulated Brillouin scattering (SBS) is often an unwanted loss mechanism in both active and passive fibers. Highly multimode excitation of fibers has been proposed as a novel route toward efficient SBS suppression. Here, we develop a detailed, quantitative theory which confirms this proposal and elucidates the physical mechanisms involved. Startin...

Wavefront shaping has become a powerful tool for manipulating light propagation in various complex media undergoing linear scattering. Controlling nonlinear optical interactions with spatial degrees of freedom is a relatively recent but growing area of research. A wavefront-shaping-based approach can be used to suppress nonlinear stimulated Brillou...

Filter synthesis is an inverse problem that is traditionally approached rationally by considering spatially disjoint resonators, approximating them as lumped elements, and engineering the coupling of selected pairs. This approach strongly limits the design space, making it challenging to build extremely tunable filters. Here, we demonstrate agile f...

Transverse Mode Instability (TMI) that results from dynamic nonlinear thermo-optical scattering is the primary limitation to power scaling in high-power fiber lasers and amplifiers. It has been proposed that TMI can be suppressed by exciting multiple modes in a highly multimode fiber. We derive a semi-analytic frequency-domain theory of the thresho...

We study a system tuned to an absorbing exceptional point and explore its use to efficiently receive and store an incoming wave with an envelope different from the absorbing-eigenmode envelope. Specifically, while absorbing states of lossless resonators have an exponentially increasing envelope, we focus on capturing naturally emitted waves with an...

We show that a laser at threshold can be utilized to generate the class of coherent and transform-limited waveforms (vt−z)mei(kz−ωt) at optical frequencies. We derive these properties analytically and demonstrate them in semiclassical time-domain laser simulations. We then utilize these waveforms to expand other waveforms with high modulation frequ...

We demonstrate a single-frequency multimode-fiber amplifier free of stimulated Brillouin scattering up to 474 W. The optical efficiency is 89 % and spectral linewidth is 19.8 kHz. We focus the output beam using input wavefront shaping.

We demonstrate a general and powerful approach based on coherent multimode excitation to suppress various nonlinear instabilities in optical fibers, including stimulated Brillouin scattering (SBS) and transverse mode instability (TMI).

We propose an efficient method of maintaining high beam quality of a highly multimode fiber amplifier by full-field wavefront shaping of a coherent seed. This approach strongly suppresses the stimulated Brillouin scattering through multimode excitation.

We show that a cavity at an absorbing exceptional point captures additional temporal orders of any incoming waveform, resulting in efficient passive state transfer and photon detection.

The key challenge for high-power delivery through optical fibers is overcoming nonlinear optical effects. To keep a smooth output beam, most techniques for mitigating optical nonlinearities are restricted to single-mode fibers. Moving out of the single-mode paradigm, we show experimentally that wavefront-shaping of coherent input light to a highly...

Transverse Mode Instability (TMI) which results from dynamic nonlinear thermo-optical scattering is the primary limitation to power scaling in high-power fiber lasers and amplifiers. It has been proposed that TMI can be suppressed by exciting multiple modes in a highly multimode fiber. We derive a semi-analytic frequency-domain theory of the thresh...

Non-Hermitian optics is a burgeoning field at the intersection of quantum physics, electrodynamics, and nanophotonics. It provides a new perspective of the role of gain and loss in optical systems. Leveraging the advanced designs inspired by non-Hermitian physics, classical optical platforms have been widely investigated to unveil novel physical co...

Above-barrier quantum scattering with truncated real potentials V(x)=−|x|p provides an experimentally accessible platform that exhibits spontaneous parity-time symmetry breaking as p is varied. The unbroken phase has reflectionless states that correspond to bound states in the continuum of the nontruncated potentials at arbitrarily high discrete re...

We show that a laser at threshold can be utilized to generate the class of dispersionless waveforms $\left(vt-z\right)^{m}e^{i\left(kz-\omega t\right)}$ at optical frequencies.We derive these properties analytically and demonstrate them in semiclassical time-domain laser simulations. We then utilize these waveforms to expand other waveforms with hi...

High-power fiber laser amplifiers have enabled an increasing range of applications in industry, science, and defense. The power scaling for fiber amplifiers is currently limited by transverse mode instability. Most techniques for suppressing the instability are based on single- or few-mode fibers in order to output a clean collimated beam. Here, we...

The key challenge for high-power delivery through optical fibers is overcoming nonlinear optical effects. To keep a smooth output beam, most techniques for mitigating optical nonlinearities are restricted to single-mode fibers. Moving out of the single-mode paradigm, we show experimentally that wavefront-shaping of coherent input light that is inci...

Stimulated Brillouin scattering (SBS) is an important nonlinear optical effect which can both enable and impede optical processes in guided wave systems. Highly multi-mode excitation of fibers has been proposed as a novel route towards efficient suppression of SBS in both active and passive fibers. To study the effects of multimode excitation gener...

We demonstrate experimentally that reflectionless scattering modes (RSMs), a generalized version of coherent perfect absorption, can be functionalized to perform reflectionless programmable signal routing. We achieve versatile programmability both in terms of operating frequencies and routing functionality with negligible reflection upon in-couplin...

We present a theory of TMI threshold for highly multimode excitations in fiber amplifiers with gain saturation. We show TMI threshold increases 6-fold when all 30-modes are excited equally in a 2D waveguide, compared to fundamental mode-only excitation.

We present a general analysis for finding and characterizing nonlinear exceptional point (EP) lasers above threshold using steady-state ab initio Maxwell–Bloch equations. For a system of coupled slabs, we show that a nonlinear EP is obtained for a given ratio between the external pumps in each resonator and that it is associated with a kink in the...

We demonstrate experimentally that reflectionless scattering modes (RSMs), a generalized version of coherent perfect absorption, can be functionalized to perform reflectionless programmable signal routing. We achieve versatile programmability both in terms of operating frequencies and routing functionality with negligible reflection upon in-couplin...

We analyze the time-domain dynamics of resonators supporting exceptional points (EPs), at which both the eigenfrequencies and the eigenmodes associated with perfect capture of an input wave coalesce. We find that a time-domain signature of the EP is an expansion of the class of waveforms which can be perfectly captured. We show that such resonators...

A class of above-barrier quantum-scattering problems is shown to provide an experimentally-accessible platform for studying $\mathcal{PT}$-symmetric Schr\"odinger equations that exhibit spontaneous $\mathcal{PT}$ symmetry breaking despite having purely real potentials. These potentials are one-dimensional, inverted, and unstable and have the form $...

High-power fiber laser amplifiers have enabled an increasing range of applications in industry, medicine and defense. The power scaling for narrow-band amplifiers is currently limited by the transverse modal instability. Various techniques have been developed to suppress the instability in a single or few-mode fiber in order to output a clean, coll...

We present a general analysis for finding and characterizing nonlinear exceptional point (EP) lasers above threshold. Using coupled mode theory and the steady-state nonlinear Maxwell-Bloch equations, we show that, for a system of coupled slabs, a nonlinear EP is obtained for a given ratio between the external pumps in each resonator, and that it is...

The response of physical systems to waves is usually analyzed using eigenmodes and their eigenfrequencies, which, in electrodynamics, are associated with lasing and perfect absorption phenomena. Non-Hermitian degeneracies with coalescing eigenvalues and eigenmodes, known as exceptional points (EPs), lead to a qualitatively different response, which...

We experimentally demonstrate efficient suppression of stimulated Brillouin scattering in multimode fibers. By distributing the power in a number of high-order modes, the SBS threshold is three times as much as that for fundamental-mode-only excitation.

We demonstrate numerically and theoretically that the transverse-mode stability for a high-power fiber amplifier is greatly increased via simultaneous excitation of many high-order modes, while the amplified light maintains spatially coherent and high beam quality.

We demonstrate theoretically that SBS threshold can be increased significantly by many-mode excitations in multimode fibers. We experimentally focus multimode excitation to a diffraction limited spot, leading to high SBS threshold with good beam quality.

We find that a time-domain signature of a bsorbing exceptional points is an expansion of the class of perfectly captured waveforms, improved performance for storage or transduction of energy, and conversion between waveforms within this class.

Stimulated Brillouin scattering (SBS) induced by narrow-linewidth high power pulses in a multimode fiber (MMF) is suppressed via controlling the input wavefront, presenting a new route to scaling power in high power fiber amplifiers.

We numerically and experimentally demonstrate that spreading power into higher order modes of a multimode optical fiber can be used to suppress stimulated Brillouin scattering for a high-power narrow linewidth system. This opens the opportunity for suppressing nonlinear effects in fibers using adaptive mode launching techniques while retaining the...

The polarization of optical fields is a crucial degree of freedom in the all-optical analogue of electromagnetically induced transparency (EIT). However, the physical origins of EIT and polarization induced phenomena have not been well distinguished, which can lead to confusion in associated applications such as slow light and optical/quantum stora...

The past few years have witnessed growing interests in exceptional points (EPs) in various domains, including photonics, acoustics and electronics. However, EPs have mainly been realized based on the degeneracy of resonances of physical systems; distinct degeneracies occur relating to the absorption properties of waves, with distinct physical manif...

Absorbingly exceptional Most oscillating systems have a resonance or multiple resonances at which they ring out and are most sensitive to excitation. In non-Hermitian systems, open systems with gain and loss, the resonances have been found to coalesce into an exceptional point when the gain and loss can be engineered. Complementing these resonant e...

Significance Electromagnetically induced transparency (EIT) describes the phenomenon that an opaque optical medium becomes transparent due to interference effects. EIT plays a pivotal role in engineering slow light and quantum memory. However, polarization effects could cause similar phenomena and therefore were considered as EIT occasionally. We i...

We develop the theory of a special type of scattering state in which a set of asymptotic channels is chosen as inputs, and the complementary set is chosen as outputs, and there is zero reflection back into the input channels at specific frequencies. These states define perfectly impedance-matched input wavefronts for arbitrary finite scattering str...

We outline a recently developed theory of impedance-matching, or reflectionless excitation of arbitrary finite photonic structures in any dimension. It describes the necessary and sufficient conditions for perfectly reflectionless excitation to be possible, and specifies how many physical parameters must be tuned to achieve this. In the absence of...

We outline and interpret a recently developed theory of impedance matching or reflectionless excitation of arbitrary finite photonic structures in any dimension. The theory includes both the case of guided wave and free-space excitation. It describes the necessary and sufficient conditions for perfectly reflectionless excitation to be possible and...

Electromagnetically induced transparency, as a quantum interference effect to eliminate optical absorption in an opaque medium, has found extensive applications in slow-light generation, optical storage, frequency conversion, optical quantum memory and enhanced nonlinear interactions at the few-photon level in all kinds of systems. Recently, there...

We investigate experimentally and theoretically the lasing behavior of dielectric microcavity lasers with chaotic ray dynamics. Experiments show multimode lasing for both D-shaped and stadium-shaped wave-chaotic cavities. Theoretical calculations also find multimode lasing for different shapes, sizes, and refractive indices. While there are quantit...

Electromagnetically induced transparency, as a quantum interference effect to eliminate optical absorption in an opaque medium, has found extensive applications in slow light generation, optical storage, frequency conversion, optical quantum memory as well as enhanced nonlinear interactions at the few-photon level in all kinds of systems. Recently,...

Open quantum systems can have exceptional points (EPs), degeneracies where both eigenvalues and eigenvectors coalesce. Recently, it has been proposed and demonstrated that EPs can enhance the performance of sensors in terms of amplification of a detected signal. However, typically amplification of signals also increases the system noise, and it has...

We develop the theory of a special type of scattering state in which a set of asymptotic channels are chosen as inputs and the complementary set as outputs, and there is zero reflection back into the input channels. In general an infinite number of such solutions exist at discrete complex frequencies. Our results apply to linear electromagnetic and...

We investigate experimentally and theoretically the lasing behavior of dielectric microcavity lasers with chaotic ray dynamics. Experiments show multimode lasing for both D-shaped and stadium-shaped wave-chaotic cavities. Theoretical calculations also find multimode lasing for different shapes, sizes and refractive indices. While there are quantita...

We identify a new kind of physically realizable exceptional point (EP) corresponding to degenerate coherent perfect absorption, in which two purely incoming solutions of the wave operator for electromagnetic or acoustic waves coalesce to a single state. Such non-Hermitian degeneracies can occur at a real-valued frequency without any associated nois...

We identify a new kind of physically realizable exceptional point (EP) corresponding to degenerate coherent perfect absorption, in which two purely incoming solutions of the wave operator for electromagnetic or acoustic waves coalesce to a single state. Such non-hermitian degeneracies can occur at a real-valued frequency without any associated nois...

Distinct from closed quantum systems, non-Hermitian system can have exceptional points (EPs) where both eigenvalues and eigenvectors coalesce. Recently, it has been proposed and demonstrated that EPs can enhance the performance of sensors in terms of amplification of detected signal. Meanwhile, the noise might also be amplified at EPs and it is not...

We point out that the polarization state of radiation from a photonic crystal slab is strongly constrained by the direct non-resonant scattering process. The phase difference between the two linearly-polarized components in the far field can be predicted analytically and is largely independent of the periodic pattern. We verify the prediction with...

A fundamental challenge in physics is controlling the propagation of waves in disordered media despite strong scattering from inhomogeneities. Spatial light modulators enable one to synthesize (shape) the incident wavefront, optimizing the multipath interference to achieve a specific behaviour such as focusing light to a target region. However, the...

Investigating the optical response of a lasing cavity to a probe signal not coinciding with the lasing wavelength can give rise to paradoxes. We address this question experimentally along with steady-state ab-initio laser theory.

Behavior of a self-oscillating cavity probed with an externally incident field has been the subject of controversy for decades. We address this issue by designing an experiment, and verify it with state-state ab-initio laser theory.

We introduce a simplified version of the steady-state ab initio laser theory for calculating the effects of mode competition in continuous wave lasers using the passive cavity resonances. This new theory harnesses widely available numerical methods that can efficiently calculate the passive cavity resonances, with negligible additional computationa...

Remote entanglement of distant, noninteracting quantum entities is a key primitive for quantum information processing. We present a protocol to remotely entangle two stationary qubits by first entangling them with propagating ancilla qubits and then performing a joint two-qubit measurement on the ancillas. Subsequently, single-qubit measurements ar...

We introduce a simplified version of the steady-state ab initio laser theory for calculating the effects of mode competition in continuous wave lasers using the passive cavity resonances. This new theory harnesses widely available numerical methods that can efficiently calculate the passive cavity resonances, with negligible additional computationa...

In this talk we discuss two novel effects in steady state microlasers. The first one is interaction-induced mode switching (IMS), where the onset of a new lasing mode switches off an existing mode via a negative power slope. It's a deterministic effect in steady state lasing and caused by cross saturation of the gain medium, hence it's different fr...

We show from ab initio laser theory that by choosing an appropriate spatial pump profile, many different spatial modes of a typical microlaser can be turned on at the same pump energy, substantially increasing the number, N, of simultaneous lasing modes. The optimal pump profile can be obtained simply from knowledge of the space-dependent saturated...

We show from ab initio laser theory that by choosing an appropriate spatial pump profile, many different spatial modes of a typical microlaser can be turned on at the same pump energy, substantially increasing the number, N, of simultaneous lasing modes. The optimal pump profile can be obtained simply from knowledge of the space-dependent saturated...

A fundamental challenge in physics is controlling the propagation of waves in disordered media despite strong scattering from inhomogeneities. Spatial light modulators enable one to synthesize (shape) the incident wavefront, optimizing the multipath interference to achieve a specific behavior such as focusing light to a target region. However, the...

Bound states in the continuum (BICs) are waves that remain localized even though they coexist with a continuous spectrum of radiating waves that can carry energy away. Their very existence defies conventional wisdom. Although BICs were first proposed in quantum mechanics, they are a general wave phenomenon and have since been identified in electrom...

Remote entanglement of distant, non-interacting quantum entities is a key primitive for quantum information processing. We present a new protocol to remotely entangle two stationary qubits by first entangling them with propagating ancilla qubits and then performing a joint two-qubit measurement on the ancillas. Subsequently, single-qubit measuremen...

Anderson localization, also known as strong localization, is the absence of diffusion in turbid media resulting from wave interference. The effect was originally predicted for electron motion, and is widely known to exist in systems of less than 3 dimensions. However, Anderson localization of optical photons in 3 dimensional systems remains an elus...

A fundamental issue that limits the efficiency of many photoelectrochemical systems is that the photon absorption length is typically much longer than the electron diffusion length. Various photon management schemes have been developed to enhance light absorption; one simple approach is to use randomly scattering media to enable broadband and wide-...

We demonstrate that due to strong modal interactions through cross-gain saturation, the onset of a new lasing mode can switch off an existing mode via a negative power slope. In this process of interaction-induced mode switching (IMS) the two involved modes maintain their identities, i.e. they do not change their spatial field patterns or lasing fr...

We review and interpret a modern approach to laser theory, steady-state ab initio laser theory (SALT), which treats lasing and amplification in a unified manner as a non-unitary scattering problem described by a non-linear scattering matrix. Within the semiclassical version of the theory the laser line has zero width as the lasing mode corresponds...

Spatial modulation of the incident wave front has become a powerful method for controlling the diffusive transport of light in disordered media; however, such interference-based control is intrinsically sensitive to frequency detuning. Here, we show analytically and numerically that certain wave fronts can exhibit strongly enhanced total transmissi...

We perform a first-principles calculation of the quantum-limited laser linewidth, testing the predictions of recently developed theories of the laser linewidth based on fluctuations about the known steady-state laser solutions against traditional forms of the Schawlow-Townes linewidth. The numerical study is based on finite-difference time-domain s...

Optical absorption is commonly considered an intrinsic property of a medium, independent of the details of the illumination source. However, for a spatially coherent illumination of a disordered medium, interference effects can modify the spatial distribution of light inside the medium, allowing the global or local absorption to be tuned by adjusti...

Described is a method of controlling the absorption of light in a cavity, a system in which absorption is so controlled, and an interferometer embodying the underlying physical concept. Materials can be made to completely absorb incident light when the light is imposed in a specific pattern of illumination. Coherent perfect absorption, as the proce...

Concurrent remote entanglement of distant, non-interacting quantum entities is a crucial function for quantum information processing. In contrast with the existing protocols which employ addition of signals to generate entanglement between two remote qubits, the protocol we present is based on multiplication of signals. This protocol can be straigh...

Direct FDTD simulations of the Maxwell-Bloch equations coupled to Langevin noise equations are shown to quantitatively agree with a recent analytic linewidth formula and predicted scaling relations.

We present a method for designing highly multimode lasers for use as effectively incoherent light sources in optical imaging techniques.

Coherent illumination and wave-front shaping can be used to make a weakly absorbing cavity perfectly absorbing and to enhance strongly the absorption of a multiple scattering medium.

We demonstrate all robust bound states in the continuum in photonic crystal slabs are vortex centers in the polarization directions of far-field radiation. They are robust because they carry quantized topological charges, which are conserved if the system is invariant under paritytime (PT) and up-down mirror flip operations. Also, we show lasing of...

We present a multimode laser-linewidth formula that generalizes previous theories, including corrections for cavity losses, nonlinear gain and dispersion, but is derived in a more general setting and is therefore applicable to complex wavelength-scale lasers.

We derive and test a generalization of the steady-state ab initio laser theory (SALT) to treat complex gain media. The generalized theory (C-SALT) is able to treat atomic and molecular gain media with diffusion and multiple lasing transitions, and semiconductor gain media in the free carrier approximation including fully the effect of Pauli blockin...